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This is the first in a series of informal conversations between colleagues at Starlab who are in similar fields but who have differing views on certain subjects within that field. In this case discussions begun at Starlab's solar eclipse party were continued some days later over coffee at the lab and via e-mail. Jack Klaff asked the questions, and the report begins with an extract from a provocative e-mail he sent them in the guise of Devil’s Advocate. All three men get on extremely well, and the discussion was devoid of animosity. However, the last line of the exchange proved to be most revealing. For a number of important reasons, concerning the publishing of scientific ideas it was decided that the text was acceptable as it stood, without mentioning the names of the two physicists involved. Jack : Richard Feynman said that discussions about quantum mechanics always come down to 'that experiment with the two holes. Physicist X: I haven't uttered those words in discussions about quantum mechanics for a long, long time. EXPLANATION: Feynman was referring to an old experiment, devised by Thomas Young in 1801, to prove that light is made up of waves, which is used in the twentieth century to prove something more complex, known to physicists as the ‘collapse of the wave function’. In Young’s test the light clearly lapped and undulated its way through and away from the slits, because there were alternating blocks of light and shade on the wall. Light had to be made up of waves. Particles of light would have flown like bullets, leaving no shading, just two clear slits. Since the early years of the twentieth century, though, whenever a particle detector was placed behind the screen and the two slits, the light was shown to be made up of particles. So nowadays what the test is taken to indicate is that light is made up of particles and waves. That is because if you use a particle detector and test for particles you get particles. If you use a wave detector and test for waves you get waves. Nobody knows how, but the test itself gives you the result. It is utterly alien to classical physics. The problem for physicists is that there are those who try to bring Consciousness into the matter, or even worse Mysticism All of which is why one of the e-mail sessions between the three men involved Jack playing Devils’ Advocate. Jack as Devil’s Advocate: People come to the question of wave/particle duality carrying their belief system on their backs. Aren’t you guys as guilty of this - in fact far more guilty of it than most. Once people have learned such relevant facts as may be ascertained from the experiment, they usually go away, lie down in a darkened room for a while and then come back with that belief system intact. Physicist Y: My belief system is not a burden as you imply, nor I am guilty of anything but an ability consistently to approach the questions involved without obfuscation. Every physicist I knew came out of the darkened room accepting that Newtonian physics was no longer sufficient to describe the world. Some physicists came out with the conviction that quantum mechanics wasn't sufficient either, at the same time agreeing that Newtonian physics was inadequate. They clearly changed their belief system. However, I know what you are groping for :) but I'll address that below. Physicist X: Whatever. Jack as Devil’s Advocate: What I want to guard against in our discussion is you two repeating what your professors said Physicist X: I'm not repeating what my professors said, because they were particle physicists, and in that community it is customary to regard quantum mechanics as no more than its probability calculus, and to avoid discussions of its problems as a physical theory. Physicist Y: Neither am I repeating what my professors say. I do not think that quantum mechanics is merely a probability calculus (which, by the way, is the position of one with "an open mind", i.e. a noncommital agnostic). I am very willing to enter into discussions regarding the essentially philosophical issues of the epistemological and metaphysical implications of the theory. Quantum mechanics is a probability calculus, certainly, but one that allows us to make definite statements about both ensembles of systems as well as individual systems. Jack as Devil’s Advocate: Serious and highly intelligent scientists have declared clearly and publicly that NOTHING IS MORE IMPORTANT about quantum mechanics than this: We can no longer think of the universe as being Out There. We have to shatter the glass. We should no longer think of the universe as being a universe for Observation, This is a universe for participation. We are INVOLVED in certain experiments, this one in particular, and Einstein may have been quite bright but he was also was a sick autistic person, who managed actually to give a child away, had a schizoid son and never managed to make real connections in his life. :-) Physicist X: I think the measurement problem is more about the participation of the measurement device. Of course, we are also measurement devices, but to overemphasize this and put us in a separate category, as many people have done in the past, doesn't help, except in mystifying the whole thing. Science is about demystification. Physicist Y: I agree completely. Jack as Devil’s Advocate: The ideas I am putting to you are not new ideas and yet you guys have not thought them or been taught them. They have been put forward by very great geniuses, thoughtful people and real scientists not some twirps on an Ashram. Physicist X: I have certainly thought about them. Physicist Y: Great geniuses sometimes say very silly things in their spare time that would be unpublishable in scientific journals and are therefore irrelevant to physics. Apart from that, there are scientists who honestly want to convey their sense of wonder to the lay public. That's perfectly all right, but I think most of the time their efforts don't have the desired result. I get the impression that a lot of lay people reading popular science books only remember the magic (i.e. the counterintuitive predictions) of quantum mechanics, not the science, and the step to mindless mystification is small. Physicist X Yes, this is so. Jack as Devil’s Advocate: The way you are arguing therefore, to the minds of a very great number of highly intelligent people, is going to come across as extremely stupid, blind and stubborn. Physicist X: If they’re highly intelligent, let them read a standard quantum mechanics textbook. The math isn't all that complicated. the people being blind and stubborn are those that don't know what quantum mechanics actually says, expressed in mathematical form. and you do need the mathematics, because quantum mechanics is a physical theory, not an Eastern religion. Physicist Y: I don't see any difference between "Eastern religions" and "Western religions" in this - in fact, Eastern religions sometimes even involve numerology! :) Physicist X: You could just as well say that Newtonian gravity proved the interconnectedness of all things as foreseen by Eastern religions, because it described a force working instantaneously and without mediation over arbitrarily large distances. However, no Eastern religion ever predicted the evolution of a physical system in a quantitative way. I repeat that quantum mechanics is a physical theory and should be treated as such. Physicist Y: Listen, I just got back from a conference on quantum approaches to consciousness. Obviously I have not suffered from any "failure to address the question" of the relationship between quantum mechanics and consciousness, much less an "utter failure." Physicist Y: I am not sure which religions we are discussing here, but we the questions we are dealing with here are clearly within the realm of science and philosophy, which together are able to give very nice responses to anyone's advocate. THE DISCUSSION ITSELF – IN PERSON, NOT VIA E-MAIL Jack: Obviously I'm not going to deny that my interest in wanting to do this is actually to find the differences between you guys. I suppose that can wait. If you want. It's up to you. Physicist Y: Let's see if there are any Physicist X:. You think there are? Physicist Y: :Depends what he wants to ask. But I want to say that quantum mechanics is a theory which supersedes other theories that are not as good, however quantum is not new kind of theory in any sense. Most physicists - that is to say the normal view of physicists - is that in quantum mechanics you have 2 kinds of dynamics. You have Schroedinger's equation that governs the evolution of the wave function, and then you have something weird like the collapse of the wave function. Which you see for me has no place in a physical theory. The collapse of the wave function might take place but then there must be some more fundamental physics that we haven't found yet. There is no sign of that new - [or newer] - physics at this time so. I believe in the ‘many worlds’ interpretation; Reaction from Physicist X [Explanatory Note: Some physicists have
not taken to the notion of the collapse of the wave function - explained
above. Physicist Y: O.K. Quantum mechanics is a classical theory. There is only 1 dynamic. Schroedinger's equation is a completely deterministic equation. You just plug in some initial conditions, say the wave function at Time T equals 0 Physicist X Say 'at some time' or people will think [you're talking about] The beginning of the universe Physicist Y: And you proceed from there with calculations that follow all the usual conventions of mathematics and physics Physicist X/ I am going to disagree with almost everything he said. First of all quantum mechanics is not a deterministic theory. And that is just what is unique to quantum theory that led to previous theory being called ``classical.'' That during part of its evolution the wavefunction obeys a differential equation strictly does not make the quantum theory classical, even if that is taken to be the only sort of evolution. The sense in which determinism applies is that Schroedinger equation is - in the often-studied cases - deterministic, which is not the sense that is relevant here and not only because of the set of mutually attributable properties corresponding to the commuting observables - is smaller that the set of all observable properties. Because it is an essentially probabilistic theory, it doesn't determine the behaviour of any individual objects. Physicist Y: But probability only comes in when you try to think of quantum objects as classical objects Physicist X I'm not sure. Probability is built into the theory axiomatically and the wave functions correspond to state preparations or sets of probabilities amplitudes. Yours is a very interpretationally-based objection. Quantum mechanics has built into it 2 dynamics, as you acknowledged initially. Collapse is according to von Neumann Process 1, whereas Schroedinger's dynamics is Process 2. Quantum mechanics, as a physical theory without interpretive colouring, puts no more emphasis on Schroedinger's equation than on the wave function collapse. In fact, if anything, von Neumann's calling collapse Process 1 suggests its primacy. I'm just saying that it is a probabilistic theory, and that as for the many worlds interpretation, it is extremely philosophically abusive. It's easy for someone who views reality as an essentially mathematical entity - which makes no sense but is more common than it ought to be - to think that the many worlds interpretation is simpler looks right, but from the proper ontological point of view its crazy and completely unparsimonious. Physicist Y: Can I answer-- Physicist X Not just now - I'm not done yet. And further, there is no explanation for how people get definite outcomes from measurements anyway - so like the Copenhagen approach to measurement - it's another example of what Einstein called a 'soft pillow'. One is stuck with a potentially infinite number of copies of every one of the universe's objects, which is patently absurd - and even non-physical, really. Physicist Y: So first of all, your argument, Physicist X, is purely based on philosophy and has nothing to do with physics. Many physical theories have large redundancy. In the case of the 'many worlds' interpretation the wave-function can be decomposed into an infinite number of components that all look classical on a macroscopic level. In other physical theories such redundancies are present as well, for example in classical electromagnetism you have something called a 'gauge symmetry' which means that the underlying object in the theory can undergo transformations and the physical result will not change. In the 'many worlds' interpretation, a similar kind of redundancy is present but people tend to have problems with that because the redundancy is much easier to understand in this view, whereas in electromagnetism it seems abstract and people don't worry about it. Physicist X This is just - Physicist Y: Not done yet. There are two viewpoints among those who believe in the many worlds interpretation. One is that the other components in the wave function are to be considered real; they insist that there is an infinite number of worlds - that is the platonic viewpoint. But you also have an Aristotelian view: I don't care whether other 'worlds' are real or not, since the linearity of the Schroedinger equation implies that we don't have access to them anyway, and I think that is really the point of view a physicist should take. If you don't have access to something you don't care. It's a bit like this: no particle physicist will start thinking about the question whether intermediate virtual particles are real or not. The fact that the Schroedinger equation is linear implies that there is no interaction between the different components. [Kerfuffle; they talk over each other for a moment] Physicist X. Let me say a few things. One does have access to measurement outcomes in quantum mechanics, obviously. However, the value of the parameter having a guage symmetry isn't even an observable, so that's a red herring. Now, the reason my objection is philosophical is because the issues are philosophical. When you talk about things existing one has a philosophical question, and this point of the linearity of the Schroedinger equation and access isn't correct in the sense that one has to assert that the real world is one of the components in order for the other to be nonexistent or irrelevant and that choice has no objective basis. The linearity of the Schroedinger equation exactly means that there is a democracy among the so-called 'worlds' - nothing physical or mathematical places any actual observer in any particular component, only the subjective experience of a measurement outcome can do that if you stick yourself with the many worlds interpretation. To claim otherwise is to be obfuscationistic. So I repeat that ignoring philosophical issues amounts to a 'soft pillow' and that quantum physics is incapable, in itself, of solving the question as to what is 'real' and how many worlds there are. You are forced to introduce philosophical assumptions as much as I am because of that. Physicist Y: I want to go on. My point - what Physicist X is ignoring I think is that the second dynamics - the collapse of the wave function – simply doesn't make sense because it supposes that something special happens when a measurement is made. Now whoever does the Measurement - a physicist or anybody making observations that ties quantum mechanics to human minds. Jack: Well, we did have to get there sometime. Physicist X Mm-hmm. Physicist Y: : I think a mind is just another physical system so unless you postulate a newer physics that somehow explains why mind are capable of making the wave function collapse, the collapse postulate does not fit into a physical theory. Physicist X This is evolving nicely. O.K. I agree that the mind is just another physical system, but going to the many worlds interpretation doesn't help because in any given world there is still an undetermined step - which you say makes no sense - into a world having just one measurement outcome at each branching node in the history of the '`multi-verse'' or of many worlds. One has to face it that, one way of another, in *our* world, collapse is part of the theory and that to remove it is to take a step that the community has rightly not tried to avoid. Physicist Y: It has Physicist X Not many people - Physicist Y: 20 per cent believe in the 'many'. Physicist X. A minority. A substantial minority. Physicist Y: I can get you the exact number [Post script – in the region of 16-17 per cent] Physicist X. A small but not completely insubstantial fraction. Physicist Y: That is just because we who believe in the 'many worlds' interpretation think the wave function collapse doesn't happen. and there really is no problem. The measurement problem doesn't exist. Physicist X It does exist, it' s a mathematical problem that hasn't hasn't been solved and that has led to heretofore unsolved quandaries. Many worlds doesn't solve it and is only a worse soft pillow than the Copenhagen interpretation. Physicist Y: That's - Physicist X We should go back I don't want to be authoritarian. I wanted to reply to this business about what's happening within mind - I agree the mind is just a physical system and I also don't think that being in the majority makes one right. The point is that any attempted solution to the measurement problem has been explicitly or implicitly philosophical including the many worlds interpretation. Until we have a mathematical solution on which almost the entirety of the community can agree, it is better to stick with the von Neumann formulation and not to introduce ontological or epistemological elements without some significant physical payback. These newer soft pillows aren't worth their price. [They agree that Jack will write it up and then they will correct it] Physicist Y: Ja, then we can bitch about the text [Laughter]
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