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Interpretations of QM? What is nature really like?

  1. Apr 16, 2006 #1
    What is quantum mechanics actually telling us about the way that nature works, the way nature "really is" deep down at the bottom? In Nick Herbert's book "Quantum Reality" he discusses eight schools of thought; would anyone would care to comment on the reasonableness of any of these ideas?

    Are there any new variants of these ideas that have appeared in the last 20 years that physicists take seriously? Are there any new ideas, i.e. interpretations of QM that don't fit into any of these eight ideological boxes? As far as I know, at the time his book came out Cramer's transactional interpretation of QM had not been developed, so am I correct in viewing this as a totally new physical interpretation of QM?

    Are there any experiments which (at least in principle) could show us which interpretations are right or wrong?

    ----


    Nick Herbert talks about "Quantum Reality":

    Quantum Reality #1 The Copenhagen Interpretation, Part I - There is no deep reality.... Everyday phenomena are themselves built not out of phenomena but out of an utterly different kind of being. Far from being a crank or minority position, "There is no deep reality" represents the prevailing doctrine of establishment physics....

    Quantum Reality #2. The Copenhagen interpretation, Part II - Reality is created by observation....The Copenhagen interpretation properly consists of two distinct parts: I. There is no reality in the absence of observation; 2. Observation creates reality ....John Wheeler's memorable maxim for separating what is real in the world from what is not: "No elementary phenomenon is a real phenomenon until it is an observed phenomenon,"

    Quantum Reality #3 - Reality is an undivided wholeness. The views of Walter Heider exemplify a third unusual claim of quantum physicists: that in spite of its obvious partitions and boundaries, the world in actuality is a seamless and inseparable whole....Heitler accepts an observer-created reality but adds that the act of observation also dissolves the boundary between observer and observed: "The observer appears, as a necessary part of the whole structure, and in his full capacity as a conscious being. The separation of the world into an 'objective outside reality' and 'us,' the self-conscious onlookers, can no longer be maintained. Object and subject have become inseparable from each other."


    Quantum Reality #4 The many-worlds interpretation. Reality consists of a steadily increasing number of parallel universes.... For any situation in which several different outcomes are possible some physicists believe that all outcomes actually occur. In order to accommodate different outcomes without contradiction , entire new universes spring into being, identical in every detail except for the single outcome that gave them birth.

    ...Invented in 1957 by Hugh Everett, a Princeton graduate student, the many-worlds interpretation is a latecomer to the New Physics scene. Despite its bizarre conclusion, that innumerable parallel universes each as real as our own actually exist, Everett's many-worlds picture has gained Considerable support among quantum theorists...



    Quantum Reality #5: Quantum logic (The World obeys a non-human kind of reasoning.) ...we must scrap our very mode of reasoning, in favor of a new quantum logic.

    ...a few creative logicians amused themselves by constructing "crazy logics" using rules other than Boole's, These deviant designs for AND/OR/NOT, although mathematically consistent, were considered mere curiosities since they seemed to fit no human pattern of discourse. However, according to some New Physicists, one of these crazy logics may be just what we need to make sense out of quantum events. Listen to quantum theorist David Finkelstein calling for mutiny against the rules of Boole: "Einstein threw out the classical concept of time; Bohr throws out the classical concept of truth . . . Our classical ideas of logic are simply wrong in a basic practical way. The next step is to learn to think in the right way, to learn to think quantum-logically."


    Quantum Reality #6. Neorealism (The world is made of ordinary objects.) An ordinary object is an entity which possesses attributes of its own whether observed or not... The clarity and ubiquity of ordinary reality has seduced a few physicists - I call them neorealists - into imagining that this familiar kind of reality can be extended into the atomic realm and beyond.


    Quantum Reality #7 Consciousness creates reality... a small faction asserts that only an apparatus endowed with consciousness (even as you and I) is privileged to create reality. The one observer that counts is a conscious observer.

    ...Eugene Wigner...comments on this ironic turn of events: "It is not possible to formulate the laws of quantum mechanics in a fully consistent way with out reference to the consciousness . . . It will remain remarkable in whatever way our future concepts may develop, that the very study of the external world led to the conclusion that the content of the consciousness is an ultimate reality."


    Quantum Reality #8. The duplex world of Werner Heisenberg (The world is twofold, consisting of potentials and actualities.) Most physicists believe in the Copenhagen interpretation, which states that there is no deep reality- QR # 1) and observation creates reality QR # 2). What these two realities have in common is the assertion that only phenomena are real; the world beneath phenomena is not.

    One question which this position immediately brings to mind is this: "if observation creates reality, what does it create this reality out of? Are phenomena created out of sheet nothingness or out of some more substantial stuff?" Since the nature of unmeasured reality is unobservable by definition, many physicists dismiss such questions as meaningless on pragmatic grounds.

    According to Heisenberg, there is no deep reality - nothing down there that's real in the same sense as the phenomenal facts are real.... "But the atoms and the elementary particles themselves are not as real; they form a world of potentialities or possibilities rather than one of things or facts . . .

    ...Heisenberg's two worlds are bridged by a special interaction which physicists call a "measurement." During the magic measurement act, one quantum possibility is singled out, abandons its shadowy sisters, and surfaces in our ordinary world as an actual event. Everything that happens in our World arises out of possibilities prepared for in that other-the world of quantum potentia. In turn, our world sets limits on how far crowds of Potentia can roam. Because certain facts are actual, not everything is possible in the quantum world. There is no deep reality, no deep reality-as-we-know-it....


    [...cutting towards the end of Nick Herbert's article...]

    Since these quantum realities differ SO radically, one might expect them to have radically different experimental consequences. An astonishing feature of these eight quantum realities, however, is that they are experimentally indistinguishable. For all presently conceivable experiments, each of these realities predicts exactly the same observable phenomena.
     
  2. jcsd
  3. Apr 16, 2006 #2
    quantum mechanics can be or could be viewed as "some kind of Classical mechanics (with stochastic behaviour) with complex time it"..make the change of variable t------>it and you get "familiar" classical mechanics of Heat, classical wave equation (4-D) or Z Partition function of Statistical mechanics, from this should be clear that the imaginary time makes sense.
     
  4. Apr 17, 2006 #3
    Have a look at http://thisquantumworld.com" [Broken]. Herbert's book is ancient—it appeared in 1985. Today the list is significantly longer.
    There are no "wheels and gears" beneath this analysis of Nature. (Richard Feynman in QED: The Strange Theory of Light and Matter)​
     
    Last edited by a moderator: May 2, 2017
  5. Jun 13, 2006 #4
    I've always been deeply unsatisfied with the prevailing Copenhagen interpretation. It originally postulated a solution to a seemingly metaphysical question: nothing happens before measurement. The solution, however, was inconsistent with the observation that closely spaced measurements yielded similar results, thus an ad hoc solution was postulated: the wave function collapses. There is no proposed intelligble mechanism of collapse, let alone a mathematical description of it. Then this collapse predicts the quantum Zeno effect which supposedly is verified, but with loopholes as I understand (including the problem of state retension due to dissipated/absorbed energy). Besides, to even have a continuous potential interacting with some quantum mechanical system effectively implies "continuous" measurement (that's all measuring a system does anyway: introduce a potential).

    The interpretation also leaves open what is meant by "measurement," which has resulted in the most idiotic proposals I've ever heard (some propose consciousness is important in the measuring process).

    There is also a problem with the Copenhagen interpretation when applied to the EPR paradox. There's all this talk of "spooky action at a distance" by relativists who want to rule out the Copenhagen interpretation or, conversely, by Copenhagenists, if you will, who want to crack open some flaw in special (hell, general) relativity (honestly, I think our understand of relativity is on firmer grounds than the Copenhagen intrepretation). Then there are those who try to ignore the whole problem and say there's nothing wrong by claiming that causal information is not instantaneously transmitted. Look, the preferred frame in quantum mechanics is the local (inertial) rest frame of the measured system. Supposedly, when the system is measured the wave function of both that system and its entangled system collapses simultaneously. The collapse of the function demands a sense of "before" and "after" the measurement, which is distinctly causal. One can then ALWAYS transform to a frame in which the wave function of the unmeasured system would collapse before the measured system is measured! This is a causal problem, no matter how you want to look at it. One can dress this up however one wants, but we can't have the Copenhagen interpretation AND SR.

    The Copenhagen interpretation introduces a lot of instantaneous interactions. Part of this may stem from the fact that quantum mechanics is not generally relativistic. Indeed, relativity says that time and space should be put on equal footing and yet the Schrodinger equation involves the first derivative in time and second derivative in space, which places the two on separate footing. This suggests to me that an intepretation of a manifestly non-relativitistic theory is being imposed upon reality and is trumping a more general description that considers issues of locality. These theories are absolutely at odds as I see it if we admit the Copenhagen interpretation.

    What then? Have any of you heard of Edward Nelson and his work in Stochasic Mechanics (SM)? He shows that a classical particle subjected to stochastic potentials or fields will behave exactly as though it were being governed by quantum mechanics and the Schrodinger equation. It admits the philosophically satisfying concept of existence before measurement; it describes trajectories as continuous, but stochastic; it is fundamentally classical in every way, just simply stochastic. The only question then becomes: what is producing the stochastic fields and potentials? I have some thoughts on this that I will only share if pressed.

    SM suffers from a few defects, so says Nelson the last I heard. First, the wave function for each particle is independent of others, thus seemingly prohibiting entanglement. Second, there is a fictional 4th order instantaneous "non-local" interaction between certain systems (I believe this would become a retarded potential if the theory were recast in relativistic terms).

    I'd like to see what comes of Stochastic Mechanics for it seems to me to be the most sensible of all interpretations and formulations of QM that I've seen. It preserves many philosophical characteristics exhibited in the rest of nature. I'm extremely disappointed that this enthusiasm is not shared by much of the physics community and I lament the fact that ad hoc, metaphysical, borderline religious and dogmatic formulations and interpretations are embraced instead.

    I apologize for being unable to provide everyone with links. Most of what I know about Nelson and Boyer was explained to me by someone who read only the hardcopy. I must hastily go unfortunately, but will return with feedback and more detailed explanations about this.

    Cheers.
     
  6. Jun 14, 2006 #5

    vanesch

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    Indeed, Nelson's work is framed in "local realist" stochastical theories, but they are not an INTERPRETATION of quantum theory, they make different predictions. As you point out, entanglement is not handled by these theories (which are in fact classical + local noise terms). The question is of course: is entanglement real or not ? Most physicists think that it is, but the only genuine test would be a violation of Bell inequalities *without* experimental corrections for detection efficiencies. Many people think that this correction is no issue, based upon the "fair sampling hypothesis", but one has to be careful. I would think that a violation of Bell inequalities on RAW DATA would exclude any stochastic classical local theory. However, I don't think that such an experiment has of yet been proposed and executed (for a pair of photons, one would need an overall efficiency of > 87% at neglegible dark current, which is very hard to achieve)

    Now, entanglement also shows up in other circumstances than in Bell experiments. One place is "configuration interaction" in quantum chemistry, where the multi-electron wavefunction is considered to be different than a Slater determinant of single-electron wavefunctions. This gives differences in, say, binding energies of the level of a few percent, which are often in agreement with experiment.
    However, it is not excluded that another, local, mechanism can take care of that too - although I don't think anyone has ever successfully proposed one.

    The entire issue of QM versus stochastical local realist theories is entanglement, and whether there will be found a "replacement mechanism" for each observed agreement with entangled states in QM.
    The only place where there is strictly no way out is in the EPR/Bell setup, with raw data.

    In fact, there IS a "local realist" interpretation of QM, and that's Everett's MWI ; the only difficulty there is that what we THINK we observe is not the entire reality, and this hurts people's intuition.
     
  7. Jun 14, 2006 #6

    ZapperZ

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    I would also add that, unless I've missed something, stochastic mechanics has never been able to derive the effects of superposition, in particular, the coherence gap between the bonding-antibonding states/bands. I know I keep harking back to the same thing, but if we consider that superposition is one of THE most fundamental aspect of QM that makes a whole series of predictions (and which makes the quantum entanglement different than simple classical conservation laws), then this is where one has to make the comparison and where they differ.

    Zz.
     
  8. Jun 14, 2006 #7
    Question :
    (a) has this superposition negative Wigner density ?
    (b) I assume it is not a thermal equilibrium state, so the experiment is done at very low temperature (close to absolute zero I presume) ?
     
  9. Jun 14, 2006 #8

    ZapperZ

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    I don't know. You may check it yourself.

    [1] J.R. Friedman et al., Nature v.406, p.43 (2000).
    [2] C.H. van der Wal et al., Science v.290, p.773 (2000).
    [3] A.J. Leggett J. Phys: Cond. Matt. v.14, p.415 (2002).

    It doesn't have to. All those experiments need was a superconducting state. They just happen to be using low Tc superconductors for their SQUID rings.

    Zz.

    P.S. I would also add the spontaneous current in tricrystal ring experiment as another phenomenon in which I haven't seen any stochastic mechanics try to describe.
     
  10. Jun 14, 2006 #9
    **
    It doesn't have to. All those experiments need was a superconducting state. They just happen to be using low Tc superconductors for their SQUID rings. **

    Hmmm, I would expect only thermal equilibrium states to be relevant for experiment, so are you saying that there is a huge energy gap to the next level or so ?

    **
    P.S. I would also add the spontaneous current in tricrystal ring experiment as another phenomenon in which I haven't seen any stochastic mechanics try to describe. **

    You expect too much from the beginning : the task set by 't Hooft and other (modern) local realists - like myself - is much more difficult than the quantum formalism we know today (which is already quite complicated). Clearly, we have very different goals for physics, but strangely enough I have noticed through your posts that we actually agree upon the nonsensical nature of comparing/unifying both FORMALISMS as we know them today. I have respect for the old local realists since even if there is no competing theory today and even if one day a perfect bell experiment might be done, their work brings new insight even in quantum mechanics.

    Careful
     
  11. Jun 14, 2006 #10
    Agreed, it isn't just an interpretation, it's a different model entirely. Nelson showed in his first paper that his stochastic dynamics also violates Bell's inequalities, so speaking of new Bell experiments to test this out doesn't really seem very applicable, unless, of course, I'm missing something.

    As for the issue of entanglement, there apparently has been some progress. Petroni and Morato discuss one proposition here: http://ej.iop.org/links/q34/kHipIB4GtZtJITUaNY9I4A/a03304.pdf [Broken]
    It works with some hidden variables apparently. I can't say much about this specific paper yet. I just found it today and haven't had any time to read much beyond the intro yet.

    I wouldn't say stochastic mechanics can be ruled out just yet.
     
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  12. Jun 14, 2006 #11

    ZapperZ

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    I'm not sure what you mean by "huge". Such coherence gap has been seen in H2 spectrum by chemist even before QM was invented. This is the gap between the bonding-antibonding band. In the Delft/Stony Brook experiment, it is called the coherence gap between superpostion of the supercurrent that goes both directions across a Josephson junction.

    Thermal effects are not that relevant here other than to get a cleaner signal.

    But with both the SQUID experiment and the tricrystal ring (and H2 molecule and a number of others), the PHASE part of the QM description of such a system plays a huge role. This is the origin of many spontaneous currents (and the origin of molecular bonds). I have not seen any attempt from stochastic mechanics to even come close to a description of such phenomena. I'm not rulling it out simply because they haven't. But in the same breath, one cannot also say that stochastic mechanics has made enough of the same basic agreement with QM and experimental observations.

    Zz.
     
  13. Jun 15, 2006 #12
    ** I'm not sure what you mean by "huge". Such coherence gap has been seen in H2 spectrum by chemist even before QM was invented. This is the gap between the bonding-antibonding band. In the Delft/Stony Brook experiment, it is called the coherence gap between superpostion of the supercurrent that goes both directions across a Josephson junction.

    Thermal effects are not that relevant here other than to get a cleaner signal. **

    Well, I want to know whether the energy gap is sufficient to ignore the other states in the quantum mechanical description (in the density function of the thermal ensemble), I am not doubting the observation of the coherence gap.


    ***
    But with both the SQUID experiment and the tricrystal ring (and H2 molecule and a number of others), the PHASE part of the QM description of such a system plays a huge role. This is the origin of many spontaneous currents (and the origin of molecular bonds). I have not seen any attempt from stochastic mechanics to even come close to a description of such phenomena. I'm not rulling it out simply because they haven't. But in the same breath, one cannot also say that stochastic mechanics has made enough of the same basic agreement with QM and experimental observations. **

    But I have never disagreed with your statement here (even the implementation of spin is still somewhat unclear to me): I only find that the topic of local realism should be taken seriously given the program of unification and certainly there are many more subtleties to all this than are usually mentioned. All I want to say is that there is no obvious conflict between both research directions.

    Careful
     
  14. Jun 15, 2006 #13

    ZapperZ

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    I'm not sure if I understand this correctly. What are the states being ignored here?

    The superfluid (or supercurrent in the case of a superconductor) is in what David Pines would term as a "quantum protectorate", in the sense that it is actually pretty robust and quite independent with the microscopic variation of its surrounding. Therefore, thermal fluctuation, especially on a localized scale of the medium does not play any significant role - that's why it can maintain such long-range coherence.

    But you also must understand that for experimentalists, and condensed matter people like me, we can stand only so much "philosphical grand-standing" before we ask "where's the beef?". One doesn't get to be taken seriously simply by asking for it. One has to earn it. And unless things have gone haywire, the only way to be taken seriously is to match all of these phenomena that I have cited. They are valid observations, highly reproducible, have a range of variables that can be manipulated and thus, allow for a range of parameters, etc... In other words, they ARE what I would consider crucial, standard QM representations (I find them to be even more crucial and more fundamental than the EPR-type experiments). And unless I've missed it, I haven't seen a single formulation to account for any of these phenomena from any of the slew of QM competition.

    Maybe such descriptions are forthcoming. However, I can't take things that seriously yet till they do.

    Zz.
     
  15. Jun 15, 2006 #14

    vanesch

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    If I may intervene...

    I think you and Careful are arguing from two totally different cultures, each with their own merits. I think that Careful doesn't dispute the computational efficiency of the quantum formalism, nor its applicability to a whole host of phenomena where it rather accurately gives correct predictions. Only, he doesn't really care much about that an sich - while this is the single most important aspect for you (and for many other experimentalists: does it work, does it give the good predictions of the experiments, and can I use it to calculate reliably some stuff).

    I think that people like Careful want to understand the deeper meaning of quantum theory, or of its replacement, because that has a huge impact upon any possible approach to a unification of general relativity and the phenomena now correctly described by quantum theory. It makes all the difference to be able to start from a local realistic viewpoint, or whether one has to avoid this. It is true that about all currently funded attempts (with their known lack of success) take quantum theory seriously on a fundamental level (and hence do explicitly NOT consider local realist approaches). So it matters for these people to know *whether there is still potentially a chance* or not that all the *experimentally verified experiments that are in agreement with quantum theory* still have the potential of being explained by a local realist theory or not.
    That doesn't mean that they already HAVE such a theory, but of course if it is strictly experimentally excluded, the search is in vain.

    The problem with "local realism" is that it is also the playground for a lot of crackpots with conspiracy theories. But there are serious names attached to the idea, such as 't Hooft or even, to a point, Penrose.

    So the question is: is there still a *potential* for a (possibly extremely complicated) local realist theory that can be equivalent with *that part of quantum theory that has been experimentally verified* as opposed to entirely equivalent with the quantum formalism.
    Because if the possibility is still open, no matter of how small the loophole, then the "unification of gravity with that part of QM that is experimentally verified" takes on a whole different face.

    This explains probably the different cultures. You, Zz, couldn't care less about a potential unification of QM and gravity for which there's a big chance that we won't see any experimental verification (or even a theoretical prediction worth of the name) in our lifetime, and you care about a formalism that allows you to do a lot of calculations to compare to experiment.
    The culture of Careful is different: those people mainly want to build a consistent theoretical model of all of physics, whether that is experimentally verifiable or not in the forseeable future. As such, they don't deny the calculational power of QM, but want to know whether the *potential* for a local realist theory is still compatible with experiment, to see whether it is worth looking for one, because it would make their quest a lot easier.

    There's a big difference between finding QM successes, and being sure that no local realist solution might potentially exist. Unfortunately, the former has often been confused with the latter.
    Personally, I don't know the answer to the question of whether local realist theories are finally excluded or not by what has been experimentally established, and I think that the beast is too difficult to capture, because one never can predict the inventivity of a theorist when driven in a corner :-)
     
    Last edited: Jun 15, 2006
  16. Jun 15, 2006 #15
    *** I'm not sure if I understand this correctly. What are the states being ignored here?

    The superfluid (or supercurrent in the case of a superconductor) is in what David Pines would term as a "quantum protectorate", in the sense that it is actually pretty robust and quite independent with the microscopic variation of its surrounding. Therefore, thermal fluctuation, especially on a localized scale of the medium does not play any significant role - that's why it can maintain such long-range coherence.
    ***

    One would expect all possible energy states of the superconductor to contribute to the measurement outcome through their Boltzmann weights (in the density matrix formulation); and not just the superpostion of two orthogonal pure states.

    ***
    But you also must understand that for experimentalists, and condensed matter people like me, we can stand only so much "philosphical grand-standing" before we ask "where's the beef?".

    Maybe such descriptions are forthcoming. However, I can't take things that seriously yet till they do. ***

    Sure, but then - as I said before - you dismiss more or less the idea of unification itself. We live in a world where some people are interested in a coherent picture, some are not, and most of them don't worry about it and have the attitude that perhaps it could fall out of the sky one day in which case it would erouse some interest. The beef is hard - you basically try out zillions of things to dismiss them afterwards :rofl: . Personally, my guess is that a TOE might be for the year 2150 or something like that, but meanwhile it is our humble task to understand how appearent non locality enters precisely in a statistical description of a local dynamics (or vice versa - how locality enters in the coarse graining of a non local theory) and meanwhile offer many steaks to the experimentalists... :wink:

    Careful
     
  17. Jun 15, 2006 #16

    ZapperZ

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    Maybe we're talking about different things. I can only point out to the Tony Leggett paper for the physical description of the Delft/Stony Brook experiment, since he was the one who came up with the idea in the first place. So you'd get it right from the horse's mouth.

    Well, first of all, I did not "dismiss" the idea of unification. I did, however, question the idea of the "theory of everything". So there's a difference.

    Secondly, I never said that such an endeavor should not occur, or should not be pursued. I do, however, question the sanity of trying to claim an equal footing with established idea when one is still struggling with trying to match empirical observation that the established theory can spectacularly describe to a T. Do I dimiss it? No. Do I take it seriously? No also. Why? Because it does me no good at the moment when it can't even back up what it wants to be.

    To me, the most convincing manifestation of QM phenomena are in condensed matter physics. Why? Because, as Carver Mead has said, it is the system where it is most robust, easily reproducible, and can be manipulate/adjusted to such fine extent. Until someone can point otherwise, I have always used these phenomena as the standard that I would measure against any other theories that want to compete in the playing field.

    Zz.
     
  18. Jun 15, 2006 #17
    **Maybe we're talking about different things. I can only point out to the Tony Leggett paper for the physical description of the Delft/Stony Brook experiment, since he was the one who came up with the idea in the first place. So you'd get it right from the horse's mouth.**

    I am talking about something very basic pointed out by Von Neumann in 1955, and that is that the only QM states relevant for experiment are thermal equilibrium states (QM contains too many of them in that sense). This point is also beautifully illustrated in the 1963 paper of Trevor Marshall where he discusses the correspondence between the classical and quantum harmonic oscillator in the Wigner density picture. There, it is well known that all excited states have negative Wigner density somewhere while the correct thermal mixture is a classical state with known classical dynamics. So, it seems strange to speak about observation of superposition of TWO orthogonal states unless you do the experiment at very low temperature (and the states in the superposition are the ground states) or when there is a serious energy gap (such that the excited states can be ignored for all practical purposes).

    **
    Well, first of all, I did not "dismiss" the idea of unification. I did, however, question the idea of the "theory of everything". So there's a difference. **

    Hmmm, they are close in practice :cool:

    **
    Secondly, I never said that such an endeavor should not occur, or should not be pursued. I do, however, question the sanity of trying to claim an equal footing with established idea when one is still struggling with trying to match empirical observation that the established theory can spectacularly describe to a T. Do I dimiss it? No. Do I take it seriously? No also. Why? Because it does me no good at the moment when it can't even back up what it wants to be. **

    Again, I agree with your urge for experimental comparison, but you are too impatient again o:) As you know, no current attempt to QG can match with observation (and in most of them the lack of predictive power even seems to be a matter of principle); in presumably background independent approaches one even looses basic notions such as locality and causality.
    I have told many times too that in my mind the first task to do is much more humle, that is to *really* try to understand the borderline between classical physics and QM. If one has two incompatible formalisms, then my brain tells me that one has to try to understand the differences between the REALISATIONS of the theories (if any), as well as the common points. That this takes time and leads to no spectacular predictions is fully acknowledged, but it bites some of us. It is not my intention to convince anyone, merely I want to initiate an honest conversation between different parties in which we can all learn.

    Careful
     
    Last edited: Jun 15, 2006
  19. Jun 15, 2006 #18

    ZapperZ

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    But to what extent would this be relevant in the SQUID experiments?

    I can write down the ground state of a supercurrent without any need to have any "thermal mixture". Does the BCS ground state have such a thing?

    Not to me, Phil Anderson, Bob Laughlin, Dave Pines, S.C. Zhang, etc.. etc. You could unify every single interactions you know, and I will bet you that you still cannot derive superconductivity out of it. So how do you conclude that the two are the same?

    Note: I didn't go around poke my nose asking for such-and-such a result. I only bring this up when people start touting such-and-such a theory as the next best thing since sliced bread. There's way too many unsubstantiated claim that so-and-so can replace QM, this, and that, or be as good as it. When such claims are made, I think it is irrational to not expect someone like me to come up with a few fundamental observations that these delightful theories have not yet been able to explain! I don't go around, with no impetus whatsoever, and start to demand these theories duplicate these experiments. However, if someone comes in here and start telling me that I should pay serious attention so such-and-such a thing, then it is within rational reason to expect to be asked for convincing evidence.

    So why would this be something "impatient"?

    Zz.
     
  20. Jun 15, 2006 #19
    **But to what extent would this be relevant in the SQUID experiments?

    I can write down the ground state of a supercurrent without any need to have any "thermal mixture". Does the BCS ground state have such a thing?**

    Sure you can write it down (you can write down anything you wish for in QM), but that is very different from saying that you measure it ! You need to include all interactions or otherwise show that they are irrelevant - so that is what I am asking for.

    **
    Not to me, Phil Anderson, Bob Laughlin, Dave Pines, S.C. Zhang, etc.. etc. You could unify every single interactions you know, and I will bet you that you still cannot derive superconductivity out of it. So how do you conclude that the two are the same? **

    But how can you say that ?? :bugeye: You see a QM explanation which appears to need non-local concepts and from that you jump to : no local realism.

    **
    Note: I didn't go around poke my nose asking for such-and-such a result. I only bring this up when people start touting such-and-such a theory as the next best thing since sliced bread. There's way too many unsubstantiated claim that so-and-so can replace QM, this, and that, or be as good as it. When such claims are made, I think it is irrational to not expect someone like me to come up with a few fundamental observations that these delightful theories have not yet been able to explain! I don't go around, with no impetus whatsoever, and start to demand these theories duplicate these experiments. However, if someone comes in here and start telling me that I should pay serious attention so such-and-such a thing, then it is within rational reason to expect to be asked for convincing evidence. **

    Nobody tells you you should pay attention to this; neither should you deny or silence about the possibility of such ansatz to work or not. If you are not interested in this, it is your good right to say/think so - and to percieve something as substantial or not is quite a subjective notion. Moreover, there is a large difference between SUGGESTING something as a possibility and selling it as a fact (the Bell freaks are guilty of the same game).

    **
    So why would this be something "impatient"? **

    Because someone who keeps on reminding you of something (you know) that has to be done, while the proposal is not in the appropriate stage yet (but has promising features) is hard to distinguish from the person
    who wishes to downsize the idea until the research has caught up with an entire community over a timespan of at least 40 years. That is an unreasonable criterion - the attitude would be much more constructive when such person would try to creatively see how a different scenario could be possible (unless he has a no go theorem) or at least tolerate that the one who suggests has good hopes that this will end up all right. If you apply this criterion to scientific publications then you can equally confess that all QG papers should be withdrawn unless some good soul proves in one paper that their new quantization procedure reproduces to a fair degree of acurracy ordinary Fock state QFT.

    Careful
     
  21. Jun 15, 2006 #20

    ZapperZ

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    You're forgetting that the BCS ground state that I write down accounts for ALL the observe phenomena of conventional superconductivity. So there's nothing missing out of it.

    What?

    I thought we're talking about the concept of "GUT" and "TOE"? I said that even when you have GUT, this doesn't imply TOE. You could come up with a "local realism" GUT and I will STILL challenge you to derive superconductivity out of it. What "no local realism"? When did I get into that?

    Here's a fact: no one has derived emergent phenomena out of all the interactions one knows of at the microscopic level. Every single emergent phenomena that we can describe started out with a many-body ground state. This has nothing to do with pushing "local" or "non-local" realism.

    Could you tell me where I did that?

    What was I selling? As I recall, someone was selling stochastic mechanics in this thread, as if it has the same footing as QM just because it can "reproduce" some of QM results. It was only then that I asked for it to reproduce what I consider to be some of the most fundamental results that verified QM and what made it different than classical mechanics of ANY flavor.

    So I wasn't the one being on the "offensive". I was questioning someone's selling point. And what do we get out of such a thing? That stochastic mechanics, despite all the grand-standing, could not reproduce these phenomena. Now you can tell me all you want that it is still new, still be worked on, still evolving, etc... etc. That's fine and dandy. But don't pull this wool over our eyes by declaring that this has the potential to will replace QM. You don't have sufficient evidence to make such a statement.

    I didn't start a thread trying to diss or diminish the importance of these alternative idea. If I did, then your criticism would be valid. However, when these things are being sold as if they have these glorious potential, and yet they can't describe something very fundamental, you just can't expect not to be challenged for it.

    And note, I did the SAME thing with those who are selling String Theory, especially when they are severely lacking in experimental evidence to even suggest (not verify) that they are on the right track, and yet these are sold to the public as if it is a done deal!

    When someone comes in here and over sell an idea, he/she would be foolish to not expect to be challenged over it.

    Zz.
     
  22. Jun 15, 2006 #21

    Physics Monkey

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    Hi ZapperZ,

    A mostly unrelated comment that you might find interesting. There is a very amusing paper by Shankar on the arxiv on just this subject of "deriving" superconductivity from a microscopic picture.

    http://arxiv.org/abs/cond-mat/0406174

    Shankar makes use of the RG to extract the relevant physics from a microscopic theory. He and his collaborators are able to show that a Fermi liquid theory is an asymptotically exact description of repulsive fermions (this was actually in his review article in RMP). Even more interestingly, they are able to obtain the instability of the Fermi liquid state to Cooper pairing in the presence of phonons. This is all without assuming broken symmetry and starting from a Fermi liquid state. The finite temperature formalism produces Eliashberg's equations for the transition temperature of a strong coupled superconductor.

    Not exactly a timely prediction! Still, it's a very interesting read if you haven't seen it, and definitely progress towards understanding the physics from the bottom up.

    My apologies for interrupting the latest episode of this hit drama.
     
  23. Jun 15, 2006 #22

    ZapperZ

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    I came across it some time but never read it, so my comment here hopefully isn't inaccurate.

    The BCS theory also started out of the Fermi liquid state, which by definition is a many-body system already. Landau renormalized a single many-body problem into a many one-body problem. The single-particle Green's function clearly has the self-energy terms that acount for the many-body interactions.

    So starting out from the Landau Fermi Liquid is emerging out of the many-body system already.

    Zz.
     
  24. Jun 16, 2006 #23
    **You're forgetting that the BCS ground state that I write down accounts for ALL the observe phenomena of conventional superconductivity. So there's nothing missing out of it.**

    Ah no, now you are turning things around ! It is not because you construct an ingeneous model of observed phenomena that you therefore have understood it from the point of QM : you reason from empirical confirmation, I HAVE to start from logical, theoretical deduction. Logically, a theory predicts only something when there is a clear sequence of well motivated steps from its foundations to the effective models. It is precisely this kind of attitude which probably makes people think today that there is no *classical* derivation of black body radiation, or that ZEP energy is something exclusively quantum. So, let me argue it like this: let H be the Hamiltonian of the system, |O>_i be its ground states and |a>_i the excited eigenstates of H. Let T be the temperature of the bath the sample is in, then the Gibbs state is the *only* state (density matrix) relevant for experiment (when you do spectroscopy, you get *all* the fuzzy spectral lines - not just one) - you alway measure a mixed state, never a pure one (unless you are at T=0).


    Therefore, you can never *measure* a superposition of two *pure* orthogonal states of the same Hamiltonian, given the claim that one can measure each of them (in the same dynamical framework (!)). What is done in practice (like in the double slit experiment) is that one is introducing new interactions (the plate) in two *different* Hamiltonians each giving rise to the measurement of the respective Gibbs states (if we want to be logical) ; later on, one ignores these interactions and *assumes* that both Gibbs states are different *pure* states of the ``interaction free'' Hamiltonian. Moreover, one then claims that the superpostion of these pure states is a measurable quantitiy, but this is only so when it is the Gibbs state of the total Hamiltonian !?! How to make a circle out of a square ? I do not deny that this somehow ``works'' but certainly do question the internal LOGICAL consistency !

    So, here I was asking for your comments and insights.

    **
    You could come up with a "local realism" GUT and I will STILL challenge you to derive superconductivity out of it. What "no local realism"? When did I get into that? **

    You clearly said : ``and I will bet that you still cannot derive superconductivity'' but now I see where you are going to beneath (miscommunication here :smile: ).

    **
    Here's a fact: no one has derived emergent phenomena out of all the interactions one knows of at the microscopic level. Every single emergent phenomena that we can describe started out with a many-body ground state. This has nothing to do with pushing "local" or "non-local" realism.
    **

    Sure, I once said this about superconductivity, but then I remember having given a paper of two japanese (?) guys who derive BCS from first principles in 1+1. But, don't you see, my interest in a deeper underlying principle and the fact that one will have to see contemporary ``fundamental'' physics as emergent is *exactly* the reason why I ask you about the existence of derivation of emergent phenomena from QM and why I am interested in people doing exactly that ! It is according to me VERY important work to see (a) wether and (b) how one theory *can* produce such and such emergent phenomena; I clearly said in the other thread that the effective model is of course the primordial working tool.


    ** Could you tell me where I did that? **

    I have seen very little intervention from you when dozen's of people were talking here about the Bell argument as being impassable. I was hinting here not about what you said, but what you did not say. You have a duty of mentor here, it is a ``job'' in which one would have to surpress one's own bias IMO, this is all I have to say about it.

    **
    What was I selling? As I recall, someone was selling stochastic mechanics in this thread, as if it has the same footing as QM just because it can "reproduce" some of QM results. It was only then that I asked for it to reproduce what I consider to be some of the most fundamental results that verified QM and what made it different than classical mechanics of ANY flavor. **


    Two answers: (a) where did you see me SELLING stochastic mechanics ? Just give me some citation, that I can feel on what treshold you see something as selling. You seem to percieve the fact that I state that SM logically can cover for QM and that in *principle* there is no distinction, as saying that it is on the same footing. The latter is btw an impossible thing given the ratio of people working on it. (b) you SELL superconductivity, black body radiation and so on as QM phenomena, so therefore I *ask you for a derivation* of the former and all you can say to me is that many emergent phenomena cannot be derived from QM (in this case). So you BELIEVE in this, that is fine, just as workers in stochastic electrodynamics believe that zero point radiation (which cannot produce a thermodynamical heat flow) can achieve classical stability (of atoms - say).

    Someone like me - who is interested in unification - is only *allowed* to know the facts, I have no particular emotions towards neither QM, neither GR (although the latter certainly fits better local realism). I don't know whether you have once given the unification of both some thought, but if so, then you would realize that sacrifices have to be made. It is of primordial importance to know *precisely* the sense in which something is a consequence of what without room for any feeling of overconfidence. *That* is where we do not understand each other.

    Careful
     
    Last edited: Jun 16, 2006
  25. Jun 16, 2006 #24

    ZapperZ

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    What is not logical about the BCS derivation? It DID start with a Hamitonian of the system. It is just that it isn't the Hamiltonian of each individual particle in the system but rather a many-body Hamiltonian. And no, it is not something just phenomenological. The Ginzburg-Landau model was the phenomenological part of superconductivity which the BCS theory could derive to a T.

    And as for what is being measured in the SQUID expt., you can easily satisfy yourself with that Leggett paper (why won't you read it?). If you think he's wrong, I'd like to see you write a rebuttal for it.

    Wait a second. So you were criticizing me for what I DIDN'T DO? Please look at other threads in this forum where I didn't participate in. Are you telling me that I'm endorsing ALL of those too just because I didn't say something? Do you realize how ridiculous this is? I didn't say anything about that thread in SR/GR about some silly conspiracy on Einstein's equation implying that Black Holes solutions do not exist. So I endorse that by not participating?

    Oy freaking vey!

    If you don't think that you're not selling SM with such statements, then how could I be selling anything when I didn't pushy ANY theory here. All I did was question the validity of such statement by asking for where SM can make the same predictions as QM.

    I didn't sell these things. Mother nature did because these are phenomena that exist whether one accept QM or not. And I said them to be QM phenomena (BTW, where did I brought up the BB radiation? Did you mix up different threads with different people?) becuase so far, QM has been the only description for them. When you can show where SM or any other theory can describe them, I'll change that phrase.

    Do you think, by reading your previous postings on PF, that you have conveyed such "humbling" point of view? I mean, just look at your constant attack against QM on many fronts, dispite the fact that, as in this thread, what you are pushing still cannot match several physical phenomena that we have observed. To me, that isn't logical, and it certainly isn't a rational act to go on the "offensive" when you still have a lot to do and to overcome. This just ruins credibility because this is like other quacks who would criticize physics theory while the theory they're pushing is still full of holes.

    I have ZERO problems with people working on alternative theories. You seem to be fixated on this false notion that I dismiss them. I don't. I ASKED, when someone tells me that so-and-so is as good as QM (or more "logical") for this thing to explain a number of emprical evidence. I still want to know why you think this isn't a valid response to such a situation.

    Zz.
     
  26. Jun 16, 2006 #25
    **
    And as for what is being measured in the SQUID expt., you can easily satisfy yourself with that Leggett paper (why won't you read it?). If you think he's wrong, I'd like to see you write a rebuttal for it. **

    Because YOU are the so called specialist in QM and condensed matter physics. The issue I raise here is very basic towards the superposition principle and the origin thereof. So I assume you have at least thought about it and read the references you give us. But somehow you do not want to give your ideas about it, which is what people do in a discussion. Very dissapointing I must say...

    **
    Wait a second. So you were criticizing me for what I DIDN'T DO?Oy freaking vey! **

    Ok, where did I hear you say (since I am here) that the Bell inequalities themselves are by far not conclusive in the issue local realism versus QM? Where did I see you steering this discussion in a sensible direction? As I remember very well, you even support some dr. Chinese who is precisely pushing this discussion in a direction where it is not, or did I misread that as well ?!

    **
    If you don't think that you're not selling SM with such statements, then how could I be selling anything when I didn't pushy ANY theory here. All I did was question the validity of such statement by asking for where SM can make the same predictions as QM. **

    You are not answering any of my objections ! And again, you are telling us that QM makes these prediction without accounting *yourself* for that :grumpy:.

    **
    I didn't sell these things. Mother nature did because these are phenomena that exist whether one accept QM or not. And I said them to be QM phenomena (BTW, where did I brought up the BB radiation? Did you mix up different threads with different people?) becuase so far, QM has been the only description for them.**

    No, BB radiation can be fully accounted for in classical physics. Read the papers of Boyer, Marshall and Cole.

    **
    Do you think, by reading your previous postings on PF, that you have conveyed such "humbling" point of view? I mean, just look at your constant attack against QM on many fronts, dispite the fact that, as in this thread, what you are pushing still cannot match several physical phenomena that we have observed. To me, that isn't logical, and it certainly isn't a rational act to go on the "offensive" when you still have a lot to do and to overcome. This just ruins credibility because this is like other quacks who would criticize physics theory while the theory they're pushing is still full of holes. **

    Who speaks about offensive here ?? I am simply asking for the FACTS, not for your religion and anytime I offer some objections I have you consider this as an ATTACK against your belief. And where is vanity here !? If you want to dig into nature, then you have to distinguish fact from belief and it appears to me that is an impossible thing for you, as you have admitted once yourself. Remember : ``I at least know in what theory I should have confidence´´ or something like that !

    You also seem to have missed that on the other thread I explicitely wrote that it is hard for me to imagine that the world is fundamentally stochastic ! So, does that sound like anyone who is SELLING stochastic theories ??? :bugeye:

    Careful
     
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