Music, Pandora's Memory Box
Contrary to popular belief, time travel has been proven. Think about it: you hear an old story, dear to the heart, and the memories come flooding back. If it is related to a specific moment, be it happy or sad, the context of the moment is all there... the faces, the places, the sounds and even certain smells pop up in our minds.
How then can a simple melody have such power on our memory, like a time machine sending us back to the past for a brief, but very real, flashback?