Accuracy of the fine-structure constant

Abstract

The fine-structure constant alpha can be determined with a precision of better than a few parts in 10/sup 7/ in four independent ways. These methods are based on the AC Josephson effect, the quantized Hall effect, the muonium hyperfine structure, and the electron anomalous magnetic moment. A determination of alpha based on an improved theoretical calculation and on the Penning trap measurement of the electron anomalous magnetic moments has now reached a precision exceeding 10/sup -8/. Its implications for physics and metrology are discussed. >