In quantum theory, quantum collapse is random and the evidence is that when a radioactive atom emits a photon is unpredictable. A random event by definition has no physical history that can explain it and in quantum theory, every physical event involves a random quantum collapse, contradicting the claim that all physical results are caused by prior physical acts.
That every physical interaction involves a random choice clearly contradicts physical realism so in 1957, Everett proposed many-worlds theory, that every quantum choice spawns a new universe. Now if an electron anywhere in the universe chooses to be say spin up, another universe magically arises in which it is spin down, so there is no choice. Everett’s idea was first seen as absurd, as it is, but today physicists prefer it 3:1 over the Copenhagen view (Tegmark & Wheeler, 2001, p6). They believe that for fourteen billion years every photon that exists has created a new universe 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.
For a scientist, 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 light that hit your eyes? Current physics does because it is the only way to dismiss quantum randomness. Some now talk of the multiverse as a fact despite no evidence at all, based on the belief that “It must be so”.
In historical terms, many-world-theory essentially replaces the clockwork universe that quantum theory demolished last century with a clockwork multiverse. Attempts to rescue this zombie theory (Note 1) by letting a finite number of universes repartition after each choice (Deutsch, 1997) only recovers the original problem, as what chooses which worlds are dropped? Yet why would the universe, like a doting parent with a quantum camera, want to store everything that might happen? The many-worlds multiverse is truly a fairy tale for physicists (Baggot, 2013).
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Note 1. 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”.