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{{Short description|Candidate "Theory of Everything"}}
{{Introductory article|M-theory|String theory}}
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{{String theory|cTopic= Theory}}
In non-technical terms, [[M-theory]] presents an idea about the basic substance of the [[universe]]
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In the early years of the 20th century, the [[atom]] – long believed to be the smallest building-block of [[matter]] – was proven to consist of even smaller components called [[protons]], [[neutrons]] and [[electrons]], which are known as [[subatomic particles]]. Other subatomic particles began being discovered in the 1960s. In the 1970s, it was discovered that protons and neutrons (and other [[hadron]]s) are themselves made up of smaller particles called [[quarks]]. The [[Standard Model]] is the set of rules that describes the interactions of these particles.
In the 1980s, a new mathematical model of [[theoretical physics]], called [[string theory]], emerged. It showed how all the different subatomic particles known to science could be constructed by hypothetical one-dimensional "strings", infinitesimal building-blocks that have only the dimension of length, but not height or width. These strings vibrate in multiple dimensions and, depending on how they vibrate, they might be seen in three-dimensional space as matter, light or gravity. In string theory, every form of matter is said to be the result of the vibration of strings.
However, for string theory to be mathematically consistent, the strings must
Five major string theories were developed and found to be mathematically consistent with the principle of all matter being made of strings. Having five different versions of string theory was seen as a puzzle.
Speaking at the
▲Speaking at the string theory conference at the University of Southern California in 1995, [[Edward Witten]] of the [[Institute for Advanced Study]] [[second superstring revolution|suggested that]] the five different versions of string theory might be describing the same thing seen from different perspectives.<ref>{{Cite web |url=http://physics.usc.edu/Strings95/program.html |title=University of Southern California, Los Angeles, Future Perspectives in String Theory, March 13-18, 1995, E. Witten: Some problems of strong and weak coupling |access-date=2017-04-08 |archive-date=2020-11-15 |archive-url=https://web.archive.org/web/20201115210233/http://physics.usc.edu/Strings95/program.html |url-status=live }}</ref> He proposed a unifying theory called "[[M-theory]]", in which the "M" is not specifically defined but is generally understood to stand for "membrane". The words "matrix", "master", "mother", "monster", "mystery" and "magic" have also been claimed. M-theory brought all of the string theories together. It did this by asserting that strings are really one-dimensional slices of a two-dimensional membrane vibrating in 11-dimensional [[spacetime]]. Vibrations of higher-dimensional objects (as in three-dimensional vibrating blob or sphere or even more possible dimensions) are certainly a part of M-theory,<ref>{{Cite web | url=https://physics.stackexchange.com/questions/73808/does-string-m-theory-address-higher-dimensional-membrane-vibration-modes | title=Quantum gravity – Does string/M-theory address higher-dimensional membrane vibration modes? | access-date=2017-08-05 | archive-date=2020-11-15 | archive-url=https://web.archive.org/web/20201115210238/https://physics.stackexchange.com/questions/73808/does-string-m-theory-address-higher-dimensional-membrane-vibration-modes | url-status=live }}</ref> but the basic theory of branes is still in progress. Higher-dimensional objects are much harder to mathematically calculate than a point in [[classical physics]] or a one-dimension string in string theory or two-dimensional membranes in M-theory.
==Status==
M-theory is not complete, and the mathematics of the approach are not yet well understood. M-theory is a theory of quantum gravity; and as all others it has not gained experimental evidence that would confirm its validity.<ref name=atlantic/> It also does not single out our observable universe as being special, and so does not aim to predict from first principles everything we can measure about it.
Nevertheless, some
One feature of M-theory that has drawn great interest is that it naturally predicts the existence of the [[graviton]], a [[Spin (physics)|spin-2]] particle hypothesized to mediate the gravitational force. Furthermore, M-theory naturally predicts a phenomenon that resembles [[black hole evaporation]]. Competing unification theories such as [[asymptotically safe gravity]], [[An Exceptionally Simple Theory of Everything|E8 theory]], [[noncommutative geometry]], and [[causal fermion systems]] have not demonstrated any level of mathematical consistency.
==See also==
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