Accuracy of the ftne structure constant

Abstract

At present the fine structure constant /spl alpha/ can be determined with a precision of better than few parts in 10/sup 7/ in four independent ways. They are based on the ac Josephson effect, the quantized Hall effect, the muonium hfs, and the anomalous magnetic.moment of the electron. Further improvements of these results and their implications to physics and metrology will be discussed.