[crdrost]

It is strange given my physics training to read this discussion.

Physicists do not directly apply Occam's razor in most circumstances, and we certainly don't do bookkeeping on how many “entities” there are, and your comment illustrates precisely why: how you count is not a given.

Here is something that did happen in classical mechanics: we transitioned from F_i = m a_i to Lagrangians even though they have roughly similar explanatory power. Here is an argument that was not made: “Lagrangians are truer because you don't have to postulate three equations of conservation of momentum and one of conservation of energy, you just have one law of least action.” Nobody even declared a confident end to the tyrrany of Newton's third law as Lagrangians no longer need it.

Furthermore nobody said that classical field theory was “better” per Occam's razor merely because you were no longer bound by the tyrrany of the least action principle and could now consider essentially a world in which F_i = m a_i was not universally true, to be replaced with a philosophical interpretation by some bloke Neverett who declares the fields on-shell “typical” and derives the least-action principle as a statement that “if you find yourself in a typical universe then almost surely your retroactive reconstruction of events satisfies the least action principle.”

No, many worlds interpretation is thriving precisely because it calls physicists attention to the importance of decoherence calculations in the understanding of various physical phenomena. It gives you an idea for how to model measurements that are somehow partial, or being continuously performed. Occam doesn't enter into the discussion in the first place.

[pontus]

You're right that you can't just count the number of postulates naively because there is generally not a well defined way to do so. A great example is the one you give: three laws of motion vs one law of least action. However, if I told you that it was possible to reproduce all of mechanics with only the first two of Newton's laws, then surely you'd agree that there wouldn't be a need for the third law and in that sense the new system of postulates would be simpler.

In other words, because MWI is obtained by removing a postulate from the usual formulation of QM, I think it's fair to say it's simpler. If, instead, MWI had been obtained by formulating all of QM in some other distinct framework where there was no mention of wave functions, measurements, or the Schrodinger equation etc, and it had one fewer postulate, then yes I would agree that you can't arbitrarily say that it's simpler.