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Schrodinger's Cat

Discussion in 'Off Topic [BG]' started by nonsqtr, Apr 11, 2005.

  1. nonsqtr

    nonsqtr The emperor has no clothes!

    Aug 29, 2003
    Burbank CA USA
    Any quantum enthusiasts here? Are you familiar with the thought experiment involving "Schrodinger's Cat"?

    Basically, the idea is, you put a cat in a spaceship, along with some highly radioactive material. Let's say the spaceship returns to earth ten days later. During that time, there is a finite probability (say 50%), that the radiation has killed the cat.

    According to the quantum theory, the state of the cat (alive or dead) is indeterminate, until someone actually opens the spaceship door and takes a look. The cat is "both alive and dead" until the moment of observation.

    Is that the most ridiculous thing you've ever heard, or what?

    Discuss. :)
  2. If a tree falls in the forest...
  3. DaveDeVille

    DaveDeVille ... you talkin' to me ?? Supporting Member

    if you were to tie a piece of buttered toast to the back
    of that cat , then drop them both from the same height ,
    would the cat land on it's feet ??
    or would the toast land butter side down ?

    sorry , i just couldn't resist the chance to unravel
    your thread ....

    don't hurt me ...
  4. This reminds me of philosophy 1100. My prof named her cat Schroedinger. She also said that philosophy was like "A blind man trying to find a black cat in a dark room." What a lousy class. :spit:
  5. Perception and reality are separate.
  6. There have been proposals that claim that this is the source to infinite energy :p

    Anyways, Schrodinger's Cat is not really a thought experiment but rather used to describe how observation works in Quantum Theory.
  7. Phil Mastro

    Phil Mastro

    Nov 18, 2004
    wasn't the cat just in a box, and the dilemma being that when the box was closed, was the cat really inside or something?
    never figured out what it meant anyways... :rolleyes:
  8. tifa

    tifa Padawan Bassist

    Mar 8, 2005
    Blackburn, UK
    According to a certain author, a cat sealed inside a box will in fact exist as one of 3 states:

    -Absolutely Furious.

  9. secretdonkey


    Oct 9, 2002
    Austin, TX
    We had a cat we named "Shrodey." Luckily we were able to pawn him off on the inlaws, before I conducted any "experiments."
  10. secretdonkey


    Oct 9, 2002
    Austin, TX
    In other words, a bizarre way of saying, "don't count your chickens before they hatch?"
  11. Bruce Lindfield

    Bruce Lindfield Unprofessional TalkBass Contributor Gold Supporting Member


    Because that is not the "Schrodinger's Cat" experiment - this is about a single, radioactive particle, acting on a canister of cyanide - not a great lump of it!! :rolleyes:

  12. ^^^
    I'm no expert in any way, I've just done some hobby research so I'm not as good at explaining it as other people.
    It is pretty much impossible to make observations at quantum level without affecting what you are observing. Light is a good example. Basically, it behaves as both a particle and a wave might. Depending on how you observe the light you will either get the result that light is a particle or that light is a wave. So, Science has decided that it is both until we observe it.
  13. Bruce Lindfield

    Bruce Lindfield Unprofessional TalkBass Contributor Gold Supporting Member

    Here's a more accurate account of the "experiment" :

    "We place a living cat into a steel chamber, along with a device containing a vial of hydrocyanic acid. There is, in the chamber, a very small amount of a radioactive substance. If even a single atom of the substance decays during the test period, a relay mechanism will trip a hammer, which will, in turn, break the vial and kill the cat. The observer cannot know whether or not an atom of the substance has decayed, and consequently, cannot know whether the vial has been broken, the hydrocyanic acid released, and the cat killed. Since we cannot know, the cat is both dead and alive according to quantum law, in a superposition of states. It is only when we break open the box and learn the condition of the cat that the superposition is lost, and the cat becomes one or the other (dead or alive). This situation is sometimes called quantum indeterminacy or the observer's paradox: the observation or measurement itself affects an outcome, so that it can never be known what the outcome would have been if it were not observed. "

    This happens because the isotope decay/non-decay creates a quantum probability wave. This is related to Heisenberg's uncertainty principle, which says that the position of any sub-atomic particle cannot be measured precisely, the best one can get is a probability wave function of its position. In other words an approximation to it's position. This happens because sub-atomic particles can be in two "states" at once. This is called superposition. For example, it can be in two locations, or in the same location but can be spinning in opposite directions at the same time. In fact it can be in many states at the same time. Heisenburg proved that this was true and not a contradiction.1 He also showed that the particle falls into one of its possible states only when it is measured, eg looked at. Thus, before measurement the particle's position cannot be described easily. The solution to this was the probability wave function, which describes every possible location and "spin" of the particle, along with a probability that the particle will be in that location.

    The probability wave function for the isotope says it is decayed and non-decayed, because of the 50/50 chance, and that both waves exist at the same moment, and only when you open the box and look in, does one wave collapse (it is reduced to a probability of zero) and the other become established as the result. This means that the cat also has a quantum probability wave (although scientists argue whether it has it's own wave of simply shares the isotope's one), which means that the cat exists as a dead cat and a living breathing cat, at the same time.

    It is a paradox!
  14. srxplayer


    May 19, 2004
    Highland, CA

    Is it wheat toast or white toast? I think it will make a difference...or not.
  15. Dan1099

    Dan1099 Dumbing My Process Down

    Aug 7, 2004
    The more quantum physics you study, the more this kind of backwards thinking makes sense. They arent REALLY saying that the cat is both alive AND dead, they are saying there is NO WAY you can know whether that cat is dead or not, so the only way to express its condition is a probabilty distrobution function which will express the likelihood that, at a given time, if you open the box, the cat will be alive. Thus, before opening the box, the cats life can only be expressed on a graph displaying its probability of being alive. To the observer, the cat is neither dead nor alive, and it won't be, until the box is opened.

    If you think this is twisted, start reading into the Twin paradox. :)
  16. BassyBill

    BassyBill The smooth moderator... Gold Supporting Member

    Mar 12, 2005
    West Midlands UK
  17. Geoff St. Germaine

    Geoff St. Germaine Commercial User

    I'm in grad school right now... had my last quantum course last semester so I guess I dabble in it a bit.

    So you need to have a state set up which is the superposition of a |decay> and a |not-decay>. Then that state hits the measuring device which breaks and not-breaks the vial and kills and not-kills the cat. Now the cat would be in the dead and alive state. When the observer opens the box, he sees either dead or alive not a superposition of the two. So the observer does the measuring in this case.

    Now the question is whether there is something else which can act as an observer and break the indeterminacy before the person opening the box, that is break the superposition state of |decay> + |not-decay> into either |decay> or |not-decay> and thus |decay>|dead> or |not-decay>|alive> but not the pure state |decay>|dead> + |not-decay>|alive> :ninja: .

    According to Schwabl Quantum Mechanics which I used for my grad QM class, the cat is linked to the other macroscopic objects which are influenced differently in the two final states such that their respective wave functions do not overlap. This means that you couldn't have a pure state that is |dead> + |alive>. The idea here is that the macroscopic apparatus consisting of the detector, hammer, actuator, vial, cat, etc is able to do measurements itself and doesn't require and outside observer.

    There could be more conjecture on this, I really don't know that much about it.
  18. Geoff St. Germaine

    Geoff St. Germaine Commercial User

    The twin paradox is actually pretty easy and obviously not a paradox. It is great example to introduce people to special relativity though.
  19. Bruce Lindfield

    Bruce Lindfield Unprofessional TalkBass Contributor Gold Supporting Member

    I think people (don't know how well-known he is outside UK) should be aware though, that Paul Merton is a comedian!! :D
  20. Toasted


    May 26, 2003
    Leeds, UK
    I think the problem is more easily philosophically approached than with quantum physics.

    My current favourite problem is that to be an atheist, you have to both believe in god, and dis-believe god.