Finally, we remark on the question of wherewe can get our supplies of energy today. Our supplies of energy are from thesun, rain, coal, uranium, and hydrogen. The sun makes the rain, and the coalalso, so that all these are from the sun. Although energy is conserved, naturedoes not seem to be interested in it; she liberates a lot of energy from thesun, but only one part in two billion falls on the earth. Nature has conservationof energy, but does not really care; she spends a lot of it in all directions.We have already obtained energy from uranium; we can also get energy fromhydrogen, but at present only in an explosive and dangerous condition. If itcan be controlled in thermonuclear reactions, it turns out that the energy thatcan be obtained from 10 quarts of water per second is equal to all of the electricalpower generated in the United States. With 150 gallons of running water a minute, you have enough fuel tosupply all the energy which is used in the United States today! Therefore it isup to the physicist to figure out how to liberate us from the need for havingenergy. It can be done.
最后，我们要说明的问题就是，我们的能量从哪里来。我们能量的来源是太阳、雨水，煤炭、铀和氢。太阳造成了雨水及煤炭，所以，所有这些，就都是来自太阳。虽然能量是守恒的，但是，大自然似乎对这点并不感兴趣；它从太阳释放了大量的能量，但是，只有20亿中的一部分，落到了地球上。自然界有能量守恒，但是，它并不在乎，它在很多方向使用了能量。我们已经从铀中获得了能量；我们还可以从氢中获得能量，但是，目前，只能从一个爆炸的和危险的状态中，来获得。如果热核反应是可控的话，那么，每秒钟从十跨脱水中所获得的能量，将等于全美所发电能。一分钟150加仑的流动水，就能满足全美国对燃料的需求。所以，物理学家的任务，就是把我们从对能量的要求中，解放出来。这是可以做到的。
脚注
1. Our point here is not so much the result, (4.3),which in fact you may already know, as the possibility of arriving at it bytheoretical reasoning.
1、我们想在这里说明的，并不是结果，事实上（4.3）你可能已经知道了，因为通过理论推导，有可能达到。
2. Counting antibaryons as −1 baryon.
2、把反重子计为-1 重子。

Chapter5. Timeand Distance第五章 时间与距离
(There was no summary for this lecture[A1] .本章无总结。)
5–1Motion 5-1运动
In this chapter we shall consider someaspects of the concepts of time and distance. It has beenemphasized earlier that physics, as do all the sciences, depends on observation.One might also say that the development of the physical sciences to theirpresent form has depended to a large extent on the emphasis which has beenplaced on the making of quantitative observations. Only with quantitativeobservations can one arrive at quantitative relationships, which are the heartof physics.
在本章，我们将考虑时间与距离概念的某些方面。早前曾强调过，物理学，正像其他科学一样，依赖于观察。我们也可以说，物理科学能发展到今天的这种样子，很大程度上，依赖于对定量观察的强调。只有通过定量观察，才能达到定量的关系。这是物理学的核心。

Many people would like to place thebeginnings of physics with the work done 350 years ago by Galileo, and to callhim the first physicist. Until that time, the study of motion had been aphilosophical one based on arguments that could be thought up in one’s head.Most of the arguments had been presented by Aristotle and other Greekphilosophers, and were taken as “proven.” Galileo was skeptical, and did anexperiment on motion which was essentially this: He allowed a ball to roll downan inclined trough and observed the motion. He did not, however, just look; hemeasured how far the ball went in how long a time.
很多人喜欢把物理学的开端，归功于350年前的伽利略所做，并称他为第一个物理学家。在此之前，对运动的研究，一直都是哲学性的，所基于的论据，都是在人脑子里所想的东西，大部分论据，都是由亚里斯多德和其他希腊哲学家所提供，并被当作“已被证明了的”。伽利略是怀疑派，他对运动做了实验，实验的本质是这样的：他让一个球，沿着一个水槽滚下来，并观察这个运动。然而，他并不只是在看，他还在计量：球滚下来要花多长时间。

The way to measure a distance was wellknown long before Galileo, but there were no accurate ways of measuring time,particularly short times. Although he later devised more satisfactory clocks(though not like the ones we know), Galileo’s first experiments on motion weredone by using his pulse to count off equal intervals of time. Let us do thesame.
计量距离的方法，在伽利略之前很久，就已经知道了，但是，并没有准确的计量时间的方法，特别是短的时间。虽然伽利略后来发明了更令人满意的时钟（虽然不是我们知道的那种），但是，伽利略在他关于运动的第一个实验中，是用他的脉搏，来计量相等的时间间隔。下面，让我们也这么做。

5–2Time 5-2 时间
Let us consider first what we mean by time.What is time? It would be nice if we could find a good definition oftime. Webster defines “a time” as “a period,” and the latter as “a time,” whichdoesn’t seem to be very useful. Perhaps we should say: “Time is what happenswhen nothing else happens.” Which also doesn’t get us very far. Maybe it isjust as well if we face the fact that time is one of the things we probablycannot define (in the dictionary sense), and just say that it is what wealready know it to be: it is how long we wait!
首先，让我们考虑，通过时间，我们究竟意味着什么。什么是时间呢？如果我们能给时间找到一个好的定义，当然美好。韦伯斯特把时间定义为，“一个时期（阶段）”，这个时期，作为时间，似乎并没有什么大用。或许，我们可以说，时间就是什么都没发生时，所发生的事情。但是，这还是不能让我们走得更远。或许，我们应该做的，就是面对这样一个事实：即时间的就是我们无法定义的一个东西（在字典的意义上），我们只能说，时间是我们已经知道的东西，它就是我们等了多久。

What really matters anyway is not how we definetime, but how we measure it. One way of measuring time is to utilize something whichhappens over and over again in a regular fashion—something which is periodic.For example, a day. A day seems to happen over and over again. But when you beginto think about it, you might well ask: “Are days periodic; are they regular?Are all days the same length?” One certainly has the impression that days insummer are longer than days in winter. Of course, some of the days in winterseem to get awfully long if one is very bored. You have certainly heard someonesay, “My, but this has been a long day!”
真正重要的，并不是如何定义时间，而是我们如何计量它。计量时间的一种方式，就是使用某种不断重复的、定期发生的事情，即某种具有规则性的东西。例如白天，白天似乎总是不断地发生，但是，当我们开始思考它，你或许会问，白天是周期性的吗？它们是规则的吗？所有的白天都是同样长的吗？我们当然会有这种印象，就是夏天的白天，比冬天的白天长，当然，冬天时，如果一个人百无聊赖，冬天的白天也会变得非常漫长。你肯定听别人这么说过：“上帝啊，这真是漫长的一天啊！”。

It does seem, however, that days are aboutthe same length on the average. Is there any way we can test whether thedays are the same length—either from one day to the next, or at least on theaverage? One way is to make a comparison with some other periodic phenomenon.Let us see how such a comparison might be made with an hour glass. With an hourglass, we can “create” a periodic occurrence if we have someone standing by itday and night to turn it over whenever the last grain of sand runs out.
然而，白天的长度，平均来看，几乎是同样的。是否有什么办法，可以让我们测试白天是否同样长呢，无论是从一天到下一天，或至少是平均值。有一种方法，就是与某种周期性的现象，相比较。让我们看看，如何用一个沙漏，来做这种比。我们让人，站在一个沙漏旁，当沙漏漏完最后一粒沙子时，就把它翻过来，这样，我们就“创造”出了一种周期性的现象。

We could then count the turnings of theglass from each morning to the next. We would find, this time, that the numberof “hours” (i.e., turnings of the glass) was not the same each “day.” We shoulddistrust the sun, or the glass, or both. After some thought, it might occur to usto count the “hours” from noon to noon. (Noon is here defined not as 12:00 o’clock,but that instant when the sun is at its highest point.) We would find, thistime, that the number of “hours” each day is the same.
然后，我们就可以计算，从每个早晨到下一个早晨，沙漏翻转的次数。这次，我们将发现，小时的数目（即沙漏翻转的次数），每“天”并不完全一样。我们可以怀疑太阳、沙漏，或两者。经过一段思考之后，或许我们会意识到，我们应该计算从中午到中午的“小时”数（中午在这里，并不被定义为12点，而是太阳到达最高点的时刻。）这一次，我们将发现，每天的小时数，都是同样的。

We now have some confidence that both the“hour” and the “day” have a regular periodicity, i.e., mark off successiveequal intervals of time, although we have not proved that either one is“really” periodic. Someone might question whether there might not be someomnipotent being who would slow down the flow of sand every night and speed itup during the day. Our experiment does not, of course, give us an answer tothis sort of question. All we can say is that we find that a regularity of onekind fits together with a regularity of another kind. We can just say that webase our definition of time on the repetition of some apparentlyperiodic event.
我们现在，就有了信心，相信“小时”和“天”，都具有规则性的周期性，亦即，它们都可以成功地标记相等的时间间隔，虽然，我们还没有证明，这两者中的任一个，是“真正”周期性的。有人或许会问，是否会有某种万能的存在，每天晚上，他都会降低沙子的流动速度，而在白天，又会加快之。对于这类问题，我们的实验当然无法回答。我们所能说的，就是我们发现了，一种规则性的东西，与另外一种规则性的东西，能够合拍。我们只能说，我们把我们关于时间的定义，基于某种明显周期性的事件的重复之上。

5–3Short times 5-3 短的时间
We should now notice that in the process ofchecking on the reproducibility of the day, we have received an important by-product.We have found a way of measuring, more accurately, fractions of a day.We have found a way of counting time in smaller pieces. Can we carry the processfurther, and learn to measure even smaller intervals of time?
我们现在应该注意到，在检查一天的重复再现这件事情上，我们得到了一个重要的副产品。我们发现了一种方法，用来计量一天，或更准确地说，计量一天的一部分。我们找到了，用更小的块，来计量时间的方法。我们能让这个过程走得更远吗，即学会计量更小的时间间隔？

Galileo decided that a given pendulum alwaysswings back and forth in equal intervals of time so long as the size of theswing is kept small. A test comparing the number of swings of a pendulum in one“hour” shows that such is indeed the case. We can in this way mark fractions ofan hour. If we use a mechanical device to count the swings—and to keep themgoing—we have the pendulum clock of our grandfathers.
Let us agree that if our pendulum oscillates3600 times in one hour (and if there are 24 such hours in a day), we shall call each period of the pendulum one“second.” We have then divided our original unit of time into approximately 102 parts. We can apply the same principles to divide the second intosmaller and smaller intervals. It is, you will realize, not practical to make mechanicalpendulums which go arbitrarily fast, but we can now make electrical pendulums,called oscillators, which can provide a periodic occurrence with a very shortperiod of swing. In these electronic oscillators it is an electrical currentwhich swings to and fro, in a manner analogous to the swinging of the bob ofthe pendulum.
伽利略判断说，只要一个单摆的摆绳比较短，那么，它就总是以同等的时间间隔，来回摆动。单摆在一个“小时”之内，可以摆动一定的次数，对此次数的测试比较，可以指出，确实如此。按照这种方式，我们就可以标记一个小时的片段。如果我们使用一个机械装置，来对摆动计数，并让它不断地运行，我们就有了我们的爷爷所有的摆钟。假设我们认同，单摆一小时震荡3600次（且如果一天有24个这种小时），那么，我们将称每一个单摆的周期，为一“秒”。这样，我们就把我们原先的时间单位，分成了大约10（的5次方）个部分{24*3600}。我们用有同样的原理，可以把秒，分成越来越小的间隔。你们将会意识到，要生产出走的任意快的机械单摆，并不实际，但是，我们现在可以制造电子单摆，称为振荡器，它可以用非常短的摆动周期，来提供周期性的表现。在这些电子振荡器中，来回震荡的，是电流，振动方式，类似于单摆的摆动。

We can make a series of such electronicoscillators, each with a period 10 times shorter than the previous one. We may “calibrate” each oscillatoragainst the next slower one by counting the number of swings it makes for oneswing of the slower oscillator. When the period of oscillation of our clock isshorter than a fraction of a second, we cannot count the oscillations withoutthe help of some device which extends our powers of observation. One suchdevice is the electron-beam oscilloscope, which acts as a sort of microscopefor short times. This device plots on a fluorescent screen a graph ofelectrical current (or voltage) versus time. By connecting the oscilloscope totwo of our oscillators in sequence, so that it plots a graph first of thecurrent in one of our oscillators and then of the current in the other, we gettwo graphs like those shown in Fig. 5–2. We canreadily determine the number of periods of the faster oscillator in one periodof the slower oscillator.
我们可以制造出一系列这种电子振荡器，每一个，都比前一个的周期，要短十倍。对于每一个震荡器，我们可以这样来校准它，即让它与相邻较慢的那个震荡器比较，计算在后者的一个摆动里，前者摆动的数目。当我们的钟表的振动周期，比一秒的一部分，还要短的时候，没有那些扩展了我们观察能力的设备的帮助，我们是不能对震荡计数的。一种这类设备，就是电子速示波器，它对短时间，扮演着类似显微镜的角色。这个设备，在一个荧光屏上，画出一个电流（或伏特）对时间的图形。，把示波器，依次与我们的两个振荡器相连，这样，它就可以先画出一个振荡器的图形，然后，画出另一个的，我们就可以得到如图5-2所示的两张图。这样，我们就可以，在较慢的震荡器的一个周期中，来规定较快的那个震荡器中的震荡周期的数目。


Fig. 5–2.Two views of an oscilloscopescreen. In (a) the oscilloscope is connected to one oscillator, in(b) it is connected to an oscillator with a period one-tenth as long. 图5-2 一个示波器屏幕的两个视图。在（a）中，示波器与一个振荡器相连，在（b）中，与它所连的振荡器，周期是前一个的十分之一。

With modern electronic techniques,oscillators have been built with periods as short as about 10−12 second, and they have been calibrated (by comparison methodssuch as we have described) in terms of our standard unit of time, the second.With the invention and perfection of the “laser,” or light amplifier, in thepast few years, it has become possible to make oscillators with even shorter periodsthan 10−12 second, but it has not yet been possible to calibrate them bythe methods which have been described, although it will no doubt soon bepossible.
借助于现代电子技术，震荡器的周期，可以做到10的-12次方秒，且它们依据我们的标准时间单位、即秒，已经得到了校正（通过我们所描述的方法）。在过去的几年中，“激光”或者说光的放大器，得到了发明和完善，借助这些，振荡器的周期，可以做到比10的-12次方秒更短，完全可能，但是，要通过我们所描述过的方法，来校准它们，还不可能，虽然，不久之后，完全有可能。

Times shorter than 10−12 second have been measured, but by a different technique. In effect,a different definition of “time” has been used. One way has been toobserve the distance between two happenings on a moving object. If, for example,the headlights of a moving automobile are turned on and then off, we can figureout how long the lights were on if we know where they were turnedon and off and how fast the car was moving. The time is the distance over whichthe lights were on divided by the speed.
比10的-12次方秒短的时间，也曾被计量过，但却是通过不同的技术。事实上，“时间”的不同定义，已经被用到了。一种方法就是：一个对象，正在移动，上面有事情发生，观察两次发生的事情之间的距离。例如，如果一个正在移动的汽车的头灯，打开，关掉，如果我们知道它在哪里打开，哪里关掉，那么，我们就会搞清楚，光亮了多长时间，及汽车移动的速度。时间，就是开灯时行驶的距离，除以速度。