Some movies do time travel right. Other movies do time travel wrong.
This is not an artistic assessment. It’s a metaphysical truth, at least according to philosophers. Regardless of whether time travel will ever be physically possible, the question we’re going to consider is how it would work logically if it did work at all. Here we explain the philosophical quandaries that mean The Terminator and Harry Potter make a certain kind of sense, while Back to the Future doesn’t quite hold up to scrutiny.