Q: If I go back in time and kill my grandfather, do I still exist?
A: Well, that's not exactly how it works. If you go back in time and kill your grandfather, you'd still exist, but you'd be a paradoxical anomaly, like a time-traveling singularity that's simultaneously born and dead. It's like trying to count how many seconds are in a day while standing on your head. It's a bit of a brain-melter, if you ask us.
Q: Can I travel back in time and change the course of history?
A: Oh, you'd think you could, wouldn't you? Newsflash: time travel is like trying to edit a Wikipedia page while it's being rewritten by a committee of mischievous monkeys. The timeline has a mind of its own, and your changes will only lead to more questions, like "Why is the Great Wall of China made of nachos?"
See also: Predestination Paradox for more on the futility of trying to change the past. Novikov Self-Consistency Principle for a more mathematical approach to time travel's inherent absurdity. Temporal Looping for the thrilling tale of a time traveler stuck in an infinite loop of 'what-ifs'.