Time travel is probably impossible both on theoretical and practical levels:

• It requires exotic, negative energy, no indication that this exists anywhere, and no indication that it can be made.

• Antimatter behaves like matter moving backwards in time, it isn't, but the point stands that any matter moving backwards in time will effectively be made of antimatter, this means you can't time travel anywhere except in a large, naturally occurring vacuum, because if you touch anything your time machine will annihilate itself.

• You have to travel faster than light to do it, so coming to a safe stop will be difficult (and ooh boy, if you crash into anything it's bye-bye planet)