Wave Function Collapse

Discussion in 'Physics & Math' started by Neverfly, May 22, 2012.

  1. Neverfly Banned Banned

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    Farsight, I have a couple of questions for you...

    Do you believe that Q.M. is just a statistical approximation to a deeper reality which is deterministic?
    What do you think of Bells Theorem?
     
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  3. Farsight

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    You might not care but I'm afraid I do, pryzk. Schrödinger did propose his cat to demonstrate that the Copenhagen Interpretation was ridiculous, but it's nowadays used in the opposite sense. It's not a statement of what the physics community thinks, it's a criticism of the media.

    Noted. I do think things have changed recently though.

    Noted.

    We'll have to agree to differ on that.

    With respect we'll have to agree to differ on that too.

    See this?

    The “hidden variable” is a random variable ǫ, with values ±1 with equal probabilities. If ǫ = 1, the particle goes along the Stern-Gerlach axis a, and if ǫ = −1, it goes opposite to it."

    I've talked about Stern Gerlach previously. It goes to the heart of the problem, which is the nature of spin.

    I really don't think he does.

    Fair enough.

    And that's what's wrong with it. It's disconnected from reality.

    How about rotations do not commute?

    Don't. I'm criticising the media that you don't read.

    It's mystic bunk, przyk. It really irritates me that people take this seriously whilst insisting that spin is intrinsic and calling Joy Christian a crackpot.
     
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  5. Farsight

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    Yes re deeper reality. I'm not sure about the deterministic.

    If might quote wiki: Bell’s theorem states that the concept of local realism, favoured by Einstein[citation needed], yields predictions that disagree with those of quantum mechanical theory. I think it's a misguided assertion somewhat disconnected from reality but nevertheless related to the notion that particles are little local things instead of "extended entities".

    To appreciate what I mean by this, imagine an ocean wave. You might think of it as a bump of water a metre high and a metre long moving at a metre per second. But there's a lot more to it than that. Look under the surface and the wave motion continues down into the water. See this image. The wave isn't as local as you might think.

    While I'm at it I ought to mention that I take the view that all particles are waves. That's why you can diffract an electron. Its electromagnetic field is part of what it is.
     
    Last edited: May 23, 2012
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  7. Neverfly Banned Banned

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    Then one last question...

    I am going to make an assumption. This assumption is based on the very little that I know- and a very small portion of what I have seen from you in a very short amount of time.

    I assume that you think we cannot practically make measurements at the quantum level at this time. That there are deeper fundamentals at work- a deeper level as Einstein thought.
    Since we cannot observe this directly, we have had to go about it indirectly. And in such was an absurdity in our descriptions. But no matter how Einstein and Bohr and Dirac and all the Greats approached this problem- they could not eliminate that absurdity.

    Then we have these... strings. A stringy universe with 1 dimensional electrons... Talk about absurd!
    But it's not done yet- it really does get worse with MWI.

    Imagine Einstein, who preferred the Marble, staring at the Wood in chagrin.
    What would he say to find out that wood had been fashioned into 1-D guitars!
    And using his General Relativity, at that?

    It is an absurdity of epic proportions. Dunno about you but... I don't like the absurdity, either.

    Which leads us to my last question...

    There's some history here and it's apparently not unusual for it to spill out into threads. History almost always demands confrontation. But maybe not the kind one might expect- but of oneself, too.

    Can you come up with a better absurdity to describe a deeper level that you cannot observe or can you cope with some absurdity?
     
  8. przyk squishy Valued Senior Member

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    Fair enough, though there's so much noise in the media I that I don't see why you'd be especially concerned with pop science.

    Disagree based on what? You can derive the possibility of doing weak measurements from standard quantum theory. That makes it consistent with any interpretation of quantum theory, Copenhagen included.

    What about it? The model you described won't permit the violation of a Bell inequality.

    That guy does an excellent job explaining what's wrong with Joy Christian's whole approach. You might like to read the last few posts by both participants in the thread.

    Here's the problem in a nutshell: in a Bell experiment, an experimenter (or pair of experimenters) is supposed to perform the experiment and measure certain event statistics. From those measured statistics, the experimenter is supposed to calculate the value of a certain correlator (e.g. CHSH) and see whether it's more or less than 2. So a physical theory should predict the thing that is actually measured (the event statistics), and only then should a theoretical expectation value for the correlator be calculated.

    What Christian does is completely bypass predicting the actual measured quantity (the detection statistics) and skips straight to predicting the correlator. He treats the correlator as if it were a fundamental quantity, as if the experimenter just pushed a button and a value for the correlator magically popped out, when it's not. The way Christian introduces his Clifford variables does not correspond to the way the experimenter performs their calculation. That makes Christian's result irrelevant to every actual Bell experiment ever performed. That's why it's actually Joy Christian himself who is disconnected from reality.

    Nothing could be farther from the truth. In fact, it would defeat the whole purpose of Bell's theorem if it tied itself down to technical details of any experiment. The point of Bell's theorem is to say that quantum physics predicts nonlocal correlations. To do that, Bell's theorem has to very broadly consider the whole class of locally causal theories, and it does just that.

    The fact that Bell's theorem does not depend on technical implementation details is precisely what makes it such a powerful result.

    That's irrelevant, since Bell's theorem does not depend on or assume anything about rotations.

    For the record, I don't read the media because I get my information from textbooks, research papers, and direct contact with other working physicists.

    What's so bad about it? I agree that it superficially sounds like mystic bunk, so I can understand why you would get that impression if you didn't actually understand the Many Worlds interpretation or the context and the problem it is intended to solve.

    I want to be clear here: proponents of the Many Worlds interpretation don't support it because of its "many worlds". They support it despite that. The "many worlds" are an annoying consequence of the interpretation. They're not the main point of it.

    But spin is intrinsic as far as we are able to detect and manipulate it, and Joy Christian really is a crackpot. The people irritating you are right in both cases.
     
  9. Farsight

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    Pretty much. I usually side with Einstein. Note though that "weak measurement" is making measurements. I'd say the issue is related to the way you're trying to measure waves with waves - you're trying to measure one extended entity with another. Hmmn, how can I put this? It's a bit like trying to get to grips with ghostly frogspawn. When your hands are made of... ghostly frogspawn.

    IMHO guys like Bohr introduced it whilst Einstein and Schrödinger fought against it.

    String theory started off OK as an improvement on point particles. But then it somehow lost its way.

    I know. Awful isn't it? How anybody can take that seriously just beats me.

    I'm OK with things like spherical harmonics and lattice models and something called "quantum harmonics". But once we're into branes I'm really losing interest because it's totally lost touch with reality.

    I won't "cope" with absurdity. I will not tolerate it. Which is part of the reason I've come up with some things that I hope will prove useful in the fight against it. Of course, some of the people who have grown enured to the absurdity aren't always too happy about that.
     
  10. Farsight

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    Let's leave it at that, pryzk.
     
  11. przyk squishy Valued Senior Member

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    If you want, but if you can't rebut what I told you, please don't repost the same stuff in two months as if nothing had happened. Joy Christian either misunderstands or is blatantly ignoring essential defining features of a Bell experiment, and you can't continue to rely on his work.
     
  12. przyk squishy Valued Senior Member

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    In short, people who take it seriously view it as the most natural way of solving the measurement problem in quantum theory. And they think it's natural because all the mechanism it depends on is already a part of quantum theory anyway. The Many Worlds interpretation is literally what you get if you take quantum physics and remove wavefunction collapse from it, but don't change it in any other way.
     
  13. RJBeery Natural Philosopher Valued Senior Member

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    A definite value confirmed through observation?

    Please Register or Log in to view the hidden image!

    I'm just yanking your chain...as I said to NeverFly, the whole concept of wavefunction collapse is elusive and unlikely to be concretely nailed down in a few words on a forum.
     
  14. Farsight

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    3,492
    OK, let's talk about "Quantum realism" separately on another thread, and I will rebut what you said. The first thing we have to cover is Stern-Gerlach and instrinsic spin. If you dig your heels in on that we'll get nowhere, because yours will then be a circular argument.

    It's not my policy to be insulting on an internet forum, and whilst I can feel myself wavering at this juncture, I shall leave this matter with: no comment.

    RJ: check out the Fourier Transform. A lens does it.
     
  15. prometheus viva voce! Registered Senior Member

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    RJ: A lens does nothing of the sort.
     
  16. RJBeery Natural Philosopher Valued Senior Member

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    Prom: Actually Farsight has forgotten that we already discussed this here. I personally don't see eye-to-eye with him on everything but I find this concept fascinating and not without merit...
     
  17. Neverfly Banned Banned

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    3,576
    Exactly!
    I mean, that's almost as bad as someone taking it seriously that time has to slow down if light moves through a curve!
    Or that ones size actually changes if moving very near the speed of light!
    Hmmm... Ok, I'm a smartass...
    But naming an "apparent absurdity" doesn't invalidate a scientific theory. Only vigorous research and a well supported presentation can do that.

    Einstein- the Marble and the Wood.

    Farsight- you gotta work on your tolerances.

    Concise and to the point.
     
  18. przyk squishy Valued Senior Member

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    Except I'm not saying anything about "quantum realism" one way or the other, whatever that is. I am simply pointing out that articles you have cited don't support your case: Joy Christian's work is bogus and based on a misunderstanding of what constitutes a Bell experiment, and weak measurements are an application of standard quantum theory so you can't use them as an argument against the Copenhagen interpretation. Also in case it's not clear, Bell's theorem is about locality, not realism.

    Why, given I've told you that Bell's theorem is not specifically tied down to the Stern-Gerlach experiment or the nature of spin? All Bell did was define what it meant for a theory to be locally causal, characterise the correlations such theories could exhibit, and show that quantum correlations were not of this type. The Stern-Gerlach experiment with entangled spins is only relevant in so far as it is an example of a setup where a Bell inequality violation can be measured.

    You can read one of the best expositions of Bell's theorem I've seen, which I keep recommending to everyone, here. The author bases his exposition on later papers by Bell himself, especially this one, and does a great job explaining just how powerful and general Bell's theorem is in a relatively light and easy to read article.

    The defining feature of a circular argument is that the argument presupposes what it is supposed to prove. Where do I do that?

    I think you're just bothered that the fact Bell's theorem doesn't rely on details of the Stern-Gerlach experiment leaves you with nothing to argue with.

    If you had a good, valid criticism, why would you need to be insulting?
     
    Last edited: May 24, 2012
  19. Farsight

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    3,492
    The MWI isn't a scientific theory, it's an interpretation, and it's unfalsifiable. It isn't a theory like general relativity that makes specific predictions and has been tested. See Clifford M Will's paper for that. What tends to happen with this sort of thing is that some guy does the vigorous research and gives a well-supported presentation of a non-mystic explanation that you can understand. This is then opposed by people whose rebuttal you cannot understand, and who pronounce that the guy is a crackpot. They don't want you to listen to what he's saying. Here's something you might find interesting by the way. It's Why Quantum Mechanics Is Not So Weird after All by Paul Quincey.

    It does. Like RJ says we've talked about this before. You should have followed my link to An Intuitive Explanation of Fourier Theory by Steven Lehar. Scroll down to The Optical Fourier Transform:

    "A great intuitive advance can be made in understanding the principles of the Fourier transform once you learn that a simple lens can perform a Fourier transform in real-time as follows. Place an image, for example a slide transparency, at the focal length of the lens, and illuminate that slide with coherent light, like a colimated laser beam. At the other focus of the lens place a frosted glass screen. Thats it! The lens will automatically perform a Fourier transform on the input image, and project it onto the frosted glass screen. For example if the input image is a sinusoidal grating, as shown below, the resultant Fourier image will have a bright spot at the center, the DC term, with two flanking peaks on either side, whose distance from the center will vary with the spatial frequency of the sinusoid".
     
  20. prometheus viva voce! Registered Senior Member

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    from the table of contents: "An Analog (sic) Analogy: The Optical Fourier Transform" (emphasis added)

    An analogy is not "doing a Fourier transform," which is a mistake you make a lot. Fourier transform is a quantitative integral transform which allows you to take a signal and decompose it into it's component frequencies. A lens cannot do this, and to say it can does nothing but oversimplify the concept.
     
  21. khan Registered Senior Member

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  22. Farsight

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    3,492
    Let's agree to differ on Joy Christian. As regards weak measurement, take a look at Jeff Lundeen's home page and then the semi-technical explanation. Note this: "So what does this mean? We hope that the scientific community can now improve upon the Copenhagen Interpretation, and redefine the wavefunction so that it is no longer just a mathematical tool, but rather something that can be directly measured in the laboratory." That supports my case. Let me translate that for you into something more pointed: Wavefunction is real, and the Copenhagen Interpretation is a busted flush.

    Because you have to understand the extended-entity nature of interacting waves along with biaxial rotation to get past first base. It's no good putting up barriers like "spin is intrinsic" or portraying the photon as a point particle like David Deutsche does. Start with that and and before too long you're encouraging the reader to express amazement that the photon is in two places at once, then you're off into something unfalsifiable and unscientific.

    Looks good. Do you want to talk about that then? On a separate thread? It's 19 pages, we could pick through it and discuss it. Re what I said above, maybe we could bring in How long is a photon? by Drozdov and Stahlhofen then follow the lead to Gunter Nimtz and Evanescent modes are virtual photons.

    You said the Bell inequality was a "black box" seemingly divorced from reality, and you seem to be using that to avoid getting into a discussion of the reality underlying quantum mechanics.

    Not really. I am however bothered with the way Stern-Gerlach is used to say that spin is something mysterious and "intrinsic" with no classical equivalent.

    Because IMHO advocates of the MWI dismiss good valid criticism and call the critic a "crackpot" to encourage other people not to listen. A bit of pot and kettle might appeal to emotion and help counter that. I wasn't thinking of insulting you by the way.
     
  23. Farsight

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    3,492
    It's the real thing prometheus. Read up on it. Then apply it to the dual-slit experiment. A photon goes through both slits but appears as a dot on the screen. Put a detector on one of the slits and the photon is transformed into a dot that goes through that slit only. Look at stuff like this. Surely it's better than the multiverse?

    Neverfly: I'll shut up for a while to avoid hijacking your thread. There's something I need to get on with.
     

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