Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

QM - What's the problem?

  1. Apr 1, 2006 #1


    User Avatar
    Science Advisor

    QM -- What's the problem?

    As I have indicated time-after-time I am no fan of alternative approaches to QM. I've been very critical in some cases, as only a retired physics professor can be; sometimes my civility has gone out the door. So , enough. What I propose is a series of questions that, I hope, will stimulate discussion on the efficacy, or lack thereof, of QM.

    1. Is QM odd because nature is odd?

    2. Does the measurement problem show up in classical systems?

    3. What's wrong with a probabilistic theory?

    4. Why should we be able to understand Nature in "classical terms" when we go past our normal spheres of perception?

    5. Why focus so much on the two slit experimet, at the expense of other phenomena?

    6. How can anyone who does not have at least a few years of experience with QM, after school, be a legitimate critic of QM?

    7. What's to complain about QM's extraordinary and manifold agreement with Nature?

    So, there they are.

    Reilly Atkinson
  2. jcsd
  3. Apr 1, 2006 #2
    There are alternatives to the standard quantum formalism and then there are alternatives to what Redhead called the "minimal instrumentalist interpretation" (MII) of the standard formalism. Alternatives of the former kind are, for instance, the spontaneous collapse theories of GRW and Pearle. Every interpretation that tries to go beyond the MII is an alternative of the latter kind.
    Yes, odd in terms of common sense, which is adapted to the macroworld. But if one wants a theory of the microworld to explain the features of the macroworld, one cannot expect the microworld to possess the features of the macroworld. Otherwise one only gets out of the theory what one has put in. So the oddness is to be expected. This was pointed out by Heisenberg. (I would be glad if someone could find the reference for me.)
    Why indeed.
    Because Feynman said it has in it the heart of quantum mechanics? There are indeed other experiments that are of equal importance for the physical interpretation of the mathematical formalism of quantum mechanics: a simple http://thisquantumworld.com/scat.htm" [Broken] of Elitzur and Vaidman, etc.
    I wonder.
    Nothing. The general complaint is that it doesn’t readily yield a sensible ontology. (Sensible doesn’t have to mean classical, whatever that means.)
    Last edited by a moderator: May 2, 2017
  4. Apr 3, 2006 #3
    Is it fair to say that the bomb testing experiment is a logical consequence of the superposition principle? So in this sense, it represents the same phenomena that a double slit experiment does, and further evidence of the physicality of superposition?
  5. Apr 4, 2006 #4
    In http://thisquantumworld.com/ev.htm" [Broken]": calculate the probability of detection by taking the absolute square of the sum of two amplitudes.
    Last edited by a moderator: May 2, 2017
  6. Apr 10, 2006 #5
    the "problem" is that a Probabilistic version without classical concepts such a force, momentum, and so on..can,t deal with a pure geometrical theory like Gravitations or Kaluza-Klein theories..but why should it be probabilistic?..makethe change t*---->it and you get that all your QM equations become similar to the equations that appear in Statistical Physics and Brownian motion
  7. Apr 10, 2006 #6
    OP: What if your wrong though :wink:

    Actually QM is very robust as far as my limited experience has been able to determine, if a little bit fuzzy.

    I do think though that looking into other alternatives isn't a bad idea, after all who knows what they may find to either support or cast doubt on QM?

    You could ask that of most critics, where's the harm in questioning scientific mainstream even if it is misinformed(out of the mouths of babes) That which does not kill science makes it stronger.

    Didn't Einstein once say I looked in the mirror for ten years and that's the only theoretical physisist I saw? Perhaps he should of stuck to the mainstream too?
    Last edited: Apr 10, 2006
  8. Apr 10, 2006 #7


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Hi reilly,

    I don't think there's anything wrong with QM (except its potential problem with GR maybe). It certainly is odd! But I don't mind nature to be odd. I don't think there's anything wrong with a probabilistic theory either.

    However, I do have a problem with the "orthodox" views on quantum theory (although, I often said this, the standard, orthodox view is by far the best to LEARN quantum theory). My problem with the orthodox view does not reside in oddness, or the fact that it is probabilistic or whatever ; it resides essentially in the fact that I have to switch descriptions between "myself", "apparatus" and "microscopic" things. Now, I know the whole story about how you should not extrapolate your daily experience to microscopic or whatever extravagant situations, but that's not the point. The fundamentalist reductionist in me requires that *everything* should be eaten with the same sauce. That might be an odd way or not, but I cannot accept that one should treat certain things in nature fundamentally differently than others. Everything should be equal for the law. No matter what strange law.
    And *this* is what goes wrong with the orthodox view (and which inspires me to consider at first sight crazy ideas such as MWI): the fact that one sets apart certain phenomena wrt to others. The fact that my voltmeter should be described in a *fundamentally* different language than an electron. I can accept that a voltmeter is a system which is quite different than an electron, but, at the bottom, both should be fundamentally be described in the same way. It might be *practical* to use certain *approximations* in certain cases. But we're not talking about approximations here. We're talking about incompatible descriptions. If it's a wave function, then a wavefunction for everybody. If it is a classical description, then a classical description for everybody. But not, one thing described in *this* formalism, and another thing described in *that* formalism - unless one can show that "that" formalism is a good approximation for "this" formalism in some peculiar cases - which is NOT the case with the relationship quantum-classical in the orthodox view.

    I have difficulties defining "measurement" as something different than "interaction", and I have difficulties defining a "measurement apparatus" as something different than "a physical system". Especially when you study the physics of measurement apparatus!

    Now, I agree that this is a purely reductionist worry. If you are a holder of the view that "every level of complexity its own theory" and that the "underlying layer has nothing to say about the theory of the next layer", then there's no difficulty in saying that some things are governed by quantum theory, and other things are governed by classical physics.
    But I'm a reductionist, and as such, I require a serious theory to be applicable - at least in principle - to everything within its scope. And as the scope of quantum theory is supposed to encompass everything (quantum theory is not known to be *an approximation* to a better theory as far as I know), then its fundamental description should apply to everything. Myself and my voltmeter included.
    This has always been the case: until we knew better, when we had classical physics, it was to be applied to everything, our bodies and measurement apparatus included. Thermodynamics is supposed to apply as well to the "system" as to the apparatus and our bodies.
    This should be the case with quantum theory too, and this is contradicted by the orthodox approach to quantum theory, where there is a FUNDAMENTAL difference between the lab apparatus (setting up the state and measuring the state) - which is classical - and the "system under study" which is quantum mechanical.

    So again, I have no difficulties with QM per se. It is a highly successful theory. And I have no difficulties with the orthodox view *as an algorithm*. It's a perfectly good way to use quantum theory.
    But I have a difficulty with the "metaphysical" picture it tries to create, and I prefer another one, namely the MWI view - because I find that a much more coherent (although admittedly very strange) picture for the reductionist in me.
    With MWI-QM I have _certainly_ no difficulties (except trying to explain to people that it is not totally absurd :smile: )... apart from the still apparent incompatibility with GR.

  9. Apr 10, 2006 #8


    User Avatar
    Science Advisor
    Gold Member

    Nothing, in my mind. :smile:

    There is bias towards assuming that cause-and-effect controls everything. This traces back at least as far as David Hume, ("An Enquiry Concerning Human Understanding", 1748). You can see my defense of the probabilistic viewpoint [URL [Broken].[/URL]

    It seems to me that most people will do just about anything to restore causality to theory... even though the world around us is filled with chance events. Does causality ultimately explain anything more than chance does?

    In the end, a useful theory trumps. And QM is certainly useful!
    Last edited by a moderator: May 2, 2017
  10. Apr 13, 2006 #9
    Hi Rielly my good man. How's it going?

    1. Is QM odd because nature is odd?


    2. Does the measurement problem show up in classical systems?


    3. What's wrong with a probabilistic theory?

    Nothing that I can see. I like it since it allows for free will and I've always hoped my will was free. But if not then I can blame some of my faults on someone else, right? :biggrin:

    4. Why should we be able to understand Nature in "classical terms" when we go past our normal spheres of perception?

    I see no reason for it myself.

    5. Why focus so much on the two slit experimet, at the expense of other phenomena?

    Its a simple barrier which one must analyze and put some thought into so that they may understand the ideas of QM. Some can say "Okay. I got the picture you're peddaling, lets move on to the next example." Unfortunately people don't tend to think that way. :cry:

    6. How can anyone who does not have at least a few years of experience with QM, after school, be a legitimate critic of QM?

    I suppose its arrogance that allows for this.

    7. What's to complain about QM's extraordinary and manifold agreement with Nature?

    No complains here dude.
    Thanks Reilly

  11. Apr 13, 2006 #10
    How? Your decisions are motivated, goal-directed. They are not random, are they? Measurement outcomes in quantum mechanics are. Free will does not act through the loopholes of quantum-mechanical indeterminism. This was pointed out long ago by Schrödinger. I have given a more detailed argument in http://thisquantumworld.com/PDF/pi.pdf" [Broken], which appeared in Journal of Consciousness Studies.
    Last edited by a moderator: May 2, 2017
  12. Apr 14, 2006 #11
    You've never heard of this? Its a famous deduction in QM. Reilly will tell you more about this I'm sure. If mechanics were deterministic then we'd be just objects which have a definite future since, for a practical example, out bodies would be just like clocks and we'd be interacting with other clocks like other people or with weather of falling leafs etc. An incredibly complex clock, yes, but still a clock and it has only one outcome.
    They occur in the mind which is a machine working.
    Are the signals inside a computer random? Are they predetermined after it recieves input?
    I fail to see why you call it a loophole.
    Reference please.

  13. Apr 14, 2006 #12


    User Avatar
    Staff Emeritus
    Gold Member
    Dearly Missed

    Pmb_phy, the idea that quantum uncertainty rescues free will is to say the least controversial among physicists as well as philosophers. You say it was "pointed out" by Schroedinger; I would rather put it that he devoutly believed that, but that you cannot derive it rigorously. I note that your explanations are all over the lot in scale, from quantum level, to clocks and computers, to our brains, but it's all hand waving. How does QM act in our brains that is DIFFERENT from the way it operates in clocks and computers? How can it provide free will to us and not to them?
  14. Apr 14, 2006 #13

    No I didn't. Someone else did and I asked for a reference.

    I got past free-will into another topic he brought up, i.e. randomness (Although I'm not sure why he brought it up. :confused:

  15. Apr 15, 2006 #14
    I've heard too much of it, as you should have gathered from my post. I suggest you read the whole before you begin replying.
    I never said it was.
    Schrödinger in Quantum Questions, edited by Ken Wilber (Boulder & London: Shambala, 1984) p. 80:
    Could perhaps the declared indeterminacy allow free will to step into the gap in the way that free will determines those events which the Law of Nature leaves undetermined? This hope is, at first sight, obvious and understandable.

    In this crude form the attempt was made, and the idea, to a certain extent, worked out by the German physicist Pascual Jordan. I believe it to be both physically and morally an impossible solution. As regards the first: according to our present view, the quantum laws, though they leave the single event undetermined, predict a quite definite statistics of events when the same situation occurs again and again. If these statistics are interfered with by any agent, this agent violates the laws of quantum mechanics just as objectionably as if it interfered - in pre-quantum physics - with a strictly causal mechanical law. Now we know that there are no statistics in the reaction of the same person to precisely the same moral situation [just as there is nothing statistical in the causal relation between the intention to act and the action intended] - the rule is that the same individual in the same situation acts again precisely in the same manner. (Mind you, in precisely the same situation; this does not mean that a criminal or addict cannot be converted or healed by persuasion and example or whatnot - by strong external influence. But this, of course, means that the situation is changed.) The inference is that Jordan's assumption - the direct stepping in of free will to fill the gap of indeterminacy - does amount to an interference with the laws of nature, even in their form accepted in quantum theory.​
  16. Apr 17, 2006 #15
    reilly---I agree with you; and, I think QM (and/or one of it's sub-theories) holds the most possibilities of getting the answers.

    I'd like to hear (read) the (your) answers to your own questions.
  17. Apr 18, 2006 #16
    Well said!
    But the question remains--how does free will arise from physical laws?How does consciousness arise?
  18. Apr 18, 2006 #17
    Does our brain decohere with the environment as readily as every other bit of experimental equipment?
  19. Apr 18, 2006 #18


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Free will might be an illusion, in that it is the physics (deterministic or probabilistic) that tells your physical body what it will do, and your subjective experience of that is simply that you "desired" to act that way.
    A bit like an apple always "desires" to fall off the tree.

    I think that this question is impossible to answer within the realm of a physical theory which limits itself to empirical observations and predictions, given the fact that there's no behavioural or empirical indication of consciousness (in the meaning: is associated with subjective experiences). In all the cases where it is claimed to do so, the concept of "consciousness" has simply be re-defined.
  20. Apr 18, 2006 #19


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Probably even faster, given its messy coupling to the environment (ever tried to have a brain working in ultra vacuum near 0 K ?)
  21. Apr 18, 2006 #20
    That's really quite odd, I've been discussing this sort of stuff at length recently on a non physics forum. If anyones actually interested in what sort of research has been done on the quantum and consciousness question. I have some data and some links for the Consciousness research centre at Colorada university. The most recent interesting although controversial results from a Scientist named Beck, show some evidence that synaptic triggers might be effected by QET in microtubials. It's all highly speculative. But I would imagine it's all pretty well known stuff or maybe not. Anyhow the question of free will and the quantum has many adherents in the philosophical world.

    I came up with the idea myself independently the first time I began to look into QM, if you even have a small inkling of QM and some knowledge of philosophy as it purtains to the free will/determinism discussion the two go together like cheese and wine. I would be surprised if most people don't stumble on the ideas sooner or later themselves if left in a vacuum like I was. It's like the wheel, every society that needs it comes up with it sooner or later.

    Only recently though has the philosophical been explored in scientific terms and there's plenty of papers out there, some credible some not so credible.

    Enzymes "use" decoherence to more efficiently process Uracil in RNA and other protein strings in DNA replication, I'd be surprised if biological areas of the body don't also make use of it at the frighteningly small level of the human brain. Who knows though?

    Don't ask me to find links to the above notion, if you can obtain papers from NASA's nanotech research areas do so, I saw an overview in NS magazine only and I can't even find that. Sorry :frown:
    Last edited: Apr 18, 2006
  22. Apr 18, 2006 #21
    Is a bacteria conscious?

    EDIT: That should actually be "Is a bacterium conscious?" or alternatively, "Are bacteria conscious?"
    Last edited: Apr 18, 2006
  23. Apr 18, 2006 #22
    Is a bacteria conscious?

    Depends on how many prepositional phrases and qualifiers are/could be included in the sentence; such as, 'of aware of a food source' or even 'of a magnetic field' , or 'if and only if it has nerve cells'.

    And, as this relates to QM (and the rest of the theories)---Which theory has the least amount of "prepositional phrases and qualifiers"? Which theory did you (anyone) choose to expend 'time' to investigate? Which one have you (anyone) invested in to 'believe'? --And, why?

    One 'funny' thing that passes my thoughts once in awhile,---Would the Wright brothers have been the first to fly if they would have been academically trained theoretical physicists?
  24. Apr 18, 2006 #23
    @ Vanesch: I just noticed free will is an illusion? Such a fad thing to say, prove it? It's no better than saying predeterminism is preposterous based on modern theoretical physics. I hear that expression so often that it's almost like everyones convinced themselves it's true despite it being a hypothesis. Since as far as I am aware no philosophers have answered the questions either way or scientists for that matter, how can you prove that it is an illusion and if you just stated that, shouldn't you have chastised yourself for saying it on a physics thread?:smile:

    Materialists are so dull. Almost as bad as secular humanists :tongue:
    Last edited: Apr 18, 2006
  25. Apr 18, 2006 #24
    Well, everything's a hypothesis in physics. If you're afraid of making hypothetical statements, then don't do physics. However, every statement can be held to be true under some model. For example, [itex]1+1 \in \mathbb{R}[/itex] is in fact true, given that we are talking about the real numbers. A similar thing holds in physics.

    Hypothesis H1: Given enough initial conditions, the classical state of a system is indefinitely determined.

    H1 is a truth in classical mechanics. Whether or not H1 holds in describing reality is equivalent to the hypothesis that classical mechanics corresponds to reality.

    Now physics aside (since this applies more generally), every statement is a hypothesis. There is no truth; if some hypothesis is held to be true by a large majority of "sane" people, we often elevate that hypothesis to truth.

    Hypothesis H2: The earth is flat.

    H2 was believed to be true by so many a few centuries ago, that it was elevated to the notion of truth. Of course, we all know it was a hypothesis. One that now has very little (if any) empirical support.

    To summarise: everything is a hypothesis; hypotheses can either have empirical support or not and this can help an individual decide if they wish to believe the hypothesis is true. Importantly, no hypothesis can be proved true in the sense of describing the universe (as we all know).

    My statements above are all hypotheses too.
    Last edited: Apr 18, 2006
  26. Apr 18, 2006 #25

    Doc Al

    User Avatar

    Staff: Mentor

    He just said it might be an illusion. :wink:

    What I find more amusing is the appeal to quantum randomness as supporting some kind of ultimate (contra-causal) free will.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook