8 ms·

This does not explain how a classical observer gets probabilities that are precisely measured. In universe-as-a-wave-function there are no probabilities. So how

by _0w8t 4y ago

This does not explain how a classical observer gets probabilities that are precisely measured. In universe-as-a-wave-function there are no probabilities. So how exactly do they arise and what they mean?

layer8 4y ago
My understanding is that this is just the law of large numbers. Most branches match the mathematical probabilities very closely, and hence that’s what we observe. Yes, people on one of the rare branches where things behave differently wouldn’t observe that, but we simply happen to not be on one of those rare branches.
- goatlover 4y ago
  So you’re endorsing Many Worlds with an appeal to the anthropic principle. That’s fine, but you do have to assume MWI is the true interpretation of the mathematical formalism.
  - layer8 4y ago
    All the other interpretations require additional assumptions on top of the mathematical formalism, hence MW seems the most plausible to me. The GP wrote “[in a] universe-as-a-wave-function”, which basically is the MWI.
  - DiogenesKynikos 4y ago
    The Many-Worlds Interpretation is not really an interpretation. It just says that the known laws of Quantum Mechanics are correct, and that any measurement process itself has to obey the laws of Quantum Mechanics. In other words, nothing un-Quantum-Mechanical happens during measurement.
    - Jensson 4y ago
      MVI doesn't solve wave function collapses, if it did it would be able to tell exactly when the universe will split into many worlds, but it can't. So it doesn't solve anything, the difficulty with the theory is still there.
      - layer8 4y ago
        The perceived wave function collapse is explained by decoherence. There is no extra “split” that happens. “World” is just a term referring to the parts of the universal wave function that are entangled with each other. As to “exactly when the universe will split into many worlds”, it happens zillions of times per second pretty much everywhere. It’s even not clear whether the branching is a discrete and countable occurrence, it could really be a continuous fanning out.
        Jensson 4y ago
        So when does decoherence happen? Provide a formula for it. That is what people struggle with in quantum mechanics, MWI just deflects the question. Without a formula for when this phenomena happens any "interpretation" is just nonsense, except as a tool to get towards that formula.
        russdill 4y ago
        There's no yes/no equation as decoherence is statistical in nature.
        Jensson 4y ago
        Statistics also has formulas... This is the problem with MWI gospel, people come and say that it solves all the math but it leaves gaping holes like this. And you didn't even solve the randomness, since as you say it is "statistical", although that is just a theory we currently have no formula for this. Calling it a wave function collapse is much more honest since it accurately describes the situation, that we have no clue at what it is, why or when it happens. All we know how to do is calculate what possibly happens when we know that a wave function collapse will happen in a certain way.
    - goatlover 4y ago
      It’s an interpretation because we don’t have any empirical evidence for the other worlds. Science requires evidence, math alone isn’t enough. MWI is metaphysics, which is fine. We all wax philosophical sometimes as humans. Even the great Feynman couldn’t help himself.
      - DiogenesKynikos 4y ago
        There is a massive amount of evidence that Quantum Mechanics is the way the Universe works, and the MWI is simply vanilla Quantum Mechanics, with zero further assumptions. The problem is that the name "Many Worlds Interpretation" sounds grandiose. "Many worlds" is simply an imaginative way of describing the existence of different states of the wavefunction - a concept that is extremely well established and universally accepted. MWI just says that we should assume that Quantum Mechanics holds in all situations, including when we make measurements (i.e., there's nothing special about the measurement process).
        goatlover 4y ago
        QM isn’t a complete description of the universe because of gravity, dark energy, dark matter, the arrow of time, and it doesn’t explain probability. So it’s a little premature to say that’s how the universe works.
        DiogenesKynikos 4y ago
        Gravity, dark energy, dark matter or the arrow of time in no way conflict with QM. There isn't yet any successful quantum theory of gravity, but it's universally believed in the physics community that there will eventually be a quantum description of gravity. Dark energy and dark matter are merely components of the universe whose precise character is not yet known, but again, everyone believes that whatever they are, they will be described quantum mechanically. The arrow of time is merely a consequence of entropy being low in the early Universe. The reason why physicists universally believe that the Universe is quantum mechanical is that it's impossible for QM to describe only a part of physics. If one aspect of physics is quantum mechanical, it "infects" every other aspect of physics and forces it to be quantum mechanical. You can't have elections obey quantum mechanical laws, but the gravity they produce be classical. It's really all or nothing.
  - kahnclusions 4y ago
    I’m not a fan of Many Worlds. Communication or even detection of the split universes is impossible, which means it is impossible to measure. And science requires measurement to confirm our theories. Which means the MWI is equivalent to a simpler interpretation that doesn’t require split universes.
    - wruza 4y ago
      MWI is equivalent to a simpler interpretation that doesn’t require split universes Under aforementioned requirement, of course. If some sort of MWI is true, there may be just no way to confirm it, and that’s it.
    - AgentME 4y ago
      If something moves far enough away from us that it exits our observable universe, should we assume it still exists, or that physics has a special collapse rule that makes it stop existing at that point? Just like the split universes, it's impossible to directly measure the existence of objects outside of our observable universe.
    - burke 4y ago
      > MWI is equivalent to a simpler interpretation that doesn’t require split universes. That simpler interpretation is also equivalent to a simpler implementation that doesn’t require apparently-arbitrary resolutions of quantum probabilities (MWI). It’s essentially a question of where you hide the “weird”. It seems likely to me that they’re both wrong, and the in-principle-untestability of all this points to our mental machinery just failing to map intuitive concepts onto this space, but I’m totally agnostic to this. I do find MWI more conceptually appealing.
TheRealPomax 4y ago
probabilities are, by definition, not precisely measured. "Real world" probabilities are derived from imprecise measurements, and model probabilities are dictated by (simplified) model constraints.
pdonis 4y ago
> In universe-as-a-wave-function there are no probabilities. There are probability amplitudes in the universal wave function, and those are complex square roots of probabilities. It is true that deriving the Born Rule purely from the unitary dynamics of the wave function is an unsolved problem. This is discussed a fair bit in the comments to Aaronson's article.

by _0w8t 4y ago

layer8 4y ago

My understanding is that this is just the law of large numbers. Most branches match the mathematical probabilities very closely, and hence that’s what we observe. Yes, people on one of the rare branches where things behave differently wouldn’t observe that, but we simply happen to not be on one of those rare branches.

goatlover 4y ago
So you’re endorsing Many Worlds with an appeal to the anthropic principle. That’s fine, but you do have to assume MWI is the true interpretation of the mathematical formalism.
- layer8 4y ago
  All the other interpretations require additional assumptions on top of the mathematical formalism, hence MW seems the most plausible to me. The GP wrote “[in a] universe-as-a-wave-function”, which basically is the MWI.
- DiogenesKynikos 4y ago
  The Many-Worlds Interpretation is not really an interpretation. It just says that the known laws of Quantum Mechanics are correct, and that any measurement process itself has to obey the laws of Quantum Mechanics. In other words, nothing un-Quantum-Mechanical happens during measurement.
  - Jensson 4y ago
    MVI doesn't solve wave function collapses, if it did it would be able to tell exactly when the universe will split into many worlds, but it can't. So it doesn't solve anything, the difficulty with the theory is still there.
    - layer8 4y ago
      The perceived wave function collapse is explained by decoherence. There is no extra “split” that happens. “World” is just a term referring to the parts of the universal wave function that are entangled with each other. As to “exactly when the universe will split into many worlds”, it happens zillions of times per second pretty much everywhere. It’s even not clear whether the branching is a discrete and countable occurrence, it could really be a continuous fanning out.
      - Jensson 4y ago
        So when does decoherence happen? Provide a formula for it. That is what people struggle with in quantum mechanics, MWI just deflects the question. Without a formula for when this phenomena happens any "interpretation" is just nonsense, except as a tool to get towards that formula.
        russdill 4y ago
        There's no yes/no equation as decoherence is statistical in nature.
        Jensson 4y ago
        Statistics also has formulas... This is the problem with MWI gospel, people come and say that it solves all the math but it leaves gaping holes like this. And you didn't even solve the randomness, since as you say it is "statistical", although that is just a theory we currently have no formula for this. Calling it a wave function collapse is much more honest since it accurately describes the situation, that we have no clue at what it is, why or when it happens. All we know how to do is calculate what possibly happens when we know that a wave function collapse will happen in a certain way.
  - goatlover 4y ago
    It’s an interpretation because we don’t have any empirical evidence for the other worlds. Science requires evidence, math alone isn’t enough. MWI is metaphysics, which is fine. We all wax philosophical sometimes as humans. Even the great Feynman couldn’t help himself.
    - DiogenesKynikos 4y ago
      There is a massive amount of evidence that Quantum Mechanics is the way the Universe works, and the MWI is simply vanilla Quantum Mechanics, with zero further assumptions. The problem is that the name "Many Worlds Interpretation" sounds grandiose. "Many worlds" is simply an imaginative way of describing the existence of different states of the wavefunction - a concept that is extremely well established and universally accepted. MWI just says that we should assume that Quantum Mechanics holds in all situations, including when we make measurements (i.e., there's nothing special about the measurement process).
      - goatlover 4y ago
        QM isn’t a complete description of the universe because of gravity, dark energy, dark matter, the arrow of time, and it doesn’t explain probability. So it’s a little premature to say that’s how the universe works.
        DiogenesKynikos 4y ago
        Gravity, dark energy, dark matter or the arrow of time in no way conflict with QM. There isn't yet any successful quantum theory of gravity, but it's universally believed in the physics community that there will eventually be a quantum description of gravity. Dark energy and dark matter are merely components of the universe whose precise character is not yet known, but again, everyone believes that whatever they are, they will be described quantum mechanically. The arrow of time is merely a consequence of entropy being low in the early Universe. The reason why physicists universally believe that the Universe is quantum mechanical is that it's impossible for QM to describe only a part of physics. If one aspect of physics is quantum mechanical, it "infects" every other aspect of physics and forces it to be quantum mechanical. You can't have elections obey quantum mechanical laws, but the gravity they produce be classical. It's really all or nothing.
- kahnclusions 4y ago
  I’m not a fan of Many Worlds. Communication or even detection of the split universes is impossible, which means it is impossible to measure. And science requires measurement to confirm our theories. Which means the MWI is equivalent to a simpler interpretation that doesn’t require split universes.
  - wruza 4y ago
    MWI is equivalent to a simpler interpretation that doesn’t require split universes Under aforementioned requirement, of course. If some sort of MWI is true, there may be just no way to confirm it, and that’s it.
  - AgentME 4y ago
    If something moves far enough away from us that it exits our observable universe, should we assume it still exists, or that physics has a special collapse rule that makes it stop existing at that point? Just like the split universes, it's impossible to directly measure the existence of objects outside of our observable universe.
  - burke 4y ago
    > MWI is equivalent to a simpler interpretation that doesn’t require split universes. That simpler interpretation is also equivalent to a simpler implementation that doesn’t require apparently-arbitrary resolutions of quantum probabilities (MWI). It’s essentially a question of where you hide the “weird”. It seems likely to me that they’re both wrong, and the in-principle-untestability of all this points to our mental machinery just failing to map intuitive concepts onto this space, but I’m totally agnostic to this. I do find MWI more conceptually appealing.

TheRealPomax 4y ago

probabilities are, by definition, not precisely measured. "Real world" probabilities are derived from imprecise measurements, and model probabilities are dictated by (simplified) model constraints.

pdonis 4y ago

> In universe-as-a-wave-function there are no probabilities. There are probability amplitudes in the universal wave function, and those are complex square roots of probabilities. It is true that deriving the Born Rule purely from the unitary dynamics of the wave function is an unsolved problem. This is discussed a fair bit in the comments to Aaronson's article.