For years now, one argument has nearly torn the country apart: which theory of time travel is more accurate, the Back To the Future theory, or the Bill and Ted's Excellent Adventure theory?
Quantum physicists at MIT have now waded into the fray, and firmly backed the Bill and Ted's theory. Cause and effect are not linear, and an effect in a quantum particle can be designed so that it could only have had one cause - or, as Dr. Low from the U of Bristol clumsily puts it, "You could think of it as postselection affecting the history of the particle, sending the state back in time."
Or, you could think of it like this:
Bill: If only we could go back to two days ago before your dad lost his keys, and steal them.
Ted: Well, why don't we?
Bill: Cuz we don't have time, dude.
Ted: We could do it after the report.
Bill: Oh yeah! Where should we put 'em?
Ted: How 'bout behind this sign?
Bill: Ok. Woah! It worked! Right, so when we're done with the report, we have to remember to do this or else it won't happen. Except it did happen! Ted, it was you who stole your dad's keys!