3 ms·

Assuming many worlds, and many here means: enormous amounts, far exceeding the number of particles in the universe, is everything but parsimonious. There happen

by tgv 3y ago

Assuming many worlds, and many here means: enormous amounts, far exceeding the number of particles in the universe, is everything but parsimonious. There happens to be a model that fits some data, but that's it. It's a grotesque assumption to avoid a conflict in a man-made theory. It's a funny thought, but no more than that. There's also nothing special about observing. Our consciousness isn't super-natural, so the idea is in desperate need of some other underpinning. And probabilities: if this is one of many, many worlds, the distribution of events as we can observe them is heavily skewed. The next observations should follow a radically different pattern, unless you also assume that each split influences the probabilities of future events.

consilient 3y ago
> Assuming many worlds, and many here means: enormous amounts, far exceeding the number of particles in the universe, is everything but parsimonious. "Many worlds" is a misnomer. MWI is just wavefunction realism + unitary evolution. There's only one world, and really only one dynamical object: the wavefunction. It evolves according to some unitary operator, and that's the whole story. No splitting, no collapse, no objective classical transition, just quantum mechanics taken at face value. > There's also nothing special about observing. Yes, that's the MWI position.
- kgwgk 3y ago
  Is it possible to observe anything at all in MWI? If yes, what does it mean to "observe something" in MWI? If not, is there any physical content in MWI?
  - consilient 3y ago
    Observations in MWI are just ordinary physical interactions. Specifically they're perturbative-regime interactions between the thing being observed and large thermalized systems (e.g. humans). From the perspective of the thermal bath, you get exponential suppression of everything but the eigenstates of the interaction Hamiltonian, which is why our observations "look classical".
    - kgwgk 3y ago
      Will other large thermalised system (e.g. rocks) also experience observations that "look classical"? Another MWI proponent here is talking about how the "look classical" thing is "simply an artifact of being a conscious being that can only observe one value". Is there something special about "large thermalised systems" (and/or humans)? How large have they to be to allow for "our observations"? Where is the boundary between the thing being observed and the observing thing? MWI seems to still face most of the difficult questions - it not all.
      - consilient 3y ago
        > Will other large thermalised system (e.g. rocks) also experience observations that "look classical"? The inner life of rocks is somewhat beyond our reach, I'm afraid. But they'll induce decoherence in the same way as a human, yes. > Is there something special about "large thermalised systems" (and/or humans)? Aside from being large and thermalized? No. > How large have they to be to allow for "our observations"? It's a continuum. The more internal degrees of freedom you have, and the more thoroughly they're mixed, the faster you'll decohere things. > Where is the boundary between the thing being observed and the observing thing? At the level of fundamental physics, there isn't one. "Observation" is an approximate and thermodynamic notion.
        kgwgk 3y ago
        > But they'll induce decoherence in the same way as a human, yes. From the perspective (?) of the (non-human) thermal bath, will that decoherence result in a single (diagonal, mixture) state or in a particular state of those N separate states that would "look classical"? Decoherence doesn't make things "look classical" by itself - at least until you define what "looking" is.
        consilient 3y ago
        Depends on whether you're talking about the "perspective" of the whole joint |Rock>|Interaction Eigenstate 1> + |Rock>|Interaction Eigenstate 2> ... system or just one of its components. > Decoherence doesn't make things "look classical" by itself - at least until you define what "looking" is. Of course; but that's true of every scientific theory. Decoherence solves the preferred basis problem, not the hard problem of consciousness.
goatlover 3y ago
Many worlds just falls out of superposition and entanglement. Those happen in quantum systems, and we are made of quantum systems. To avoid that you have to stipulate something additional that avoids putting macroscopic objects like devices, cats and brains into superpositions.
captainclam 3y ago
Correct, it is an enormous amount...Under Everett, the "number of worlds" practically exists on a continuous spectrum, so basically an infinitude of worlds. But this doesn't violate parsimony in terms of building a model of reality. I don't have the greatest comprehension of the history of science, but I imagine the behavior of water and gas was not initially explained as being the collective behavior of moles (6.02x10^23) and moles of individual molecules. The parsimony of thermodynamics is measured by the simplicity of the underlying equations that describe their behavior, not the staggering number of atoms involved. As for observation, I didn't suggest there was anything special about observing. In fact, this is part of what makes Everett among the most parsimonious interpretations: While some (not all) other interpretations are tasked with explaining the nature of observation (what counts as observation, how quickly does collapse propagate, etc), under Everett, there is no notion of observation at all. My point about consciousness is that, being conscious, we are forced to have a point of view which depends on where we exist in/on the wave function. I wasn't suggesting that consciousness has any actual effect whatsoever on the wavefunction. I admit that the nature of probability is among the most difficult parts of Everett to wrestle with, though I'm not sure I understand why subsequent observations should follow a radically different pattern? It's still the same wavefunction with the same distributions as before...Schrodinger's equation is the same wherever you are on the wavefunction.

by tgv 3y ago

consilient 3y ago

> Assuming many worlds, and many here means: enormous amounts, far exceeding the number of particles in the universe, is everything but parsimonious. "Many worlds" is a misnomer. MWI is just wavefunction realism + unitary evolution. There's only one world, and really only one dynamical object: the wavefunction. It evolves according to some unitary operator, and that's the whole story. No splitting, no collapse, no objective classical transition, just quantum mechanics taken at face value. > There's also nothing special about observing. Yes, that's the MWI position.

kgwgk 3y ago
Is it possible to observe anything at all in MWI? If yes, what does it mean to "observe something" in MWI? If not, is there any physical content in MWI?
- consilient 3y ago
  Observations in MWI are just ordinary physical interactions. Specifically they're perturbative-regime interactions between the thing being observed and large thermalized systems (e.g. humans). From the perspective of the thermal bath, you get exponential suppression of everything but the eigenstates of the interaction Hamiltonian, which is why our observations "look classical".
  - kgwgk 3y ago
    Will other large thermalised system (e.g. rocks) also experience observations that "look classical"? Another MWI proponent here is talking about how the "look classical" thing is "simply an artifact of being a conscious being that can only observe one value". Is there something special about "large thermalised systems" (and/or humans)? How large have they to be to allow for "our observations"? Where is the boundary between the thing being observed and the observing thing? MWI seems to still face most of the difficult questions - it not all.
    - consilient 3y ago
      > Will other large thermalised system (e.g. rocks) also experience observations that "look classical"? The inner life of rocks is somewhat beyond our reach, I'm afraid. But they'll induce decoherence in the same way as a human, yes. > Is there something special about "large thermalised systems" (and/or humans)? Aside from being large and thermalized? No. > How large have they to be to allow for "our observations"? It's a continuum. The more internal degrees of freedom you have, and the more thoroughly they're mixed, the faster you'll decohere things. > Where is the boundary between the thing being observed and the observing thing? At the level of fundamental physics, there isn't one. "Observation" is an approximate and thermodynamic notion.
      - kgwgk 3y ago
        > But they'll induce decoherence in the same way as a human, yes. From the perspective (?) of the (non-human) thermal bath, will that decoherence result in a single (diagonal, mixture) state or in a particular state of those N separate states that would "look classical"? Decoherence doesn't make things "look classical" by itself - at least until you define what "looking" is.
        consilient 3y ago
        Depends on whether you're talking about the "perspective" of the whole joint |Rock>|Interaction Eigenstate 1> + |Rock>|Interaction Eigenstate 2> ... system or just one of its components. > Decoherence doesn't make things "look classical" by itself - at least until you define what "looking" is. Of course; but that's true of every scientific theory. Decoherence solves the preferred basis problem, not the hard problem of consciousness.

goatlover 3y ago

Many worlds just falls out of superposition and entanglement. Those happen in quantum systems, and we are made of quantum systems. To avoid that you have to stipulate something additional that avoids putting macroscopic objects like devices, cats and brains into superpositions.

captainclam 3y ago

Correct, it is an enormous amount...Under Everett, the "number of worlds" practically exists on a continuous spectrum, so basically an infinitude of worlds. But this doesn't violate parsimony in terms of building a model of reality. I don't have the greatest comprehension of the history of science, but I imagine the behavior of water and gas was not initially explained as being the collective behavior of moles (6.02x10^23) and moles of individual molecules. The parsimony of thermodynamics is measured by the simplicity of the underlying equations that describe their behavior, not the staggering number of atoms involved. As for observation, I didn't suggest there was anything special about observing. In fact, this is part of what makes Everett among the most parsimonious interpretations: While some (not all) other interpretations are tasked with explaining the nature of observation (what counts as observation, how quickly does collapse propagate, etc), under Everett, there is no notion of observation at all. My point about consciousness is that, being conscious, we are forced to have a point of view which depends on where we exist in/on the wave function. I wasn't suggesting that consciousness has any actual effect whatsoever on the wavefunction. I admit that the nature of probability is among the most difficult parts of Everett to wrestle with, though I'm not sure I understand why subsequent observations should follow a radically different pattern? It's still the same wavefunction with the same distributions as before...Schrodinger's equation is the same wherever you are on the wavefunction.