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费曼物理学讲义翻译:1卷2章1节:介绍

(2020-10-01 15:34:34)
分类: 费曼物理学讲义

Chapter2. Basic Physics 基础物理学

2–1Introduction 介绍

In this chapter, we shall examine the most fundamental ideas that we have about physics—the nature of things as we see them at the present time. We shall not discuss the history of how we know that all these ideas are true; you will learn these details in due time.

在这章中,我们将检查我们关于物理的最基本的想法,即我们现在所看到的事物的本质。至于我们是如何知道这些想法是真的,现在不讨论;你将在合适的时候,学到这些细节。

The things with which we concern ourselves in science appear in myriad forms, and with a multitude of attributes. For example, if we stand on the shore and look at the sea, we see the water, the waves breaking, the foam, the sloshing motion of the water, the sound, the air, the winds and the clouds, the sun and the blue sky, and light; there is sand and there are rocks of various hardness and permanence, color and texture. There are animals and seaweed, hunger and disease, and the observer on the beach; there may be even happiness and thought. Any other spot in nature has a similar variety of things and influences. It is always as complicated as that, no matter where it is. Curiosity demands that we ask questions, that we try to put things together and try to understand this multitude of aspects as perhaps resulting from the action of a relatively small number of elemental things and forces acting in an infinite variety of combinations.

我们在科学中所关心的事物,以无数的形式显现,且有多种属性。如果我们站在海岸,眺望大海,我们就会看到水、波浪粉碎、泡沫和水的击打运动、声音、空气,风还有云彩,太阳、蓝天和阳光;还有沙子,及各种不同硬度、永久性、颜色和质地的岩石。有动物和海草,饥饿和疾病,海滩上的观察者;甚至还有快乐与思想。自然中任何其它的观察点,都有类似的不同事物和影响。不管在哪里,其复杂性,总是这样。好奇心要求我们提出问题,我们尝试把万事万物,放在一起,去理解它们,它们有可能是通过一些相对较小数量的事物和力量,通过有限的组合变化,而形成的。

For example: Is the sand other than the rocks? That is, is the sand perhaps nothing but a great number of very tiny stones? Is the moon a great rock? If we understood rocks, would we also understand the sand and the moon? Is the wind a sloshing of the air analogous to the sloshing motion of the water in the sea? What common features do different movements have? What is common to different kinds of sound? How many different colors are there? And so on. In this way we try gradually to analyze all things, to put together things which at first sight look different, with the hope that we may be able to reduce the number of different things and thereby understand them better.

例如:沙子与岩石有何不同?也就是说,沙子或许无非就是大量非常小的石头?月亮是不是一块巨大的岩石?如果我们理解了岩石,我们是否也就理解了沙子和月亮?风是空气的拍打,它与海里面水的拍打,是否可类比?不同的运动,有什么共同的特点?不同的声音,有什么共同的特点?总共有多少种不同的颜色?如此等等。我们尝试以这种方式,逐渐分析所有事物,把第一眼看上去不同的事物,放在一起,寄希望我们可以减少不同事物的数量,从而对其理解更深。

A few hundred years ago, a method was devised to find partial answers to such questions. Observation, reason, and experiment make up what we call the scientific method. We shall have to limit ourselves to a bare description of our basic view of what is sometimes called fundamental physics, or fundamental ideas which have arisen from the application of the scientific method.

几百年前,发明了一种方法,可以发现这些问题的部分答案。观察、思考原因、和实验,形成了我们今天称为科学方法的东西。从科学方法的应用,产生了我们有时称为基础物理学基础想法的东西,对这些东西,我们有个基本观点,现在,我们将把我们自己,限制在仅仅对此基本观点的描述上。

What do we mean by “understanding” something? We can imagine that this complicated array of moving things which constitutes “the world” is something like a great chess game being played by the gods, and we are observers of the game. We do not know what the rules of the game are; all we are allowed to do is to watch the playing. Of course, if we watch long enough, we may eventually catch on to a few of the rules. The rules of the game are what we mean by fundamental physics. Even if we knew every rule, however, we might not be able to understand why a particular move is made in the game, merely because it is too complicated and our minds are limited. If you play chess you must know that it is easy to learn all the rules, and yet it is often very hard to select the best move or to understand why a player moves as he does. So it is in nature, only much more so; but we may be able at least to find all the rules. Actually, we do not have all the rules now. (Every once in a while something like castling is going on that we still do not understand.) Aside from not knowing all of the rules, what we really can explain in terms of those rules is very limited, because almost all situations are so enormously complicated that we cannot follow the plays of the game using the rules, much less tell what is going to happen next. We must, therefore, limit ourselves to the more basic question of the rules of the game. If we know the rules, we consider that we “understand” the world.

我们所说的“理解”某事,究竟是什么意思呢?我们可以想象,组成这个世界的巨大的事物阵列,就像一个巨大的国际象棋游戏,它由上帝来玩,我们只是这个游戏的旁观者。我们并不知道这个游戏的规则是什么,我们被允许做的,只是“观察”这个游戏。当然,如果我们观察的足够久,最终,我们可以发现一些规则。游戏的规则就是我们称为基础物理学的东西。即便我们知道每条规则,我们还是不能理解,为什么游戏中会有某个移动,这只是因为,这个游戏太复杂,而我们的心智有限。如果你学过象棋,就会知道,学会所有规则很容易,但是,做出最佳选择,或者理解一个选手为什么要那样做,还是很难。在自然中,也是如此,只是要更复杂一些;但是,我们至少有可能找到所有这些规则。实际上,我们现在还没有找到所有这些规则。(偶尔,像‘国际象棋中的王车易位’这种事情,还是会发生,但我们还是不理解。)抛开不知道所有这些规则,我们能按照这些规则所解释的事情,还是非常有限,因为几乎所有的情况,都非常复杂,以至于,我们无法使用规则,来跟随这个游戏去玩,更不用说,预测下一步会发生什么了。因此,我们应该把我们限制在:关于游戏规则的更基本的问题上。如果我们知道了规则,我们就可以认为,我们“理解”了这个世界。

How can we tell whether the rules which we “guess” at are really right if we cannot analyze the game very well? There are, roughly speaking, three ways. First, there may be situations where nature has arranged, or we arrange nature, to be simple and to have so few parts that we can predict exactly what will happen, and thus we can check how our rules work. (In one corner of the board there may be only a few chess pieces at work, and that we can figure out exactly.)

对于这个游戏,如果我们不能分析的很好的话,那么,我们怎么才能知道,我们所猜测的这些规则,是正确的呢?简单地说,有三种方式。第一,可能有一些情况,它们是自然安排的、或是我们安排的,这些情况,可能很简单,且只有很少的组成部分,以至于,我们可以准确地预测,将会发生什么,这样,我们就可以检查我们的规则是如何工作的了。(在棋盘的一角,可能只有几个棋子在工作,这样,我们就可以准确地想出,将会发生什么了。)

A second good way to check rules is in terms of less specific rules derived from them. For example, the rule on the move of a bishop on a chessboard is that it moves only on the diagonal. One can deduce, no matter how many moves may be made, that a certain bishop will always be on a red square. So, without being able to follow the details, we can always check our idea about the bishop’s motion by finding out whether it is always on a red square. Of course it will be, for a long time, until all of a sudden we find that it is on a black square (what happened of course, is that in the meantime it was captured, another pawn crossed for queening, and it turned into a bishop on a black square). That is the way it is in physics. For a long time we will have a rule that works excellently in an overall way, even when we cannot follow the details, and then some time we may discover a new rule. From the point of view of basic physics, the most interesting phenomena are of course in the new places, the places where the rules do not work—not the places where they do work! That is the way in which we discover new rules.

第二种检查规则的好方法,就是依据从这些规则推出的具体性稍差的规则。例如,在棋盘上,相移动的规则,就是它只在对角线上移动。我们就可以推导,无论某个相移动多少次,它肯定总是在红方块上。于是尽管不能跟踪相移动的具体路线,我们总是可以通过发现它是否总是在红方块上,来检查我们的相的运动的想法。当然,很长时间,它都会是在红方块上,直到某时,我们会突然发现,它在一个黑的方块上(发生了什么呢?当然是它被俘了{被吃了},同时,一个卒子走到底线,变身成为了一个黑方块上的相)。这就是物理上的方式。在很长一段时间里,我们所拥有的规则,在所有方面,都会工作的很好,即便当我们不能跟踪细节的时候也如此,然后在某时,我们会发现一条新的规则。从基础物理学的观点看,最有趣的现象当然是在新的地方,新的地方,是指规则不能工作的地方,而不是指现象不起作用的地方!这就是们发现新规则的方式。

The third way to tell whether our ideas are right is relatively crude but probably the most powerful of them all. That is, by rough approximation. While we may not be able to tell why Alekhine moves this particular piece, perhaps we can roughly understand that he is gathering his pieces around the king to protect it, more or less, since that is the sensible thing to do in the circumstances. In the same way, we can often understand nature, more or less, without being able to see what every little piece is doing, in terms of our understanding of the game.

我们的想法是否正确,第三种告诉我们此事的方式,可能相对粗鲁一点,但也可能是这三种方式中最有力的。此方法就是通过粗略的近似。我们可能无法知道,为什么阿廖欣要移动这个棋子,但或许我们可以粗略地理解,他在国王的周围,部署这些棋子,或多或少是为了保护它,因为,在那个环境下,这样做,是一件有意义的事情。以同样的方式,我们通常也可以或多或少的理解自然,而不用能够看到:依据我们对这个游戏的理解,每一个小的棋子正在做什么。

At first the phenomena of nature were roughly divided into classes, like heat, electricity, mechanics, magnetism, properties of substances, chemical phenomena, light or optics, x-rays, nuclear physics, gravitation, meson phenomena, etc. However, the aim is to see complete nature as different aspects of one set of phenomena. That is the problem in basic theoretical physics, today—to find the laws behind experiment; to amalgamate these classes. Historically, we have always been able to amalgamate them, but as time goes on new things are found. We were amalgamating very well, when all of a sudden x-rays were found. Then we amalgamated some more, and mesons were found. Therefore, at any stage of the game, it always looks rather messy. A great deal is amalgamated, but there are always many wires or threads hanging out in all directions. That is the situation today, which we shall try to describe.

首先,自然现象被粗略地分类,比如热学、电学、力学、磁学、材料学、化学现象、光或光学、x射线、和物理学、万有引力、介子现象等。然而,分类的目的,是把完整的自然,看作是一组现象的不同方面。这就是今天基础理论物理学的课题,找出实验背后的规律去融合这些类。从历史上讲,我们总是能够融合它们,但随着时间的推移,又会发现新的事物。曾经我们融合的很好,突然又发现了x射线。随后,我们融合的更多,但接着又发现了介子。因此,这个游戏的任何阶段,看上去总是比较乱。很多东西都被融合了,但是,总有一些线头,挂在外面,伸向四面八方。这就是今天的情况,下面将会讲到。

Some historic examples of amalgamation are the following. First, take heat and mechanics. When atoms are in motion, the more motion, the more heat the system contains, and so heat and all temperature effects can be represented by the laws of mechanics. Another tremendous amalgamation was the discovery of the relation between electricity, magnetism, and light, which were found to be different aspects of the same thing, which we call today the electromagnetic field. Another amalgamation is the unification of chemical phenomena, the various properties of various substances, and the behavior of atomic particles, which is in the quantum mechanics of chemistry.

历史上一些融合的例子如下。首先,是热学和力学。当原子处于运动中时,运动越大,则系统包含的热量就越多,于是,热量和所有温度效果,都可以通过力学规律来表现。另外一个巨大的融合,是发现了电、磁、和光之间的关系,它们的被发现是同一个事物的不同方面,它们现在被称为电磁领域。再一个融合,就是化学现象的统一,不同实质体的不同属性,及原子中的诸粒子的表现,这些统一在化学量子力学之中。

The question is, of course, is it going to be possible to amalgamate everything, and merely discover that this world represents different aspects of one thing? Nobody knows. All we know is that as we go along, we find that we can amalgamate pieces, and then we find some pieces that do not fit, and we keep trying to put the jigsaw puzzle together. Whether there are a finite number of pieces, and whether there is even a border to the puzzle, is of course unknown. It will never be known until we finish the picture, if ever. What we wish to do here is to see to what extent this amalgamation process has gone on, and what the situation is at present, in understanding basic phenomena in terms of the smallest set of principles. To express it in a simple manner, what are things made of and how few elements are there?

问题当然就是:把所有的事情都融合在一起,是否可能?从而最终发现这个世界,只是表现着同一个事物的不同方面?没人知道答案。我们所知道的只是,在我们前进的时候,我们发现我们能够融合一些碎片,然后,我们又发现了一些东西,并不与前面的适合,我们的尝试去完成这个拼图游戏。这个拼图,是否是由有限的部分组成,及是否有边界,当然是不知道的。在我们完成这副画之前--如果我们能完成的话,永远也不会知道。我们希望在这里做的,就是要看看,这个融合过程已经走了多远?现在的情况如何?为的是依据最小数量的原理集,来理解基础现象。简单地说就是:万物是由什么构成的,及构成万物的最基本的元素有多少?

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