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

Applying Schrodinger's Cat Experiment

  1. Jan 4, 2013 #1
    I know that Schrodinger's Cat experiment is a thought experiment, but why not apply it and see if sound waves are impacted by quantum uncertainty. If the cat, or any other animal dies you can make it sound off by a heart rate monitor or something else. Would this act remove the uncertainty aspect of the experiment?
     
  2. jcsd
  3. Jan 4, 2013 #2

    Bill_K

    User Avatar
    Science Advisor

    Schrodinger's Cat requires that the cat must be completely isolated from the outside. That means you can't listen for the cat to meow, weigh the box, shake it, monitor its temperature, etc.
     
  4. Jan 4, 2013 #3

    jtbell

    User Avatar

    Staff: Mentor

    i.e. it has to be in a vacuum (which would use up some of its nine lives :smile:)

    which (the cat being in a vacuum) could reveal itself only via radiation. To prevent radiation, the cat would have to be at absolute zero, which means using up the rest of its lives. :biggrin:
     
  5. Jan 4, 2013 #4
    So uncertainty is dictated by observation as in the double slit experiment. Is that what I am understanding? Only observation after the fact determines the actual result?
     
  6. Jan 4, 2013 #5
    Would this not mean that you have to place the cat into a position of uncertainty, a position where the experimenter must be uncertain whether or not the cat is alive or dead in order for the cat to be "said" to be both dead and alive? That would seem to imply that it is not the decay of the radioactive atom that produces the results of the experiment, but it is the experimenter.

    Taking this back to the double slit experiment, this conclusion would also seem to imply that it is not the electron beam which produces the interference pattern, but the experimenter, who, in order to produce the interference pattern, must not be able to "measure" the "electrons" passing through the two slits.

    In other words, could we not say that it is the experimenter's uncertainty that produces the superposition of states (dead and alive; interference pattern), rather than the subjects of the experiment (the radioactive atom/cat; the electron beam)?
     
  7. Jan 4, 2013 #6

    DrChinese

    User Avatar
    Science Advisor
    Gold Member

    Welcome to PhysicsForums, markb287!

    In a sense, that is correct. The experimenter creates what is sometimes called a measurement (or observation) context. That context, when properly arranged, creates a situation in which the superposition can exist. For a double slit experiment, that means a context where the which-slit information is obscured to get the interference pattern.

    In essence, the number of target outcomes (relative to some source) is somehow restricted, controlled or funneled. Other outcomes are then ignored.
     
  8. Jan 4, 2013 #7
    Thank you, DrChinese, for your response and welcome!

    Going further, could we not also say that electrons (or protons, neutrons, photons, etc.) are neither particles nor waves, but are simply, for lack of better words, "quantum stuff" or "subatomic stuff" that, when placed in situations of relative certainty (e.g. turning on the light to observe which slit they went through), produce results consistent with what we can describe as particle behavior, and that, when placed in situations of uncertainty (e.g. we turn off the light), produce results consistent with what we can describe as wave behavior?

    In other words, can we say that electrons only act as particles when placed in situations of relative certainty and only act as waves when placed in situations of uncertainty?

    I apologize if my questions sound very picky, repetitive, or haven't taken the conclusion very far. I just want to be as concise as possible because I think it is the language behind quantum mechanics that makes the subject even more difficult to understand than it already is.
     
  9. Jan 4, 2013 #8

    BruceW

    User Avatar
    Homework Helper

    Yeah. The principle is that the state is not originally in an eigenstate of the quantity we are measuring, so when we make a measurement, the state changes (with some probability) to one of the eigenstates associated with the observable quantity.

    Whether the same principles of quantum mechanics applies to dead or alive cats is still untested. But also, it has not been disproven. But also, it would be very difficult to make an experiment that actually puts a cat into a pure quantum state which is not an eigenstate of "dead or alive".
     
  10. Jan 4, 2013 #9

    DrChinese

    User Avatar
    Science Advisor
    Gold Member

    Sure, fine descriptions!

    However, usually one says a quantum object is like a particle when it's position is relatively certain but it's momentum is not. And vice versa for a wave, uncertain position and more certain momentum.
     
  11. Jan 4, 2013 #10
    I see. So let me modify my statement:

    Electrons (or any quantum object) exhibit particle behavior when they are in a situation where their position is relatively certain, but their momentum is not; and they exhibit wave behavior when their momentum is relatively certain, but their position is not.

    The main point behind this is that quantum objects are neither particles nor waves, but are simply phenomena that exhibit particle or wave behavior according to the experimenter's degree of measurable certainty. In other words, their behavior is dependent upon the experimenter's uncertainty in some aspect (position or momentum).

    In addition, as per Bohr's Complementarity Principle as well as Heisenberg's Uncertainty Principle, an electron cannot exhibit particle behavior and wave behavior at the same time. Rather, the behavior is mutually exclusive, dependent on the type of experiment you conduct (relative certainty in measuring position requires uncertainty in measuring momentum, and vice versa).

    So let's return back to the double slit experiment/Schrodinger's Cat experiment. If we place the electron beam (or the cat) in a position of uncertainty with regards to its position or state (i.e. turn the light off; isolate the cat), so that we cannot measure its position or state, thereby producing wave behavior as well as excluding the possibility of producing particle behavior, what point is there in interpreting the interference pattern or superposition as a probability of the electron's arrival or the cat's state? Wouldn't the term "probability" be a misnomer, since the electron (or the cat) doesn't express a position (particle behavior) when placed in a position of uncertainty, since the behavior of positionality cannot be produced?

    It would seem to me that since the electron's position is held in a position of uncertainty, the electron doesn't express positionality. And it is this uncertainty with regards to positionality that actually produces the interference pattern.

    In other words, there is no "probability of the electron's arrival" because the electron doesn't express an arrival (i.e. its arrival is not being measured). The only value expressed is the momentum of the electron beam, to the degree to which it can be measured by the backdrop.

    Unless, of course, the backdrop re-establishes relative certainty with respect to the electron's position. Would this be the case? If not, the question as to what the wave function actually represents is, I believe, still left unanswered by quantum mechanics.
     
  12. Jan 5, 2013 #11

    mfb

    User Avatar
    2017 Award

    Staff: Mentor

    If you could isolate/freeze/... the cat sufficient to get a superposition of two different cat states, you could do interference experiments with cats. You have to describe it as superposition and not as probabilities of (cat lives) and (cat is dead).

    While position and momentum uncertainty have some relation to particle-like and wave-like behavior, they are not the same.
     
  13. Jan 5, 2013 #12
    You are right. Position is not the same as particle-behavior, nor is momentum wave-like behavior. However, the act of measuring the position of a quantum object produces particle-behavior in that object, just as the act of measuring the momentum of a quantum object produces wave-behavior. When you use an apparatus to see if the electron is passing through slit A or slit B, you are treating the electron as a particle, which it ends up acting as (i.e. you can tell whether or not it passed through slit A or slit B).

    However, it only acts this way when you treat it like a particle. If you don't, then it produces an interference pattern, acting as a wave. My argument is that the probabilistic interpretation, which reads the interference pattern as a probability of the electron's arrival on the backdrop, is not adequate, since an electron cannot be said to have an "arrival" -- i.e. since its positionality depends upon our ability to measure it.

    It simply "appears" on the backdrop as the backdrop measures its position.
     
  14. Jan 5, 2013 #13

    mfb

    User Avatar
    2017 Award

    Staff: Mentor

    If you measure the slit (but not the precise position in the slit), you still get interference: single-slit interference. It is not "particle OR wave", you always have both.

    There is some time where the electron arrived in every interpretation.
     
  15. Jan 5, 2013 #14

    dlgoff

    User Avatar
    Science Advisor
    Gold Member

    OMG :rofl:

    I'd love the those interference patterns on a screen. :bugeye:
     
  16. Jan 6, 2013 #15
    You are right -- it is not "particle OR wave." However, it is producing particle-behavior OR producing wave-behavior. You cannot produce both particle results AND wave results at the same time. This is inherent in both the Principle of Complementarity and the Principle of Uncertainty.

    This is because physicists still are relying on the idea of electron as particle. Even the Born interpretation does this. But there's no sense in talking about an electron "arriving" at the screen when its position -- between the time we stop measuring and the time it appears on the screen -- is fundamentally uncertain. Uncertainty is a state of existence that we can produce experimentally, and it is our job not to "deal" with the state of uncertainty by using probabilities, but to understand it.
     
  17. Jan 6, 2013 #16

    mfb

    User Avatar
    2017 Award

    Staff: Mentor

    No, it is just a language thing. No physical law has "particle" or "wave" in its formulas.

    You can consider the time when the wave, probability distribution or whatever arrived, it does not matter. They are just models, using different words to describe the same experimental result.
     
  18. Jan 6, 2013 #17
    That's because no physical law has "formulas." The formulas are "just a language thing" also.

    The issue is not whether the models describe the same experimental results. I could provide many different models that describe the results of any experiment. The issue is whether or not the model helps produce a better understanding of the results. That's the whole game of science.
     
  19. Jan 6, 2013 #18

    mfb

    User Avatar
    2017 Award

    Staff: Mentor

    Formulas require interpretation, too, but they are way better than english (or any other spoken language). Their language is mathematics, this avoids ambiguity.

    If they have a similar complexity (easier=better of course) and applicability range as to the current ones: Publish them.
     
  20. Jan 6, 2013 #19
    Mathematics, on its own, cannot avoid ambiguity; it is only the context of the communication that can do that. If we don't have the same context for understanding the communication (e.g. that electrons are neither particles nor waves; that electrons do not "arrive" at the screen, and therefore do not express a probability of arrival when they are not measured, etc.), then we will be misunderstanding each other or the results.

    To publish them requires actually having ideas, which I don't (I have only suspicions and hypotheses, but nothing even close to being publishable). I simply wish to establish for my own understanding what it is that we can reasonably conclude from the experimental results of the double-slit experiment in order to establish what is possible or not possible to interpret.
     
    Last edited: Jan 6, 2013
  21. Jan 6, 2013 #20

    mfb

    User Avatar
    2017 Award

    Staff: Mentor

    Well, let me phrase it differently: mathematics allows to communicate without ambiguity.

    This can happen if you do not use mathematics.

    In other words, you do not have new good models.
    Finding good models is a hard part of science. And if you include the relation between models and experimental results, it is the interesting part of science.

    See interpretations of quantum mechanics.
     
  22. Jan 6, 2013 #21
    I doubt that. If that were the case, the Born interpretation would have satisfied quantum physicists all on its own. And yet it is a continual problem for physicists and was ever since it was proposed, although the mathematics is all there. This was the case when Heisenberg had developed matrix mechanics to describe quantum phenomena, and when Schrodinger had come up with wave mechanics to do the same. Both had problems knowing how to "interpret" the mathematics -- i.e. to find the right context for understanding the phenomena.

    Again, the only way we can get out of that problem is if there is a specific context for understanding the mathematics, and this context must be, by nature, non-mathematical (and non-linguistic, to be exact).

    Of course, this is not to say that mathematics is not helpful (it's extremely helpful), but on its own it cannot allow for unambiguous communication.

    I agree completely. But my goal in posting right now is not to establish a model, but, as I just said, to establish what could be usable for a new model, since I'm arguing that the "standard" model is not adequate.

    Again, I have read interpretations of quantum mechanics, and none of them seem to me to be adequate, unless there is something that I'm missing.

    If so, please illuminate for me.
     
  23. Jan 6, 2013 #22

    mfb

    User Avatar
    2017 Award

    Staff: Mentor

    Careful, you are mixing theory and interpretation here. Quantum mechanics is a theory - it is extremely successful, and its results are not ambiguous. Interpretations of quantum mechanics are different - but you do not need them, "shut up and calculate" (with Born rule, not interpretation) works.

    Well, if that would be known, we would have an alternative to QM, I think.

    All of them can be used to do science. They all have some parts which are not intuitive, or parts with unclear mechanisms, but they all work and give correct results.
     
  24. Jan 6, 2013 #23
    I think we have two different "interpretations" for the term "interpretation." An interpretation is simply a statement that expresses some kind of understanding regarding some aspect of something (in this case, nature). It's something you express in order to produce an understanding of some event or phenomena. Interpretations can be proven or unproven.

    A scientific theory is quite simply a set of propositions that describe certain aspects of nature and whose truthfulness can be demonstrated experimentally. A proposition (in the context of science) is a declarative statement that expresses a specific interpretation of nature.

    So a scientific theory is a type of interpretation. And if a scientific theory doesn't produce a strong enough understanding of some phenomena of nature, then it is not an adequate interpretation, regardless of whether or not it is able to produce reliable experimental results. Newton's theory of gravitation, for example, is able to produce accurate results, but that doesn't mean it was an accurate theory. Accuracy is not simply dependent upon results, but upon understanding. In this way, the probability theory of quantum mechanics is an interpretation. My argument is that it is not an adequate one.

    Now, the imperative, "Shut and calculate," is not a theory. It has nothing to do with the theory itself, but with how we should "treat" the theory (i.e. to let it go). Someone could have just as easily told Einstein to "shut and calculate" when it came to discrepancies in Newtonian physics. But that has nothing to do with Newtonian physics itself.
     
  25. Jan 6, 2013 #24

    BruceW

    User Avatar
    Homework Helper

    I agree with mfb. Mathematics is the least ambiguous part. With pure maths, we have very rigorous definitions and proofs. In physics, we have less rigorous definitions and proofs. (Which is why they are often called 'derivations' rather than strict mathematical proofs). The more we keep to the mathematical side, the more rigorous we stay.

    For example, a dirac delta function is a mathematical object. The mathematical formulae associated with it are unambiguous and rigorous. We could then associate it with the 'position' of a 'particle' in our theory. When we do this, there are going to be issues with interpretation, and what it actually is supposed to mean.

    Edit: I suppose I am saying that any physical theory has some element of interpretation, and that element is the non-mathematical part. I guess I am agreeing with both of you really. Since it seems mfb is taking 'theory' to mean the very core, most-mathematical part. And markb287 seems to be taking 'theory' in a broader sense.
     
    Last edited: Jan 6, 2013
  26. Jan 6, 2013 #25

    mfb

    User Avatar
    2017 Award

    Staff: Mentor

    There are no proofs in physics.
    I use "interpretation" as in interpretations of QM.

    You can fail to falsify a theory, but you cannot prove it - a (useful) theory can be used for an infinite set of predictions, and you cannot perform infinitely many experiments.

    There are probabilistic interpretations - and non-probabilistic ones.

    No, he could not - Einstein would have gotten wrong results. This quote has a special meaning in quantum mechanics, and its application is unique to QM, where interpretation (see first part) is not trivial. Newtonian gravity and SR/GR do not need a separate interpretations.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook