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

Philosophy of Copenhagen

  1. Jun 18, 2011 #1
    How many percentage of physicists believe Copenhagen is pragmatism and how many percentage believe Copenhagen is actual in that the particles attributes are really nonexistent before measurement?

    Quoting Herbert in Quantum Reality:

    "Some physicists confuse the Copenhagen doctrine with a pragmatic interpretation of quantum theory. The pragmatist regards any theory as mere mathematical machine for generating numbers which he then compares with experiment. A pragmatist is concerned with results, not reality. The pragmatist refuses on principle to speculate about deep reality, such a concept being meaningless from his point of view. Pragmatism is an intellectually safe but ultimately sterile philosphy.

    A pragmatist would refuse on principle to comment on the existential status of an unmeasured electron's attributes. No timid pragmatists, there students of Bohr! The Copenhagenists claim not that such attributes are meaningless but they are nonexistent. They based their conclusions about an unseen quantum reality not on some abstract philosophical principle applicable in all cases but on the specific structure of quantum theory itself. Some theories of the world (Newtonian mechanics, for instance) allow us to believe or not that unobserved entities possess their own attributes. Quantum theory, according to the followers of Bohr, does not permit this option."
  2. jcsd
  3. Jun 18, 2011 #2

    Ken G

    User Avatar
    Gold Member

    Here I think Hebert strays a bit-- a Copenhagenist would never see any distinction between "meaningless" and "nonexistent." To them, anything that is meaningless is nonexistent, so they would be quite content to call it meaningless, and would not be troubled by the distinction Hebert draws. They hold that existence is subject to what we can know about what exists, it is not something that exists independently of what we can know about it. That's why I would call the central principle of the CI the subordination of ontology to epistemology.

    Hebert is also mistaken here. They don't "base their conclusions on an unseen quantum reality," the whole point of Copenhagen is that no conclusions at all can be drawn on that reality. Instead, in CI, all conclusions are drawn on the outcome of observations, and all observations occur at the classical level. This is the crux of Copenhagenism, an admission of a fundamental distance between us and what we wish to understand, so if Hebert doesn't get that, he is no authority to talk about Copenhagenism. He is correct that the observations only present the kinds of problems he is talking about in the case of observations of quantum systems, but remember the correspondence principle-- observations on classical systems are nothing but aggregates of quantum systems. Hence, one can have a particular effect go away during the aggregation, but it's still there behind the scenes of that huge sum. I'm not sure where Hebert is going with this quote, but I don't think he's off to a good start.

    ETA: It sounds like his basic point is that CI is not the same as the purely pragmatic "shut up and calculate." I agree with that, and I also agree that "shut up and calculate" is not really a philosophy at all, and I've never actually seen anyone who adheres to it, even those who claim that they do. So CI does make assertions that are not purely pragmatic, but they have the flavor "we should not say things that we cannot support with observations." Even if saying those things makes a nice tidy mathematical picture (like the way many worlds supports unitarity), or even if they allow us to imagine that the universe supports certain properties we'd like (like the way Bohmian mechanics supports determinism). So the CI does make some assertions, but I wouldn't frame them quite the way he does, he's not being careful enough. Since it sounds like he will be critical of the CI, he has to be more careful to state it correctly.
    Last edited: Jun 18, 2011
  4. Jun 18, 2011 #3
    Nick Herbert argument is that quantum particles possess no dynamic attributes before measurement. Do you deny this? If you agree with it. Then it's an ontology that actually occurs. Quoting Herbert:

    "This does not mean that the quantum world is subjective. The quantum world is as objective as our own: different people taking the same viewpoint see the same thing, but the quantum world is not made of object (different viewpoints do not add up). The quantum world is objective but objectless."

    Herbert completely contradicts what you are saying Ken G. I'd like to know where you get all your information. Are you a physicist or a philosopher? How many percentage of physicists hold your view and Herbert view? I'd like to know this, hope others who have idea can share as I'm getting a bit confused by all this already.
  5. Jun 18, 2011 #4

    Ken G

    User Avatar
    Gold Member

    Then it seems Hebert is a Copenhagenist. I thought from his earlier comments he would criticize them.
    I still have not seen anything said by Hebert that contradicts anything I said, actually, except for minor tinges of emphasis. Exactly what do you think I said that Hebert is "completely contradicting"?
    A physicist.
    I don't see it as one or the other. Actually, I see Hebert as being pretty close to my views, though I would split some hairs about his language choices as I mentioned above. There certainly are many physicists with drastically different views from both mine and the way you describe Hebert's. Many physicists take the many-worlds interpretation, and many more the Bohmian. I can debate the issues with them, but a prevailing fact I'm not sure you're getting is that the reason we can all communicate scientifically, and indeed easily be co-authors on the same science papers, is that the interpretations matter almost negligibly to the actual science.
  6. Jun 18, 2011 #5
    I wonder what percentage of physicist do not care. I would put those in the majority. I cannot blame them either.
  7. Jun 19, 2011 #6

    Ken G

    User Avatar
    Gold Member

    I think most have a closet interest, it's hard not to! But the one thing that is really the consensus is that it doesn't matter to the science.
  8. Jun 19, 2011 #7


    User Avatar
    Gold Member

    The problem is that any account of CI stresses that it is in fact a variety of interpretations and stances, so it is hard to know which you, or anyone else stands for. Which interpretation of Copenhagenism are we actually dealing with here? :smile:

    To me, there seem two general positions.

    1) The pragmatic, positivist, operationalist "shut up and calculate" position": All we have is a consistent epistemology and we can say nothing definite about ontology as a result of that.

    2) Or the position I prefer, which agrees that basically there is only the epistemology, but quantum theory does give us actual grounds to posit constraints on ontology. Generally speaking, we can already say "reality is not classical". And so therefore it must be something else. This something else looks to have some definite ontological features of its own such as complementarity and indeterminism. These are not "ontic nothings" but ontic somethings. For example, complementarity involves dualities, not trialities (or other higher orders). Indeterminacy is not determinacy, but it also isn't randomness.

    So new metaphysics seems directly suggested and justified by CI. It is not necessarily agnostic at all. It says behind the screen of epistemological limitation, only certain things can still be the case. It is not a story that "just anything could be happening". CI still places contraints on ontic possibilities. It is just less constraining (perhaps) than a classical view of reality.

    So you are not supporting position 1 - the arch positivist.

    Yet you are also not then allowing CI to act as a definite constraint on ontology. You are stressing what CI says we cannot say about reality, but not admitting what it also allows us to say.

    Observation says that reality - when observed in that particular way - is complementary and indeterminate.

    That then gives metaphysics some definite open ended research programme - to consider how complementarity and indeterminacy can be fundamental to a worldview.
  9. Jun 19, 2011 #8
    Yep, that its even better than what I said.

    On the issue of Nick Herbert, I tried to read his book "Superluminal Loopholes in Physics". Maybe I did not read enough but I got disgusted that he never mentioned the "energy condition" violations under various version. I do not mind going on intellectual journeys outside the standard, but such things need to be discussed first and any so called loophole needs to at least end with some comments about those "energy condition" assumptions.

    I have my doubts that he wrote those books with any intention of articulating science. I think it likely he wrote them for public notoriety. This is where the distinction between perfectly valid logical exercises, such as Schroedinger's cat, get obfuscated and blurred into claims of what physics says.
  10. Jun 19, 2011 #9
    The major difference between your view and Herbert is the following:

    Herbert: Quantum world is objective but objectless
    Ken: Quantum world is undefined

    Herbert: Particles have no dynamic attributes before measurement.
    Ken: We don't know. It is meaningless. Just "shut up and calculate"

    The major difference is that Herbert has ontology of what goes on in the quantum world which is that it is objective but objectless and particles don't have dynamic attributes before measurement. But in your view. You "don't know: and "don't care" and just want to deal with equations and measurements. There's the difference. You are anti-ontology. Herbert addresses the ontology.
  11. Jun 19, 2011 #10
    Although Bohmian Mechanics, Many Worlds, Copenhagen variants produce the same predictions as QM without interpretation. There are consequences. This is because we don't know what is consciousness and whether it can have extra degrees of freedom. In Many Worlds. There are actual duplicate worlds, what if consciousness can bridge them. In Bohmian Mechanics, there are pilot waves and implicate order. What if consciousness can interact with them. In Copenhagen variant where quantum world is a potentia of unmanifested energy, what if consciousness can interact with the quantum world and can manifest particles directly. This is the importance of studying interpretations.. because we don't know what is consciousness and it may have extra degree of freedom that can distinguish the true interpretations and other emergences.
  12. Jun 19, 2011 #11

    Ken G

    User Avatar
    Gold Member

    Yes, I wouldn't really even call CI positivist, even though it is clearly positivist-related, because positivism is really a pretty radical philosophy. It is basically the philosophy that elevates scientific knowledge above all others, even to the point of holding that it is the only kind of knowledge there is. I would say that CI believes that science invokes positivism, without marrying it till death do you part. Indeed, this is what I would call another founding principle of CI-type ontologies: a basic skepticism around the inherent limitations we face when we choose to do science. So I agree that no two CI users agree on all issues, but I would define the CI-type via these two principles, and I think they are pretty close to what Bohr might have said:
    1) science is a two-edged sword-- we accept certain limitations in order to make certain types of progress. One of those limitations is having to pass the square peg of quantum systems through the round hole of our classical experience.
    2) ontology is nice, but not when it extends beyond epistemology. In other words, we are allowed to assert ontic entities in support of our epistemological endeavor, but only in its support-- not as its own separate concern. We should not speak about what exists, except as it becomes necessary to give form to the lessons of our experiments.
    Both of these principles essentially come down to fleshing out Feynman's admonition to "not fool ourselves, given that we are the easiest people to fool." Interestingly, I once saw a quote by Feynman that suggested he was sympathetic to the many-worlds view, but many of his other quotes, like that one, sounded very CI to me.
    That's only because the things CI allows us to say are generally the minimum set that most everyone who knows quantum mechanics agrees on, so the differences generally involve what we should not say. But you're right, it should be stressed that CI is not really anti-ontology, it's just anti ontologies that extrapolate beyond what empirical epistemology can support or require.
    Yes, the principle of complementarity (related to the HUP) and the principle of correspondence (that quantum predictions must correspond to classical ones when the systems get large enough, so the classical world is a kind of "true witness" to quantum phenomena, it can lose some part of it but not bring in anything totally new) are lynchpins of the CI, right up front and center of Bohr's approach.

    Yes, that's well put. And I would add that any such metaphysical project that is faithful to the CI must begin with the expectation that the outcome shall be a kind of mediation between what is true and what we can know about what is true, rather than just the former. This is the decisive element of the CI approach-- the change in focus of the purpose of the endeavor, from knowing reality, to getting reality to fit into what we can know.
  13. Jun 19, 2011 #12
    To say that "We don't know" does not mean we do not care. That is where the issue came in with my debate with Ken, and Ken has shown an understanding of the 'potential' conceptual value of jumping ontologies. But Ken and I both agree that the resulting value is still defined by the predictive power, not the ontologies involved in deriving it. So the "shut up and calculate" is a non-issue in this respect. I think Ken would agree that a better and more complete "shut up and calculate" models would be a great and possible result of ontology jumping in search of how to derive it.

    If you want to know something funny, my approach is to take the (transfinite) objects as real while their properties are essentially subjective in a relativistic sense. Yet that makes the world as we can even in principle know it (empirically) purely subjective in a relativistic sense.

    I have pointed out the difference between "don't know", "can't know", and "don't care" before. Reassociating them as the same thing here does not seem valid.
  14. Jun 19, 2011 #13

    Ken G

    User Avatar
    Gold Member

    Those are actually not very much in disagreement, frankly. The basic point is that what we call "objects" are classical entities, because that's all we can really understand. This was very much Bohr's point as well. So if we can't understand something, one person might call it "objectless", and another might call it "undefined", but it amounts to the same thing. Hebert's key point, which I agree with, is that we can still do science on something we cannot understand (or define) the fundamental "objects" in, as long as we can still interact with it in an objective way. This is classic CI: what we know is what stems from the epistemology of the scientific method, and we can know something that way, even if we cannot know the basic objects that exist there because they are too far from the kinds of objects we can define from our experience.
    Let me get this straight. In the vast array of quantum ontologies, where some people think that a multitude of incoherently separate worlds were generated seconds ago when I blew my nose, and others think that the necessity of my blowing my nose was encoded in the state of the universe in the first instants of its origin, you think Hebert and I are having some kind of fundamental disagreement because he says particle dynamics is actualized by measurement and I think there's a limiit to what we can say about the particle dynamics until we measure it? I'm sorry, but I'm just not seeing this great gulf in our mindsets.
    Now you are just putting words in my mouth that I never said nor even thought. I'm perfectly fine with a basic quantum ontology, it pretty much says we know what exists when it bonks us on the nose, whether it be a baseball or an electron. I see science as a conversation with nature, where the entities we are talking to on that other end have vastly different qualities in different scientific contexts, but the person on our end is always the same, and that has very important implications for the nature of the conversation. I'll bet that Bohr would have said almost the same thing, if he didn't.
    Last edited: Jun 19, 2011
  15. Jun 19, 2011 #14
    Here's another major difference between Herbert and Ken's take on Copenhagen Interpretation (CI). I think Herbert believes in CI superpositions actually occur in the object while Ken believes in CI it is in the equations. What's your pick?

    Quoting Nick Herbert "Quantum Reality"

    "One of the drawbacks of the Copenhagen view is that it assigns a priveleged role to measuring devices, describing them in terms of definite actualities, while every other entity is represented by superpositions of possibilities. Surely the world itself is not so divided but consists of a single reality. Another conceptual weakness of the Copenhagen interpretation is that it regards both the M device and the measurement act as ultimately unanalyzable. Thus, in the Copenhagen view quantum theory can explain with great exactitude the behavior of atoms, but it is powerless to cope with the attributes of cats and apples in their role as unscrutinized parts of "the entire experimental situation"

    (Ken, pls. comment on the above "weaknesses")

    The following is my conversations between Ken and me in another thread here (where I take it that the weakness Herbert mentions, Ken simply put it under the rug of the "equations", agree guys?):

    Varon: And how else can there be superposition without wave function being in the object (not merely knowedge of the observer??)

    Ken: There's definitely interference in the mathematics, what is not clear is what is actually intefering. Terms in an equation, or something real? CI says the former, thus avoiding strange problems like "real" entities comprised of imaginary numbers, or mutually coherent pockets of outcomes coexisting alongside noncoherent other worlds that make no contribution because they have random phase relationships with our world.

    Varon: Look. You mentioned terms in an equation is interfering. But just look at the detector screen, there interference patterns are there. It is something real.

    Ken: The pattern is real, yes. But the interference? How is that real? It is an inference you make when you see the pattern. Inferences are not real, they are mental constructs. I'd say the crux of CI is noticing the difference between what is in the reality and what is in our minds. Granted, even the outcome of an observation is in our minds, but CI sees that kind of outcome as more concrete than the mathematical stories we build up around them.

    How many here believe the interference is only in the equation and nothing actually interferes in the double slit? Even SpectraCat believes something should be interfering as logically should be the case.
  16. Jun 19, 2011 #15
    If one day consciousness were entirely charted out and the conclusion was our brain was simply machine and we could construct purely mechanical robots with special algorithm that produce self-awareness and there is nothing more to it. Then if there is no way to distinguish Copenhagen, Many Worlds, Bohmian, etc. then we could consider Copenhagen as the final say. But now that we still don't know what is consciousness. We must explore interpretations. This means that present people who just want to accept Copenhagen and don't care about the other interpreations simply don't have time for philosophy and just want to focus on practical applications, right?

    To those people like Ken. Aren't you concerned that Copenhagen has a great flaw. For example. In the CI entry in wikipedia, I read this:

    "Steven Weinberg in "Einstein's Mistakes", Physics Today, November 2005, page 31, said:

    "All this familiar story is true, but it leaves out an irony. Bohr's version of quantum mechanics was deeply flawed, but not for the reason Einstein thought. The Copenhagen interpretation describes what happens when an observer makes a measurement, but the observer and the act of measurement are themselves treated classically. This is surely wrong: Physicists and their apparatus must be governed by the same quantum mechanical rules that govern everything else in the universe. But these rules are expressed in terms of a wave function (or, more precisely, a state vector) that evolves in a perfectly deterministic way. So where do the probabilistic rules of the Copenhagen interpretation come from?
    Considerable progress has been made in recent years toward the resolution of the problem, which I cannot go into here. It is enough to say that neither Bohr nor Einstein had focused on the real problem with quantum mechanics. The Copenhagen rules clearly work, so they have to be accepted. But this leaves the task of explaining them by applying the deterministic equation for the evolution of the wave function, the Schrödinger equation, to observers and their apparatus."

    I don't know what Weinberg mean by considerable progress. Is it Many Worlds or Zurek Interpretations? Doesn't this affect the pragmatists holder of Copenhagen I. at all? Maybe their motto is still "Copenhagen all the way"?
    Last edited: Jun 19, 2011
  17. Jun 19, 2011 #16


    User Avatar
    Gold Member


    So that would be a constraint in the other direction :wink:. The nature of the theory is going to be constrained to what we can achieve epistemically anyway. So accept that as a fact and work with it.

    I think that is probably the right view, but also it is one that is a little too close to "shut up and calculate" for me personally. Philosophy would have more freedom than science in this regard.

    BTW, given Feynman is so often wrongly identified as the source of "shut up and calculate", here is a neat little quote where he defends the need for ontological intuitions.

  18. Jun 19, 2011 #17
    You said it again without even acknowledging my post. "Don't know" and "don't care" is two different things, nor does the ontology of a theory have anything to do with its validity.

    Consciousness is a study in itself, spanning many different disciplines. I could go over models and the empirical data we have, much of which is likely to be shocking. But what consciousness is or is not has NOTHING to do with the validity of some interpretation of QM. Not even if is was proven our brains made direct use of QM effects.

    If you flip a coin and ask me to guess which side it landed on is say "I do not know" a flaw? No. Does saying ""I do not know" man that I do not care? No. Does saying "I do not know" mean that I think it landed on both and neither side? No. So why do you keep insisting it does?

    See the red part? Now any theory that gets accepted will do so because it works, not because the interpretation it contains is absolutely true.

    Stop and think about this. First you say you "don't know what Weinberg mean by considerable progress", then the only two options you give for how "progress" can be made is by way of two interpretations. Here is what you need to understand: interpretations have NOTHING to do with the progress. They were mere conceptual tools to get at that progress that had NOTHING to do with the "truth" of QM. The progress is a long series of more detailed empirical constraints obtained NOT by interpretation but by experiment. Interpretation does NOT define science, no matter how much we might use it for conceptual leads to push the boundaries or as functional elements of the theory itself.

    Think about this. CI is merely the same principle Einstein used to moot the ether theories of his day. Hence CI was around before QM was even developed. Ironically it was Einstein who then backtracked on the strong positivist stance and insisted on finding models which were not models but defined what the system was 'really' doing. But it was some Einstein created.

    So, until there is some recognition that interpretation is not theory and does not define what a theory is, regardless of what interpretations the theory uses, your question is like me asking why you do not have bones. You saying, but I do have bones. To which I respond well then what happened to your bones? You say nothing. To which I respond, but you said you had bones? You are talking around our responses rather than to them. I sympathize with realist (am one), but if I let that blind me to the realities of what I can 'know', and the very real issues realist face, I am just yanking my own chains while ignoring the science and the things I can know.
  19. Jun 19, 2011 #18
    This was basically the crux of my point when I debated Ken. Only Ken had no issues with this point, though he can speak out for himself, so long as the epistemology is accepted for the constraint it is. So I see no problem here as you have accepted that in the above quote also. I think we all agree on the value of ontology in terms of human creativity and epistemological development, but epistemology is always the end result of what we can 'know'.
  20. Jun 19, 2011 #19
    Bottomline is, some physicists don't know but they care. While some hard core pragmatist physicists who don't know also don't care. I know "don't know" and "don't care" are two different things, as emphasis.

    See bottom of this message for comment.

    I mentioned "flaw" because I read the passage in the Weinberg paragraph I shared there: "The Copenhagen interpretation describes what happens when an observer makes a measurement, but the observer and the act of measurement are themselves treated classically. This is surely wrong: Physicists and their apparatus must be governed by the same quantum mechanical rules that govern everything else in the universe.". Here Weinberg mentioned "This is surely wrong".. so I thought it was synonym for "flaw". Wrong is related flaw, not?

    I should have added "like" as in "Is it LIKE Many Worlds or Zurek Interpretations?" which gives different context. You know my native language is not english. I rarely speak english.

    The purpose for this thread is to know how to tell if a variant of Copenhagen Interpretation is valid. This is because I'd like to know if the Quantum Mystic variant of Copenhagen Interpretion is valid... stuff like Fritjof Capra's Tao of Physics and dozens of other books that elevate consciousness into quantum importance. For example. In Physicist Bruce Rosenblum Quantum Enigma: Physics Encounter Consciousness. It is mentioned:

    "In quantum theory there is no atom in addition to the wavefunction of the atom. This is so crucial that we say it again in other words. The atom's wave-functions and the atom are the same thing; "the wave function of the atom" is a synonym for "the atom".

    "Quantum probability is not the probability of where the atom is. It's the objective probability of where you (or anyone) will find it. The atom wasn't in that box before you observed it to be there. Quantum theory has the atom's wavefunction occupying both boxes. Since the wavefunction is synonymous with the atom itself, the atom is simultaneously in both boxes."

    "According, before a look collapse a widely spread-out wavefunction to the particular place where the atom is found, the atom did not exist there prior to the look. The look brought about the atom's existence at that particular place - for everyone."

    "For example, according to quantum theory, an object can be in two or many places at once - even far distant places. Its existence at the particular place it happens to be found becomes an actuality upon its (conscious) observation)"


    Now the above is different than what Ken was describing. But is the above valid? If it is. Then I'll hold it instead of Ken's. Again this thread is wanting to ask how to tell if a Copenhagen variant is valid or not. I'd like to think that in between emission and detection in the double slit experiment, the particle literally morphs or shapeshift into wave in between measurement. Upon reaching the detector, the wave shapeshifts physically into a particle again just as the above text by Bruce Rosenblum is suggesting. Is this a valid way of looking at it? If not, why not?
  21. Jun 19, 2011 #20

    Ken G

    User Avatar
    Gold Member

    The first weakness is resolved by recognizing that the key point about measurement is not that it is classical, but that it is done by an agent capable of registering experience (and this is more true of the experimenter than the experiment). This was discussed at length in another thread, and I have little desire to trot out once again all the ways that statement can be misconstrued, but I will say I think this is a minor issue the CI got wrong. Since our classical nature, and our conscious nature, are easily mistaken for each other, it's not a terribly important oversight, and no doubt would be considered controversial. As for the second "weakness", I see that as no weakness at all-- it's not the least bit surprising that quantum mechanics has as much trouble with the biology of cats as Newton's laws would, a cat is just way too complicated for either one and none of that has anything to do with CI. I mostly agree with Herbert, but here I think he is "shooting the messenger" when he attributes that problem to CI.

    Here you are simply taking my words out of context, an extremely sophomoric tactic that is way below you.
    Last edited: Jun 19, 2011
  22. Jun 19, 2011 #21

    Ken G

    User Avatar
    Gold Member

    Agreed. We are probably in the minority for wanting to give philosophy such free rein! I'm fine with it, if it comes under philosophy. What I dislike is the people who adopt the attitude "it's only philosophy if I don't agree with it."
    Another Feynman gem, to be sure.
  23. Jun 19, 2011 #22

    Ken G

    User Avatar
    Gold Member

    I think that's a good page for us all to be on.
  24. Jun 19, 2011 #23

    Ken G

    User Avatar
    Gold Member

    I think it is apparent to us all that you have a significant chip on your shoulder, and you are trying to shoehorn an intepretation of QM that can be consistent with certain prejudices you bring in. This is not uncommon, actually, it may be said that this is probably the usual way that people select a favored interpretation. But you are mostly mischaracterizing things you don't really understand. First of all, I never claimed that my way of explaining the CI was anything but my way of explaining it. Most who know it well seem fine with how I've explained it, but you can find some other version if you prefer. Also, it's not at all clear to me Rosenblum claimed to be explaining the CI. Indeed, many of his pronouncements sound singularly un-CI to me. Instead, they are just ways of thinking of quantum mechanics that you like. Many people have written books about how to think about QM, and some of them were people who really understand it quite well, and even so they can use very different language for expressing their understanding. They can even flatly disagree with the pictures each other evoke. That would certainly be true in this case-- I think Rosenblum trots out some seriously inferior rhetoric to talk about quantum phenomena, but the observations he describes are accepted scientific fact, and on that common ground we all find that the rhetoric is of far less importance. The Weinberg quotes deserve additional attention, because it must be noted that Weinberg believes in a "multiverse" of not only the many worlds of quantum mechanics, but also different physical parameters and maybe even different physical laws, all so he can use anthropic thinking to make go away certain difficult philosophical questions. His Nobel-prize-winning contributions to physics are beyond reproach, but his philosophy is controversial at best. And I couldn't help noticing that in the same breath he intimated that the CI has fatal flaws, he also said it worked fine. Curious that.
    Last edited: Jun 19, 2011
  25. Jun 19, 2011 #24
    Here's the complete conversation from the thread Qualia & Quantum Mechanics spanning many messages that discussed this particular interference issues:

    Varon: And how else can there be superposition without wave function being in the object (not merely knowedge of the observer??)

    Ken: There's definitely interference in the mathematics, what is not clear is what is actually intefering. Terms in an equation, or something real? CI says the former, thus avoiding strange problems like "real" entities comprised of imaginary numbers, or mutually coherent pockets of outcomes coexisting alongside noncoherent other worlds that make no contribution because they have random phase relationships with our world.

    Varon: Look. You mentioned terms in an equation is interfering. But just look at the detector screen, there interference patterns are there. It is something real.

    Ken: The pattern is real, yes. But the interference? How is that real? It is an inference you make when you see the pattern. Inferences are not real, they are mental constructs. I'd say the
    crux of CI is noticing the difference between what is in the reality and what is in our minds. Granted, even the outcome of an observation is in our minds, but CI sees that kind of outcome as more concrete than the mathematical stories we build up around them.

    Varon: So if the interference is in the equation. Pls. tell me what physically happens to a single photon or electron between the emission and the detection in the double slit experiment.

    Ken: The central thesis of the CI is that there is no answer to your question. Not just that we don't yet know the answer, that there is none. The reality is not set up to allow our intelligence a means of answering the question, and that is just exactly the same thing as the question having no answer.

    Varon: You are saying that it is possible nothing physically actually happens?

    Ken: I'm saying the CI interpretation is that "what physically happens" is whatever we can assert, with our apparatus, physically happened. There is no other meaning to the term, the rest is practically identifiable with mysticism. I'd say it's a bit like watching a movie-- we are told that all we are seeing is a string of still pictures, yet our minds interpret motion there. Is that motion something physically happening? With the "movie magic" that is done these days, say in superhero epics, oftentimes the motions we perceive never occured in any reality, the still pictures on the film are the only things that are real there. I believe the CI takes a similar skeptical approach to "the quantum realm"


    I think what you are saying is that since we don't know what occurs between emission and detection, then we can just state interference happens in the equation. But I don't like this philosophy. I'd like to know what could be interfering physically, so I won't be satisfied with Copenhagen. Can we know what's interfereing. Remember we still don't know what is consciousness so we can't discount the possibility consciousness can probe what happens between emission and detection.
  26. Jun 19, 2011 #25

    Ken G

    User Avatar
    Gold Member

    What is uncontroversial is that what is interfering in the equations is the wavefunction. At the experimental level, we can say that what is interfering is the particle, in the sense that we have a particle exhibiting an interference pattern, so the particle is undergoing some kind of interference. Where the issues get sticky is if we attribute reality to the wavefunction or not. In CI, we say the wavefunction is a mathematical tool, so its interference describes the interference exhibited by the particle, but that doesn't mean there's a real wavefunction with physically actualized complex numbers adding up and cancelling each other at some location in space. How does a complex number become a real thing anyway? The mathematics of the interference is mathematics, and it lives in the realm of mathematical concepts. Whether one imagines some kind of Platonic reality where those mathematical concepts really exist, rather than just as a processing step in someone's brain, is a philosophical question that has been debated for thousands of years. All I'm telling you is that the CI takes the positivist approach, without necessarily adopting positivism as a life philosophy, of saying that a concept is in someone's head, and a measurement is in the real world, and the connection between them is still completely mysterious.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook