Grandfather paradox

Grandfather paradox is a time travel paradox. It explains what would happen if you could travel back in time and then make changes to the past that might prevent your own birth.

Imagine you are a time traveler and able to travel to the past, for example, back to when your grandparents were young. If you do something that would make it so that your grandparents would never have kids, that would mean that you (their grandchild) would never exist. So you wouldn't be around to go back in time and make changes, but if you did, that would mean you would never exist either. It's a paradox because it's a situation that has no solution.