In my earlier post I pointed out the morally disastrous consequences of such a parallel universes theory, and pointed out that it is not accepted by a majority of physicists. I pointed out there are simpler ways to interpret quantum mechanics, without going to the extreme of believing in parallel universes.
Yesterday the widely read Science Daily web site had an article Physicist Disentangles "Schrodinger's Cat" Debate that reports on a paper published by physicist Art Hobson in the scientific journal Physical Review A.
Hobson makes conclusions that (if correct) demolish the theoretical foundation of the parallel universe theory. If Hobson is right, quantum mechanics does not support any theory of parallel universes.
Schrodinger's Cat is a famous thought experiment in which we imagine a cat in a closed box, connected to a strange machine that includes a radioactive isotope (something that decays a subatomic particle at random times). The machine is set up so that if a nucleus in the radioactive isotope decays within a particular interval, the cat dies, and if the decay does not occur, the cat lives.
This thought experiment has led some thinkers to conclude that a cat in such a box is both alive and dead. The thinkers imagine a “superposition of states” for the cat – a dead state superimposed over a live state. They then extend this idea to the conclusion that there is a “superposition of states” involving everyone and everything, extended to the utmost. Hence the theory of an infinite number of parallel universes (including not just you, but an infinite number of copies of you).
Hobson cuts this theory off at its root – the idea that Schrodinger's Cat is both alive and dead. He argues that the “superposition” is not a superposition of physical states but merely a superposition of correlations.
According to the Science Daily summary of Hobson's paper, “That means with Schrodinger's cat, the cat is no longer predicted to be both dead and alive. It is instead dead if the nucleus decays, and alive if the nucleus does not decay, just as one would expect.”
The latest paper by Hobson is blocked by a pay wall, but you can get for free a very similar paper here. Hobson concludes:
In particular,Schrodinger's cat is in a non-paradoxical mixture of being alive when the nucleus didn't decay, and dead when the nucleus decayed, with a randomness stemming from the quantum randomness of the decay. This state of affairs comes about with no assistance from a human mind, other worlds, hidden variables, the environment, collapse mechanisms, or other entities beyond the quantum system and its measuring apparatus, even in the case that both are microscopic. The analysis is exact and not "for all practical purposes."
The reference to “other worlds” is a reference to the Everett Many Worlds theory, which Hobson is suggesting is entirely unnecessary for explaining the paradox of Schrodinger's Cat (contrary to what its proponents claim).
Hobson says that his conclusions are backed up by experiments on quantum entanglement done during the 1990's, such as the experiments of Rarity and Tapster. See this paper by Hobson for more details on how those experiments back his position.