Everyone knows how Schrodinger's Cat is set up, so the question becomes whether there's a quantum/classical boundary and what that boundary is. Some people say everything is quantum while some may think there's a line that separates quantum/classical.

So the cat in the box would have to be a mixture of live/dead cat until one of two things happened. Decay occurred and poison gas is released that kills the cat or it doesn't occur and the experimenter opens the box and sees a live cat.

Wouldn't the wave function be a quantum ensemble of these two states described in Hilbert space until one of these measurements occurred?

What state is the cat in before one of these measurements occur? Doesn't it have to be in a quantum ensemble of both states until one of these measurements occur?

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    $\begingroup$ Well, that's what Schrodinger was talking about. He thought the construction that lead to a "dead/alive cat" was kind of ridiculous, and so the interpretation that leads you to conclude "it must be a dead+alive cat!" must be wrong. It's kind of a pity we forget the reductio ad absurdum bit of this argument usually... $\endgroup$
    – zeldredge
    May 22, 2015 at 16:52
  • $\begingroup$ @zeldredge I think it was just the opposite. He knew the construction of live/dead cat was correct he just didn't think it should extend to a classical object like the cat. He actually had a more spiritual view towards quantum mechanics later in life as he said he would go to the Upanishads. I think if there's no quantum/classical boundary than the cat must be in a quantum ensemble of live/dead cat. $\endgroup$
    – user46759
    May 22, 2015 at 17:13
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    $\begingroup$ The true answer is " yes.... and no." $\endgroup$ May 22, 2015 at 20:30

2 Answers 2


The point of this thought experiment has been widely taken out of context and misused by new age science supporters. Schrodinger initially considered this experiment to show the RIDICULOUSNESS of the situation, not because it was physically what is happening.

Additionally, anyone who says that there is a line between the quantum and classical regime is wrong. The universe is one which obeys quantum mechanics(as far as we can tell) because the predictions of quantum mechanics(field theory) are by far the most accurate that we can make. Classical physics is "correct" only in the limit of large quantum numbers, and even then it is only approximately correct. Just because one can ignore relativity in the limit of low gravity/speeds does NOT mean relativity is only correct in some regime, it is always correct. The same applies to quantum mechanics.

  • $\begingroup$ I don't think it was ridiculous at all and later in life Schrodinger himself became a "new age supporter" whatever that means. I think the cat beat out Schrodinger's objections as he began to talk about the Upanishads. He said in his book What is Life? “The multiplicity is only apparent. This is the doctrine of the Upanishads. And not of the Upanishads only. The mystical experience of the union with God regularly leads to this view, unless strong prejudices stand in the West.” The point is, can you separate an observable state from it's wave function. Is the cat an observable state? $\endgroup$
    – user46759
    May 22, 2015 at 17:06
  • $\begingroup$ @user46759 We use classical measurements because our detectors are bulk matter and classical mechanics and electrodynamics describe macroscopic effects. Studying tracks in bubble chambers macroscopically gives us crossections that can only be described by quantum mechanics. The cat in this example is a detector, and conforms due to bulk matter to classical equations. It will be alive until it is dead. Once the quantum mechanical probability release poison it is dead. $\endgroup$
    – anna v
    May 22, 2015 at 17:21
  • $\begingroup$ No line? Yet somewhere between fullerenes and baseballs we stop seeing interference. $\endgroup$
    – user66309
    Dec 22, 2015 at 9:49

The Schrodinger's cat thought experiment was an attempt by Schrodinger to show that cat cannot be alive and dead when it was not looked at. The thought experiment was appreciated by Einstein and Einstein said he appreciated Schrodinger for putting forth the experiment. This is where quantum and classical (the world we see around) physics mismatch. Some would say that the Geiger counter that measures the decay of the chemical collapsed the wave function.

People that do not agree with the experiment would say that the Geiger counter collapsed the wave function because it measured/observed the decay that released the gas. I agree with this view. In my understanding, any measurement, observation, and calculation collapses the wave function and the cat takes a stand (alive or dead)

Einstein put another experiment saying that if you looked at the moon, the moon is there and you see it, and if you turn around, you are still pretty sure that the moon is still there behind you. These experiments are just a different way of looking at quantum mechanics and how it contradicts classical mechanics. These experiments base on whether if you agree wave function collapse occurs or not, whether there is fundamental contradiction between quantum and classical mechanics, you think whether wave-particle duality is real, how you interpret this duality if wave particle duality exists, if you think the Geiger counter collapsed the wave function or no wave function collapse occurred.

I honestly don't know how to answer Schrodinger cat thought experiment, but if I have to answer in some form, the wave function was already collapsed and if we weren't looking at the cat the cat is alive or dead and there is no contradiction between quantum and classical mechanics in this case. The Geiger counter collapsed the wave function because it was observing/measuring the chemical and the decay will "take a stand," and it will decay or not and depending on that the cat will be alive or dead.

  • $\begingroup$ If the moon stopped existing, it would release a lot of energy, which would be very destructive for Earth. Without looking, you are still receiving information (from what hasn't happened) $\endgroup$
    – user66309
    Dec 22, 2015 at 9:54

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