Sean Carroll has a nice post at Cosmic Variance explaining how Occam’s razor, properly interpreted, does not weigh against Many Worlds or multiverse theories. Sample quote:
When it comes to the cosmological multiverse, and also the many-worlds interpretation of quantum mechanics, many people who are ordinarily quite careful fall into a certain kind of lazy thinking. The hidden idea seems to be (although they probbly wouldn’t put it this way) that we carry around theories of the universe in a wheelbarrow, and that every different object in the theory takes up space in the wheelbarrow and adds to its weight, and when you pile all those universes or branches of the wave function into the wheelbarrow it gets really heavy, and therefore it’s a bad theory.
That’s not actually how it works.
It is in response to some remarks by philosopher Craig Callender, who comes to join the discussion in the comments.
By these standards, the ontological commitments of the multiverse or the many-worlds interpretation are actually quite thin. This is most clear with the many-worlds interpretation of quantum mechanics, which says that the world is described by a state in a Hilbert space evolving according to the Schrodinger equation and that’s it. It’s simpler than versions of QM that add a completely separate evolution law to account for “collapse” of the wave function. That doesn’t mean it’s right or wrong; but it doesn’t lose points because there are a lot of universes. We don’t count universes, we count elements of the theory, and this one has a quantum state and a Hamiltonian. A tiny number!
I agree with all that (except for “and that’s it” part for MWI, given that the Born rule is still a separate assumption).
Counting worlds or universes towards complexity of a quantum theory is as silly as counting species towards complexity of the theory of evolution.
Sean Carroll has a nice post at Cosmic Variance explaining how Occam’s razor, properly interpreted, does not weigh against Many Worlds or multiverse theories. Sample quote:
It is in response to some remarks by philosopher Craig Callender, who comes to join the discussion in the comments.
Another quote:
I agree with all that (except for “and that’s it” part for MWI, given that the Born rule is still a separate assumption).
Counting worlds or universes towards complexity of a quantum theory is as silly as counting species towards complexity of the theory of evolution.