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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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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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