2018 CODATA recommended value is 7.297 352 5693 x 10-3 It is a dimensionless number; not a value in units. Symbol, α
For a long time, it was speculated that 1/α = 1/187, and a great deal of ink was spilled over the significance of that integer. As it turns out, α 1/etc.
If α does change, the change must be less than around 1 part in 10¹⁷ per year.
In 2019, scientists proposed a way of detecting even such a small change¹, based on the spacing of atoms in materials. They calculated that if, for example, α is increasing by 1 part in 10¹⁷ per year, a gold bar would shrink by 1 part in 10⁻18 per year, while a germanium crystal would grow by 10⁻21 per year. Developments in the measuring of lengths, as for example in the gravitational wave detetectors, bring measuring such small changes within the range of possibility.
M. T. Murphy, J. K. Webb, V. V. Flambaum.
Further evidence for a variable fine-structure constant from Keck/HIRES QSO absorption spectra.
Monthly Notices of the Royal Astronomical Society, vol 345, issue 2, pages 609–638 (21 October 2003).
Peter J. Mohr, Barry N. Taylor, and David B. Newell.
CODATA recommended values of the fundamental physical constants: 2006.
Reviews of Modern Physics, 80, 633 – Published 6 June 2008 doi:https://doi.org/10.1103/RevModPhys.80.633
Tara M. Fortier, Neil Ashby, James C. Bergquist, Marie Delaney, Scott A. Diddams, Thomas P. Heavner, Leo W. Hollberg, Wayne M. Itano, Steven R. Jefferts, K Kim, Windell Oskay, Thomas E. Parker, Jon H. Shirley, Jason Stalnaker, Filippo Levi, Luca Lorini.
Improved limits on variation of the fine structure constant and violation of local position invariance.
Proceedings of the IEEE International Frequency Control Symposium Jointly with the 21st European Frequency and Time Forum. May 27-June 1, 2007.
<1.3 x 10⁻¹⁶ per year.
1. Lukáš F. Pašteka, Yongliang Hao, Anastasia Borschevsky, Victor V. Flambaum, and Peter Schwerdtfeger.
Material size dependence on fundamental constants.
Physical Review Letters, vol 122, issue 16 (24 April 2019).
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Last revised: 26 September 2020.