The fine structure constant

The fine structure constant alpha is one of the fundamental constants of nature characterizing the whole range of physics including elementary particle, atomic, mesoscopic and macroscopic systems. This diversity is reflected in a large number of independent and competitive physical methods available for measuring alpha. Included in this review are high precision determinations of alpha based on the measurements of the neutron de Broglie wavelength, the quantum Hall effect, the ac Josephson effect, the electron anomalous magnetic moment, and some simple QED bound systems. Also discussed are new promising approaches based on atom beam interference and single electron tunnelling. Possible implications to physics that might arise from the comparison of alpha's obtained by these methods are explored.