“Well, time has a kind of strange role in modern physics. It’s not a completely resolved question. The nature of time still has real ambiguities about it. Scientifically we don’t understand why time has one direction, and one direction only. Yes, I can never go backwards, but in space I can go both directions. Always. In any direction of space. I can always go in both directions. And there’s some confusion why I can’t do that with time. We can’t see anywhere in the mathematization of physics that requires that time goes forward only. So this has been something that many people have labored over for a long time trying to understand that.”

“Formally everything that we’ve written down is more or less what’s called ‘time-reversal invariance.’ It runs the same forwards as backwards. The laws don’t point forward in any way. And so we don’t understand why we know when you a watch a movie of a glass shattered on the floor reconstituting itself on the table that we all know that that’s running backwards. So, so there’s a lot of discussion about what might generate the arrow of time. And it’s a deep question. And there’s some very abstruse ideas, like maybe time always exists forward and backward, it’s just our path through it that’s very specific.”

— Janna Levin, Theoretical Physicist

Found while going through some old notes. This was from an interview in December of 2010.