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Another explanation of that poor, poor cat

  1. YES! I love it!

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  1. Oct 12, 2003 #1
    Heisenberg's Uncertainty Principle/Schrodinger's Cat
    Couples engaged in a romantic relationship usually have large amounts of physical contact with one another. However, when someone seems near, physically, to them, they begin acting normally again, even if blushing a bit. We therefore see that the couple has a probability wave function associated with them. Whenever an observer goes to see what they're doing, their wave function collapses and becomes a stable state. This is exactly the same concept that is illustrated in the Schrodinger's cat thought experiment. In this case, a cat is placed in a box along with a Geiger counter, a bottle of poisonous gas hooked up to the Geiger counter, and a radioactive particle source. If the source decays and triggers the counter, the poison is released and the cat dies. However, if the source doesn't decay, the cat lives. This is only a thought experiment, and no cats have ever been killed in one of these experiments. However, be that as it may, you have to open the box to see if the cat is still alive. If you do this, however, you collapse the probability waveform into one of two states: either the cat is alive or dead. While the box remains closed, the cat could be either alive or dead, but once opened, the cat has to choose a state. Just the same, the couple in question may or may not be making out, but when approached, they either will or will not be doing so.
     
  2. jcsd
  3. Oct 13, 2003 #2

    jcsd

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    Haven't you heard of a little thing called 'decoherence'?
     
  4. Oct 13, 2003 #3
    no...

    i haven't.
    what is it?
     
  5. Oct 13, 2003 #4

    jcsd

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    Decohernce shows why large systems exhibit classical rather than quantum behaviour shwing that a) Schroedinger's cat while an intersting thought experiment is one that could never be performed as the wave function in the box would decohere in a fraction of a second and b) that your kissing couople can only be treated classically.
     
  6. Oct 13, 2003 #5

    chroot

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    A quantum system is very delicate. A system that is in a superposition of states will collapse into a stationary state on its first interaction with the outside world. That means it takes only one little photon, or one happenstance atom to come nearby and disrupt the system and collapse its wavefunction.

    It's hard enough to isolate a microscopic object from other objects to observe its quantum properties. It's absolutely impossible to isolate a macroscopic object.

    The common example is a playing card. If you balance a perfect playing card very precisely, exactly on its edge, it should actually fall to both the left and right simultaneously. The reason it doesn't, of course, is that there are billions of jiggling atoms inside it, all "measuring" the others, and there are air molecules and photons of heat radiation and so on all interacting with it from the external world. The action of all this is called "decoherence." The reason we don't observe quantum phernomena macroscopically is because it's impossible to isolate a macroscopic system well enough to protect its fragile wavefunction.

    The only way to get macroscopic quantum behavior is at very low temperatures, where the thermal jiggling and radiation are diminished. Low temperature liquid helium, for example, becomes superfluid -- a sort of macroscopic quantum playground with billions of atoms all in the same quantum state, moving together without viscosity. Superconductors are another macroscopic quantum playground, but the slides are different colors.

    - Warren
     
  7. Oct 13, 2003 #6

    LURCH

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    This is the part of the experiment where I always get hung up. The generally accepted proerties of gravitation include the traits of being impervious to interveening matter (cannot be blocked) and unlimited range. So it would seem that, through gravitation, every quantum system is in constant interaction with outside world. There is never a time when the unstable isatope is not being "observed" or "measured", is there?
     
  8. Oct 13, 2003 #7

    chroot

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    Well, gravitation is not part of the standard model. ;) It's a good question, one I'll have to think about.

    - Warren
     
  9. Oct 13, 2003 #8

    jcsd

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    Roger Penrose has speculated that quantum gravity may indeed cause the collapse of the wavefunction when a macroscopic system is in a delocalized state, which could provide a mechanism for GRW theory (spontaneous collapse), but importantly as chroot says gravity doesn't have a palce in the standard model yet, so it's just speculation.
     
  10. Oct 13, 2003 #9
    erm...

    first of all, the idea was just to show what a probability waveform was all about.

    secondly, and more importantly, if gravity affects all systems, then why is it that even at the smallest levels, quantum phenomena still occur? wouldn't they be influenced enough by gravity to not occur?
     
  11. Oct 14, 2003 #10
    That's what I was just wondering as I read this thread, it never occured to me that it doesn't make sense for gravity to not be included in the list of things that'll destroy a wave function. I may not be able to sleep over this!
     
  12. Oct 14, 2003 #11

    jcsd

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    Re: erm...

    It's unknown, but here's some wild speculation on my part, perhaps the gravity of microsco[ic system is so small that it's indistinguishable from quantum fluctuations.
     
  13. Oct 15, 2003 #12
    Isn't the dead cat just an explanation to show that on such scales we can't know for sure so must assume both are true, basically that proabilities are fundamental to QM at these scales? If so it still seems a very roundabout way to say we can't know so must assume both.
     
  14. Oct 15, 2003 #13

    jcsd

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    It's just a thought experiment, the conclusion that the cat can be in a supposition of states is rejected.
     
  15. Oct 15, 2003 #14
    Re: erm...

    Correct.

    Of course the cat is dead or alive. It's only the human measuring problem.
    Uncertainty in relation to measuring is OK (there are many manufacturing limits related to machinery limits and material limits when you make for example tennis-racquets) , but making from that measuring-problem a general projection on "concepts" is quiet questionable. These are different things.
    It's like saying as an tennis-racquet inventor to the tennis manufacture: This is the concept design in general but I don't know exactly how you must fix the strings 10 to 15 to that part of the tennis frame ... so please start production and finish it ... and start to deliver to Nike".

    Some months ago Osher (postings a reaction on superstringtheory.com) pointed out that : "There are two meaning of Uncertainty, (1) error, like x2 - x1 or dx, and (2) standard deviation or its square variance which is the only technically correct definition used by mathematical probability and statistics people. Error itself is replaced by standard deviation precisely because it is so fluctuating (negatively and positively) that it often cancels itself out or else overexaggerates in random directions, but standard deviation isn't a major tool for engineering or for that matter for physical laws because most physical laws relate VARIABLES (even RANDOM VARIABLES) rather than their statistical population standard deviations or population means. Einstein, Schrodinger, Bohr, Heisenberg, all made the mistake of not understanding that."

    Maybe it's better to rename Quantum Mechanics to Qualm Mechanics.
     
  16. Oct 15, 2003 #15

    chroot

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    Actually, pelastration, quantum uncertainty has nothing to do with our limited measurement technology. This is one of the most common misunderstandings. It's not that we just can't build a good enough measuring device -- it's that no such device can exist.

    - Warren
     
  17. Oct 15, 2003 #16
    I am convinced now that this thought experiment was originated by someone trying desperately to explain basic probability theory applied to QM in such an elaborate and indirect "thought experiment" kind of way that it has led to more confusion and been confusing me for some time and if the cat isn't dead yet I would like to kill it at this point.
     
  18. Oct 15, 2003 #17

    marcus

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    recent paper about the cat

    http://arxiv.org/gr-qc/0306007

    "Schroedinger's Cat and the Clock: Lessons for Quantum Gravity"

    a short paper with some original ideas by Robert Oeckl, a post-doc working with Carlo Rovelli

    as I recall Oeckl did his doctorate in Non-commutative Geometry with Shawn Majid in the UK, has now wandered over into Loop Gravity.

    the cat has some meaningful connection to time and to gravity

    what Oeckl says may relate to what was being discussed here
     
  19. Oct 15, 2003 #18

    jcsd

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    Also pelastration, the measurment problem is not the same thing as uncertainty, the measurment problem is the problem in QM that a measurment isn't a mathematically defined concept.
     
  20. Oct 15, 2003 #19
    Thanks Croot,

    the problem is that from a measuring problem a world/reality image is created that is based on super-position. Super-position is anti-unity as a concept. From the top there is causality, hierachy, ... not anarchy. The start maybe chaotic but the further developments - on the brane - were historical consequent. Uncertainty only exists is the human ignorance and the lack of logic explanation.
     
  21. Oct 15, 2003 #20

    chroot

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    Umm.. I'm pretty certain you've just gone off the scientific radar now. Good luck.

    - Warren
     
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