according to quantum physics it is theoretically possible but, you'd likely end up back in an alternate universe. It is mathematically possible and that's a fact not SyFy.
I agree with this. If a person were able to travel back in time it would create an alternate universe at that point. Your presence at that time would change things going forward.
That solves what is called the "Grandfather Paradox". That is when you travel back in time and kill your grandfather so you would never be born. However, if you killed your grandfather a different universe would not include you but the universe you came from would continue to exist so you could continue to exist as well.
The problem I can't figure out is that if you travel back in time, what would prevent someone from your future arriving just before you killed your grandfather and stopping you from killing him?