The concept of time travel is complicated enough on its own without the possibility of killing a vital relative and negating your own existence. Even for time lords who aren't particularly interested in testing the limits of their own mortality by offing their teenage dad, things don't look great, because as this video explains, every time you travel back in time, you're probably killing off the previous version of yourself.
But if going back in time and killing your grandfather negates your own existence, because how coud you exist if your dad's dad didn't, do you just spontaneously vapourise the moment he stops breathing? How is that even possible?
No wait, don't try to answer this question on your own, MinutePhysics is here to help.
The first solution to this famous paradox is that when you go back in time to kill your grandfather, you're not going back to your own history, but a copy of your history, and everything you do in this version of your history will affect the alternate future of that universe, not your own.
This follows the same logic as the idea that Star Trek-style transporters are basically suicide machines. As we explained back in March, quantum physics doesn't 'allow' for perfect copies of yourself to exist - either in time travel or teleportation.
To read more and view the video, click here.