The Present Key Importance of the Fine Structure Constant,α, to a Better Knowledge of All the Fundamental Physical Constants

The dilemma is described which exists at the present time between the two present best sources of information as to the numerical value of the Sommerfeld fine structure constant, α. These two sources are the fine structure splitting in deuterium, determined in 1953 by Triebwasser, Dayhoff and Lamb, and the hyperfine structure splitting in hydrogen, measured more recently using the Ramsey hydrogen maser. The theoretical connection between the fine structure measurements and α is subject to little question but the experimental difficulties to obtain a precision of a few ppm are considerable. The relative precision obtained with the hydrogen maser on the other hand, is phenomenal (of order 10-11) but the theoretical connection between the hyperfine splitting and α is subject to a controversial correction for the internal field structure of the proton. Assuming this correction term to be correct at its present value, the hf splitting in Η implies a value of α 26 ppm higher than the fs splitting in D. Present existing sources of evidence, some favourable to the lower and some to the higher value of α, are presented and discussed and the key importance of a better knowledge of this fundamental constant is stressed.