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In Schrodinger's cat, somehow the cat is dead and alive at the same time until someone opens the box, observes that cat's state, and collapses the wave function. Of course, something can't be dead and alive at the same time (unless...), so this makes no sense.

I still can't quite wrap my head around this idea. What if the cat is the observer and collapses the wave function while in the act of dying or staying alive? Is that a possibility? Which raises the question, can observation by other animals collapse the wave function? What counts as observation?

esi
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    The point of a paradox is to highlight that something might be wrong with the model or the reader's understanding of how to apply the model, by showing something that seems to be predicted by the model but doesn't make sense. If it doesn't make sense, that's the point. – g s Mar 07 '22 at 00:18
  • The Schrodinger's Cat thought experiment is meant to introduce someone to the idea of superposition without that person having any background knowledge in physics.

    The thought experiment itself does not really provide anything physically meaningful, but does a good job of expressing the idea of 'states'.

    Quantum mechanics should not make sense initially - it is a description of reality that we do not inherently notice on a macroscopic scale. But when we start noticing things experimentally, like in Young's double slit experiment done with electrons, we need a new description of reality.

     – bleuofblue Mar 07 '22 at 04:40
  • That is the premise of the Schrodinger's cat - how can this description of reality be explained to the general public in a way that is familiar and makes sense..... Even if it does not hold any actual physical significance. – bleuofblue Mar 07 '22 at 04:42
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    Maybe my answer here will help to understand that the cat is just a recording medium, the actual quantum mechanical interaction is the nuclear/atomic decay. recording mediums do not affect the quantum interaction to be recorded. https://physics.stackexchange.com/questions/266606/extension-of-schr%c3%b6dingers-cat-thought-experiment/266617#266617 – anna v Mar 07 '22 at 05:31
  • This might help - Parallel Worlds Probably Exist. Here’s Why – mmesser314 Mar 07 '22 at 05:37
  • There is absolutely no version of the Schrodinger's cat thought experiment in which the cat is both alive and dead at the same time. Indeed, since dead is defined to mean "not alive", no such version is possible. – WillO Mar 08 '22 at 05:38

2 Answers2

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Let's suppose the cat will be killed when an atom undergoes radioactive decay. What happens is:

  1. A live cat goes in the box.
  2. The cat knows it is alive. From the cat's point of view, the wavefunction has collapsed and the atom has not decayed. From the human's point of view, outside the box, the wavefunction has not collapsed and the cat might be alive or dead.
  3. Sometimes, at a later point, the atom decays. If that happens, the cat knows it is dead and the cat's perspective shows a collapsed wavefunction. For the human, outside the box, the wavefunction has not collapsed and the cat might be alive or dead.
  4. The box is opened. Now the cat and the human agree about the cat's status and they both observe a collapsed wavefunction.

In summary, the cat can collapse the wavefunction for itself, but not for the rest of the universe.

Anonymous Physicist
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Everywhere in the world, something is happening all the time without our intervention or observation. However, if we observe a macroscopic binary system, we can give information about the state of the system at any time (with certain time delays).

If we have a macroscopic binary system that we cannot observe immediately (it is in a box or it is too far away from us), we do not KNOW what state the system is in at the moment. However, it has a unique state.
If a friend of ours observes this system, he knows its state. And as long as he does not give us any information about it, we can operate with a mathematical function that defines this state as undecided. But this does not change the actual state of the system. The cat is always already dead or still alive.

What we cannot do is make a definite statement about states at the quantum level. Every attempt of observation influences this system. But this has nothing at all to do with the poor cat.

Whether cat or human, observation at the macroscopic level does not affect the process.

HolgerFiedler
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