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Hearing at all implies sound waves. If there are soundwaves there is air inside the box. If there is air inside the box the system can't be in a superposition b

Hearing at all implies sound waves. If there are soundwaves there is air inside the box. If there is air inside the box the system can't be in a superposition because it has long since decohered. In other words it's not the act of "listening" that collapses the wave function but the interaction of air molecules that creates the sound in the first place, even if no one is there to listen. A "measurement" or an "observation" doesn't actually require a human, or a living thing. It's just a physical interaction.

rvbissell 2y ago
Catch 22: and if there is no air inside the box, then you are certain the cat is dead.
Maxatar 2y ago
This isn't quite right, wave function collapse is relative so while within the box an observer's wave function of the box will be in a definite eigenstate, the wavefunction of the box for an observer isolated from the box will still be in a superposition of its states. In other words, the fact that an observation takes place from within the box and collapses the wave function for an observer in the box does not mean that the wave function for every observer also collapses. A wave function collapse for one observer does not imply a wave function collapse for any other observer.
- Jensson 2y ago
  > wave function collapse is relative No it isn't, why do you think this? If it was we wouldn't be able to see it in our experiments, as where the particle ends up would depend on which observer is looking, which would get absurd consequences.
  - Maxatar 2y ago
    I provided my explanation for why this is the case. A measurement device only collapses the wave function for itself, it does not collapse the wave function for every other observer/measurement device. Of course, a second measurement device that's completely isolated from the first measurement device can eventually interact with the first measurement device and the two will converge and share the same wave function. However, until the second measurement device interacts with the first one or with the original quantum system being observed, then from the point of view of the second measurement device, the first measurement device is in a superposition of all the possible states that it could have observed. This can continue on and on, with a third measurement device which is entirely isolated from the second measurement device having a wavefunction that's a superposition of all the possible observations that the second measurement device will observer...
    - Jensson 2y ago
      > A measurement device only collapses the wave function for itself, it does not collapse the wave function for every other observer/measurement device. Wave function collapse is a real measurable phenomena, what you describe is not measurable so just a belief, don't mix in your beliefs with actual results.
      - Maxatar 2y ago
        Wave function collapse is one of many equivalent (so far as we know) interpretations of quantum mechanics and not all interpretations have wave function collapse whatsoever. With that said even in the Copenhagen interpretation which is the most popular interpretation of quantum mechanics, the moment in time when the wave function collapses is relative to each measurement device. It is not the case that just because some measurement device that has been entirely isolated from me happens to perform a measurement on a quantum system, that my wave function of that quantum system will also collapse. On the contrary my wave function remains exactly as is until the moment I perform a measurement on the quantum system which collapses my wave function of said system.
        Jensson 2y ago
        Double slit experiment disproves you here, the observed pattern is the same for every observer and shows a collapse happened.
        danbruc 2y ago
        One common view is that there is THE wave function of the universe. If it collapses, it collapses, there is no way it can collapse for some observers and not others. You might not know that it has collapsed but that does not make it not collapsed. There is a different view that the wave function is just an representation of the knowledge someone has about the state of the universe or some part of it, in which case it can collapse for some and not others. On the other hand there is not really any collapse at all in this case, it is just a fancy term for updating once believe about the state of the universe or some system. It is also important to note that a collapse is not a total collapse into a point. Measuring different things will collapse the wave function along different dimensions, only measuring everything in the universe would collapse the wave function along all dimensions into a point, or as far as the uncertainty principle permits.
  - tsimionescu 2y ago
    This is actually an open problem in QM. We don't understand what constitutes a measurement, and so we don't know if two perfectly isolated observers could disagree on the "state" of a system in this way (as in, collapsed or not collapsed). And given special relativity, it is definitely possible that two different observers could disagree on the order that two independent measurements of the same system happened. Do note that the result of the experiments is not going to differ, it is guaranteed to be consistent by the fact that both experiments are measuring the same quantum system. It's just that one observer is unsure of what result they will get for a subsequent experiment, while the other observer can know it exactly. And in the many worlds interpretation, it is indeed believed that apparent wave function collapse is a relative phenomenon, caused by entanglement with the classical environment, which spreads out at the speed of light.
    - Jensson 2y ago
      > We don't understand what constitutes a measurement, and so we don't know if two perfectly isolated observers could disagree on the "state" of a system in this way (as in, collapsed or not collapsed) We do know that they can't disagree as collapsed particles behave differently than uncollapsed particles. > It's just that one observer is unsure of what result they will get for a subsequent experiment, while the other observer can know it exactly. Quantum systems aren't about knowledge or statistics, the wave function is an actual physical thing that changes how the particle behaves. If the wave function has collapsed it no longer behaves the same as before, so what you said here is wrong.
      - Maxatar 2y ago
        You're now arguing against claims no one has made, which is apparent from the fact that you seem to only quite very tiny snippets of what's said while ignoring the main argument. You seem to just want to argue for the sake of arguing.
        Jensson 2y ago
        Wasn't the argument that two observers can disagree whether a collapse has happened? I offered evidence that they can't, as otherwise they would see different results in the double slit experiment.
danbruc 2y ago
This does not help at all, quantum systems - even messy complex ones, boxes containing cats and air - evolve unitarily and do not destroy a superposition. The box and the air and the cat can interact all they want, you will still have a superposition of cat dead - and box and air in some state - and cat alive - and box and air in some other state. And no point are we addressing how we get rid of one half of the entangled state. And even if I see the box wiggle a bit, we only declare that me watching the box somehow was an measurement and that collapsed the wave function without answering the question why I did not simply get entangled with the box, too.
- Jensson 2y ago
  > quantum systems - even messy complex ones, boxes containing cats and air - evolve unitarily and do not destroy a superposition This is wrong, they do collapse, you can test this using the double slit experiment. No human has to be there for the wavefunction to collapse and thus break entanglement. If what you said was true then this wouldn't be a part of physics, physics is only about stuff we can measure not nonsense that has no meaning.
  - tsimionescu 2y ago
    It's not at all clear how, when, and why wave function collapse happens. The only known quantity there, decoherence, is related to interaction between a coherent quantum system and a noisy decohered environment, which causes the original system to decohere itself. Theoretically, as far as it is known today, it is possible for a quantum system of any size, and at any temperature, to remain in a coherent state, if it could be perfectly isolated from the rest of the world. Any limits to this process, where a perfectly isolated system would undergo wave function collapse without any outside interference, would be a Nobel-prize worthy discovery and would constitute a new theory of physics: quantum mechanics and QFT allow no such process. Edit: and the double slit experiment is unrelated - the screen and the slit are noisy classical systems that are not in any way isolated from the rest of the classical world. In principle, if you performed the experiment using a screen and slits made entirely of atoms entangled with the emitter, and isolated perfectly from the rest of the world and the CMB and everything, you'd get a different result: this is what QM predicts.

rvbissell 2y ago

Catch 22: and if there is no air inside the box, then you are certain the cat is dead.

Maxatar 2y ago

This isn't quite right, wave function collapse is relative so while within the box an observer's wave function of the box will be in a definite eigenstate, the wavefunction of the box for an observer isolated from the box will still be in a superposition of its states. In other words, the fact that an observation takes place from within the box and collapses the wave function for an observer in the box does not mean that the wave function for every observer also collapses. A wave function collapse for one observer does not imply a wave function collapse for any other observer.

Jensson 2y ago
> wave function collapse is relative No it isn't, why do you think this? If it was we wouldn't be able to see it in our experiments, as where the particle ends up would depend on which observer is looking, which would get absurd consequences.
- Maxatar 2y ago
  I provided my explanation for why this is the case. A measurement device only collapses the wave function for itself, it does not collapse the wave function for every other observer/measurement device. Of course, a second measurement device that's completely isolated from the first measurement device can eventually interact with the first measurement device and the two will converge and share the same wave function. However, until the second measurement device interacts with the first one or with the original quantum system being observed, then from the point of view of the second measurement device, the first measurement device is in a superposition of all the possible states that it could have observed. This can continue on and on, with a third measurement device which is entirely isolated from the second measurement device having a wavefunction that's a superposition of all the possible observations that the second measurement device will observer...
  - Jensson 2y ago
    > A measurement device only collapses the wave function for itself, it does not collapse the wave function for every other observer/measurement device. Wave function collapse is a real measurable phenomena, what you describe is not measurable so just a belief, don't mix in your beliefs with actual results.
    - Maxatar 2y ago
      Wave function collapse is one of many equivalent (so far as we know) interpretations of quantum mechanics and not all interpretations have wave function collapse whatsoever. With that said even in the Copenhagen interpretation which is the most popular interpretation of quantum mechanics, the moment in time when the wave function collapses is relative to each measurement device. It is not the case that just because some measurement device that has been entirely isolated from me happens to perform a measurement on a quantum system, that my wave function of that quantum system will also collapse. On the contrary my wave function remains exactly as is until the moment I perform a measurement on the quantum system which collapses my wave function of said system.
      - Jensson 2y ago
        Double slit experiment disproves you here, the observed pattern is the same for every observer and shows a collapse happened.
      - danbruc 2y ago
        One common view is that there is THE wave function of the universe. If it collapses, it collapses, there is no way it can collapse for some observers and not others. You might not know that it has collapsed but that does not make it not collapsed. There is a different view that the wave function is just an representation of the knowledge someone has about the state of the universe or some part of it, in which case it can collapse for some and not others. On the other hand there is not really any collapse at all in this case, it is just a fancy term for updating once believe about the state of the universe or some system. It is also important to note that a collapse is not a total collapse into a point. Measuring different things will collapse the wave function along different dimensions, only measuring everything in the universe would collapse the wave function along all dimensions into a point, or as far as the uncertainty principle permits.
- tsimionescu 2y ago
  This is actually an open problem in QM. We don't understand what constitutes a measurement, and so we don't know if two perfectly isolated observers could disagree on the "state" of a system in this way (as in, collapsed or not collapsed). And given special relativity, it is definitely possible that two different observers could disagree on the order that two independent measurements of the same system happened. Do note that the result of the experiments is not going to differ, it is guaranteed to be consistent by the fact that both experiments are measuring the same quantum system. It's just that one observer is unsure of what result they will get for a subsequent experiment, while the other observer can know it exactly. And in the many worlds interpretation, it is indeed believed that apparent wave function collapse is a relative phenomenon, caused by entanglement with the classical environment, which spreads out at the speed of light.
  - Jensson 2y ago
    > We don't understand what constitutes a measurement, and so we don't know if two perfectly isolated observers could disagree on the "state" of a system in this way (as in, collapsed or not collapsed) We do know that they can't disagree as collapsed particles behave differently than uncollapsed particles. > It's just that one observer is unsure of what result they will get for a subsequent experiment, while the other observer can know it exactly. Quantum systems aren't about knowledge or statistics, the wave function is an actual physical thing that changes how the particle behaves. If the wave function has collapsed it no longer behaves the same as before, so what you said here is wrong.
    - Maxatar 2y ago
      You're now arguing against claims no one has made, which is apparent from the fact that you seem to only quite very tiny snippets of what's said while ignoring the main argument. You seem to just want to argue for the sake of arguing.
      - Jensson 2y ago
        Wasn't the argument that two observers can disagree whether a collapse has happened? I offered evidence that they can't, as otherwise they would see different results in the double slit experiment.

danbruc 2y ago

This does not help at all, quantum systems - even messy complex ones, boxes containing cats and air - evolve unitarily and do not destroy a superposition. The box and the air and the cat can interact all they want, you will still have a superposition of cat dead - and box and air in some state - and cat alive - and box and air in some other state. And no point are we addressing how we get rid of one half of the entangled state. And even if I see the box wiggle a bit, we only declare that me watching the box somehow was an measurement and that collapsed the wave function without answering the question why I did not simply get entangled with the box, too.

Jensson 2y ago
> quantum systems - even messy complex ones, boxes containing cats and air - evolve unitarily and do not destroy a superposition This is wrong, they do collapse, you can test this using the double slit experiment. No human has to be there for the wavefunction to collapse and thus break entanglement. If what you said was true then this wouldn't be a part of physics, physics is only about stuff we can measure not nonsense that has no meaning.
- tsimionescu 2y ago
  It's not at all clear how, when, and why wave function collapse happens. The only known quantity there, decoherence, is related to interaction between a coherent quantum system and a noisy decohered environment, which causes the original system to decohere itself. Theoretically, as far as it is known today, it is possible for a quantum system of any size, and at any temperature, to remain in a coherent state, if it could be perfectly isolated from the rest of the world. Any limits to this process, where a perfectly isolated system would undergo wave function collapse without any outside interference, would be a Nobel-prize worthy discovery and would constitute a new theory of physics: quantum mechanics and QFT allow no such process. Edit: and the double slit experiment is unrelated - the screen and the slit are noisy classical systems that are not in any way isolated from the rest of the classical world. In principle, if you performed the experiment using a screen and slits made entirely of atoms entangled with the emitter, and isolated perfectly from the rest of the world and the CMB and everything, you'd get a different result: this is what QM predicts.