5 ms·

> The main difference is that the MWI has trouble explaining the Born rule. To re-phrase, the claim in that article is that once MWI has done away with the Bor

by platz 7y ago

> The main difference is that the MWI has trouble explaining the Born rule. To re-phrase, the claim in that article is that once MWI has done away with the Born rule, it has to deal with how the probabilities that we find in experiment are calculated under MWI. .. Which is not obvious at first glance, because MWI seems to suggest everything happens with probability = 1. Carroll acknowledges it is one of the challenges against MWI that needs to be answered. Carroll offers "self-location uncertainty" as a way to recover the probabilities predicted by the Born Rule despite the determinism of the Schrodinger Equation > But even if both people know the wave function of the universe, there is now something they don’t know: which branch of the wave function they are on. There will inevitably be a period of time after branching occurs but before the observers find out what outcome was obtained on their branch. They don’t know where they are in the wave function. That’s self-locating uncertainty, as first emphasized in the quantum context by the physicist Lev Vaidman. (https://news.ycombinator.com/item?id=20927410 https://news.ycombinator.com/item?id=20927410) * edit - OP's post was edited but i'm leaving this post as-is. > MWI insists that experiments have multiple outcomes in point of metaphysical fact. That doesn't seem right. under MWI there is only one Wafefunction and one big quantum state. There are not additional 'worlds'

lisper 7y ago
> OP's post was edited For the record, the original just said (as quoted in the above response) "The main difference is that the MWI has trouble explaining the Born rule." Upon reflection I decided that wasn't really the main difference, that the main difference is the difference in ontology. But the fact that the MWI has to recover the Born rule from the linear dynamics is a major consequence of this difference in ontology. The jury is still out about whether or not self-location uncertainty actually allows the Born rule to be recovered without begging the question. If it works, it would be a major breakthrough. Personally, I'll give long odds against. [UPDATE]: > There are not additional 'worlds' Um, what do you think that the "MW" in "MWI" stands for?
- platz 7y ago
  > the main difference is the difference in ontology Sure, I'm not sure how much Science has to say about ontology but I'm interested in the outcome.
- jbay808 7y ago
  > Um, what do you think that the "MW" in "MWI" stands for? Ok yes, it is named that, but what the theory postulates is really just that "when Schrodinger opens the box to check on his cat, he himself is in a superposition just like the cat was -- and what it feels like to be in a superposition is that you don't notice you're in a superposition, because your superposed states each only observe one cat."
  - lisper 7y ago
    > your superposed states each only observe one cat Again, I have to ask: what do you think "many worlds" means? Because what you've just described is exactly what the advocates of the MWI describe when they talk about "many worlds", which they absolutely do. The MWI literature is festooned with references to "copies" or "versions" of yourself, and "the branching structure of the multiverse".
    - lmm 7y ago
      > The MWI literature is festooned with references to "copies" or "versions" of yourself, and "the branching structure of the multiverse". Many MWI advocates will describe that physical wavefunction in those terms, but that's a metaphor/model/aid to understanding, not a "point of metaphysical fact". The only thing that MWI demands we take as metaphysically real is the wavefunction. Given a wavefunction like 1/sqrt2(|experimenter who observed a live cat> + |experimenter who observed a dead cat>) many people find it convenient to think of this as "two Everett branches with ...", in the same way that people who hear a particular pattern of sound might find it convenient to think of it as a chord of two or three notes. But if you prefer to think of it as simply a unitary (in the everyday sense) wavefunction that's fine, you'll make exactly the same experimental predictions.
      - lisper 7y ago
        Here's a quote from David Deutsch's "The Fabric of Reality": "When I introduced tangible and shadow photons I apparently distinguished them by saying that we can see the former, but not the latter. But who are ‘we’? While I was writing that, hosts of shadow Davids were writing it too. They too drew a distinction between tangible and shadow photons; but the photons they called ‘shadow’ include the ones I called ‘tangible’, and the photons they called ‘tangible’ are among those I called ‘shadow’. Not only do none of the copies of an object have any privileged position in the explanation of shadows that I have just outlined, neither do they have a privileged position in the full mathematical explanation provided by quantum theory. I may feel subjectively that I am distinguished among the copies as the ‘tangible’ one, because I can directly perceive myself and not the others, but I must come to terms with the fact that all the others feel the same about themselves. Many of those Davids are at this moment writing these very words. Some are putting it better. Others have gone for a cup of tea." And his summary: "the whole of physical reality, the multiverse, contains vast numbers of parallel universes" So no, Deutsch, who is arguably the leading advocate of MWI, does not consider parallel universes to be a "metaphor/model/aid to understanding". He insists that they are real. He even defends this position at extraordinary length in chapter 10 of TFOR.
- ncallaway 7y ago
  The label "Many Worlds Interpretation" is a popular label for the theory, but it's not a particularly accurate one. The original paper by Hugh Everett was titled '"Relative State" Formulation of Quantum Mechanics'. The underlying principle of Many Worlds isn't actually that there are many worlds. Is that there is a singular wave function, which is the true reality. The things we refer to as "worlds" are massively-complicated entanglements and superpositions within that wave function, of which we—for some reason—can only observe one position of that superposition.
  - lisper 7y ago
    Everything you say is true. Nonetheless, if you read papers written by self-identified advocates of Everett, they invariably refer to it as "many-worlds" and they talk about "the branching structure of the multiverse" and "copies" or "versions" of yourself. So regardless of what you or I think Everett meant, the present-day advocates of his theory are clearly trying to advance the idea that there are, in point of metaphysical fact, many worlds.
    - platz 7y ago
      If you agree on that math/science then this point you're adamant about whether it is or is not a "world" reduces to a semantics/ontology/philosophy question, which we're not going to get further clarity on in a thread about trying to gain a proper or better understanding as laypeople of the scientific theories, unless you want to advance the conversation to the understanding of those scientific theories into a semantic/ontological/philosophic realm.
    - ncallaway 7y ago
      Sure, but I would think every one of those advocates would also agree with what I wrote. That the "world" described by many worlds is a convenient short-hand for a single position in a massively entangled system of particles in a complex-superposition. It's the "Many Worlds" is common moniker, and the rhetoric does use the concept of worlds all the time, but whenever you get down to the specifics of the theory there really aren't many worlds. I think it's unfair to hold the shorthand rhetoric against people when they attempt to get to that more precise level. It would be like using the plain english definition of "observation" against someone trying to provide a more rigorous definition of what an "observation" is under the Copenhagen interpretation. Ultimatley, this discussion all stems from the original statement: "MWI insists that experiments have multiple outcomes in point of metaphysical fact." It's a fairly moot point at this point since that statement was removed.
tim333 7y ago
"self-location uncertainty" seems to still assume what is basically the Born rule: >MWI probability postulate: The probability of self-location in a world with a given set of outcomes is the absolute square of that world’s amplitude. (http://philsci-archive.pitt.edu/14389/1/defence-location-uncertainty.pdf http://philsci-archive.pitt.edu/14389/1/defence-location-unc...) It just applies the absolute square of the amplitudes to the chance of being in a given world rather than the chance of an event. The thing that needs explaining is why either probability is given by the square of the amplitudes.
- platz 7y ago
  Fair enough - I'm not a physicist or read papers on physics. I'm just trying to re-tell the best version of the theories as I've understood them by steel-manning arguments laid out (by scientists that have some media exposure), rather than try to straw-man each theory with prima-facie criticisms that have already been answered. I know MWI has significant gaps, this appears to be one of the biggest. thank you for citing that paper directly.
  - tim333 7y ago
    Ta. As far as I can tell a lack of an explanation for the Born rule is a feature of all quantum interpretations, not just many worlds. It's pretty much the central mystery of quantum mechanics.

by platz 7y ago

lisper 7y ago

> OP's post was edited For the record, the original just said (as quoted in the above response) "The main difference is that the MWI has trouble explaining the Born rule." Upon reflection I decided that wasn't really the main difference, that the main difference is the difference in ontology. But the fact that the MWI has to recover the Born rule from the linear dynamics is a major consequence of this difference in ontology. The jury is still out about whether or not self-location uncertainty actually allows the Born rule to be recovered without begging the question. If it works, it would be a major breakthrough. Personally, I'll give long odds against. [UPDATE]: > There are not additional 'worlds' Um, what do you think that the "MW" in "MWI" stands for?

platz 7y ago
> the main difference is the difference in ontology Sure, I'm not sure how much Science has to say about ontology but I'm interested in the outcome.
jbay808 7y ago
> Um, what do you think that the "MW" in "MWI" stands for? Ok yes, it is named that, but what the theory postulates is really just that "when Schrodinger opens the box to check on his cat, he himself is in a superposition just like the cat was -- and what it feels like to be in a superposition is that you don't notice you're in a superposition, because your superposed states each only observe one cat."
- lisper 7y ago
  > your superposed states each only observe one cat Again, I have to ask: what do you think "many worlds" means? Because what you've just described is exactly what the advocates of the MWI describe when they talk about "many worlds", which they absolutely do. The MWI literature is festooned with references to "copies" or "versions" of yourself, and "the branching structure of the multiverse".
  - lmm 7y ago
    > The MWI literature is festooned with references to "copies" or "versions" of yourself, and "the branching structure of the multiverse". Many MWI advocates will describe that physical wavefunction in those terms, but that's a metaphor/model/aid to understanding, not a "point of metaphysical fact". The only thing that MWI demands we take as metaphysically real is the wavefunction. Given a wavefunction like 1/sqrt2(|experimenter who observed a live cat> + |experimenter who observed a dead cat>) many people find it convenient to think of this as "two Everett branches with ...", in the same way that people who hear a particular pattern of sound might find it convenient to think of it as a chord of two or three notes. But if you prefer to think of it as simply a unitary (in the everyday sense) wavefunction that's fine, you'll make exactly the same experimental predictions.
    - lisper 7y ago
      Here's a quote from David Deutsch's "The Fabric of Reality": "When I introduced tangible and shadow photons I apparently distinguished them by saying that we can see the former, but not the latter. But who are ‘we’? While I was writing that, hosts of shadow Davids were writing it too. They too drew a distinction between tangible and shadow photons; but the photons they called ‘shadow’ include the ones I called ‘tangible’, and the photons they called ‘tangible’ are among those I called ‘shadow’. Not only do none of the copies of an object have any privileged position in the explanation of shadows that I have just outlined, neither do they have a privileged position in the full mathematical explanation provided by quantum theory. I may feel subjectively that I am distinguished among the copies as the ‘tangible’ one, because I can directly perceive myself and not the others, but I must come to terms with the fact that all the others feel the same about themselves. Many of those Davids are at this moment writing these very words. Some are putting it better. Others have gone for a cup of tea." And his summary: "the whole of physical reality, the multiverse, contains vast numbers of parallel universes" So no, Deutsch, who is arguably the leading advocate of MWI, does not consider parallel universes to be a "metaphor/model/aid to understanding". He insists that they are real. He even defends this position at extraordinary length in chapter 10 of TFOR.
ncallaway 7y ago
The label "Many Worlds Interpretation" is a popular label for the theory, but it's not a particularly accurate one. The original paper by Hugh Everett was titled '"Relative State" Formulation of Quantum Mechanics'. The underlying principle of Many Worlds isn't actually that there are many worlds. Is that there is a singular wave function, which is the true reality. The things we refer to as "worlds" are massively-complicated entanglements and superpositions within that wave function, of which we—for some reason—can only observe one position of that superposition.
- lisper 7y ago
  Everything you say is true. Nonetheless, if you read papers written by self-identified advocates of Everett, they invariably refer to it as "many-worlds" and they talk about "the branching structure of the multiverse" and "copies" or "versions" of yourself. So regardless of what you or I think Everett meant, the present-day advocates of his theory are clearly trying to advance the idea that there are, in point of metaphysical fact, many worlds.
  - platz 7y ago
    If you agree on that math/science then this point you're adamant about whether it is or is not a "world" reduces to a semantics/ontology/philosophy question, which we're not going to get further clarity on in a thread about trying to gain a proper or better understanding as laypeople of the scientific theories, unless you want to advance the conversation to the understanding of those scientific theories into a semantic/ontological/philosophic realm.
  - ncallaway 7y ago
    Sure, but I would think every one of those advocates would also agree with what I wrote. That the "world" described by many worlds is a convenient short-hand for a single position in a massively entangled system of particles in a complex-superposition. It's the "Many Worlds" is common moniker, and the rhetoric does use the concept of worlds all the time, but whenever you get down to the specifics of the theory there really aren't many worlds. I think it's unfair to hold the shorthand rhetoric against people when they attempt to get to that more precise level. It would be like using the plain english definition of "observation" against someone trying to provide a more rigorous definition of what an "observation" is under the Copenhagen interpretation. Ultimatley, this discussion all stems from the original statement: "MWI insists that experiments have multiple outcomes in point of metaphysical fact." It's a fairly moot point at this point since that statement was removed.

tim333 7y ago

"self-location uncertainty" seems to still assume what is basically the Born rule: >MWI probability postulate: The probability of self-location in a world with a given set of outcomes is the absolute square of that world’s amplitude. (http://philsci-archive.pitt.edu/14389/1/defence-location-uncertainty.pdf http://philsci-archive.pitt.edu/14389/1/defence-location-unc...) It just applies the absolute square of the amplitudes to the chance of being in a given world rather than the chance of an event. The thing that needs explaining is why either probability is given by the square of the amplitudes.

platz 7y ago
Fair enough - I'm not a physicist or read papers on physics. I'm just trying to re-tell the best version of the theories as I've understood them by steel-manning arguments laid out (by scientists that have some media exposure), rather than try to straw-man each theory with prima-facie criticisms that have already been answered. I know MWI has significant gaps, this appears to be one of the biggest. thank you for citing that paper directly.
- tim333 7y ago
  Ta. As far as I can tell a lack of an explanation for the Born rule is a feature of all quantum interpretations, not just many worlds. It's pretty much the central mystery of quantum mechanics.