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→Spatial variation – Australian dipole: Fixed section where beginning of sentence seems to have been unintentionally deleted or omitted; small wording change for encyclopedic tone. |
Undid revision 1308068403 by Papybare (talk): obscure proposals by one guy aren't suitable for inclusion here, even if they technically made it through peer review somewhere (in other words, surviving peer review is the first step, not the last) |
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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}}}}
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.
| 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}}<sub>prev</sub> − {{mvar|α}}<sub>now</sub> . 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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== Anthropic explanation ==
The [[anthropic principle]]
{{cite journal
|last=Barrow |first=John D.
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