Déjà vu washes over you. Something about this current life feels familiar, as if you’ve been here before or have done this before. What if you have? You may not remember, but your soul certainly does.

Your past, present, and future are all happening right now—at least in your mind. As American writer and Nobel Prize laureate, William Faulkner famously put it, “The past is never dead. It's not even ...