Physics (Internal)

Arrow of time in quantum mechanics

This event is part of the Condensed Matter Theory Seminar Series.

Abstract: Why does the time flow only in one particular direction? This is a very big and fundamental question of physics, called the problem of "the arrow of time." In the present talk, I am going to discuss the following problem. The Schroedinger equation is time-reversal symmetric but we see that the excited states always decay. How can this inconsistency arise? We answer the question in the following way. We succeeded in deriving a time-reversal symmetric decomposition of the time evolution operator which contains both decaying states and growing states symmetrically. If we watch the time evolution starting from an initial condition, we pick all the decaying states, whereas if we watch the time evolution ending in a terminal condition, we pick all the growing states. This shows that the arrow of time is generated by the difference in the way we watch the time evolution.