What's the deal with the arrow of time in physics?

CRISTIAN LÓPEZ

Munich

Workshop; Work in Progress Talk - MCMP; 2017

Munich Center for Mathematical Philosophy

Intuitively we believe time goes by. We have learned whilst future is something which ?everyone reaches at the rate of sixty minutes an hour, whatever he does, whoever he is? (as C.S. Lewis has wrote), past remains untouchable, only reachable by memory. Time seems to be asymmetric and directed: it always ?flows? from past to future, and never the other way around. Things are unavoidably devoured by time, slipping into non-existence, over and over. As Heraclitus nailed down: "everything flows and nothing abides?. Nothing remains, everything must go: this is just the way that world goes. Philosophical enquiry starts out when we raise the question for the very bedrock of such daily belief: what does ?time passes by? mean? What is our human experience about a passing time grounded in?However, fundamental physics seems to suggest that we live in a Parmenidean world, where time is just an illusory impression: there seem to be a broad agreement among philosophers and physicists that fundamental physical theories are blind to the passage of time as they are time reversal invariant. Nothing at the formal level of physical theories would allow us to discriminate the past-to-future direction from the future-to-past one. Such a conclusion is quite disappointing for those particularly interested in grounding our intuitions about time in the world, since we would really live in a timeless reality.In this WIP talk, I will take a stand against this widely assumed conclusion. Firstly, I will show that such a "pessimistic scenario" stems from the fact that the approach to the arrow of time that has been most commonly assumed is reductionistic: time is a world?s secondary feature stemmed from dynamics, particularly, from its property of being non-time reversal invariant. Secondly, notwithstanding that conventional wisdom, there is no an unequivocal and objective manner to get a neat concept of time reversal as there is no suitable time reversal operator to work with. This situation is particularly critical in non-relativistic quantum mechanics, where there would be at least two mathematical possibilities for a time-reversal operator, leading to two quite different scenarios. Finally, I will suggest that this argument will pave the way for a non-reductionist approach to time, according to which the arrow of time, if exists, is an intrinsic property of space-time.