Originally posted by sonhouse
Is this many worlds deal just supposition to try to explain quantum physics?
Originally posted by apathist
The MWI fails to provide a deterministic resolution for the indeterminate quantum event.
Hence the word interpretation in the phrase Many Worlds Interpretation. The difficulty isn't what apathist is on about which misses the point - the purpose is to explain quantum mechanics in a way that makes sense not "to save determinism in physics". The problem with the Copenhagen Interpretation is that it simply does not explain why the wavefunction collapses, the Many Worlds Interpretation does and is complete in that sense. The problem with apathist's argument is that he's criticising it for succeeding in what it's setting out to do.
In the Many Worlds Interpretation determinism is preserved for an observer outside the universe - in other words there's a "God's eye view" from which it is deterministic and just an ensemble of universes evolving as one would expect by applying the Schrodinger equation. For an actual observer the outcome is not deterministic. An observer inside the universe is part of it so when the universe splits they do too, the indeterminism in physics is then due to the way we can only observe the parts of the global wavefunction that are coherent with our knowledge. So if we were to do the Schrodinger's cat experiment our measurement tells us that we are in the copy of the universe where the cat is alive, copies of us are in the dead cat universe but we no longer have access to them. I think up to here the concept works well. It succeeds in providing an account which explains the
apparent indeterminism in physics in terms of partitioning of the wavefunction.
However, there's a problem. In something like the EPR experiment the two states are equally likely. So, we have the universe splitting into two equal parts. But, as is the case in most real world scenarios, what if the two or more outcomes are not equally likely? The account then has to provide an explanation as to why a universe has a weighting associated with it. I think that this is the real gap in MWI.