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  1. Standard member sonhouse
    Fast and Curious
    06 Feb '13 11:18
    http://phys.org/news/2013-02-probability-quantum-physics.html

    Anyone have any idea what this is all about?
  2. 06 Feb '13 13:03
    Originally posted by sonhouse
    http://phys.org/news/2013-02-probability-quantum-physics.html

    Anyone have any idea what this is all about?
    Some folks think that the double split experiment proves that photons do not exist until we actually observe them. They are just a wave form of probability. Something about our observation collapses the wave function and then they are particles. Our observation plays a part in reality which then begs the question again of whether or not if a tree falls and nobody is around, Does it make noise? I personally think it does because it is a macro system but it is a different world in the quantum realm.
  3. 06 Feb '13 15:21
    The article is a bit inaccurate, and this guy is a bit weird.

    There are basically two ways theorists have tried to approach the problem of adapting quantum physics to the "real world," Albrecht said: You can accept it and the reality of many worlds or multiple universes, or you can assume that there is something wrong or missing from the theory.


    I work in quantum physics and I fall into neither category. Surely Albrecht must know it's not that clear-cut.
  4. Standard member sonhouse
    Fast and Curious
    06 Feb '13 16:08
    Originally posted by KazetNagorra
    The article is a bit inaccurate, and this guy is a bit weird.

    [quote]There are basically two ways theorists have tried to approach the problem of adapting quantum physics to the "real world," Albrecht said: You can accept it and the reality of many worlds or multiple universes, or you can assume that there is something wrong or missing from the theor ...[text shortened]... physics and I fall into neither category. Surely Albrecht must know it's not that clear-cut.
    Can you do a double slit experiment where there is a measurement but not observed, but the measurement recorded for viewing later, is the disconnect from the observation by a conscious mind or does the quantum properties come into play with just a mindless machine doing the measurement?

    In other words would there be a difference in the result if only a machine does the measurement versus having a human observe the results? That would mean we could never know what the results were anyway.

    If it was not recorded but measured and not observed by humans would it have the same result as if it were never measured?

    I guess I am trying to see if it is the interaction of a 'field' of a conscious being doing the actual analysis of the results or in the absence of such a being analyzing the results but results are available, would that be the same as the human watching anyway?
  5. 06 Feb '13 19:30
    Originally posted by sonhouse
    Can you do a double slit experiment where there is a measurement but not observed, but the measurement recorded for viewing later, is the disconnect from the observation by a conscious mind or does the quantum properties come into play with just a mindless machine doing the measurement?

    In other words would there be a difference in the result if only a ...[text shortened]... ng the results but results are available, would that be the same as the human watching anyway?
    Humans play no role in quantum mechanics. This is more of a philosophical viewpoint than an empirical one; clearly humans can never observe something without a human interfering at some point. But to me it seems rather absurd if human intervention was required. In any case, the theory does not require it. In quantum mechanics, "measurement" can be regarded as a shorthard for "some interaction with a macroscopic system", which is as vague as it sounds. The process of wavefunction collapse is not well-understood.

    The important thing to note about the double slit experiment is that if you "measure" you are really looking at a very different system. It would be inaccurate to say that the measurement "changes" the system, but I prefer to look at it as regarding the system + measurement rather than the system.
  6. Standard member sasquatch672
    Don't Like It Leave
    07 Feb '13 05:24
    Originally posted by KazetNagorra
    The article is a bit inaccurate, and this guy is a bit weird.

    [quote]There are basically two ways theorists have tried to approach the problem of adapting quantum physics to the "real world," Albrecht said: You can accept it and the reality of many worlds or multiple universes, or you can assume that there is something wrong or missing from the theor ...[text shortened]... physics and I fall into neither category. Surely Albrecht must know it's not that clear-cut.
    I don't feel like getting up and looking for the book, but if I recall correctly Green offered an excellent layman's treatment of precisely this topic in The Elegant Universe. The value of a constant called h-bar determines the "solidity" of the universe; individual particles do behave unpredictably, but the value of h-bar either suppresses the magnitude of the unpredictability or the number of particles exhibiting (statistically speaking) unpredictable behavior at any one time. So h-bar is a smoothing constant, or something to that effect...how's my memory/understanding?
  7. 07 Feb '13 12:27
    Originally posted by KazetNagorra
    Humans play no role in quantum mechanics. This is more of a philosophical viewpoint than an empirical one; clearly humans can never observe something without a human interfering at some point. But to me it seems rather absurd if human intervention was required. In any case, the theory does not require it. In quantum mechanics, "measurement" can be regar ...[text shortened]... but I prefer to look at it as regarding the system + measurement rather than the system.
    Sounds crazy to me too but it looks like it is true that observation creates reality. I never believed it until recently.
  8. 07 Feb '13 14:40
    Originally posted by joe beyser
    Sounds crazy to me too but it looks like it is true that observation creates reality. I never believed it until recently.
    No. There is no reference to a human or conscious observer anywhere in quantum theory.
  9. 07 Feb '13 14:52
    Originally posted by sasquatch672
    I don't feel like getting up and looking for the book, but if I recall correctly Green offered an excellent layman's treatment of precisely this topic in The Elegant Universe. The value of a constant called h-bar determines the "solidity" of the universe; individual particles do behave unpredictably, but the value of h-bar either suppresses the ...[text shortened]... h-bar is a smoothing constant, or something to that effect...how's my memory/understanding?
    I'm not sure what you're aiming at, but h-bar, or the reduced Planck's constant, is an important constant of nature used frequently in quantum mechanics. Roughly speaking, you will notice quantum effects at the scale of h-bar.
  10. Standard member sonhouse
    Fast and Curious
    07 Feb '13 19:30
    Originally posted by KazetNagorra
    I'm not sure what you're aiming at, but h-bar, or the reduced Planck's constant, is an important constant of nature used frequently in quantum mechanics. Roughly speaking, you will notice quantum effects at the scale of h-bar.
    Except now they are finding quantum effects in biological molecules and such also. It is getting a lot closer to macro size now, the effects we notice.
  11. 07 Feb '13 21:23
    Originally posted by sonhouse
    Except now they are finding quantum effects in biological molecules and such also. It is getting a lot closer to macro size now, the effects we notice.
    Am right in thinking photosynthesis requires a quantum effect to operate ? (I think the source was The Naked Scientist)
  12. Standard member DeepThought
    Losing the Thread
    08 Feb '13 03:00
    Originally posted by KazetNagorra
    Humans play no role in quantum mechanics. This is more of a philosophical viewpoint than an empirical one; clearly humans can never observe something without a human interfering at some point. But to me it seems rather absurd if human intervention was required. In any case, the theory does not require it. In quantum mechanics, "measurement" can be regar ...[text shortened]... but I prefer to look at it as regarding the system + measurement rather than the system.
    I don't think what you are saying is quite true - although I agree with the bit about the universes existence not depending on observers. But the theory is not the thing itself. A theory is a way of predicting results of experiments to some degree of precision and hopefully for a qualitative insight into the system of interest. In the theory of Quantum Mechanics all the operators correspond to physically observable things, so observers are built into the theory from the start. Things like the phase aren't observable so the theory is required to be invariant under a change of gauge. This is a different statement to "the universe doesn't exist if we're not around to observe it." which is nonsense based on confusing the theory with the thing the theory is about.

    This gets stronger in quantum field theory where the theory is initially written down in terms of quantities which aren't observable as a consequence of which the results all come out infinite. When one switches to quantities that can be measured it all works out.

    If you change quantum mechanics to remove the observer then really it's a different theory, since you then have to justify the presence of operators.

    I skim read the paper - so it's easy for me to have missed the point of what they were saying. But at first glance, it's all a load of handwavium. I don't see their point. Classical probability is to do with a lack of information - in a Newtonian universe the information exists, you just don't know it. Quantum probability is different as the outcome of a measurement depends on the question the observer asks. They claim that quantum fluctuations can influence the outcome of coin tosses. Well so what - we already know the macroscopic world is build on the large scale average of the quantum world, during a coin flip no one does any measurements precise enough to make any kind of prediction anyway. If you had arbitrarily good measuring devices then you will find a maximum precision governed by Planck's constant which every physicist could have told you anyway.

    Also they don't consider the possibility of classical probability as an emergent phenomenon - so they haven't considered a major alternative source of uncertainty - except in a "well it's all built quantum mechanics kind of way."

    They don't look at the semi-classical regime - where there's of the order of 100 or so atoms - which in my opinion is an important for this question.
  13. Standard member black beetle
    Black Beastie
    08 Feb '13 05:31
    Originally posted by KazetNagorra
    No. There is no reference to a human or conscious observer anywhere in quantum theory.
    However, for example Penrose said clearly that "the behaviour of the seemingly objective world that is actually perceived depends on how one's consiousness threads its way through the myriads of quantum-superposed alternatives", oh well;

    On the other hand, as regards the wf, for one, the fact that it cannot occupy space in the same way as matter idicates its ideal nature. For two, any nymber of wfs can existe together within an overall superposition.
    Now, since the wf requires an interaction with consiousness in order to produce macroscale experiences, methinks it is not absurd to state that over here there is an indication that the wf and consiousness must share a common nature. So methinks it is not absurd to conclude that the wf is ideal-like and of the same nature as consiousness/ awareness
  14. 08 Feb '13 08:32 / 1 edit
    Originally posted by KazetNagorra
    No. There is no reference to a human or conscious observer anywhere in quantum theory.
    Correct -and the much-quoted idea that quantum physics says that something only exists when observed is not only a myth but is a piece of pure metaphysical unscientific claptrap.
  15. 08 Feb '13 12:23
    Originally posted by humy
    Correct -and the much-quoted idea that quantum physics says that something only exists when observed is not only a myth but is a piece of pure metaphysical unscientific claptrap.
    I think you're very brave, didn't many top scientists level a similar criticism of quantum theory when it was first suggested?