Fine-structure constant: Difference between revisions

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{{block indent|{{math|1=''α'' = {{sfrac|''e''{{sup|2}}| 4''πε''{{sub|0}}''ħc''}}}} {{=}} {{physconst|alpha|ref=no}}.}} This has a relative standard uncertainty of {{physconst|alpha|runc=yes|after=.}}

This value for {{math|''α''}} gives the following value for the [[Vacuum permeability|vacuum magnetic permeability]] (magnetic constant): {{nowrap|1={{mvar|µ}}{{sub|0}} = 4''π'' × {{val|0.99999999987|(16)|e=-7|u=H.m-1}}}}, 0.8 times the standard uncertainty away from its old defined value, with the mean differing from the old defined value by only 0.13 [[parts per billion]], 0.8 times the standard uncertainty (0.16 parts per billion) of its recommended measured value.

Historically, the value of the [[multiplicative inverse|reciprocal]] of the fine-structure constant is often given. The [[CODATA]] recommended value is {{physconst|alphainv|ref=only}}

{{block indent|{{math|{{sfrac|1|''α''}}}} {{=}} {{physconst|alphainv|ref=no}}.}}

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| 2022 Dec

| 0.0072973525643(11)

| 137.035999177035999206(21)

| CODATA 2022

|-

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In the experiments below, {{math|Δ''α''}} represents the change in {{mvar|α}} over time, which can be computed by {{mvar|α}}_prev − {{mvar|α}}_now . If the fine-structure constant really is a constant, then any experiment should show that

<math display="block">\frac{\ \Delta \alpha\ }{\alpha} ~~ \overset{\underset{\mathsf{~def~}}{}}{=} ~~ \frac{\ \alpha _\mathrm{prev}-\alpha _\mathrm{now}\ }{\alpha_\mathrm{now}} ~~=~~ 0 ~,</math>

or as close to zero as experiment can measure. Any value far away from zero would indicate that {{mvar|α}} does change over time. So far, most experimental data is consistent with {{mvar|α}} being constant, up to 10 digits of accuracy.

=== Past rate of change ===

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|website=ScienceBlogs.com

}}</ref>

that the study may contain wrong data due to subtle differences in the two telescopes.<ref>

{{cite web

|first=S. M. |last=Carroll |author-link=Sean M. Carroll

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|url=http://www.preposterousuniverse.com/blog/2010/10/18/the-fine-structure-constant-is-probably-constant/

}}</ref>

aCarroll totallytakes an altogether different approach;: he looks at the fine-structure constant as a scalar field and claims that if the telescopes are correct and the fine-structure constant varies smoothly over the universe, then the scalar field must have a very small mass. However, previous research has shown that the mass is not likely to be extremely small. Both of these scientists' early criticisms point to the fact that different techniques are needed to confirm or contradict the results, a conclusion Webb, ''et al''., previously stated in their study.<ref name=Zyga-2010-10-21/>

Other research finds no meaningful variation in the fine structure constant.<ref>

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== Anthropic explanation ==

The [[anthropic principle]] isprovides an argument aboutas to the reason the fine-structure constant has the value it does: stable matter, and therefore life and intelligent beings, could not exist if its value were very different. One example isFor thatinstance, if modern grand unified theories are correct, then {{mvar|α}} needs to be between around 1/180 and 1/85 to have proton decay to be slow enough for life to be possible.<ref>

{{cite journal

|last=Barrow |first=John D.

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|pages=[https://archive.org/details/briefhistoryofti00step_1/page/7 7], 125

}}</ref>

The most recent calculation of the constant in the form of its reciprocal value, equal to 137,035999090084835866869811317585378…, can be found in the work of Vyacheslav A. Ivanov [59], based on the assumption of the existence of two semi-virtual spaces of the Universe - the space of Account and the physical space, so that this constant is one of the coupling constants used by the Universe to coordinate physical quantities in two different interacting geometries.

== Quotes ==