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Is Consciousness involved in wave function collapse?

  1. Jun 15, 2011 #1

    I know it's a rather subjective title. But I am no expert in the subject and I've read a lot of information in the Internet that is contradictory.

    I have read that the collapse of the wave function requires interaction with an observer. But is that collapse in any way related to the awareness of the observer or to interference with the measuring device alone?. I understand that all the founders of quantum mechanics, like Bohr and Einstein rejected this idea, right?

    I would appreciate, if it’s not too much trouble, any links or references that discuss the subject.

  2. jcsd
  3. Jun 15, 2011 #2
    this comes up often.

    the answer is No.

    experiments have proved that it's the setup that causes the "collapse" ....

    the collapse happens even when no human/living-entity is watching.....

    now one could argue further and say/ask -

    how do you know if collapse has happened, even if no human is watching?

    there is an answer...but then.... there's no end to such a line of questioning...
    Last edited: Jun 15, 2011
  4. Jun 15, 2011 #3

    Ken G

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    The basic problem is that physics itself demonstrably comes from the consciousness (nothing unconscious is doing any physics), consciousness is built right into the fabric of the scientific method (and here I make no attempt to distinguish "consciousness" from "awareness" or "intelligence" or "understanding", you can try to parse those words if you want!). So the basic problem is, we have no idea to what extent our own thinking processes are inherent to our physics, including our concepts like collapse of the wavefunction. The best we can do is recognize that the concept of a hypothetical observer, with a hypothetical consciousness if necesary, suffices to understand our physics. So there is not a need for a real observer or consciousness to be present to understand the outcome of some physical event, but that is not quite the same thing as saying there doesn't have to be a consciousness at all. Physics is, above all, a kind of language, spoken by an intelligence, that is conscious. Make of that fact whatever you will.
  5. Jun 15, 2011 #4


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    In quantum physics, the state of a system is given in terms of the statistics of measurements obtainable on the system. Formally, this statistics is given in terms of the 'wavefunction' [itex] |\Psi \rangle [/itex]. When an irreversible interaction between the atomic objects and the measuring apparatus occurs, the wavefunction which for t < [the time of measurement/interaction] previosly represented the probabilities of various values no longer defines the state of the object. Thus the 'collapse' of the wavefunction is due to the irreversibility inherent in the concept of observation itself.
  6. Jun 15, 2011 #5
    The collapse of states or wave functions is traditionally related to 'observations'. However there are several common natural systems where states collapse by themselves. Human consiousness or awareness is not relevant at all. You could just make a measuring device that didn't show the results and the measured system would still collapse.

    In other words, you can't obtain (exact) information of a quantum system without collapsing its states. But it doesn't work the other way around. You can collapse the state without obtaining any information at all.
  7. Jun 15, 2011 #6


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    What does this have to do with the actual question at hand? Of course, only a conscious intelligence could imagine a hypothetical thought experiment, but this is entirely beside the point. This is not what the OP is asking about.

    The OP is asking whether the presence of an actual conscious observer effects the outcome of a quantum measurement. The answer is that it does not.

    I think the reason this question comes up so often is semantic. We use the word "observation", but we should use the word "measurement", or as dx says above, "interaction."

    During the measurement, the quantum system must interact with the measurement device. The measurement device is inherently classical, being built from many atoms. So, the effect is such that when the measurement happens, our quantum system interacts with the measuring device. This causes decoherence to set in in our quantum system and the wavefunction collapses. Or, in other words, the interaction with the measuring device "washes out" the the interference terms of the systems density matrix.

    The point is that consciousness has nothing to do with measurement. By no means do all measurements have to include a conscious observer. Wavefunction collapse will happen because of an interaction with an external environment(the measuring device). The interaction, and thus, the WF collapse, happens regardless of whether the device is run by a human or is a mindless automated robot.
  8. Jun 15, 2011 #7


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    I'm glad to see that I agree with most of the responses on this thread. I was worried that I'd see a lot of non-mainstream opinions on this :)
  9. Jun 15, 2011 #8

    Ken G

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    That is not entirely clear. The OP admits to two very separate interpretations, and even recognizing the existence of those two interpretations is important for understanding the answer to either one. "Is consciousness involved" could mean:
    1) "Does a conscious observer need to be present to get a wave function collapse?"
    Answer: no.
    2) "Is consciousness/awareness/intelligence/perception involved in giving meaning to the entire concept of doing a measurement that collapses a wave function?
    Answer: yes.
    Of course we could always satisfy ourselves with #1, but there's no need to sell short the full ramifications of the question. A naive interpretation of what physics is causes a lot of problems in understanding quantum mechanics, relativity, and thermodynamics, in regard to what is the role of the physicist/observer. I just put it out there, and everything I said is true. It doesn't need to start a whole thread on the issue, unless the OPer wants to go there. As I said, the question itself is unclear on the point.
    Correction, that is your interpretation of what was asked. The actual words included "is that collapse in any way related to the awareness of the observer..." So I answered the "in any way" part, because I think the OPer would like to know. Apparently this pushes a button for you.

    Yes, it is certainly a semantic issue. Unfortunately, a lot of people equate "semantic" with "unimportant", when in fact, "semantic" means "cuts to the heart of how we use language in physics, and how impossible physics would be without language." Of course, that returns us to the role of consciousness/intelligence etc., where you do not wish to go.
    Exactly. Now you are ready for the next question: why do some devices correspond to "quantum observables"? Does nature ever do observations, or just undergo unitary evolution? This will lead you inevitably to interpretations of QM, like Copenhagen and many worlds. It all opens right up when you ask what role does the physicist play in all this. Of course, you don't have to ask yourself that, but maybe the OPer would like to, and I gathered from the OP that it is indeed their interest.

    The point is, that statement is patently false. The truth is that measurement, as defined and understood and contemplated and used by the conscious physicist, can happen even if no such physicist is present. However, to give semantic meaning to what a measurement even is, this does indeed require a conscious intelligence (so far as we understand what those words mean), who has been there in a fully analogous situation for us to be able to use any of those words meaningfully. In short, a universe with no intelligent beings is a universe that has no measurements, and no wave functions to collapse. That is not an opinion, it is a fact-- in such a universe there are not the words "wavefunction", there is not the concept "amplitude", because there are no words and no concepts in the first place, stuff just happens, presumably the same as it does now minus any concept of "measurement" or "collapse" of anything. The significance of this fact opens up a lot of what physics really means, but does indeed get a bit philosophical, so if the OPer has any specific questions about it, they should probably frame them in terms of quantum mechanical predictions for this section.

    Yes, that's why I said the intelligence that says "what happened" in the first place does not need to be present every time it happens, but they certainly do need to present somewhere that it happens, to even say what the words mean. That turns out to be important to understanding what quantum mechanics is, and in choosing which interpretation you favor.
    Last edited: Jun 15, 2011
  10. Jun 15, 2011 #9


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    The first question is a question about physics and what a physical theory says about the measurement process, meaning the process described in my previous post whereby a quantum system is put into a classical state via decoherence.

    The second question is a philosophical question.

    Since the OP posted this in the Quantum physics subforum and not the Philosophy subforum. I assumed (I think rightfully) that the OP was interested in the first question. I think the context of the forum this question was posted in removes the ambiguity you describe.

    Again, this falls into the realm of philosophy of science, and thus, if this is what the OP was concerned about, should be posted in the philosophy forum.

    I do not think that was the OP was asking about, but either way, we won't know unless he/she posts again.

    The "role of consciousness/intelligence," in the context you are using the phrase is a philosophical question, not a scientific one. That is why "I do not wish to go there."

    My statement was not false. This is exactly what I was saying above. Measurement, as defined in the context of the quantum mechanical measurement problem, does not require the presence of a conscious observer, or as I said above,

    assuming the standard definition of "measurement" used in QM.
    Last edited: Jun 15, 2011
  11. Jun 15, 2011 #10
    Thanks to all for your replies. You've been very helpful. I study engineering and am new to Quantum Mechanics. I'm glad I asked because I was starting to get a mystical idea of the double-slit experiment, which thankfully I'm done with. Nevertheless I find Quantum Mechanics exiting and intriguing.

    With all the misleading information about Quantum Mechanics in the web I got a little off track.
    I deduce then, from your answers that the people that claim to have collapsed the wave function merely by looking at some results are making it up(They say the device was still on but it was when they looked at the results that the interference pattern disappeared).

    If it's not too much trouble I'd like to know the answer. Just out of curiosity.

  12. Jun 15, 2011 #11


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    Yes, The wavefunction collapse occurs when the measurement is taken, i.e. whenever you actually interact with the system, not when you look at the results of that measurement.
  13. Jun 15, 2011 #12
    Sure nickelite. You have actually provided the answer (or said what I was thinking .....) ....and so i quote you...below....;)

    or in my words:

    Mr Argumentative: how do you know WF has collapsed, without the observer looking at it
    Physicist: we know from the results that WF collapsed when the photon was detected/measured
    Mr Argumentative: well maybe the WF collapsed when the observer looked at it and not before (when it was measured)? can you disprove this?
    Last edited: Jun 15, 2011
  14. Jun 15, 2011 #13

    Ken G

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    Correct, though the line between the two is not as clearly drawn as some would like to imagine. This is actually important for understanding quantum mechanics-- as almost any new student of quantum mechanics knows, setting up and solving the equations can be learned easily enough in a kind of "trained monkey" mode, but understanding what it is saying is the difficult part. I think the OP is in the latter mindset, hence the question.
    I think you should really take a look at the questions currently being discussed in the quantum physics subforum. I estimate about half have a significant philosophical component that is quite evident in the OP question, this one included.

    And I will choose to reserve judgement on that until hearing if the OPer has any follow-up questions.

    Again, no. Indeed right now there are several threads in this subforum grappling with essentially purely philosophical issues about de Broglie-Bohm interpretations and just what "quantum information" really entails. Issues of determinism as a fundamental truth, or just a modeling assumption, are also being addressed. None of those come under the heading of what the quantum theory says about measurement, because the quantum theory only says one thing about measurements: it predicts them.
    Agreed. And I also agree that their question was largely relevant to the answer you gave, it just isn't the whole story about the role of consciousness in quantum mechanics, so I gave a pointer to the rest of the tale. It was not my intention to start a thread on the various different interpretations of QM unless the OPer had follow-up questions, but I do see their initial question as an excellent entry point into such a discussion. If the forum thinks all issues of interpretations should go to the philosophy subforum instead of the quantum physics subforum, I would completely agree, actually-- it is many of the other members here who instead do not think that is philosophy.

    Nor does any scientist really, it is the bugbear in the corner. But sometimes, quantum mechanics gives us no choice, unless we strictly adhere to "shut up and calculate". In my experience, no one ever actually does.

    Except to be there when the "quantum mechanical measurement problem" gets defined in the first place, which is my point (and is the point of Bohr's school of thought also, I might add). If quantum mechanics measurements teach us anything, it is that the "physicist is just a fly on the wall that we can ignore" attitude just doesn't cut it. That's the issue I would like to raise to the awareness of the OPer, so they don't walk away imagining that naive realism continues to work even in quantum mechanics.
  15. Jun 15, 2011 #14
    Just to clarify:

    I was asking about the more technical question, regarding whether awareness from the results is required in order to collapse the wave-function. Although I enjoyed the more philosophical discussion saying that consciousness is needed for there to exist physics at all.

    It seems to me that the hype that has been created around the double slit experiment has made a diffuse line between the scientific question and the philosophical question.

    It has led many to assume that it is the consciousness, PER SE, what collapses the wave function, and makes an electron appear in a determinate position. But from what I have learned in this discussion, it's not the observer but the act of measuring, it is the device used to measure itself what changes the results of the experiments.

    Hence the confusion in the interpretation of my question. Either way is fine, I'm glad to take all the views in the subject since I'm new to QM.
  16. Jun 15, 2011 #15

    Ken G

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    I agree. And personally, I'd prefer if the lines were kept drawn more clearly, but that's just not what happens.
    Here's the problem. Decoherence can explain with no difficulty how different "pointer positions" of a macro instrument get coupled to certain "quantum outcomes," with no cross-talk (i.e., no interference) between different pointer positions. This is the state of affairs before we look at the outcome of the measurement-- we have only a statistical understanding of the possibilities. The problem comes when we actually look at the pointer ourselves, and at that point, something happens that there is no consensus about in quantum measurement theory. The Copenhagen school says that the statistical prediction is all we can use quantum mechanics for, and the actual looking is something different, something outside the ability of quantum mechanics to describe (expressly because it is outside the ability of quantum mechanics to predict, and Copenhagen likes to equate science with prediction). The many-worlds school says that all the pointer positions actually occur, and each sub-world spawns its own intelligent analyses of their own particular pointer, so each consciousness is trapped by, or born into if you prefer, a kind of coherent sub-world of the incoherent and non-interfering many worlds. You can see how it is a little hard to talk about the differences in these interpretations without talking about consciousnesses. Finally, the third main school is deBroglie-Bohm, which says that there is only one world, and it is computable and deterministic, we just don't have access to the information one needs to do the computation (which is called a "pilot wave" and is not directly observable at present).

    To summarize, the role of consciousness is quite substantially different in the three interpretations. To Copenhagen, consciousness is paramount, because quantum mechanics is just a tool that the consciousness uses to predict outcomes, and some elements of the outcome are simply not describable so must be treated as random. To many worlds, the consciousness is a kind of minor player in the vast array of many worlds (and I do mean vast), because some of the worlds spawn consciousnesses and some don't, and the physics doesn't really care if there's a consciousness in there or not. To deBroglie-Bohm, the consciousness is neither paramount nor minor-- the deterministic physics is the "truth" of the situation, just as in many worlds, but now there is just one world that is being determined, and so that one world must be the home to all the consciousnesses.

    The bottom line is, all these interpretations make the same successful predictions, so choosing between them (or ignoring them altogether) is really a matter of personal taste. The choice is very often motivated by how you like to think about the role of consciousness, and that's why consciousness continues to play a key role in, not the predictions of quantum mechanics about measurable outcomes, but in understanding what quantum mechanics is really describing, what it really is.
  17. Jun 15, 2011 #16


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    Ken G, the standard interpretation of QM doesn't depend at all on consciousness.
    The macro pointer instrument itself causes wavefunction collapse.
    It doesn't require a human looking at it to cause collapse.
    This is why human consciousness is not required for the standard interpretation.
  18. Jun 15, 2011 #17


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    Here's the crux of my problem with the question labelled 2) in your post above. For reference,

    This just seems to boil down to the old "If a tree falls in the woods..." question.

    Of course, we need conscious observers to do science. Without conscious observers no one would be around to question how nature works. Yes, I get that.

    However, I still think it's entirely beside the the point regarding the nature of consciousness in QM. Consciousness does not play a role in collapsing the wavefunction. No viable mainstream QM interpretation assigns human consciousness a role during measurement.

    Thus, I don't see how changing the conversation into a conversation about the philosophical role of consciousness in doing science helps. I think they are separate conversations.
  19. Jun 15, 2011 #18
    I think people should admit ignorance on this subject. The question inherently involves a physically ill-defined and ill-understood object, i.e. consciousness.

    Does consciousness create our reality? Or is it the other way around? Do they coexist in some sort of "symbiotic" fashion? We don't know the answers to these questions. All people are doing is speculating on something they know very little about, reasonably so; consciousness is one of the most difficult things to understand even though it is the heart of our experience.
  20. Jun 15, 2011 #19

    Ken G

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    Well, you are taking us in this philosophical direction, but I did not because this has nothing to do with the usual question about the tree in the woods. That's the whole reason I introduced the concept of a hypothetical observer. Instead, what this means is we can say the tree falls if we can imagine what a hypothetical observer would experience. But if we cannot, then exactly what does "a tree falls in the woods" even mean? So everything we say about reality, including every equation of physics, comes through the filter of "what if we were there", that's the point here. This is why we call physics an empirical science, pure and simple.
    No, but it plays a role in what we mean by "collapsing the wavefunction." I described quite specifically how that phrase means three different things in interpretations that treat consciousness in three different ways.

    You must be a realist, who sees a firewall between the observer and the observed. It's very hard to get a consistent view of quantum mechanics that way. Quantum mechanics is fundamentally a language, a language with a mathematical syntax that deals in testable predictions, but a language all the same. Your position is basically "I don't see how the mind of the speaker has anything to do with the language they are speaking." I don't think that's very likely.
  21. Jun 15, 2011 #20

    Ken G

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    There are two very different stages to "wavefunction collapse" that people often misconstrue, and only the first stage is independent of interpretation. It sounds like you are talking about simple decoherence, by which a pointer and an outcome become coupled, and pick up random or noncoherent phases with respect to all other pointer/outcome couplings. This is called a "mixed state" when you project onto either the pointer or the quantum alone, but it is still a unitary state when you consider the full wavefunction of the combined system. So far we have nothing but basic quantum mechanics, no need for any interpretation, and it describes the situation before anyone looks at the outcome of the experiment.

    Enter the next stage of the "collapse", when someone does look at the outcome. Now we desperately need an interpretation, because we no longer have a unitary state. We just have one pointer result, and one quantum state. What happened to the rest of the unitary state-- it's gone! This is clearly the part that involves consciousness, because consciousness is the whole reason we need an answer to this part of the question. As I said above, if we adopt many-worlds, we solve the problem by saying the consciousness is in some sense "mistaken" or "under an illusion" that the unitary state is gone. The full state of "many worlds" is still there, the consciousness is just not aware of it. So absolutely yes, this is all about perception and consciousness.

    Copenhagen also requires that we address the consciousness issue. Here, we do not say the consciousness is deluded or tricked, because we say that physics is ultimately a task for that consciousness. Instead we say the mathematics is not the reality. Bohm says the consciousness also gets the reality, but there's a different mathematics that is the fundamental reality-- though one we cannot directly interact with, it seems (some wonder if maybe we can).

    So as you can see, consciousness is all over the hard problem of collapse, it's just not in the easy problem-- the decoherence.
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