Every Variation of Your Life May Coexist

The universe as a whole has every possible history, says the Many-Worlds interpretation of quantum mechanics. This does not just mean that every possible history could have happened - it means that every possible history DID happen. This is in obvious contradiction to our intuition which tells us that the past exists as one, definite series of events. How could this be possible?


Quantum mechanics has found that the motion of every particle and object in nature is governed by a characteristic wave function. The wave function describes the probability that a particle will be in a certain location at a certain time, because in fact, again contrary to our intuition, particles do not have definite locations.  The best that you can do is know the probability distribution of its location. The truth to this idea can be verified by the famous Double-Slit experiment.  It showed that if a single electron encounters a barrier with two separated slits, it somehow goes through both slits simultaneously!  This happens because the particle's wave function gives it an appreciable probability of going through either of the slits, and according to the Many-Worlds interpretation, since both events can happen, both events do happen.

Thus, like the future, the Many-Worlds interpretation says that the past only exists as an indefinite spectrum of possibilities. Not only that, but our observations seem to affect a particle's past, as shown by the Delayed-Choice experiment. In a variation of the Double-Slit experiment, the decision of how to measure a photon of light is delayed until after the photon passes through the slits. Since the type of measurement determines whether the photon acted like a wave or a particle as it passed through the slits, it seems as though the measurement chose which past the photon had!

This has been extrapolated to mean that the entire universe has every single possible past and that every past happened and now continues to this day. This is the basis for the idea of parallel universes coexisting in an infinite multiverse.  For more on this, see Occam's Razor: Which is Less Ridiculous, Parallel Universes or God? .