The fine structure constant: a review of measurement results and possible space-time variations

TL;DR

This review discusses methods for measuring the fine structure constant, recent results, potential space-time variations, and implications for metrology and frequency standards, highlighting unresolved issues and practical applications.

Contribution

It provides a comprehensive overview of measurement techniques, recent findings, and the debate on the variability of the fine structure constant, including potential technological applications.

Findings

No confirmed long-term variations at high accuracy

Possible slight lower values in the past suggested by some data

Potential for new optical frequency standards based on ytterbium-171

Abstract

A brief description of the main methods for determining the fine structure constant is given. It is shown that the exact value of the fine structure constant is important for the new International System of Units (SI) and for fundamental metrology. Recent measurement results and theoretical calculations of the fine structure constant, as well as its possible space-time variations, are presented. The results of laboratory experiments on the search for long-term variations of the fine structure constant are described. The astrophysical and cosmological observational data on possible variability of the fine structure constant are displayed. The possibility of slightly lower values of the fine structure constant in the remote past as compared to its modern value, as well as the existence of unresolved problems related to possible space-time variations of the fine structure constant and the spread of the results of its precise laboratory measurements, are mentioned. Despite the absence of experimentally confirmed long-term variations of the fine structure constant at a high level of accuracy, possible practical applications of the results are noted, namely, the construction of an optical frequency standard with high stability and frequency reproduction accuracy based on the ytterbium-171 ion and a laser frequency synthesizer which may replace the caesium frequency standard.