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Does the cat collapse itself?

  1. Jul 18, 2011 #1
    Hi, I'm an 11 year old kid so I won't get any mathematics too complicated, but I don't want an answer simplified too much.
    So in schrodingers cat experiment, the cat and the Geiger counter used to detect the decaying atom do not decohere the system because they are a part of that closed system. But then i say, if we want to know what's going on inside that box, couldn't we just replace the cat with a person, and the poison with something less lethal? Would the person inside the box just have one version of himself sent to a parallel universe, with the other version stepping out of the box with a definite answer as to what happened inside? But that would have to mean that a conscious person had both if his superpositions collapse, ergo having two states of himself exist in the group of universes we supposedly live in. So is this experiment possible? Would we get the disappointing, seemingly classical result I suggested?
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  3. Jul 18, 2011 #2


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    Cat or person makes no difference. Person in box will collapse the state of everything in the box.

    However there are still two states existing from an observer outside the box: one where the person in the box did observe the hammer break the poison vial, and one where he observed the hammer to not break the poison vial.

    Once the box is opened, the observation of the external observer will collapse those two states in one.
  4. Jul 18, 2011 #3
    That's the fastest answer I've ever gotten :) I hadn't even left the site yet. So the person in the box collapses it only for himself, but for the person on he outside, it is still a wave function? How is that possible? It wouldn't mean much to call it alternate realities for the two people, especially when talking about quantum weirdness, but how does that happen? Ty!
  5. Jul 18, 2011 #4


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    Dave what do you think about the argument that goes as follows. The external observer collapses two states inside the box, but then his lab assistant who went to take a pee comes back and has two possible states to observe; first his boss saw the cat dead and second his boss saw the cat alive. Taking this to its logical extreme you get that it's not possible to collapse anything in the first place because it requires the whole universe to be in on it.

    I find this an interesting point of view but don't know enough to judge it on any merits.
  6. Jul 18, 2011 #5


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    Hold on, this is a complicated theory to explain completely and there are many misconceptions with the cat in the box. First of all, the cat in a box is only a thought problem. It serves to represent the fact that until you measure something, you don't know what the outcome is. It could be any of the possibilities!

    If you pull out a ruler and go to measure something, do you know what the exact size will be? Let's say you take a guess and come up with 6 inches for the length of a stick. Until you measure it, you don't know whether it is more than 6, less than 6, or so close to 6 that you can say it is exactly 6. Like the cat in the box, you don't know what it is until you measure it! (In this case, our "observation" will be the measuring of the stick) As far as you know it could be any of them! While this isn't the usual explanation, I don't know how in depth your knowledge of science is, so I'm trying not to make it too complicated.

    Many people take this a step further and say that ALL of the possibilities exist until they are observed. I think that is an issue for people well beyond you and I at the moment, so I wouldn't think too much on it right now.
  7. Jul 18, 2011 #6


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    Remember that this can not really happen. Particles are interacting with each other continually throughout the universe. It is only because of the hidden nature of the contents of the box that the wave functions can get superposed.
  8. Jul 18, 2011 #7


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    Clearly I'm going to have to do more reading on this. The whole thing about wave function collapse is just something I can't seem to get my head around.

    Saying " this can not really happen" seems to imply that there is nothing strange with the cat. It's always either alive or dead (and if dead, there's some point at which it became dead) we just can't know which one until we open the box. My belief, from what reading I HAVE done, it that it's more complicated than that, otherwise there would never have been an issue in the first place. I think the cat thing has gotten about as much play in laymen's physics conversation as anything except maybe black holes.
  9. Jul 18, 2011 #8
    As far as I know, Schrodinger originally used that argument to illustrate the disconnect between quantum processes (wavefunction collapse in particular) and what we experience.

    It would be ridiculous for the cat to be both dead and alive. So the wavefunction must have collapsed at some time, but when? This is still a bit of an unresolved issue.

    As for quantum ontologies... you can pretty much go hog wild.
  10. Jul 19, 2011 #9
    The experiment is really to show how to know when a measurement has taken place. Some physicists say, you have a combination of the cat being alive, and dead. However, once the observer (person checking the box) looks inside and the cat is dead, then the observer pretty much killed the cat because there was a chance the cat was still alive, and thus, the observer made a measurement

    Some physicists choose to believe that the measurement takes place when the Geiger counter is triggered by an atom decaying.

    As I said before, the experiment is asking "how do we know when a measurement has taken place?"

    EDIT: Never learned about this, but I looked in the back of "Introduction to Quantum mechanics second edition by David J. Griffiths", and he use no math to explain it, so I would check it out if you could!
    Last edited: Jul 19, 2011
  11. Jul 19, 2011 #10
    I don't agree with this, even though the general prescription for QM would imply this is what happens.

    The original argument (if memory serves) was to point out this scenario as ridiculous, and illustrate that quantum mechanics seems to break down at the macro level (at some point the wavefunction collapses).
    Last edited: Jul 19, 2011
  12. Jul 19, 2011 #11
    Ah yes, it says most physicists call it ridiculous; however, there is no proof (that I know of) to say the cat cannot be the linear combination of the two! I had to offer both sides of the argument (the one that says the cat is in both states until the observer opens the box, and the one that when the Geiger counter slams the hammer down due to the atom decay).

    I should probably edit my post and take out the "In reality" part haha
  13. Jul 19, 2011 #12
    I think superpositions can only occur to observables like position, spin, momentum. Since being dead and alive are not observables. Then it's not possible to have superpositions of dead and alive.

    But in Many Worlds, it seems the rule changes such that everything can be in superposition... you just separate them into alternative histories.
  14. Jul 19, 2011 #13
    That's all a cat is made of. A collection of particles with the mentioned properties.
    Living is the particles in a certain state, so is dead.

    So (to play devils advocate) QM does say that the cat will be alive/dead at the same time.
    But few people actually think that's what happenes.
  15. Jul 19, 2011 #14
    Always remember that in Copenhagen, the collapse is only in the equations. This is because no collapse agent can be found. So you have to look at the world thru the lens of equations. And only observables can be in superposition. I think Copenhagen is like a dumb down mode in which one has induce in onself some kind of Schizophrenia in viewing the world as mere equations on paper. Physicists love its mindset because it would prevent them from thinking deeper.

    For those who want to think deeper. They are offered Many Worlds which split worlds and this sound a bit silly.

    For Bohmians, collapse doesn't occur too.. instead something is piloting the wave.

    We need to entertain others. I wonder if the above 3 are the only "main" possibilities. Can't there be something else better?
  16. Jul 19, 2011 #15


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    Some strange views here.

    Physicists are the deepest thinkers of all, since they more than any other profession, deal with the very foundation upon which reality itself and all other sciences rest. You can't get any deeper.

    The reason they deal with equations is that any other form of thinking uses analogies and models which compare themselves to things we already know, and thus, since they're comparisons, must be flawed.

    Are we doing science here or writing a movie script?
  17. Jul 19, 2011 #16
    The fact that the cat is a macroscopic object can be ignored, because it's only meant to describe how it works at the subatomic level. It IS in a superposition because if you measure a photons horizontal/vertical polarization, and get 100% V, and then measure it's diagonal/antidiagonal polarization and get 100% D, and then measure it on H/V again, you have a 50% chance of getting H and a 50% chance of getting V! it proves that measurements DO affect systems by collapsing their wave function.
  18. Jul 19, 2011 #17
    It's not meant to describe how it works at the subatomic level. You cannot ignore the fact that the cat is a macroscopic object. If you have read my previous posts you will see that Shrodinger came up with that thought experiment to show how ridiculous it would be for a cat to be both live and dead.

    Like I said, particles do not behave like macroscopic objects.
  19. Jul 19, 2011 #18
    No, it is the other way around, Wavefunction can be in superposition, but when it comes to actual measurement only one outcome is observed. Also superposition is a relative thing, what looks like a single pure state in one basis look like a superposition in another.
  20. Jul 19, 2011 #19
    Just want to bump this thread and maybe get another reply ty!
  21. Jul 19, 2011 #20


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    Uh. Three hours is a little slim to be needing a bump - even here at PF.

    Was there more to say? I didn't see any new questions.
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