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Copenhagen: Measured or Observed?

  1. Aug 31, 2009 #1
    I don’t like CI. But I was always thinking that CI is an idealistic interpretation, based on the consciousness and the existence of intelligent observers.

    In Bohr’s time it was simple. He believed in a sharp line between quantum world and macroscopic world. Quantum event Q was registered by the Measurement device M et voila: wavefunction collapse.

    Q -> M

    But we know how tiny the measurement devices can be. On the other hand, we can put millions of particles into entangles state. So, what happens when we store a result of a quantum event in some tiny qbit measurement device? Why it does not collapse?

    Q -> M1

    CI proponents say: well, storing Q in M1 is NOT a measurement. Only then, when we observe status of M1 we perform a measurement:

    Q -> M1 -> M2

    Now we have 2 devices: small M1 and a bigger one: M2. But wait, we can make this chain of measurement devices much longer, making a ‘consequent measurement’

    Q -> M1 -> M2 -> M3 -> … => Mn

    So what measurement is ‘real’? There are only 2 options:
    1. CI is not about the measurement. It is about the observation. CI is idealistic and it requires a consciousness C to collapse a wavefunction:

    Q -> M1 -> M2 -> M3 -> … => Mn -> C

    2. CI must give an exact definition of what Mi *IS* a measurement device. Knowing that measurement devices can be tiny and consist of few atoms, CI must give a detailed explanation of what combinations of atoms are measurement devices and what combinations are not measurement devices (and clearly it can’t do it)

    So why CI talks about measurement while “wavefunction is not real, it is just an information” which clearly suggests the consciousness as an only collapse agent. So instead of thinking about the superstrings about the most fundamental things, we should think about the consciousness as something irreducible to simpler things.

    It makes some sense, but it is definitely not the way how CI proponents see that interpretation.
     
  2. jcsd
  3. Aug 31, 2009 #2
    Bohr:
    “It lies in the nature of physical observation, nevertheless, that all experience must ultimately be expressed in terms of classical concepts, neglecting the quantum of action.”

    Bohr doesn't talk much about measurement devices. The primacy of classical properties is more due to a failure of the human understanding than anything ontological. Physics is about epistemology. It's about knowledge. Our knowledge is limited to classical concepts.

    "A close connection exists between the failure of our forms of perception, which is founded on the impossibility of a strict separation of phenomena and means of observation, and the general limits of man’s capacity to create concepts, which have their roots in our differentiation between subject and object.”

    It is also a failure of our understanding that we necessarily view things as being objective, ignoring the fact that they are necessarily context dependent. His answer:

    "For describing our mental activity, we require, on one hand, an objectively given content to be placed in opposition to a perceiving subject, while, on the other hand, as is already implied in such an assertion, no sharp separation between object and subject can be maintained, since the perceiving subject also belongs to our mental content. From these circumstances follows not only the relative meaning of every concept, or rather every word, the meaning depending upon our arbitrary choice of view point, but also that we must, in general, be prepared to accept the fact that a complete elucidation of one and the same object may require diverse points of view which defy a unique description."

    QM isn't even the game changer for Bohr, relativity is.
    “The theory of relativity reminds us of the subjective … character of all physical phenomena, a character which depends essentially upon the state of motion of the observer.”

    “[Quantum mechanics] may be regarded as a natural generalization of the classical mechanics with which in beauty and self-consistency it may well be compared. This goal has not been attained, still, without a renunciation of the causal space-time mode of description that characterizes the classical physical theories which have experienced such a profound clarification through the theory of relativity.”

    He also thanks Einstein “with respect to our emancipation from the demand for visualization.”

    For Bohr, QM isn't about measurement devices and it isn't about collapse. Take classical entities and call them real (macroscopic realism - the chair is real, particles are real). Add relativity and QM to show that our classical view of causation is wrong, and you are forced to throw out the causal implications of having real, persistent, classical entities. You can't understand what causes the classical events we see; you can't visualize anything beneath the classical level.

    It would be a mistake to say that Bohr placed any emphasis on consciousness though.

    “We are here so far removed from a causal description that an atom in a stationary state may in general even be said to possess a free choice between various possible transitions to other stationary states.”

    Even atoms can have free will. Furthermore, the appearance of consciousness is simply an irreducible phenomenon dually and inconsistently describing the world in the same way that wave-particle duality appears. It is a failure of our understanding that we necessarily can't reduce the two concepts to something more basic, but must inconsistently consider each to be basic.

    "When considering the contrast between the feeling of free will, which governs the psychic life, and the apparently uninterrupted causal chain of the accompanying physiological processes, the thought has, indeed, not eluded philosophers that we may be concerned here with an unvisualizable relation of complementarity."

    Measurement, for Bohr, is simply the manifestation of classical properties, which can't exist persistently due to their falsified causal implications, but which must exist necessarily as the basic elements of our reality due to the epistemological limits of our conceptions/perceptions/visualizations.

    There is no objective collapse. The wave function doesn't represent anything real. Observation plays no physical role.
    "We meet here in a new light the old truth that in our description of nature the purpose is not to disclose the real essence of the phenomena but only to track down, so far as it is possible, relations between the manifold and aspects of our experience."​
    Physics is about human knowledge and understanding, nothing more.

    Jan Faye has a good description of CI at http://plato.stanford.edu/entries/qm-copenhagen. Also, sorry for the long read. It's all from a chapter in my thesis, so I had all these quotes. I'll spare you the rest though :smile:. I hope it's helpful in clearing up some of the collapse garbage out there.
     
    Last edited: Aug 31, 2009
  4. Aug 31, 2009 #3
    I don't like CI either. But I think you may be thinking about one of many different flavors of the CI. Von Neumman, Wigner?
    The decoherence program is usually considered to be just a mathematical fomalism which does not imply any interpretation. I am not too sure about that. But nevertheles, you can analyze environment-induced decoherence from both the CI and MWI.
    In the CI, if you consider decoherence as what causes "collapse" then you are not necessarily involving the brain in the collapse process.
    CI also considers a macroscopic apparatus to be an observer and often considers collapse as happening during interaction with the first macroscopic apparatus.
    Now, the decoherence theory should be able to explain how the interaction of a single particle in a superposition with something that is composed of a large number of atoms brings about collapse. I haven't seen any convincing explanation of how the decoherence theory does that. But maybe I have not read the right articles.
    I posted a question some time ago that nobody answered: If a quantum system interacts with an apparatus, before interaction the composite system may be described by the vector product of the individual Hilbert spaces. There are no correlations and all different combinations of the individual components of each system are present. When the particle gets entangled with the apparatus, each etate of the particle gets linked to one particular "pointer state" of the apparatus. So it looks like now the realm of possibilities is restricted to a smaller Hilbert space where some combinations are not allowed anymore. It is claimed in many places (Including in Everett's paper) that this process, (also called pre-measurement) represents a unitary transformation. I can't understand how something that reduces the size of the Hilbert space can be unitary. Maybe I am missing something.
    In Everett's paper, he considers a Hamiltonian acting for a fixed time. This seems like a trick that would not normally be done in nature. How does the hamiltonian how long to act? It seems to me that to get these correlations you should have a damping constat and an irreversible process, where you see overall increase in entropy.
    Then you have the problem of which of the different eigenstates to choose. I don't see an easy way to explain that outside of the MWI.
     
  5. Aug 31, 2009 #4
    The statements above are inconsistent.
    If consciousness is irreductable then it is a fundamental notion (that you for confirming it in CI), like may be spacetime, universe etc.
    But then Bohr made a mistake by not placing any emphasis on that.
     
  6. Aug 31, 2009 #5
    alexepascual, before we even start talking about the decoherence: CI had only one "collapse agent": measurement. It was long before the discovery of decoherence. So the decoherence is something CI really does not want, it is an alternative explanation of the same thing. After all that blah-blah-blah stuff explaining the collapse if appeared that no collapse was needed at all to explain what we see! it is the strongest argument against CI!
     
  7. Aug 31, 2009 #6
    Consciousness as something objective or ontological is not something proposed by Bohr. What is basic is epistemological human knowledge. There is a subtle difference. As being necessary to human knowledge, Bohr also thought that space-time and classical properties were necessarily basic. His thoughts here were very similar to Kant's categories of perception.

    Also, the appearance of consciousness does not in any way interfere with a complementary physical description of events.
     
  8. Aug 31, 2009 #7
    kote, so do you think that consciousness is a fundamental irreductable notion or not?
     
  9. Aug 31, 2009 #8
    Personally, no, but that's another thread. Bohr, however, barely ever talked about consciousness. I've quoted about the only times I could find where he discussed the issues. Consciousness was just not part of physics for Bohr. Knowledge, on the other hand, was very basic for him. The titles of his books are "Atomic Theory and the Description of Nature" and a few collections of essays on "Atomic Physics and Human Knowledge."

    From Jan Faye on SEP:
    Bohr therefore believed that what gives us the possibility of talking about an object and an objectively existing reality is the application of those necessary concepts, and that the physical equivalents of “space,” “time,” “causation,” and “continuity” were the concepts “position,” “time,” “momentum,” and “energy,” which he referred to as the classical concepts. He also believed that the above basic concepts exist already as preconditions of unambiguous and meaningful communication, built in as rules of our ordinary language.​
    Consciousness is not a part of Bohr's philosophy. Neither are observers. It's all about knowledge and real classical properties and objects.
     
  10. Aug 31, 2009 #9

    Fredrik

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    This is just crazy talk, but maybe that was your point?

    It isn't possible to define measurement devices exactly. This is a problem for all scientific theories. Take SR for example. Minkowski space is a beautiful mathematical model, but it's not a theory. One of the axioms that define SR says that a clock measures the proper time of the curve in spacetime that represents its motion...but a clock isn't defined by the theory. It can only be defined intuitively. This is a limitation of science, not of the CI.

    It can't give you the kind of detailed explanation you want, because it isn't possible to define the measurement devices in that kind of detail, but if you're familiar with decoherence (which is a phenomenon that can be studied in the framework of the CI), you already know a good definition of a measurement. It's an interaction between the system and its environment that entangles the eigenstates of one of the system's observables with macroscopically distinguishable states of a system that for all practical purposes can be treated as classical. (So qubits won't do).
     
  11. Aug 31, 2009 #10
    1 Yes, I believe it is close to Fra's point of view.
    I can accept it as an option even I dont like it
    But for CI proponents it is not fair to switch from completely idealistic "it is just a knowledge" point of view to an objective point of view. If it is just a knowwledge - then everything is just a knowledge, just a shadow in our consciousness.

    2 Well, TOE should be word "baggage" free. Just formulas.

    3 No, no, dont try to save CI! :) In CI Decoherence DOES NOT replace collapse! No, no, and no! jambaugh (the very last CI proponent here) had confirmed it explicitly: there is Decoherence and there is collapse. 2 different things!
     
  12. Aug 31, 2009 #11

    Fredrik

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    This is completely wrong. Decoherence is a physical phenomenon that doesn't in any way contradict a "Copenahagenish" formulation of QM. In fact, it can be derived from its axioms.

    What decoherence has added to QM is a definition of a what a measurement is. This solves some of the problems that were confusing in the past, e.g. the Wigner's friend scenario: Wigner performs a Schrödinger's cat experiment, and his friend walks in and asks him about the result. Is the question a measurement? The answer is that it's not, because the interaction that entangled the eigenstates of the observable with the macroscopically distinguishable states of the "almost classical" system has occurred before the friend walked in.
     
  13. Aug 31, 2009 #12
    Well, we cant speculate on how Bohr would change his mind when he learnt about the microscopic "measurement" devices.

    So even if Bohr never talked about the consciousness, what do you think? Or, what is a CURRENT flavor of the CI?
     
  14. Aug 31, 2009 #13
    What Fredrik said... Also, Bohr gives clues that he feels the same way about measurement later in life as he clarifies his language to try to avoid some of the confusion. From Faye again:
    Bohr no longer mentioned descriptions as being complementary, but rather phenomena or information. He introduced the definition of a “phenomenon” as requiring a complete description of the entire experimental arrangement, and he took a phenomenon to be a measurement of the values of either kinematic or dynamic properties.​
    A measurement is the result you get from producing a phenomenon by arranging a system such that it manifests classical properties.

    Similarly he stopped talking about uncertainty. The emphasis was that there is no phenomenon and there are no uncertain hidden variables when objects aren't interacting classically. Classical properties, while real, only exist during measurement/manifestation/interaction.

    A measurement is a classical output from a system.
     
    Last edited: Aug 31, 2009
  15. Aug 31, 2009 #14
    Sorry, my post was not clear.

    You are correct, it does not contradicts on the formal level. But agree with me, the whole motivation for inventing the collapse thing was to explain the macroscopic behavior, which was not able to be derived directly from QM at Bohr's time. After the discovery of the Decoherence the reason for inventing the collapse had completely dissapeared! And CI ended with 2 things to explain the same.
     
  16. Aug 31, 2009 #15
    No, no!
    See my very first post!

    Classical output = no superposition of states = collapsed to a definite outcome = measured

    Classical is measured, and to be measured is to get a classical outcome.


    You see, I am fighting here against the hidden recursive definitions which are almost everywhere!
     
  17. Aug 31, 2009 #16
    I can't think of any developments that would challenge Bohr's original views. He was very aware of Schrodinger's cat and he didn't think anything special about measurement that is inconsistent with current views. Any inconsistency would simply be semantics and Bohr would stick with his own original definitions or tell you how to make things work out linguistically.

    The whole notion of "collapse" was not an issue for Bohr and was not anything he ever talked about or would need to talk about. Bohr never considered the formalism to be real. Classical objects were always real and basic for Bohr. The wave function represents the probability that when we look in the box we'll see a dead cat.
     
    Last edited: Aug 31, 2009
  18. Aug 31, 2009 #17
    It's a tautology not a recursion :smile:. Unmarried man = bachelor. Superpositions of states are not real. There is nothing else that needs to be explained.

    The problem with CI that I see is that theoretically we can't explain why we see the results we do at any deeper level. We will never do any better than the current theory. If you can accept that we may be at the limits of our knowledge, then CI works out beautifully. There are no collapse issues and we get macroscopic and microscopic entity realism (as opposed to theory realism). The question is just, which pill is easier to swallow? The one required by CI or the ones required by other interpretations? Edit: As for switching between knowledge and objectivity... the wave function is about incomplete knowledge (no theory realism) but classical objects are objectively real (entity realism).

    I'll add that Bohr would define classical properties not by what is measured, but by preexisting and necessary notions of classical concepts per my previous post. Measurements are always classical, yes, but classical properties can be defined without measurement. They are innate and a priori and are a necessary part of human understanding.

    From SEP's description of Kant's categories:
    Although these are categories of the understanding, they nonetheless retain a certain sort of ontological import, as it is a priori that they apply universally to all objects of possible cognition (A79/B105). In this way, by delineating the concepts that are a priori necessary for the cognition of objects, we can acquire knowledge of categories governing any possible object of cognition, and so acquire a sort of descriptive set of ontological categories, though these must be understood explicitly as categories of objects of possible cognition, not of the thing in itself.

    http://plato.stanford.edu/entries/categories/#KanCon
     
    Last edited: Aug 31, 2009
  19. Aug 31, 2009 #18

    Fra

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    I am not sure what's close to my view? I don't quote recognize myself in the preceeding.

    The need for consioussness or intelligence sounds like the repeated association that QM would have anything to do with the human brain, and the QM is a phenomenon of the human brain. That is definitely not what I think, I think I tried to make that point several times.

    From what I remember about your reasoning, you have a much stronger realist view that I do. This is the root of our disagreement. So I somehow see why you have a difficulty to appreciate my reasoning, and from your point of view, my reasoing appears circular - right? Am I right? :)

    I replace in my interpretation Bohr's classical reference with the inside perspective in that sense that instead of thinking of the references as a fix objectivity, I see it as a rational calculated basis for the action, as part of a game. The action of a system, observing a second system, is as if the first system's view of the second is correct and objective, while in fact all the difference it makes is to provide a basis for the action. But this "basis" is deformning or updating throughout the interaction.

    The circularity you see, is the time evolution. On each iteration there is progress. If you want, I view TIME as an inference process, but due to the inertia inferences are not immediate. The time evolution takes place as I see it at several hierarchial levels, the most vibrant level is the ordinary time evolutiom, the slowest level correspond to the evolution of physical law.

    So if you see my view as a "clean interpretation", it is correct that it doesn't make sense. But if you take it even more seriously, it suggest how to improve QM - that is how I see it.

    So, I would say that my view does not make sense if you insist that the QM formalism as we know it is fundamentally correct without expcetion at alla scales. If you think however, that QG requires a modificaton of QM, THEN I think it does make sense.

    This is why I reserved myself several times in this interpretational discussions that I don't see my view as a clean interpretation. Among the plain interpretations though, CI or something like Bohrs original reasoning is what I find the most sensible.

    But my preferred view goes beyond that.

    /Fredrik
     
  20. Aug 31, 2009 #19

    Fra

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    I speak only for my own view and in my view, there is self-reference, this is correct.

    But this is not a problem. You seek a timeless static conclusion. For me, the indication is instead that such static timeless characterisation of physics does not exist.

    There is a problem of time buried in this discussion. If you look around, the universe isn't static, what is the basis for expecting static conclusions?

    Again I see here a clear preference to your view if you have a realist view of physical law. I think difference explains most of our differences in reasoning.

    /Fredrik
     
  21. Aug 31, 2009 #20

    Fra

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    As an historical analyg, perhaps one can ask what was Einstein's reason to insist on a static universe?
    http://en.wikipedia.org/wiki/Static_universe

    Eventually, it after all seemed like the universe isn't static.

    In any learning process, knowledge is never static. I see no good reason why a inferrable physical law should be static or timeless. Sure, physical law is by construction somehow "timeless" but only when the time refers to a limited history, and the in that sense "timeless" law is itself evolving.

    I think your main objection is the circularity here, but does it seem totally unreasonable to you, that this self-reference rather than a problem is a key to understanding something we yet don't?

    /Fredrik
     
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