If scientists are to be believed — and they probably should be — time travel is really finicky, particularly when it comes to going backwards in time. That’s one thing most Hollywood movies get wrong when tackling time travel stories. For example, a causal loop or the bootstrap paradox — theoretical or not — is not generally factored into how time travel plots work. The term was originally coined by science fiction author Robert A. Heinlein who, coincidentally, is the author of the original book