Current theories that seek to unify gravity with the other fundamental interactions suggest that spatial and temporal variation of fundamental constants is a possibility, or even a necessity, in an expanding Universe. Several studies have tried to probe the values of constants at earlier stages in the evolution of the Universe, using tools such as big-bang nucleosynthesis, the Oklo natural nuclear reactor, quasar absorption spectra, and atomic clocks (see, e.g. Flambaum & Berengut (2009)).
Memorie della Societa Astronomica Italiana (Journal of the Italian Astronomical Society): incorporating proceedings Joint Discussion 9, the 27th IAU General Assembly, Rio de Janeiro, 10-11 August 2009,
Vol. 80, no. 4 (2009), pp. 795-801