Yes and no. If we use time dilation, say accelerating at light speed around a blackhole, you could go to the future. If you found a way to travel faster than light, you could go back in time. That's how Superman does it when he orbits the Earth in reverse.

What do you mean can nature allow black holes? They exist lol. As for the time travel and wormholes I have no idea. Time Dilation is real as well