Myths of Copenhagen (philosophy of science)

#1
http://philipball.blogspot.com/2018/06/m...hagen.html

EXCERPT: Discussing the Copenhagen interpretation of quantum mechanics with Adam Becker and Jim Baggott makes me think it would be worthwhile setting down how I see it. I don’t claim that this is necessarily the “right” way to look at Copenhagen (there probably isn’t a right way) [...] Part of the problem too, as Adam said (and reiterates in his excellent new book What is Real?, is that there isn’t really a “Copenhagen interpretation”. I think James Cushing makes a good case that it was largely a retrospective invention of Heisenberg’s, quite possibly as an attempt to rehabilitate himself into the physics community after the war. [...] when we talk about “Copenhagen”, we ought really to stick as close as we can to Bohr – not just for consistency but also because he was the most careful of the Copenhagenist thinkers.

It’s perhaps for this reason too that I think there are misconceptions about the Copenhagen interpretation. The first is that it denies any reality beyond what we can measure: that it is anti-realist. I see no reason to think this. People might read that into Bohr’s famous words: “There is no quantum world. There is only an abstract quantum physical description.” But it seems to me that the meaning here is quite clear: quantum mechanics does not describe a physical reality. [...] Quantum mechanics is the formal apparatus that allows us to make predictions about the world. There is nothing in that formulation, however, that denies the existence of some underlying stratum in which phenomena take place that produce the outcomes quantum mechanics enables us to predict.

Indeed, what Bohr goes on to say makes this perfectly clear: “It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature.” (Here you can see the influence of Kant on Bohr, who read him.) Here Bohr explicitly acknowledges the existence of “nature” – an underlying reality – but doesn’t think we can get at it, beyond what we can observe.

This is what I like about Copenhagen. I don’t think that Bohr is necessarily right to abandon a quest to probe beneath the theory’s capacity to predict, but I think he is right to caution that nothing in quantum mechanics obviously permits us to make assumptions about that. Once we accept the Born rule, which makes the wavefunction a probability density distribution, we are forced to recognize that.

Here’s the next fallacy about the Copenhagen interpretation: that it insists classical physics, such as governs measuring apparatus, works according to fundamentally different rules from quantum physics, and we just have to accept that sharp division.

Again, I understand why it looks as though Bohr might be saying that. But what he’s really saying is that measurements exist only in the classical realm. Only there can we claim definitive knowledge of some quantum state of affairs – what the position of an electron “is”, say. This split, then, is epistemic: knowledge is classical (because we are).

Bohr didn’t see any prospect of that ever being otherwise. What’s often forgotten is how absolute the distinction seemed in Bohr’s day between the atomic/microscopic and the macroscopic. Schrödinger, who was of course no Copenhagenist, made that clear in What Is Life?, which expresses not the slightest notion that we could ever see individual molecules and follow their behaviour. To him, as to Bohr, we must describe the microscopic world in necessarily statistical terms, and it would have seemed absurd to imagine we would ever point to this or that molecule.

Bohr’s comments about the quantum/classical divide reflect this mindset. It’s a great shame he hasn’t been around to see it dissolve – to see us probe the mesoscale and even manipulate single atoms and photons. It would have been great to know what he would have made of it.

But I don’t believe there is any reason to suppose that, as is sometimes said, he felt that quantum mechanics just had to “stop working” at some particular scale, and classical physics take over. And of course today we have absolutely no reason to suppose that happens. On the contrary, the theory of decoherence (pioneered by the late Dieter Zeh) can go an awfully long way to deconstructing and demystifying measurement. It’s enabled us to chip away at Bohr’s overly pessimistic epistemological quantum-classical divide, both theoretically and experimentally, and understand a great deal about how classical rules emerge from quantum. Some think it has in fact pretty much solved the “measurement problem”, but I think that’s too optimistic, for the reasons below....

MORE: http://philipball.blogspot.com/2018/06/m...hagen.html


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#2
(Jun 10, 2018 05:13 AM)C C Wrote: ...it would be worthwhile setting down how I see it. I don’t claim that this is necessarily the “right” way to look at Copenhagen (there probably isn’t a right way) [...] Part of the problem too, as Adam said (and reiterates in his excellent new book What is Real?, is that there isn’t really a “Copenhagen interpretation”. I think James Cushing makes a good case that it was largely a retrospective invention...

...It’s perhaps for this reason too that I think there are misconceptions about the Copenhagen interpretation.

Is that sentence consistent with the material I quoted above it? If there isn't really a single coherent metaphysics expressed in the 'Copenhagen Interpretation' and what we call by that name is subsequent authors reading their own interpretations into Bohr's speculations, then what does 'misconceptions' mean? Misreading Bohr's intentions?

Quote:The first is that it denies any reality beyond what we can measure: that it is anti-realist. I see no reason to think this. People might read that into Bohr’s famous words: “There is no quantum world. There is only an abstract quantum physical description.” But it seems to me that the meaning here is quite clear: quantum mechanics does not describe a physical reality. [...] Quantum mechanics is the formal apparatus that allows us to make predictions about the world. There is nothing in that formulation, however, that denies the existence of some underlying stratum in which phenomena take place that produce the outcomes quantum mechanics enables us to predict.

Indeed, what Bohr goes on to say makes this perfectly clear: “It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature.” (Here you can see the influence of Kant on Bohr, who read him.) Here Bohr explicitly acknowledges the existence of “nature” – an underlying reality – but doesn’t think we can get at it, beyond what we can observe.

I think that most contemporary physicists and philosophers interpret the 'Copenhagen Interpretation' instrumentally in the manner this writer suggests. I'm not enough of a scholar to know what Bohr really believed or intended to say. (Or why we should take his views as gospel if we did.) One would have to carefully study his surviving correspondence and notes, what his contemporaries said about his views, the positions he took in the controversies he participated in, and so on.

(It's kind of interesting how the problem of interpreting writers and their intentions parallels the problem of interpreting quantum mechanics.)

Quote:This is what I like about Copenhagen. I don’t think that Bohr is necessarily right to abandon a quest to probe beneath the theory’s capacity to predict, but I think he is right to caution that nothing in quantum mechanics obviously permits us to make assumptions about that.

I'm inclined to disagree more with that statement. Whatever reality prevails on the microscale has to be such that the experiments come out as they do. So the situation is basically the same as it is for classical physics: our experimental results place constraints on our metaphysical speculations, such that the latter have to be consistent with the former. Metaphysics has always been cognizant of physics, common sense physics in Aristotle's day, and the more amd more obstruse productions of observation and experiment subsequently.

Quote:Once we accept the Born rule, which makes the wavefunction a probability density distribution, we are forced to recognize that.

Maybe... maybe not. I'm less eager to pronounce on what conclusions we are "forced" to embrace.

Quote:Here’s the next fallacy about the Copenhagen interpretation: that it insists classical physics, such as governs measuring apparatus, works according to fundamentally different rules from quantum physics, and we just have to accept that sharp division.

So we have two different and seemingly inconsistent mathematical/conceptual apparatuses that both work well in predicting experimental results in their respective spheres.

That just seems to fall out of the instrumental sort of interpretations pretty naturally. It only becomes a problem when classical and quantum physics are interpreted metaphysically (as accounts of how the reality we are observing fundamentally is) rather than as descriptions of how it is observed to behave. Then we are faced with seeming inconsistencies in how we conceive of how reality fundamentally is. The idea that that physical reality is fundamentally inconsistent is more troubling than the idea that physical reality (whatever it is) looks different and can be described differently at different scales.

Quote:But I don’t believe there is any reason to suppose that, as is sometimes said, he felt that quantum mechanics just had to “stop working” at some particular scale, and classical physics take over.

If physics is the mathematical and interpretive scheme that we apply to our observations of the world, and if two different and seemingly inconsistent schemes both produce good results at their particular ranges of applicability, then we would seem to have the missing reason for saying that. But our intellectual drive for consistency rebels against the dichotomy. (That's probably one of the underlying motives for 'Ockham's razor'.) Believing that there are two radically different and seemingly inconsistent sets of physical principles at work at different scales in the same physical reality offends our sensibilities. We want a simpler and more consistent reality underlying our measurements and comprising our world.

Quote:And of course today we have absolutely no reason to suppose that happens. On the contrary, the theory of decoherence (pioneered by the late Dieter Zeh) can go an awfully long way to deconstructing and demystifying measurement. It’s enabled us to chip away at Bohr’s overly pessimistic epistemological quantum-classical divide, both theoretically and experimentally, and understand a great deal about how classical rules emerge from quantum.

Sure, it's possible to create an underlying metaphysics (a quantum-physical "interpretation") that promises to restore the consistency between classical and quantum. (In this case by treating quantum as fundamental and by trying to reduce classical to it.) Unfortunately, it's possible to create these kind of consistent classical/quantum interpretative schemes in multiple ways. So we still don't have the simplicity we seek, we've just pushed it from the instrumental sphere to the metaphysical/interpretive sphere.
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#3
(Jun 11, 2018 05:36 PM)Yazata Wrote:
(Jun 10, 2018 05:13 AM)C C Wrote: ...it would be worthwhile setting down how I see it. I don’t claim that this is necessarily the “right” way to look at Copenhagen (there probably isn’t a right way) [...] Part of the problem too, as Adam said (and reiterates in his excellent new book What is Real?, is that there isn’t really a “Copenhagen interpretation”. I think James Cushing makes a good case that it was largely a retrospective invention...

...It’s perhaps for this reason too that I think there are misconceptions about the Copenhagen interpretation.

Is that sentence consistent with the material I quoted above it? If there isn't really a single coherent metaphysics expressed in the 'Copenhagen Interpretation' and what we call by that name is subsequent authors reading their own interpretations into Bohr's speculations, then what does 'misconceptions' mean? Misreading Bohr's intentions?

Trying to cram further interpretative assumptions into an interpretation that specifically features the fewest assumptions is just counterproductive. If he wants an explicitly realist interpretation, there are plenty to be found without trying to shoehorn it into Copenhagen.
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#4
Yazata Wrote:
Quote:But I don’t believe there is any reason to suppose that, as is sometimes said, he felt that quantum mechanics just had to “stop working” at some particular scale, and classical physics take over.

If physics is the mathematical and interpretive scheme that we apply to our observations of the world, and if two different and seemingly inconsistent schemes both produce good results at their particular ranges of applicability, then we would seem to have the missing reason for saying that. But our intellectual drive for consistency rebels against the dichotomy. (That's probably one of the underlying motives for 'Ockham's razor'.) Believing that there are two radically different and seemingly inconsistent sets of physical principles at work at different scales in the same physical reality offends our sensibilities. We want a simpler and more consistent reality underlying our measurements and comprising our world.  

But that's just it! How the brain perceives reality would dictate why we want a simpler and more consistent underlying theory. The methods of science exploit this ability to perceive, it is inseparable from it, that is why it can never be complete without metaphysics - our subjective reality includes perception. This basic fact is what Psychology attempts to explore but never reaching full accessibility.
Quote:
Quote:And of course today we have absolutely no reason to suppose that happens. On the contrary, the theory of decoherence (pioneered by the late Dieter Zeh) can go an awfully long way to deconstructing and demystifying measurement. It’s enabled us to chip away at Bohr’s overly pessimistic epistemological quantum-classical divide, both theoretically and experimentally, and understand a great deal about how classical rules emerge from quantum.

Sure, it's possible to create an underlying metaphysics (a quantum-physical "interpretation") that promises to restore the consistency between classical and quantum. (In this case by treating quantum as fundamental and by trying to reduce classical to it.) Unfortunately, it's possible to create these kind of consistent classical/quantum interpretative schemes in multiple ways. So we still don't have the simplicity we seek, we've just pushed it from the instrumental sphere to the metaphysical/interpretive sphere.

I have recently been under the impression that QM was a theory of matter but essentially shifting its fundamental make-up to the concept of wavefunctions. The article may indicate otherwise. The Quantum/ Classical divide might indicate that when it comes to Metaphysics, we still haven't got a clue about which side reality might assume, hence we need an underlying metaphysics.
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