system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is it thought that if travelled faster than light, we would go back in time?
gpt
Because the speed of light is the speed of 'causality'. Its the fastest that something can affect something else somewhere else (Yes that sentence is correct). 

So think of shooting a laser beam from point A to point B. You turn on the laser beam, and then it hits point B, and that's the order of things. If you could travel faster than the speed of light, than you could be standing at point A and then beat the beam of light to point B. But since we agree that things can't happen faster than the speed of light ('causality'), you'd be at point B *before* the laser was turned on at A, even though you were previously at point A right as it was turned on. So you went backwards in time.