标题: Gell-Mann on simplicity and complexity,mind, free will, etc [打印本页] 作者: liver411 时间: 2010-5-6 14:06 标题: Gell-Mann on simplicity and complexity,mind, free will, etc
The Intuition Network, A Thinking Allowed Television Underwriter, presents the following transcript from the series Thinking Allowed, Conversations On the Leading Edge of Knowledge and Discovery, with Dr. Jeffrey Mishlove.
THE SIMPLE AND THE COMPLEX Part I: THE QUANTUM AND THE QUASI-CLASSICAL with MURRAY GELL-MANN, Ph.D.
JEFFREY MISHLOVE, Ph.D.: Hello and welcome. I'm Jeffrey Mishlove. Our topic today is "The Simple and the Complex." With me is Professor Murray Gell-Mann, the recipient of the Nobel Prize in physics in 1969 for his theoretical work which led up to the idea of the quark. Professor Gell-Mann is on the staff of the Santa Fe Institute, a think tank in Santa Fe, New Mexico devoted to the problems of complexity. His distinguished career includes 38 years of work at Cal Tech in Pasadena in the field of theoretical physics, as well as distinguished work in the environment, in foreign policy, and in science policy. Welcome, Professor Gell-Mann.
MURRAY GELL-MANN, Ph.D.: Very nice to be here.
MISHLOVE: It is a pleasure to be with you. In your book The Quark and the Jaguar you are looking at the relationship between the most fundamental and simple known physical units and some of the most complex adaptive systems that exist, from human beings to galaxies, and you find, I believe, similiarities. If we look at a jaguar we can see qualities that are reminiscent or evocative of what we might see if we could see a quark.
GELL-MANN: Well, I would say it a little bit differently from that. What I try to do in the book is to trace the chain of relationships running from elementary particles, fundamental building blocks of matter everywhere in the universe, such as quarks, all the way to complex entities, and in particular complex adaptive system like jaguars. And it's not so much similarities but the relationship between them that I explore. How do you get from elementary particles, each of which is absolutely identical to all the othersof its type anywhere in the universe -- a thing that has no individuality -- to the richly diverse and individual and complex entities that we see around us, and which we are ourselves?
MISHLOVE: One of the issues that you raise has sometimes been called the problem of free will, because, as I understand it, science conventionally doesn't like to think about free will. It resembles the idea of teleology too much, which I think is a forbidden notion in science. You suggest that perhaps the principle of indeterminacy, which occurs at the subatomic level, might be related to the free will which we seem to experience, and I would presume other animals might experience.
GELL-MANN: Well, I mention that. I must say my remarks about free will are not the place where my knowledge and understanding are best revealed. But I don't actually adopt the point of view that our subjective impression of free will, which is a kind of indeterminacy behavior, comes from quantum mechanical indeterminacy. I just mention it as a logical possibility. I say it's much more likely that it stems mainly from other things, and from rather simple things like partial information. If we look at the way the universe behaves, quantum mechanics gives us fundamental, unavoidable indeterminacy, so that alternative histories of the universe can be assigned probability. Sometimes the probabilities are very close to certainties, but they're never really certainties. And often the probabilities are quite distributed. As a result the alternative possible histories of the universe form a kind of branching tree. Jorge Luis Borges in one of his marvelous imaginative short stories imagined someone building a model of the alternative branching histories of the universe in the form of a garden of forking paths. Now, what that means is that there is fundamental indeterminacy from quantum mechanics, but besides that there are other sources of effective indeterminacy. A famous one is the phenomenon of chaos, one that's recently become famous. Of course the word chaos is used in rather a vague sense by a lot of writers, but in physics it means a particular phenomenon, namely that in a nonlinear system the outcome is often indefinitely, arbitrarily sensitive to tiny changes in the initial condition.
MISHLOVE: Perhaps even quantum mechanical fluctuations.
GELL-MANN: Exactly. Perhaps even little quantum mechanical fluctuations could be amplified by the classical phenomenon of chaos, to make very large changes in the output. Since you never know the input exactly, that gives a second source of indeterminacy. The third source has been known for centuries and understood for centuries, and that is simply that in predicting things one always has only partial information.
MISHLOVE: Right. We can never make precise measurements, for example.
GELL-MANN: In my rather naive remarks about free will, which are not the central theme of the book by any means, I mention that probably all these sources of indeterminacy contribute to our subjective impression of free will, and that it's most likely more of the last kind than it is of the first kind. In other words, when human beings act in certain ways and it seems that the acts are not predetermined and therefore there's an element of free will, perhaps more likely we're acting from hidden motives than because we have a quantum mechanical random number generator concealed within us. But the main point I'm trying to make is not my personal speculation about which of these is more important, but simply that I think questions like that can be phrased as scientific questions.
MISHLOVE: Well, that's very important, because for a long time the very notion of consciousness or free will or mind was sort of considered an unscientific area to begin with.
GELL-MANN: Yes, and it still is by many scientists, I think. A friend of mine who lives in this area and is very interested calls it the C word. In fact mind he refers to as the M word, and many scientists don't want to use either of them.
MISHLOVE: And how do you feel about that?
GELL-MANN: Well, I think they're perfectly reasonable words that a scientist can employ. Mind, after all, is the name we give to the phenomenological aspects of what the brain and related organs do, and consciousness is a real phenomenon which we don't understand very well, but it's certainly there, exists in human beings, and probably exists to some extent also in other organisms. One thing it appears to be is the following -- that thinking appears to be a parallel processing operation, with many different strands, but at any moment the spotlight of consciousness seems to be on some particular strand. So it's sequential.
MISHLOVE: Consciousness seems to be sequential.
GELL-MANN: Consciousness seems to be sequential, a spotlight which is sequentially focused on one thing after another in this set of parallel-processing strands --
MISHLOVE: Whereas we know the brain can process lots of things at once.
GELL-MANN: Right. And some of that, I understand from psychologist friends, can be reduced to experimental considerations. When you think you're listening to several conversations at once, they tell me, you may really simply be time sharing -- that is, listening a little bit to this one, a little bit to that one. And since conversation is somewhat redundant, you can fill in a little bit between moments of attention, and therefore apparently follow several things at once, whereas really you're switching back and forth.
MISHLOVE: Like a time-sharing computer.
GELL-MANN: Right. But, they say, if the people are talking nonsense, then you can no longer do that.
MISHLOVE: Aha.
GELL-MANN: Because the nonsense no longer allows interpolation.
MISHLOVE: You can no longer track.
GELL-MANN: Exactly. So presumably it can be reduced in that way to something experimental. But exactly what it is and how it works, and so on, we don't know. But it's reasonable to guess that since complex adaptive systems probably are present on planets scattered throughout the universe, in many, many different parts of the universe, and complex adaptive systems have the wonderful property of exploring new possibilities and trying out new possibilities and spawning new complex adaptive systems, and so on, that most likely in very many places they have produced something like consciousness, whatever it is.
MISHLOVE: You're not one of those who would maintain we are alone in the universe.
GELL-MANN: I certainly don't think so. But of course that's just my personal guess, based on what scientific evidence exists. Our planet doesn't seem to be the result of anything very special. You know, there was a time, just before I started to study physical science, when astronomers thought that systems such as we have here in the solar system required a rare triple collision of stars. At that time one might argue that perhaps planets like this, suitable to the evolution of complex adaptive systems, were very rare. But then shortly after that astronomical theorists reverted to the old idea of the condensation of planets from dust, just like the central star. When you have gravitational condensations the central star, in our case the sun, condenses, and so do the planets. That's not a difficult process, and presumably happens all the time. Astronomers are just beginning to get observational evidence now of planets elsewhere.
MISHLOVE: Yes.
GELL-MANN: But of course they're not near stars like ours, and they presumably aren't relevant to this question of the evolution of complex adaptive systems.
MISHLOVE: Well, we may not have adequate instruments.
GELL-MANN: Exactly. That's the reason. Planets are too dim to be detected with existing equipment, far away, except in these very special circumstances where they're seen by their gravitational effect.
MISHLOVE: In principle you're saying they ought to be there anyway.
GELL-MANN: It seems very likely, theoretically.
MISHLOVE: And the same kind of process of complexification that led to the development of life and civilization as we know it on this planet is likely to occur on other planets that have similar conditions.
GELL-MANN: That's what I would conclude, but of course we don't know for sure. That's certainly what I would conclude.
MISHLOVE: I'd like to go back to the discussion of quantum physics, because certainly that's one of your fields of great expertise. In fact I know you are involved in developing what you call the modern interpretation of quantum mechanics, which is important for people, because so many of us hear over and over again about the mysteries of quantum mechanics, but nobody seems to be able to really quite interpret it.
GELL-MANN: Well, there is an interpretation, developed in the 1920s when quantum mechanics was new, that is generally taught. It's sometimes called the Copenhagen interpretation, after Niels Bohr.
MISHLOVE: It's a hidden variable --
GELL-MANN: No -- not hidden variable. And that interpretation, my friends and I believe, while not wrong, is approximate and special. It refers to a situation in which some phenomenon is being studied which is reproducible, can be produced over and over again in a laboratory, it's being studied by a scientist with a piece of apparatus who is outside the system, and then quantum mechanics gives probabilities for the various outcomes of this situation, reproducible situation, and those are essentially the same as the proportions of the different outcomes over a long sequence of repetitions. But that's very special, and what we who are developing, in different parts of the world, the modern interpretation of quantum mechanics want to see, is an interpretation that allows quantum mechanics to be applied to the whole universe -- quantum cosmology, it's called. And in that case, obviously, you can't have an observer outside; you can't have results that are reproducible, and so on. Also it would be nice for quantum mechanics to apply to situations where there is a lot of complexity and a lot of individuality. It must apply in those situations. So the old Copenhagen interpretation needs to be generalized, needs to be replaced by something that can be used for the whole universe, and can be used also in cases where there is plenty of individuality and history. And so those of us who are doing it are concentrating on histories, histories of the entire universe -- alternative histories forming a branching tree, with probabilities at each branching.
MISHLOVE: Now, let me just interject for a moment, because I understand the key issue here is whether these alternative branching universes exist ontologically, meaning really exist, or whether they exist sort of in theory only.
GELL-MANN: Well, I don't like to get involved in these philosophical issues very much. I think there's been a certain amount of confusion as a result of that sort of discussion. One of the pioneers of this modern approach was Hugh Everett III, who was a graduate student at Princeton in the late 1950s.
MISHLOVE: Who worked with John Wheeler.
GELL-MANN: Worked with John Wheeler, and afterwards went to the Pentagon, where he was a member of the weapon systems evaluation group, and I believed stayed with that group until he died rather young, unfortunately. Hugh Everett's work has been described by many people in terms of many worlds, the idea being that every one of the various alternative histories, branching histories, is assigned some sort of reality. And that has confused a number of people, and led some scientists, actually, to reject this kind of approach to quantum mechanics.
MISHLOVE: For that very reason.
GELL-MANN: Yes, it's confused them. For instance, one very distinguished physicist, student of quantum mechanics, has said that he doesn't like any such approach, because if it were right, then you should be encouraged to play Russian roulette for high stakes, since in one of the equally real worlds you would win. Well, it's kind of silly, because we experience, of course, at every branching only one branch, and to talk about the others being real is confusing.
MISHLOVE: But these confusions and paradoxes seem to come up everywhere in quantum physics.
GELL-MANN: Well, I don't think it's necessary. I think one can try to reduce the amount of confusion, and also to reduce the amount of nonsense that's talked about quantum mechanics. I have a chapter in my book called "Quantum Mechanics and Flapdoodle," because people have talked a great deal of nonsense about quantum mechanics.
MISHLOVE: But these people, as I understand it, are some of the great physicists. You mentioned Niels Bohr.
GELL-MANN: I didn't say that Niels Bohr had said anything foolish. I said that his Copenhagen interpretation may now be regarded as partial and approximate, but not wrong.
MISHLOVE: I understand that.
GELL-MANN: And not foolish, either.
MISHLOVE: I certainly didn't mean to imply that. I think we would agree that he's one of the founders of quantum physics, and he's universally honored. But didn't he say that if you look at quantum physics and you don't get dizzy by it, you don't understand it?
GELL-MANN: Let's see if I can translate the sentence carefully. If someone says that he can think or talk about quantum physics without becoming dizzy, that shows only that he has not understood anything whatever about it.
MISHLOVE: Now, I understand that your approach is to sort of reduce that situation.
GELL-MANN: Yes. That's what we're trying to do.
MISHLOVE: That must make every leader -- I'm trying to think of the right word, because you're certainly in the forefront of your discipline -- all of the founders of the field must be very uncomfortable with that.
GELL-MANN: Well, I don't think people are so uncomfortable, actually. It's not the kind of scientific work that brings a great deal of honor, because at first people say that it's silly or wrong or unnecessary, and if finally you get something straight in this sort of work, then people say they knew it all the time. Nevertheless, we do it, because we think it's important to try to straighten out these ideas, and in particular to see how the rich, complex world that we see around us, which is quasi-classical, emerges from quantum mechanics. And back in the 1920s physicists thought they had more or less licked that problem, but we believe that it requires a lot more work, really to understand the relationship.
MISHLOVE: You talked about chaos theory earlier, and I thought that was very striking, because in my understanding many of the people who talk about the relationship between the quantum world and the classical world, the world of our sensory experience, say, "Well, there really is no relationship. These quantum uncertainties and fluctuations have no influence or effect in the larger world." But to chaos theory there seems to be a mechanism.
GELL-MANN: Well, that's not the way most chaos theorists look at it, actually. But I think it's a pretty good description of some interactions between quantum fluctuations and chaos. The chaos can act as a magnifier of quantum fluctuations so that they can produce sizable effects in the world around us. But we know that that can happen often. In fact any experiment that measures a quantum effect is one in which the quantum effect is aligned with the behavior of some heavy, macroscopic object; that's how we measure it.
MISHLOVE: The measuring equipment.
GELL-MANN: Right, and that piece of measuring equipment, that heavy, macroscopic object, is correlated with the quantum fluctation. If the quantum event goes one way, the apparatus shows one result. If the quantum event goes another way, the apparatus shows a different result. So it's very familiar to have large-scale events around us controlled by probabilistic quantum alternatives. It's not unusual. And when Schroedinger wrote about his hypothetical cat -- a cat that was poisoned if a quantum event went one way, and was not poisoned if the quantum event went another way -- he was talking about the same kind of thing. Likewise, in principle, although it's not very nice, you could arrange for a city to be blown up by thermonuclear weapons if a radioactive disintegration were to proceed so that an alpha particle came out to the right, whereas if the alpha particle came out to the left the city would not be destroyed. Since the two are equally probable, and there's absolutely no way of predicting which way it will go, it's a clear case of a quantum probabilistic event being coupled to some macroscopic thing.
MISHLOVE: The paradox here, if I understand it, is that in quantum theory the probabilistic event is sort of viewed as a probability function, or sometimes I've even heard the term a probability cloud. It's as if both true and false are occurring at the same time.
GELL-MANN: Yes, and that's what I think is very misleading, and my colleagues think is very misleading. In the Schroedinger cat story, for example, the part I told is very reasonable and simply illustrates that a probabilistic quantum event can be coupled to some classical change in the heavy, macroscopic objects around us. That's fine. But the other thing people say is, "Well, suppose the cat is in a box, and the quantum event occurs, but you don't know which way it went, and the cat is dead if it went one way and alive if it went the other, and so until you open the box and see, well, the cat is in some sort of funny quantum-mechanical, coherent mixture of being dead and being alive. That's very strange and paradoxical and weird, and so on." It isn't really true.
MISHLOVE: That was the point Schroedinger tried to make.
GELL-MANN: Well, I don't know exactly what he was after, but it's a point that people have belabored after Schroedinger, and I think it's not really a very good way to look at it, because a live cat certainly is in interaction with its environment. It's not isolated.
MISHLOVE: That's right.
GELL-MANN: Even the dead cat is in interaction with its environment. It's decaying, emanating various chemicals. The live cat of course is breathing and in contact with its environment. Even if the cat is in a box, the box is in contact with the environment. It's being hit by photons from elsewhere in the universe. It's radiating a certain number of photons because it's not at absolute zero; if it were at absolute zero it would certainly not contain a live cat. And so on and so forth. Therefore, whatever it is that we're talking about, it's in interaction with other things, and those other things are being averaged over and integrated over and not seen. And under those conditions, the two situations, alive and dead, decohere, as we say. There is no interference between them; they are simply alternatives -- just like the alternatives at the race track when either one horse wins or another horse wins; there's nothing mysterious or peculiar about it. And when you open the box it's no different from the experience that you may actually have of going to the airport and accepting a cat box and not knowing whether the poor animal is alive or dead until you open the box. It's exactly the same. The two situations are on different branches of history. They are not coherent with each other because of the interaction with the rest of the world that's averaged over.
MISHLOVE: This is very deep material. I can't claim to understand everything that you've said, Dr. Gell-Mann, but it seems as if you're saying the environment itself is affecting the situation.
GELL-MANN: Well, that's how the alternatives become decoherent with one another.
MISHLOVE: What does decoherent mean? We only have a minute now.
GELL-MANN: It means that you can assign a probability to each alternative, and you don't have interference terms that prevent you from assigning those probabilities. In other words, it means that the situation is no different from that at the race track.
MISHLOVE: OK, and a quantum system is coherent, which means you can't separate it out.
GELL-MANN: If you treat a system in too much detail -- too fine-grained a history -- then you will end up with these interference problems, and you cannot assign probabilities to such fine-grained histories, and you mustn't do so. You cannot discuss them as alternatives.
MISHLOVE: I suppose in summary one might say that the fine-grained, quantum world is really very, very different from the coarse world.
GELL-MANN: And the coarse world is the only one that can be dealt with, and the only one that is dealt with. The other one is just in the background.
MISHLOVE: Professor Murray Gell-Mann, it's been a pleasure getting into the intricacies of the relationship between the very small and the very simple, which turns out to be enormously complex, and the very complex, which somehow seems to be simpler. It's been a pleasure discussing this with you, and I hope for those of our listeners and viewers who are intrigued by this discussion, you will stay tuned for Part 2 of our program on "The Simple and the Complex." Thank you so much for being with me.
The Intuition Network, A Thinking Allowed Television Underwriter, presents the following transcript from the series Thinking Allowed, Conversations On the Leading Edge of Knowledge and Discovery, with Dr. Jeffrey Mishlove.
THE SIMPLE AND THE COMPLEX Part II: THE SCIENCE OF COMPLEXITY with MURRAY GELL-MANN, Ph.D.
JEFFREY MISHLOVE, Ph.D.: Hello and welcome. I'm Jeffrey Mishlove. Today we're continuing our discussion on "The Simple and the Complex" with Professor Murray Gell-Mann. Professor Gell-Mann received the Nobel Prize in 1969 for his theoretical work which led up to the idea of the quark. He is on the faculty of the Santa Fe Institute in Santa Fe, New Mexico, where he is also the founding chairman. In addition he has been a professor of physics for 38 years at Cal Tech in Pasadena, California. He is the author of a book called The Quark and the Jaguar. Welcome back again, Professor Gell-Mann.
MURRAY GELL-MANN, Ph.D.: Very nice to be here, Jeffrey.
MISHLOVE: Nice to be with you. We really need to talk more about complexity itself. It's a term which is becoming very courant, and I don't think people always understand what is meant by complexity.
GELL-MANN: Well, it probably takes several definitions to cover the various meanings that we attribute to complexity and simplicity, but we can try to examine a couple and see the virtues and flaws in them. Something that we might call crude complexity would be the length of a message describing the system, but then we have to qualify that.
MISHLOVE: You mean the longer it takes me to describe some system, the more complex it would be?
GELL-MANN: Something like that. But then we have to put in a lot of qualifications.
MISHLOVE: Like the use of language.
GELL-MANN: For instance, right. It depends somewhat on the language; We mustn't allow you to invent a special pet name for the thing you're talking about. A system, no matter how complex, could be called Sam or Judy, and then the length of the description of course wouldn't mean anything. So it should be in a language previously agreed upon. And you shouldn't be able to point to it either, because that's also cheating. So it should be described to a distant correspondent, or something like that. And of course it also depends on the shared knowledge and understanding of the world, how long the description has to be. Furthermore it depends on the level of detail at which the system is being described. Suppose you're talking about a natural community, like a forest. Ecological scientists have argued for a long time about whether up to a point it's the simpler or the more complex forest that's more robust with respect to natural or artificial changes in the environment.
MISHLOVE: A more complex forest might have more species in it.
GELL-MANN: Well, exactly. If you ask, "What do you mean by a more complex forest?" for one thing it would have more species. A tropical forest might have several hundred species of trees, whereas the kind of coniferous forest you see from a ski lift in North America might have only five or six. The number of mammals would be much smaller; the number of insects would be much smaller, and so on, so you would have a simpler forest. But what do you count when you measure the complexity of a forest? Do you count just mammals and trees and flowering plants? What about microorganisms? And of course ecologists would count the interactions among species -- predator-prey, pollinator-pollinated, host-parasite, and so on. Do you count very obscure interactions? So it depends on the coarse graining, on the level of detail at which the system is being described.
MISHLOVE: I suppose if one attempted a quantum physical description they'd all be equal.
GELL-MANN: In any case, clearly, complexity is not an intrinsic property of the thing being described, but depends also on who or what is doing the describing.
MISHLOVE: Yes.
GELL-MANN: Now, crude complexity, with all those qualifications, would be the length of a message describing the system. It doesn't really correspond to what we normally mean by complexity, for the following reason. Suppose we compare the works of Shakespeare with a passage of equal length typed by the proverbial monkeys, supposed to be typing at random and producing mostly gibberish. The work of the monkeys would be largely random, and would have therefore a longer description, because the work of Shakespeare could be compressed using some of the regularities of language, the regularities of images, and so on and so forth.
MISHLOVE: Some of the compression techniques that are used all the time in computers could apply to Shakespeare, but not to the monkeys.
GELL-MANN: Exactly. And therefore by the definition of crude complexity the work of the monkeys would be more complex, which is certainly not what we usually mean.
MISHLOVE: That's right.
GELL-MANN: So I would use rather what I call effective complexity, which is something like the length of the message describing the regularities of the system. So whoever or whatever is doing the describing picks out perceived regularities and then compresses the description of those regularities into a brief message or model or schema, and the length of that is the effective complexity of the thing being described. Now suppose we compare the two quantities. When you have complete order, then both of them are very small; the system is certainly simple, if it's completely orderly. For instance, a string of ones -- 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 -- or a crystal at absolute zero temperature, something like that, completely orderly, would have essentially no crude complexity, and essentially no effective complexity. At the other end, let's look at a sequence that's completely random, or a gas at very, very high temperature. That has very high crude complexity, but again almost no effective complexity. So effective complexity can be large in the region in between order and disorder.
MISHLOVE: This seems to be very crucial, because it has something to do, I'm sure, with living systems. We live in this middle region ourselves.
GELL-MANN: Absolutely right. Complex adaptive systems flourish in that middle region, and cannot exist at the ends. For example, life can't exist in a crystal at absolute zero, and life doesn't exist in the middle of the sun either.
MISLOVE: So it's something about our intelligence as well. That use of effective complexity is often the way our minds work.
GELL: Exactly so. That perception of regularities, and then compression of those regularities into a brief schema or model or theory, that's what characterizes what I call complex adaptive systems, including living things. A complex adaptive system receives a stream of data, and it picks out regularities in that data stream, perceived regularities, compresses their description into a very brief message of some kind which I call a schema, and then it uses that schema for description or prediction, or for prescription of behavior for itself. And that description or prediction or behavior has consequences in the real world, and those consequences feed back to competition among alternative schemata. The schema, while it's robust, can be transformed into another schema, or replaced by another schema, and the competition among the schemata is affected by the real-world consequences of the prediction or the description or the behavior. You might say that there's a feedback loop in which effects in the real world feed back to influence the competition among schemata. For example, science, the scientific enterprise, is a wonderful example of a complex adaptive system.
MISHLOVE: Of a complex adaptive system.
GELL-MANN: The scientific enterprise -- the schemata or theories. The scientific enterprise generates theories which are very brief, concise descriptions of the regularities of phenomena. Those theories then can be modified or replaced by other theories, but the theories have predictive value, and they predict behavior in the real world, behavior of nature. They predict how nature works, and if observation confirms the results of the theory, that feeds back to promote or establish the theory. If observation -- experiment, for example -- shows that the predictions of the theory are wrong, that has a negative effect on the survival of the theory. Another example would be biological evolution, in which the schemata are genotypes -- DNA of organisms. There the genome, acting together with a whole lot of events in development and early life of the organism, lead up to an adult organism. The adult organism is codetermined by the genome, the DNA, and by all the events occurring in development and in early life. And then in adulthood there's a test, namely, sexual selection, if you're dealing with a sexual species like ours -- sexual selection, procreation, the survival of the offspring. And those determine whether the genotype, or something like the genotype, is passed on.
MISHLOVE: You've used the term complex adaptive systems to describe the whole of science and also the whole of biology.
GELL-MANN: The whole of biological evolution.
MISHLOVE: And at the same time I see it could apply equally well to a single organism, or perhaps even to a robot.
GELL-MANN: It could apply to a robot if the robot is adaptive, if the robot has the characteristics we just described. And computer systems have already been designed that act as complex adaptive systems. It can also apply to a part of an organism. For example, the immune system in mammals, including human beings, is a complex adaptive system. It acts very much like biological evolution, but on a much, much shorter time scale. Instead of hundreds of thousands of years, or millions of years for a major adaptation, it takes hours or days, and it has to in order to cope with invaders of the body.
MISHLOVE: What I'm getting from this discussion is the notion of emergence -- that at a certain level of complexity these systems emerge.
GELL-MANN: Complex adaptive systems can evolve, and when they do they explore, they create and fill niches, they try things, and they have a great tendency in the course of that to spawn other complex adaptive systems -- the way biological evolution has given rise to organisms and to ecological communities, but also to parts of organisms like the immune system, and also to learning and thinking. And then with human language it's given rise to sophisticated human enterprises like the scientific enterprise, like markets, societies, and then to the invention of computers which can be designed or programmed to be themselves complex adaptive systems -- for instance, to evolve strategies for playing games, strategies that no person ever thought of.
MISHLOVE: In Part 1 of our discussion you referred to one of the goals of quantum mechanics would be to have a theory of the whole universe, not just a special theory.
GELL-MANN: Well, those of us who are constructing what I call the modern interpretation of quantum mechanics would like it to apply to the whole universe.
MISHLOVE: Would you say the whole universe, then, is a complex adaptive system?
GELL-MANN: One or two people speculate about that, but I don't. I haven't dealt with that speculation myself. As far as I'm concerned, there's no evidence of that, and there's no evidence that galaxies or stars or planets or rocks are complex adaptive systems. They all undergo evolution, but it's not, as far as we know, the kind of evolution that we were discussing, where the experience of the system is separated into perceived regularities and perceived randomness, and then the perceived regularities are compressed into a brief message or schema, and then the schema is one of many alternative schemata related by mutation and variation, and then the competition among the schemata is affected by their consequences in the real world. We don't have evidence that galaxies do that, or stars or planets or rocks, and I don't think we have evidence that the universe does it either.
MISHLOVE: Now, in Part 1 of our discussion we refer to the M word and to the C word -- mind and consciousness. I think what you're saying when you refer to these schemata and the way they interact, it seems like perhaps a more operational discussion of what might otherwise be called consciousness.
GELL-MANN: No, not necessarily. All of these things that we were just discussing can exist even when there is minimal consciousness.
MISHLOVE: As that robot.
GELL-MANN: A robot, or organisms that are less sophisticated than human beings, much less sophisticated than human beings. You probably wouldn't ascribe a great deal of consciousness to a paramecium or a worm or something, but they are complex adaptive systems.
MISHLOVE: You're willing to consider that there might be some consciousness at that level.
GELL-MANN: There might, but probably -- I mean, we haven't defined it very well, but however we define it, there probably isn't very much. However, in many parts of the universe, as we were saying, complex adaptive systems presumably have evolved and will evolve, and I would guess that in the course of poking around, exploring possibilities, spawning new systems that are complex adaptive systems, and so on, that they give rise to consciousness here and there -- that it's not a unique phenomenon here on earth. Presumably it exists in very many places, and in very many forms, which it would be fascinating to know about.
MISHLOVE: I gather that you're suggesting then that consciousness emerges at a certain level of complexity, much the way chemistry emerges, or biology emerges.
GELL-MANN: That's what I would guess.
MISHLOVE: Rather than that it's, say, fundamental to the elementary level of physics that you've explored all your life.
GELL-MANN: There is no evidence of that whatsoever, as far as I know.
MISHLOVE: Well, there is the theory, I think put forth by Wigner and von Neumann, that consciousness is somehow involved in -- I'm not a physicist, but I believe they would say the collapse of the wave function.
GELL-MANN: Yes, but in the modern interpretation of quantum mechanics, one tries to describe that process differently, and it becomes, I think, much less mystical, much more comprehensible, and generally more satisfactory. Namely, as we were discussing in our earlier incarnation, the alternative outcomes of a quantum event have to be described in sufficiently coarse-grained fashion that they decohere from one another, they don't interfere. Only those non-interfering, coarse-grained histories can be assigned probabilities that have any meaning in quantum mechanics. That means that if you can divide the world into a system and its environment -- which you can't always do, but let's suppose for simplicity you can -- that the interaction with the environment, which is then averaged over, destroys the phase relations among the different outcomes. In that case the outcomes are just like very familiar outcomes -- outcomes of a horse race, or outcomes of any other probabilistic event. And in that case you don't have to worry about this -- this so-called collapse of the wave function, when the alternatives are decoherent, is no different from the collapse that occurs when you're at the races and in the first race there are a lot of horses with different probabilities of winning, but at the end of the race one of them has won, and do you say the wave function has collapsed to the victory of that one horse, and it's very mysterious and paradoxical? No, you say there were various possibilities, one of them happened, and the rest of them no longer have anything but zero probability because they didn't happen. That's all it is. It's no more complicated than that.
MISHLOVE: In other words, you're saying, if I understand you, that the quantum world is no more complicated than a horse race.
GELL-MANN: Once it is coarse-grained to the point where the alternatives decohere, and that's the only level at which it can be utilized. Only at that level can it be utilized. Once that's done, then it's no different from a horse race, and there's nothing peculiar about it anymore. That's, I think, quite a useful observation that those of us who are constructing the modern interpretation of quantum mechanics make.
MISHLOVE: And if this interpretation succeeds, then you will in effect have proved Niels Bohr wrong when he said you have to be dizzy if you contemplate quantum mechanics.
GELL-MANN: I'm afraid there is still some dizziness left. We haven't gotten rid of it all yet, but we try. We would like to get rid of it. We would like to demystify quantum mechanics as much as possible. Now, there is still the point that if quantum mechanics gives only probabilities, that's useful only if there is something around to bet on those probabilities. So it is still true that a complex adaptive system is an interesting system, because it is the thing that can utilize the quantum mechanical probability. So to have a complex adaptive system around, watching what happens, observing that this happened and not that, is still interesting; but it doesn't play the central role that it played in the standard Copenhagen interpretation.
MISHLOVE: Earlier you said that whether you choose to look at the system from a fine-grained perspective or a coarse-grained perspective, that's always a decision of the observer.
GELL-MANN: Not necessarily a decision, no. I think to talk about it as a decision is not a very good way. It's perhaps a more old-fashioned way to talk. I would say simply that there exist coarse grainings, and that those coarse grainings can lead to a quasi-classical world.
MISHLOVE: Quasi-classical.
GELL-MANN: Quasi-classical, because there's always the branching, the quantum-mechanical branching; but a quasi-classical world which obeys roughly classical laws, subject to very frequent small fluctuations and occasional very large branchings. And this quasi-classical world, then, is what is actually dealt with, and in the quasi-classical world there are then no more paradoxes, no more difficulties. But complex adaptive systems then evolve to exploit such a quasi-classical world, and they need the regularity that comes from the quasi-classicality in order to find regularities -- in order to behave like complex adaptive systems, in order to find patterns, they need the regularity associated with the quasi-classical domain, as we call it. And of course there's always plenty of indeterminacy to supply the disorder.
MISHLOVE: Now, in the branching that occurs in the many-worlds interpretation, you've speculated, I think, referring to some of the Russian science fiction writers, about the idea of gremlin universes that interact with each other.
GELL-MANN: Something like that. Let's try and get it clear. The idea there is that such a quasi-classical domain as we were talking about is based on simple, familiar variables, in practice. The one that we have evolved to exploit, everything that we know about has evolved to exploit, is a particular quasi-classical domain involving electric charge densities and momentum densities and energy densities and things of that kind, variables like that, taken over small volumes which are large enough for certain criteria to apply, and small enough for other criteria to apply. Those are sometimes called hydrodynamic variables. They're very familiar variables, things like the amount of energy contained in a little volume, things of that kind. You follow those through time at certain intervals, frequent intervals of time. Those are your coarse-grained histories. We have evolved to exploit that kind of coarse-grained history, that kind of quasi-classical domain. Then we raise, not completely with tongue in cheek, the question of whether there might be other, very different quasi-classical domains with which we are not familiar, and whether complex adaptive systems might then evolve to exploit those. We don't know if there is such a thing. We don't know if there are these alternative quasi-classical domains, very different from the one we are familiar with, and so we don't know whether complex adaptive systems evolve to exploit it. But we just ask whether that might be possible. If so, what would be the relationship between the complex adaptive systems in one quasi-classical domain, and those in another quasi-classical domain skew, so to speak, to the first one?
MISHLOVE: Right.
GELL-MANN: It's a kind of weird question, but we ask it. And a Russian theorist told us that he believes that in science fiction such domains would be referred to as goblin domains, but I have no idea whether that's true. It's something we were told.
MISHLOVE: It's something one would find in mythology as well, not just science fiction.
GELL-MANN: Well, I don't know, but anyway it's amusing. Jim Hartle, my collaborator, and I -- Jim Hartle is a very distinguished quantum cosmologist; in fact he and Stephen Hawking founded the field of quantum cosmology with their famous paper, "The Wave Function of the Universe" -- Jim and I worked together on these things for a number of years, seven or eight years. And he and I speculate about whether there might be these additional quasi-classical domains, skew to ours, and maybe complex adaptive systems in each, and if so, how they would relate to each other. And to one system the other would be accessible, perhaps by some shared variables, or if there are no shared variables, they might be accessible only by making a quantum mechanical calculation or a quantum mechanical measurement. In other words, one kind of thing would appreciate what the other kind of thing can see and work with only by a complex calculation or measurement. You might argue that that's something like the relation between men and women.
MISHLOVE: Like ships passing in the night. Sometimes we can make a quantum mechanical measurement and get together.
GELL-MANN: Anyway, that's not the most serious part of our work.
MISHLOVE: Indeed, but I guess it does suggest that even yet quantum mechanics still has a few mysteries.
GELL-MANN: It has some. Certainly it has some mysteries.
MISHLOVE: Professor Murray Gell-Mann, it's been such a pleasure discussing the issues of simplicity and complexity with you. At the end of our first program I was sort of feeling that the simple is really complex, and the complex is really quite simple. But I think you've really clarified this time how simple the simple can be, and how complex the complex can be. So we've covered the entire spectrum.
GELL-MANN: Thank you very much. It's been a pleasure.
MISHLOVE: Thanks so much for being with me.
- END -作者: liver411 时间: 2010-5-6 14:08
Average people read smart stuff; sub-average read stupid stuff作者: 走遍四方 时间: 2010-5-6 14:17
