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Interpretations of QP

  1. Jan 17, 2015 #1
    Hello everybody, I am new to these forums, and am curious to hear from people who know QP what in their opinion, is the best interpretation? I have heard many ways it can be interpreted, and none of them seem satisfactory to me. For example, is it a possibility that the conscious observer is indeed crucial to reality, and is the missing link in QP?? Or is true that all the outcomes occur in infinite unobservable universes?

    One thing I was thinking is this. Regardless of if this universe is truly mechanistic or not...how can consciousness ever be eliminated from any system ever? To specify more clearly. So far as I've seen, the evidence and data all conclude that consciousness cannot be eliminated from any system--by the very fact that they (scientists) look at the data.

    See what I am saying? All things existed in a multitude, possibly infinite set of potentialities and physical locations in space and time simultaneously--until we look at it, or is 'registered' by consciousness. In addition, at the moment we look at it, all things tied together by any potentiality or possibility with this thing come into being...this would explain why the wave function can supposedly 'collapse' simply by measuring the system, but ultimately that state, and what ever was doing the measuring, come into being once it is observed.

    Any attempt to describe any system while disregarding consciousness, is first and foremost, a system that I am unfamiliar with, because I am conscious. In fact 'I' am the only thing I am certain of truly exists in this universe. I am more sure I exist than the chair I am sitting on.
     
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  3. Jan 17, 2015 #2

    phinds

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    The necessity for a conscious observer was considered in the early days of quantum mechanics but the idea has been defunct for many many decades except in incorrect and misleading pop-sci.
     
  4. Jan 17, 2015 #3
    Why was it defunct? To my knowledge, nothing has been presented to refute it. Only alternate theories have been presented. If the 'founding fathers' of QP said it was quite possible, why did the later generations throw the Copenhagen interpretation under the bus?
     
  5. Jan 17, 2015 #4

    phinds

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    It is an interpretation. It does not describe anything that cannot be described with an interaction, not a conscious observer. ALL valid interpretations of QM give the same experimental results. If an interpretation without a conscious observer gets the same results as one with, then obviously the consciousness is not required, just "observation" which is really more appropriately called "interaction".

    EDIT: by the way, these interpretations are, as far as I know, no longer given much consideration in serious QM, which now has more of a "shut up and do the math" point of view. That is to say, what matters is deriving math that describes reality and leaving philosophy to philosophers since it has no bearing on the results.
     
  6. Jan 17, 2015 #5

    Nugatory

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    The Copenhagen interpretation does not, and never did, require a conscious observer. It did, and still does, contain a notion of "wave function collapse".

    It is clear that an observation by a conscious observer will lead to collapse, but it does not follow that that is the only way of producing collapse.
     
  7. Jan 17, 2015 #6
    I see. And yes I know ultimately the calculations are correct independent of which interpretation you subscribe to. The one thing I wonder is this, when you said "an experiment without a conscious observer". What exactly to you mean? At some point down the line the experiment interacts with a conscious observer...there is no way around this. So as you said, this might be getting into philosophical stuff. Essentially the only common element in any observation and any experiment ever, was the conscious observer.
     
  8. Jan 17, 2015 #7

    phinds

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    Yes, things that happen in the universe are sometimes seen by a conscious observer, but the point is that what the conscious observer sees has already happened and was not caused by him/her.
     
  9. Jan 17, 2015 #8
    How would we know 'things were happening' in an unconscious universe?
     
  10. Jan 17, 2015 #9
    I see what you are saying though. That my consciousness doesn't effect a supernova millions of miles away, or that stardust in between planets isn't effected by my observation of it.
     
  11. Jan 17, 2015 #10
    If you want some books that consider 'consciousness in QM' you can try
    "Quantum Mechanics and Experience" by David Albert
    "Conscious Mind in the Physical World" by Euan Squires
    "The Mind Matters" by David Hodgson

    [mentor note: edited to keep on topic]
     
  12. Jan 17, 2015 #11
    Is there a difference between QP and QM? Are they one and the same thing?
     
    Last edited by a moderator: Jan 17, 2015
  13. Jan 17, 2015 #12
    No. Quantum Physics and Quantum Mechanics are the same thing.
     
  14. Jan 17, 2015 #13
    what are the every day applications of QM?
     
  15. Jan 17, 2015 #14
    Chapter 9 of 'Quantum Enigma' by Bruce Rosenblum and Fred Kuttner give some examples including:
    - the laser
    - transistor
    - MRI

    Future:
    - quantum dots
    - quantum computing
     
  16. Jan 17, 2015 #15

    Nugatory

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    We don't, but as far physics is concerned, it doesn't matter.

    Because you raised this question in the context of quantum mechanics, there are several things that you'll want to know but that are often mishandled by the pop-sci press:

    1) Schrodinger's cat. Schrodinger didn't suggest his thought experiment because he or anyone else seriously that the cat might be both (or neither) dead and alive until we opened the box and looked. He was pointing out a weakness in the then-current understanding of QM: of course the cat has to be one or the other, but 1925-vintage QM didn't say it had to be that way. The discovery of decoherence (google for "quantum decoherence") decades later went a long ways towards addressing this problem.

    2) Einstein's famous "Surely you think the moon is there even when no one is looking?" was a rhetorical question. No one has ever seriously argued that it isn't there, nor that we should believe something is bad wrong with science just because we can't prove that it is there when we aren't looking.

    3) In quantum mechanics, the words "observer" and "observation" mean any interaction with anything that leads to macroscopic effects. If a particle reaches a particle detector and a needle in the detector twitches, that's an "observation" whether anyone knows about or not. It's a historic accident that word "observation" is generally used instead of "interaction".
     
  17. Jan 17, 2015 #16
    Ok. And for the Schrodingers cat thought experiment, I was thinking, schrodinger wasn't counting the cat as conscious was he?
     
    Last edited: Jan 17, 2015
  18. Jan 17, 2015 #17

    Nugatory

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    That was part of the problem. If you say that the cat is conscious, then we can rerun the experiment with a guppy, or a cockroach, or an oyster, or a bacterium. Or in the other direction we could put the entire laboratory, including the scientist and the box with cat, into a larger sealed box and ask why the whole shebang shouldn't be in a superposition of dead and alive until we open that larger box. Can it possibly matter whether there's a scientist, or a robot, or a camera, or nothing but the little box with cat in it, inside that larger box?

    Conscious observer is a dog that won't hunt, and that was Schrodinger's point.
     
  19. Jan 17, 2015 #18
    Weren't schrodinger, Oppenheimer, Bohr etc. very deeply religious men? I think they were, but people like to forget that.
     
  20. Jan 18, 2015 #19

    bhobba

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    IMHO the best interpretation is to understand what the theory says.

    For that check out:
    http://www.scottaaronson.com/democritus/lec9.html

    I have to head off now but, if the thread is still alive when I get back, I have a few comments on this conciousness thing in a historical context - why it was proposed, and now why its very backwater.

    Thanks
    Bill
     
    Last edited: Jan 18, 2015
  21. Jan 18, 2015 #20

    phinds

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    What difference does it make? Physics and the universe do not care in the least if you are religious. If your answer is right it is right and if it is wrong, it is wrong. Being religious is not going to change that in the least.
     
  22. Jan 18, 2015 #21
    It has no bearing on the results so far, anyway. The various interpretations all explain quantum mechanics as it stands today equally well, and so experimental results can't yet distinguish between them. But aren't people trying to make the various interpretations (e.g. Copenhagen, Many Worlds, De Broglie-Bohm, etc.) testable, though, and come up with predictions from them that can be tested empirically, so that some day experimental results may be able to distinguish between them while they can't yet now?

    As far as I understood it, the "shut up and calculate" view is a temporary, pragmatic position taken by the majority of working physicists applying QM as a tool/paradigm for understanding other areas of physics and other problems, until someone manages to experimentally find evidence for one or the other interpretations - apply your quantum mechanics to your lasers, semiconductors, chemical bonds and nuclear reactions, but leave the question of what those equations actually mean in the real world to those who are working on it. We'll have to stick with "shut up and calculate" now, in practice, but in theory there must be a correct interpretation and some day we'll know which one it is (or more likely none of the ones we have now!) Am I wrong about this, then?

    Are you implying it's a permanent position taken by physicists, implying that nobody should ever bother with the interpretations because they can never be tested on principle? But doesn't that shut off research in the direction of making the interpretations testable and imply it'll never be worth looking into? After all, cosmology for example was considered philosophy rather than physics and a collection of untestable, metaphysical ideas before General Relativity and the discovery of the expanding Universe gave it a scientific basis on theoretical and observational grounds, respectively. And while string theory and the multiverse, for example, are grounded in physical laws and mathematical rigour, as far as I know nobody has come up with testable predictions of either yet - yet they're still found in scientific journals, since the mathematics is still being ironed out and physicists are working hard on coming up with some testable predictions for these ideas and bringing them into the realm of empirical science in future.

    It would be sad indeed if physics - the discipline whose main goal is understanding the Universe and how it works at a fundamental level - would be forced to give up and throw in the towel prematurely and admit that its single most experimentally successful and wide-reaching theory will never have a physical explanation!
     
  23. Jan 18, 2015 #22

    phinds

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    It is my understanding that there is general agreement these days that interpretations are philosophy, not science, but perhaps more knowledgeable folks can chime in if I'm wrong.
     
  24. Jan 18, 2015 #23

    bhobba

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    Not necessarily - its the testability thing. Some such as primary state diffusion are testable, others like MW may become testable and minimalist interpretations like Copenhagen (most versions anyway) and Ensemble that hinge on interpretations of probability are inherently untestable.

    Thanks
    Bill
     
  25. Jan 18, 2015 #24

    bhobba

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    Yes and no. Many physicists ascribe to it because they aren't really worried about interpretational issues.

    That said it may be just how nature is - we simply don't know.

    Also it comes in a number of variants none of which can't really be distinguished from each other - the difference being their interpretation of probability.

    Here is the modern view on what QM is all about - its basically the most reasonable generalised probability model that allows the continuous transformation between so called pure states:
    http://arxiv.org/pdf/quant-ph/0101012.pdf

    Physically that's a pretty obvious property because if you can apply something that changes a system for one second, during that its applied for half a second.

    Thanks
    Bill
     
    Last edited: Jan 19, 2015
  26. Jan 18, 2015 #25

    bhobba

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    As promised just to expand on this conciousness thing in QM it was first introduced by the great mathematician and polymath Von-Neumann. He was the first to do a fully quantum analysis of the measurement process. QM is a theory about observations that occur in a common-sense classical world that exists independent of if a concious observer observes it or not. But what Von-Neumann found was the quantum classical cut could be placed pretty much anywhere. In trying to find a place that was different he traced it back to a concious observer so that's where he put it, despite the considerable philosophical baggage of such a weird position. It never really caught on because it is rather weird, but did have another high profile adherent - the equally great mathematical physicist - Wigner.

    Anyway unfortunately Von-Neumann died young and didn't live to see developments in the area of decoherence that showed there was a place that was different - just after decoherence - and in modern times either explicitly, or implicitly, that's where its usually placed - its connected with the difference between proper and improper mixtures. Wigner did live to see this development and when he saw some early work on it by Zurek did a 180% about face and actually advocated some kind of objective collapse.

    These days its generally considered very backwater because the reason for its introduction has long since disappeared and its formidable philosophical issues, especially now we have computers that can record observations in memory and that memory can be copied endlessly.

    Thanks
    Bill
     
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