Is time travel possible?

[Egann]

Time travel, eh?

It's possible in the forward direction for sure. We have measurements confirming that much. Backwards? It's theoretically impossible, at least for macroscopic objects (larger than a molecule) traveling large stretches of time (longer than a nanosecond).

That doesn't necessarily mean that it's impossible, but that our theories about how the universe works need to be wrong for us to do it. Personally, I expect that time travel isn't possible. Time viewing might be (particularly in the past direction) but the universe has been largely self-consistent in our experiences and time travel to the past would challenge that.

That's not to say I think all the classic "time travel paradoxes" hold water. Remember the grandfather paradox, where you travel back in time and kill your own grandfather, thus making yourself invalid? How is that supposed to work? The universe does not concern itself with the future of an object or it's past, so when you travelled back in time you became a valid object in the past. Killing your own grandfather means a parallel you won't be born, but you won't suddenly become an invalid object when your grandfather dies.