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Wednesday, February 03, 2010
2:30 PM - 4:00 PM
T-DO Conference Room, Bldg 123, Room 121

Quantum Lunch

Quantum Physics and the Arrow of Time

Lorenzo Maccone

The arrow of time dilemma: the laws of physics are invariant for time inversion, whereas the familiar phenomena we see everyday are not (i.e. entropy increases). I show that, within a quantum mechanical framework, all phenomena which leave a trail of information behind (and hence can be studied by physics) are those where entropy necessarily increases or remains constant. All phenomena where the entropy decreases must not leave any information of their having happened. This situation is completely indistinguishable from their not having happened at all. In the light of this observation, the second law of thermodynamics is reduced to a mere tautology: physics cannot study those processes where entropy has decreased, even if they were commonplace. Nonetheless, it seems that this observation may not be used as a completely satisfactory solution of the arrow of time dilemma: it seems necessary to separately postulate a low entropy initial state.

Host: Wojciech Zurek