The cosmological origin of time-asymmetry

MARIO CASTAGNINO; OLIMPIA LOMBARDI

Trieste

Congreso; Conference on Irreversible Quantum Dynamics; 2002

Centro Internazionale di Fisica Teorica “Abdus Salam”

Since the nineteenth century, the problem of the direction of time has been one of the most controversial questions in the foundations of physics. Many theoretical contributions have been made in the seeking of an answer to the problem. However, despite of all the debates, very little progress towards a consensus has been achieved. Our impression is that this situation is mainly due to the fact that different concepts are usually confused in the discussions and different problems are traditionally subsumed under the same label. For this reason, we will attempt to disentangle and clarify some of the issues involved in the debates about the direction of time. In particular, we will argue that it is necessary to carefully distinguish between the problem of irreversibility and the problem of the arrow of time: whereas the first one can be addressed in local terms, the second one requires global considerations. On this basis, we will define the arrow of time as an intrinsic, geometrical feature of space-time, rejecting the traditional entropic approach according to which the direction of time is defined by the gradient of the entropy function of the universe.