6 ms·

> 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

> 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.
    - lmm 7y ago
      Deutsch may believe that. (Heck, I believe it). It's a natural interpretation of the MWI wavefunction. But it is an interpretation, a layer on top of the physical claims, a model - not a mandatory part of MWI. Deutsch may interpret a given wavefunction as describing a particular ensemble of 'tangible' and 'shadow' objects, but someone who interprets that same wavefunction a different way (but agrees on the same wavefunction, and expects it to evolve according to the same laws of quantum mechanics) will still generate the same experimental predictions and, more to the point, still be doing MWI.
      - TheOtherHobbes 7y ago
        That makes MWI a "no true parallel Scotsman" interpretation. Either the other versions of reality are tangible, or they're not. If they're just abstractions, you have't solved the problem - you've taken a long way around a circular argument that starts with the wavefunction and ends with it doing something that results in a measurement, maybe. Unfortunately explaining how that happens is the problem you're trying to solve. It's not an answer to the problem. If they are real, there are all kinds of other issues, the Born Rule being the most obvious.
        lmm 7y ago
        > Either the other versions of reality are tangible, or they're not. If they're just abstractions, you have't solved the problem - you've taken a long way around a circular argument that starts with the wavefunction and ends with it doing something that results in a measurement, maybe. The wavefunction is physically real. Whatever you interpret it as is your business. We've solved a real problem: we can explain the evolution of the wavefunction and the results of experiments without needing some weird collapse/decoherence concept that breaks all the usual rules. The Born Rule is still something that remains to be explained, agreed, but it's a much smaller something than the full Copenhagen style collapse.
    - jbay808 7y ago
      I think Deutsch is doing a very good job of explaining exactly the concept I'm trying to explain. But you still have to peel back the words to think about what kind of mechanism they are describing, which Deutsch is trying to communicate. You can't just complain that he says "reality contains parallel universes" without accepting that he's taken the time to map "parallel universes" to a well-defined concept.
- jbay808 7y ago
  There seems to be some confusion here, based around the usage of words. You seem annoyed by the terminology of words like "worlds" or "multiverse", but are you also thinking about what a MWI advocate is referring to by the usage of those words? They are shorthand for "the observable wave function" and "the global wave function". There being "copies" of Schrodinger observing his cat is the most intuitive and expressive way to summarize Schrodinger being in a linear superposition of two states in a (cat alive, cat dead) basis. It's not any different from how a Copenhagenist would treat a photon passing through a polarizating beamsplitter as being in a superposition of having passed through and having been reflected; if the photon then goes and interacts with other things, they would keep track of what would have happened in each "branch" of the superposition. If you have an issue with those, why don't you have an issue with the idea of superposition itself? It's exactly the same concept. (UPDATE) In particular, when MWI people say "multiverse", it's not a sleight of hand where we are being deceptive when we actually mean "observable and unobservable components of the wave function". The term "multiverse" had no prior meaning in physics; MWI is defining it to mean the global wave function, using that word to draw attention to the fact that it has unobservable components. These words are being given rigorous definitions that align with their intuitive meaning. You seem to be arguing against that practice? Should I complain that when a Copenhagenist says "collapse", nothing is actually falling down and so it's misleading?
  - lisper 7y ago
    No it isn't. Copenhagenists insist that the wave function "collapses" upon "measurement" and so measurements only have one outcome in point of metaphyisical fact. Many-worlders insist that the wave function does not collapse, and hence measurements have many outcomes in point of metaphyiscal fact. You may consider this a distinction without a difference, but the fact of the matter is that people do argue about this. A lot.
    - platz 7y ago
      Your usage of "many outcomes" is what may be causing contention/confusion for those looking for answers in what is described by the mathematical equations, and scientific theories. If you want to justify "many outcomes" on metaphysical grounds, that is not a scientific conversation. Also "metaphysical fact" is a questionable term.

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.
  - lmm 7y ago
    Deutsch may believe that. (Heck, I believe it). It's a natural interpretation of the MWI wavefunction. But it is an interpretation, a layer on top of the physical claims, a model - not a mandatory part of MWI. Deutsch may interpret a given wavefunction as describing a particular ensemble of 'tangible' and 'shadow' objects, but someone who interprets that same wavefunction a different way (but agrees on the same wavefunction, and expects it to evolve according to the same laws of quantum mechanics) will still generate the same experimental predictions and, more to the point, still be doing MWI.
    - TheOtherHobbes 7y ago
      That makes MWI a "no true parallel Scotsman" interpretation. Either the other versions of reality are tangible, or they're not. If they're just abstractions, you have't solved the problem - you've taken a long way around a circular argument that starts with the wavefunction and ends with it doing something that results in a measurement, maybe. Unfortunately explaining how that happens is the problem you're trying to solve. It's not an answer to the problem. If they are real, there are all kinds of other issues, the Born Rule being the most obvious.
      - lmm 7y ago
        > Either the other versions of reality are tangible, or they're not. If they're just abstractions, you have't solved the problem - you've taken a long way around a circular argument that starts with the wavefunction and ends with it doing something that results in a measurement, maybe. The wavefunction is physically real. Whatever you interpret it as is your business. We've solved a real problem: we can explain the evolution of the wavefunction and the results of experiments without needing some weird collapse/decoherence concept that breaks all the usual rules. The Born Rule is still something that remains to be explained, agreed, but it's a much smaller something than the full Copenhagen style collapse.
  - jbay808 7y ago
    I think Deutsch is doing a very good job of explaining exactly the concept I'm trying to explain. But you still have to peel back the words to think about what kind of mechanism they are describing, which Deutsch is trying to communicate. You can't just complain that he says "reality contains parallel universes" without accepting that he's taken the time to map "parallel universes" to a well-defined concept.
jbay808 7y ago
There seems to be some confusion here, based around the usage of words. You seem annoyed by the terminology of words like "worlds" or "multiverse", but are you also thinking about what a MWI advocate is referring to by the usage of those words? They are shorthand for "the observable wave function" and "the global wave function". There being "copies" of Schrodinger observing his cat is the most intuitive and expressive way to summarize Schrodinger being in a linear superposition of two states in a (cat alive, cat dead) basis. It's not any different from how a Copenhagenist would treat a photon passing through a polarizating beamsplitter as being in a superposition of having passed through and having been reflected; if the photon then goes and interacts with other things, they would keep track of what would have happened in each "branch" of the superposition. If you have an issue with those, why don't you have an issue with the idea of superposition itself? It's exactly the same concept. (UPDATE) In particular, when MWI people say "multiverse", it's not a sleight of hand where we are being deceptive when we actually mean "observable and unobservable components of the wave function". The term "multiverse" had no prior meaning in physics; MWI is defining it to mean the global wave function, using that word to draw attention to the fact that it has unobservable components. These words are being given rigorous definitions that align with their intuitive meaning. You seem to be arguing against that practice? Should I complain that when a Copenhagenist says "collapse", nothing is actually falling down and so it's misleading?
- lisper 7y ago
  No it isn't. Copenhagenists insist that the wave function "collapses" upon "measurement" and so measurements only have one outcome in point of metaphyisical fact. Many-worlders insist that the wave function does not collapse, and hence measurements have many outcomes in point of metaphyiscal fact. You may consider this a distinction without a difference, but the fact of the matter is that people do argue about this. A lot.
  - platz 7y ago
    Your usage of "many outcomes" is what may be causing contention/confusion for those looking for answers in what is described by the mathematical equations, and scientific theories. If you want to justify "many outcomes" on metaphysical grounds, that is not a scientific conversation. Also "metaphysical fact" is a questionable term.