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Schroedinger's cat from the cat's point of view

  1. Apr 27, 2013 #1
    Hello all. I was thinking about the famous cat thought experiment. I was wondering if anyone could explain to me(or point me in the right direction) what the various interpretations of quantum mechanics(copenhagen, many-worlds) say about this thought experiment from the cat's point of view.
    The many-worlds interpretation would seem to me not have any problem. If the measurement shows the cat being alive then, in our universe, it has always been alive and that is what the cat has also perceived. Is this correct?
    How do the other interpretations of QM deal with the cat's point of view?
  2. jcsd
  3. Apr 27, 2013 #2
    I don't think it makes a difference whether you look at that experiment from the cat's point of view or the point of view of someone outside the box.
    What you have there are two regions of space that are isolated from each other such that there is no interaction. Which of the two regions is bigger shouldn't matter.
    In other words, from the cat's point of view the outside world is in a superposition.
  4. Apr 27, 2013 #3
    Well there is a difference that the cat is the point of interest in this experiment as we likely assume the observer (human outside the box) probably stays alive during all of the experiment so the cat is the one in question here.
    But from the cat's point of view it is kinda easy for him as when the atom would decay the poison would be released and the cat would clearly feel or know when he would die.In a sense that a death cannot go unnoticed by the one who dies...

    So in other words speaking about this particular case the cat is the one who is in a superposition not the human outside as the experiment conditions are set so that the cat is in the condition to be killed by a probable decay of an atom not the human.

    But from the cat's point of view death would not go unnoticed even when the box is still closed so it is the human who is left wondering about the conditions in the box before it is opened.
  5. Apr 27, 2013 #4
    The problem with Schroedinger's Cat analysis...

    The problem with your question is that it assumes that both physical results (dead or alive cat) must manifest itself. But I don't think that is necessarily the case.

    Once a result (and I'm not talking about one reality or the other) is manifested it should not be necessary that the other result manifests in some alternate universe.

    For as long as the state of the particle is unobserved/unmeasured, possible realities can interfere with each other. But once measured or interacted outside of the superpositioned system (which then brings about decoherence or collapsing of the wavefunction), only one reality is created.

    In a nutshell, after decoherence both the cat and the observer share the same singular reality. There is no difference between the point of view of the cat and that of the observer.
  6. Apr 27, 2013 #5
    After decoherence in many cases there is no more live cat so from a standard viewpoint the only observer left is the human so only one observer.

    But even before that I would like to say that there is a difference between the viewpoint of the cat and the observer outside.because the observer outside knows the reality around him but not the one inside the box, now when opening the box there is a great chance of a sudden change in that reality in the box.
    But the cat in the box (assuming he is conscious enough to understand that he is alive) does know perfectly good his state of things at any given point.He knows whether he is dying from a decayed atom hours before anyone even comes close to the box or whether he dies in the moment when one opens up the box and photons hit the atom which then decays and releases the poison.
    Now you may say that the cat while being alive doesn't know the sate of matters outside but he doesn't need to because outside there is no decaying atom that could suddenly release a gas which would kill the observer (human).So we can just assume that for the sake of the experiment the unknown part is inside the box which makes the two observers (cat and human) viewpoints rather different.
  7. Apr 27, 2013 #6
    I think we need to separate ourselves from the notion that reality depends on a "conscious observer". Whether or not the cat lives or dies is irrelevant to reality, because there is only one reality/viewpoint- not two.

    Decoherence just means that the two possibilities (actually it must be trillions of possibilities in this case) have settled into a definite state. Again please realize that I am talking about a superposition of possibilities and NOT a superposition of realities.
  8. Apr 27, 2013 #7
    Hey Everyone.

    I just want to ask this: Should i look at this experiment from a life / death point of view (Should i inmagine the cat alive or death)? Or look at it from a atomic decay point of view (Did an atom decay or not)?

    Im no physicist or anything, but in my opinion doesnt the `frame` of this experiment move according to how i think about the outcome?
  9. Apr 27, 2013 #8
    Look at it from a atomic decay point of view. Also think about the double slit experiment. What happens when the detector screen is moved closer to the slits? What would happen if the detector screen was right next to the slits?

    If it were then the interference pattern would not exist at all. Having the cat so close to the experiment makes death a certainty if the atom decays. But not isn't like the double slit experiment interference.

    The cat needs to be a certain distance away from the experiment so that a decayed atom in the experiment results in the cat having at 50 percent survival rate at that distance. Then you alter the experiment so that the atom decays all the time.

    That would be more closer to an approximation coherence like we see in the double slit experiment.
    Last edited: Apr 27, 2013
  10. Apr 27, 2013 #9
    You know schrodinger was on einsteins side and said that the cat died or lived and that it did not matter what the observer saw. It was the bohr crew that believed in wave collapse. so in the cats point of view acording to einsteint and schrodinger he dies if the bobm explodes or lives if it doesnt, and then later the observer finds out what happened; no wave collapse.
  11. Apr 27, 2013 #10


    Staff: Mentor

    Think about it a minute. The quantum weirdness manifests itself at the particle detector - from that point on everything is classical and not of any concern.

    Basically what happens is the detector, vial, gas and cat are entangled with the quantum system. Since all of those things do not interfere there is no issue - regardless of if you are the person opening the box or the cat.

  12. Apr 28, 2013 #11
    the cat's point of view and the "outside" observers point of view are the same.

    the cat (as a whole/single unit) is/was NEVER is a superposition.

    superposition happens, and stays, only on much smaller scale/size.

    the superposition breaks-down before reaching the cat. Measurement alone (for example by a Geiger counter) is sufficient to collapse a quantum wave function before there is any conscious observation of the measurement

    Schrödinger was trying to illustrate (via the Schrödinger's cat thought experiment) the absurdity of extrapolating from micro to macro scale, as well as a critique of some of the interpretations of quantum mechanics

    "the flapping of a butterfly wings does not cause a storm/rain in another part of the world because there are numerous other factors involved"
    Last edited: Apr 28, 2013
  13. Apr 28, 2013 #12
    The laws of quantum mechanics are fundamental and apply at all scales.
    Here is a nice experiment that demonstrates this
    However I guess you could argue about whether it is really correct to say that a system in a superposition is actually in different states at the same time. Sure, it's one possible interpretation of the math but is it the only way to interprete it?
    Either way, the phenomenon of superposition can at least in principal occur at all scales, whatever the correct philosophical interpretation of superposition is, if there even is such a thing as a correct interpretation.
  14. Apr 28, 2013 #13


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    Sigh, even Nature puts it in this "weird" way :cry: It starts with the sentence: "They then used the weird rules of quantum mechanics [...]" (emphasis mine). This is typical popular-science gibberish. The rules of quantum mechanics are not weird but very concise and consistent. It's the best mathematical description of an overwhelming large part of nature. The only part, we do not yet really understand in terms of quantum theory is gravitation and space-time structure. The space-time description itself is thus classical, and gravitation is described only in (semi-)classical approximation by GR. That's the only "weird", or better say ununderstood part of nature from a fundamental point of view.

    Next, they say "According to quantum theory, particles act as waves rather than point masses on very small scales." This is not true either. The whole point of quantum mechanics is that our classical world view, trained from everyday experience with macroscopic objects in interaction with the environment and thus states, where coherence effects of quantum theory are absent because of decoherence due to interaction of the many-body objects with the environment. It's not very surprising that this experience is invalid for the realm of microscopic objects or also macroscopic objects that are prepared in a state, where these coherence effects become important.

    That doesn't mean that this topic isn't fascinating, but one should not sell science as something "weird" to the public but as a means to learn about the behavior of nature in many details we don't see in everyday life, but of course have implications for this everyday experience in explaining some "obvious facts" like the stability of matter around us, which is in fact a quantum phenomenon.
  15. Apr 28, 2013 #14


    Staff: Mentor

    Too true

    No its not

    I think it occurs at all scales and quantum 'superposition' has certainly been demonstrated with objects you would not think it should be such as buckyballs. And while not a demonstration of superposition I think there is quite a bit of truth in what is said about liquid helium - its Quantum Mechanics written large. The reason we don't see it at the classical level is objects are constantly being 'observed' by the environment and entangled with it. While it is a technological tour de-force doing it, it is possible to have macroscopic objects show quantum effects.

    Personally I have always scratched my head about peoples concern with Schrodinger's Cat. IMHO the issue it raises is not what Schrodinger had in mind when he proposed it - Bohr and other Copenhagenists never believed the cat was in some superposition of alive and dead. They believed an observation was when something made its appearance in the classical macro world. And that occurs at the particle detector - not the cat or observer. The real issue IMHO is it points to this distinction between the quantum and classical world. There should be no distinction and what was needed was a quantum theory of measurement. A lot of progress has been made towards that and research is ongoing.

  16. Apr 29, 2013 #15
    Thanks for correcting my mistake DrZoidberg

    I guess - it would be very difficult to maintain superposition at a larger scale because too many factors/variables would be involved that would tend to de-cohere the superposition.
  17. Apr 29, 2013 #16


    Staff: Mentor

    It is - but not impossible.

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