Our buddy MinutePhysics has delved into the parallel possibilities of parallel universes before, but this breakdown of the "many worlds" idea is a great little explainer for why we think it might exist, and how we haven't been able to prove anything yet. Is everything you ever thought you knew wrong? Probably, somewhere. But with any luck that's not in this timeline. [MinutePhysics]
Why Scientists Think Our Timeline Could Be Splitting