Fine-structure constant: Is it really a constant?

Jacob D. Bekenstein
Phys. Rev. D 25, 1527 – Published 15 March 1982
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Abstract

It is often claimed that the fine-structure "constant" α is shown to be strictly constant in time by a variety of astronomical and geophysical results. These constrain its fractional rate of change α̇α to at least some orders of magnitude below the Hubble rate H0. We argue that the conclusion is not as straightforward as claimed since there are good physical reasons to expect α̇αH0. We propose to decide the issue by constructing a framework for α variability based on very general assumptions: covariance, gauge invariance, causality, and time-reversal invariance of electromagnetism, as well as the idea that the Planck-Wheeler length (1033 cm) is the shortest scale allowable in any theory. The framework endows α with well-defined dynamics, and entails a modification of Maxwell electrodynamics. It proves very difficult to rule it out with purely electromagnetic experiments. In a cosmological setting, the framework predicts an α̇α which can be compatible with the astronomical constraints; hence, these are too insensitive to rule out α variability. There is marginal conflict with the geophysical constraints; however, no firm decision is possible because of uncertainty about various cosmological parameters. By contrast the framework's predictions for spatial gradients of α are in fatal conflict with the results of the Eötvös-Dicke-Braginsky experiments. Hence these tests of the equivalence principle rule out with confidence spacetime variability of α at any level.

  • Received 25 September 1981

DOI:https://doi.org/10.1103/PhysRevD.25.1527

©1982 American Physical Society

Authors & Affiliations

Jacob D. Bekenstein

  • Physics Department, Ben Gurion University of the Negev, Beer Sheva 84120, Israel

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Issue

Vol. 25, Iss. 6 — 15 March 1982

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