Talk:Quantum mechanics and Baby of the House: Difference between pages

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'''Baby of the House''' is the unofficial title given to the youngest member of the [[British House of Commons|House of Commons]] in the [[Parliament of the United Kingdom]]. There are no specific duties associated with the honour.

{{FormerFA}}

{{V0.5|class=B|category=Natsci}}

{{Mainpage date|August 1|2004}}

{{physics | class=B | importance=top}}

{{maths rating|class=A|importance=Top|field=Mathematical physics|comment= Presumably the B-class rating of WP Physics and WP V0.5 are older. [[User:Tompw|Tompw]]}}

{{WikiProjectNotice|Science}}

{{authoronlinesource2005|section=June

| author=Miranda Devine

| title=Being sure is never a certain thing

| org=Sydney Morning Herald

| date=June 16, 2005

| url=http://smh.com.au/articles/2005/06/15/1118645868843.html?oneclick=true}}

{{FAOL|Arabic|ar:ميكانيكا الكم|lang2=Ukrainian|link2=uk:Квантова механіка|lang3=Vietnamese|link3=vi:Cơ học lượng tử}}

----

Discussion archives: [[/Archive1]] – [[/Archive2]] (2004)

----

==Australia==

==Image Excellence==

In Australia the term is rarely used, as most MPs and Senators are elected usually only in their thirties and later but some prominent MPs have been elected rather early in life including Prime Ministers [[Malcolm Fraser]] and [[Paul Keating]] who were both elected at age 25 in 1955 and 1969 respectively. The current baby of the house is the 29 year old [[Kate Ellis]] ([[Australian Labor Party|Labor]], [[Division of Adelaide|Adelaide]]).

Just wanted to mention that the image (the red and black one on top) is excellent! However, is there a source for it? I highly doubt that that picture was taken by a home camera. :D

:If you click on the image you can see the image description page. This particular image was uploaded by [[User:FlorianMarquardt]], who I'm sure used some software to create the image rather than a camera. His user page says he mostly uses Yorick (I would've guessed [[Matlab]]), but if you want to know for sure how they're done, you can always ask him on his talk page. — [[User:Laurascudder|Laura Scudder]] | [[User talk:Laurascudder|Talk]] 15:58, 18 October 2005 (UTC)

==Canada==

==Experimental confirmation of predictions==

The currect Baby of the House for the Canadian House of Commans is Pierre Poilievre born on {{birth date and age | 1979|06|03}} who was first elected in 2004 at the age of 24.

As it stands, experimental confirmation of the theory seems to be mentioned only within the "philosophical consequences" section, where it crops up in relation to the Bell tests and entanglement. Perhaps "Experimental confirmation" should be a section of its own? [[User:Caroline Thompson|Caroline Thompson]] 17:14, 14 Jan 2005 (UTC)

:I suggest a separate article; otherwise , too much in one article.

==wordingUnited quibbleKingdom==

Becoming the Baby of the House is regarded as something of an achievement, and for example, [[Jeffrey Archer]] falsely claimed to have been the youngest MP at the time of his election. However, some MPs who have held the position for a considerable period — [[Matthew Taylor (politician)|Matthew Taylor]] was the Baby of the House for over ten years — have found it somewhat embarrassing, as it may suggest that they have a lack of experience, although a perusal of the list shows that many ''babies'' in fact went on to enjoy long, significant and distinguished parliamentary careers. From August 1999 to September 2001, all three of the leaders of the main political parties had been the youngest MPs in the party when they began their political career ([[William Hague]], [[Tony Blair]], [[Charles Kennedy]]).

"Quantum mechanics is a physical theory which, for very small objects such as atoms, produces results that are very different and much more accurate than those of classical mechanic"

First, it's not just small things, there are macroscopic q. phenomena, eg superconductivity/fluidity/lasers blackbody radiation spectra, heat content of solids, etc ; and it's not that for atoms it provides a more accurate theroy than classical mech, it's that classical mech. doesn't provide ANY theory that's EVEN CLOSE to the facts, for atoms, and those other things I just mentioned. Needs rewriting.[[User:67.118.116.145|67.118.116.145]] 04:38, 21 Jan 2005 (UTC)

:I agree with your points. I made an attempt to address them. Tell me what you think. -[[User:Lethe/sig|Lethe]] | [[User talk:Lethe/sig|Talk]] 05:14, Jan 21, 2005 (UTC)

Of those whose age can be verified, the youngest MP since the [[Reform Act 1832]]<ref>Prior to 1832 minors could be elected; precise information on those MPs is often unclear.</ref> was [[Esmond Harmsworth, 2nd Viscount Rothermere|Esmond Harmsworth]], elected on [[15 November]] [[1919]] from [[Isle of Thanet (UK Parliament constituency)|Isle of Thanet]] aged 21 years 170 days. The youngest female MP was [[Bernadette Devlin McAliskey|Bernadette Devlin]], elected on [[17 April]] [[1969]] from [[Mid Ulster (UK Parliament constituency)|Mid Ulster]] aged 21 years 359 days.

== Gnome!? ==

The oldest '''Baby''' at first election in modern times is [[Sarah Teather]] elected in 2003 aged 29 years 109 days.

In a recent edit, someone added a picture of a garden gnome and nothing else. I could just be missing some obvious connection between gnomes and quantum mechanics, but I doubt it. I'm removing it for the moment.

===List of Babies of the House of Commons===

==Feynman==

{| class="wikitable"

Richard Feynman was not among the founding fathers of QM. I added Pauli's name there instead.--[[User:Ashujo|Ashujo]] Feb 11, 2005

!Elected !! Name !! Constituency !! colspan=2 | Party !! Age

|-

|[[United Kingdom general election, 1895|1895]] || [[William Charles de Meuron Wentworth-Fitzwilliam|William Wentworth-Fitzwilliam]] || [[Wakefield (UK Parliament constituency)|Wakefield]]

{{Party name with colour|Liberal Unionist Party}}

|22

|-

|[[West Down by-election, 1898|1898]]^b || [[Arthur Hill (politician)|Arthur Hill]] || [[West Down (UK Parliament constituency)|West Down]]

{{Party name with colour|Conservative Party (UK)}}

|24

|-

|[[United Kingdom general election, 1900|1900]] || [[Richard Rigg]] || [[Appleby (UK Parliament constituency)|Appleby]]

{{Party name with colour|Liberal Party (UK)}}

|23

|-

|[[Horsham by-election, 1904|1904]]^b || [[Edward Turnour, 6th Earl Winterton|Edward Turnour]] || [[Horsham (UK Parliament constituency)|Horsham]]

{{Party name with colour|Conservative Party (UK)}}

|21

|-

|[[United Kingdom general election, 1906|1906]] || [[John Wodehouse, 3rd Earl of Kimberley|John Wodehouse]] || [[Mid Norfolk (UK Parliament constituency)|Mid Norfolk]]

{{Party name with colour|Liberal Party (UK)}}

|22

|-

|[[United Kingdom general election, 1910 (January)|1910]] || [[Charles Thomas Mills]] || [[Uxbridge (UK Parliament constituency)|Uxbridge]]

{{Party name with colour|Conservative Party (UK)}}

|22

|-

|[[Hythe by-election, 1912|1912]]^b || [[Philip Sassoon]] || [[Hythe (UK Parliament constituency)|Hythe]]

{{Party name with colour|Conservative Party (UK)}}

|23

|-

|[[North Tipperary by-election, 1915|1915]]^b || [[John Esmonde (politician)|John Esmonde]] || [[North Tipperary (UK Parliament constituency)|North Tipperary]]

{{Party name with colour|Irish Parliamentary Party}}

|21

|-

|[[North Louth by-election, 1916|1916]]^b || [[Patrick Joseph Whitty]] || [[North Louth (UK Parliament constituency)|North Louth]]

{{Party name with colour|Irish Parliamentary Party}}

|21

|-

|[[Liverpool Abercromby by-election, 1917|1917]]^b || [[Edward Stanley, Lord Stanley (1894-1938)|Edward Stanley]] || [[Liverpool Abercromby (UK Parliament constituency)|Liverpool Abercromby]]

{{Party name with colour|Conservative Party (UK)}}

|22

|-

|[[United Kingdom general election, 1918|1918]]¹ || [[Joseph Aloysius Sweeney]] || [[West Donegal (UK Parliament constituency)|West Donegal]]

{{Party name with colour|Sinn Féin}}

|21

|-

|[[Isle of Thanet by-election, 1919|1919]]^b || [[Esmond Harmsworth]] || [[Isle of Thanet (UK Parliament constituency)|Isle of Thanet]]

{{Party name with colour|Coalition Conservative}}

|21

|-

|[[United Kingdom general election, 1922|1922]] || [[Henry Arthur Evans]] || [[Leicester East (UK Parliament constituency)|Leicester East]]

{{Party name with colour|National Liberal Party (UK)}}

|24

|-

|[[United Kingdom general election, 1923|1923]] || [[Charles Arthur Uryan Rhys]] || [[Romford (UK Parliament constituency)|Romford]]

{{Party name with colour|Conservative Party (UK)}}

|24

|-

|[[United Kingdom general election, 1924|1924]] || [[Hugh Lucas-Tooth]] || [[Isle of Ely (UK Parliament constituency)|Isle of Ely]]

{{Party name with colour|Conservative Party (UK)}}

|21

|-

|[[North Lanarkshire by-election, 1929|1929]]^b || [[Jennie Lee]] || [[Lanarkshire (UK Parliament constituency)|North Lanarkshire]]

{{Party name with colour|Labour Party (UK)}}

|24

|-

|[[United Kingdom general election, 1929|1929]] || [[Frank Owen]] || [[Hereford (UK Parliament constituency)|Hereford]]

{{Party name with colour|Liberal Party (UK)}}

|23

|-

|[[United Kingdom general election, 1931|1931]] || [[Roland Robinson, 1st Baron Martonmere|John Roland Robinson]] || [[Widnes (UK Parliament constituency)|Widnes]]

{{Party name with colour|Conservative Party (UK)}}

|24

|-

|[[Rutland and Stamford by-election, 1933|1933]]^b || [[Gilbert James Heathcote-Drummond-Willoughby, 3rd Earl of Ancaster|Lord Willoughby de Eresby]] || [[Rutland and Stamford (UK Parliament constituency)|Rutland and Stamford]]

{{Party name with colour|Conservative Party (UK)}}

|25

|-

|[[Eastbourne by-election, 1935|1935]]^b || [[Charles Taylor (UK politician)|Charles Taylor]] || [[Eastbourne (UK Parliament constituency)|Eastbourne]]

{{Party name with colour|Conservative Party (UK)}}

|24

|-

|[[United Kingdom general election, 1935|1935]] || [[Malcolm Macmillan]] || [[Western Isles (UK Parliament constituency)|Western Isles]]

{{Party name with colour|Labour Party (UK)}}

|22

|-

|[[Kettering by-election, 1940|1940]]^b || [[John Profumo]] || [[Kettering (UK Parliament constituency)|Kettering]]

{{Party name with colour|Conservative Party (UK)}}

|25

|-

|[[Berwick-upon-Tweed by-election, 1941|1941]]^b || [[George Charles Grey]] || [[Berwick-upon-Tweed (UK Parliament constituency)|Berwick-upon-Tweed]]

{{Party name with colour|Liberal Party (UK)}}

|22

|-

|1944² || [[John Profumo]] || [[Kettering (UK Parliament constituency)|Kettering]]

{{Party name with colour|Conservative Party (UK)}}

|29

|-

|[[Chelmsford by-election, 1945|1945]]^b || [[Ernest Millington]] || [[Chelmsford (UK Parliament constituency)|Chelmsford]]

{{Party name with colour|Common Wealth Party}}

|29

|-

|[[United Kingdom general election, 1945|1945]] || [[Edward Carson (English politician)|Hon. Edward Carson]] || [[Isle of Thanet (UK Parliament constituency)|Isle of Thanet]]

{{Party name with colour|Conservative Party (UK)}}

|25

|-

|[[Southwark Central by-election, 1948|1948]]^b || [[Roy Jenkins]] || [[Southwark Central (UK Parliament constituency)|Southwark Central]]

{{Party name with colour|Labour Party (UK)}}

|27

|-

|[[United Kingdom general election, 1950|1950]] || [[Peter Baker (UK politician)|Peter Baker]] || [[South Norfolk (UK Parliament constituency)|South Norfolk]]

{{Party name with colour|Conservative Party (UK)}}

|28

|-

|[[Belfast West by-election, 1950|1950]]^b || [[Thomas Teevan]] || [[Belfast West (UK Parliament constituency)|Belfast West]]

{{Party name with colour|Ulster Unionist Party}}

|23

|-

|[[United Kingdom general election, 1951|1951]]³ || [[Tony Benn]] || [[Bristol South East (UK Parliament constituency)|Bristol South East]]

{{Party name with colour|Labour Party (UK)}}

|26

|-

|[[Bournemouth West by-election, 1954|1954]]^b || [[John Eden, Baron Eden of Winton|John Eden]] || [[Bournemouth West (UK Parliament constituency)|Bournemouth West]]

{{Party name with colour|Conservative Party (UK)}}

|28

|-

|[[United Kingdom general election, 1955|1955]]⁴ || [[Philip Clarke]] || [[Fermanagh and South Tyrone (UK Parliament constituency)|Fermanagh and South Tyrone]]

{{Party name with colour|Sinn Féin}}

|21

|-

|1955⁴ || [[Peter Michael Kirk|Peter Kirk]] || [[Gravesend (UK Parliament constituency)|Gravesend]]

{{Party name with colour|Conservative Party (UK)}}

|27

|-

|[[Bristol West by-election, 1957|1957]]^b || [[Robert Cooke (politician)|Robert Cooke]] || [[Bristol West (UK Parliament constituency)|Bristol West]]

{{Party name with colour|Conservative Party (UK)}}

|26

|-

|[[Aberdeenshire East by-election, 1958|1958]]^b || [[Patrick Wolrige-Gordon]] || [[Aberdeenshire East (UK Parliament constituency)|Aberdeenshire East ]]

{{Party name with colour|Conservative Party (UK)}}

|23

|-

|[[Southend West by-election, 1959|1959]]^b || [[Paul Channon]] || [[Southend West (UK Parliament constituency)|Southend West]]

{{Party name with colour|Conservative Party (UK)}}

|23

|-

|[[United Kingdom general election, 1964|1964]] || [[Teddy Taylor]] || [[Glasgow Cathcart (UK Parliament constituency)|Glasgow Cathcart]]

{{Party name with colour|Conservative Party (UK)}}

|27

|-

|[[Roxburgh, Selkirk and Peebles by-election, 1965|1965]]^b || [[David Steel]] || [[Roxburgh, Selkirk and Peebles (UK Parliament constituency)|Roxburgh, Selkirk and Peebles]]

{{Party name with colour|Liberal Party (UK)}}

|26

|-

|[[United Kingdom general election, 1966|1966]] || [[John Ryan (UK politician)|John Ryan]] || [[Uxbridge (UK Parliament constituency)|Uxbridge]]

{{Party name with colour|Labour Party (UK)}}

|25

|-

|[[Nuneaton by-election, 1967|1967]]^b || [[Leslie Huckfield]] || [[Nuneaton (UK Parliament constituency)|Nuneaton]]

{{Party name with colour|Labour Party (UK)}}

|24

|-

|[[Mid Ulster by-election, 1969|1969]]^b || [[Bernadette Devlin]] || [[Mid Ulster (UK Parliament constituency)|Mid Ulster]]

{{Party name with colour|Unity (Northern Ireland)}}

|21

|-

|[[United Kingdom general election, February 1974|1974]] || [[Dafydd Elis-Thomas]] || [[Merioneth (UK Parliament constituency)|Merioneth]]

{{Party name with colour|Plaid Cymru}}

|27

|-

|[[United Kingdom general election, October 1974|1974]] || [[Hélène Hayman]] || [[Welwyn and Hatfield (UK Parliament constituency)|Welwyn and Hatfield]]

{{Party name with colour|Labour Party (UK)}}

|25

|-

|[[Liverpool Edge Hill by-election, 1979|1979]]^b || [[David Alton, Baron Alton of Liverpool|David Alton]] || [[Liverpool Edge Hill (UK Parliament constituency)|Liverpool Edge Hill]]

{{Party name with colour|Liberal Party (UK)}}

|28

|-

|[[United Kingdom general election, 1979|1979]] || [[Stephen Dorrell]] || [[Loughborough (UK Parliament constituency)|Loughborough]]

{{Party name with colour|Conservative Party (UK)}}

|27

|-

|[[Fermanagh and South Tyrone by-election, 1981 (April)|1981]]⁵^b || [[Bobby Sands]] || [[Fermanagh and South Tyrone (UK Parliament constituency)|Fermanagh and South Tyrone]]

{{Party name with colour|Anti H-Block}}

|27

|-

|1981² || [[Stephen Dorrell]] || [[Loughborough (UK Parliament constituency)|Loughborough]]

{{Party name with colour|Conservative Party (UK)}}

|29

|-

|[[Fermanagh and South Tyrone by-election, 1981 (August)|1981]]⁵^b || [[Owen Carron]] || [[Fermanagh and South Tyrone (UK Parliament constituency)|Fermanagh and South Tyrone]]

{{Party name with colour|Anti H-Block}}

|28

|-

|[[United Kingdom general election, 1983|1983]] || [[Charles Kennedy]] || [[Ross, Cromarty and Skye (UK Parliament constituency)|Ross, Cromarty and Skye]]

{{Party name with colour|Social Democratic Party (UK)}}

|23

|-

|[[Truro by-election, 1987|1987]]^b || [[Matthew Taylor (politician)|Matthew Taylor]] || [[Truro (UK Parliament constituency)|Truro]]

{{Party name with colour|Liberal Party (UK)}}

|24

|-

|[[United Kingdom general election, 1997|1997]]⁶ || [[Christopher Leslie]] || [[Shipley (UK Parliament constituency)|Shipley]]

{{Party name with colour|Labour Party (UK)}}

|24

|-

|[[Tottenham by-election, 2000|2000]]^b|| [[David Lammy]] || [[Tottenham (UK Parliament constituency)|Tottenham]]

{{Party name with colour|Labour Party (UK)}}

|27

|-

|[[Brent East by-election, 2003|2003]]^b || [[Sarah Teather]] || [[Brent East (UK Parliament constituency)|Brent East]]

{{Party name with colour|Liberal Democrats (UK)}}

|29

|-

| [[United Kingdom general election, 2005|2005]] || [[Jo Swinson]] || [[East Dunbartonshire (UK Parliament constituency)|East Dunbartonshire]]

{{Party name with colour|Liberal Democrats (UK)}}

|25

|}

:^b [[by-election]].

== More founding experiments? ==

:¹ [[Joseph Aloysius Sweeney]] did not take his seat; the youngest MP actually sitting in the House of Commons was [[Oswald Mosley]] (Conservative, aged 22)

:² Became the youngest MP for a second time, on the death of the previous youngest MP.

:³ [[Tony Benn]] was first elected at the [[Bristol South East by-election, 1950]], aged 25, but only became the youngest MP from the 1951 general election, on the defeat of Teevan.

:⁴ Elected on an [[abstentionism|abstentionist]] ticket, [[Philip Clarke]] did not take his seat. [[Peter Michael Kirk|Peter Kirk]] was first elected at the 1955 general election, when he became the youngest MP to take his seat, but only became the youngest MP with the disqualification of [[Philip Clarke]] later in the year.

:⁵ Elected on an [[abstentionism|abstentionist]] ticket, [[Bobby Sands]] and [[Owen Carron]] did not take their seats; [[Stephen Dorrell]] remained the youngest MP actually sitting in the House of Commons.

:⁶ Although several sources claim [[Claire Ward]] was the youngest MP during this period, she was 50 days older than [[Christopher Leslie]].

{{expand list}}

Doesn't the line spectra of atomic hydrogen hold its place among the ones mentioned? I am from Sweden so I might be biase to Rydberg, but I guess Bohr migh side with me on this...

==United States==

Maybe also the photo-ekectric effect - connecting Plank's constant with something else than the black-bodies?

:I tried to add the citation to Rydberg, but it would take the addition of [[Fraunhofer lines]] etc. etc. So perhaps the citation should go into History of Physics with a link to QM? [[User:Ancheta Wis|Ancheta Wis]] 14:49, 28 August 2005 (UTC)

Currently the "Baby of the House" is [[Patrick T. McHenry]] who was born on {{birth date and age|1975|10|22}}. The "Baby of the House" before McHenry who was elected at the age of 26 in [[2000]] was, [[Adam H. Putnam]] who was born on {{birth date and age|1974|07|31}} .

== more fundamental theory ==

Currently the "Baby of the Senate" is [[John E. Sununu]] who was born on {{birth date and age | 1964|09|10}}. The "Baby of the Senate" before Sununu who was elected at the age of 38 in [[1998]] was, [[Blanche Lincoln]] who was born on {{birth date and age|1960|09|30}}

[[User:CYD|CYD]], I noticed that you removed my remark about quantum mechanics being suitable a more fundamental theory. Didn't you like it? Basically, I have in mind that any theory with the larger ___domain of applicability should be said to be more fundamental. -[[User:Lethe/sig|Lethe]] | [[User talk:Lethe/sig|Talk]] 08:00, Mar 3, 2005 (UTC)

==See also==

:Okay, now I see what you are getting at. I put it back in a slightly different form. -- [[User:CYD|CYD]]

*[[Father of the House]]

== new intro Notes==

<div class="references-small"><references/></div>

"It is believed to be a more fundamental theory than Newtonian mechanics, because it provides accurate and precise descriptions for many phenomena where Newtonian mechanics drastically fails. Such phenomena include the behavior of systems at atomic length scales and below (in fact, Newtonian mechanics is unable to account for the existence of stable atoms), as well as special macroscopic systems such as superconductors and superfluids."

==References==

Many of these failures are more accurately attributed to the failure of Maxwellian electromagnetism.

*[http://www.election.demon.co.uk/youngmp.html Youngest Members of Parliament]<!-- contains some factual errors -->

[[Category:Parliament of the United Kingdom]]

Also, there needs to be mention of the discovery of the photoelectric effect by Hertz.

I disagree with the above.

""Believed" is superfuous—This fact is more certain than almost anything else in this encyclopedea.

Whether something is mechanical or electromagnetic is not a matter of accuracy.

Einstein explained the photoelectric effect. I have not seen it mentiond who observed it first. Heinrich Hertz varified Maxwell's equations by inventing radio. I do find a refference to the Frank/Gustav Hertz experiment http://hyperphysics.phy-astr.gsu.edu/hbase/FrHz.html#FH, but that is not exactly the photoelectric effect.

--[[User:David R. Ingham|David R. Ingham]] 15:42, 27 July 2005 (UTC)

I have some comments about the new intro:

# I like the idea of the new intro. It would be useful to put quantum mechanics into the larger context of other kinds of mechanics.

# but don't just insert a new intro in front of the existing intro

# respect the conventions of the article. For example, this article uses the phrase "quantum mechanics" to mean any theory that is quantized. Therefore, to distinguish quantum mechanics from relativistic quantum mechanics is confusing.

# furthermore, I would not seperate relativistic quantum mechanics from nonrelativistic quantum mechanics. The only difference between the two is basically a choice of Hamiltonian.

# quantum field theory, on the other hand, is the true marriage of quantum mechanics and relativity. And it is a qualitatively different theory from quantum mechanics (single particle).

# what you consider to be a significant fraction of the speed of light depends of course on your needs. GPS satellites probably don't even go 0.1% the speed of light, but still the engineers use relativistic mechanics with them. Because they require great accuracy.

# we changed in the old intro some wording to make clear that it's not the smallness that makes quantum mechanics apply. Some atoms are classical, and some macroscopic systems are quantum. So it's inaccurate to just say "small things like atoms" are quantum systems. and again, it depends on the level of accuracy.

#Classical mechanics includes many things besides Newtonian mechanics. I would distinguish Hamiltonian and Lagrangian mechanics from Newtonian mechanics. I might also distinguish fluid mechanics, statistical mechanics.

# what about general relativity? Shouldn't it fit in some where?

-[[User:Lethe/sig|Lethe]] | [[User talk:Lethe/sig|Talk]] 23:40, Apr 13, 2005 (UTC)

:

:To make the article less tedious, how about moving the first five paragraphs elsewhere to other articles in the physics category? This preliminary non-quantum prose might even be a welcome addition to a section of the major physics article. The state of the article when it had just become featured was pretty good. Right now, a re-run of other topics makes for tedious reading. There isn't an equation in sight, for some reason. [[User:Ancheta Wis|Ancheta Wis]] 00:38, 14 Apr 2005 (UTC) My thanks to LauraScudder for the improvements as I was typing this.

:As of 08:36, 14 Apr 2005 (UTC), the first paragraph belongs to a parent article. My vote is to move it to [[physics]] or [[mechanics]]. [[User:Ancheta Wis|Ancheta Wis]] 08:36, 14 Apr 2005 (UTC)

:The new intro has got us arguing over whether [[Newtonian mechanics]] is all there is to [[classical mechanics]] and I've been editing such things too until I realized that the subfields of [[classical mechanics]] have nothing to do with quantum mechanics and just distract and confuse the unintiated while boring the others. I shortened that segment to:

::''Most physicists would divide [[mechanics]] into four major areas: [[classical mechanics]], [[Theory of relativity|relativistic]] mechanics, and quantum mechanics.

::But in [[physics]], '''quantum mechanics''' can be regarded as ''the'' fundamental [[theory]]. ''

:I think it simplifies the intro significantly and takes it back to the spirit of the first featured version while still putting the field into context for those who want to clicky clicky like mad. The distinction between nonrelativistic quantum mechanics and relativistic quantum field theory is made on the appropriate [[quantum field theory]] pages.--[[User:Laurascudder|Laura Scudder]] 18:28, 14 Apr 2005 (UTC)

== Introduction ==

You are losing our reader with this introduction, although the worst was taken care of during the last few days. Please consider the frame-of-mind of someone seeking info on "quantum mechanics" as a fairly unfamiliar topic. This reader does not want to hear about Newtonian mechanics, or relativity, or any number of other fancy classifications, at least not until later. Give the reader a break, at plainly start by telling '''what it is about'''. And '''why anyone should take an interest''', besides the specialists. April 15, 2005 - Guest

:I agree, in making the introduction more "accessible", we have severely bogged it down. Also doesn't really match the [[Wikipedia:WikiProject Science|Wikiproject science]] guidelines now either. I'll [[Wikipedia:Be bold in updating pages|be bold]] and if people disagree, edit away and/or discuss here. --[[User:Laurascudder|Laura Scudder]] 18:13, 14 Apr 2005 (UTC)

::Yes, much nicer. However, I have to say that "relativistic" should not be extracted from either classical or quantum mechanics. Both include relativity (special, of course), and one takes a non-relativistic limit as the need arises. I know that most university course plans start out non-relativistically, and this should of course be mentioned, and is quite reasonable, but it is not really fundamental. We don't hit students with relativity on day one, of course (we wait a couple of months:-). Also, something must be done for the general readers, there has got to be many at this place, and they should be able to come away with something too. -Guest April 15, 2005

It appears you are advocating the position of a reader who has not yet considered the microcosm. This suggests that the article might start off with the atomic hypothesis, then radioactive decay, or perhaps cosmic rays (leakage from a Leyden jar, etc.). ... This approach might then culminate with the statement about general applicability of QM as a fundamental theory, and the current non-relationship to [[GR]]. A complete rewrite or new article [[history of quantum mechanics]]. [[User:Ancheta Wis|Ancheta Wis]] 10:32, 15 Apr 2005 (UTC) ( By the way, you can date-time-stamp your posts with the 5-tilde notation: <nowiki>~~~~~</nowiki> )

:Well, yes and no, advocating "the position of a reader that has not yet considered the microcosm". Of course, the large scale history as you describe it belongs elsewhere. However, as anyone who teaches (science not least) will confirm, it is very easy to assume too much pre-knowledge, and not advisable. In a *pedia one really should be forthcoming towards uninitiated readers, at least when dealing with a difficult topic (if ever there was one) which receives much public attention. For instance, consider the general use of the term "theory" as some sort of idle speculation, while quantum theory is often presented in the media as a collection of "puzzles and paradoxes". It ought to be clearly stated up front how most serious an enterprise it really is.

:Here is what I had in mind - hope I managed to incorporate your latest contributions. It would perhaps be fair of me to let you know a little of my background, but on the other hand, it's the words that count, so maybe better to do without. -Guest April 15, 2005

Umm, no. An introduction has to introduce the topic clearly and concisely. ''Quantum mechanics is regarded by virtually all physicists as the most fundamental framework currently available for understanding physical nature (but it is not the only one in use)'' is a terrible way to start an article. -- [[User:CYD|CYD]]

:I can assure it is true, and what people want to be sure of when paying tuition - but suit yourself. -Guest April 15, 2005

:Let me elaborate on that sentiment. I think, Guest, that you're trying to do an admirable thing by making this article more accessible to the unititiated, especially since it has become featured, but are going about it the wrong way. For someone who doesn't understand the distinctions between fields of physics well, the most important thing to know right off the bat is that quantum mechanics means quantization and that it's the best theory we've got right now (argue that one with the string theorists).

:According to [[Wikipedia:WikiProject Science|Wikiproject science]] guidelines, we do need to put it into context, but too much context is just making distinctions the newcomer doesn't understand ([[quantum physics]] versus [[quantum mechanics]] versus [[quantum field theory]] - not to mention that I disagree that studying [[field (physics)|fields]] is outside of [[mechanics]]) while boring the experienced. I think saying its the best theory we've got and has some mindbending consequences ([[wave-particle duality]]) is a pretty good motivation take an interest in it. --[[User:Laurascudder|Laura Scudder]] | [[User talk:Laurascudder|Talk]] 16:42, 15 Apr 2005 (UTC)

::It's the centuries-old question: my kid would do well to become a lawyer or a doctor, but he/she wants to be a physicist (it used to be astronomer) - but that's all up-in-the-air, or isn't it? When coming to an article like this, the reader is entitled to a clear and unambigous statement, of what this subject means in the world, and not to go directly into some jargon for the initiated. As a professional physicst, who has taught quantum mechanics to those kids for a long time, I know very well that the point is quantization, but that makes no sense at all outside of physics. First question to answer: is it any good?

And by the way, from your quotes it seems like you're not looking at my version - which was the "soft learning curve" one. -Guest April 15, 2005

:Thank you for your thoughts on the intro. Here is my take on your 4-paragraph precis of QM:

#QM is a fundamental framework for understanding [[Nature]]. It has withstood a century of experimentation, and therefore is worth your intellectual investment required to learn it (as the student).

#QM applications and successes.

#QM has some surprises for anyone wishing to invest time learning it.

#as for QM vs GR, the story is not complete yet; there is hope that you (the student) can add to the physics, should you care to accept the challenge.

:I do not disagree that the 4-part story is intriguing. The English is immaterial and can be word-smithed if everyone is agreeable that the 4-part structure (+the 5th para. of names) makes a good intro. I like what I see. [[User:Ancheta Wis|Ancheta Wis]] 02:25, 16 Apr 2005 (UTC)

::Now if I may, Prof. G., ask you some questions: The [[Schrödinger picture]] is really how I think of the topic, based on my brainwashed view of the flow of time, but I am told that Dirac espoused the [[Heisenberg picture]]; it takes an odd frame of mind to view the system using time as an independent variable upon which we can travel at will. I have to admit difficulty visualizing such a system. But if we take a GR POV, and view the cosmos as evolving in time and space, much like a tree growing, I can visualize that. Might it be possible that the Heisenberg picture is more like GR (or statistical mechanics) that way? That would give me more of a feel for the evolution operator. So right away, the framework aspect of QM comes up for explication and evaluation. (Your paragraph 1 of the intro) It's difficult, in another way. Unless the student can take that on faith, somehow. It's like the student has to start all over again, on another kind of kinematics. I would imagine that the dropout rate would be high, to get through the framework part. That implies that the successes (paragraph 2) are what sustains the student. [[User:Ancheta Wis|Ancheta Wis]] 02:25, 16 Apr 2005 (UTC) Yet upon reflection, to state that the framework is the general entry point for learning QM, has to be a ''conclusion'' based on the century of development and experimentation; QM certainly didn't start out with that status at all. So the 4 part intro can't be the TOC for an article or course, it would have to start with experiment, perhaps a failed hypothesis or two, and then the string of successes.

::Another line of questioning: QM is the basis for [[computational chemistry]], which takes up a ton of computing power. Yet we do not hear much about the codes currently in use by [[Peter Coveney]] et. al. I would think that your students could gain some significant experience if they got some background for that area. I still am unclear on how much the QM computer codes compare in processing load, compared say to [[Earth Simulator]].

::I recognize that the questions are unfair, but it doesn't hurt to ask. Maybe we can find some answers. [[User:Ancheta Wis|Ancheta Wis]] 02:25, 16 Apr 2005 (UTC)

Umm, most of this is dealt with in the rest of the article, if one bothers to read anything apart from the introduction. See, in particular, the section ''Interactions with other scientific theories''. See also [[Wikipedia:Manual of Style#Introduction]]. -- [[User:CYD|CYD]]

Reply to [[Ancheta Wis]]: Thanks for taking time with my suggested intro (which is at "intro with softer learning curve" [http://en.wikipedia.org/w/index.php?title=Quantum_mechanics&oldid=12345900 here]>; it was immediately thrown out by [[CYD]]).

Just passing by as a guest, I got somewhat disturbed at the impression an uninitiated reader of this featured article would get. Science is not faring too well among young people, and I find that it is partly due to the way it gets represented in the media: too much nerdy whizzkid, too little serious business. Choosing a line of study, we all need to see the long professional aspect, not just the instant gratification entertainment value. Therefore I find it important to provide a readable and understandable intro, where the reader can hang on as long as possible. I'm pleased to see that you recognize this.

My contribution is/was an attempt to simplify the flow of ideas, which seemed to me to have gotten rather entangled (with all due respect, probably an artefact of the editing procedure). As we all know, of course, to start a fresh version can often help.

Here are my answers to your (welcome) questions (and some thoughts while we're at it):

> QM is a fundamental framework for understanding Nature. It has withstood a century of experimentation, and therefore is worth your intellectual investment required to learn it (as the student).

Indeed, and your financial investment too (as a parent). As a community, physicists can assert this in absolute honesty, and with complete confidence. The scientific test procedures involved in that so many physicists have worked on this, everywhere, every day, for a hundred years, is so tremendous that it needs to be asserted explicitly. No one outside science or technology can possibly have any realistic idea of the degree of certainty that has been achieved here. Now, I am well aware, of course, that as an academic one tends to shy away from making such blunt statements - and that's why it's not well understood outside of science. Now, since practically every professional physicist (and chemist as well, I suppose) agrees, I believe it should be said here, in this article, in an unambigous statement, that, this is what most of us find, and that many of us use quantum mechanics day in and day out (except, of course, ... you know). It does not have to be presented as an absolute and final truth (which no physicist of course would subscribe to), but the strong confidence must come through. It is justified.

> QM applications and successes.

Yes, most readers will appreciate this when listed in general terms. And I linked to the quantum specific pages.

> QM has some surprises for anyone wishing to invest time learning it.

Now that we have said that quantum mechanics is serious, and works, it's motivating to know this.

> as for QM vs GR, the story is not complete yet; there is hope that you (the student) can add to the physics, should you care to accept the challenge.

Yes, we really hope that one of you (students) will be the one to make a discovery, like what Planck did, to find the more fundamental framework of the future.

> I do not disagree that the 4-part story is intriguing. The English is immaterial and can be word-smithed if everyone is agreeable that the 4-part structure (+the 5th para. of names) makes a good intro. I like what I see. Ancheta Wis 02:25, 16 Apr 2005 (UTC)

Thanks.

> Now if I may, Prof. G., ask you some questions: The Schrödinger picture is really how I think of the topic, based on my brainwashed view of the flow of time, but I am told that Dirac espoused the Heisenberg picture; it takes an odd frame of mind to view the system using time as an independent variable upon which we can travel at will. I have to admit difficulty visualizing such a system. But if we take a GR POV, and view the cosmos as evolving in time and space, much like a tree growing, I can visualize that. Might it be possible that the Heisenberg picture is more like GR (or statistical mechanics) that way? That would give me more of a feel for the evolution operator. So right away, the framework aspect of QM comes up for explication and evaluation. (Your paragraph 1 of the intro)

As you know, the Heisenberg picture is mathematically and physically equivalent to the Schrödinger picture, by unitary transformation. It is good for theoretical work, and is quite widely used. For visualization, I recommend using the H picture with the Ehrenfest procedure, to recover the Newton equations of motion, where the time dependence nicely associates with the observables, as we are used to. Indeed, in this way I derive classical relativistic electrodynamics, for the (graduate) students in relativistic quantum mechanics, so it is basically all there.

> It's difficult, in another way. Unless the student can take that on faith, somehow. It's like the student has to start all over again, on another kind of kinematics. I would imagine that the dropout rate would be high, to get through the framework part. That implies that the successes (paragraph 2) are what sustains the student. Ancheta Wis 02:25, 16 Apr 2005 (UTC)

Yes, we wait until the second year to do q.m., but in principle one could start with it, in principle. If systematically presented it is not hard to understand, but the mathematical framework must be taught in mathematics beforehand. Many students, of course, are more interested in other things, and just need to see a bit of it, at some stage, to be convinced that it works, and understand how material properties get deduced in q.m. Some day we may even be able to compute masses, some day...

> Yet upon reflection, to state that the framework is the general entry point for learning QM, has to be a conclusion based on the century of development and experimentation; QM certainly didn't start out with that status at all. So the 4 part intro can't be the TOC for an article or course, it would have to start with experiment, perhaps a failed hypothesis or two, and then the string of successes.

Indeed, so we should imply these empirical foundations via the Part 2. Anyhow, It still helps to know that there is a reliable mathematical framework, even if you do not intend to become a specialist in it. So the general framework part is important for building confidence, although the learning is done via more specialized calculus formulations. Hope I understood your question here.

> Another line of questioning: QM is the basis for computational chemistry, which takes up a ton of computing power. Yet we do not hear much about the codes currently in use by Peter Coveney et. al. I would think that your students could gain some significant experience if they got some background for that area. I still am unclear on how much the QM computer codes compare in processing load, compared say to Earth Simulator.

This topic is beyond my scope, so I have to pass on that.

> I recognize that the questions are unfair, but it doesn't hurt to ask. Maybe we can find some answers. Ancheta Wis 02:25, 16 Apr 2005 (UTC)

Not at all. Let's hope it becomes possible to have an introduction that part of the way, at least, makes sense to all readers. -Guest April 16, 2005

Dear writers. Quantum Mechanics is a difficult and confusing subject. What is the essence ? How can it be explained shortly and understandably ? To me it is the following. "''Quantum Mechanics identifies energy and frequency''. The unit of frequency, the hertz, is also a unit of energy. The number of joules per hertz is [[Planck's constant]]. As energy is a property of particles and frequency is a property of waves, quantum mechanics identifies particles and waves. When the frequency is low, the particle aspect fades away and it looks like 'classical' waves like those on the sea. When the energy is high, the wave aspect fades away and it looks like 'classical' particles like grains of sand. So Quantum Mechanics merges two distinct classical theories into one. It is actually a conceptual simplification". [[User:Bo Jacoby|Bo Jacoby]] 09:49, 13 September 2005 (UTC)

Yes, that's why I added electromagnetism in the first paragraph, but I am not sure "unifies" is the best word.

I think "Quantum mechanics is a theory of mechanics, a branch of physics that deals with the motion of bodies" is wrong. It is not a theory, it is the theory, and as above it is not just about mechanics, or at least that implies lack of generality. I'll see if I can find an improvement.

--[[User:David R. Ingham|David R. Ingham]] 16:30, 13 September 2005 (UTC)

=== Needs a more simplified definition for the lay person ===

"Quantum mechanics is a fundamental physical theory that extends, corrects and unifies Newtonian mechanics and Maxwellian electromagnetism, at the atomic and subatomic levels." is going to tell a person SQUAT unless they already know what newtonian mechanics and maxwellian electromagnetism is. A more simplified basic definition is needed before expounding in the excellent detail this article gives.

well i am a layman (high school student infact) and i dont find the introduction difficult

-protecter

I wouldn't have had any problem understanding that when I was in high school either, because I had already read a lot of physics and astronomy, but not everyone is so interested in science.

How about adding, at the very top, something like "Quantum mechanics is based on the observation that, on a very small scale, waves and particles are not different sorts of object but complementary properties of all objects." --[[User:David R. Ingham|David R. Ingham]] 20:29, 19 September 2005 (UTC)

Or how about, at the very top, "Quantum mechanics accounts for the fact that motion, as well as matter, does not have unlimited detail, but is built up of tiny elements. The tiney elements of matter are called atoms. The tiney elements of motion are called quanta."

This is the way I started to introduce the idea to a smart ten year old (and her mother).

(This omits optics, but, at this level, that is appropriate.)

[[User:David R. Ingham|David R. Ingham]] 17:57, 28 September 2005 (UTC)

I have to agree with David. Having a good basic layman's knowledge of the subject, I found the intro overwelming. There is no mention of what makes Quantum mechanics so exciting, a simple explaination of wave/partical duality. Maybe an early reference to the "double slit" experiment to give the newer readers an idea what it's all about. Everything in the intro is needed, but maybe not all of it in the intro. Intro should be shorter, more attention grabbing.

Just a thought. [[User:12.218.132.240|12.218.132.240]] 13:17, 7 December 2005 (UTC) S. O'Reilly 12/7/2005

=== generality ===

People took out my generalization of the introduction. Please read [[The Feynman Lectures on Physics]], vol. 3 first. He words it much differently, but he does explain the generality when he introcuces the subject. So what I said is not only true, but it is the best known way to teach quantum mechanics. If this makes it too hard to read, then re-word it or add something more basic, as my suggestions in the previous sub-heading, above it.

[[User:David R. Ingham|David R. Ingham]] 17:57, 28 September 2005 (UTC)

== Navbox ==

In order to make the quantum-theory Navbox more accessible in the other articles, I propose that it move up just under a heading, such as [[Quantum mechanics#Quantum mechanical effects]]. Thus by inserting a parenthetical link ''([other articles on QM])'' in the child articles, the Navbox becomes more accessible other places. Is that alright with everyone? Alternatively, smaller versions of the quantum-theory Navbox might be placed in the child articles; as its transclusion would overwhelm many of them, currently. [[User:Ancheta Wis|Ancheta Wis]] 08:25, 19 Apr 2005 (UTC) {{TopicInQuantum-theory}} As it turns out, the first article I had chosen , on the commutation relation, did not have a link back to QM, so I inserted a small version of the Navbox there. The other articles appear to at least mention this page, so the need for a link to the Navbox is partially answered already. The little navbox is titled <nowiki>{{TopicInQuantum-theory}}</nowiki>

== Minor edit ==

I removed this paragraph, which can't be understood (to put it nicely):

:Another difficulty with quantum mechanics is that the nature of an object isn't known, in the sense that an object's position, or the shape of the spatial distribution of the probability of presence, is only known by the properties (charge for example) and the environment (presence of an electric potential).

-Guest April 19, 2005

I am reading a book "Quantum Generations: The History of Physics in the Twentieth Century" by Helge Kraugh that details all the inaccuracies and crises in quantum theory as it developed over the past century. The statement: "The predictions of quantum mechanics have never been disproved after a century of experiments." (introduction, 7th paragraph) is completely false and I removed the sentence. It had repeatedly been contradicted and the science has very clumsily evolved due to all these contradictions.

-Brian, February 5th, 2006

You know, how do you reconcile the predictions of Quantum Electrodynamics with your categorical statement? Are you in fact talking about the shift from the Classical to a QM viewpoint? Are you disagreeing with the QM framework? The QM framework is very broad. Curious to hear more critique by Helge Kraugh . --[[User:Ancheta Wis|Ancheta Wis]] 22:21, 5 February 2006 (UTC)

I am not talking about Quantum Electrodynamics specifically but about QM as a whole. Each major experimental or theoretical development (discovery of new particles, uncertainty/complimentary theory, properties of high energy cosmic particles, etc) was argued and often rejected or ignored among the leading physicians at the time it was concieved. While many of these were wrong, the ones that were right often conflicted directly with the current theories and provoked serious modifications. Some of these (that are currently accepted) weren't taken seriously until decades after they were formulated.

I am not rejecting quantum mechanics. What I am rejecting is a theory of quantum mechanics that was developed in the early 1900's and remained unchanged and accounted for everything. Quantum mechanics evolved as scientists gathered more experimental evidence and dispelled groundless theories. Even the basics of quantum theory (such as the existance of the nucleus, the proton and the neutron) wasn't even accepted or confirmed by experiment until less than 100 years ago. The neutron wasn't confirmed until 1932.

The statement "The predictions of quantum mechanics have never been disproved after a century of experiments." is false not because quantum mechanics is entirely wrong (it is not) but because quantum mechanics has historically been a very unstable field. Disproofs and contradictions have been a major force driving its development throughout its history.

-Brian, February 5th

:The 6th [[Solvay Conference]] (1930) is the one where Einstein decisively lost his debate with Bohr; thereafter Einstein refrained from direct attacks and instead used philosophical arguments against QM. Using the QM machinery, he formulated the [[EPR paradox]], leading to [[Schrödinger's cat]] etc. I am curious what Helge Kraugh has to say about this; we, as a civilization, have not yet come to terms with what QM has to say about this. The QM framework includes definite predictions, some of which have subsequently been observed. Those observations have to be counted as successes for the framework (i.e., [[Schrödinger equation]] etc.). --[[User:Ancheta Wis|Ancheta Wis]] 03:23, 6 February 2006 (UTC)

::BTW we need an article on [[Théophile De Donder]] (he wrote on relativistic QM and was a supporter of Einstein). De Donder was a major influence on [[Ilya Prigogine]]. Does Kraugh mention De Donder? [[User:Ancheta Wis|Ancheta Wis]]

Hmmm, we might be arguing along different lines. Kraugh repeats exactly what you said above.

I just read the history section and I see where a problem could arise: between old quantum theory and new quantum theory. Since the wording was "a century" I intepreted the meaning to be "since 1900". But it is probably since the mid to late 30's, which I have little knowledge of. The 1920's and early 30's were full of the crises, dead ends, the freak discoveries and ignorance to correct theories that I was talking about. Specifically, Helge Kraugh mentions that high energy particles, available at that time only from cosmic rays, did not fit the mathematical model used for lower energy particles. The problems with the 1929 Heisenberg-Pauli theory of QED was emphasized. She states:

"In spite of promising features, it was infected with paradoxes and divergent quantities. In particular, the self-energy of the electron (the energy of an electron in its own electromagnetic field) turned out to be infinate, which was, of course, an unacceptable result."

She also includes a 1933 letter from Robert Oppenheimer to his brother:

"As you undoubtedly know, theoretical physics- what with the haunting ghosts of neutrinos, the Copenhagen conviction, against all evidence, that cosmic rays are protons, Born's absolutely unquantizable field theory, the divergent difficulties with the positron, and the utter impossibility of making a rigorous calculation at all- is in a hell of a way"

The Einstein-Bohr arguments, as well as other examples (the faulty early atomic models; the electromagnetic view of the early 1900's; the often rejected theories of relativity; and the problems that erupted when antiparticles and other non-fundamental particles were discovered) are some examples of how the physics community was not all on the same page. Helge Kraugh continually depicts the early years of quantum physics (atleast till the mid 30's) as a period where quantum physics confused the most brilliant minds and divided the whole community over a number of issues. She details many theories of quantum physics which couldn't be agreed upon unless proven or disproven through experiments. Are you referring to the QEM models from the late 30's?

I have been looking for references to De Donder but have not been able to find any yet. Sorry about that. I'll let you know if I do.

-Brian, February 6

:QM arose historically from [[spectroscopy]], [[cosmic ray]]s, and [[radioactivity]] (called 'modern physics' -- the physics after Newton and Maxwell's pictures of the world). At the beginning of the twentieth century, there was still the concept that the atom was the ultimate [[Platonic]] [[object]], indivisible and immortal (or 'hard spheres', in physics-talk). [[Statistical mechanics]] can be formulated from this mental picture, which can be used to derive [[thermodynamics]]. But in 'reality' the hard spheres are in flux - the neutron decays into its constituent parts in 15 minutes. Our very bodies are in flux. QM takes this as a given. It has taken a century (loosely speaking) to renounce the little spheres and replace them with jello -- a world of approximate objects with finite lifetimes. (Now I admit that protons have very long lifetimes.) Even in the realm of very low temperatures, the objects are still jello-like; they jiggle. [[Eric Cornell]] has illustrated this very well in his public lectures. The pictures of Newton and Maxwell are still valuable, of course; the engineered objects we use today were built from this worldview, but there are more POV's out there, resting on QM, like [[laser]]s. --[[User:Ancheta Wis|Ancheta Wis]] 11:14, 8 February 2006 (UTC)

From up top of this section, "difficulty with quantum mechanics" is entirely wrong. The "difficulty" is with ordinary language, which is not intended to deal with the microscopic world. [[User:David R. Ingham|David R. Ingham]] 09:45, 12 February 2006 (UTC)

From the bottom paragraph, "Statistical mechanics can be formulated from this mental picture" is not correct. First, one cannot directly formulate equations from mental pictures, in the sense of pictures that can be expressed easily in words. Historically, part of the origin of qm was that the statistical mechanics that was formulated from the classical view of nature, that it had unlimited detail like the [[Mandelrot set]], was inconsistent or gave unrealistic results.

:David R. Ingham, I appreciate your comment; the hard sphere approach is the program of Kerson Huang's ''Statistical Mechanics''. Huang was a collaborator with [[Max Born]], as well. [[Michael Faraday]] formulated the picture which [[Maxwell]] proceeded to express in his equations. --[[User:Ancheta Wis|Ancheta Wis]] 11:54, 12 February 2006 (UTC)

"engineered objects we use today were built from this worldview" is not exactly correct. Did you mean the simpler objects like floor mops and earth dams? Qm has been used to understand semiconductors since at least the time Bell Labs invented the transistor. Chemistry has depended heavily on qm, at least since Linus Pauling explained the chemical bond. Lasers, though in principle a classical phenomenon, have always been understood using quantum mechanics. As an engineer as well as a physicist, I feel slighted by that remark.

:[[User:David R. Ingham|David R. Ingham]] 10:30, 12 February 2006 (UTC)

::David R. Ingham, I do not disagree, and actually believe that [[laser]]s are squarely in the QM world because lasers ''use'' QM phenomena for the laser action. My personal belief is that QM's most useful contribution is the solid explanation of the [[periodic table]]. But even a [[transistor]] can be understood, from an [[engineer]]ing POV, without QM. 'Guest' is the one who removed the sentence in the 'minor edit'; Guest mentioned that the Ehrenfest procedure can be used to map a QM description (in the [[Heisenberg picture]]) to a time-averaged description which seems somehow less abstract to me. So I admit that the [[Schrödinger picture]] feels more real to me. But I am trying to formulation a question for you. Something seems entangled here (pun intended). If a macroscopic-scale observer, who seems to get [[time]] from his scale , were to shrink down to electron-sized scale, would time flow equally for him? I am not trying to trip you up. I am honestly trying to get an insight here. If the Ehrenfest procedure is an important-enough process to give us time, then it ought to be possible to come up with a phenomenon which transcends time, just as q. entanglement transcends space. From a macroscopic perspective, that seems to contradict my prejudices. If we somehow could define ''simultaneity'' using some natural feature like [[polarization]] or [[spin]], we could define some pretty good clocks, etc. --[[User:Ancheta Wis|Ancheta Wis]] 11:54, 12 February 2006 (UTC)

::I can sharpen my question -- QM applies even at regions of low temperature, where the celebrated [[BEC]] phenomena occur, and which show QM up at macroscopic scale. Obviously QM applies to the very small, with apparent applications at macroscopic scale (lasers, transistors, etc.). There are other continuous parameters out there; mass is one example. If we could shrink the quantity of mass for an object, what would happen? Would time flow equally for two synchronized objects, one of which was subject to decay in mass? Conversely, what would remain invariant? --[[User:Ancheta Wis|Ancheta Wis]] 12:16, 12 February 2006 (UTC)

Ancheta Wis, I think I finally understand your intepretation of that sentence. You meant "Quantum mechanics as a worldview has never been discredited by experimentation during its century long development. Experiments support this jello-like existance of the atom." I completely agree with that intepretation. As you have probably guessed, I derived a very literal meaning of the sentence: "The sole Quantum mechanical theory, proposed around 1900, has predicted a whole bunch of stuff that can't be disproven by experiments." You can see why this bothered me.

"The predictions of quantum mechanics have never been disproved after a century of experiments." may need to be reworded before it is reinserted.

-Brian, February 13

==Entanglement, 1905==

Looking back on a certain historic event, it is possible to characterize the following as an type of [[quantum entanglement]] -- just view the clocks referred to below as [[Atomic clock|Cesium clocks]] : [[Einstein]]'s [[1905]] [[special relativity]] challenged the notion of an absolute definition for times, and could only formulate a definition of synchronization for clocks that mark a linear flow of time{{ref|fn_4}}:

:''If at the point A of space there is a clock ... If there is at the point B of space there is another clock in all respects resembling the one at A ... it is not possible without further assumption to compare, in respect of time, an event at A with an event at B. ... We assume that ...''

::''1. If the clock at B synchronizes with the clock at A, the clock at A synchronizes with the clock at B.''

::''2. If the clock at A synchronizes with the clock at B, and also with the clock at C, the clocks at B and C also synchronize with each other.''

*{{note|fn_4}} [[Einstein]] [[1905]], ''Zur Elektrodynamik bewegter Körper'' [On the electrodynamics of moving bodies] reprinted [[1922]] in ''[[Special relativity|Das Relativitätsprinzip]]'', B.G. Teubner, Leipzig. '''''[[Special relativity|The Principles of Relativity]]: A Collection of Original Papers on the Special Theory of Relativity''''', by H.A. Lorentz, A. Einstein, H. Minkowski, and W. H. Weyl, is part of ''Fortschritte der mathematischen Wissenschaften in Monographien, Heft 2''. The English translation is by W. Perrett and G.B. Jeffrey, reprinted on page 1169 of ''On the Shoulders of Giants'':The Great Works of Physics and Astronomy (works by [[Copernicus]], [[Johannes Kepler|Kepler]], [[Galileo]], [[Newton]], and [[Einstein]]). [[Stephen Hawking]], ed. [[2002]] ISBN 0-7624-1348-4

== Quantum Physicists are just catching up with Relativity! ==

I understand [[quantum mechanics]] just enough, not to make any great discoveries in the field, but enough to understand the basics. [[Special Relativity]] is the same way. I found something interesting though, relativity implies both wave-particle duality and supersymmetry! A wave is a carrier of eneergy from place to place. A paritcle can be viewed as a carrier of mass from place to place. Relativity says energy is the fourth-dimensional extendsion of momentum (which is mass times velosity). This implies that waves are fourth-dimensional extendsion of particles! This also implies that the carriers of energy ([[Bosons]]) are extendsions of the carriers of mass ([[Fermions]])! Wave-particle duality and supersymmetry. It seems so simple I'm surprized that this was overlooked for so many years.--[[User:SurrealWarrior|SurrealWarrior]] 18:35, 20 Jun 2005 (UTC)

== Reverted contribution. ==

If we are going to retain the "Bohm interpretation" which is "not popular among physicists", surely we also need the main stream interpretation that I was taught in graduate school by famous physicists.

I propose including the following:

"According to a lecture by Herbert P. Broida to his students at UCSB, the probabilities and other difficulties always come from the relation between quantum and classical physics, not from quantum mechanics in isolation. To explain the meaning of this, since Classical Mechanics is now only an approximation to quantum mechanics (the same approximation as Geometric Optics) and not an independent theory, this makes the probabilities belong to classical physics, not to quantum mechanics. The difficulty is that one cannot do any experiment without using Classical Mechanics to describe the apparatus."

There is also a problem that the "interpretations" listed here don't confine themselves to philosophical interpretation. The "Bohm interpretation", as described, is physically verifiable and therefore physics rather than philosophy. The "Everett many-worlds interpretation" on the other hand is so unverifiable that it is not even philosophy.

Quantum mechanics has become established, over a full century and is in no way in question. If it were in question, that would be a matter of physics, not philosophy. The philosophical issue is how to speak about it. The way that research physicists do speak about it is to call the quantum wave function "reality" and Classical Mechanics an "approximation".

[[User:David R. Ingham|David R. Ingham]] 4 July 2005 17:48 (UTC)

: I think the paragraph is vague, except for the last sentence: "The difficulty is that one cannot do any experiment without using Classical Mechanics to describe the apparatus." With a little more clarity, this is more of a [[measurement in quantum mechanics]] type of contribution. Also, skip the Broida reference unless you want to explain who he is. [[User:PAR|PAR]] 4 July 2005 19:59 (UTC)

I'll think about it some more.

I strongly feel that it is wrong, to ascribe probability to quantum mechanics, when it really belongs to the Classical Mechanics (= Geometric Optics) ray approximation to the quantum mechanics of massive particles, and to the zero energy per particle approximation to the quantum mechanics of light and sound. The Copenhagen Interpretation did not go far enough in this direction. The statement that "all of the mathematical consequences of quantum mechanics can be trusted" is enough to get right answers, but it is not philosophically tidy— One might be led away from using wave packets to account for details of the interaction between microscopic and macroscopic systems, when they are needed.

[[User:David R. Ingham|David R. Ingham]] 5 July 2005 23:23 (UTC)

:I sympathize. I have my own personal points of view on quantum mechanics, which are at odds with or not addressed in this article, but I don't think this article is the place to air them. This article should contain only those aspects of quantum mechanics where there is rather broad agreement, and a list of contentious areas with enough information so that someone who is interested can follow up. [[User:PAR|PAR]] 5 July 2005 23:45 (UTC)

::I agree. [[User:Karol Langner|Karol]] July 6, 2005 07:31 (UTC)

== The Ultimate Unified Theory? ==

It seems that in the 20th century, Quantum Mechanics and Relativity are the only leading theories, because General Relativity is not capable of describing the beginning of the universe etc., another "ingredient" is required to make the "recipe" perfect, and it seems that Quantum Mechanics is the best candidate. If unified, the new theory shall be named as Quantum Theory of Gravity, which Wikipedia has an excellent on it, we should start working!

For information on the grand unified theory, superstring theory is the best candidate that can unify everything, I am not very sure about that, and superstring theory also seems to be the most popular theory. When you try to apply to work as a researcher in a physics working office, it seems that you will be instantly selected to work in their office if you study superstring theory, and if you study other theory, they will consider considering you as their researcher colleage, which is quite a pain. Anyway, I think that a unified theory, or the Grand Unified Theory (which is quite of an exaggeration) is definately needed to describe our own cosmic habitat.

Feel free to email me to discuss about issues on quantum mechanics and physics etc.: [e-mail]

== uncertainty principle ==

i have a question about degenerated matter. when a star shrinks, the maxium uncertainty in the position of a particle for example electron decreases, so it minimum uncertainty in momentum increase. what i dont understand is ''what is uncertainty in momentum?'' does it mean that the particle is traveling with multiple momentum at the same time? because i read from somewhere as the minimum uncertain momentum increase the particle's minimum velocity increase, and i just dont get it (is it like the particle's velocity can be 0-something?)

Yes, a particle does have multiple momenta and multiple velocities at the same time, just like a particle of light goes through both holes in a diffraction experiment or through both sides of the lens of a camera or telescope. To really understand this you have to accept that the description of a particle's motion with a single momentum and single position is an approximation that breaks down on a very small scale. It is the same approximation as Geometric Optics. To really understand quantum mechanics you need to give up thinking that a particle really is in a single place. The only reality (though not the only mathematical description of reality†) is the wave function. If you want to get closer to what you see directly, take up art or literature. --[[User:David R. Ingham|David R. Ingham]] 17:59, 18 July 2005 (UTC)

†The Heisenberg formulation does not take the form of a function.

* Robert Martin Eisberg, ''Fundamentals of Modern Physics'', John Wiley and Sons, 1961, p. 177

--[[User:David R. Ingham|David R. Ingham]] 04:41, 26 August 2005 (UTC)

== Bohm interpretation ==

There seem to be other problems with this paragraph, besides not being elegant physics.

The Schrödinger equation is not a function but a unique and explicit formula for the time development of the wave equation.

Non-locality is a property of equations, not of functions.

If distant particles interact instantaneously, that is not described by the Schrödinger equation, which is local.

Non-locality is physics and not philosophy.

--[[User:David R. Ingham|David R. Ingham]] 21:19, 24 July 2005 (UTC)

==Improvement Drive==

A related topic, [[Astrophysics]] is currently nominated on [[Wikipedia:This week's improvement drive]]. Come and support the nomination or comment on it.--[[User:Fenice|Fenice]] 07:31, 6 August 2005 (UTC)

== spin ==

can someone please tell me what is spin? i heard it can be oriented in up and down and its parallel/antiparallel to the local magnetic field, but whats all that "spin 1/2, 2,1, 0"? like everywhere i read about spin it never says what it is, only it is an intrinsic angular momentum. what does that mean? maybe i just dont know when it is telling what it is, can someone just tell me in ordinary language? (not like everyday language, just dont use a technical term in every sentence)

thanks

-protecter

To begin with, it is the angular momentum of a particle, in units of ℏ (h bar is Planck's constant deviede by 2 π). Angular momentum can change only by integer multiples of ℏ, that is, it is quantized.

--[[User:David R. Ingham|David R. Ingham]] 23:45, 8 August 2005 (UTC)

Revised in format--[[User:David R. Ingham|David R. Ingham]] 16:34, 9 August 2005 (UTC)

----

[[angular momentum]] tells you stuff like how much how long you'll have to apply a [[torque]] to something to get it to stop moving, and how fast other things will will start spinning if they collide with that something. Angular momentum usually comes from things that are rotating, but [[elementary particle]]s also have a built-in angular momentum, just like they have a built in [[charge]]. The total angular momentum of something is the sum of all the [[intrinsic angular momentum|intrinsic angular momenta]] as well as the [[orbital angular momentum|orbital angular momenta]] (which are the angular momenta that come from rotating).

you can't take away intrinsic angular momentum from a particle, it's always there, so the analogy with torques and collisions doesn't apply. But you can still tell that the intrinsic angular momentum is there from things like the [[dipole moment]] ([[electric]] or [[magnetic]]) of a particle.

The number you hear associated to [[spin]] (0, 1/2, 1, 2) tells you how the thing behaves under rotation. Like, a dipole behaves like a pointing finger, when you rotate it 30 degrees, the finger points 30 degrees further. Other things behave slightly differently. Like if you rotate your coordinate system 30 degrees, and consider the moment of inertia of an object, you have to apply two 30 degree rotations to two coordinate axes to get the new [[moment of inertia]]. That's because moment of inertia is a [[rank of a tensor|second rank]] [[tensor]].

So that spin number really tells you how things behave under rotation. [[Electric field]]s behave like [[vector]]s, and anything that behaves like a vector is called spin 1. anything that behaves like a second rank tensor is called spin 2. things that behave like invariants (look the same no matter how you rotate) are called spin 0.

And when you add quantum mechanics into the mix, you gain the possibility of things that have half integer spin. These guys pick up a minus sign when you rotate all the way around.

according to the [[spin statistics theorem]], spin also determines whether things act like [[fermion]]s (with the [[Pauli exclusion principle]]) or like [[boson]]s (which have no Pauli exclusion principle.

After you plug through some math, you find that the spin number, which tells you how things behave under rotation, is proportional to the angular momentum, which tells you how torques apply and how collisions happen. so spin tells you both how things behave when you rotate your coordinates, as well as how much angular momentum something has. the fact that some angular momentum is intrinsic just means that it doesn't come from rotating objects, but is just there. -[[User:Lethe/sig|Lethe]] | [[User talk:Lethe/sig|Talk]] 01:37, August 9, 2005 (UTC)

thankyou for your explanation, i have now a faint idea of what it means. however i am finding it a bit advanced for me. (never heard of second rank tensor). so are you basically saying spin describes the direction of the ''field'' (like dipole) around a particle under rotations?

also, this may sound silly, when do they teach the full concept of spin?

-protecter

the easiest way to think of a second rank tensor is just to think of it as a 3x3 matrix (although that misses a lot of the meaning). when you do a change of basis to a matrix A, you have to multiply it something like D^TAD, where D is the change of basis matrix. The point is to notice that you have to multiply by the change of basis matrix twice, once on the left (which a transpose or inverse) and once on the right. A third rank tensor would get multiplied three times. This is one way to understand tensors, though eventually you'll want a more intrinsic understanding.

a vector is a first rank tensor, because when you change basis, the vector v goes to Dv. a vector can be represented by 3 components while a second rank tensor uses 9 components. So it's not 100% accurate to think of a second rank tensor as a pointing arrow. On the other hand, it is sometimes possible. (technical stuff: if the tensor is symmetric and traceless, for example. then it lives in a faithful irrep of the rotation group, and we can assign a unique rotation to it.)

so yes, to answer your question, the spin describes the direction of thhe field (like a dipole). that's the general idea. to understand it better of course, you'll have to learn the math.

so, where do they teach spin? of course, everyone's first introduction is in their Quantum Mechanics class, but I find that the lessons learned there are unsatisfactory. You'll get some more mathematical machinery in quantum field theory, although some of the more experimental particle physics text (Peskin and Schroder?) still leave you confused. The best way to learn it is to take a course in representation theory (of Lie groups, especially), and then just sit and think about how physical systems have to live in irreps of the rotation group (or its central extension, in the case of a quantum system). you will have learned what the irreps of the rotation group are in your representation theory course. there are 1, 2, 3, 4... etc dimensional representations. then you write down a field theory and discover that a system that lives in the n-dimensional rep has intrinsic angular momentum (n-1)/2. When you learn how to construct these representations, you'll see that the 1 dimensional rep is just a scalar (scalars have 1 component), the 2 dimensional rep is a spinor (spinors have 2 components), like you learn in QM, the 3 dimensional rep is a vector (3 components), the 4 dimensional rep is a spin-3/2 space like a vector times a spinor, the 5 dimensional irrep is a rank-2 symmetric traceless tensor, so that's what describes a spin-2 system. (2 = (5-1)/2)

To sum up, representation theory tells you what possible multicomponent guys there are that behave simply under rotations. how they behave under rotations tells you what their angular momentum is, and the rep tells you what kinds of objects can have that angular momentum. Quantum field theory books have the most relevant coverage, but they're notoriously hard to read if you don't already know what they're talking about. -[[User:Lethe/sig|Lethe]] | [[User talk:Lethe/sig|Talk]] 08:05, August 16, 2005 (UTC)

To sum up,

=== Spin of light ===

In quantum mechanics, the polarization of light and other wave length ranges of [[electromagnetic]] radiation is called the spin or [[helicity]] of the photons (particles). Linearly polarized light consists of photons that have a linear combination of positive and negative helicity.--[[User:David R. Ingham|David R. Ingham]] 17:33, 9 August 2005 (UTC)

== quantum mechanics and general relativity, in the introduction ==

I am not sure about the statement that this combination is a problem, but I don't know enough to change it, at this time. The theory of the decay of black holes seems to indicate that the two can work together. As I remember, propagating gravitons (gravity particles) present no problem.

:There is a very real problem in describing gravity quantum mechanically; Google for it. The Hawking black hole radiation theory is not really relevant, because it's only a "semiclassical" theory. You could say that it describes the effect of gravity on quantum mechanics, while ignoring the effects of quantum mechanics on gravity. -- [[User:CYD|CYD]]

What does this sentence in the introduction mean: "Often, it is the answer to questions when general relativity fails." ? <br/>I find it a weak sentence and am going to change it but before I do that would someone like to pipe up if there is a deep signifigance to it that should keep it as is?

-- [[User:Sajendra|Sajendra]]

== Category ==

Why is it in the category "Unsolved problems in physics"?

== the article quantum teleportation ==

i have posted here because i think no one will respond at the discussion there

it says:

Indistinguishability

Let's say that Alice has a rubidium atom (the element physicists in this field like to use for their experiments), which is in its ground state, and Bob also has such an atom, as well in its ground state. It is important to see that these two atoms are indistinguishable; that means that there really is no difference between them.

If Alice and Bob had, say, two glass balls, which exactly look alike, and they exchanged them, then something would change. If you had a powerful microscope, you could certainly find some difference between the two balls. For atoms of the same kind and in the same quantum state, however, there really is no difference at all. The physical situation with Alice having the first atom and Bob the second is exactly the same as vice versa.1 In a certain sense, it is even wrong to say that the two atoms have any individuality or identity. It would be more appropriate to say that the two locations in space both have the property that the fundamental quantum fields have those values which define the ground state of the rubidium atom.

how can rubidium atoms be in the same quantum state? are they like helium 4 or something? or does the exclusion principle apply only through a maximum distance?

sorry for the stupid question but im the person who asked the spin so you would know i dunno much

-protecter

== plain English section needed! ==

I am an (ex-)physicist, but also a writer, and frankly the article on Quantum Mechanics causes me pain to read, or at least the introduction. There should be a plain English paragraph at the start for the non-technical reader who has stumbled here or just wants a quick idea what's going on. This article reads like it was written by physicists for physicists. This is an encyclopaedia, not the Feyman lectures!

In fact, I propose that every technical article of any length should have a plain English paragraph. Feynman said (I'm paraphrasing) that if you can't explain something to a 1st year college student then you don't understand it fully. We need a paragraph for an even lower level than this, in essence making the absolute minimum assumptions of the reader's prior knowledge.

Alternatively, I propose that long technical articles could have a separate "explanatory" article written in the simplest language possible.

Here is a quick shot:

"Quantum Mechanics is a theory in physics which primarily tries to explain how extremely small bodies, such as atoms, behave. Scientists generally agree that it is a very accurate and successful theory and it has very important applications in today's world as all electronic devices, such as computer chips, depend on Quantum Mechanics is some way. It is also important in understanding how large objects such as stars and the Universe as a whole are the way they are.

Despite how successful Quantum Mechanics is at explaining what we see, it does it does have some controversial elements. For example, the behaviour of microscopic objects is very different from the behaviour of everyday objects, and some of its results appear to contradict the Theory of Relativity." [[User:Paulc1001|Paulc1001]] 13:03, 1 October 2005 (UTC)

:To paraphrase [[Eric Cornell]], we might add to "extremely small bodies" the phrase "wavelike entities". Their wavelike character becomes become more and more apparent as we explore the regimes of extremely low temperatures. In other words, their edges cease to become distinct but merge into each other, even at macroscopic scale. For example, in his public lectures he displays a picture of [[rubidium]] [[Bose Einstein condensate]] at millimeter scale for a collection of about a million Rb atoms in a magnetic trap, at a millionth of a Kelvin, with a common [[wave function]]. A wave function 1 millimeter across! (He actually characterized it as a picture of a wave function squared.) I am trying to ascertain the license conditions for his images, as he works for [[NIST]]. They would be a dramatic addition to the QM article as examples of wave functions. [[User:Ancheta Wis|Ancheta Wis]] 15:12, 15 October 2005 (UTC)

::Meh. The fact that you can see quantum mechanics on a macroscopic scale in BEC's is nice but hardly new. BEC's are basically another type of [[superfluid]]. We've had experimental evidence of ''those'' for around [[superfluid|sixty]] or [[superconductivity|ninety]] years, depending on how you count. -- [[User:CYD|CYD]]

::The distribution of the superfluid vortices in Cornell's image is highly regular, beautiful even. I am trying to find a good public image for others to see. The image is nontrivial. [[User:Ancheta Wis|Ancheta Wis]] 10:16, 24 October 2005 (UTC)

::: Again, the vortices that you see in BEC are exactly the same as vortices in superfluid helium and superconductors (in fact, the ability to form vortices is "built-in" to the idea of a superfluid). Here's an image of vortices in a superconductor from 1967: [http://www.fys.uio.no/super/vortex/essmann.html] -- [[User:CYD|CYD]]

:I tried to read this to learn more on the topic and gave up. I strongly suggest a very simplified page in the simple english wiki.

::One thing that is wrong in the proposed Plain English description is the characterization of atoms as "extremely small bodies": common experience would make those bodies 'little hard ball bearings' but that is exactly the point of the BEC discussion above -- they are not little -- they can be 1 millimeter across, acting 'together' in an extremely coordinated way -- millions of atoms (but not little balls, more like waves, all behaving identically) together. The Plain English discussion needs to integrate the [[Heisenberg principle]], so that the little ball picture can be left behind. [[User:Ancheta Wis|Ancheta Wis]] 10:06, 29 October 2005 (UTC)

The discussion above exemplifies bullets ii) and iii) in the 3rd paragraph in the introduction to the article. 10:35, 29 October 2005 (UTC)

== Spatial quantization ==

I wonder if someone can explain how we know that energy states, momentum and various other quantities are quantized, yet space is not. It has often seemed to me that if we are unable to unify gravity fully with quantum mechanics, then one or other of them must be wrong in some fundamental manner. What would the consequences be on physical theory if in fact the universe was fully quantized? And would there be an easy test to prove that the universe is not in such a state? Has anyone done any work in this area?

== Yeah. Plain English Please ==

I'm a general studies student and I'm writing an anthropology paper about technology in post-modern society. I'm pretty sure quantum physics is a big part of this but I couldn't understand a thing in this article. Some plain 'explain it to a novice' language would be really nice. Also that this article has recieved so much attention is great but it doesn't help the lay person and in fact it makes one feel kind of intellectually inadequate.

:No slight is intended. In a nutshell, our common-sense ideas about place (ie position in [[space]]) would have to change if we truly were to integrate the knowledge of QM into our current civilization; you can [[model]] the [[world]] at many levels; look at [[History of science]] for an overview in the broadest terms. In fact Newtonian physics (1700) (approximating the world with hard spheres and rigid bodies) is adequate for understanding a huge part of our civilization. We are just now reaping the benefits of [[Maxwell's equations]] (1865) with the [[electronic circuit]]s of today ( not derived from QM). Look at [[solid state physics]] (which uses some QM) if you want to see the physical basis of our understanding of microelectronic technology. The precision and repeatability of our [[integrated circuit]]s are applications of [[optics]], especially [[photography]] and [[camera]]s, and the ideas behind the [[printing press]] (1041) and [[lithography]] (1798). But [[laser physics]] (1960) and [[physics of condensed matter]] (1900-present) is just starting to reap the benefits of the QM viewpoint. In other words, you don't need to understand the QM viewpoint until you start studying physics, engineering and especially chemistry. And you don't meet too many people who worry about the nature of [[spacetime]] or [[matter]] on an everyday basis. It truly is a subject for specialized study, in our current civilization. --[[User:Ancheta Wis|Ancheta Wis]] 23:25, 26 November 2005 (UTC)

==QM, the uncertainty principle in all of its quantum weirdness==

I wrote this illustration on the "uncertainty principle" talk and wanted to share. Also, I haven't looked at this article on QM in awhile and it has improved, but still may be too complicated in the intro. I'm going to "think on it".

To explain QM, especially the uncertainty principle, I will use a simplified anthropomorphic illustration of electrons in orbits around the atom applying the principles of uncertainty and QM to show how "strange" strange really is. First, let's start with the retained QM features of the Bohr atom model. Imagine an electron as a person, in fact, say you are the electron and you are running around a circular track about 10 feet wide. There is another inside track in further from your track by another few yards. This inside track is also 10 feet wide. There is a refreshment stand at the center of the track which is the nucleus and although you are attracted to it, the probability of you ever being able to get to the refreshment stand is zero. No can do. You are using up more energy to do laps running on the outside track, so you want to move to the inside track. However, the probability of you being able to cross those few yards to the inside track is zero. Therefore, you pull out your handy triquarter and say, "Beam me up Scotty," and you are instantaneously transported to the inside track. (quantum leaping) Another weird thing is that if someone is looking at you (but not measuring where you are), they think they have very blurred vision because you seem to be blurred across the whole ten feet of the track. Most of your body is concentrated at your position, but the rest of you is stretched out across the track. (uncertainty) Now there is another guy who comes along and wants to run on the inside track with you. You look at him and you see that he is identical to you in every way. In fact, no one looking at either of you can ever tell you apart. (indistinguishable particles) Now he starts running on the inside track with you but in the opposite direction. (spin) He is also spread out over the 10 foot width of the track and is fuzzier and less distinct toward the edges of the track. All of a sudden, you decide to turn around and run in the same direction he is running. But as you turn around, he turns around too as if reading your mind. This happens every time. (quantum entanglement) --- I could go on, but this should be weird enough. The true facts are that the track would describe a sphere and you would be stretched out all over the sphere at once which is even harder to imagine. Not only that, but you would be standing still (standing wave) and moving at the same time (angular momentum). That is why Bohr said "if you don't think QM is strange, you haven't understood a single word."

I love what Einstein had to say about all this:

*(after Heisenberg's 1927 lecture) "Marvelous, what ideas the young people have these days. But I don't believe a word of it."

*"The Heisenberg-Bohr tranquilizing philosophy - or religion? - is so delicately contrived that, for the time being, it provides a gentle pillow for the true believer from which he cannot very easily be aroused. So let him lie there.

Further, the fact that Einstein didn't like uncertainty didn't mean he wasn't still a brilliant genius. In fact, the challenges that Einstein brought to QM have transformed it and tweaked it and refined it.

My personal favorite anachronistic quote about QM is the ironic fact that it came out of Copenhagen in Denmark and Shakespeare said in Hamlet as if speaking of QM itself:

*"There is something rotten in the state of Denmark...There are more things in heaven and earth, Horatio, Than are dreamt of in your philosophy."

--[[User:Voyajer|Voyajer]] 16:51, 23 December 2005 (UTC)

:It is much easier and much more physical to imagine the electron in the atom to be not some tiny point jumping from place to place or orbiting around (there are no orbits, there are orbitals), but to imagine the electron being an '''occupation''' of an extended '''[[orbital]]''' and an orbital being a '''vibrating wave confined to the neighbourhood of the nucleus''' by its attracting force. That's why [[Chladni's figures]] of acoustics and the [[normal mode]]s of electromagnetic waves in a resonator are such a good analogy for the orbital pictures in quantum physics. Quantum mechanics is a lot less weird if you see this analogy. The step from electromagnetic theory (or acoustics) to quantum theory is much easier than the step from point mechanics to quantum theory, because in electromagnetics you already deal with waves and modes of oscillation and solve eigenvalue equations in order to find the modes. You just have to treat a single electron like a wave, just in the same way as light is treated in classical electromagnetics.

:In this picture, the ''only'' difference between classical physics and quantum physics is that in classical physics you can excite the modes of oscillation to a continuous degree, called the classical amplitude, while in quantum physics, the modes are "occupied" discretely. -- Fermionic modes can be occupied only once at a given time, while Bosonic modes can be occupied several times at once. Particles are just occupations of modes, no more, no less. As there are superpositions of modes in classical physics, you get in quantum mechanics [[quantum superposition]]s of occupations of modes and the scaling and phase-shifting factors are called (quantum) amplitudes. In a Carbon atom, for example, you have a '''combination of occupations''' of 6 electronic modes of low energy (i.e. frequency). [[Entangled state]]s are just '''superpositions of combinations of occupations of modes'''. Even the states of [[quantum field]]s can be completely described in this way (except for hypothetical topological defects).

:As you can choose different kinds of modes in acoustics and electromagnetics, for example plane waves, spherical harmonics or small wave packets, you can do so in quantum mechanics. The modes chosen will not always be '''decoupled''', for example if you choose plane waves as the system of acoustic modes in the resonance corpus of a guitar, you will get reflexions on the walls of modes into different modes, i.e. you have coupled oscillators and you have to solve a coupled system of linear equations in order to describe the system. The same is done in quantum mechanics: different systems of eigenfunctions are just a new name for the same concept. Energy eigenfunctions are decoupled modes, while eigenfunctions of the position operator (delta-like wavepackets) or eigenfunctions of the angular momentum operator in a non-spherically symmetric system are usually strongly coupled.

:What happens in a measurement depends on the interpretation: In the [[Copenhagen interpretation]] you need to postulate a collapse of the wavefunction to some eigenmode of the measurement operator, while in Everett's [[Many-worlds theory]] an entangled state, i.e. a superposition of occupations of modes of the observed system and the observing measurement apparatus, is formed.

:--[[User:DenisDiderot|DenisDiderot]] 21:07, 23 December 2005 (UTC)

**Thanks for your unnecessary explanation. I am well versed in physics. My analogy was meant to be humorous and over-simplified.--[[User:Voyajer|Voyajer]] 21:12, 23 December 2005 (UTC)

:Please don't feel insulted by my clarification which adresses many other readers as well. Most beginners are confused and demoralized when the weirdness of quantum mechanics is overemphasized and they are confronted with lots of contradicting statements. --[[User:DenisDiderot|DenisDiderot]] 21:29, 23 December 2005 (UTC)

Au contraire, I am not insulted. I just think you don't have a sense of humor. My colleagues found my analogy highly amusing.

What does bother me though is that you think your explanation above is for '''beginners''' in physics or beginners in anything for that matter. I would think you would have to have a pretty heavy knowledge of waves, acoustics, and optics to understand your analogy at all. You would need to understand the concept of standing waves as normal modes of bounded systems such as harmonics and the quality of sound. You would need to understand the significance of Chladni's figures. You would need to understand ultrasonic and infrasonic waves. You would need to understand the concept of waves in media like transverse waves in a uniform string, gravity waves and ripples, superposition of waves such as in linear homogeneous equations and nonlinear superposition. Also, you wouldn't be using the terms fermionic and bosonic to beginners and using the terms eigenvalues and eigenfunctions to a neophyte in physics is ludicrous. In other words, your so-called explanation for "beginners" appears simply absurd and conveys the idea that you are simply trying to make a display of your erudition. If you really want to help the beginner, then you should describe in detail the idea of a standing wave, why we view the electron as a standing wave, what an orbital actually is, why an electron is said to be an occupation of an orbital, and the basics of wave-particle duality. Of course, that is just my opinion. It appears to me that much of the "talk" here is by people complaining that everyone is answering questions and explaining things in a pseudo-intellectual fashion not for the edification of the beginner but simply to show off. Of course, all of this is just my opinion, so take it for what it's worth.--[[User:Voyajer|Voyajer]] 00:36, 24 December 2005 (UTC)

:Your way to discuss things is obviously highly aggressive, and I wonder what it is that makes you so furious and arrogant. I'll just ignore any further aggressive remarks on your part. Maybe it is you who needs some sense of tolerance and humour (''humour does not mean forcing other people to laugh about your jokes'').

:I have a long experience in explaining quantum mechanics to students the way described above (of course, the text given above is just a sketch), and I found it to be highly successful. Even children can easily grasp the concept of waves and of superpositions of waves, and it is a lot of fun for them to see [[Chladni's figures]]. You can do many experiments with standing and propagating waves without any complicated instrumentation, and acoustics is interesting in itself. Much of this is already common knowledge at the age of 12, and in Wikipedia, you can read about all this if you follow the links I provided. The concepts of fermionic and bosonic occupations are ''defined'' by the sentence given above, and they are easily grasped by students after delving a little further into some examples and explaining the [[Pauli exclusion principle]] and [[stimulated emission]] in this context. As soon as the students have grasped the picture and have overcome the prejudice that the electron had to be some pointlike object as they see the orbital to be quite extended, all the weirdness disappears. Of course, many questions arise -- as is always the case when people are bursting with curiosity -- and I'm happy to answer them, because if people are demoralized and think quantum mechanics is just some incomprehensible mess, they cease asking questions.

:--[[User:DenisDiderot|DenisDiderot]] 11:07, 24 December 2005 (UTC)

Not to be annoying; but I'm not a neophyte in quantum mechanics (although I'm not a physicist either), and I had to read your statement twice over, and with the care of reading a college textbook to understand what you were trying to say. And Voyajer is right; using the word eigenvalue for anyone without knowledge of linear algebra, let alone for a total novice in a field, is an improper approach. Nor can you expect someone without a mathematical, engineering, or scientific background to understand 'phase-shifts'. Words like 'Bosonic'--even if explained--will probably throw most people off, and force them to re-read the sentence to understand your prose. Jargon like 'system of linear equations', 'spherical harmonics', and the like don't help out either; nor does the fact that one would have to click on numerous links just to understand some of the ideas you use.

My Two Cents.

[[User:69.84.100.123|69.84.100.123]] 02:25, 28 December 2005 (UTC)Don

: It was just a sketch of the main ideas of how such an explanation for beginners (including [[quantum field theory]]) avoiding all the weirdness could look like. See [[Quantum mechanics explained]] for more details. Feel free to ask questions on the talk page.

:--[[User:DenisDiderot|DenisDiderot]] 02:30, 28 December 2005 (UTC)

== Prose ==

[http://en.wikipedia.org/w/index.php?title=Quantum_mechanics&diff=32568028&oldid=32410097 Can we please call a break here? I think I need to draw the line at ''Line 44''] in the diff. This is a Featured Article. It took work to get it to this state. Line 44 is attempting to state in words what can be said in only a few math symbols. If we want some Simple English we might be able to work this out on the Talk Page. Another alternative is to create a link to some tutorial material on another page, much like a '<nowiki>{{main}}</nowiki>' template to main article. It is also possible to lose Featured status on an article due to overworking the prose. --[[User:Ancheta Wis|Ancheta Wis]] 08:10, 24 December 2005 (UTC)

:One tactic we might use is something like the 'Ants and Martians' device that Feynman used with his son Carl. It ought to be possible to devise a transforming mechanism which allows the sympathetic editor some freedom in explanation for an absolute beginner. But again, the Line 44 diff highlights the need for a stylistic "zoom lens". Or perhaps a stylistic "instant replay" for explanations for the absolute beginner. One possibility that comes to mind is a Portal treatment for the prose of the Line 44 diff. --[[User:Ancheta Wis|Ancheta Wis]] 08:22, 24 December 2005 (UTC)

:Oops. I just re-read the Line 27 diff. We need to walk carefully here. One possible interpretation of the diff is to call into question the 'eigenstate' formulation, which is very basic to the QM picture and which does not contravene the Uncertainty principle. --[[User:Ancheta Wis|Ancheta Wis]] 08:33, 24 December 2005 (UTC)

:I have just re-read DenisDiderot's formulation above and believe it might be possible to use an [[optical cavity]] as a device for some explication of QM ideas. That is pretty concrete, is intimately tied to the ideas of QM and allows us to tie into some laser physics, which rests on QM ideas. --[[User:Ancheta Wis|Ancheta Wis]] 08:56, 24 December 2005 (UTC)

:OK - here is a possibility for some Line 44 rework: we use the [[http://en.wikipedia.org/wiki/Max_Planck#Black-body_radiation Black-body EM radiator]], which is the experimental root of QM anyway, and then use [[optical cavity]] to explain some basics about waves. Just like the pictures of electron orbitals in the article. That frees us from the need to have a wave travel from position A to position B - a mechanical picture which we don't need (its Newtonian physics, well established and not the problem being addressed). What we ''do'' need is some explanation of the ''radiators'' -- that is what [[Planck]] was worrying about anyway. That is intimately tied to the laser physics I was referring to above -- which is matter-dependent, and where QM shines. --[[User:Ancheta Wis|Ancheta Wis]] 09:19, 24 December 2005 (UTC)

::Let's see if we can work through a revision which is sympathetic to beginners without destroying QM's Featured status. --[[User:Ancheta Wis|Ancheta Wis]] 11:08, 24 December 2005 (UTC)

''A contrary argument''

*Line 44 reverted back and as is now in the article: "The first type of quantum effect is the [[quantization (physics)|quantization]] of certain physical quantities. In the example we have given, of a free particle in empty space, both the position and the momentum are continuous observables. However, if we restrict the particle to a region of space (the so-called "[[particle in a box]]" problem), the momentum observable will become discrete; it will only take on the values <math>n \frac{h}{2 L}</math>, where <math>L</math> is the length of the box, <math>h</math> is [[Planck's constant]], and <math>n</math> is an arbitrary nonnegative integer number. Such observables are said to be [[Quantization (physics)|quantized]], and they play an important role in many physical systems. Examples of quantized observables include [[angular momentum]], the total [[energy]] of a bound system, and the energy contained in an [[electromagnetic wave]] of a given frequency."

*Ancheta Wis reverts from prose explanation because he says: "Line 44 is attempting to state in words what can be said in only a few math symbols."

'''Reasons this approach is flawed:'''

*1. There are many complaints in the "talk" regarding: "plain English please".

*2. Mathematical formulae in the form of notation and symbols that can only be known and accessible to people who are already acquainted with the language of science is an inappropriate shortcut in encyclopedia article.

*3. It's true, perhaps the prose was too wordy, not concise enough, but necessary. In other words, it should be re-worked but not eliminated.

*4. The QM featured status will not be destroyed by a more accessible explanation if it is worded expertly in the manner of the major encyclopedia. In other words, all the major encyclopedia do not simply state a formula to explain a concept. It isn't done. Especially without an accessible explanation of the scientific notation in the formula.

*5. Also, this article on QM underemphasizes the importance of Planck's constant by not explaining it. In the Encyclopedia Brittanica, the second paragraph on QM says: "In the equations of quantum mechanics, Max Planck's constant of action h = 6.626 ´ 10-34 joule-second plays a central role. This constant, one of the most important in all of physics, has the dimensions energy ´ time. The term “small-scale” used to delineate the ___domain of quantum mechanics should not be literally interpreted as necessarily relating to extent in space. A more precise criterion as to whether quantum modifications of Newtonian laws are important is whether or not the phenomenon in question is characterized by an “action” (i.e., time integral of kinetic energy) that is large compared to Planck's constant. Accordingly, if a great many quanta are involved, the notion that there is a discrete, indivisible quantum unit loses significance."

*6. It is important to delineate what Planck's constant is, its importance in QM, its pervasiveness throughout QM, BEFORE any mathematical formula are introduced that include the constant h and just say it is Planck's constant in some off-hand manner.

*7. Wikipedia is becoming an inaccessible encyclopedia due to the fact that many articles on physics are simply reduced to mathematical formulae. This is very ''uncommon'' in the major encyclopedia like Encyclopedia Britannica and MSN Encarta where formulae are kept to a strict minimum and prose dominates.

*8. MSN Encarta before introducing any formulae states in its introductory article on QM: "Momentum is a quantity that can be defined for all particles. For light particles, or photons, momentum depends on the frequency, or color, of the photon, which in turn depends on the photon’s energy. The energy of a photon is equal to a constant number, called Planck’s constant, times the frequency of the photon. Planck’s constant is named for German physicist Max Planck, who first proposed the relationship between energy and frequency. The accepted value of Planck’s constant is 6.626 × 10-34 joule-second. This number is very small—written out, it is a decimal point followed by 33 zeroes, followed by the digits 6626. The energy of a single photon is therefore very small." Again another example of properly explaining and emphasizing Planck's constant and its place in QM.

*9. So finally, the simple mathematical formula used alone as a definition for quantization is actually a ''faux pas'' in the world of major encyclopedia.

*IN CONCLUSION, it is therefore a necessity, a priority, and a duty to find a way to include a '''prose''' explanation of Planck's constant before introducing mathematics. So instead of simply erasing my prose explanation, either edit it yourself or come up with a better prose explanation. I agree it needs honing down and was unnecessarily wordy. --[[User:Voyajer|Voyajer]] 13:32, 24 December 2005 (UTC)

:I much appreciate your responsive edit. There is yet another custom in this community of encyclopedists, which is that we work together by consensus. But it actually harms us to see the prose of Encarta, which is a tertiary source (doubly filtered). Back when the encyclopedia started, we had nothing. So the prose you see is the result of the community. We agree not to publish original thoughts, but that does not prevent us from having thoughts which we think through on our own, and then find [[citation]]s for the original sources, for which we can cite our (and their) thoughts. That means, on a practical level, that the other editors on this article have a say, and that we do not attempt to browbeat others. After all, they have something to contribute as well. (But we also do not slavishly copy Encarta, etc.) There is actually a template which exists to flag the existence of copied text.

:Back to [[Planck's constant]], h. ''Deutschland's'' greatest physicist, for which [[Max Planck Institute]] is aptly named, solved a problem which caused a crisis in the philosophical foundations of his science. We are privileged to have witnessed a century of development of a framework for that science which has not yet been integrated into our civilization, other than for a tiny fraction of the billions on our planet. In one of his popular lectures Richard Feynman wrote out a decimal point, followed by 33 zeros wandering around the board, with the significant figures for h. Perhaps that is why Encarta took the trouble to write out the value. And Planck actually came up with that number ''before'' (1899) the blackbody radiation calculations (1900).

:[[natural unit|So there is something going on here]] which we can write about, or simply link to. I personally hope that you and DenisDiderot can work out a conversation here, or perhaps on the article page itself, one thought leading to another, one editor talking to another, using the prose of the article, but doing justice to the subject, with a conscious effort to use the skills and viewpoints of each other as well as our own.

::As an aside, I hope that someday ''[[Helgoland]]'' will somehow get a mention under the QM rubric, which is, after all, where QM was born. --[[User:Ancheta Wis|Ancheta Wis]] 17:05, 24 December 2005 (UTC)

*I thought the Encyclopedia Britannica quote was infinitely more important than the MSN Encarta quote because I agree whole-heartedly with you on that particular point.

*I am not quite clear on what equation exactly that Heisenberg first formulated in Helgoland.

*I am not sure exactly how to go about expanding the article on QM to include the information that DenisDiderot presented since it would look more like the length of a textbook than an article. You appear to be proposing a link to something else with more clarification on QM. But I'm not quite sure what that would be either. Do you have any ideas? Personally, I think many readers would appreciate more clarification, more background on Planck, more history of development, and more illustrations relating to waves and acoustics, that is, if they were given enough background to understand the connection to QM. I just did a search and found an article that made me cringe when reading it called [[Quantum Mechanics - simplified]]. I suppose this could used as a page for the type of further clarification we were discussing. --[[User:Voyajer|Voyajer]] 18:09, 24 December 2005 (UTC)

:Well, what immediately comes to mind is the picture that DenisDiderot is filling in below this text: There is a medium (called the field -- but the name is immaterial, it is something that fills a [[manifold]] ) which is shaped/affected by the boundaries upon which the system (The Operator) works. For the picture below, it is air, but what the heck. For example, if we have a thing (and ''wave'' is not too far from my intuition) which is ''affected'' by the energy we/Nature are pouring into it, then the medium takes on shapes. Like the electron orbitals in the article. Now the geometrical part (the manifold) is the mathematical side, and the System (the Energy,etc Operators) is the physics side. Like in GR, where the math side (the pretty side)= the physics side (the messy part with Stress-Energy). So for an [[optical cavity]] we have light filling it, and that light is augmenting the energy states of the ''material'' in the cavity. But since we have artificially shaped the boundaries of the cavity, and since we are pumping in energy, we are getting back specific transitions of electron energy levels in the material, which is specific frequencies of light. The specific equations of QM, depending on the picture ([[Schrödinger picture]] or [[Heisenberg picture]]) describe the System under consideration. I have to admit more comfort with the wave (Schrödinger) description than the more rigorous state description (Heisenberg). But - and this is the non-intuitive part - the Heisenberg picture, '''which does not operate in space'''/time can be translated to a wave-like (more intuitive) view by the 'Ehrenfest procedure' (discussed by Guest in the talk page above) which allows the computations of time averages, occupying space. That's the crazy part which as a macroscopic being brought up on large time and space scales, I personally do not have a feeling for. The best description I have seen is Feynman's characterization of the Uncertainty principle as something like silly putty, where if you squeeze it, it (the medium/air/field) fights back. But that is where you have a nice description, given above. --[[User:Ancheta Wis|Ancheta Wis]] 19:04, 24 December 2005 (UTC)

::Some of the ramifications of "...which does not operate in space..." can be seen in [[Bell's theorem]] and [[quantum entanglement]].

* Although you gave a nice explanation, that isn't what I was asking. I meant where does Helgoland come into the picture? What was Heisenberg working on in Helgoland? Heisenberg born 1901 Wuerzbrug, Bavaria was Sommerfeld's student and in 1922 he co-authored two papers on the atomic theory of X-ray spectra and the so-called anomalous Zeeman effect. In 1921 Heisenberg published his own paper on the anomalous Zeeman effect introducing half-interger quantum numbers. In 1923 Heisenberg collaborated with Born on perturbation methods to describe the helium atom after which Heisenberg went to Goettingen. In 1924 Heisenberg went to Copenhagen to develop quantum theory with Bohr. In 1925 Heisenberg wrote "On a quantum theoretical re-interpretation of kinematical and mechanical relationships" based on anharmonic oscillators which became known as matrix mechanics. In 1927 Heisenberg developed the uncertainty principle. QUESTION: Therefore, which of the above theories was developed in Helgoland?--[[User:Voyajer|Voyajer]] 21:21, 24 December 2005 (UTC)

:Google tells me it was Matrix Mechanics. --[[User:Ancheta Wis|Ancheta Wis]] 21:44, 24 December 2005 (UTC)

*"In June 1925, while recuperating from an attack of hay fever on Helgoland, he solved the problem of the stationary (discrete) energy states of an anharmonic oscillator:

*Heisenberg (1925), "Über quantentheoretische Umdeutung kinematischer und mechanischer Beziehungen" ("About the Quantum-Theoretical Reinterpretation of Kinetic and Mechanical Relationships"), ''Zeitschrift für Physik''.

== Time-out. ==

OK folks, those of you who are watching the show, please go to the refrigerator or switch to another channel while we take a game-break. Otherwise, stay tuned while we work thru some details about this article's construction. What I am seeing is several sincere editors who have clearly stated programs for making this Featured article more accessible to beginners. Some of the differences I see are stylistic, others are philosophical.

I will be taking the phrases that pop-out at me and will attempt to place them in outline form, for starters. Please feel free to interrupt, re-arrange, etc. --[[User:Ancheta Wis|Ancheta Wis]] 11:21, 24 December 2005 (UTC)

[[Image:Max planck.jpg|100px|thumb|[[Planck]]]]

*a standing wave,

: A standing wave is considered a one-dimensional concept by many students, because of the examples (waves on a spring or on a string) usually provided. In reality, a standing wave is a synchronous oscillation of all parts of an extended object in which the oscillation profile (in particular the nodes and the points of maximal oscillation amplitude) doesn't change. This is also called a normal (= uncoupled) mode of oscillation. You can make the profile visible in [[Chladni's figures]] and in vibrational holography. In unconfined systems, i.e. systems without reflecting walls or attractive potentials, traveling waves may also be chosen as normal modes of oscillation (see [[boundary conditions]]).

*why we view the electron as a standing wave,

: An electron beam (accelerated in a cathode ray tube similar to TV) is diffracted in a crystal and diffraction patterns analogous to the diffraction of monochromatic light by a [[diffraction grating]] or of X-rays on crystals are observed on the screen. This observation proved [[de Broglie]]'s idea that not only light, but also electrons propagate and get diffracted like waves. In the attracting potential of the nucleus, this wave is confined like the acoustic wave in a guitar corpus. That's why in both cases a standing wave (= a normal mode of oscillation) forms. An electron is an occupation of such a mode.

*what an orbital actually is,

: An orbital is a normal mode of oscillation of the electronic [[quantum field]], very similar to a light mode in an optical cavity being a normal mode of oscillation of the [[electromagnetic field]].

*why an electron is said to be an occupation of an orbital, and

: In my view, this is the main new idea in quantum mechanics, and it is forced upon us by observations of the states of electrons in multielectron atoms. Certain fields like the electronic [[quantum field]] are observed to allow its normal modes of oscillation to be excited only once at a given time, they are called fermionic. If you have more occupations to place in this quantum field, you must choose other modes (the spin degree of freedom is included in the modes), as is the case in a carbon atom, for example. Usually, the lower-energy (= lower-frequency) modes are favoured. If they are already occupied, higher-energy modes ''must'' be chosen. In the case of light the idea that a photon is an occupation of an electromagnetic mode was found much earlier by Planck and Einstein, see below.

*the basics of wave-particle duality.

: If you do a position measurement, the result is the occupation of a very sharp [[wavepacket]] being an eigenmode of the position operator. These sharp wavepackets look like pointlike objects, they are strongly coupled to each other, which means that they spread soon.

---

[[Image:DiderotVanLoo.jpg|100px|thumb|[[Diderot]]]]

*waves

*superpositions of waves

: Waves can go through each other without disturbing each other. It just looks like there were two superimposed realities each carrying only one wave and not knowing of each other. That's what is assumed if you use the superposition principle mathematically in the equations.

*Chladni's figures.

: On page [[Chladni's figures]] you find some very enlightening pictures in the links provided.

* What about emission, absorption, particle processes?

: All '''processes''' in nature can be reduced to the time evolution of modes and to (superpositions of) '''reshufflings of occupations''', as described in the [[Feynman diagrams]]. For example in an emission of a photon by an electron changing its state, the occupation of one electronic mode is moved to another electronic mode of lower frequency and an occupation of an electromagnetic mode (whose frequency is the difference between the frequencies of the mentioned electronic modes) is created. --[[User:DenisDiderot|DenisDiderot]] 11:44, 25 December 2005 (UTC)

*experiments with standing and propagating waves

*fermionic and bosonic occupations

: Electrons and photons become very similar in quantum theory, but one main difference remains: Electronic modes cannot be excited/occupied more than once (= [[Pauli exclusion principle]]) while photonic/electromagnetic modes can and even prefer to do so (= [[stimulated emission]]). --[[User:DenisDiderot|DenisDiderot]] 12:17, 24 December 2005 (UTC)

: This property of electonic modes and photonic modes is called fermionic and bosonic, respectively. Two photons are indistinguishable and two electrons are also indistinguishable, because in both cases, they are only occupations of modes: all that matters is ''which'' modes are occupied. The order of the occupations is irrelevant except for the fact that in [[odd permutation]]s of fermionic occupations, a negative sign is introduced in the amplitude.

: Of course, there are other differences between electrons and photons:

:* The electron carries an [[electric charge]] and a [[rest mass]] while the photon doesn't.

:* In physical processes (see the [[Feynman diagrams]]), a single photon may be created while an electron may not be created without at the same time removing some other fermionic particle or creating some fermionic antiparticle. This is due to the conservation of charge. --[[User:DenisDiderot|DenisDiderot]] 11:44, 25 December 2005 (UTC)

*Pauli exclusion principle and

*stimulated emission

---

[[Image:Optical-cavity1.png|100px|thumb|[[optical cavity]]]]

*Now let's look at [[Planck]]'s problem. From his article, we see that he was trying to solve a practical problem, which was to derive an expression for the energy radiating from a light bulb and the rest is history, (well-known, etc., etc.) ...

: Planck was the first to suggest that the electromagnetic modes are not excited continuously but discretely by energy quanta <math>h \nu</math> proportional to the frequency. By this assumption, he could explain why the high-frequency modes remain unexcited in a thermal light source: The thermal exchange energy <math>k_B T</math> is just too small to provide an energy quantum <math>h \nu</math> if <math>\nu</math> is too large. Classical physics predicts that ''all'' modes of oscillation -- regardless of their frequency -- carry the average energy <math>1/2 k_B T</math>, which amounts to an infinite total energy (called [[ultraviolet catastrophe]]). This idea of energy quanta was the historical basis for the concept of occupations of modes, designated as photons by Einstein. --[[User:DenisDiderot|DenisDiderot]] 12:59, 24 December 2005 (UTC)

---

What about operators, eigenstates, measurements and all that?

: The system of modes to describe the waves can be chosen at will. Any arbitrary wave can be decomposed into contributions from each mode in the chosen system. For the mathematically inclined: The situation is analogous to a vector being decomposed into components in a chosen coordinate system. Decoupled modes or, as an approximation, weakly coupled modes are particlularly convenient if you want to describe the evolution of the system in time, because each mode evolves independently of the others and you can just add up the time evolutions. In many situations, it is sufficient to consider less complicated weakly coupled modes and describe the weak coupling as a [[perturbation theory|perturbation]].

: In every system of modes, you must choose some (continuous or discrete) '''numbering''' (called "[[quantum number]]s") for the modes in the system. In [[Chladni's figures]], you can just count the '''number of nodes''' of the standing waves in the different space directions in order to get a numbering, as long as it is unique. For decoupled modes, the '''energy''' or, equivalently, the frequency might be a good idea, but usually you need further numbers to distinguish different modes having the same energy/frequency (this is the situation referred to as [[degenerate energy level]]s). Usually these additional numbers refer to the symmetry of the modes. Plane waves, for example -- they are decoupled in spatially homogeneous situations -- can be characterized by the fact that the only result of shifting (translating) them spatially is a '''phase shift''' in their oscillation. Obviously, the phase shifts corresponding to unit translations in the three space directions provide a good numbering for these modes. They are called the wavevector or, equivalently, the '''momentum''' of the mode. Spherical waves with an angular dependence according to the [[spherical harmonics]] functions (see the pictures) -- they are decoupled in spherically symmetric situations -- are similarly characterized by the fact that the only result of rotating them around the z-axis is a phase shift in their oscillation. Obviously, the phase shift corresponding to a rotation by a unit angle is part of a good numbering for these modes; it is called the '''magnetic quantum number''' m (it must be an integer, because a rotation by 360° mustn't have any effect) or, equivalently, the '''z-component of the orbital angular momentum'''. If you consider sharp wavepackets as a system of modes, the '''position''' of the wavepacket is a good numbering for the system. In [[crystallography]], the modes are usually numbered by their '''transformation behaviour''' (called [[group representation]]) in symmetry operations of the crystal, see also [[symmetry group]], [[crystal system]].

: The mode numbers thus often refer to physical quantities, called '''observables''' characterizing the modes. For each mode number, you can introduce a mathematical operation, called '''operator''', that just multiplies a given mode by the mode number value of this mode. This is possible as long as you have chosen a mode system that actually ''uses'' and is characterized by the mode number of the operator. Such a system is called a '''system of eigenmodes''', or '''eigenstates''': Sharp wavepackets are no eigenmodes of the momentum operator, they are eigenmodes of the position operator. Spherical harmonics are eigenmodes of the magnetic quantum number, decoupled modes are eigenvalues of the energy operator etc. If you have a superposition of several modes, you just operate the operator on each contribution and add up the results. If you chose a ''different'' modes system that doesn't use the mode number corresponding to the operator, you just decompose the given modes into eigenmodes and again add up the results of the operator operating on the contributions. So if you have a superposition of several eigenmodes, say, a superposition of modes with different frequencies, then you have contributions of different values of the observable, in this case the energy. The superposition is then said to have an '''indefinite value''' for the observable, for example in the tone of a piano note, there is a superposition of the fundamental frequency and the higher harmonics being multiples of the fundamental frequency. The contributions in the superposition are usually not equally large, e.g. in the piano note the very high harmonics don't contribute much. Quantitatively, this is characterized by the '''amplitudes''' of the individual contributions. If there are only contributions of a single mode number value, the superposition is said to have a '''definite''' or '''sharp value'''.

: In '''measurements''' of such a mode number in a given situation, the result is an eigenmode of the mode number, the eigenmode being chosen at random from the contributions in the given superposition. All the other contributions are supposedly eradicated in the measurement -- this is called the [[wave function collapse]] and some features of this process are questionable and disputed. The probability of a certain eigenmode to be chosen is equal to the absolute square of the amplitude, this is called Born's probability law. This is the reason why the amplitudes of modes in a superposition are called "'''probability amplitudes'''" in quantum mechanics. The mode number value of the resulting eigenmode is the result of the measurement of the observable. Of course, if you have a sharp value for the observable ''before'' the measurement, nothing is changed by the measurement and the result is certain. This picture is called the [[Copenhagen interpretation]]. A different explanation of the measurement process is given by Everett's [[many-worlds theory]]; it doesn't involve any wave function collapse. Instead, a superposition of combinations of a mode of the measured system and a mode of the measuring apparatus (an [[entangled state]]) is formed, and the further time evolutions of these superposition components are independent of each other (this is called "many worlds").

:--[[User:DenisDiderot|DenisDiderot]] 21:12, 24 December 2005 (UTC)

: As an example: a sharp wavepacket is an eigenmode of the position observable. Thus the result of measurements of the position of such a wavepacket is certain. On the other hand, if you decompose such a wavepacket into contributions of plane waves, i.e. eigenmodes of the wavevector or momentum observable, you get all kinds of contributions of modes with many different momenta, and the result of momentum measurements will be accordingly. Intuitively, this can be understood by taking a closer look at a sharp or very narrow wavepacket: Since there are only a few spatial oscillations in the wavepacket, only a very imprecise value for the wavevector can be read off (for the mathematically inclined reader: this is a common behaviour of [[Fourier transform]]s, the amplitudes of the superposition in the momentum mode system being the Fourier transform of the amplitudes of the superposition in the position mode system). So in such a state of definite position, the momentum is very indefinite. The same is true the other way round: The more definite the momentum is in your chosen superposition, the less sharp the position will be, and it is called Heisenberg's [[uncertainty relation]].

: Two different mode numbers (and the corresponding operators and observables) that both occur as characteristic features in the ''same'' mode system, e.g. the number of nodes of one of [[Chladni's figures]] in x direction and the number of nodes in y-direction or the different position components in a position eigenmode system, are said to '''commute''' or be compatible with each other (mathematically, this means that the order of the product of the two corresponding operators doesn't matter, they may be commuted). The position and the momentum are non-commuting mode numbers, because you cannot attribute a definite momentum to a position eigenmode, as stated above. So there is no mode system where both the position and the momentum (referring to the same space direction) are used as mode numbers.

:--[[User:DenisDiderot|DenisDiderot]] 12:32, 25 December 2005 (UTC)

* What about the Schrödinger equation, the Dirac equation etc?

: As in the case of [[acoustics]], where the direction of vibration, called [[polarization]], the [[speed of sound]] and the [[wave impedance]] of the media, in which the sound propagates, are important for calculating the appearance and the frequency of modes as seen in [[Chladni's figures]], the same is true for electronic or photonic/electromagnetic modes: In order to calculate the modes (and their frequencies or time evolution) exposed to potentials that attract or repulse the waves or, equivalently, exposed to a change in [[refractive index]] and wave impedance, or exposed to magnetic fields, there are several equations depending on the polarization features of the modes:

:* Electronic modes (their polarization features are described by [[Spin]] 1/2) are calculated by the [[Dirac equation]], or, to a very good approximation in cases where the [[theory of relativity]] is irrelevant, by the [[Schrödinger equation]] and the [[Pauli equation]].

:* Photonic/electromagnetic modes (polarization: Spin 1) are calculated by [[Maxwell's equations]] (You see, 19th century already found the first quantum-mechanical equation! That's why it's so much easier to step from electromagnetic theory to quantum mechanics than from point mechanics).

:* Modes of Spin 0 would be calculated by the [[Klein-Gordon equation]].

:--[[User:DenisDiderot|DenisDiderot]] 13:08, 25 December 2005 (UTC)

---

*But let's also look at [[Helmholtz]]. He ran an experiment which clearly showed the physical reality of [[resonance]]s in a box. (He predicted and detected the [[Acoustics#Helmholtz_resonator|eigenfrequencies]].)

---

***DenisDiederot and Ancheta Wis have put together some wonderful fundamental information on QM here. It seems a shame that it will eventually get lost in the "talk" discussion section. Does anyone have any idea of how to include this information in Wikipedia? Will it bog down the current article? If so, under what article title could this information be included, as a whole, as a further explanation of QM? --[[User:Voyajer|Voyajer]] 18:26, 24 December 2005 (UTC)

: Thank you very much. I'm sure we'll find a solution, maybe on a page like [[Quantum mechanics explained]]. Merry Christmas to everybody! --[[User:DenisDiderot|DenisDiderot]] 21:12, 24 December 2005 (UTC)

:And Merry Christmas to you both! --[[User:Ancheta Wis|Ancheta Wis]] 21:52, 24 December 2005 (UTC)

::Merry Christmas ,From TW.--[[User:HydrogenSu|HydrogenSu]] 07:20, 25 December 2005 (UTC)

I moved the texts to the new page [[Quantum mechanics explained]], because this talk page might otherwise get too large. Let's see if we can create a text providing an exact (non-simplified) explanation for beginners. --[[User:DenisDiderot|DenisDiderot]] 13:35, 25 December 2005 (UTC)

== 25 Dec 05 is over ==

[[24.91.73.141]] plopped [http://www.nytimes.com/2005/12/27/science/27eins.html http://www.nytimes.com/2005/12/27/science/27eins.html] in external links. I suppose the travel of enlightenment seekers is apt to be in the other direction: from the there to here. How can something actually be two contradictory things may be the question. Honest-liar, clod-swoosh, correct-incorrect. Here's a quote from that article: "This fall two Nobel laureates, Anthony Leggett of the University of Illinois and Norman Ramsay of Harvard argued in front of several hundred scientists at a conference in Berkeley about whether, in effect, physicists were justified in trying to change quantum theory, the most successful theory in the history of science. Dr. Leggett said yes; Dr. Ramsay said no." Wouldn't it exact if both were right? The Times links the article to some quotes, for instance: " 'I don't like it, and I'm sorry I ever had anything to do with it.' -- Erwin Schrödinger about the probability interpretation of quantum mechanics". If you can bring yourselves to call the eigenwhosis "discrete value" it might help the jargon averse. Is not precision proven to be unobtainable in a reality sure to be uncertain? Unless it both is and isn't, of course. [[User:207.172.134.175|207.172.134.175]] 07:05, 28 December 2005 (UTC)

:See [[cat state]]. --[[User:Ancheta Wis|Ancheta Wis]] 11:13, 28 December 2005 (UTC) Note: |0> |1> are [[bra-ket|ket]]s, or [[Eigenvalue, eigenvector and eigenspace|state]]s. i.e. It is possible to be [[precise]] and [[abstraction (mathematics) |abstract]] at the same time. A '''cat state''' might be |00...0> + |11...1>. In this [[notation]] 0 and 1 are labels like [[True]] and [[False]]. Or [[spin]] [[Up]] and [[Down]]. etc. Upon re-reading I see that one issue is the existence or nonexistence of precise states without human action. The current experiment which generated a cat state was artificially induced. It will take work to observe a natural 6-atom cat state.

::Yes, quantum mechanics wouldn't state that a person was honest and a liar or an object was clod or swoosh at the same time. It would rather state that there's a superposition of the person being honest and of him being a liar or that there's a superposition of the object being clod and being swoosh -- or, for that matter, a superposition of the cat being alive and being dead. Quantum mechanics routinely deals with superpositions of situations, and it is forced to do so by results as seen in the [[double-slit experiment]]. [[Many-worlds theory]] takes this idea at face value. Ancheta gave the mathematical notation for superpositions. --[[User:DenisDiderot|DenisDiderot]] 13:18, 28 December 2005 (UTC)

:::F. Lindner, M. G. Schätzel, H. Walther, A. Baltuska, E. Goulielmakis, F. Krausz, D. B. Milosevic, D. Bauer, W. Becker, G. G. Paulus in ''Attosecond double-slit experiment'' Physical Review Letters 95, 040401 (2005) conclude "The observation of interference and its absence '''at the same time for the same electron''' ''(emphasis added)'' is a beautiful demonstration of the principles of quantum mechanics," and (oh, by the way) attosecond interferometry will have practical applications. The website of [http://faculty.physics.tamu.edu/ggp/ Gerhard Paulus] explains the experiment. "Superposition" is certainly more firmly established than Jung's [http://members.aol.com/projbin/plerjung.htm Pleroma]; note there, "time as relative concept; all historical processes complemented by 'simultaneous' existence in the Bardo or pleroma". Reality is pretty weird. [[User:207.172.134.175|207.172.134.175]] 22:38, 28 December 2005 (UTC)

::::[[Roger Penrose]]'s ''omnium'' appears to be the Bardo or Pleroma, as well. By the way, Penrose, a mathematician who happens to be vitally interested in physics, as evidenced by his new book ''Road to Reality'' (I recommend it; it has a very nice discussion of the mathematical concept called a ''connection'' as well as a graphic representation for tensor notation; -- his wife illustrated the book) has found a viewpoint that more firmly supports GR than QM. So you might discover that this thread is currently leading to Penrose and GR, as far as I can tell, rather than to QM. --[[User:Ancheta Wis|Ancheta Wis]] 18:02, 29 December 2005 (UTC)

::::But hold on, this image [[Image:Roger-Penrose-Kachelstruktur.jpg|thumb|Penrose tiling]] which resembles the vortex distribution of a [[BEC|bose-einstein condensate]] shows there is some application of Penrose's ideas to QM. It closely resembles the symmetries in a [[BEC]] bose-einstein condensate picture that [[Eric Cornell]] recently displayed at a public lecture of his - his picture was blue with each superfluid vortex a dark spot corresponding to a polyhedron in the Penrose tiling, except that the spots followed a hexagonal distribution rather than the pentagonal distribution you see. --[[User:Ancheta Wis|Ancheta Wis]] 20:44, 29 December 2005 (UTC)

:::::Amazon said they'll ship [http://www.amazon.com/gp/product/0679454438/qid=1135963369/sr=8-1/ref=pd_bbs_1/104-1504452-5387168?n=507846&s=books&v=glance The Road to Reality] to me next year. Congrats on your sysopship - don't let them overwork you. GR & QM facets of the same thing? If so, the connection is opaque to the duality mired (i.e. all of us). Happy New Year! Anon user [[User:207.172.134.175|207.172.134.175]] generally also me, [[User:Metarhyme|Metarhyme]] 17:52, 30 December 2005 (UTC)

:::::Thank you! Like the old [[Texas Ranger]]s, who made their star-shaped badges from 5-peso silver coins, I formed an 8-pointed badge out of an [[Aztec calendar]]. And a happy [[J2000]]+6 to you! --[[User:Ancheta Wis|Ancheta Wis]] 19:46, 30 December 2005 (UTC)

== OPERATION to Schrödinger equation ==

*By the way show given as :

:<math>-\frac{\hbar^{2}}{2m}[(\frac{d^2}{dx^2}+\frac{d^2}{dy^2}+\frac{d^2}{dz^2}+\frac{d^2}{dt^2})\Psi(x,y,z,t)]+V\Psi(x,y,z,t)=E\Psi(x,y,z,t)</math>

[[Schrödinger equation]]'s coefficient of the extreamly left can be〝operated〞to 2 parts.

One is for [[Uncertainty Principle]] exactly well.<math>\Longrightarrow \frac{\hbar}{2}</math> which is good for the limited value of the product by <math>\Delta P</math> and <math>\Delta X</math>.

The other is for <math>\frac{\hbar}{m}</math>,recently without any sense in physics well.

--[[User:HydrogenSu|HydrogenSu]] 09:58, 30 January 2006 (UTC)

:The left side is just Kinetic + Potential energy. The left half of the left side is Kinetic energy, the V half of the is Potential energy, for a single particle. If you use the heuristic that 'Observables (Kinetic + Potential energies) are Operators', you get the right side of the Schrödinger equation. --[[User:Ancheta Wis|Ancheta Wis]] 10:55, 30 January 2006 (UTC)

::Can we take apart by seprated operation on <math>\hbar \over 2m</math> without any reasons of "Observables or not"? (Just in Math to seperate them away?)Thank you,this is my question after reading your reply.--[[User:HydrogenSu|HydrogenSu]] 18:10, 30 January 2006 (UTC)

This equation confuses me. Why are time and space treated the same way, on the left side in a non-relativistic equation? Why are there time derivatives but a constant energy. [[User:David R. Ingham|David R. Ingham]] 07:56, 12 February 2006 (UTC)

== A Question of Linear Operators ==

I have a question on

[http://en.wikipedia.org/wiki/Image:Modern_physics001.jpg].

Why does

:<math>\mathcal <p^2>={\Delta}p^2+<p>^2 </math>?

--[[User:HydrogenSu|HydrogenSu]] 09:48, 26 January 2006 (UTC)

:I switched it to momentum because thats what the picture said. --[[User:Ancheta Wis|Ancheta Wis]] 11:37, 26 January 2006 (UTC)

::My question of that belongs to Quantum mechanics. I hope it be kept.:)

::By the way thank you.

:To answer your question

::<math>\Delta p^2 \equiv <(p-<p>)^2></math>

::<math>\mathcal = <p^2 - 2p<p> + <p>^2> </math>

::<math>\mathcal =<p^2> - 2<p><p> + <p>^2=<p^2>-<p>^2 </math>

:::Thanks a lot. By the way I edited some of your Math view for good-browsing. It was too long for looking. Sorry:)--[[User:HydrogenSu|HydrogenSu]] 18:23, 30 January 2006 (UTC)

== [[Quantum darwinism]] ==

I started the article a while back and placed a link here; I'm sure it was removed for a good reason... but couldn't it be linked to somewhere in this article? And or going in the Quantum topic template? - [[User:RoyBoy|Roy]][[User talk:RoyBoy|'''Boy''']] ^{[[User:RoyBoy/The 800 Club|800]]} 08:15, 30 January 2006 (UTC)

== My changes: http://en.wikipedia.org/w/index.php?title=Quantum_mechanics&diff=39241812&oldid=39099331 ==

There is so much discussion here that my edit comments may not be considered sufficient explanation for my changes.

"Quantum mechanics uses [[complex number]]" The probabilities are not part of the mathematical formulation. The formulation is in terms of complex wave functions, and so forth.

"These are related to classical physics and ordinary language largely with the use of [[probability]]." This is essential to interpretation of classical physics and ordinary language in terms of quantum mechanics. Encyclopedia readers will be looking at it from the other direction, but this wording can be read from the classical point of view also.

"Newton's laws of motion" Gravity has little to do with atoms.

"obeys" qm "arises from" all observations of nature.

"the classical [[position]]" in qm, things have wave functions. "position", in the sense of an exact position of a particle is a uniquely classical concept. (Position doesn't seem to have a good link so maybe I will remove the link.)

"instead of describing" This change may not be necessary, but is based on the same argument as above.

"Therefore, quantum mechanics, translated to Newton's equally deterministic description, leads to a probabilistic description of nature." I expect a lot of argument about "equally deterministic", but the time dependent Schrödinger equation is first order in time, which makes it ''explicitly'' deterministic. The probabilities do not arise until the classical approximation is first used. The (new) probabilities belong only to the relation between qm on one hand and classical physics and ordinary language on the other.

Perhaps "Newton's equally deterministic description" may be inadequate here, because it is not really his view, it is the view of everyone before Schrödinger and Heisenberg.

[[User:David R. Ingham|David R. Ingham]] 08:59, 12 February 2006 (UTC)

"probabilistic description of nature" I don't like this phrase, but it is explained now. [[User:David R. Ingham|David R. Ingham]] 09:09, 12 February 2006 (UTC)

:Thank you for the careful writing. As Feynman would have said, ''[[good]]!'' --[[User:Ancheta Wis|Ancheta Wis]] 12:32, 12 February 2006 (UTC)

Thank your [[User:Ancheta Wis|Ancheta Wis]], but I hope that a favorable comment by an administrator has not inhibited others from expressing their views. Some of these ideas have been controversial in Wikipedia, and I hope to have a chance to continue to support my points of view. I have found already that mention of [[Richard Feynman]] or [[Julian Schwinger]] often discourages further argument, like "kings X" in children's games. This is especially useful to me, because I have heard them speak and don't have to cite anything that can be checked. [[User:David R. Ingham|David R. Ingham]] 08:50, 21 February 2006 (UTC)

== High School Student here ==

Dear Scientists,

I am a 10th grader. I am supposed to do a project on Quantum Mechanics for my school and I really do not have the slightest clue about what any of you are talking about. :( If you really want to make a good page you are going to have to simplify it down. Like that guy above said, if you really understand this stuff, then you should be able to explain it to an idiot. So this is a challenge for you guys, please tone the level of scientific facts and words down on here and I think that people will like you more.

I am a big fan of Quantum Mechanics. I think that they are great. However I would really like to learn more about them because I am supposed to write a children's book about them. :(

Well I hope some of you people can take my request to heart and maybe you could try to make

:Dear Student. You might want to start with [[spectroscopy]] or [[radioactivity]], or even a [[blackbody]] (a light bulb). QM doesn't impinge too much in our daily lives, unless you want to count the operation of a [[transistor]] or [[laser]]. It takes years to understand Quantum physics, although [[classical mechanics]] appears on every kid's [[playground]] with [[slide]]s and [[Swing (seat)|swing]]s and [[merry-go-round]]s. If you look at the [[star]]s you might even wonder [[thermonuclear fusion|why do the stars shine]]. If you are trying to understand how an atom could exist, you will have just asked a QM question. You should start with the first link at the top of the article. --[[User:Ancheta Wis|Ancheta Wis]] 18:32, 19 February 2006 (UTC)

::Thinking about it, your book assignment should be answering ''[[what]], [[when]], [[where]]''. ''[[How]]'' and ''[[why]]'' are more difficult questions. The physics of the playground answers the first 3 w's only. If you start with ''[[why]]'' then your level of understanding and and search for answers will take years. 19:03, 19 February 2006 (UTC)

:Here is a start at ''[[what]]'':

::QM can explain the [[periodic table#Methods for displaying the periodic table|periodic table]] of the [[chemical element]]s.

:Now you can start filling in ''[[when]], [[where]]'' in your book. The illustration for the article shows the first few [[electron orbital]]s for [[chemical element]] number 1: [[hydrogen]]. 19:36, 19 February 2006 (UTC)

:But how will you know when you are done with your study for the book? -- When you don't have to click on any link in the Wikipedia article you are studying because you already know what it is going to say. When that is true then you are ready to write. 19:52, 19 February 2006 (UTC)

:And what if the words in the articles are foreign to you? Well, you are fortunate enough to still be in school. Ask your teacher about the meanings of those foreign words. I recommend grouping your unknown words or ideas in fewer than seven unknowns at a time. Write each question/ word on a separate index card. When you don't know something, write the unknown down on the card. When you get the answer, write that down on the card as well. Eventually you will have a bunch of cards which you can start sorting into related groups. Use Wikipedia to help you sort the cards. If the words are related, they will be on the same Wikipedia page. Then take the cards with the words on them and construct sentences from the formerly unknown words. If you still can't write a sentence about the words, wait. It takes time to understand anything that is important. That does not mean memorizing everything on the card. If you care about the word, it will remain with you (sometimes for the rest of your life). I hope that you understand that ''your questions are the most important part'' of all this research. You can always find answers on the Internet or in a book or article or person you have found. But answers will come to you in their own time, when you are finally ready to understand them. Just wait; I hope you are ready when the answers come.

When the [[periodic table]] was invented, it was discovered by a man who also wrote down the [[Chemical element|elements]] on index cards. He laid his index cards on the table and grouped like-elements together. When he found a missing element he wrote down a card which [[prediction|predicted]] the properties of that element.

When [[Ward Cunningham]] was inventing the [[wiki]] he also used index cards.

(Where did the signature go?)

* The signiture "23:14, 19 February 2006 Ancheta Wis" seems to have been omitted here.

I am answering a point at a time, without reading everything first.

There is an attempt to simplify called [[Basics of quantum mechanics]], but I disagree with its claim to avoid advanced topics: most of quantum mechanics can be understood without worrying about probabilities.

Writing a children's book about qm is an even more ambitious project than trying to explain it to high-school students. I think it would be of great value if someone could succeed in writing one that would really be read and understood, because I believe that qm, like foreign languages, is best understood if started early.

I told my 11 year old niece "If you keep on looking through more and more powerful microscopes, you don't keep on seeing more detail forever. Eventually matter is composed of units called atoms and motion is composed of units called quanta." I am not sure that helped her more than it confused her, but I can't think of anything better I could have said. Atoms are traditionally taught before quantum mechanics, but are not more fundamental. There would be no explanation of why they form molecules and crystals. [[User:David R. Ingham|David R. Ingham]] 04:39, 20 February 2006 (UTC)

Classical mechanics does not have a greater effect on in our everyday lives than qm does. It is just more intuitive and closer to direct observation. When you throw a baseball, where it goes is mostly explained by classical mechanics and your thoughts as you catch it are related to Newton's laws. Why it stays together and occupies space and how you can see it are only fully explained with quantum mechanics. But the qm takes too much mathematics to use on the baseball field. It is used to support technology, mostly in chemistry and engineering, to make things that can be used without understanding their design principles. [[User:David R. Ingham|David R. Ingham]] 05:44, 20 February 2006 (UTC)

=== Children's book ===

How about:

Once upon a time there was a particle of yellow light. We call her Goldielocks, though light particles can't really have names. She wandered until she came to an atom that had three bare electrons. One electron was stuck too hard in the atom. One was too loose. The third was just right, so he and Goldielocks became a photoelectron. ? [[User:David R. Ingham|David R. Ingham]] 06:20, 20 February 2006 (UTC)

Explanation:

Quantum mechanics explains the fact that light is composed of particles.

If elementary particles like light and electrons could be labeled with names, much of modern physics would not work. Exchanging two identical particles does not change anything.

The term "bare electron" is used a lot, but it doesn't have any justification here beyond resembling the original version of the tale.

A light particle can excite a "loose" electron but that may be less likely than one that is "just right".

One of Einstein's important early discoveries was an explanation of individual light particles knocking individual electrons out of their atoms. The light particle becomes a part of the electron's motion. [[User:David R. Ingham|David R. Ingham]] 05:59, 21 February 2006 (UTC)

== Introducton ==

* JA: Re:

<blockquote>

Quantum mechanics; 03:48 ... David R. Ingham (Talk) (→Description of the theory - I think this is a further improvement, but I don't think we are done. This is a good paragraph technically, but is it simple enough for the introducton?)

</blockquote>

* JA: I dunno, it would depend on the charge of the introducton. [[User:Jon Awbrey|Jon Awbrey]] 04:00, 9 March 2006 (UTC)

==Schrödinger's QM philosophy==

What if the Philosophy section were a separate page, [[Philosophy of quantum mechanics]], currently a redirect. Much could be written on this topic, but separately. For example, Schrödinger, Bohr, Born, Einstein were passionate about their viewpoints; [[Ernest J. Sternglass]]' memoir, p. 125, notes that Bohr was influenced by [[Soren Kierkegaard]]. --[[User:Ancheta Wis|Ancheta Wis]] 11:00, 9 April 2006 (UTC)

:I agree. There is much to right on Philosphical views of Quantum Mechanics.-[[User:Holy Ganga|Holy Ganga]] 17:21, 9 April 2006 (UTC)

:''HG's contribution copied here for further discussion.''

::Regarding mystical philosophical insights on Quantum mechanics, [[Erwin Schrodinger]] said, [[Vedanta]] teaches that consciousness is singular, all happenings are played out in one universal consciousness and there is no multiplicity of selves. This life of yours which you are living is not merely apiece of this entire existence, but in a certain sense the whole; only this whole is not so constituted that it can be surveyed in one single glance. This, as we know, is what the Brahmins express in that sacred, mystic formula which is yet really so simple and so clear; tat tvam asi, this is you. Or, again, in such words as “I am in the east and the west, I am above and below, I am this entire world". There is no kind of framework within which we can find consciousness in the plural; this is simply something we construct because of the temporal plurality of individuals, but it is a false construction....The only solution to this conflict insofar as any is available to us at all lies in the ancient wisdom of the Upanishad. The multiplicity is only apparent. This is the doctrine of the Upanishads. The mystical experience of the union with God regularly leads to this view, unless strong prejudices stand in the west.

:::Is there a citation for this? I know a few things about philosophy of physics, and this doesn't ring a bell. --best, kevin <b>[</b>[[User:Kzollman|kzollman]]<b>][</b>[[User talk:Kzollman|talk]]<b>]</b> 17:38, 9 April 2006 (UTC)

::::Kevin and HG, I would be grateful for a discussion of the role of the observer in the QM framework. What would be the basis of an [[observation]] when the scale of the [[observer]] far exceeds the scale of the system under discussion? --[[User:Ancheta Wis|Ancheta Wis]] 17:44, 9 April 2006 (UTC)

:::::I'm not sure what your asking about. Are you worried about the [[measurement problem]]? This has received substantial treatment by both physicists and philosophers of physics. We have a very good article on at least one [[interpretation of quantum mechanics]] the [[many-worlds interpretation of quantum mechanics]]. Is this what you're getting at? --best, kevin <b>[</b>[[User:Kzollman|kzollman]]<b>][</b>[[User talk:Kzollman|talk]]<b>]</b> 04:49, 10 April 2006 (UTC)

::::::Last I looked, I did not agree that those were very good articles. In my opinion, these questions can only be seriously addressed, after learning the mathematics necessary to understand the basics of qm. Discussing them here in non-mathematical language appears to be endlessly frustrating. [[User:David R. Ingham|David R. Ingham]] 05:08, 10 April 2006 (UTC)

== Inaccuracies in Paragraph 5 of the introduction ==

I'm very new to editing wikipedia, as in never done it before. :)<BR>

I don't want to just delete a line from the article as my first edit, with out a comment about it.

The last line in para 5 "It was from this view that the uncertainty principle, the foundation of quantum mechanics, arose." this = wave particle duality<BR>

This statement is not true, as far as I know. The uncertainity principle is a mathmatical property of operators, which leads to be the [[Canonical_commutation_relation]]. The Heisenburg uncertainity principle is just a specific application of the cannonical commutator.<BR>

If I understood how to do math here I would show the derivation of it. Specifically I'd be following the equation 2.50 on page 43 of Introduction to Quantum Mechanics 2nd ed, by Griffiths, as support for it not being from the wave particle duality that gave rise to it.<BR>

I'm ignoring the part about the uncertainity principle being the foundation of quantum mechanics when it would be much more proper to say that the Schrödinger Equation is the foundation of Quantum Mechanics.<BR>

I'll admit that there may be history where the wave particle duality lead to this that I don't know about, but it doesn't seem a proper statement to have in the article. It makes it seem that because there is the duality it was derived from there to have this result. Which isn't the case as it came from existing mathmatical properties.

<BR>

Thanks for any patience to this newb as he tries to make articles better.

[[User:NijaMunki|NijaMunki]] 07:32, 18 April 2006 (UTC)

:Go ahead and change it. [[WP:BB|Be bold!]]

:By the way, you don't have to type <code><nowiki><BR></nowiki></code> and you don't have to put underscores in links. For help with math markup, see [[Help:Formula]]. —[[User:Keenan Pepper|Keenan Pepper]] 17:02, 18 April 2006 (UTC)

== Quantum mechanics and free will discussion - missing ==

I couldn't find anything on the quantum mechanics pages on the relation between quantum mechanics and free will. I think it's an interesting philosophical discussion, but unfortunately I know next to nothing about it. Anyone who does?

:You might try Max Jammer's book, which is listed in [http://www-groups.dcs.st-and.ac.uk/history/HistTopics/References/The_Quantum_age_begins.html ]. See also the [[:Category:Quantum mechanics]] for the current articles on the topic. Warning: the topic is currently considered one of the [[imponderables]]. We do not seem to know enough yet. That is one reason you may not have found too much. Have you investigated the [[free will]] article, as a start? --[[User:Ancheta Wis|Ancheta Wis]] 19:05, 7 May 2006 (UTC)

== Needs a longer lead ==

The current lead at one short paragraph is not enough for a featured article its size. A FA should have a 3, at least 2 paragraph lead that actually says something, rather than the hollow thing currently sitting there that says little more than Quantum Mechanics is a theory of physics. I think the lead needs improvement to meet the ever-increasing FA standards. [[User:Loom91|Loom91]] 17:52, 9 May 2006 (UTC)

:No. The suggested number of paragraphs need not be 2, 3, etc. It depends on the article; a FA can be short, in which case 1 paragraph suffices.

:I would be careful about categorical statements like this, as a FARC notation generates a lot of work when each point is not met head-to-head by the single lead-editor of a good article.

:Your carefully selected FARC contributions point out a structural difficulty in the popular FAs which have been accreting content by dozens, or even hundreds of editors. --[[User:Ancheta Wis|Ancheta Wis]] 08:24, 12 May 2006 (UTC)

::Ancheta makes a good point. The actual criteria at [[WP:WIAFA]] only state that an FA should have a concise lead. At [[WP:FAC]], editors have recently been insisting on three paragraphs, but that isn't essential; even if it was, it wouldn't merit demotion (see my comments at the [[Wikipedia:Featured article removal candidates/Quantum mechanics|FARC page]]).

== Relation to gravity ==

At the moment, the paragraph on quantum mechanics and gravity (general relativity) is deeply misleading. On the other hand, a coherent description of the actual problems requires perhaps more technical sophistication than the average reader will have. The article [[quantum gravity]] describes the real problems. The actual situation is that gravity can be quantized, but only as a low energy effective theory below the Planck scale. Since we have no means of experimentally probing this scale, the effective theory of quantum mechanics and general relativity is perfectly valid and able to describe all known phenomena. The claim that determinacy is somehow relevant is false; quantum mechanics, in fact, is perfectly deterministic as a theory. It is only when we attempt to apply it to the complicated decohering dynamics of objects that are effectively classical that probabilities arise. In any case, such issues exist for all quantum theories, not just the quantum theory of gravity. I could attempt to explain this in more detail in the entry itself, but I fear it would get too technical, and be revised anyhow by overzealous editors with limited understanding of the issues. So I merely point it out here for now. -- MR

:MR, perhaps some discussion might clarify how a theory based on [[probability amplitude]]s might be called [[deterministic]]. Might not this theory be called [[stochastic]] instead? Might it not be more accurate to distinguish an [[indeterminate form]] from a [[deterministic]] one? --[[User:Ancheta Wis|Ancheta Wis]] 11:02, 27 May 2006 (UTC)

So I guess you're referring to the effective field theory given by perturbative GR as a nonrenormalizable field theory. Does that theory predict any new results? I'm not very familiar with that theory, it seems a lot of particle physicists are loathe to have anything to do with nonrenormalizable field theories (though I guess maybe solid state physicists and string theorists don't mind them as much).

Anyway, I can't figure out which particular part of the article you're complaining about. The paragraph about gravity and quantum mechanics doesn't seem to say anything controversial, and does not mention determinism. But it sounds like you might be referring to this fact: some people questioned the need for a quantum theory of gravity. Perhaps quantum theories of matter could be coupled to classical gravity. This turns out not to be the case, because you can't write a correlation function for fields if you don't know where they become spacelike separated (which depends on the metric). Maybe that's what's meant? Can you point out which text in particular you meant? -[[User:Lethe/sig|lethe]] ^{[[User talk:Lethe/sig|talk]] [{{fullurl:User talk:Lethe|action=edit&section=new}} +]} 17:24, 27 May 2006 (UTC)

: I mean the paragraph that says:

::"It is believed that the theories of general relativity and quantum mechanics, the two great achievements of physics in the 20th century, contradict one another for two main reasons. One is that the former is an essentially deterministic theory and the latter is essentially indeterministic. Secondly, general relativity relies mainly on the force of gravity while quantum mechanics relies mainly on the other three fundamental forces, those being the strong, the weak, and the electromagnetic."

: This does mention determinism, and that has nothing to do with the difficulties. Also, the fact that GR deals with gravity and the SM with the other forces is not a "contradiction." The use of this word is strange and misleading. The difficulty, as you say, is that gravity is nonrenormalizable. This does not mean that it "contradicts" quantum mechanics, it simply means that it is at best a low energy effective theory. But that's fine, for the scales we have been able to probe. In other words, there is no contradiction between the theories in the regimes where they make testable predictions about the real world. I think it is important to clarify this.

:I am definitely not talking about the idea of coupling quantum mechanics to classical gravity; I think that is manifestly silly.

: Also, as far as nonrenormalizable theories go, many particle physicists these days are all <i>too</i> willing to deal with them (extra dimensions), but that's beside the point. The point is that GR is well-tested as a low energy effective theory, and presents no contradictions as such. Of course we would like to have a quantum theory that makes Planck-scale predictions, but the lack thereof doesn't mean our current theories are incompatible. --MR

: Put another way: in the days of the Fermi theory of weak interactions, no one said (as far as I know) that it was fundamentally incompatible with quantum theory. It was just a nonrenormalizable theory, which eventually got replaced by the Weinberg-Salam theory, which could make predictions that didn't break down at the weak scale. For some reason with gravity people like to talk as if there's all this extra metaphysical angst associated with the problem. There isn't; it's just that the relevant scale is much farther away and harder to explore. --MR

::OK, I'm sorry, I was looking at a different part of the text. Now that we're on the same page, let me respond. OK, so renormalizability of GR is a property of the quantum field theory of perturbative GR, not a property of the classical theory of nonperturbative GR (which is not really a field theory). So when we say that quantum mechanics is incompatible with GR, we really mean just that: GR the classical theory and the quantum mechanics of matter (in any of its guises) contradict each other. It is not at all referring to the nonrenormalizability of the perturbative GR field equations.

::Now, as for whether it's silly, well I suppose it is. Isn't it stupid to try to couple a quantum theory of matter to a classical theory of fields? But maybe not as stupid as it first seems. I mean, you do it all the time in quantum mechanics in the presence of an EM field, where it's known as the semiclassical approximation. There is a semiclassical approximation with gravity too. In both cases, the quantum matter couples to a nondynamic field. I guess coupling matter to a nondynamical EM field violates the gauge principle, which dictates that the field be promoted to a dynamical variable and gives you Maxwell's equations. Similarly, coupling matter to a nondynamical background metric violates the equivalence principle, which dictates that the metric be a dynamical variable and gives you Einstein's equations.

::One way to conform to the equivalence principle is to make the classical spacetime metric dynamical and set ''G'' = <''T''> where the brackets denote the expectation value of the matter fields. This is what I meant when I said couple classical GR to quantum matter. I totally agree with you that this is just silly. However, it has been investigated in the literature and is mentioned in the first week of any string theory class, where the cited result is that it is inconsistent. This is I think what is meant in the article. So I don't think it says anything wrong, if you interpret it the right way.

::But yes, the nonrenormalizability of perturbative GR doesn't indicate anything other than the fact that either quantum gravity isn't a field theory or else that perturbation is inappropriate for gravity (both sides have their proponents). It does not mean that one contradicts the other (as indeed they cannot, or else we live in an inconsistent universe). -[[User:Lethe/sig|lethe]] ^{[[User talk:Lethe/sig|talk]] [{{fullurl:User talk:Lethe|action=edit&section=new}} +]} 19:43, 27 May 2006 (UTC)

::: <i>OK, so renormalizability of GR is a property of the quantum field theory of perturbative GR, not a property of the classical theory of nonperturbative GR (which is not really a field theory).</i>

::: Classical GR is a field theory. That's why it's in the Landau & Lifshitz book on field theory, for instance. Of course, <i>quantum</i> GR might not be, but it certainly looks like one at long distances.

::: <i>So when we say that quantum mechanics is incompatible with GR, we really mean just that: GR the classical theory and the quantum mechanics of matter (in any of its guises) contradict each other. It is not at all referring to the nonrenormalizability of the perturbative GR field equations.</i>

::: Huh? We don't say Maxwell's equations and QED are incompatible, we say one reduces to other in some limit. The same is true of the effective field theory of quantum GR and the classical theory of GR. There's absolutely no incompatibility in sight, and it's misleading for the article to claim that there is.

::: There <i>is</i> a definite difficulty in quantum gravity, and that's finding a well-defined quantum theory of gravity valid at short distances. I think that's the only claim the article should make along these lines. As you say, it might be solved in field theory (if gravity plus matter turns out to be asymptotically safe), or it might not.

::: When you say "perturbation is inappropriate for gravity", what do you mean? We certainly ignore nonperturbative gravity effects constantly when doing calculations of, well, pretty much anything. Of course perturbation theory applies to gravity on weakly curved backgrounds, no one disputes this. Unfortunately, we don't really have any strongly curved ones around to study. -- MR

Whether you want to call GR a field theory is a matter of definition I guess, so I won't argue that. My point was simply that when you say say GR is nonrenormalizable, you're not actually talking about GR, you're talking about the field theoretic quantization of perturbative GR. So when the article says that GR and quantum mechanics are contradictory, it does not mean that GR cannot be quantized (presumably it can), it rather means that ''classical'' GR and quantum mechanics are incompatible.

''Huh? We don't say Maxwell's equations and QED are incompatible''. Here is what we would say: the quantum mechanics of charged particles is incompatible with the gauge principle of classical EM fields. In order to have quantum matter ''and'' the gauge principle, you must have quantum EM fields. I think you probably aren't even considering this point, because you think it's silly (and it is), but what I'm saying is roughly that classical field theories are incompatible with quantum matter theories (and I might or might not be counting Yang-Mills as a matter theory here).

Listen, let me find some old notes and try to rework that paragraph so that it's not so ... ''wrong'', and word clearly what I think it (and I) am trying to say, so then we can have something much more definite to argue about. -[[User:Lethe/sig|lethe]] ^{[[User talk:Lethe/sig|talk]] [{{fullurl:User talk:Lethe|action=edit&section=new}} +]} 22:27, 27 May 2006 (UTC)

:Well, MR, I couldn't find the notes which contain the bit which I thought was relevant. Basically, there is some pretty little argument by which you can see that quantum mechanical matter coupled to classical GR leads to a violation of the Heisenberg uncertainty principle. It's a fairly heuristic argument, simple enough for a layman to understand I think, so I'm annoyed that I can't remember it, but I'm sure that it's what the author had in mind when he wrote the paragraph under discussion, and if done right, might make a nice addition to the article. Anyway, the point is that it's not quantized gravity which is incompatible with quantum mechanics, it's GR, which is a classical theory. You can have quantum wood on a classical background, but you can't have a coupled classical background. -[[User:Lethe/sig|lethe]] ^{[[User talk:Lethe/sig|talk]] [{{fullurl:User talk:Lethe|action=edit&section=new}} +]} 23:27, 28 May 2006 (UTC)

::lethe, perhaps the QFT section [[gauge covariant derivative#Quantum field theory]] and the GR section below it pertain to the statements above. --[[User:Ancheta Wis|Ancheta Wis]] 01:49, 29 May 2006 (UTC)

::: Hmm, despite the article header names, nothing in that article seems to be in any way related to quantum mechanics. Rather, that seems to be a place to list some formulas from differential geometry in a place where the mathematicians can't get to them and make them indecipherable. :-) -[[User:Lethe/sig|lethe]] ^{[[User talk:Lethe/sig|talk]] [{{fullurl:User talk:Lethe|action=edit&section=new}} +]} 01:58, 29 May 2006 (UTC)

:::: No, the idea I'm trying to remember was a cute little gedanken experiment. Something along the lines of: assume you have a quantum particle in a superposition of two quantum states and then you arrange some (classical) gravitational interactions, and then you can perform a measurement to tell you the position and the momentum of the particle. -[[User:Lethe/sig|lethe]] ^{[[User talk:Lethe/sig|talk]] [{{fullurl:User talk:Lethe|action=edit&section=new}} +]} 02:02, 29 May 2006 (UTC)

=== Anville's revision ===

I just went to the article to see if I could rewrite the paragraph under dispute, and it wasn't there! I see that [[User:Anville|Anville]] [http://en.wikipedia.org/w/index.php?title=Quantum_mechanics&diff=55618650&oldid=55577316 had already done it]. Anville removes the weird sentiment that because GR deals with one fundamental force and quantum mechanics deals with the other three, they are therefore incompatible. Anville also axes the determinism stuff. I had been planning to mention some of the particular difficulties with quantum mechanics and GR, something from what MR and I have been discussing, whereas Anville's simply alludes to "serious problems". Upon further reflection, I'm not sure that this article is the appropriate place to mention, even in a passing summary, what those serious problems are, therefore I think Anville's approach is better than mine (would have been). In short: good work, Anville, and thanks. Have you anything to add, MR? -[[User:Lethe/sig|lethe]] ^{[[User talk:Lethe/sig|talk]] [{{fullurl:User talk:Lethe|action=edit&section=new}} +]} 01:54, 29 May 2006 (UTC)

: I'm aware of the gedanken experiment you were thinking of (I seem to recall a nice discussion in Wald's book, but I won't have a chance to check until later this week), but in any case I'm not sure it belongs in this article. Anville's rewritten paragraph is much better, in my opinion. I still have some minor misgivings about saying QM works for the very small and GR for the very large, but it's reasonably accurate for an article at this level of technical detail, I think. Referring the reader to the article on quantum gravity is really the right thing to do, so I'm pretty happy with the paragraph as it stands now. -- MR, 29 May 2006

::On your suggestion, I'm looking in Wald. He has quite a bit of nice discussion, including the idea that I brought up before of setting ''G''=<''T''> (classical gravity coupled to the expectation of quantum matter). He doesn't mention the particular gedanken experiment I'm looking for, but that's OK. I agree with you, it doesn't belong in this article. -[[User:Lethe/sig|lethe]] ^{[[User talk:Lethe/sig|talk]] [{{fullurl:User talk:Lethe|action=edit&section=new}} +]} 05:18, 29 May 2006 (UTC)

:::I vaguely recall a gedankenexperiment along those lines in ''The Feynman Lectures on Gravitation.'' (Oh, and I'm glad I could help with the rewriting.) [[User:Anville|Anville]] 19:23, 2 June 2006 (UTC)

== Link purge ==

I zapped several crufty and/or downright crackpotterly links from the "External links" section. Misinformation does not need the implied endorsement and the added publicity that our "encyclopedia" provides. For a dress-down of the Hindu "Vedanta" flavor of pseudophysics, see [[Alan Sokal]]'s article "[http://www.physics.nyu.edu/faculty/sokal/pseudoscience_rev.pdf Pseudoscience and Postmodernism: Antagonists or Fellow-Travelers?]" (2006). [[User:Anville|Anville]] 19:19, 2 June 2006 (UTC)

== Relational Quantum Mechanics and Modal Interpretations of Quantum Theory ==

We need some people who are comfortable with this topic to describe these interpretations of QM. [[User:RK|RK]] 19:15, 17 June 2006 (UTC)

* [[Interpretation of quantum mechanics]]

==Rename and Reform?==

Isn't "Quantum Physics" or "Quantum Theory" a more appropriate title, with "Quantum mechanics" linked to this article? The application of quantum theory to, say, electromagnetic fields surely isn't in the ___domain of "mechanics," at least not as understood by the college student who is introduced to mechanics and electromagnetism as separate subjects. Quantum theory has much broader scope than mechanics; surely the Wikipedia naming conventions aren't so deferential to commonly familiar terms that we should apply such a misnomer to this article. (?!?)

In general, with respect to those who have undertaken the difficult task of contributing, this article is a sprawling, incoherent mess. Perhaps it would be appropriate to give a concise introduction to the theory with clear links to articles at several levels of sophistication. Technically sophisticated readers will benefit little from wordy paragraphs or sentences which begin with "An equation known as the Schroedinger Equation...," while novices can hardly be expected to follow the equations and mathematically rigorous language which is sorely needed in this article. As it stands, this is hardly a "technical" article, as implied by the statement at the top.

Is there any hope that a group of concerned physics professors from major universities will take responsibility for maintaining this important page???

[[User:Gnixon|Gnixon]] 23:59, 23 July 2006 (UTC)

:Please append your edits to the end of the page --[[User:Ancheta Wis|Ancheta Wis]] 01:20, 24 July 2006 (UTC) moved

== Quantum causality ==

I was under the impression that causality (cause begets effect) does not apply as definitely in the quatum realm as it does in the classical, that effects can chronologically preceed their supposed causes. After watching ''The Elegant Universe'' and doing some brief reading on the subject, this was one of the things that I gathered. It is, to me, interesting enough to include on the QM page, if accurate. Though, since I have no formal experience with QM I did not want to add it to the article without backing. --[[User:Tyco.skinner|HantaVirus]] 14:47, 27 July 2006 (UTC)

== Entanglement objection ==

Under the discussion of entanglement under "Quantum mechanical effects" the issue of the violation of special relativity is not handled with much care. "If quantum mechanics is correct, entangled particles can display remarkable and counter-intuitive properties. For example, a measurement made on one particle can produce, through the collapse of the total wavefunction, an instantaneous effect on other particles with which it is entangled, even if they are far apart. ('''This does not conflict with special relativity because information cannot be transmitted in this way.''')" August 2nd 2006 11:13 PST. This last statment is simply false and was the major issue posed to Bohr by Einstein. The thought experiment goes something like this: Imagine two particles with known opposite spin (because of a paramagnetic effect or whatever). Both particles have underknown spin until one is measured, then the other is instantaniously known, before information (which can't travel faster than the speed of light, no matter what the article claims) can travel to the other particle, thus violating SR. A few experiments have been preformed, but nothing conclusive has come from any of them, and this remains a major question in QM from my understanding. I would hope this could be corrected by someone with a little more technical background than myself.

No, I'm pretty sure you cannot transmit information via QM entanglement. Unless you are the particle in question and the information you are transmitting is your unknown state. What I mean is that an experimenter cannot use entanglement to transmit arbitrary information faster than light. Even if, at some level, in order to make things work out, it seems that some "information" must be moving faster than light, it is not information that we can ever use. It is certainly not information that would allow someone to violate special relativity (send information beyond a light cone, predict the future, etc.) and it is not transmitted by a wave or particle as far as we know, so it doesn't violate relativity. A faster-than-light quantum entanglement "radio" can never exist. And I've never heard that that is somehow a controversial issue or that any physicists disagree that QM cannot transmit information faster than light. I'm not a physicist, but I've asked a couple of them about it and this is what I was told. [[User:Xezlec|Xezlec]] 16:43, 5 August 2006 (UTC)

: No information can be transmitted by Bell states without classical communication. Though the quantum state is changed by the measurement of the first particle(collapse of wavefunction), there is no observable change in the state unless the measurement outcome is first communicated to the second particle.[[User:Waxigloo|Waxigloo]] 17:43, 26 August 2006 (UTC)

== Entangled cat ==

To avoid repeating the same text again, I am putting a link to my comment about Schrödinger's cat: [[http://en.wikipedia.org/w/index.php?title=Talk%3ASchrödinger%27s_cat&diff=71453054&oldid=70488139]]. [[User:David R. Ingham|David R. Ingham]] 20:50, 23 August 2006 (UTC)

:See also [[Introduction to quantum mechanics#Quantum entanglement ]] which is only about locality. Bohr's answer to Einstein, that 'what is described is a system', means that no new info is transmitted (it's the same system). --[[User:Ancheta Wis|Ancheta Wis]] 21:42, 23 August 2006 (UTC)

== Merge with quantum field theory ? Definition ? Spawn a [[quantum theory]] instead==

I wish that the articles on quantum theories were more clear on terminology, so that it is more clear what is a subset of what. The lead section should make it clear what [[quantum mechanics]] is in relation to [[quantum field theory]], [[quantum electrodynamics]], and quantum physics in general. In general, if several meaning are attached to a word, the lead sections should discuss the various meanings, and which is retained in wikipedia. The articles should then be consistent with these definitions.

I see the following inconsistencies:

* quantum mechanics was said to be a subset of quantum field theory in the lead section of quantum mechanics, while the introduction section of the article suggests that (relativistic) quantum mechanics is synonym with quantum field theory. I have now changed the lead section to distinguish the 2 uses of the "quantum mechanics" words

* if (relativistic) quantum mechanics is a synonym of quantum field theory, as the introduction section says, shouldn't the two articles be merged ? Why does the "quantum field theory" articles says that it is the application of quantum mechanics to fields ?

I see different options here:

# consider that "quantum mechanics" has 2 meanings. We would thus split / merge the current quantum mechanics page into "quantum field theory", and a new "non-relativistic quantum mechanics". The "quantum mechanics" page would then be a disambiguation page with links to both articles.

# consider that "quantum mechanics" has 1 main meaning, as a synonym of quantum physics or quantum field theory. In that case, I'm not sure how to position it compared to quantum field theory: shouldn't the article be merged with quantum field theory ?

# consider that "quantum mechanics" has 1 main meaning, as a synonym for non-relativistic quantum theory. I'm not sure this is really the most common meaning though. If it is, then we should clearly say it in the lead section of the quantum mechanics article, and change its "introduction" section.

# We could also use the otheruses4 template to say :"This article is about non-relativistic quantum mechanics. For relativistic quantum mechanics, please see quantum field theory". This is the option I prefer. We should then need to make sure that the article discusses non-relativistic quantum mechanics only.

Whatever we choose, there would be some work to verify that the use of the 'quantum mechanics' word is consistent throughout wikipedia. I have added the merge tag to help resolve this issue. [[User:Pcarbonn|Pcarbonn]] 06:03, 29 August 2006 (UTC)

:Quantum mechanics and quantum field theory are different subjects and are taught as such at colleges/universities. QM is non-relativistic, the fields are not quantised and the particle number is fixed. In QFT all these restrictions are lifted. --[[User:MichaelCPrice|Michael C. Price]] ^{[[User talk:MichaelCPrice|talk]]} 08:04, 29 August 2006 (UTC)

::So, you choose option 3 or 4, is that it ? [[User:Pcarbonn|Pcarbonn]] 20:50, 29 August 2006 (UTC)

:::3, although an important qualification is that "quantum mechanics" means "non-relativistic, classical field quantum theory". --[[User:MichaelCPrice|Michael C. Price]] ^{[[User talk:MichaelCPrice|talk]]} 21:10, 29 August 2006 (UTC)

:'''Disagree''': I do not approve of a merge. They are not the same thing. [[User:Waxigloo|Waxigloo]] 18:48, 29 August 2006 (UTC)

::So, which option do you choose ? Or you don't see a problem with the lead section and the last paragraph of the "introduction" section? [[User:Pcarbonn|Pcarbonn]] 20:50, 29 August 2006 (UTC)

:::Sorry; I forgot to say-- I think I agree with option 4. Limiting this article to non-relativistic QM and putting a link at the top for QFT seems to be the most informative and accurate thing to do.[[User:Waxigloo|Waxigloo]] 00:59, 30 August 2006 (UTC)

Thank you for your feedback. I agree that a merge with [[quantum field theory]] does not make sense, so I removed the tag.

Reason for the split tag: In addition to the proposals above, I propose to create a [[quantum theory]] article, and move some of the general content of the [[quantum mechanics]] article to it (I suspect that some statements made in the quantum mechanics article apply to all quantum theories).[[User:Pcarbonn|Pcarbonn]] 06:16, 30 August 2006 (UTC)

:What do you propose: that "quantum theory" includes "quantum field theory" and "quantum mechanics" plus some other stuff? --[[User:MichaelCPrice|Michael C. Price]] ^{[[User talk:MichaelCPrice|talk]]} 07:41, 30 August 2006 (UTC)

::yes, indeed, it would be an overview of all quantum theories, and could explain some common features of them (eg. duality of wave and particles). I've created a stub already (see [[quantum theory]]). Alternatively, the article could be called [[quantum physics]]. I suspect that some people (and the current version of the article) use "quantum mechanics" to mean "quantum physics" in general, for historical reason (quantum mechanics was first, right ?). Hence the confusion. [[User:Pcarbonn|Pcarbonn]] 11:04, 30 August 2006 (UTC)

:::Sounds a good plan. I suggest that [[quantum theory]] redirect to [[quantum physics]] (or vice versa) -- ah I see you're already done that. Keep the article brief (as it is already) and have QM, QFT, etc as main articles within. --[[User:MichaelCPrice|Michael C. Price]] ^{[[User talk:MichaelCPrice|talk]]} 12:02, 30 August 2006 (UTC)

== Religious objections ==

I don't think the content should be removed. Also, I think the reasons for removing it is false.

After the revert, I'm going to add a ref to what Hawking thinks on the subject of Einstein's "dice" quote.

I think it very much does belong here. Quantum Mechanics has it's opponents. And those reasons are valid reasons. Some of those reasons are religious. I'm a religious man myself, I put the section in on Miracles, because I'm actually reading the book now. Contrary to C.S. Lewis, I believe in quantum mechanics, almost religiously so. But I think that the other viewpoints are important to providing a NPOV. [[User:Mckaysalisbury|McKay]] 23:31, 18 September 2006 (UTC)

:The Einstein quote, which is often misused and misunderstood (as it was here), is not a "religious objection" that Einstein had. I have even seen arguments that Einstein was not even all that Hell-bent on the necessity of determinism, and that that quote has been played up beyond all fairness proportional to the seriousness with which Einstein said it, and the stock he put in it. But we can assume he meant it: i.e., QM is incomplete because he felt the universe ought to be deterministic. Fine.

:But Einstein was some sort of pantheist-thingummy, if I have understood him correctly. He was certainly not a dogmatic believer in any religion (on the contrary). So really, while the "dice" quote ''does'' represent some of the reservations he had about QM, they are reservations he had on ''aesthetic'' grounds, and from his sharp instinct for physical truth, not religious inclinations. There is ''no'' way that it can be accurately termed a "religious objection".

:Note that I am not disputing that Einstein said the "dice" thing (so simply providing links to quote sites is unnecessary) - I am disputing that he meant it as a "religious objection". [[User:Byrgenwulf|Byrgenwulf]] 06:24, 19 September 2006 (UTC)

::Yes, Einstein was not Jewish (except by heritage). His religous beliefs were not judeo-christian. But he did have religous beliefs. saying "he had reservations on ''atheistic'' grounds" is false. I will admit that this quote is oft used incorrectly. But not in the manner in which you speak. It is oft used to establish that he was Jewish, or Christian or something. He did not believe in this manner, but he did "believe in Spinoza's God who reveals himself in the orderly harmony of what exists, not in a God who concerns himself with fates and actions of human beings." His statement that he disliked QM because he felt that it was out of the orderly harmony of the universe, is most definitely a religous statement. Without further evidence that it wasn't religous grounds, I think that your claims that it wasn't religious is dubious. [[User:Mckaysalisbury|McKay]]

:::*I said "'''[[aesthetics|aesthetic]]'''" not "atheistic". [[User:Byrgenwulf|Byrgenwulf]] 14:48, 19 September 2006 (UTC)

:About the "religious objections" section in general, then...I do agree that giving coverage to all viewpoints is important, of course. But, it should be remembered that C.S. Lewis was a professor of English, not of physics. He happens to be a real scholar, one for whom I have some respect, even; but by adding English professors' criticisms of things like Heisenberg's uncertainty principle, I very much fear we are opening the flood gates for other people to come and add ''their own'' particular "religious objections" to QM, which will no doubt also be objections raised by non-experts, and in the end the article will be bogged down by this. The bottom line is that people have "religious objections" to ''all'' forms of science, and QM is no exception; the "religious objections" to QM that I have seen are not even taken as seriously, as, for example "[[intelligent design]]".

:Is every science article now to include a "religious objections" section? And "objections" from what religion? All the religions that "object"? Just how respectable do the "objections" have to be, before they can be included? For I very much doubt that Prof. Lewis knew exactly what he was talking about, and was rather just deciding what ''he thought'' the scientists meant by "Heisenberg uncertainty" - but an English professor, no matter how respectable, is simply not qualified to make pronouncements like that, I don't think. [[User:Byrgenwulf|Byrgenwulf]] 06:24, 19 September 2006 (UTC)

::I would say that if the religous objections are notable, then they should be included. Some Joe Schmoe's comments are not notable, but Prof. Lewis's, I would claim are. Sure, his claims were objections to what he thought scientists meant, but according to the book, he was actually correct in what he thought that scientists meant. He was opposed to the indeterminstic nature of the universe. Which is basically the point of Quantum Mechanics. Evolution has a religious objections section. While he is an "english professor" he is also a popular religionist. What he says on the matter of religion is notable. And he had a religious objection to QM. That's kinda like saying [[User:Mckaysalisbury|McKay]] 14:04, 19 September 2006 (UTC)

:::What Lewis said is notable in Lewis' article. If Lewis were famed for having objected to Heisenberg's Uncertainty Principle (or, more specifically, claiming it is merely an [[epistemology|epistemic]] limitation on human beings but not an indicator of how the world "really is"), then it could be included here. But that isn't what Lewis is noted for, either: does the Lewis article have a section on "how quantum mechanics differs from Lewis's ideas on the world"? No. The exact interpretation of Heisenberg's Uncertainty Principle is also a far more subtle and intricate matter than simply dismissing it as "a limit on how accurately humans can know the world", because a statement like that carries a host of implications for how the rest QM is viewed, but which are not properly worked through in the article as it stands, so the matter is left dangling, a little like your post above.

:::Also, the "indeterministic nature of the universe" is not "the point" of QM. "The point" of QM is that it is the best theory of motion that we humans have at the moment.

:::Here's an idea. In the "philosophy" subsection of the article, whether the question of determinism is discussed, why not include a sentence like "''Some Christian writers, such as C.S. Lewis (reference), share the view that the QM is incomplete, because notions of indeterminism do not agree with their religious beliefs''"? That way, the point is covered, in such a way as Lewis is cited as one key example, but it doesn't open the gates to infinitely many more people making the same point and bogging down the article in unnecessary ancillary discussion. [[User:Byrgenwulf|Byrgenwulf]] 14:48, 19 September 2006 (UTC)

::::I like that suggestion. I still think that Einstein's should be similarly included as well. But this is a good start. [[User:Mckaysalisbury|McKay]] 06:14, 21 September 2006 (UTC)

:::OK, let me try to clear some things up here. Lewis' objection is not a "religious objection": it is a philosophical objection, but the philosophical position which Lewis adopted stems from his religious outlook. Einstein's God/dice quote is not a religious objection either, because the philosophy of Spinoza (or more generally a belief in [[pantheism]] and [[Cosmic Ordering|cosmic order]]) is not a religion.

:::Also, Einstein was not "objecting" to quantum mechanics. QM works: we know this because we are writing an ''Internet-based encyclopaedia'', which uses technology based on quantum mechanical principles (like [[electron tunneling]]). I cannot speak for Lewis in this regard, but from what I know of him he was not a complete fool, so I don't think he was actually "objecting" to QM either.

:::The real question here is whether QM is a complete theory or not. Einstein (and apparently Lewis) felt that it was ''not''; although Einstein relaxed his objections later in his life. It is also a question of the ''philosophical interpretation'' of the uncertainty principle. These are not religious in nature, and nor are they real "objections" to quantum mechanics: they are objections to ''particular understandings'' of what quantum mechanics is.

:::Religious beliefs may have inspired Lewis' comment, and so did Einstein's personal philosophy inspire his, but it would be grossly inaccurate to class comments of these sorts as "religious objections to quantum mechanics".

:::I trust my recent revision will be acceptable. [[User:Byrgenwulf|Byrgenwulf]] 17:04, 21 September 2006 (UTC)

The footnote [2] right after the comment about lewis leads to a hawking page that doesn't reference lewis. The citation should be to one of lewis's books, probably Miracles chapter 3. This needs to be fixed.

:Wow. The paragraph in Lewis' book, Miracles, that sparked this discussion of Lewis has been terribly misunderstood.

:First, there is the idea that his philosophical objection to QM stems from his religious beliefs. That is ridiculous. Simply notice that the pages preceding this paragraph of discussion were dedicated to constructing an argument against naturalism (material monism) based on QM. Lewis had just finished drawing philosophical implications of QM that supported his religious beliefs. That would all be very pointless if Lewis felt his religious beliefs negated the possibility of QM.

:This brings us very nicely to the second misunderstanding, which is that Lewis is even definitively objecting to QM. He's not even so much objecting to QM as he is expressing his reservations over putting much stock in his argument from QM. Let's look at the paragraph.

::There are actually two "objections." This first of these objections is the one cited previously, that the motion of particles is not random and lawless but merely incalculable. Read more carefully. At best all he is really saying here is that his philosophical sensibilities, so to speak, lend him to wonder if this so-called objection is actually what experts really mean by their theories. (Note his humility). My best guess as to what his philosophical ground for this reservation actually is is that QM possibly undermine the law of causation's implication that an effect cannot exceed its cause, that order can't spontaneously arise from chaos. However, this is purely speculative on my part. Hey, I like exploring possibilities. Sue me.

::The second objection made is not even itself philosophical but practical. We've seen theory topple theory, only itself to be soon toppled. The fickleness of science seemed to Lewis good reason to not put all of his eggs in the quantum mechanical basket. This apprehension is one that fades in time as QM prevail.

:Thus, it is obvious that Lewis did not propose any substantive objection to QM. He is simply disowning his previous argument, as he said he would at the outset of his discussion of QM (I'm aware that Lewis presents his previous argument in a way that suggests it is not his, but he doesn't cite anyone else). However, in Lewis another issue is raised that I'm interested in. Aside from philosophy waged against QM, what about philosophy that follows from it. One criticism of Lewis is that he was an English professor offering his opinion of physics. However, he offers his understanding of QM and then draws out his philosophy accordingly. Such is the work of philosophers. Physicists would be very helpful if they would temper us non-experts' understanding of these physics, rather than trying isolate each discipline from one another.

:I encourage you to read Lewis' argument against naturalism from QM, if for no other reason than because it's fairly intriguing. Essentially, it goes as such:

::(1)Naturalism claims that nature is a systematic totality and every event within her "interlocks" with everything else, including the movements of particles. There is nothing beyond her--no doors to be opened.

::(2)Apparently these particles don't move in accordance with the general laws of nature, but rather move randomly and indeterminately. The determinate laws of motion we observe are actually normative renderings of an underlying sea of randomness.

::(3)This indeterminate realm cannot be integrated into the naturalist's understanding of nature. QM are antithetical to the naturalist understanding of nature as systematic. The random motion of particles is not itself natural, but rather sub-natural, admitting something other than that which is natural.

::(4)Naturalism collapses if all of nature's events arise from what is subnatural. The possibility of a supernatural is then unscathed by such a crippled philosophy.

:So now I ask what someone well-studied in QM would have to say about this line of thought, even though I've completely digressed from the original topic. Progress can't be stifled by topics, you know. Okay, that's just an attempt at justifying my bringing up of what I'm interested in ...

:[[User:Stephen Howard|Stephen Howard]] 06:09, 18 October 2006 (UTC)

=== Weinberg quote ===

Let me repeat a quote from [[Steven Weinberg]] with which, in my experience, at least most field theorist and experimentalists agree.

''Physics Today'', April 2006, "Weinberg replies", p. 16,

: ... but the apparatus that we use to measure these variables—and we ourselves—are described by a wave function that evolves deterministically. So there is a missing element in quantum mechanics: a demonstration that the deterministic evolution of the wave function of the apparatus and observer leads to the usual probabilistic rules [Copenhagen interpretation].

QM, as a microscopic theory, is fully tested and is deterministic, in the sense that whenever it is possible to do an unambiguous and purely quantum mechanical calculation of how a something evolves, QM always gives a unique and correct state vector. There are empirical rules, that have not yet been fully justified theoretically, for using classical approximations in quantum experiments. So one can say that it is intuition and classical physics that introduce the probabilities into QM and not the theory in isolation.

It is a matter of choice whether to take the state vector, that we cannot directly observe, as reality or to insist that reality must have a direct correspondence to our intuition and perceptions. It is the nature of physics that its concepts tend to evolve away from intuition and direct experience, so to me the former is the more obvious choice.

Some, such as [[Roger Penrose]], and many Wikipedia editors still believe that [[wave function collapse]] is a fundamental process that goes on in nature. My view is that this is a sort of "quantum [[Lamarckism]]" that accepts the results of QM without really accepting its content. [[User:David R. Ingham|David R. Ingham]] 21:58, 19 October 2006 (UTC)

=== Back to Einstein ===

It seem that what he was objecting to was QM with the Copenhagen Interpretation, as that was all that was available? In that case, he won his point with the EPR paper, if my vague understanding of the Copenhagen Interpretation is right. [[User:David R. Ingham|David R. Ingham]] 15:30, 22 October 2006 (UTC)

== "first quantized" in the first pagagraph ==

Roger Penrose in ''The Road to Reality'' points out that the term "second quantized" is confusing. That makes " first quantized" too misunderstood to be in the first paragraph. [[User:David R. Ingham|David R. Ingham]] 05:35, 30 September 2006 (UTC)

== First paragraph ==

The present first paragraph makes me wish I had been more attentive to my watch list. QM is a specific theory (Schrödinger and Heisenberg) that includes whatever are meant by first and second quantization. It has relativistic and non-relativistic forms. The current relativistic form is called quantum field theory. It is ''not'' just a replacement for classical mechanics, but for ''all'' classical physics, including E & M. The only other quantum physics that I know of is "the old quantum theory", which may still be used as an approximation. [[User:David R. Ingham|David R. Ingham]] 05:51, 30 September 2006 (UTC)

:I think I catch what you're saying, but I'll bet noone understands better what you mean than you, perhaps you should be [[WP:BOLD]], and make the change yourself. If someone doesn't like it, it will get reverted, no harm done. Please, make this article better. [[User:Mckaysalisbury|McKay]] 05:58, 30 September 2006 (UTC)

I reverted to the best version I could find in the history, Revision as of 23:25, 16 June 2006 by [[Keenan Pepper]].

The "first quantization" idea is not appropriate to mention here. "Second quantization" means the use of raising and lowering operators to account for particles appearing and disappearing. This happens if QFT, but it also happens purely within the non-relativistic many body Schrödinger equation. When one describes a solid or a nucleus with the Schrödinger equation, phonons (particles of sound, called vibrational excitations in nuclear physics) appear as collective behavior. These are created and annihilated the same way that photons are in quantum electrodynamics. Penrose says the term "second quantization" is confusing.

Secondly, I have never heard the term QM used anywhere else to single out only non-relativistic quantum physics, excluding QFT. Schrödinger and Heisenberg knew that the real world is relativistic, but did not yet see how to do relativistic quantum calculations, which is well known to be quite tricky. [[User:David R. Ingham|David R. Ingham]] 19:48, 30 September 2006 (UTC)

:See how 1st, 2nd and 3rd quantisation are defined at [[quantum theory]]. --[[User:MichaelCPrice|Michael C. Price]] ^{[[User talk:MichaelCPrice|talk]]} 03:31, 1 October 2006 (UTC)

::The Dirac and Klein-Gordon equations are relativistic quantum mechanical model, that is not a QFT, but simply the tree-level result of QED. Relativistic QM and QFT are not necessarily the same thing.[[User:Jameskeates|Jameskeates]] 11:16, 2 November 2006 (UTC)

== wave functions or wave funciton in the introduction ==

Penrose makes a big issue of the fact that a state is described by a function of the coordinates of ''all'' the particles and not by a wave function for each particle. This is how the extra variable that describe [[quantum entanglement]] come in. [[User:David R. Ingham|David R. Ingham]] 06:03, 30 September 2006 (UTC)

== '''Theory''' section ==

"probability distributions" is mentioned too early. These issues are related to classical approximations rather than to quantum theory proper. [[User:David R. Ingham|David R. Ingham]] 06:20, 30 September 2006 (UTC)

== All over the place... ==

I think we need a page like [[History of quantum mechanics]]...Thoughts? --[[User:HappyCamper|HappyCamper]] 02:00, 7 October 2006 (UTC)

Yes it is a large subject and different people are interested in the theory itself and its history. [[User:David R. Ingham|David R. Ingham]] 21:09, 19 October 2006 (UTC)

==AfD raised on [[Quantum theory]]==

If you have view on this please go to [[Wikipedia:Articles_for_deletion/Quantum_theory]] and cast your vote. --[[User:MichaelCPrice|Michael C. Price]] ^{[[User talk:MichaelCPrice|talk]]} 06:02, 20 October 2006 (UTC)

==Removed "electron should be thought of as being spread out over space"==

That statment was wrong. End of story

[[User:Kevin aylward|Kevin aylward]] 24th Oct 2006

== Spread out electrons ==

"It should be stressed that the electron itself is not spread out over such cloud regions. It is either in a particular region of space, or it is not."

Is this really correct? How can single photons interfere with themselves, then, as they do in two-slit experiments? Also, it seems to conflict with the following -- from Physics Web:

"Quantum particles such as electrons can be in a superposition of two or more quantum states. This means that an electron can, for instance, be in two places at the same time."

(from http://physicsweb.org/articles/news/4/1/7)

I'm just a lowly English grad student, so I don't feel qualified to make the change myself. But then, I've been reading about quantum mechanics since I was in the fourth grade, and I've never heard anyone suggest that, prior to decoherence, there's any such thing as an "electron itself" that "is either in a particular region of space, or... is not." There's only a quantum wave function that dictates the odds of an interaction taking place at a particular ___location. Am I wrong? [[User:Solemnavalanche|Solemnavalanche]] 05:03, 6 November 2006 (UTC)