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Comment by pred_ | Hacker News Reader

> Is wave function collapse is a real thing or just an approximation of what happens when a large system is entangled?

I've listened to enough Carroll to convince myself that I think MWI makes sense, but what I never got is that it doesn't seem to offer much in terms of explanation of how the entangled state ends up being what it is: We see a particular result of an experiment with many possible a priori outcomes, but is there a mechanism that determines which particular entangled state we end up in? Something like the phases of the wave functions on individual Hilbert space sectors conspiring to produce a certain outcome, so that an omnipotent observer with full access to both parts would be able to tell what happens a priori, no dice being rolled? Or is that just hidden variable theory?

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> it doesn't seem to offer much in terms of explanation of how the entangled state ends up being what it is:

According to MWI, all possible results of an experiment are manifest and real. You're asking "which particular entangled state we end up in?". You end up in all of them. For a 2-state superposition system, there are 2 versions of "you" that exist after the experiment, both of which are equally real. Subsequent measurements of the quantum system will appear to be "collapsed" for both versions of you but each will see different and opposing values.

> You end up in all of them.

Except that I've only ever experienced ending up in one of them, so exactly how did the "I" that is typing this right now wind up here, and not in some other branch?

There's an unexplained bifurcation of consciousness implied by MWI which it cannot explain (although I think it suggests the appeal of MWI since it gives enough wiggle room that people think that their free will could control which universe they wind up in, which appeals to everyone's inner Malcolm Gladwell).

You end up in all branches and your consciousness ends up in all branches, where your mind works. MWI works best with physicalism, yep :)

Maybe your copy in another branch even posted the same comment.

But how does bifurcation of consciousness happen and how does it diagonalize the state so that we never see a cat in a complex linear superposition of |alive> and |dead> at the same time? 1/sqrt(2) |alive> + 1/sqrt(2) |dead> should be an equally valid outcome of the experiment via purely unitary evolution.

I feel like this is a pretty reasonable question being met with non answers. And it's a shame bc I think MWI is the frontrunner as of 2022, but this is a pretty significant question with Many Worlds I had not considered before.

Well I stole it from Roger Penrose (same Penrose as in the title article) which I think he presented in either The Emperor's New Mind or Shadows of the Mind. I think its the latter book which has more concrete arguments like this diagonalization argument. Also, the idea that collapse of the wave function could be mediated by virtual gravitons or something like that once the superposition state got sufficiently "massive" (which is the genesis of the ideas in the title article here).

Both are worthwhile if you like thinking about these kinds of things.

I've generally found nearly zero people who have read those books and of them most people poo-poo it all, and don't really engage with some of the issues presented in them.

He may be wrong. Einstein was also wrong about the EPR paper. But it seems like he's trying to engage with the problems and do science rather than just provide philosophical justification.

Consciousness is not a thing that gets bifurcated. It is just a word for an information state that is aware. If you create two information states, you have two awareness states. That is not bifurcation any more than copying a movie and editing one pixel on one frame (or as a better analogy having an effectively infinite number of frames with every possible pixel combination some of which describe aware states).

I don't see how that would allow or require seeing a cat in a complex linear superposition. You just have one set of frames which describe a live cat and another set of frames that describe a dead cat.

The state and result of observation depends on the method of interaction, i.e. hamiltonian. In principle it's possible to observe the cat in a mixed state, we just don't use interaction that gives that result.

I’m currently reading Anathem so this is an interesting topic.

For simplicity, let’s say that all quantum interactions have two possible outcomes, 0 or 1.

The first point is that we can only talk about what interactions appear to have done in the past in our worldline/universe, which is randomly distribute themselves between 0 and 1. If we happened to be on a worldline where all interactions had always resulted in 0 for the whole history of the universe then that universe almost certainly wouldn’t support complex life. So perhaps there’s an observership bias here: if quantum interactions hadn’t decently distributed themselves between 0 and 1 then we wouldn’t be asking this question (just like the values of all the other fundamental constants).

As far as I can tell there’s nothing in current theories which would rule out all future interactions happening to result in a 0. Let’s hope our consciousness don’t end up on that worldline (unless you believe in quantum invulnerability).

That’s just hidden variable theory. The answer for MWI is “all of them”.

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