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How the Many-Worlds Theory of Hugh Everett Split the Universe

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Re: How the Many-Worlds Theory of Hugh Everett Split the Universe

#21

Post by lmm »

smackay wrote: post #19
fallingfrog wrote: post #8

You can do a really simple thought experiment that provides a persuasive argument in favor of the many worlds theory. Or at least, it shows that wave function collapse is relative to an observer, not universal everywhere. Start with Schroedingers cat: the cat is in a box, it’s in a state of quantum superposition. It’s 50/50 alive or dead. Now a researcher opens the box: the cat is found to be either alive, or dead, a…

But surely the first researcher is also in a state of quantum superposition and they are 50/50 opening/not opening the box. So how does time come into the equation? And does that mean that any observation is localised and there's no need for many worlds except in unobserved areas of the universe?

> But surely the first researcher is also in a state of quantum superposition and they are 50/50 opening/not opening the box.

In this simple thought experiment we're assuming they're not. Imagine that the first researcher is definitely going to open the inner box after 10 minutes and then the second researcher is definitely going to open the outer box after 20 minutes.

> And does that mean that any observation is localised and there's no need for many worlds except in unobserved areas of the universe?

Well the whole problem with non-many-worlds is that it has this idea that observed areas and unobserved areas are different. Which can work in very simple thought experiments but gets crazy as soon as you try to apply it to the real world: any interaction between two particles can be seen as an "observation", every part of the universe is gradually "observing" every other part, how do you draw a line between which parts are in superposition and which parts aren't? Many worlds simplifies all this and says that everyone is always in a superposition, there's never a "collapse", and observing outcome A or outcome B with 50% probability is just what being in a superposition of A or B feels like from the inside.

Re: How the Many-Worlds Theory of Hugh Everett Split the Universe

#22

Post by platz »

fallingfrog wrote: post #8

You can do a really simple thought experiment that provides a persuasive argument in favor of the many worlds theory. Or at least, it shows that wave function collapse is relative to an observer, not universal everywhere. Start with Schroedingers cat: the cat is in a box, it’s in a state of quantum superposition. It’s 50/50 alive or dead. Now a researcher opens the box: the cat is found to be either alive, or dead, a…

The wavefunction is the thing that is in a state of quantum superposition.

It all depends on whether you think the wavefunction describes the macroscopic world (MWI), or the wavefunction merely calculates amplitudes&probabilities for things that happen in the macroscopic, classical world (Copenhagen)

Is the electron it's wavefunction (MWI), or is the electron a particle/field that is influenced by the wavefunction (Copenhagen)?

Re: How the Many-Worlds Theory of Hugh Everett Split the Universe

#23

Post by lisper »

lmm wrote: post #20
lisper wrote: post #13

Earlier quoted context omitted.

Right, most of them just take it as an axiom. But the MWI explicitly rejects the Born rule as an axiom, insisting that the Schrödinger equation is all the actual physics there is.

MWI is not incompatible with postulating the Born rule if you want to. It just doesn't elevate it to an axiom of the theory. It's like doing constructive mathematics: you're not denying the law of excluded middle, you can postulate it and it will have the usual consequences, but the core theory doesn't rely on it, and it's possible to hope for a more elegant alternative.

Yes, you can just add the Born rule as an additional axiom, but that undermines the whole point of adopting the MWI in the first place, which is to remain mathematically "clean" with no ad-hoc assumptions.

Re: How the Many-Worlds Theory of Hugh Everett Split the Universe

#24

Post by lmm »

lisper wrote: post #23
lmm wrote: post #20

Earlier quoted context omitted.

MWI is not incompatible with postulating the Born rule if you want to. It just doesn't elevate it to an axiom of the theory. It's like doing constructive mathematics: you're not denying the law of excluded middle, you can postulate it and it will have the usual consequences, but the core theory doesn't rely on it, and it's possible to hope for a more elegant alternative.

Yes, you can just add the Born rule as an additional axiom, but that undermines the whole point of adopting the MWI in the first place, which is to remain mathematically "clean" with no ad-hoc assumptions.

Yes and no. I'd argue that the Born rule as a rule for subjective probabilities in a MWI context is much cleaner than a full Copenhagen-style collapse operation.

Re: How the Many-Worlds Theory of Hugh Everett Split the Universe

#25

Post by platz »

lisper wrote: post #23
lmm wrote: post #20

Earlier quoted context omitted.

MWI is not incompatible with postulating the Born rule if you want to. It just doesn't elevate it to an axiom of the theory. It's like doing constructive mathematics: you're not denying the law of excluded middle, you can postulate it and it will have the usual consequences, but the core theory doesn't rely on it, and it's possible to hope for a more elegant alternative.

Yes, you can just add the Born rule as an additional axiom, but that undermines the whole point of adopting the MWI in the first place, which is to remain mathematically "clean" with no ad-hoc assumptions.

He didn't say to re-add it as an axiom. He's pointing out that the "born rule" (or something that gives you probabilities in the way that you need to agree with experiment) can potentially "emerge" i.e. be recovered (if they can find the right proof for it), without having had to assume that up front.

It's like when GR can "recover" F=MA, despite not having assumed F=MA that as an axiom.

Re: How the Many-Worlds Theory of Hugh Everett Split the Universe

#26

Post by lisper »

platz wrote: post #25
lisper wrote: post #23

Earlier quoted context omitted.

Yes, you can just add the Born rule as an additional axiom, but that undermines the whole point of adopting the MWI in the first place, which is to remain mathematically "clean" with no ad-hoc assumptions.

He didn't say to re-add it as an axiom . He's pointing out that the "born rule" (or something that gives you probabilities in the way that you need to agree with experiment) can potentially "emerge" i.e. be recovered (if they can find the right proof for it), without having had to assume that up front. It's like when GR can "recover" F=MA, despite not having assumed F=MA that as an axiom.

> He didn't say to re-add it as an axiom

Yes, he did:

> MWI is not incompatible with postulating the Born rule if you want to

"Postulate" (as a noun) and "axiom" are synonyms.

Re: How the Many-Worlds Theory of Hugh Everett Split the Universe

#27

Post by yters »

fallingfrog wrote: post #8

You can do a really simple thought experiment that provides a persuasive argument in favor of the many worlds theory. Or at least, it shows that wave function collapse is relative to an observer, not universal everywhere. Start with Schroedingers cat: the cat is in a box, it’s in a state of quantum superposition. It’s 50/50 alive or dead. Now a researcher opens the box: the cat is found to be either alive, or dead, a…

The problem with many worlds is why do I think I'm in a particular timeline? If many worlds is correct, there is no "I", there are many rapidly branching "I"s, which intuitively doesn't make sense. Of course, each "I" will have the perception of being the sole "I", but the overall view that there is no singular "I" is very counter to my self conception. I prefer to preserve intuitions over conjectures, so I count that as a strike against the many worlds interpretation.

So, it seems like both the Copenhagen and the many worlds interpretations of quantum physics are wrong, given a preference for non arbitrary reference point and preserving intuitions. Is there a reason that those two must be the only possible interpretations?

Re: How the Many-Worlds Theory of Hugh Everett Split the Universe

#28

Post by lisper »

lmm wrote: post #24
lisper wrote: post #23

Earlier quoted context omitted.

Yes, you can just add the Born rule as an additional axiom, but that undermines the whole point of adopting the MWI in the first place, which is to remain mathematically "clean" with no ad-hoc assumptions.

Yes and no. I'd argue that the Born rule as a rule for subjective probabilities in a MWI context is much cleaner than a full Copenhagen-style collapse operation.

You are, of course, free to argue that. But most advocates of the MWI will disagree with you. That's why they put so much effort into trying to derive the Born rule.

Re: How the Many-Worlds Theory of Hugh Everett Split the Universe

#29

Post by sousavdouglas »

yters wrote: post #27
fallingfrog wrote: post #8

You can do a really simple thought experiment that provides a persuasive argument in favor of the many worlds theory. Or at least, it shows that wave function collapse is relative to an observer, not universal everywhere. Start with Schroedingers cat: the cat is in a box, it’s in a state of quantum superposition. It’s 50/50 alive or dead. Now a researcher opens the box: the cat is found to be either alive, or dead, a…

The problem with many worlds is why do I think I'm in a particular timeline? If many worlds is correct, there is no "I", there are many rapidly branching "I"s, which intuitively doesn't make sense. Of course, each "I" will have the perception of being the sole "I", but the overall view that there is no singular "I" is very counter to my self conception. I prefer to preserve intuitions over conjectures, so I count tha…

YES
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