I think the measurement problem is a much bigger ‘theory cost’ to Copenhagen than just assuming wavefunction mechanics continues even after measurements are made.
Copenhagen isn't even clear on if the states have a concrete reality or not - there certainly are no hidden variables, at least.
A discernible state is an entity. More discernible states requires more entities or more discernible features of an entity. This is the only way to make the concept of discernible state intelligible. To deny this is just to engage in magical thinking. But each posit has a cost associated with it. We don't know what that cost is exactly (relative to other theories with different features). But we do know that an exponential growth in discernible states overshadows the theoretical cost of the whole regardless of how we quantify the cost of any individual posit. MWI is almost maximally profligate; any empirically adequate theory without this cost should be preferred.
"sure, we can observe bacteria and viruses in the lab individually - but when we move to the physical world disease spread is described by miasma which is simpler and thus this is the more parsimonious theory." there are fewer entities in miasma - but you still have to posit this additional thing (the miasma) on top of the already observed viruses and bacteria.
similarly, i don't agree that 'count of entities' is the correct criterion for what makes a theory more or less parsimonious/occam's razor preferred. it is about the number of rules even if there is a single rule that creates exponential entities. Copenhagen would also predict this 'exponential branching' in the system under observation - it just proposes that it collapses when measured by the apparatus: an additional rule that makes it less parsimonious than many worlds
>i don't agree that 'count of entities' is the correct criterion for what makes a theory more or less parsimonious/occam's razor preferred.
I mean, its literally in the original formulation of Occam's razor: "plurality should not be posited without necessity". But there are many ways to justify this. My preferred argument is that fewer entities means fewer resources with which to "bake in" the explananda into the theory. The more knobs to turn to generate your empirically adequate theory, the less likely your theory will capture reality.
>[Copenhagen] just proposes that it collapses when measured by the apparatus
Measurement isn't limited to an "apparatus". Collapse of superposition is a feature of large scale interactions. While there is branching, in practice it is bounded because interactions tend to cause collapse.
The multiplicity of MWI is like that: just a maximally extended coordinate system.
Where the MWI takes additional theory burden is where it explains how the born rule translates to our lived experience - ie. why do we only experience one path of the wavefunction
From an outside viewer that hasn't been entangled with you, no branching happens and they see the overall state evolve according to the Schrodinger equation.
Imagine that w create very small machines that could perform some observations and record them into some internal log.
Now imagine creating a particle in some state and have that machine measure that state and record it internally. Provided that the particle+machine system is isolated from the environment (and us) you'd probably agree that the particle and machine are entangled and that the state of the "log" is not in a defined state until we measure it.
Now, that information processing machine is not a human but I think it may be useful to describe how the external world would look like from it's point of view. For example, if that machine performed several experiments on that test particle or other particles it would note in its log data that would confirm that it obeys the Born rule.
In that sense, it's "useful" to imagine how things look like from the "point" of view of that machine and it's possible outcomes in the many worlds, although these worlds might not really matter to us since we can describe the system that includes that machine as having been in a mixed state all along until we humans actually observe its "log"
The likelihood that people start to object to this though experiment gets higher and higher s as soon as one starts to imply that we humans ourselves are exactly like that machine.
For me, the observation that our ability to accept or reject this interpretation is so much tied to our intuitions about our own _self_ is a strong hint that actually favours the theory. We humans have been known to be trapped by our point of view
Discernible in principle. Either the states are distinguishable from within the system (e.g. two branches that disagree on the state of the world), from an outside observer, or a God's eye view. If none of this is true then there is no other world.
>Now imagine creating a particle in some state and have that machine measure that state and record it internally. Provided that the particle+machine system is isolated from the environment (and us) you'd probably agree that the particle and machine are entangled and that the state of the "log" is not in a defined state until we measure it.
Lets further imagine a large collection of these machines connected in series. Each machine can perform one of two experiments at any given trial, and which experiment they run depends on the most recent outcome of the prior machine in the series (e.g. the direction of a particle's spin). There are an exponential number of scenarios as the number of machines in series grows. If we imagine this system entangled until we observe it, and we expect that the definite state is consistent in terms of which particle the machine measured and the corresponding prior outcome in the series, then the entangled system just has to carry discernible state in proportion to the exponential state space of the system. If not, then the system isn't in an indefinite state until observed. The concerns about exponential theory cost remain. Unless the state space is bounded by collapse or some other means, the theoretical cost to MWI or any theory based on Schrodinger without additional posits is supreme.
>In that sense, it's "useful" to imagine how things look like from the "point" of view of that machine and it's possible outcomes in the many worlds, although these worlds might not really matter to us since we can describe the system that includes that machine as having been in a mixed state all along until we humans actually observe its "log"
There's a tension here that needs to be released somehow. On the one hand, you have an external observer determining the system is in a superposition of states. On the other hand, you have the perspective from within the system of everything being definite. You can't just carry both forward simultaneously without addressing the disagreement on the state of reality. Either there are really an unbounded number of branches, the branches are bounded by some mechanism, or there are no branches and the evolution of reality happens asynchronously.
Are you saying that under this scenario of N such machines in series the MWI would make different predictions that just solving the Schrodinger equation?
Some people when they hear that MWI implies that there are many worlds and that the wave function branches they think that implies that MWI is "adding" something so Occam's razor should work against it.
OTOH what MWI postulates that the Schrodinger equation is all there is and the collapse of the wave function is observed because the observer is entangled with the system it measured.
In order to make an intuitive sense of what's going on, MWI invokes the "worlds" and the "branching" but that's just a way for us to grasp how it would feel if ourselves are part of the entangled system. But as many analogies whose purpose is to tickle the intuition it doesn't work for everybody and may be confusing the discourse more than helping it.
But the thing is: the everett interpretation is simpler and it requires less additional rules and mechanisms to explain what we observe. So Occam's razor should favor it.