4 ms·

I won't defend popsci presentations, but formally MWI is pretty precisely defined. It's defined by assuming the postulates of quantum mechanics without includin

I won't defend popsci presentations, but formally MWI is pretty precisely defined. It's defined by assuming the postulates of quantum mechanics without including the Born rule. States are unit vectors, operations are unitary matrices, systems combine using the tensor product. That's many worlds. It's sort of like constructivist mathematics in that it involves dropping an extremely useful axiom, and then rederives basically all the same results in a more roundabout way.

kgwgk 4y ago
If the "precise definition" of MWI doesn't go beyond "QM mathematical formalism when you get rid of its link with the physical world" what's the use of it? https://www.quantamagazine.org/why-the-many-worlds-interpretation-of-quantum-mechanics-has-many-problems-20181018/ https://www.quantamagazine.org/why-the-many-worlds-interpret... "Attempts to explain the appearance of probability within the MWI come down to saying that quantum probabilities are just what quantum mechanics looks like when consciousness is restricted to only one world. [...] What the MWI really denies is the existence of facts at all. It replaces them with an experience of pseudo-facts (we think that this happened, even though that happened too). In so doing, it eliminates any coherent notion of what we can experience, or have experienced, or are experiencing right now. We might reasonably wonder if there is any value — any meaning — in what remains, and whether the sacrifice has been worth it."
- Strilanc 4y ago
  Why are you assuming that measurement is the link between quantum mechanics and the real world? Quantum mechanics doesn't need to be linked to the real world, it is the real world. That quote is simply wrong when it says that MWI "restricts consciousness to one world". As a simple matter of calculation, you can work out what MWI predicts a complex agent will report as its experience. Here for complex agent I want you to picture a computer program recording events and accumulating statistics, not a person, just because it makes the thinking clearer. Anyways, the prediction is that the recordings will be consistent with a classical type view, for lack of a better word, as opposed to a superposition of experiences. Even if the computer program was in fact run in superposition and interacted with superposed objects. But this is not surprising, because we already know that all the interpretations of quantum mechanics give the same predictions. So of course many worlds is not going to disagree with collapse type theories on what people say they experience. Because it is mathematically equivalent to the others. Observationally indistinguishable.
  - kgwgk 4y ago
    I didn't even say "real world", I said "physical world". Physics, unlike mathematics, is an experimental science. Edit: where does the MWI define “complex agent” and “experience”, by the way? I thought that MWI was precisely defined by assuming the postulates of quantum mechanics without including the Born rule, but it seems that there may be more to it!
  - q-big 4y ago
    > Because it is mathematically equivalent to the others. Observationally indistinguishable. By Occam's Razor, if there exist multiple theories that are indistinguishable, we should take the one that has minimal assumptions (i.e. no assumption of the existence of some "multiverse" like in the many worlds interpretation).
  - n4r9 4y ago
    > you can work out what MWI predicts a complex agent will report as its experience There's kind of an ontological trick at this point. Using decoherence, self-locating uncertainty, and one or more assumptions about rational decision-making, you can derive what rational credence you might apportion to each of the agent's possible experiences. I feel like this is different from actually predicting the agent's experience.
    - kgwgk 4y ago
      What’s an agent? What’s an experience? Those questions do not seem easier to answer than “what’s a measurement”.
      - n4r9 4y ago
        Fair point. All you can really do, without making some quite strong ontological assumptions, is derive which rational credences to assign to the outcomes of one's own future interactions with the world. Which suddenly sounds a lot like QBism.

kgwgk 4y ago

If the "precise definition" of MWI doesn't go beyond "QM mathematical formalism when you get rid of its link with the physical world" what's the use of it? https://www.quantamagazine.org/why-the-many-worlds-interpretation-of-quantum-mechanics-has-many-problems-20181018/ https://www.quantamagazine.org/why-the-many-worlds-interpret... "Attempts to explain the appearance of probability within the MWI come down to saying that quantum probabilities are just what quantum mechanics looks like when consciousness is restricted to only one world. [...] What the MWI really denies is the existence of facts at all. It replaces them with an experience of pseudo-facts (we think that this happened, even though that happened too). In so doing, it eliminates any coherent notion of what we can experience, or have experienced, or are experiencing right now. We might reasonably wonder if there is any value — any meaning — in what remains, and whether the sacrifice has been worth it."

Strilanc 4y ago
Why are you assuming that measurement is the link between quantum mechanics and the real world? Quantum mechanics doesn't need to be linked to the real world, it is the real world. That quote is simply wrong when it says that MWI "restricts consciousness to one world". As a simple matter of calculation, you can work out what MWI predicts a complex agent will report as its experience. Here for complex agent I want you to picture a computer program recording events and accumulating statistics, not a person, just because it makes the thinking clearer. Anyways, the prediction is that the recordings will be consistent with a classical type view, for lack of a better word, as opposed to a superposition of experiences. Even if the computer program was in fact run in superposition and interacted with superposed objects. But this is not surprising, because we already know that all the interpretations of quantum mechanics give the same predictions. So of course many worlds is not going to disagree with collapse type theories on what people say they experience. Because it is mathematically equivalent to the others. Observationally indistinguishable.
- kgwgk 4y ago
  I didn't even say "real world", I said "physical world". Physics, unlike mathematics, is an experimental science. Edit: where does the MWI define “complex agent” and “experience”, by the way? I thought that MWI was precisely defined by assuming the postulates of quantum mechanics without including the Born rule, but it seems that there may be more to it!
- q-big 4y ago
  > Because it is mathematically equivalent to the others. Observationally indistinguishable. By Occam's Razor, if there exist multiple theories that are indistinguishable, we should take the one that has minimal assumptions (i.e. no assumption of the existence of some "multiverse" like in the many worlds interpretation).
- n4r9 4y ago
  > you can work out what MWI predicts a complex agent will report as its experience There's kind of an ontological trick at this point. Using decoherence, self-locating uncertainty, and one or more assumptions about rational decision-making, you can derive what rational credence you might apportion to each of the agent's possible experiences. I feel like this is different from actually predicting the agent's experience.
  - kgwgk 4y ago
    What’s an agent? What’s an experience? Those questions do not seem easier to answer than “what’s a measurement”.
    - n4r9 4y ago
      Fair point. All you can really do, without making some quite strong ontological assumptions, is derive which rational credences to assign to the outcomes of one's own future interactions with the world. Which suddenly sounds a lot like QBism.