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Quantum confusion

  1. Dec 25, 2010 #1
    I am confused by the philosophical assumptions behind Quantum Mechanics. Are physicists logical positivists? The reason I ask that is because it seems that they believe that if something in intrinsically unknowable it does not exist as a truthful proposition. For example before the collapse what is happening? Suppose, I have an impregnable box ( even logically necessarily impregnable) . I do not know if there is a brick ( particle) or water ( wave) inside. Does that mean that one possibility is not correct and the other is also not correct? I am totally confused! Please help!
  2. jcsd
  3. Dec 25, 2010 #2
    WHAT? Do you know what bricks and water are made of?
  4. Dec 25, 2010 #3
    It's a metaphor.* My point ( in using a concrete metaphor) is to see what the philosophical assumptions behind QM are. For example, if one asks," suppose one is on a photon, what would the universe look like?" It would not have anything to do with the speculation to say that no one can ride a photon.
    PS; Einstein pondered that absurd metaphor and it inspired Relativity.
    * Yes, matter ( bricks and water) are composed of quantum . But that totally misses the point.
  5. Dec 25, 2010 #4
    If I told you the philosophical assumptions of physics were intrinsically unknowable and provided a reasonable explanation why, would you continue to ask that question?

    I'll give the usual answer and then go on to provide a helpful answer and point you in the right direction to form your own philosophical assumption of physics.

    Physics does not delve into ideas that cannot be impirically evaluated and understood, so asking questions like

    Q: "what would it be like to be a photon?", "whats outside of the observable universe?", "whats is smaller than the smallest observable parts of the universe?" are asking for nothing but a speculative answer.
    A: "Because of time contraction, you would experience nothing and feel as if you had never existed", "pixies and pink dragons", "it's turtles all the way down"

    Pondering the absurd can be a useful tool of imagination, but it not part of the scientific process. It's inspiration for an idea.

    Your Schrodinger's box analogy is way off. The Schrodinger's box example is a tool used to explain the mathematical process of determining the probability of some quantum state. It is not some magical property of the universe which turns every sealed box and crate into a wave-particle limbo machine. Uncertainty arises from the physical contraints imposed by the methods used to probe properties of the smallest pieces of matter we know. To probe the small, we must prod it (using light, electrons, etc), and know approximately where the particle is. So we can either not look at it (box is closed) or look at it and not know it will be in the future (open box).
  6. Dec 25, 2010 #5


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    The most useful way to think of QM is not as a description of reality, but as a set of rules that tells us how to calculate probabilities of possible results of experiments.

    If "QM" refers to the theory defined by the standard Hilbert space axioms, then there's nothing in QM that tells us unambiguously what the system "is doing" at times between state preparation and measurement.

    The "interpretations of QM" are attempts to turn QM into a description of reality. The most straightforward way to do that is to simply add new axioms on top of the ones that define QM, in order to give us a picture of what "actually happens" without changing the theory's predictions. The fact that the predictions are unchanged means that these interpretations are unfalsifiable, so they are strictly speaking not a part of science.

    Another approach, which is also considered to be a part of "interpretations of QM", is to find another theory, that makes the same predictions but is defined by a different set of axioms, and see if it suggests a different picture of what "actually happens". A good example is de Broglie-Bohm pilot wave theory.
    Last edited: Dec 25, 2010
  7. Dec 25, 2010 #6


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    Hi Wittgenstein! Not Ludwig I presume? :smile:

    Fredrik’s & geophysics10’s explanations are excellent, but in case you didn’t get it, here’s my "version":

    1) QM is without competition the most precise theory we have. Mathematically, it works perfect, period.

    2) When trying to "translate" the mathematics of QM to human language, we run into different paradoxes. This has in turn created a set of Interpretations of quantum mechanics. All interpretations uses exactly the same mathematics, but have different explanations for what’s "going on" in nature.

    I think your "impregnable box" is a "confused" version of Schrödinger's cat. Erwin Schrödinger made this paradox – of a cat being both alive and dead at the same time – to show that something was wrong with the Copenhagen interpretation (Niels Bohr, Werner Heisenberg, et al.)

    We know that a cat can’t be both alive and dead at the same time. It’s stupid, right?


    Niels Bohr’s answer to the paradox was that we don’t need an observer (human) to make the collapse of the wave function (cat = alive/dead). A measurement alone, by a Geiger counter, is sufficient to collapse a quantum wave function before there is any conscious observation of the measurement.

    Today, we know for sure that QM particles, like photons and electrons, indeed can be both "alive & dead", in a superposition of states before measurement. This is a fact.

    Now, we all know that a cat is only "made of" trillions of QM particles, right? So what happens if we manage to "screen off" the macroscopic cat to the same level as the microscopic electron? Could the cat be in a "superposition of states" as well??

    I think that many contemporary professors would say it could...

    Personally, I have absolutely no idea. All I know is that it’s very interesting to learn and follow the development of QM. Who knows... some day it might be possible to go to the pet shop and buy a Norwegian Blue parrot that is both dead and alive!! :smile:
  8. Dec 25, 2010 #7
    I don't even know what this means. Please enroll in a Modern Physics course before trying to 'uncover' the meaning of Quantum Mechanics.
  9. Dec 26, 2010 #8
    And you sir should take a course in civilized discourse and stop name calling like a 12 year old. Also, you cannot understand that sentence? Good grief! Its fairly basic. It's that fundamentally, when you break things down , everything is made of quantum particles and or waves.
    See this site to refresh your education
    Anyway, enough with the troll. Thanks for everyone elses responses. Informative, but unfortunately disappointing. It seems to me that you are all saying that physics ( at least QM physics) is not about describing reality, its about experimental results. My impregnable box analogy was based on the Schrodinger's cat paradox. And yes, I understand the basic principle of Heisenberg's uncertainty , that the photon ( or whatever particle is used) disrupts the object and so that therefore one can only obtain position OR momentum. My point was that I wanted to see if physicists are actually claiming that before collapse the state is not a particle or a wave. From what you all have been saying it seems that it is one or the other, its just that we do not know.And it is impossible to know and so therefore the question ( what is it) is meaningless for a physicist. Like I said that's logical positivism.
    PS Yes my computer name is in honor of the famous philosopher.
  10. Dec 26, 2010 #9
    No, physicists are not necessarily logical positivists.

    Physics doesn't make metaphysical assumptions anymore than my auto mechanic. So long as they both produce results everyone is happy and no one bothers to ask their auto mechanic what his metaphysical beliefs might be.
  11. Dec 26, 2010 #10
    That is what a logical positivist is. One that does not believe in metaphysics. One must remember that in this context "metaphysics" is not about anything new age or whatever. For example the belief that there is an objective reality separate from our personal subjective reality is a metaphysical belief. The opposite belief solipsism is also a metaphysical belief.
  12. Dec 26, 2010 #11
    One of Einstein's objections ( and the most pertinent one for this thread) to QM is that many of its advocates are logical positivists. Einstein did not just give equations that could be experimentally verified he provided a description ( in this sense Einstein was metaphysical , see above post). For example gravity is curved space-time.* The interesting thing is that in academic philosophy logical positivism is considered the only belief system that self destructed. It is based on the rejection of metaphysics ( an over all description of reality) and yet its basic premise is metaphysical!
    * Einstein's genius was to approach a problem by visualizing a thought experiment. For example Relativity is the result of his visualizing and speculating about what the universe would look like if one rode a photon. Of course Einstein knew that that was impossible and to make that objection is nonsense.
  13. Dec 26, 2010 #12
    But, you said:
    That word, by itself, has no meaning. Unless you make sense, you can't expect for people to have a meaningful discussion with you.
  14. Dec 26, 2010 #13
    So if I said,"Yes, matter ( bricks and water) are composed of atoms." You would find that sentence too confusing to understand?
  15. Dec 26, 2010 #14
    Seriously Dickfore I have no hatred for you. I just think that this petty path you seem to want us to take is boring. Lets talk about the subject, which I at least find more interesting than if one or the other of us is an idiot. I can speak for myself and say that I am pretty sure I am not an idiot. And I am willing to bet that you are not an idiot also.
  16. Dec 26, 2010 #15


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    That too makes no sense.

    An electron is a "matter". Yet, do you think it is "composed of atoms"?

    I think you've made an oversimplification of physics, especially quantum mechanics. That is what is causing so much confusion with your question. You may not think it is confusing. But I can certainly tell you that if you have learned QM, your question borders on nonsensical. "everything is quantum" doesn't say anything meaningful, whether you like it or not.

    Before you can make any kind of "philosophical" discussion of something in physics, it is imperative that you actually understands that part of physics that you want to talk about. This means it has to go beyond just a superficial understanding of what it is. If not, we get into something like this, where the starting point or the object of the discussion is lost due to confusing understanding of it.

  17. Dec 26, 2010 #16


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    Hi W. I’m no expert on logical positivism but it seems to me the intent is not that physical things have a single, specific existence (such as a single, specific position and momentum) or that events have a single, specific occurrence (such as Schrödinger’s cat being either alive or dead). From the definitions of logical positivism I'm looking it, it only says that physical things and events must be verifiable as being true, false or meaningless. So a photon passing through a diffraction grating for example, may not have a defined position, and that’s ok (as far as I can tell) from a logical positivist perspective. Logical positivism (as far as I can tell) only requires there be some ability to form a true/false meaning when we talk about such things. It doesn’t seem to require that we have an ability to form a definitive mental representation of something. Like I said, I'm no expert on it, but having read through a few articles, that's the impression I get.
    lol That's one of my favorite MP skits.
  18. Dec 26, 2010 #17
    "An electron is a "matter". Yet, do you think it is "composed of atoms"?"
    ???????????? When did I say that? Good grief! If you have that much of a misunderstanding of what I said no wonder you have no clue as to what I said.
    Here, I'll make it simple. If I said " All dogs are composed of cells" and then I said," all dogs are composed of atoms" I am not saying,or even implying," all atoms are composed of cells."
  19. Dec 26, 2010 #18
    But you didn't say that, did you?
  20. Dec 26, 2010 #19
    Good grief! I cannot believe I am having this discussion. For some reason if I said ( here I'll make it even simpler) "Bricks are made of atoms." One of you would say "that is stupid , electrons are not composed of atoms."
    How am I supposed to respond to that? It is so obviously a misunderstanding that any explanation would be like saying 1+1=2 and that would only be insulting.
  21. Dec 26, 2010 #20
    Do you know what 'matter' means?
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