Quantum theory states that quantum collapse is random and the evidence agrees, e.g. a radioactive atom really does emit a photon when it wants to, in a way that we can’t physically predict. Quantum randomness means that choices are being made for no known physical cause. Since in quantum theory every physical event arises from a quantum collapse, this threatens the primacy of physical causality. That every physical act is partly random contradicts the physical realism claim that only physical events cause physical events.
In 1957, Everett devised many-worlds theory to meet this threat by proposing that every quantum choice spawns an entire new universe. So when an electron anywhere in the universe chooses to be say spin up, another universe is magically created in which it chose to be spin down, so quantum randomness isn’t random at all. Everett’s idea was first seen as absurd, as it is, but today physicists prefer it 3:1 over the Copenhagen view because it supports physical realism (Tegmark & Wheeler, 2001, p6). A majority of physicists now believe that for fourteen billion years every photon that exists has been creating new universes with its every act! With up to 1043 universes being created per photon per second, it isn’t hard to see that the:
“… universe of universes would be piling up at rates that transcend all concepts of infinitude.” (Walker, 2000) p107.
From a scientific perspective, this doesn’t just offend Occam’s razor, it outrages it. Do you believe that in the time it took to read this sentence, a billion, billion universes arose just from the photons that hit your eyes? Current physics does because it is the only way to dispel the ghost of quantum randomness. So many now talk of the multiverse as a fact despite no evidence at all, based only on the belief that “It has to be so”. The multiverse idea is truly a fairy tale for physicists (Baggot, 2013).
Historically, the multiverse is a reincarnation of the clockwork universe idea that quantum theory demolished last century. It just replaces a clockwork universe with a clockwork multiverse. Deutsch attempts to rescue this zombie theory by letting a finite number of universes repartition after each choice (Deutsch, 1997) but this only recovers the original problem, as what chooses which worlds are dropped? Why would the universe, like a doting parent with a quantum camera, want to store everything we might do? The ex-post-facto multiverse fairy tale shows how far some will go to support a belief in physical realism.
PS. Zombie theories make no new predictions and can’t be falsified. Like zombies, they have no progeny nor can they be killed by falsification, as they are already scientifically “dead”..