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Robert Tulip
2007-Nov-01, 11:29 AM
A recent book, Faust in Copenhagen: A Struggle for the Soul of Physics by Gino Segrè (Viking, 310 pp., $25.95) has just been reviewed by Freeman Dyson in the New York Review of Books, available at http://www.nybooks.com/articles/20700 for $3. Dyson’s comments about Bohr’s views are quoted below. My question is, what do BAUT members think about Dyson’s views on Bohr’s theory of complementarity?

“a bunch of bright young physicists, assembled at the Institute for Theoretical Physics in Copenhagen in the year 1932 for their annual Easter conference, decided to entertain their elders by performing a spoof of Goethe's Faust. … In the front row sat Bohr, Ehrenfest, Meitner, Werner Heisenberg, Paul Dirac, and Delbrück, all of them famous physicists... All of them carried away memories of an evening that was a high point of the Copenhagen Institute and of twentieth-century physics. … Einstein has a minor role in the play, as a king with a retinue of trained fleas who cause considerable annoyance to the other characters. The fleas are Einstein's unified field theories, which in 1932 were already becoming an obsession. ... The main question that the book raises is whether the quantum revolution of the 1920s was a unique event in the history of science, or whether it may some day recur. …Bohr's understanding of quantum mechanics was based on a philosophical principle which he called complementarity. Two descriptions of nature are said to be complementary when they are both true but cannot both be seen in the same experiment. In quantum mechanics, the wave picture and the particle picture of an electron or a light-quantum are complementary …. Complementarity in quantum mechanics is an established fact. But Bohr in 1932 proposed to extend the idea of complementarity to biology, suggesting that the description of a living creature as an organism and the description of it as a collection of molecules are also complementary. In this context, complementarity would mean that any attempt to observe and localize precisely every molecule in a living creature would result in the death of the organism. The holistic view of a creature as a living organism and the reductionist view of it as a collection of molecules would be both correct but mutually exclusive. … When Crick and Watson discovered the double helix, they loudly claimed to have discovered the basic secret of life. The discovery came as a disappointment to Delbrück. It seemed to make complementarity unnecessary. Delbrück said it was as if the behavior of the hydrogen atom had been completely explained without requiring quantum mechanics. He recognized the importance of the discovery, but sadly concluded that it proved Bohr wrong. Life was, after all, simply and cheaply explained by looking in detail at a molecular model. Deep ideas of complementarity had no place in biology…. [A] seminal paper by the biologist Carl Woese with the title "A New Biology for a New Century," point[s] the way toward the next revolution. Woese's new biology is based on the idea that a living creature is a dynamic pattern of organization in the stream of chemical materials and energy that passes through it. … In Woese's picture of life, complementarity plays a central role, just as Bohr said it should. At the same time, while Carl Woese and others are debating the future of biology, the great debate over the future of physics continues. It is still a debate over the same questions that caused the disagreement between Bohr and Einstein. Does the quantum theory of the 1920s, together with the standard model of particles and interactions that grew out of it, give us a solid foundation for understanding nature? Or do we need another revolution to reach a deeper understanding? Theoretical physicists are now divided into two main factions. … String theory may be considered to be the counterattack of those who lost the debate over complementarity in physics in Copenhagen in 1932. It is the revenge of the heirs of Einstein against the heirs of Bohr. The new discipline of systems biology, describing living creatures as emergent dynamic organizations rather than as collections of molecules, is the counterattack of those who lost the debate over complementarity in biology in 1953. It is the revenge of the heirs of Bohr against the heirs of Einstein.”

GOURDHEAD
2007-Nov-01, 01:00 PM
Complementarity is useful as a "channel definition buoy" and helps to make constraints detectable.

jlhredshift
2007-Nov-01, 01:42 PM
Complementarity is useful as a "channel definition buoy" and helps to make constraints detectable.

I think the same could be said of the weak anthropic principal; resonance of the carbon atom, Hoyle. I also think that systematics "evolved" from inadequacies of the Linnaean system.

Warren Platts
2007-Nov-01, 02:57 PM
Complementariy in biology. . . . Now that's a false analogy. :)

Cougar
2007-Nov-02, 02:45 PM
My question is, what do BAUT members think about Dyson’s views on Bohr’s theory of complementarity?
I don't know, but Murray Gell-Mann said, "Neils Bohr brainwashed a whole generation of physicists into thinking that the job was done fifty years ago."

papageno
2007-Nov-02, 09:28 PM
I don't know, but Murray Gell-Mann said, "Neils Bohr brainwashed a whole generation of physicists into thinking that the job was done fifty years ago."


Yes, I read that the young generation was a bit too quick to accept Bohr's arguments against Einstein's objections.

Today the situation is different, because there is a whole lot of experimental results to rely on.

Ken G
2007-Nov-03, 06:51 PM
My question is, what do BAUT members think about Dyson’s views on Bohr’s theory of complementarity?
I find Dyson's analysis to be supremely insightful, thank you for pointing it out.

Robert Tulip
2007-Nov-03, 07:29 PM
Complementarity in biology. . . . Now that's a false analogy. :)

Warren
Bohr’s idea about complementarity in biology makes sense, and not only as an analogy. Just as quantum waves and particles are complementary – ie they cannot be explained in terms of each other – so are organisms and molecules complementary – in that explaining biochemistry or biophysics goes only a small way to explaining the reality of the organism. This illustrates the philosophical weakness of the reductionist theory that in principle biology could ultimately be explained by physics. Niels Bohr effectively claims the whole is more than the sum of the parts, whereas traditional physics, including visions of a unified field theory, is reductionist, seeing nothing more in the whole (eg the organism) than can be explained by its physical mechanism. I am sympathetic to the idea of complementarity in biology because phenomena such as intentions are features of the dynamic organism and its ecology and are not helpfully explained by physics.
Dyson makes the following point in his review, in addition to those I quoted above: “In my opinion, the double helix is much too simple to be the secret of life. If DNA had been the secret of life, we should have been able to cure cancer long ago. The double helix explains replication but it does not explain metabolism. Delbrück chose to study the phage because it embodies replication without metabolism, and Crick and Watson chose to study DNA for the same reason. Replication is clean while metabolism is messy. By excluding messiness, they excluded the essence of life. The genomes of human and other creatures have now been completely mapped and the processes of replication have been thoroughly explored, but the mysteries of metabolism still remain mysteries. The phage is still the only living creature whose behavior is simple enough to be completely understood and predicted. To understand other kinds of creatures, from fruit flies to humans, we need also a deep understanding of metabolism. The understanding of metabolism will perhaps be the theme of the next revolution in biology.”
Robert

Ken G
2007-Nov-03, 11:02 PM
And of course one must not forget cognition, a later stage still. For even life is somewhat empty and uninteresting in the absence of all cognition.

By the way, before it gets too widely accepted that particles and waves are in contrast somehow, I would point out that a view popularized by Lande (and which I think is spot on) is that the particle and wave pictures function hand in hand. This is the truer meaning of complementary-- neither has its full meaning without the other. Wave mechanics tell particles where to go, particle attributes are what give the wave mathematics physical meaning. Neither means much without the other, once the problematic concept of "trajectory" is dispensed with.

Warren Platts
2007-Nov-04, 05:43 AM
Warren
Bohr’s idea about complementarity in biology makes sense, and not only as an analogy. Just as quantum waves and particles are complementary – ie they cannot be explained in terms of each other – so are organisms and molecules complementary – in that explaining biochemistry or biophysics goes only a small way to explaining the reality of the organism. This illustrates the philosophical weakness of the reductionist theory that in principle biology could ultimately be explained by physics. Niels Bohr effectively claims the whole is more than the sum of the parts, whereas traditional physics, including visions of a unified field theory, is reductionist, seeing nothing more in the whole (eg the organism) than can be explained by its physical mechanism.

I am sympathetic to the idea of complementarity in biology because phenomena such as intentions are features of the dynamic organism and its ecology and are not helpfully explained by physics.


And of course one must not forget cognition, a later stage still. For even life is somewhat empty and uninteresting in the absence of all cognition.

If complementarity is merely a restatement of the commonplace that wholes have properties that their parts do not, then what's the use of calling that "complementarity"? (I would have thought for something in biology to count as partaking in complementarity, it would have to be something really crazy-making, like cats that are both dead and alive at the same time.)

For example, a bomb has the property of being dangerous, but its parts taken separately are comparatively harmless. But is that complementarity?

What about the angle of repose of a mere sand pile? The angle of repose is a property that only the pile as a whole exhibits--individual sand grains don't have an angle of repose--so the whole is more than the sum of its parts. Yet it's equally clear that the angle is determined by the properties of the parts: sand consisting of unweathered, angular grains produces steeper angles of repose than does sand consisting of worn, round grains; i.e., the angle of repose is easily reduced. So is that complementarity, or would that be more of an example of something that's non-complementarity?

But even for more complex phenomena like higher life forms, if intentional behavior cannot be reduced to the behavior of atoms and molecules, then how else is it supposed to happen? We all agree that it doesn't happen by magic, yet I suspect that you are prepared to import something into the scene that sand piles and bombs do not have. A G-d-given soul perhaps, or an entelechy, or maybe a sui generis consciousness. After all, wasn't it Bohr who said that consciousness is necessary to round out the theory for at least some quantum phenomena?

Ken G
2007-Nov-04, 11:22 PM
If complementarity is merely a restatement of the commonplace that wholes have properties that their parts do not, then what's the use of calling that "complementarity"? (I would have thought for something in biology to count as partaking in complementarity, it would have to be something really crazy-making, like cats that are both dead and alive at the same time.)I can't speak for Bohr's meaning there, but it could be that the point of complementarity is like the complementarity of momentum and position in the uncertainty principle-- that knowledge of one precludes knowledge of the other, yet both are present and can be known independently. Thus the idea would be that you can describe a living thing by all its parts, but in the process losing their united function, or you can consider the united function, but then you cannot understand what is happening at the molecular level. It goes deeper than the whole being more than the sum of parts, which can be said for a good poem for example-- it is more like, to know the poem is to lose information about what words went into it, or to know every word in the poem is to not be able to understand the poem. That's a much trickier principle, found only (so far) in quantum mechanics.

For example, a bomb has the property of being dangerous, but its parts taken separately are comparatively harmless. But is that complementarity?No.


What about the angle of repose of a mere sand pile? That is also an example of an "emergent property", so is part of what Bohr probably meant, but not all. The emergent property is seen in a lot of places, like your examples or my poem, but complementarity was only even imagined in Bohr's day.
After all, wasn't it Bohr who said that consciousness is necessary to round out the theory for at least some quantum phenomena?Not to my knowledge, though Wigner did think along those lines. Rest assured there are no quantum phenomena that benefit from the inclusion of consciousness, and no predictions are made that way.

Warren Platts
2007-Nov-05, 01:24 PM
Thus the idea would be that you can describe a living thing by all its parts, but in the process losing their united function, or you can consider the united function, but then you cannot understand what is happening at the molecular level. . . . it is more like, to know the poem is to lose information about what words went into it, or to know every word in the poem is to not be able to understand the poem. That's a much trickier principle, found only (so far) in quantum mechanics.

Well then, what happens in biology is just the opposite of complementarity. The functional and molecular explanations reinforce each other: to know about one only deepens the understanding of the other, and vice versa; whereas in QM, knowing about position obscures knowledge of momentum, or observing particle-like properties obscures wave-like properties.

Ken G
2007-Nov-05, 03:18 PM
I think that indeed has been the conclusions in biology since Bohr, but Dyson is suggesting that we may yet see the pendulum swing back, when biologists start tackling the difficult problems (like cognition). Dyson suggested that the simple systems, like the phage, were first addressed, and for good reason (they are simpler), but that may be the very reason why Bohr's complementarity was not encountered. It may be quite a long time, actually, before we can address systems where it may appear-- all pretty hypothetical at this point.

Len Moran
2007-Nov-05, 08:17 PM
I can't speak for Bohr's meaning there, but it could be that the point of complementarity is like the complementarity of momentum and position in the uncertainty principle-- that knowledge of one precludes knowledge of the other, yet both are present and can be known independently.



I would like to clarify this for myself since it links to my current reading on the subject of weak objectivity at the quantum level within d'Espagnat's book. As I understand it, atomic particles, unlike macro objects, are not said to possess attributes independently of the experimental set up, so I was wondering in what context you say momentum and position are "present". It does seem to me that there is no momentum or position of a particle outside of the experimental setup (it is weakly objective in nature), unlike, for example, a traveling ball where we can say the measured momentum is a strongly objective quantity - we do not have to measure it in order to ascribe a momentum to it.

In terms of quantum mechanics, I would say the complementarity aspect does not give two strongly objective views, each view is weakly objective, consisting holistically of the object and the experimental set up which always carries the notion of an observer. And whatever attributes we assign in this measurement process, those same attributes do not exist independently of this setup. So I think that in terms of quantum mechanics, complementarity quite importantly refers to a notion of underlying reality that can never be accessed objectively.

In this sense then, I'm not sure about the use of complementarity within the OP quote in relation to its use with quantum mechanics. The holistic view and the reductionist view of a creature are both correct, but they are both (I would say) strongly objective in nature, molecules can be thought of as possessing attributes independent of any verification, and the "life force" of a creature can be thought of as being present without any notion of any experimental setup to verify the creature is alive. So it seems to me that to use complementarity in the way the OP quote does is to use it in the sense of having different complementary perspectives of a known object.

Hence the use of the term complementarity differs I think quite importantly between quantum mechanics and biology for the reasons suggested, but having said that, I have read that Bohr never gave any explicit definition of what he meant by complementarity, and the OP quote does refer specifically to Bohr as well as quantum mechanics, but I would say that the nature of quantum mechanics is such that the description I have outlined of weak objectivity follows naturally from experiment.

Ken G
2007-Nov-06, 02:53 AM
As I understand it, atomic particles, unlike macro objects, are not said to possess attributes independently of the experimental set up, so I was wondering in what context you say momentum and position are "present".I don't mean present in some transcendent way, I simply mean that they are available parameters to be teased out by the appropriate experiment. Your understanding is quite right.
It does seem to me that there is no momentum or position of a particle outside of the experimental setup (it is weakly objective in nature), unlike, for example, a traveling ball where we can say the measured momentum is a strongly objective quantity - we do not have to measure it in order to ascribe a momentum to it.I would not quite say there's no momentum or position, I'd say they don't have precise values. What you generally do is prepare the particle in a given state, which means it has a wave function. The wave function embodies the uncertainty-- there are now possible ranges to any momentum or position measurement. So before you do such an experiment, you have some fuzzy concept of both position and momentum, but you can't make either one precise without messing up the other.


In terms of quantum mechanics, I would say the complementarity aspect does not give two strongly objective views, each view is weakly objective, consisting holistically of the object and the experimental set up which always carries the notion of an observer. Yes, this piece also comes in when you "prepare" the particle, which is tantamount to starting off with one measurement and later doing another. That's what physics really does, it connects the results of two measurements, on we call the "initial state" and the other we call the "final state".
And whatever attributes we assign in this measurement process, those same attributes do not exist independently of this setup. Right, there is no definition outside the setup-- the devices that prepare the state and those that measure it.


So I think that in terms of quantum mechanics, complementarity quite importantly refers to a notion of underlying reality that can never be accessed objectively.I'd say it refers to a notion of the limits one invokes automatically when one seeks objectivity. There is no precise notion there of something that cannot be accessed objectively, because we have no means to describe such a notion. That's the real point, I'd say, that we cannot even talk about anything that is deeper than complementarity-- words fail us, because we base the words on objectivity.



Hence the use of the term complementarity differs I think quite importantly between quantum mechanics and biology for the reasons suggested, but having said that, I have read that Bohr never gave any explicit definition of what he meant by complementarity, and the OP quote does refer specifically to Bohr as well as quantum mechanics, but I would say that the nature of quantum mechanics is such that the description I have outlined of weak objectivity follows naturally from experiment.One can only guess what Bohr meant, but it seems the Dyson thinks he might have been talking about a complementarity between what is objectively describable by prescribing the location (say, form) of a bunch of molecules, and how they are dynamically interacting (say, function). To study their interaction is to study their motion, but when considered to be in motion, they no longer have a clearly defined spatial configuration at the quantum scale. I think it is interesting that we do not use quantum thinking to describe living systems, because many of the processes occur on larger scales (the atomic scale is normally treated as an "interaction" only). But if the key to the process is indeed happening on that interaction scale, he may have a point. Certainly there are molecules with a certain "shape" because it is convenient for quantum effects like tunneling, yet if one is considering tunneling, one is accepting that no system configuration is being precisely specified. That may be along the lines of his thinking, I don't know-- we normally just think of the protons classically and the electrons quantum mechanically.