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As I understood it, the Multi World Interpretation (MWI) was meant to avoid the problem of resorting to randomness, by replacing the random wavefunction collapse in Copenhagen Interpretation with multiple universes where all possibilities in the wavefunction do happen.

However, I wonder if it actually accomplished what it set out to do. MWI still leaves us with a major question of "which universe does my consciousness experience?", in which randomness can very much play a part.

If that is the case, does MWI have anything to offer over Copenhagen Interpretation in eliminating randomness in quantum mechanics?

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  • Sure. Man plays dice. (The stupid stack exchange algorithm requires me to type this useless sentence here if my answer is too short.)
    – Marxos
    Nov 23, 2023 at 19:37
  • this might have come up on physics stackexchange try google first
    – user67675
    Nov 23, 2023 at 20:00
  • i googled it, and it seems that we don't know why we are experiencing this universe. so it doesn't so much introduce randomness but ignorance. does that help?
    – user67675
    Nov 23, 2023 at 20:09
  • It would be more accurate to say that MWI makes the order/randomness question moot. Its answer to "which universe does my consciousness experience?" is all of them, the "I" splits along the branches. On another interpretation, the question is analogous to "which rock am I looking at right now" and the only meaningful answer is "this one". When "everything happens", as in MWI, it makes little sense to talk about order or randomness.
    – Conifold
    Nov 24, 2023 at 5:48

6 Answers 6

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The crucial advantage of MWI is not that it eliminates randomness, but that it eliminates the complexity of "wavefunction collapse."

The Copenhagen interpretation needs to explain when the wavefunction collapses, and what the probabilities of the different states are after collapse (the Born rule). These have to be some extra assumptions in addition to the Schrodinger equation.

In contrast, MWI assumes only the Schrodinger equation. There's no extra part to the theory. The Born rule in MWI is derived, not assumed. This makes MWI more parsimonious and therefore more likely, provided that it agrees with observations, and so far it seems to.

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This is just a variant of "why am I me and not someone else?". It doesn't matter whether you and the someone else are in the same room, or so far from each other that their observable universes don't overlap, or in different MWI worlds.

If you take this to be a form of randomness, then only a solipsistic world model could be nonrandom.

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  • i saw your answer about this on physics stacckexchange, and it seems right, as we are indeed asking why we are this person and not another, but a citation might help in a way
    – user67675
    Nov 23, 2023 at 22:44
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No, the populist idea of MWI does not eliminate randomness- it just spreads it across multiple universes. According to MWI, if you were to repeatedly toss a quantum dice, there would be some worlds, like ours, in which the probability of any particular number being thrown would be one in six, worlds in which only sixes were ever thrown, worlds in which only fives were ever thrown, worlds in which your throws alternated between two and four, and so on. My personal opinion is that in a thousand years, if humans still exist then, people will look back on MWI in the same bemused way that we look back on countless other bizarre ideas that now seem nonsense. However, other people seem to take MWI seriously, so perhaps there will be Universes in which I might be wrong. That said, if MWI is correct, there will be Universes in which people never realise it is correct.

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I will answer this as philosophical question. It seems to me that the MWI violates the principle of parsimony because it introduces unnecessary complexity. If it does not resolve the issue that it was introduced to address, then it is doubly invalid. It is also questionable scientifically since it proposes an untestable hypothesis.

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I think the answer would make more sense if we construct a simple analogy.

Imagine you have programmed a little simulated universe on your computer, and in your simulation you have a conscious being called Steve. In your simulated universe, Steve has access to a button which rolls a virtual dice.

Now, imagine you've programmed the universe such that, when he presses the button, the window splits into 6 different windows, and each one has one of the different possibilities of where the dice would land: 1,2,3,4,5,6.

So, you start running your program, Steve presses the button, 6 new windows spawn, with one version of Steve seeing every possible dice roll. The version who sees 6 says 'Wow, that's lucky'. The version that sees 1 says 'Oh, unlucky this time'. The other 4 just say 'hmmm interesting'.

You close down the program, and then restart it from scratch. Again, Steve presses the button, 6 new windows spawn, with one version of Steve seeing every possible dice roll. The version who sees 6 says 'Wow, that's lucky'. The version that sees 1 says 'Oh, unlucky this time'. The other 4 just say 'hmmm interesting'.

To Steve, the result he sees seems random every time. Every time he sees 6, he feels like it's lucky. Every time he sees 1, he feels like it's unlucky.

But you, from outside the universe, can see that it wasn't lucky for him to get 6 nor unlucky for him to get 1. Both of those results were guaranteed by the rules of the universe (which would be analogous to the Schrodinger equation here). It's not lucky, EVERY time you run the universe, some version sees 6 and says it's lucky, and EVERY time you run the universe, some version sees 1 and says it's unlucky.

If MWI is the case, we are Steve. It's effectively indistinguishable from randomness from our vantage point, but there's a sense of meta-determinism above the world we live in, which we don't have full access to, just like Steve can't see the meta-determinism governing his experience.

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To my understanding, it's exactly the other way around. Since that "randomness" was not so random at the end, God (as an underlying principle of the phenomena) was not playing dice. So in order to avoid this, they say that all possibilities are instantiating. The main goal was to remove the concept of God not that of the dice.

Well, you somehow changed the question, I have answered a diff. question, sorry.

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