Claudio Bunster (Centro de Estudios Científicos, CECs, Valdivia, Chile)

ABSTRACT: The issue of the enormously small value that the gravitational constant G takes when expressed in microscopical units is revisited. A simple mechanism is discussed, which could implement Dirac's idea of G actually decaying; from an initial value commensurable with microscopical units to its value in the present epoch of the universe. The mechanism is based on the possibility of having, within one universe, domains with different values of G, whose borders are crossed by particles and forces. The dynamics of the novel kind of domain wall that separates two such dominions is largely dictated by the second law of thermodynamics as applied to a black hole. It is argued that this is a satisfactory state of affairs, since the expression of the entropy of a black hole is the formula in physics where all the constants characterising its different realms appear together in a poignant manner.