Life just got an update, time travelling is now impossible.
Stop trying to hack life.
NEVARR! I B HAX0R FUR LFIEF!
On a serious note, it is impossible at this point, and if it did work, we would have chaos.
Portals, or teleportation on the other hand, could be useful.
Teleportation exists but they haven't found out a way to put the molecules back together.
And it won't work with such huge subjects, and breaking down every molecule of your body would probably (It WILL) kill you.
Portals are basically a wormhole