演讲视频链接:Murray Gell-Mann: Beauty, truth and physics


Thank you for putting up these pictures of my colleagues over here. (Laughter) We’ll be talking about them. Now, I’m going try an experiment. I don’t do experiments, normally. I’m a theorist. But I’m going see what happens if I press this button. Sure enough. OK.



I used to work in this field of elementary particles. What happens to matter if you chop it up very fine? What is it made of? And the laws of these particles are valid throughout the universe, and they’re very much connected with the history of the universe.



We know a lot about four forces. There must be a lot more, but those are at very, very small distances,and we haven’t really interacted with them very much yet. The main thing I want to talk about is this: that we have this remarkable experience in this field of fundamental physics that beauty is a very successful criterion for choosing the right theory.



And why on earth could that be so? Well, here’s an example from my own experience. It’s fairly dramatic, actually, to have this happen. Three or four of us, in 1957, put forward a partially complete theory of one of these forces, this weak force. And it was in disagreement with seven — seven, count them, seven experiments. Experiments were all wrong. And we published before knowing that, because we figured it was so beautiful, it’s gotta be right! The experiments had to be wrong, and they were. Now our friend over there, Albert Einstein, used to pay very little attention when people said, “You know, there’s a man with an experiment that seems to disagree with special relativity. DC Miller. What about that?” And he would say, “Aw, that’ll go away.” (Laughter)

但原因何在呢?先让我讲一个我自己的经历吧。它非常有戏剧性。在1957年,我们三四位同僚一起提出了一个还算完整的弱相互作用理论。这理论和当时7个实验结果都不吻合,足足七个!大家想想看。后来知道那些实验都是错的。虽然我们当时并不知道后来知道那些实验都是错的,我们还是出版了我们的理论。因为我们认为这个理论太美了,它必定是对的。那些那些实验必须是错的,它们的确也是错的。我们的朋友爱因斯坦,他在那儿,听到别人说D.C.米勒的实验结果与他的狭义相对论不符时,他完全不放在心上,他会说:“哦,那实验肯定是错的!” (众笑)


Now, why does stuff like that work? That’s the question. Now, yeah, what do we mean by beautiful? That’s one thing. I’ll try to make that clear — partially clear. Why should it work, and is this something to do with human beings? I’ll let you in on the answer to the last one that I offer, and that is, it has nothing to do with human beings.



Somewhere in some other planet, orbiting some very distant star, maybe in a another galaxy, there could well be entities that are at least as intelligent as we are, and are interested in science. It’s not impossible; I think there probably are lots. Very likely, none is close enough to interact with us. But they could be out there, very easily. And suppose they have, you know, very different sensory apparatus, and so on. They have seven tentacles, and they have 14 little funny-looking compound eyes, and a brain shaped like a pretzel. Would they really have different laws? There are lots of people who believe that, and I think it is utter baloney. I think there are laws out there, and we of course don’t understand them at any given time very well — but we try. And we try to get closer and closer. And someday, we may actually figure out the fundamental unified theory of the particles and forces, what I call the “fundamental law.” We may not even be terribly far from it. But even if we don’t run across it in our lifetimes, we can still think there is one out there, and we’re just trying to get closer and closer to it.



I think that’s the main point to be made. We express these things mathematically. And when the mathematics is very simple — when in terms of some mathematical notation, you can write the theory in a very brief space, without a lot of complication — that’s essentially what we mean by beauty or elegance.

PPT上是我接下来要阐述的观点。(A theory appears to be beautiful or elegant, or simple, if you prefer,when it can be expressed concisely in terms of mathematics we already have.)我们用数学描述理论,而数学是简明的,就一些数学符号而言,你可以把一个理论简洁的表示出来,一点也不复杂,这种理论就是美丽和优雅的。


Here’s what I was saying about the laws. They’re really there. Newton certainly believed that. And he said, here, “It is the business of natural philosophy to find out those laws.”



The basic law, let’s say — here’s an assumption. The assumption is that the basic law really takes the form of a unified theory of all the particles. Now, some people call that a theory of everything. That’s wrong because the theory is quantum mechanical. And I won’t go into a lot of stuff about quantum mechanics and what it’s like, and so on. You’ve heard a lot of wrong things about it anyway. (Laughter) There are even movies about it with a lot of wrong stuff. But the main thing here is that it predicts probabilities. Now, sometimes those probabilities are near certainties. And in a lot of familiar cases, they of course are. But other times they’re not, and you have only probabilities for different outcomes. So what that means is that the history of the universe is not determined just by the fundamental law. It’s the fundamental law and this incredibly long series of accidents, or chance outcomes, that are there in addition. And the fundamental theory doesn’t include those chance outcomes; they are in addition. So it’s not a theory of everything. And in fact, a huge amount of the information in the universe around us comes from those accidents, and not just from the fundamental laws.

这里有一个关于基本定律的假设:基本定律是关于所有粒子的一种统一理论。有些人称其为“万有理论”。那不对,因为那个理论是关于量子力学的。我不会讲一些关于量子力学的知识,比如什么是量子力学之类。你们一定听说过很多关于量子力学的错误说法。(众笑)甚至还有几部与之相关的电影,里面也是错误百出。但最主要的是量子力学能预测可能性。有时它的预测是接近正确的,在很多常见的情况下,他们一定如此,但在其他时候则未必。你能获知的只是各种可能性而已。因此,这说明决定宇宙的历史不仅仅有基本定律。它们应包括基本定律和不确定性, 还有偶发事件。而基本定律可不包括这些结果,他们是额外附加的。所以基本定律不是万有理论。事实上,我们周围宇宙中大量的信息从这些不确定性而来,而并非来自基本定律。


Now, it’s often said that getting closer and closer to the fundamental laws by examining phenomena at low energies, and then higher energies, and then higher energies, or short distances, and then shorter distances, and then still shorter distances, and so on, is like peeling the skin of an onion. And we keep doing that, and build more powerful machines, accelerators for particles. We look deeper and deeper into the structure of particles, and in that way we get probably closer and closer to this fundamental law.



Now, what happens is that as we do that, as we peel these skins of the onion, and we get closer and closer to the underlying law, we see that each skin has something in common with the previous one, and with the next one. We write them out mathematically, and we see they use very similar mathematics.They require very similar mathematics. That is absolutely remarkable, and that is a central feature of what I’m trying to say today. Newton called it — that’s Newton, by the way — that one. This one is Albert Einstein. Hi, Al! And anyway, he said, “nature conformable to herself” — personifying nature as a female. And so what happens is that the new phenomena, the new skins, the inner skins of the slightly smaller skins of the onion that we get to, resemble the slightly larger ones. And the kind of mathematics that we had for the previous skin is almost the same as what we need for the next skin. And that’s why the equations look so simple. Because they use mathematics we already have.

当我们剥下这些洋葱皮,从而接近下一层的定律时,我们发现每一层洋葱皮和它前一层 、后一层之间都存在共性。当我们用数学把它们表示出来时,我们发现他们使用的数学是相似的。他们需要十分相似的数学。那绝对是惊人的发现,那也正是我今天最想说的。牛顿称它为……,顺便说一下那就是牛顿,这是爱因斯坦。你好,小爱。无论怎样,他说:“大自然是自适应的。”并赋予自然以女性的形象。这个新现象,新的”洋葱皮”,洋葱内小的那层,当我们接近它时,它就像大的那些层。关于之前一层“洋葱皮”的数学机制和后面的一层几乎一样。这就是为什么这些方程看起来如此简单。因为它们使用的数学是我们已经熟知的。


A trivial example is this: Newton found the law of gravity, which goes like one over the square of the distance between the things gravitated. Coulomb, in France, found the same law for electric charges.Here’s an example of this similarity. You look at gravity, you see a certain law. Then you look at electricity. Sure enough. The same rule. It’s a very simple example. There are lots of more sophisticated examples. Symmetry is very important in this discussion. You know what it means. A circle, for example,is symmetric under rotations about the center of the circle. You rotate around the center of the circle, the circle remains unchanged. You take a sphere, in three dimensions, you rotate around the center of the sphere, and all those rotations leave the sphere alone. They are symmetries of the sphere. So we say, in general, that there’s a symmetry under certain operations if those operations leave the phenomenon, or its description, unchanged.

这有一个小例子:牛顿发现了万有引力定律。万有引力的大小与物体间距离的平方成正比。法国的库伦发现电荷间的作用也遵循同样的规律。这就是相似性的一个例子。当你看万有引力时,你会看到一定的定律。而当你看电荷间的作用时,你将会发现相同的规律。这是一个非常简单的例子。还有更多复杂的例子。对称性在这里是非常重要的。你们对此一定很了解。举个例子来说,一个圆绕中心旋转是对称的。你绕圆心旋转,圆会保持不变。当你绕着一个三维的球旋转时 所有这些旋转都不会使球发生变化,它们就是球的对称性。所以大体上来说,如果一个物体或一种现象经过某种操作后能够保持不变,那么它就具有对称性。


Maxwell’s equations are of course symmetrical under rotations of all of space. Doesn’t matter if we turn the whole of space around by some angle, it doesn’t leave the — doesn’t change the phenomenon of electricity or magnetism. There’s a new notation in the 19th century that expressed this, and if you use that notation, the equations get a lot simpler. Then Einstein, with his special theory of relativity, looked at a whole set of symmetries of Maxwell’s equations, which are called special relativity. And those symmetries, then, make the equations even shorter, and even prettier, therefore.




Let’s look. You don’t have to know what these things mean, doesn’t make any difference. But you can just look at the form. (Laughter) You can look at the form. You see above, at the top, a long list of equations with three components for the three directions of space: x, y and z. Then, using vector analysis, you use rotational symmetry, and you get this next set. Then you use the symmetry of special relativity and you get an even simpler set down here, showing that symmetry exhibits better and better.The more and more symmetry you have, the better you exhibit the simplicity and elegance of the theory.



The last two, the first equation says that electric charges and currents give rise to all the electric and magnetic fields. The next — second — equation says that there is no magnetism other than that. The only magnetism comes from electric charges and currents. Someday we may find some slight hole in that argument. But for the moment, that’s the case.



Now, here is a very exciting development that many people have not heard of. They should have heard of it, but it’s a little tricky to explain in technical detail, so I won’t do it. I’ll just mention it. (Laughter) But Chen Ning Yang, called by us “Frank” Yang — (Laughter) — and Bob Mills put forward, 50 years ago, this generalization of Maxwell’s equations, with a new symmetry. A whole new symmetry. Mathematics very similar, but there was a whole new symmetry. They hoped that this would contribute somehow to particle physics — didn’t. It didn’t, by itself, contribute to particle physics.



But then some of us generalized it further. And then it did! And it gave a very beautiful description of the strong force and of the weak force. So here we say, again, what we said before: that each skin of the onion shows a similarity to the adjoining skins. So the mathematics for the adjoining skins is very similar to what we need for the new one. And therefore it looks beautiful because we already know how to write it in a lovely, concise way.



So here are the themes. We believe there is a unified theory underlying all the regularities. Steps toward unification exhibit the simplicity. Symmetry exhibits the simplicity. And then there is self-similarity across the scales — in other words, from one skin of the onion to another one. Proximate self-similarity. And that accounts for this phenomenon. That will account for why beauty is a successful criterion for selecting the right theory.



Here’s what Newton himself said: “Nature is very consonant and conformable to her self.” One thing he was thinking of is something that most of us take for granted today, but in his day it wasn’t taken for granted. There’s the story, which is not absolutely certain to be right, but a lot of people told it. Four sources told it. That when they had the plague in Cambridge, and he went down to his mother’s farm — because the university was closed — he saw an apple fall from a tree, or on his head or something. And he realized suddenly that the force that drew the apple down to the earth could be the same as the force regulating the motions of the planets and the moon.

牛顿曾说: “自然是和谐和自相似的。”他的这种思想在我们今天看来是天经地义的,然而在他的那个时代人们可不这么想。这有一个故事,这个故事并不一定是真的,但很多人都讲过。它有四个来源。当剑桥大学爆发瘟疫时,牛顿回到到他母亲的农场,由于大学停课了。他看到苹果从树上落下来,砸到了他的脑袋或者其他什么东西,他突然意识到这种把苹果吸向地面的力很有可能和规范月球和行星运动的力是一致的。


That was a big unification for those days, although today we take it for granted. It’s the same theory of gravity. So he said that this principle of nature, consonance: “This principle of nature being very remote from the conceptions of philosophers, I forbore to describe it in that book, lest I should be accounted an extravagant freak … ” That’s what we all have to watch out for, (Laughter) especially at this meeting. ” … and so prejudice my readers against all those things which were the main design of the book.” Now, who today would claim that as a mere conceit of the human mind?



That the force that causes the apple to fall to the ground is the same force that causes the planets and the moon to move around, and so on? Everybody knows that. It’s a property of gravitation. It’s not something in the human mind. The human mind can, of course, appreciate it and enjoy it, use it, but it’s not — it doesn’t stem from the human mind. It stems from the character of gravity. And that’s true of all the things we’re talking about.They are properties of the fundamental law. The fundamental law is such that the different skins of the onion resemble one another, and therefore the math for one skin allows you to express beautifully and simply the phenomenon of the next skin.



I say here that Newton did a lot of things that year: gravity, the laws of motion, the calculus, white light composed of all the colors of the rainbow. And he could have written quite an essay on “What I Did Over My Summer Vacation.” (Laughter)



So we don’t have to assume these principles as separate metaphysical postulates. They follow from the fundamental theory. They are what we call emergent properties. You don’t need — you don’t need something more to get something more. That’s what emergence means.



Life can emerge from physics and chemistry, plus a lot of accidents. The human mind can arise from neurobiology and a lot of accidents, the way the chemical bond arises from physics and certain accidents. It doesn’t diminish the importance of these subjects to know that they follow from more fundamental things, plus accidents. That’s a general rule, and it’s critically important to realize that. You don’t need something more in order to get something more.

生命源于物理和化学,再加上很多意外。人类的智慧源于神精细胞和很多意外因素。这些化学作用源于物理和特定的意外因素。这并不会较少其重要性,当 了解到它们遵循基本定律和一些意外因素,那是一个大体上的原则,意识到这点很重要。你不需要更多的东西来得到更多的东西。


People keep asking that when they read my book, “The Quark and the Jaguar,” and they say, “Isn’t there something more beyond what you have there?” Presumably, they mean something supernatural. Anyway, there isn’t. (Laughter)



You don’t need something more to explain something more.



Thank you very much. (Applause)





未经允许不得转载:文华程序化 » 诺贝尔物理学奖得主默里·盖尔曼浅谈物理中的美与真
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