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The observer problem(?)

  1. Sep 7, 2013 #1
    I'm studying quantum mechanics and I can't seem to understand what qualifies as an observer. Does the "observer" need to be a conscious one? Yes or no and why? Thanks in advance :)
     
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  3. Sep 7, 2013 #2
    No. Observation in quantum mechanics means interaction/measurement with e.g. an instrument in general.

    Hmm. Let's try this: You have many small (biological) photodetectors in your eyes, which enables you to detect light. But we can build a lot of other kinds of photodetectors, which obviously are not conscious.
     
  4. Sep 10, 2013 #3
    I don't really mean to imply that a conscious observer is absolutely necessry to collapse the probability wave, but I do have a couple of problems with your answer.

    Here you defined observation as interaction/measurement, which can sometimes leave people with the wrong impression, that interaction alone is enough to collapse the probability wave, which it absolutely isn't. Only measurement collapses the probability wave, and then only for the property for which the state of the particle is thus known. Thus in the double slit experiment you could interact with, and measure the particle, until the cows come home, you could knock the heck out of it, but if none of those measurements gives you which path information, then the interference pattern isn't going anywhere. The probability wave ain't gonna collapse for just any old measurement, it's gotta be specific. The particle somehow seems to know what you're measuring, but not only that, it also seems to know what you may indirectly learn from that measurement. So while the observer may not need to be a conscious one there appears to be more going on here than merely, I measure it, it collapses.

    While it's true that we can easily build a photodetector to "see" the particle in question, in what way is this evidence that such a detector could collapse the probability wave? The last time that I checked, every biological photodetector is connected to a biological brain, and who's to say that it's not the latter that actually collapses the probability wave? Is there indisputable evidence that detection alone collapses the probability wave?

    It does seem logical that there is no need for a conscious observer, but is there evidence? After all, this is science, right?
     
  5. Sep 10, 2013 #4

    meBigGuy

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    Does that mean that the particle hitting a photo detector does not collapse until 20 years later when the data is checked by a human?
     
  6. Sep 10, 2013 #5
    I'm not surprised. I guess that's why there are 17+ interpretations of quantum mechanics :wink:.

    Nevertheless, I don't think that details on interpretations is very useful to a person (post #1) who (which I presumed) has recently started to study QM. That's why I did not bring it up (personally I try to keep a certain distance to discussions on interpretations).

    The notion of wave function collapse originates from the Copenhagen interpretation, and there is no scientific consensus which interpretation is most satisfactory. Yes, there are issues to consider; Measurement in quantum mechanics and Measurement problem.

    I take the scientific method very seriously, and just like Carl Sagan I say "extraordinary claims require extraordinary evidence".

    So let me put it this way:

    Is there any scientific evidence there is any need for a conscious observer?
    I'd say there is none whatsoever. The burden of "proof" lies on those who makes the claim; they need to show experiments that demonstrate it. And there are none as far as I know.

    My photodetector example was just a little hint to the OP (which the OP btw thanked me for), but here is a somewhat more detailed thought experiment:

    Imagine a quantum experiment done by a machine placed on the far side of the Moon - there are obviously no conscious observers there. Then let the results of the experiment be printed out and sent back to me here on Earth by rocket. Am I supposed to believe that when I read the results here on Earth, this retrocausally collapses any wave functions on the far side of the Moon? I can imagine a lot, but that idea is just too extreme for me.

    Well, quantum mechanics is science. Some interpretations of quantum mechanics are, how shall I put it, science with a twist. I personally try to stay away from them :smile:.
     
  7. Sep 10, 2013 #6
    Good point.
     
  8. Sep 10, 2013 #7

    meBigGuy

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  9. Sep 10, 2013 #8

    bhobba

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    An observation is anything capable of leaving a mark here in the common sense macro world. A conscious observer is most definitely NOT required. A measurement apparatus is a device capable of displaying the results of such observations as numbers, or at least allow it to be simply mapped to numbers. QM is a theory about such measuring devices observing quantum systems.

    You will find this explained clearly and concisely in my go-to book on QM - QM - A Modern Development by Ballentine:
    https://www.amazon.com/Quantum-Mechanics-A-Modern-Development/dp/9810241054

    Get it, study it and you will understand QM. Pretty soon you will realize a lot of the stuff written in the popular press, such as this idea you need a conscious observer for an observation - is laughable. That's not to say the consciousness causes collapse is not a viable interpretation - it is - but required it certainly aren't. Indeed when you really understand whats going on you probably will, like me, wonder why anyone wants such an extreme view anyway - but that is a discovery you need to make - me telling it to you is not the way to understand such things - you need to think about it yourself.

    You will also understand the true basis of much of QM - stuff like Schrodinger's Equation - is symmetry. Once that is understood its a mind blowing revelation about what really lies at the fundamental foundations of physics.

    At a more non technical level the following is pretty good as well:
    https://www.amazon.com/Symmetries-R...48&sr=1-1&keywords=Symmetries+and+Reflections

    I read it years ago - didn't have a huge impact on me then until I really thought hard about it and came to understand something called Noethers Theorem - then I realized it was very important - but want to read it again because it really is fundamental - absolutely fundamental.

    Thanks
    Bill
     
    Last edited: Sep 10, 2013
  10. Sep 10, 2013 #9

    bhobba

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    Yea - it really does make a nonsense of consciousness causes collapse. Computer science would be rendered laughable if true.

    Thanks
    Bill
     
  11. Sep 10, 2013 #10
    I know that my previous post gave the impression that I believe that a conscious observer is necessary to collapse the probability wave, but that is actually not the case. My own personal opinion, (and that's all that it is) is that a conscious observer is not necessary to collapse the probability wave. Indeed my view is much in line with what bhobba proposed, that "An observation is anything capable of leaving a mark here in the common sense macro world." I believe that so long as the information about which state a particle is in exists anywhere, then the particle will absolutely be in that state. Simply put, if the information exists, then the state exists.

    I don't believe that it matters, whether the information won't be seen until 20 years from now, or whether the event happened on the dark side of the moon, if it left a mark as bhobba says, then it happened. To me, and to most other people, wave collapse occurs based upon the information the environment has, not based upon the information I have.

    But the problem is that I can't state this as being categorically true. It's only my opinion, and as quantum physics shows, what's intuitively logical, may not be true, and so the question of just what constitutes an observer is still open for debate. The OP was looking for a yes or no answer. But there isn't a yes or no answer. To claim otherwise wouldn't be completely honest.

    And we all want to be completely honest, right?
     
    Last edited: Sep 10, 2013
  12. Sep 10, 2013 #11
    I have no problem whatsoever with this :smile:. And I did not get the impression you believed in e.g. "consciousness causes the collapse".

    Yes. I was short in post #2, but I think I was honest. There is no notion of consciousness in formal quantum mechanics. And - as a sidenote - consciousness is as far as I know a very slippery term. How should it be defined with pure physics - can it be defined with pure physics? I guess the consciousness question is a question mainly for biologists and possibly chemists.
     
    Last edited: Sep 10, 2013
  13. Sep 10, 2013 #12

    bhobba

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    There is a definite no answer is the sense QM requires a conscious observer - it doesn't. There is a definite yes answer in the sense you cant prove consciousness doesn't cause collapse. But consciousness causes collapse does lead to a very weird view of the world - so weird I think anyone that understands its full implications, such as what happens if you replace the conscious observer with a computer (think about it) will reject it.

    And I didn't get the impression you were advocating it either - simply putting it out there as a possibility - which it is. The issue though is not that - its some books, especially those of the pop-sci type give the impression its whats QM says - it isn't.

    To the OP - don't take my word for it - get the book I mentioned by Ballentine - it really is that good. It's unusual in it gives a full account of foundational issues rather than being a cookbook to solve problems.

    Oh - I am assuming you are a serious student - its a serious book for serious students.

    Thanks
    Bill
     
    Last edited: Sep 10, 2013
  14. Sep 10, 2013 #13
    It's good that we're somewhat in agreement as to the necessity of a conscious observer, but I don't believe that I'm as steadfastly against the idea as others may be. It would help if I had a clearer understanding of what exactly constitutes an observer.

    For example, in the double slit experiment, if we put a detector at the slits, such that it measures which slit the particle went through, but we don't attach this detector to any type of data storage device, then the interference pattern will remain. What is it about the detector that keeps it from acting as an observer? Isn't it part of the environment? Perhaps its state has simply become entangled with that of the particle, and the subsequent system is in its own quantum state. But the two do constitute an environment, just not a very complex one. If we add a bunch of mirrors and filters to the setup, but we gain no information by doing so, then the probability wave still won't collapse. Even if we add a data storage device, but we make the data inaccessible, the wave still won't collapse.

    So the question becomes, at what point is the environment complex enough to cause the collapse? It may well be that an environment is capable of causing the collapse only when that environment contains a conscious observer. It isn't necessarily required that an observer actually be involved in any way with the measurement, or the subsequent data, but it could very well be a requirement, that the environment at least contain a conscious observer. Show me a collapsed quantum system in which a conscious observer is not a part of that system, and I would be a lot more certain that a conscious observer isn't necessary.

    Until then it is perfectly reasonable to argue that a conscious observer is indeed necessary, at least indirectly. It's a whole other debate as to what actually constitutes a conscious observer.

    Until you rule it out, even the outrageous is possible.
     
  15. Sep 10, 2013 #14
    Could be the case.
     
  16. Sep 10, 2013 #15
    I would not even start to go down that path without a proper definition of conscious observer. So, what is your definition of a "conscious observer"?

    I don't agree. I do not think it's reasonable that quantum mechanics on the far side of the Moon (or Mars etc - choose any place you like in the Universe) would work differently than quantum mechanics on Earth.

    Possible - well, with a considerable grain of salt. But is it probable? Well, that's certainly up for debate. Extraordinary claims require extraordinary evidence. I also personally like to apply the tools in Carl Sagan's so-called Baloney Detection Kit;

     
  17. Sep 10, 2013 #16

    meBigGuy

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    Well, it could also be the case that Fred in Pittsburg actually monitors all quantum interactions and decides which ones collapse.

    My personal view is that collapse is a relative view (relational) and that things are as defined as they need to be (relative to other things) to properly correlate. I haven't gotten to decoherence in the susskind lectures yet, so maybe that will change my mind. But I expect not.
     
  18. Sep 10, 2013 #17

    bhobba

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    No - it goes away ie regardless of if it is connected to a storage device or not the interference pattern disappears. An observer, detector or whatever you want to call it, is anything capable of leaving a mark here in the macro world. If its a particle detector it will click or flash. The storage thing is just to bring out what kind of a weird view you are led to if you think its consciousness that causes collapse. In modern parlance the detector becomes entangled with the particle and its position becomes localized through one slit or the other so it can no longer interfere.

    There is a nice set of lectures by Lenny Susskind that explains it all really well, and the modern take involving decoherence and entanglement:
    http://theoreticalminimum.com/courses/quantum-entanglement/2006/fall
    'The old Copenhagen interpretation of quantum mechanics associated with Niels Bohr is giving way to a more profound interpretation based on the idea of quantum entanglement. Entanglement not only replaces the obsolete notion of the collapse of the wave function but it is also the basis for Bell's famous theorem, the new paradigm of quantum computing, and finally the widely discussed "many-worlds" interpretation of quantum mechanics originated by Everett.'

    Make no mistake - its a valid explanation - but the world view you are led to if you accept it is very very bizarre and totally unnecessary.

    The great mathematical physicist, Eugine Winger, was one of the high priests of consciousness causes collapse. The reason was Von Neumann's famous analysis that showed the collapse could be put anywhere and the only real place that was different is the consciousness of an actual organic observer - so that's where he put it. But over the years progress was made, especially in the area of decoherence, and what that showed is its likely the best place to put the collapse - right after decoherence. When Wigner heard of some early work on decoherence by Zurek he realised the consciousness thing was no longer required and abandoned it.

    I also want to add, and to be very clear about it, decoherence does NOT solve the measurement problem to everyones satisfaction. Without going into he details, it merely gives the APPEARANCE of wave-function collapse, the exact meaning of which you need to investigate the detail to understand. If you want to do that check out:
    http://philsci-archive.pitt.edu/5439/1/Decoherence_Essay_arXiv_version.pdf

    That paper reaches the correct conclusion it leaves the central problem untouched - which is true - the debate about if it solves the measurement problem is if that central problem, issue, or whatever you want to call it, is worth worrying about in light of what decoherence does do - I don't believe it is - but opinions vary and you will find a number of, sometimes heated, discussions about it on these forums.

    Thanks
    Bill
     
    Last edited: Sep 10, 2013
  19. Sep 10, 2013 #18

    bhobba

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    That's a perfectly valid interpretation, just in the light of decoherence overkill because once decoherence occurs all observers agree. Its examined in the link I gave before (see section 3.2.3):
    http://philsci-archive.pitt.edu/5439/1/Decoherence_Essay_arXiv_version.pdf

    Modern versions, such as Zureck's version, takes all this into account and leads to a very clean interpretation:
    http://arxiv.org/pdf/0707.2832v1.pdf

    Thanks
    Bill
     
    Last edited: Sep 10, 2013
  20. Sep 10, 2013 #19

    meBigGuy

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    That doesn't say anything about what could be significant lengths of time during which observers don't agree. It seems to just define that away. I'll try to say what I am thinking, but I'll probably screw it up. If one thinks of entanglement as any interaction that allows continued superposition (correlation), you could imagine that two entangled (correlated) entities see each other as a definite state, but an external entity still "sees" (actually, doesn't see) an indefinite system until it interacts. And this state of different relative views is stable.
     
  21. Sep 10, 2013 #20

    bhobba

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    Its provable to be on time scales that even with modern equipment you cant detect. It has been possible to rig it so it occurs slower to actually observe it - and that has been done - ie decoherence has been observed - but that is a very special experimentally designed setup for that purpose - it never occurs in practice.

    If you want to hold to the relational view I suggest a version similar to Zurec's in the paper I linked to - it takes into account modern developments since Rovelli proposed it.

    Thanks
    Bill
     
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