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FYI, I am the author of the blog post. > This undercuts the critics' argument. No, it doesn't, for all of the reasons given in the blog post and the subsequen

by lisper 4y ago

FYI, I am the author of the blog post. > This undercuts the critics' argument. No, it doesn't, for all of the reasons given in the blog post and the subsequent discussion. The Born rule is an observable fact of nature, and you cannot derive it from the Schroedinger equation, Duetsch and Wallace's claims to the contrary notwithstanding.

boole1854 4y ago
Maybe you can help me understand your argument better. If the Schrodinger equation describes a density of universes, doesn't that undercut the argument in the blog post? Edited to add my understanding: if the cardinality of the multiverse is uncountable, one has to talk about densities of branches. In that scheme, the problems which branch counting introduce do not arise.
- lisper 4y ago
  > If the Schrodinger equation describes a density of universes, It doesn't (see below) but even if it did... > doesn't that undercut the argument in the blog post? No. It's really very simple: the SE is linear. The BR is not. You can't derive a non-linear result from a linear equation. The only thing that is even a tiny bit complicated about this is figuring out where the Deutsch-Wallace argument fails, because Deutsch and Wallace are not idiots and they hid their questionable assumption very well. So... why does the SE not describe a "density of universes"? It's because the SE does not describe universes at all! Deutsch and Wallace specifically acknowledge this, which makes their argument all that much more untenable. The SE describes the behavior of a function called "the wave function". The wave function is not a description of anything physical. The domain of the wave function is not physical space, it is configuration space. This is the reason entanglement seems weird to us, because we live in physical space and the wave function does not. In order to get anything physical out of the wave function -- particles, universes, anything resembling our classical reality -- you have to add some additional assumption, and any additional assumption that you add will be in some sense isomorphic to the Born rule. There is no way around this. Trying to derive the BR from the SE is like trying to prove Euclid's fifth postulate.
  - hither_shores 4y ago
    > The wave function is not a description of anything physical. The domain of the wave function is not physical space, it is configuration space. This is the reason entanglement seems weird to us, because we live in physical space and the wave function does not. This is circular: you're assuming that realism about the wave function is incorrect to argue against the (tragically misnamed) many-worlds interpretation, but the only substantive claim the MWI makes is that realism about the wave function is true.
    - lisper 4y ago
      > you're assuming that realism about the wave function is incorrect No, I'm not assuming it. I simply observe that the SR by itself does not describe the outcomes of experiments. And I'm not even talking here about quantum experiments. The SR cannot by itself even account for the fact that we live in a three-dimensional space or that there is an arrow of time. And it certainly cannot account for the Born rule, which is also an experimentally observed fact. > the only substantive claim the MWI makes is that realism about the wave function is true. Yes, I know. The problem with this is that it is violently at odds with observations that every human makes every moment of their lives, and it does not account for the Born rule. Other than that there's no problem with it.
      - hither_shores 4y ago
        > I simply observe that the SR by itself does not describe the outcomes of experiments. No formalism describes the outcome of experiments by itself. There always needs to be an interpretation attached, and our choice of interpretation is always underdetermined by observation. > The problem with this is that it is violently at odds with observations that every human makes every moment of their lives Like all other interpretations of all other physical theories, MWI isn't and can't be at odds with our observations alone, because our observations alone aren't enough to imply any particular relationship between observations in general. And like all other interpretations, it is and must be at odds with competing interpretations, and in particular with the folk-physics model we're naturally inclined to use. But this means very little, because folk-physics is wrong, and this far from the paleolithic savanna, it's wrong in ways that matter. Intuition is evidence, but it's not particularly strong evidence, and it's certainly not proof. > and it does not account for the Born rule. Sure, it still needs a separate account of subjective probability. But so does everything else: it's just a little harder to notice in the classical regime, since the relevant probabilities are always either 1 or 0.

by lisper 4y ago

boole1854 4y ago

Maybe you can help me understand your argument better. If the Schrodinger equation describes a density of universes, doesn't that undercut the argument in the blog post? Edited to add my understanding: if the cardinality of the multiverse is uncountable, one has to talk about densities of branches. In that scheme, the problems which branch counting introduce do not arise.

lisper 4y ago
> If the Schrodinger equation describes a density of universes, It doesn't (see below) but even if it did... > doesn't that undercut the argument in the blog post? No. It's really very simple: the SE is linear. The BR is not. You can't derive a non-linear result from a linear equation. The only thing that is even a tiny bit complicated about this is figuring out where the Deutsch-Wallace argument fails, because Deutsch and Wallace are not idiots and they hid their questionable assumption very well. So... why does the SE not describe a "density of universes"? It's because the SE does not describe universes at all! Deutsch and Wallace specifically acknowledge this, which makes their argument all that much more untenable. The SE describes the behavior of a function called "the wave function". The wave function is not a description of anything physical. The domain of the wave function is not physical space, it is configuration space. This is the reason entanglement seems weird to us, because we live in physical space and the wave function does not. In order to get anything physical out of the wave function -- particles, universes, anything resembling our classical reality -- you have to add some additional assumption, and any additional assumption that you add will be in some sense isomorphic to the Born rule. There is no way around this. Trying to derive the BR from the SE is like trying to prove Euclid's fifth postulate.
- hither_shores 4y ago
  > The wave function is not a description of anything physical. The domain of the wave function is not physical space, it is configuration space. This is the reason entanglement seems weird to us, because we live in physical space and the wave function does not. This is circular: you're assuming that realism about the wave function is incorrect to argue against the (tragically misnamed) many-worlds interpretation, but the only substantive claim the MWI makes is that realism about the wave function is true.
  - lisper 4y ago
    > you're assuming that realism about the wave function is incorrect No, I'm not assuming it. I simply observe that the SR by itself does not describe the outcomes of experiments. And I'm not even talking here about quantum experiments. The SR cannot by itself even account for the fact that we live in a three-dimensional space or that there is an arrow of time. And it certainly cannot account for the Born rule, which is also an experimentally observed fact. > the only substantive claim the MWI makes is that realism about the wave function is true. Yes, I know. The problem with this is that it is violently at odds with observations that every human makes every moment of their lives, and it does not account for the Born rule. Other than that there's no problem with it.
    - hither_shores 4y ago
      > I simply observe that the SR by itself does not describe the outcomes of experiments. No formalism describes the outcome of experiments by itself. There always needs to be an interpretation attached, and our choice of interpretation is always underdetermined by observation. > The problem with this is that it is violently at odds with observations that every human makes every moment of their lives Like all other interpretations of all other physical theories, MWI isn't and can't be at odds with our observations alone, because our observations alone aren't enough to imply any particular relationship between observations in general. And like all other interpretations, it is and must be at odds with competing interpretations, and in particular with the folk-physics model we're naturally inclined to use. But this means very little, because folk-physics is wrong, and this far from the paleolithic savanna, it's wrong in ways that matter. Intuition is evidence, but it's not particularly strong evidence, and it's certainly not proof. > and it does not account for the Born rule. Sure, it still needs a separate account of subjective probability. But so does everything else: it's just a little harder to notice in the classical regime, since the relevant probabilities are always either 1 or 0.