Using decision theory to explain quantum mechanics seems like a huge mistake for a very simple reason: It confuses "ought" for "is". Decision theory makes state

Using decision theory to explain quantum mechanics seems like a huge mistake for a very simple reason: It confuses "ought" for "is". Decision theory makes statements about what one should do if one wants a certain outcome. As the author points out, what statements are we making about what we want? We are free to decide that dividing ourselves and dividing an outcome are not equivalent. But really the whole idea should look silly long before we come up with such a specific counterexample: the laws of physics have no dependency on the wants of human beings, in fact the wants of human beings are fully dependent on the workings of physics (humans being physical systems), so an explanation of physics in terms of statements about wants should appear absurdly circular. There does not need to be an agent optimizing outcomes in order for the predictions of quantum mechanics to be correct. There doesn't need to be agents at all, since the laws of physics worked just fine in the billions of years before there were people. This seems a bit like dressing up the problematic Copenhagen notion of a privileged "observer" in different clothes. I have never understood what is left to be explained in many worlds, and maybe someone with deeper understanding can explain it: what is the problem with simply saying that the squared amplitude gives the fraction of the wavefunction that has evolved from the initial state into the final state? What need is there to bring probability into the physics? If we are accepting the initial wavefunction state as a premise x, and we associate each configuration in the final state y with an experience we might have, then isn't asking the "probability" of experiencing y given x, in a Bayesian sort of way, naturally, emergently the same thing as asking the fraction of [the wavefunction that evolved from all the configurations associated with x] which is associated with y? What is missing and what is the dispute? Last, what is this talk of "splitting"? I thought it was true that the wavefunction is "incompressible", in that if some measurable that becomes more confined, there is always some other measurable that becomes correspondingly less confined? That is to say, if there is some axis in state space which splits (distinguishes) universes by narrowing possibilities, there must always be some other axis that merges (confuses) universes by widening possibilities? That is to say, if ever you know more about what universe you are in, you must know less (along some orthogonal axis) about what universe you came from? I.e. for every "branch" there is a "merge".