Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

I A bit confused about Schrödinger's cat

  1. Apr 2, 2016 #1
    I am certain this has been asked before many times before since the cat in the box first did not come out, and I am just overlooking it. And I am using the cat in the box for the exact purpose it was orginally created as I understood, to simplify the concept to its very base pieces to allow quick and easy discussion and understanding. So cat in box both alive and dead till observed, then it assumes either one or the other state at the moment of observation. My question is, how is it that the observed which has multiple states available is what is assuming a state and not the observer with it's single perception that chooses a state to perceive? So basically how can you be sure that the cat isn't always both alive and dead and through what ever unknown factors a perception of a state is chosen.

    Could this make the random seeming event of which state is chosen possibly predictable by switching the focus from the observed with all its quantum weirdness over to the observer and what is effecting the choice of perception. Could that then be taken from possibly predicting which perception is chosen and carry it on into controlling which perception is chosen? Would it even be relevant to be able to predict or choose which is precieved?

    And back to the cat in his box, if the cat is always both alive and dead, should that be taken into account when calculating the actual mass of the cat? Instead of just calculating the mass of the cat in the precieved state, now that he is both alive and dead all the time, would the way his mass is actually calculated need to be changed to account for his existing in both States, simultaneously? To account for what is really there and not just what you precieved as being there?

    And would it now be possible to get constantly changing result from the same cat in the same box opening and closing the box? Alive, dead, alive, dead.
     
  2. jcsd
  3. Apr 2, 2016 #2

    DaveC426913

    User Avatar
    Gold Member

    To clarify, its original purpose was designed to refute the notion that quantum effects could scale up to macro effects.

    We know that the cat really is either alive or dead, we're just trying to find the threshold between QM and the classical world.

    In reality, a cat is an object composed of uncountable atoms, all of which interact, collapsing the superposed wave function, leaving a cat that is either alive or dead.
     
  4. Apr 3, 2016 #3

    bhobba

    Staff: Mentor

    The cat is decohered by the environment to have definite position - like all everyday objects. The position of the constituent parts of an alive and dead cat are entirely different ie an alive cat's heart beats - a dead cat's heart doesn't. It is impossible, utterly impossible, for the cat to be alive an dead - end of story.

    The only issue is why everyday objects have definite position. It turns out to be related to the radial symmetry of most interactions ie they do not have a preferred direction. You can find the detail here if it interests you:
    https://www.amazon.com/Decoherence-Classical-Transition-Frontiers-Collection/dp/3540357734

    If you want to disuses it, its a bit off this threads topic so start a new one.

    Thanks
    Bill
     
    Last edited by a moderator: May 7, 2017
  5. Apr 4, 2016 #4

    Kyx

    User Avatar

    Quantum weirdness only happens when you are not observing. The cat is a living organism, so can be classed as an observer. Therefore, no quantum weirdness occurs.
     
  6. Apr 4, 2016 #5

    Nugatory

    User Avatar

    Staff: Mentor

    This idea that a conscious observer is required was discarded many decades ago - it's a wrong turn that was taken early in the development of the theory. Unfortunately the idea was picked up by the popular press and has been repeated ever since, but it's not accurate.

    You might want to give David Lindley's book "Where does the weirdness go?" a try.
    [Edit: I had the author's name wrong. It's fixed now]
     
    Last edited: Apr 4, 2016
  7. Apr 4, 2016 #6

    Kyx

    User Avatar

    I'm sure that's what Jim Al Khalili said in his book?
     
  8. Apr 4, 2016 #7

    bhobba

    Staff: Mentor

    I doubt it because its wrong. It must be said however that explaining QM at the lay level, and even in beginning textbooks, is difficult so some ideas may not be expressed 100% clearly.

    Here is the skinny devoid of any possible confusion. QM is a theory about observations that appear in a common sense world that objectively exists independent of us. What is going on when not observed the theory is silent about - it may be weird, it may be common-sensical, it may be all sorts of things - we simply do not know - although interpretations have various takes.

    Thanks
    Bill
     
  9. Apr 5, 2016 #8
    I think you better clarify your definition of "observations" here, or the OP is going to be confused. Most of us laypeople use that word in the "participatory" sense, but I know that's not how you meant it.
     
  10. Apr 5, 2016 #9

    bhobba

    Staff: Mentor

    It marks left in the world out there. That's as good as can be done at the beginner level.

    Thanks
    Bill
     
  11. Apr 6, 2016 #10
    You've got to remember that as soon as the box is opened, the "observer" is part of the "system". So, theoretically, his/her perception would have "multiple states available" as well... all either perceiving a live cat or dead cat, and nothing in between.
    The general concept of your question might seem reasonable to us curious laypeople. But, the technicalities of this thought experiment are complicated, and the mathematical formalism describing the evolution of the quantum state "mixture" is challenging (unless you can master density matrix transforms - which is well beyond my capabilities).
    As the mentors explained, the quantum state evolution is limited by a process called "decoherence", and that prevents the evolution of observable "macroscopic" states where superposition is allowed. So, even in the closed box, the state of the cat is ALWAYS either dead OR alive.
    But even without drowning in the math, you can get the basic idea by remembering the "triggering" mechanism of the potential feline termination. The quantum uncertainty lies in the state of the radioactive particle. Either the particle decays OR it doesn't decay. There is no in between. Therefore, the measurement made by the Geiger counter either releases the cyanide OR it doesn't... again no in between. From this point forward, the possible quantum states of the larger system (within the box) diverge (become decohered) in a similar either/or existence.
    When you then consider an observer that opens the box, the observer is also included in the system. But, at that point the potential states of the observer have already been "diverged" (decohered) by the previous either/or event of the radioactive decay.
    If we assume continuity of quantum state evolution, you can clearly understand that you can't go back and forth in the macroscopic state of the cat. Again, the "decohered" potential states of the cat permanently diverge as a result of the preceding "either/or" radioactive event.
     
    Last edited: Apr 6, 2016
  12. Apr 6, 2016 #11
    For whatever it's worth, and while I don't believe Al Khalili is one of them, there are still some physicists that believe in the need for a "conscious" observer to "collapse" the quantum state... though my understanding is that they're becoming increasingly rare as the idea tends to suggest a panpsychism type of ontology to physical existence.
    Regardless, that's an interpretational matter and has no direct bearing on the formalism of quantum theory. While it might make a great deal of difference from a philosophical/metaphysical perspective, it changes nothing from the "shut up and calculate" perspective. Whether consciousness has any fundamental role in Nature or not, it is not "necessary" for the purposes of quantum theory. So, the question can effectively be ignored... aside from the fact that pursuing the concept ultimately leads to overtly philosophical concerns that are not appropriate for this forum.
     
    Last edited: Apr 6, 2016
  13. Apr 6, 2016 #12
    - just found this quote (is it about a panpsychism type of ontology?) :

    To us ... the only acceptable point of view appears to be the one that recognizes both sides of reality - the quantitative and the qualitative, the physical and the psychical - as compatible with each other, and can embrace them simultaneously ... It would be most satisfactory of all if physis and psyche (i.e., matter and mind) could be seen as complementary aspects of the same reality.

    Wolfgang Pauli

    http://www.azquotes.com/quote/573538

    ( - that reminds of the ancient assertion, "Creation is twofold, one spiritual and one perceptible" . )
     
    Last edited: Apr 6, 2016
  14. Apr 6, 2016 #13
    :) Well, it suggests a dualistic description of ontology which is ultimately problematic for arguments that consciousness has any type of causal effect on a physical system. Panpsychism is one avenue to alleviate that problem in a monistic manner that might allow conscious observation to have a causal relationship to state reduction. But, as much as I'd like to, we better not head down that path. I'm pretty sure we wouldn't get too far before the philosophy police put the thread behind bars.
    It's a little deviation from the OP's initial question, but maybe it would be enlightening if we asked for the professionals here to give us they're best arguments against the classical (if outdated) Copenhagen role of consciousness.

    I should add... "It's not necessary" with regard to quantum theory formalism isn't really an argument for or against.
     
    Last edited: Apr 6, 2016
  15. Apr 6, 2016 #14
    See my post here: https://www.physicsforums.com/threads/decoherence-clarification.828712/page-11#post-5434769 as well as page 241 of "Modern Physics and Ancient Faith" by Stephen M. Barr (publisher: University of Notre Dame Press).
     
  16. Apr 6, 2016 #15

    bhobba

    Staff: Mentor

    A lot of water has passed under the bridge since Pauli's and other early pioneers time. Their views are now of rather dubious value. Conciousness, psyche, whatever you want to call such philosophical musings 100% for sure is no longer required - if ever it was.

    Thanks
    Bill
     
  17. Apr 6, 2016 #16

    bhobba

    Staff: Mentor

    Copenhagen never had any role for conciousness - it was introduced by the great polymath Von Neumann in his classical mathematical foundations of QM where QM was presented with full mathematical rigour for the first time - Dirac's approach used math that wasn't rigorously developed then - it now is. It was introduced for reasons not relevant these days with our current understanding of decoherence. The issue with Copenhagen is it was a theory about observations that appeared here in the classical world. The problem is, and this is the rock bottom essence of the difficulty with QM - not conciousness, particles being in two places at once etc etc - how does a theory that assumes a classical world from the start explain that world? Great progress has been made in resolving it, and more modern interceptions like Consistent Histories avoid it, but some issues still remain and research is ongoing.

    Thanks
    Bill
     
  18. Apr 7, 2016 #17
    “Natural science, does not simply describe and explain nature; it is part of the interplay between nature and ourselves.”
    Werner Heisenberg


    Therefore, as long as consciousness is considered beside the point, any explanation of the world is also entirely beside the point; - and what remains is, Shut up and calculate...
     
    Last edited: Apr 7, 2016
  19. Apr 7, 2016 #18

    bhobba

    Staff: Mentor

    I think you need to stick to context. The context here is if its involved in QM observation - not that theories are the creation of concious beings.

    Thanks
    Bill
     
  20. Apr 7, 2016 #19
    Well, since modern QM observations are performed by computers, you may well say nowadays consciousness is not involved. But, then, you must be completely satisfied with the consistent histories approach and give up the goal of explaining the real world quantum-mechanically.
     
  21. Apr 7, 2016 #20

    bhobba

    Staff: Mentor

    It's got nothing to do with computers, although it brings the issue out clearly. May I suggest you think about it a bit more carefully, for example a double slit where the photographic plate is developed later. Before going any further, in your own worlds, why would you think conciousness is involved in what appears on the photographic plate when developed.

    I have issues with consistent histories (although I like the interpretation) but that is whole new thread. I hold to ignorance ensemble.

    Thanks
    Bill
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: A bit confused about Schrödinger's cat
  1. Schrödinger's cat (Replies: 33)

  2. Schrödinger's cat (Replies: 5)

  3. Schrödinger's cat? (Replies: 37)

  4. Schrödinger's cat (Replies: 21)

Loading...