Title: Why the expansion of the Universe is accelerated

Speaker: Diego Pavon, Universidad Autonoma de Barcelona

Time and place: 14:00-15:00,May.28（Tuesday）, 2013, CAA Lecture Hall,jianchuan Road 955

Abstract:

Nowadays there is compelling evidence that, at present, the expansion of the Universe is accelerated. Einstein gravity explains this acceleration by invoking an exotic energy with a huge, negative, energy pressure. More general gravity theories simply modify the Einstein-Hilbert action in an ad hoc manner. Here we show that whathever its origin, this acceleration is consistent with the second law of thermodynamics in the sense that the entropy of the horizon plus that of matter and fields inside it must never decrese and it should approach a finite maximum in the long run. In this light, we may say that the acceleration could have beeen anticipated on thermodynamic grounds well before its actual discovery. On the other hand, based on this insights, we propose three parametrizations of the deceleration parameter that never diverge and hold from the matter era to far future.