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Layman's Question on Quantum Mechanics

  1. Jan 8, 2006 #1
    If no human has observed the moon or been able to calculate its existence through studying its physical effects.... does the moon exist under the terms and formulations of quantum mechanics? Please be kind!!!:bugeye:
     
  2. jcsd
  3. Jan 8, 2006 #2
    Can anything be said to "exist" if you can't, in principle, observe its effects or it directly?
     
  4. Jan 9, 2006 #3
    Absolutely - the moon will exist if you dont observe it or if humanity ceases to observe it or if it never had observed it. There are many astronomical objects that have never been seen before but get discovered by humans. It is illogical to believe that they did not exist prior to observation. There is no force in nature that has been discovered, or could even be conceived, that can bring a planet into existence once it is observed by humans for the first time. For one thing this force will have to defy relativity. If anybody is claiming this, then they should provide proof of such a force, and as long as they are unable to do so, such claims are not worth a dime a dozen.

    This meme that something must be observed by a conscious being in order for it to exist is simply a creation of some people's imagination, who have difficulty accepting that there is an objective reality out there irrespective of their own existence.

    Now if the object was a quantum particle, again the answer is an emphatic no. For a quantum particle to get realized, all that has to happen is for its wavefunciton to decohere. This is as simple as the wavefunction collapsing on an atom and the particle getting absorbed or knocking off an electron. Again, there is NO OBSERVATION, NO MEASUREMENT, NO CONSCIOUSNESS, and NO HUMANITY involved.

    What you are referring to are certain myths pushed by religionists, mystics and other obfuscators who, unlike scientists, have no idea how reality works, who cannot accept that their self is utterly insignificant in the grand scheme of things, and who are beholden to their own subjective emotions and petty rationalizations.
     
  5. Jan 9, 2006 #4

    vanesch

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    I don't think the origin of the view that there is a potential relationship between the "existance" (which should be defined of course) finds its sole origin in religionists and mystics. I count myself amongst the people that think that consciousness MIGHT have something to do with the claim to existence, but this is NOT based upon my desire for religion (I'm not religious) nor mysticism (I have no desire for any mysticism). In fact, my personal opinion grew out of the study of the FORMALISM of quantum theory (which means that from the moment that the formalism will change, the view will change). There is a fundamental incompatibility between the "real world" you describe and the world description that results if you take the formalism of quantum theory seriously. That formalism states that ALL physical interaction is given by a strictly unitary operator - which unavoidably leads to a world where all possibilities are realised - while clearly what we subjectively observe does NOT correspond to such a world. So there are two outcomes to this: this strict unitarity does not hold (very well possible, but this is NOT what the current formalism says), OR we consciously only observe PART of the state of the universe (ONE branch, or world). Now, once you enter into these waters, and the link between subjective experience and objective world is not the trivial relation anymore you are advocating, one should take into account the philosophical reflexions that have been made in these issues.

    Again, I'm not claiming that "the moon isn't there when you don't look at it" (in the necessary secondary degree). I'm only claiming that this is what quantum theory as we know it today, tells you, when you take it seriously as an ontological description of "reality", and that the origin of this is not some desire for mysticism, but is a hard statement in the quantum formalism, namely the requirement for unitarity.
     
  6. Jan 9, 2006 #5
    As a kind of addendum to my question:

    the idea that there is a "potential" for a moon to exist, even without observation or awareness of its existence, seems like it could be part of the quantum way of analyzing existence.

    Is the potential for a moon to exist, the potential for humans to observe a moon to exist and other potentials like of no moon existing etc... part of a quantum equation with regard to the "existence" of the moon or matter in general? Remember that matter is simply a configuration of energy, wave function etc...
     
  7. Jan 9, 2006 #6

    ZapperZ

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    But at some point, there is a "transition" from quantum behavior to the classical behavior that we all know and love. You must make such a distinction or else you will get into the mystical world of mumbo-jumbo.

    Treat a classical entity as it should, and treat a quantum entity as it should. But don't mix them up or you'll get absurdities. When you apply a set of rules that were never meant to be applied to that particular situation, you get quackeries.

    Zz.
     
  8. Jan 9, 2006 #7
    What you have written here constitutes a warning. We could heed your warning if we had a definition for "mumbo-jumbo" and "quackeries". A reason why we need to avoid them would come in handy as well... is this a yellow or orange alert with regard to in-coming absurdities?

    I have no wish to indulge in the dog-chase-tail-chase-dogma religiousities that so many entrepreners have milked when it comes to quantum physics.

    I am simply interested in the objective views of quantum mechanics and how they may apply to awareness. You will please notice I am trepedaciously avoiding the word "consciousness" because it seems this word has been trade-marked, patented and copyrighted by every guru and swami on the planet... and for no good reason other than to sound "universal".

    If it is true that quantum theorys and the classic, relativity theorys are like an oil and water scenario, there is still something emulsifying the two and that is what we are experiencing... at this moment. Surely one system supports the other... or, even more probable, one system gives rise to the other. There must be common elements in both systems that can be or have been observed. Is this true?
     
    Last edited: Jan 9, 2006
  9. Jan 10, 2006 #8
    Conjectured objects that have never been observed might exist, but we have no way of knowing for sure. Conjectured events that have never been observed might have happened, but we have no way of knowing for sure. If no human had ever observed the moon, and if there also were no observed events ("physical effects") that would lead to the conjecture that there is a moon orbiting the earth, then we could feel justified in the belief that the earth has no moon --- and neither quantum theory nor any other physical theory would contradict this view. However, humans have been observing and tracking the moon for millenia, so the belief that it's there even during intervals when no one on earth happens to be observing it seems justified --- and neither quantum theory nor any other physical theory contradicts this belief.

    As far as I know (which isn't that far ... I'm just a student of this stuff), the "terms and formulations" of QM don't deal with moons. Moons and, say, photons are different. The main difference has to do with the scale of compositional and interactional complexity ... I think. :rolleyes:

    Anyway, there are no unambiguous physical referents for photons other than the symbolic representations and the experimental events which define them.

    Do the math symbols on some piece of paper and the materials and instruments in some experimental setup exist when no one is looking at them? Yes ... at least that's the standard working assumption --- which is firmly grounded wrt our collective experience and pertains to any and all objects amenable to our direct sensory perception.

    Do the photons that you might expect your experiment to produce exist if your experiment doesn't produce them? No ... at least not in any physical form other than their mathematical representation.
    In other words, the, eg., click of the PMT isn't caused by the photon ... the click is the photon.

    So ... what is quantum theory? It's a basic algorithm (employing various mathematical models) for predicting the results of quantum experiments. What does it tell us about our world, about existence? It tells us that a certain instrument (or set of instruments) has a certain probability of being in some three-dimensional configuration (amenable to our direct sensory perception) at a certain time wrt a certain experimental preparation.

    Does the quantum mechanical algorithm mirror an underlying reality, an underlying quantum world? That's not its purpose. It was designed as, and functions as, an instrumental theory. It's about mathematically organizing and relating the data wrt the materials and instruments which are associated with the data --- and so far the only thing that this tells us about an underly quantum world is that it apparently can't be understood in terms of the persistent images from the world of our sensory perceptual experience. (I personally think that it tells us that nature is fundamentally waves, but, as I mentioned earlier, I don't know very much yet.)

    In a letter in the October 2005 PHYSICS TODAY (pp. 15-16), Aage Bohr, Ben R. Mottelson, and Ole Ulfbeck write:
    In his Reference Frame column "What's Wrong With This Quantum World?" (PHYSICS TODAY, February 2004, page 10), David Mermin comments on a statement attributed to Niels Bohr by his associate Aage Petersen:
    When asked whether the algorithm of quantum mechanics could be considered as somehow mirroring an underlying quantum world, Bohr would answer
    "There is no quantum world. There is only an abstract quantum physical description. It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature."[1]

    Mermin's column describing different physicist's reactions to the statement touches on issues that remain central to the understanding of quantum mechanics.

    Although "quantum world" was not part of Bohr's terminology, we can imagine that he might have responded as indicated to the question posed. We see the statement in relation to his basic view that the algorithm of quantum mechanics is a purely symbolic formalism accounting for observations that are obtained under specified conditions. That view is illustrated by his advocacy that the word "phenomenon" be used exclusively to refer to "an observation obtained under specified circumstances, including an account of the whole experimental arrangement. In such a terminology, the observational problem is free of any special intricacy, since, in actual experiments, all observations are expressed by unambiguous statements referring, for instance, to the registration of the point at which an electron arrives at a photographic plate."[2]

    Interpreted in this manner, the dismissal of a quantum world leaves the particle as an object capable of directly producing the basic event of observation, such as the registration of an electron arriving at a photographic plate or a click produced in a counter. As is evident in the conflicting reactions that Mermin reports, the issue of which world these objects belong to remains controversial.

    Mermin asks, What's wrong with this quantum world? Our answer is that the rejection of it in the form described does not go far enough. As we have recently argued,[3] the perceived need to explain the click as being caused by a particle is a remnant from classical imagery, which has obscured the full implications of fortuitousness and thereby the principle underlying quantum mechanics. Thus all experimental evidence is consistent with a complete break with causality in that the click comes without any cause, as a genuinely fortuitous event. The event is recognized as a macroscopic discontinuity in the counter. Thus genuine fortuitousness unavoidably eliminates the particles. Although fortuitousness has been a central innovation of quantum physics, a complete break with causality was beyond the horizon of the pioneers of quantum mechanics. Indeed, if there were no particles producing the clicks, what would the theory be all about?

    Perhaps surprisingly, the very notion of genuine fortuitousness is powerful in its implications. With particles excluded, only geometry is left on the stage, and the symmetry of spacetime itself, through its representations, provides the mathematical formalism of quantum mechanics. Once that point is recognized, quantum mechanics emerges from the principle of genuine fortuitousness combined with the embodiment of spacetime symmetry, without any reference to degrees of freedom of particles or fields. The theory, exclusively concerned with probability distributions of genuinely fortuitous clicks, thus differs from previous physical theories in that it does not deal with objects to be measured -- which eliminates the issue of a quantum world.

    References
    1. A Petersen, Bull. At. Sci. 19, 8 (1963).
    2. N. Bohr, Essays 1933-1957 on Atomic Physics and Human Knowledge, Ox Bow Press, Woodbridge, CT (1987), p. 64.
    3. A. Bohr, B.R. Mottelson, O. Ulfbeck, Foundations of Physics 34(3), 405 (2004).
     
    Last edited: Jan 10, 2006
  10. Jan 10, 2006 #9

    ZapperZ

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    Let me give you a very clear example of such a discontinuity that you have ALREADY accepted - phase transition.

    If you look at the thermodynamics description of the properties of water, just because you have understood it doesn't mean you can make a smooth transition when you lower its temperature until it becomes ice. Several state variables become discontinuous at the phase transition temperature. You now have to shift gears and use a different set of description. This hasn't bothered anyone yet.

    QM has many features that merge into the classical properties, especially at high quantum number, high temperatures, or large interactions (decoherence). But this doesn't mean that using QM description for classical, macroscopic system is any more valid than using classical physics for QM systems. There are a bunch of things we still don't quite know at the mesoscopic scale where these two extremes clash their heads. All we know right now is that one should not simply adopt QM's "world view" on classical systems. It will produce absurd conclusions.

    Zz.
     
  11. Jan 10, 2006 #10
    Think this question belongs in the philosophy Section under existentialism:wink:

    I'm hoping that there is no oil and water thing between quantum and classical worlds, that there is an underlying unifier we're missing, but then I've always been a dreamer:smile:

    Personally I think we're missing something somewhere, whether it's misinterpreting data or being ill equiped or too technologicaly backward to really understand what it is we're attributing to the quantum world and all it's vagueries; I don't know but there's just a nagging suspicion there, I can't quite put my finger on.

    Schrodinger himself longed for the time that quantum mechanics shuffled off it's mortal coil and was replaced by a better theory, just as Newtons gravitational laws we're superceeded by Einsteins relativity. His dying regret was that he wouldn't be alive to see it. Who knows maybe we will:smile:
     
  12. Jan 10, 2006 #11

    ZapperZ

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    As long as the discussion is physics based, with concrete physics examples, then it belongs here. I have tried to stick by that by bringing in actual physics examples to illustrate my arguments. However, if it degenerates into semantics, hand-waving, unsubstantiated, or "pure-logic" arguments that totally ignores actual physics examples, then it will be moved to the philosophy forum.

    Zz.
     
  13. Jan 10, 2006 #12
    I admit my question raises a potential for esoteric "quackery" and I apologise for this if it is deemed an oppoprium. I have brought it to the quantum physics section because of the idea of location-nonlocality that has been observed on the extreme sub-atomic level and because it has been postulated that the observation of activity at this level changes the activity in question.

    These observations, hypothetically, appear to suggest that awareness and observation had or have a fundamental role in the behaviour of energy/matter.

    I see here that Sherlock and ZapperZ are refering to scale and how congruence of results is inconsistent as observations traverse the vast differences of scale. And, as a layman, I can only accept this as the stumbling block to finding a unifyer between Quantum and Relative theories. However, again, as a layman, let me offer another example that may help in this regard and suggest that applying fractal geometry or fractal theory to bridge the gap between a sub-atomic quantum reality and the classic, relative macroscopic reality we all "know and love".

    At any rate, please let me thank you for the cool posts to date!
     
  14. Jan 10, 2006 #13

    ZapperZ

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    Exactly what "observation" are you talking about? And putting a hand-waving statement about a "fundamental role in the behavior of energy/matter" only adds to the ambiguity of whatever it is you're trying to get across. Remember, if you can't use a clear, exact, physics example, this goes to the philosophy forum.

    There is a very clear definition of what is meant by an "observable" in QM. We spend hours and hours in school being taught the meaning of a hermitian operator, its properties, its commutation relation, etc., not for nothing. Maybe that would be something you need to look into before making the connection of "observation" in QM.

    Er... are you not aware that Special Relativity has been incorporated within QM already? Dirac pioneered this work a long time ago.

    Besides, what are "Relative theories"?

    Wolfram has tried this in his book. Yet, when questioned at Brookhaven during his talk if he has produced any new physics, he said no. When asked if his approach can derive emergent phenomena such as superconductivity, he said no.

    So before you suggest that such a thing can "bridge" the gap between QM scale and classical scale, maybe you need to show that it can, first and foremost, already able to do what we already know within such a scale. Derive the QM emergent phenomena first, and then we can put some confidence in such assertion.

    Zz.
     
  15. Jan 10, 2006 #14
    Are you guys checking out the Skepticism and debunking : Heim theory thread? A step in the right direction perhaps? I'd asy ask Niel armstrong if the moon exists personally; oh no wait a minute we nver actually went there it was all a cold war propoganda excersise.

    Seriously though I think the gravitational evidence alone is compelling. I don't wake up every morning and wonder if the sun exists because the warmth from the light on my face is concrete enough under my criteria, OK it may not be scientifically concrete but if I only believed things that were concrete, I'd believe very little. I don't need QM or Relativity to prove or disprove the existence of the sun or the moon, or the planets etc,etc. Frankly I have better things to do with my time than prove the obvious.:wink: if it turns out I'm wrong and the sun and moon don't exist then mah ignorance is bliss.:biggrin:

    QM relativity are simply a matter of scale on a small scale the quantum effects overcome the relativistic effects and on a macro scale the contrary is true. Working out why this is the case is simply a matter of understanding why gravity dominates the macro and strong/weak etc the very small. I think it would be interesting if in the Heim theory, the macro world Gravity and Electromagnetism rule and in the micro strong and weak rule. strong increases with distance gravity decreases as does electromagnetism which is now unified as Elecro gravity. Maybe that's all the answers we need?
     
    Last edited: Jan 10, 2006
  16. Jan 10, 2006 #15

    ZapperZ

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    Hint: there is a reason that discussion is in S&D forum and NOT in the physics forum.

    Zz.
     
  17. Jan 10, 2006 #16
    Disprove it or prove it that's all I'm asking for.

    If it's tosh fair enough but I'd so love it to be true:wink:
     
  18. Jan 10, 2006 #17
    What Bohr said about the idea of a quantum world seems to be the best answer to my question. Credit to Sherlock for the quote.

    Is Bohr a well accomplished physicist?
     
  19. Jan 10, 2006 #18
    This is from the website address:
    http://www.tcm.phy.cam.ac.uk/~bdj10/papers/bell.html

    and also seems to address my question. I'm not ascerting any theory I've conccocted. I am simply exploring supportive and non-supportive objective analysis's with regard to awareness and the extent to which it plays a role in determining the constructs of nature. That's why part of the question involves whether or not the power of awareness is fundimental to the existence of matter.

    My mention of fractal geometry was just my apparently misguided way of giving back in return for the generous assistance I am receiving in answer to my question.

    Here is another example of the type of observation I am talking about and whether or not observation/awareness changes the behaviour of an observed field/wave/particle.

    From:
    http://prola.aps.org/abstract/PRA/v25/i4/p2208_1


    And another example of what I'm talking about:

    [\"The running of the universe and the quantum structure of time'

    From:
    http://arxiv.org/pdf/quant-ph/0105013


    this is a very cool source and thank you for motivating me to look for it!
     
    Last edited: Jan 10, 2006
  20. Jan 10, 2006 #19

    ZapperZ

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    Again, I will point out the idea of a "measurment" in QM that you need to understand FIRST before going into something as in-depth as the quantum eraser. You should expect to be able to deciper something that involved, when you haven't fully understood the idea of linear operators in QM. This is a recipe for disaster based on all my years at looking people trying to tackle QM without understanding the fundamental mathematics.

    You may also want to do a search on the tons of postings that I have made regarding "emergent phenomena", especially in my journal entry. As a condensed matter physicist, I've done nothing but work with emergent phenomena, and superconductivity in particular. So before you buy wholesale of the stuff you're cutting and pasting, be VERY aware that these concepts in physics have underlying mathematical definition, and that you MAY be understanding the stuff you're endorsing differently than the way they are being meant! Do not use the pedestrian definition of these words and phrases and think you've understood what they are. Would you buy the spiel if I tell you that fractional quantum hall effect is an "emergent phenomenon"? Would you be able to explain why it is so?

    Zz.
     
  21. Jan 10, 2006 #20
    I don't "endorse" any of the material I have copied and pasted or linked here. I am supplying, as requested, what I perceive to be examples of what I'm asking with regard to the function of awareness as concerned with matter and the nature of nature.

    I welcome you're recommendations, however, since you claim to be and appear to be clearly more qualified than I am in decifering the complex and seemingly unreachable concepts of quantum mechanics. I know its frustrating to look back on people who want to understand a concept like quantum physics but who have also not spent the time doing the math or the experiments that formulate the foundations of the concept(s).

    The fact that one person has "suffered through" the training and discovery of a complex discipline or concept can either help them or hinder them in their effort to teach less experienced people what they have learned. The choice between helping or hindering is in the hands of the experienced person.

    I'll put this thread to rest-mass or to a "non-local" rather than see it shuffled off to the nebulous, hand-wavey and non-commital philosophy section once I determine that there are no other contributions that support or don't support the idea that without biological observation and awareness of nature, nature does not exist.

    The last paper I sited goes into some detail in that regard covering what they term as "consciousness" and the "quantum computer"..... which may be running a program, metaphorically speaking, of "awareness" to keep tabs on its progress. "QUACKERIE":surprised

    Here's what I dug up... mind you... I haven't done the hands on work or the calculations and measurments as you have recommended ... so I still don't buy any of the speil or the wholesale goods until I grow them and handle them myself (as per your suggestion)!

     
    Last edited: Jan 10, 2006
  22. Jan 11, 2006 #21
    I'm just a layman, and a casual student of QM. ZapperZ is a working physicist -- I think he's currently at Argonne National Laboratory. Neils Bohr was one of the original developers of quantum theory.

    I don't think there's anything necessarily wrong with speculating about the possible makeup and behavior of an underlying reality in terms of imagery from our ordinary experience. But that's not how QM was developed or what QM means, afaik.

    If QM is about experimental setups and results (which it is), and not a description of an underlying quantum reality (which, afaik, it isn't), then the existence of nonlocal propagations in nature, or the idea that the existence of some object or event in nature depends on our consciousness of it, isn't entailed by QM.

    QM books often weave metaphysical (using classical analogs/imagery) language with the physical, instrumentalist/mathematical language in a way that makes it sort of unclear that, say, the word 'particle' as it's used in QM has only a mathematical (and instrumental) existence and meaning. Phrases like, "the probability that the particle will be found ...", used in contexts involving detector clicks or dots on a screen tend to obscure the fact that it's the detector clicks or dots on a screen, and their probability of occurance wrt specified experimental setups, that are being talked about mathematically and not some underlying quantum world of particles and waves.

    It's not that anybody is denying the possibility, or existence, of an underlying quantum world. But how are you going to talk about it unambiguously? This was one of the main problems that the developers (including Niels Bohr, who you've asked about) of quantum theory were faced with. Whatever it might be, it's not amenable to our direct sensory perception and can only be approximately tracked by instruments. So, QM is about what can be unambiguously stated wrt the various experimental results that have historically defied classical explanation -- that is, QM is all about the experimental results not their possible underlying causes. It's a purely correlational theory, not a causal one.

    Of course the underlying quantum world, whatever it might be, is presumed to be a bit more sensitive to observational probing than the moon is.

    However, the existence of quantum phenomena in the physical forms of experimental preparations and results, and the math which describes these, (which are the only physical forms in which quantum phenomena can be unambiguously said to exist) doesn't depend on our consciousness of them any more than the existence of the moon depends on our consciousness of it.

    The physical fact that the experimental preparations and the math have the specific forms that they do has of course something to do with the conscious decisions that went into their construction. But those conscious decisions were preceded by sensory apprehensions of the physical world which didn't just pop into existence because we wanted or willed them to be there. The physical facts are what they are -- and to the extent that all people with normal (and sober) sensory capabilities see the same physical facts, then they're considered to be objective (not just subjective, ie., not just in your or my imaginings) and part of our physical world.

    The working assumption in all of the physical sciences is that the world of our objective sensory experience exists whether you or I or anybody is paying attention to it.

    And there's nothing in either quantum theory or quantum experiments which contradicts this view ... at least as far as I'm aware.

    In order to really understand what Bohr and ZapperZ and others are saying it's necessary to put down the QM popularizations and actually start learning the theory -- and then a fascinating (not just the physical/experimental phenomena themselves, but also the ingenious ways that physicists have devised to produce them) world of discovery will be revealed to you.
     
    Last edited: Jan 11, 2006
  23. Jan 11, 2006 #22

    ZapperZ

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    But that is exactly what I am questioning, where you actually understood the significance of the example you're citing. I've seen many people citing stuff in which the perceived to understand, and yet got it completely wrong. QM isn't a series of words - it's a series of mathematical formulation. That is what makes learning QM so difficult for a lay person.

    I can do better. Look in my journal entry under "Theory of Everything?". There's a series of appers by Laughlin (and citing Anderson) on this subject. You'll realize how ironic it is for you to indicate TO ME what an emergent phenomenon is.

    Zz.
     
  24. Jan 11, 2006 #23
    Sorry I've diverted this post enough. But had to say there are some fascinating insights into scientific method here. I'm as guilty of anyone of not understanding the finer points of the maths, but then I haven't studied much of it yet. I came into Physics by way of popualrist material and thus have yet to fully apreciate any theory which is why I wouldn't know where to start in commenting on the maths behind the science, and which is why I'll wait 'till I've studied the math before I make any comments that are pertainent.

    Having said that I do know this, our perception is derived from our environment, evolution has geared us in a way to percieve the world that increases the chances of our surviving/formulating survival strategies and aquiring what we need. Whether this is in fact the objective truth is a subject for philosophy and has no real place in science as such, although it is a valid point to say, what you percieve is not necessarily the truth. An objective reality has it's limitations place on it by the environment you exist in. Is it what's really there? God knows:wink:

    If we could build a computer to percieve the world as it really is it wouldn't work, because we don't know what it is we're looking for and wouldn't know it if we saw it.
     
  25. Jan 11, 2006 #24

    ZapperZ

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    Rather than repeat everything that I have written down, I will be downright tacky and simply point to the essay that I've previously written and posted in a number of places.

    http://www.physicspost.com/science-article-208.html [Broken]

    [Thanks to Greg for putting this on Physics Post, even though I didn't get any credit for it] :)

    Zz.
     
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  26. Jan 11, 2006 #25

    vanesch

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    As ZapperZ noted in his journal entry "A theory of everything?", there is indeed at the basis a difference in philosophy (between him and me) and the "quantum quackeries" are indeed only a reason to worry for people like me. The fundamental distinction is essentially the "belief in reductionism" which he cites in his journal entry and to which I adhere and to which some others don't - this is probably because both attitudes reflect different (successful) working attitudes in different domains.

    However, I don't agree 100% with ZapperZ's definition of "reductionism". Reductionism (at least, how I understand it) does NOT have to mean that many-particle effects are simply the addition of few-particle interactions. Reductionism (as I understand it) simply holds that there is supposed to be a single, coherent, mathematical description of ALL what happens in nature. In other words, that there is a 1-1 mapping between a certain mathematical structure, and all physical aspects of the universe. That doesn't mean that we think that we KNOW of such a structure, but we assume that such a structure exists and we try to discover aspects of it. Another way of stating that is that there exist universal physical laws that apply to everything. It has always been my idea that this was the very working hypothesis of physics, and as such am surprised that there are physicists (good ones even, like those ZapperZ cites, and ZapperZ himself :approve: ) claiming the opposite.

    Of course, the simplest ways (in the mind of a reductionist) to find hints of that structure is to explore the most "elementary" interactions, in the few-particle case. (and that's probably why most adherents of this view are particle physicists)
    Their idea is that, from these basic laws, once we know them, we can in principle mathematically deduce what will happen in more complicated settings, with gazillions of particles - under the hypothesis that we found the correct behaviour for ANY set of particles, starting from the study of a few, and good mathematical and esthetic intuition for building a theory.
    Now, condensed matter physicists (like ZapperZ) have of course a different approach. They observe certain phenomena in the lab, and try to build models of those phenomena, finding out sometimes general laws of behaviour that way. And some take on the attitude that each phenomenon can have its own different laws, INDEPENDENT of what lies underneath. This is then a holistic approach: the whole follows laws that are independent of the laws followed by the underlying constituents.

    I would first like to point out that "emergent phenomena" are, in themselves, NOT a proof that the holistic view is correct. Indeed, there are a lot of toy examples of simple laws governing constituents that give rise to "special" behaviour of a whole set of those constituents. Phase transitions included. The school example of the Ising model comes to mind of course. The problem is more with real-world situations, where 1) deriving the special behaviour of the constituents and 2) solving for the behaviour of the entire system is mathematically so hopelessly complicated that it is much more PRODUCTIVE to use the condensed matter people approach, and build directly a model around the observed properties, without bothering with the underlying constituents and their laws.

    But the whole discussion is:
    is this "model building approach" (practical holism) just a matter of getting results in a feasible way, or is this fundamental ? It is the discussion between reductionism and holism.

    I have, however, an argument, that, to me, goes strongly against holism. It goes as follows. Any possible measurement we could make on a many-constituent system, and from which holistic models could be build, will have some (statistical or definite) regularity. In the reductionist vision, it will hence correspond to a property of the mathematical structure that maps onto the many-constituent system, as built up by the rules given by the theory that ALSO governs the few-constituent systems and for which the theory is supposed to be known. The mathematical property that corresponds to the measurement on the macroscopic theory will hence have a (at least Platonic) existance. It may be practically intractable, but it is supposed to exist (as in "existence proofs" in mathematics).
    Now, there are two possibilities: or this mathematical property corresponds to the effectively measured property, in which case holism is not necessary (we DEDUCED the property from the fundamental laws of the constituents, exactly as reductionism claims), OR this mathematical property does NOT correspond to the measured property, in which case the theory of the fundamental interactions has been falsified, and there is a CLASH between the fundamental laws from which a certain prediction is derived, and the observations.
    But in no case, we can have living happily together, a holistic vision, and a theory of interactions of fundamental constituents.

    To make the above statement more concrete: imagine we are looking at the evaporation of water (a phase transition). We can measure, for instance, the bending of a light beam through a bottle of water, when we heat it by sending a current through a resistance in the water, and observe that when the water is evaporated, then the index of refraction has changed and the spot of the beam changes position. The position of the light beam corresponds to the "possible measurement" I was talking about in the abstract, above, and, *in principle* it corresponds to a clear property of the EM field (beam left or beam right), which is a property of the mathematical structure of the entire field structure of the whole experimental setup (including the matter fields of the electrons, protons,... in the water, the wire, the resistor, the battery, the light source...). No matter how mindbogglingly complicated this setup is, there is no reason why this mathematical structure doesn't exist: there are rules for setting up, say, the Hilbert space of 10^30 particles. Even though it cannot be done in practice, by a human, or a humanly designed computer, mathematically, this structure exists. As such, there will, in this mathematical structure describing the entire setup starting from fundamental principles, be an observable that corresponds to the measurement of the position of the beam after the resistor has been heating the water. It might be a probabilistic answer, but no matter, there will be *A* response to the question: is the beam here or there ?
    This answer can be, or cannot be, in agreement with what is observed. But it is not INEXISTANT. The reductionist answer to a potentially holistic phenomenon EXISTS (in a mathematical sense). In most cases it is hopeless to FIND it, but nevertheless it exists.

    In the case that there is agreement, we've then simply shown that (for the case at hand) no holism is involved: this aspect of the boiling of water is entirely contained in the elementary interactions of its constituents.
    In the case that there is disagreement, well, we've falsified the theory of behaviour of the constituents of water in this case (because IF they were all following the proposed laws, then there wouldn't be any disagreement). But you cannot have that the constituents follow individually certain laws, and the whole follows OTHER laws, without there being a clash at some point.

    What has all this to do with the OP ?
    The point is of course that QM "pretends" to be a universal theory. So in the reductionist view, well, that means that it should make just as well sense to talk about the Hilbert space of states of a human being as it makes sense to talk about the hilbert space of states of the electron and proton in a hydrogen atom. Everybody agrees that it is for sure NOT PRACTICAL to talk about the hilbert space of states of a human being, but reductionists say: well, if that's to be the case for a set of atoms, it is also the case for a BIG set of atoms (unless my theory says that it only works for less than exactly N atoms). And then you run in a few difficulties. Bohr resolved the issue in the "holistic" way, by simply saying that there is some kind of "phase transition" between a classical world of humans and so, and the "weird microscopic world" of atoms. If you take on that view, there is no difficulty. The Born rule and the projection postulate simply TELL you how to link both theories. The totally unanswerable question in this view is then: WHEN do we apply the Born rule ? Because if there were a precise answer, that would be in reductionist terms!

    There is of course a kind of "intermediate" view between the holistic and reductionist view. The mathematical structure of reality (the theory of everything) MIGHT not reveil all its aspects by only studying elementary interactions ; or, in other words, the laws we deduce from studying elementary interactions MAY of course be approximations to the "true" laws, which are so very good in the case of elementary interactions that we do not have data with enough accuracy to notice the approximation. As such, reductionists, with their misplaced arrogance, will only deduce "tangent laws" to the true mathematical structure of nature, and then claim that they know everything, if only they could solve the mathematical problem of many particle interactions. But that is not a blow to reductionism as such. It is only a blow to the hope that we can deduce the mathematical structure of reality from JUST elementary interactions. It might be then, indeed, that condensed matter experiments are more sensitive to the approximations made. We are now in the case of "disagreement" in the above explanation. But it has not undone the belief that there EXISTS a single mathematical description of all of nature. It only showed that there were limits to the structure we derived from our elementary interactions. If this is the case, however, our hopes of EVER deriving the true mathematical structure of nature may be totally hopeless, and as such, a practical form of holism is itself an emergent property of reductionism :rofl:

    As far as I know, the above situation has never been found (that there is a clear prediction of a macroscopic behaviour from elementary laws, and that observation is in contradiction with it). That's of course cheap, because of the mathematical difficulty in DERIVING the predictions for big systems, the test has not been conducted very often (predict interesting condensed-matter properties ab initio).

    cheers,
    Patrick.
     
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