VARIATION OF FUNDAMENTAL CONSTANTS FROM THE BIG BANG TO ATOMIC CLOCKS: THEORY AND OBSERVATIONS

Theories unifying gravity with other interactions suggest the possibility of temporal and spatial variation of the fundamental "constants" in an expanding Universe. In this review we discuss the effects of variation of the fine-structure constant and fundamental masses on measurements covering the lifespan of the Universe from a few minutes after Big Bang to the present time. Measurements give controversial results, including some hints for variation in Big Bang nucleosynthesis and quasar absorption spectra data. Furthermore there are very promising methods to search for the variation of fundamental constants by comparison of different atomic clocks. Huge enhancements of the relative variation effects happen in transitions between accidentally degenerate nuclear, atomic, and molecular energy levels.