Smell is processed in the same area of he brain as memory, that's why it's such an intense memory trigger. Sights, sounds etc can consciously remind us of things--remind us to remember them--but the right smell can drop us into being-memory of entire parts of our lives, without any collaboration on our part.

So, idk, I just kinda go with that one. Only way we'll ever be able to time travel, after all.