The enduring popularity of "Back to the Future" (BTTF) movie trilogy has made a lot of us fascinated with the idea of time travel. Since the movies came out, alas, nobody actually has developed a trash-powered DeLorean that's able to zoom back and forth between decades or centuries. Even so, some scientists think that time travel might be at least theoretically possible [source: Russon].
Assuming that this could happen, we could run the same danger that BTTF protagonist Marty McFly encountered — the risk of inadvertently doing something to alter a past event, which in turn triggers a series of events to alter the course of history. In the initial BTTF, as you might remember, McFly, accidentally prevented an event that led to his parents dating and falling in love, which threatened to erase him from the family's snapshots. That necessitated a lot of plotting and McFly's part to ensure that they actually did get together and procreate.
But as Gizmodo writer George Dvorsky noted in a 2015 article, the existence of a multiverse would make all of those antics unnecessary. "The presence of alternate worlds means there isn't a single timeline to screw up," he wrote. Instead, if a person went back in time and changed things, he'd simply spawn a whole new set of parallel universes.