It's a dream come true, right? Go back in time and fix all your mistakes or shoot ahead to the future to see what's on the horizon. But not so fast—according to the stories and films in this sci-fi subgenre, time really doesn't like being mucked around with.
The Predestination Paradox: In a nutshell, you travel through time and do something that had to be done in order for time to flow in its proper course. Think of "Back to the Future"; Marty had to go back in time to make sure his mother and father hooked up, otherwise he wouldn't exist.
The Grandfather Paradox: This is a rule that explains why you can't go back in time and change something about your own life. Say you want to go back to make sure you study for an important test. Problem is, you change the timeline, pass the test and never had to go back in the first place -- so you didn't. Got it?
The Butterfly Effect: Little things that happen can compound into big effects, kind of like how a single nail left on a street can result in death if the nail pops the tire on an ambulance called to the home of someone dying of a heart attack.
Doubling: This can happen if you travel along your own timeline and meet yourself. There are two yous existing at the same time!
Time Travel Links:
"All You Zombies"
"The Sound of Thunder"
Dinosaurs, hunters and butterflies ... oh, my!