Why Can't Time Run Backwards?
Professor Anthony J Leggett
We can all tell when a movie of some everyday event, such as a kettle boiling or glass shattering, is run backwards. Similarly we all feel that we can remember the past and affect the future, but not vice versa. So there is a very clear "arrow" of time built into our interpretation of our everyday experience. Yet the fundamental microscopic laws of physics, be they classical or quantum mechanical, look exactly the same if the direction of time was reversed. So what is the origin of this "arrow" of time? This is one of the deepest questions in physics; I will review some relevant considerations, but do not pretend to give a complete answer