MW theories have to specify when and how decoherence occurs. Decoherence isn’t simple.
They don’t actually. One could equally well say: “Fundamental theories of physics have to specify when and how increases in entropy occur. Thermal randomness isn’t simple.” This is wrong because once you’ve described the fundamental laws and they happen to be reversible, and also aren’t too simple, increasing entropy from a low entropy initial state is a natural consequence of those laws. Similarly, decoherence is a natural consequence of the laws of quantum mechanics (with a not-too-simple Hamiltonian) applied to a low entropy initial state.
MW has to show that decoherence is a natural consequence, which is the same thing. It can’t be taken on faith, any more than entropy should be. Proofs of entropy were supplied a long time ago, proofs of decoherence of a suitable kind, are a work in progress.
So once that research is finished, assuming it is successful, you’d agree that many worlds would end up using fewer bits in that case? That seems like a reasonable position to me, then! (I find the partial-trace kinds of arguments that people make pretty convincing already, but it’s reasonable not to.)
The other problem is that MWI is up against various subjective and non-realist interpretations, so it’s not it’s not the case that you can build an ontological model of every interpretation.
They don’t actually. One could equally well say: “Fundamental theories of physics have to specify when and how increases in entropy occur. Thermal randomness isn’t simple.” This is wrong because once you’ve described the fundamental laws and they happen to be reversible, and also aren’t too simple, increasing entropy from a low entropy initial state is a natural consequence of those laws. Similarly, decoherence is a natural consequence of the laws of quantum mechanics (with a not-too-simple Hamiltonian) applied to a low entropy initial state.
MW has to show that decoherence is a natural consequence, which is the same thing. It can’t be taken on faith, any more than entropy should be. Proofs of entropy were supplied a long time ago, proofs of decoherence of a suitable kind, are a work in progress.
So once that research is finished, assuming it is successful, you’d agree that many worlds would end up using fewer bits in that case? That seems like a reasonable position to me, then! (I find the partial-trace kinds of arguments that people make pretty convincing already, but it’s reasonable not to.)
The other problem is that MWI is up against various subjective and non-realist interpretations, so it’s not it’s not the case that you can build an ontological model of every interpretation.