2–4Nuclei and particles 原子核与粒子
What are the nuclei made of, and how are theyheld together? It is found that the nuclei are held together by enormousforces. When these are released, the energy released is tremendous comparedwith chemical energy, in the same ratio as the atomic bomb explosion is to a TNTexplosion, because, of course, the atomic bomb has to do with changes insidethe nucleus, while the explosion of TNT has to do with the changes of theelectrons on the outside of the atoms. The question is, what are the forces whichhold the protons and neutrons together in the nucleus? Just as the electricalinteraction can be connected to a particle, a photon, Yukawa suggested that theforces between neutrons and protons also have a field of some kind, and that whenthis field jiggles it behaves like a particle. Thus there could be some otherparticles in the world besides protons and neutrons, and he was able to deducethe properties of these particles from the already known characteristics ofnuclear forces. For example, he predicted they should have a mass of two or threehundred times that of an electron; and lo and behold, in cosmic rays there wasdiscovered a particle of the right mass! But it later turned out to be thewrong particle. It was called a μ -meson, or muon.
{居然有敏感词}

However, a little while later, in 1947 or1948, another[A1] particle was found, the π -meson, or pion, which satisfied Yukawa’s criterion. Besides theproton and the neutron, then, in order to get nuclear forces we must add thepion. Now, you say, “Oh great!, with this theory we make quantum nucleodynamicsusing the pions just like Yukawa wanted to do, and see if it works, andeverything will be explained.” Bad luck. It turns out that the calculationsthat are involved in this theory are so difficult that no one has ever been ableto figure out what the consequences of the theory are, or to check it againstexperiment, and this has been going on now for almost twenty years!
然而，不久之后，在1947或1948，另外一个粒子被发现，它就是π -meson,或π介子，它满足了汤川的判断标准。因此，为了得到原子核的力，除了质子和中子之外，我们还应该增加π介子。现在你说，“真伟大，用这个理论，我们就可以让量子和动力学，使用汤川所想的那些，然后，看是否可行，这样，所有事情，都会被解释。”但是糟糕！结果证明，这个理论所牵扯到的计算太难，以至于没有人可以想出，这个理论的结果会是什么，或者用实验来检查它，这个情况，到目前已经持续了近20年。这样，我们就被卡在一个理论上了，我们不知道，它是对还是错，但我们确实知道，它的错误很小，或者说，它是不完整的。
[A1]

While we have been dawdling aroundtheoretically, trying to calculate the consequences of this theory, theexperimentalists have been discovering some things. For example, they hadalready discovered this muon, and we do not yet know where it fits. Also, incosmic rays, a large number of other “extra” particles were found. It turns outthat today we have approximately thirty particles, and it is very difficult tounderstand the relationships of all these particles, and what nature wants themfor, or what the connections are from one to another. We do not today understandthese various particles as different aspects of the same thing, and the factthat we have so many unconnected particles is a representation of the fact thatwe have so much unconnected information without a good theory. After the greatsuccesses of quantum electrodynamics, there is a certain amount of knowledge ofnuclear physics which is rough knowledge, sort of half experience and halftheory, assuming a type of force between protons and neutrons and seeing whatwill happen, but not really understanding where the force comes from. Aside fromthat, we have made very little progress. We have collected an enormous numberof chemical elements. In the chemical case, there suddenly appeared arelationship among these elements which was unexpected, and which is embodiedin the periodic table of Mendeleev. For example, sodium and potassium are aboutthe same in their chemical properties and are found in the same column in theMendeleev chart. We have been seeking a Mendeleev-type chart for the newparticles. One such chart of the new particles was made independently by Gell-Mannin the U.S.A. and Nishijima in Japan. The basis of their classification is anew number, like the electric charge, which can be assigned to each particle,called its “strangeness,” S . This number is conserved, like the electric charge, in reactions whichtake place by nuclear forces.
当我们还在理论上闲荡，并尝试去计算出这个理论的结果时，实验学家们已经发现了某些事物。例如，他们发现了μ-介子，而我们还不知道，μ-介子适合于哪里。另外，在宇宙射线中，也发现了大量其他“额外的”粒子。结果就是，我们今天有大约30个粒子，但要理解这些粒子之间的关系，非常困难，自然用它们做什么，或者，它们之间的关系是什么，都不知道。对于这些粒子是同一个事物的不同方面这一点，我们今天还不理解，这么多粒子，相互之间没有联系，这一事实，恰恰说明，我们有如此众多的互不联系的信息，但我们缺乏一个好的理论。量子电动力学，取得了巨大的成功，在此之后，有相当数量的原子核和物理学的知识，是一种比较粗糙的知识，半经验半理论性之类，即假定在质子和中子之间，有一种力，然后，看会发生什么，但并不真正理解：这个力是从哪里来的。除此之外，我们的进步很小。我们已经收集了大量的化学元素。在化学中，这些元素的关系，突然出现，有点出乎意料，并且，它们是体现在门捷列夫周期表中的。例如钠和钾，化学属性几乎相同，并且，在门捷列夫周期表中的同一列中。我们想为新的粒子，也寻找一种门捷列夫型的表。一种这类关于新粒子的图表，由美国的盖尔曼{ Gell-Mann }和日本的西岛{ Nishijima }，分别独立完成。它们分类的基础，是一个新的数字，就像电子电荷，它可以被分配给每一个粒子，被称为它的“奇异数，”S。在通过原子核的力所产生的反应中，这个数字被保全，就像电子的电荷一样。

Table 2–2Elementary Particles 表2-2 基础粒子
In Table 2–2 arelisted all the particles. We cannot discuss them much at this stage, but thetable will at least show you how much we do not know. Underneath each particleits mass is given in a certain unit, called the MeV. One MeV is equal to 1.783×10−27 gram. The reason this unit was chosen is historical, and weshall not go into it now. More massive particles are put higher up on thechart; we see that a neutron and a proton have almost the same mass. Invertical columns we have put the particles with the same electrical charge, allneutral objects in one column, all positively charged ones to the right of thisone, and all negatively charged objects to the left.
表2-2列出了所有的粒子。在目前这个阶段，对于它们，我们不能讨论太多，但这个表，将至少会给你指出，我们不知道的有多少。在每个粒子下面，它的质量都给了，用一个确定的单位，称为兆电子伏（Million electron Volts）。1MeV等于1.783×10−27克。为什么选这个单位，有历史原因，现在不讲。更多大质量的粒子，放在表的较高部分；我们可以看到，中子和质子的质量，几乎相同。在垂直的列中，放的是拥有相同电荷的粒子，所有中性的对象，在一列中，所有带正电的对象，在此列的右面，带负电的对象，在此列的左面。

Particles are shown with a solid line and“resonances” with a dashed one. Several particles have been omitted from thetable. These include the important zero-mass, zero-charge particles, the photonand the graviton, which do not fall into the baryon-meson-lepton classificationscheme, and also some of the newer resonances (K∗ , ϕ , η ). The antiparticles of the mesons are listed in the table, but theantiparticles of the leptons and baryons would have to be listed in anothertable which would look exactly like this one reflected on the zero-chargecolumn. Although all of the particles except the electron, neutrino, photon,graviton, and proton are unstable, decay products have been shown only for theresonances. Strangeness assignments are not applicable for leptons, since theydo not interact strongly with nuclei.
粒子下面是实线，“共振”下面是虚线。从表中忽略掉了几个粒子。被忽略的包括重要的零质量、零电荷的粒子，光子和引力子并没有落入重子-介子-轻子这一分类规划，以及一些较新的共振(K∗ , ϕ , η )。介子的反粒子列在了表中，但是轻子和重子的反粒子，应列入另一张表，那个表看上去，应与这个表的零电荷列类似。虽然除了电子、中子、光子、引力子、和质子之外，所有粒子都是不稳定的，但是，这里只显示了共振的衰减产品。轻子的奇异数得不到，因为轻子与原子核的交互作用不强。

All particles which are together with theneutrons and protons are called baryons, and the following ones exist:There is a “lambda,” with a mass of 1115 MeV, and three others, called sigmas, minus, neutral, and plus,with several masses almost the same. There are groups or multiplets with almostthe same mass, within one or two percent. Each particle in a multiplet has thesame strangeness. The first multiplet is the proton-neutron doublet, and thenthere is a singlet (the lambda) then the sigma triplet, and finally the xi doublet.Very recently, in 1961, even a few more particles were found. Or are theyparticles? They live so short a time, they disintegrate almost instantaneously,as soon as they are formed, that we do not know whether they should be consideredas new particles, or some kind of “resonance” interaction of a certain definiteenergy between the Λ and π products into which they disintegrate.
所有与中子和质子在一起的粒子，为重子，下面是其中的一些：有一个“拉姆不大”，质量是1115 MeV，另外三个被称为为西格玛子，电荷为负、中性和正，质量几乎一样。还有组或组合，其成员的质量几乎相同，差别在1到2个百分点。同一个组合中的每个粒子，都有相同的奇异数。第一个组合，是质子-中子，两个一组，然后，是一个一个一组（拉姆不大），然后是西格玛，三个一组，最后是xi，两个一组。不久之前，1961年，又找到了几个粒子。或者说，它们是粒子吗？因为它们的生存时间很短，刚形成，马上就分裂成小块，所以，我们不知道，它们是否能被认为是新的粒子，还是被认为是某种确定能量的“共振”交互作用，这种能量，在Λ 和 π的产品之间，它们分解后，就是落入这个区间。

In addition to the baryons the otherparticles which are involved in the nuclear interaction are called mesons.There are first the pions, which come in three varieties, positive, negative,and neutral; they form another multiplet. We have also found some new thingscalled K-mesons, and they occur as a doublet, K+ and K0 . Also, every particle has its antiparticle, unless a particle is itsown antiparticle. For example, the π− and the π+ are antiparticles, but the π0 is its own antiparticle. The K− and K+ are antiparticles, and the K0 and K¯¯¯¯0 . In addition, in 1961 we also found some more mesons or maybemesons which disintegrate almost immediately. A thing called ω which goes into three pions has a mass 780 on this scale, and somewhat less certain is an object whichdisintegrates into two pions. These particles, called mesons and baryons, andthe antiparticles of the mesons are on the same chart, but the antiparticles ofthe baryons must be put on another chart, “reflected” through the charge-zerocolumn.
参与原子核的交互作用的粒子，除重子之外的其他粒子，被称为介子。首先是派介子，它有三种：正的、副的、和中性的；它们形成了另外一个组合。我们还发现了一些新的事物，被称为K介子，它们出现时，是两个一组，K+和K0。每个粒子，都有它自己的反粒子，除非一个粒子就是它自己的反粒子。例如，π−和π+ 就是反粒子, 但是π0则是它自己的反粒子。K−和 K+是反粒子, 而K0 and K¯¯¯¯0是反粒子{？}。另外，1961年，我们也发现了更多的粒子、或介子，它们几乎是立即分解。在这个层面上，还有一个被称为 ω的东西，质量为780，它会分解成三个派介子，有时候，它是一个不确定的对象，会分解成两个派介子。这些被称为介子和重子的粒子，及芥子的反粒子，在同一张图表上，但是，重子的反粒子，应该放在另一张图表上，通过零电荷的列来“反映”。

Just as Mendeleev’s chart was very good,except for the fact that there were a number of rare earth elements which werehanging out loose from it, so we have a number of things hanging out loose fromthis chart—particles which do not interact strongly in nuclei, have nothing todo with a nuclear interaction, and do not have a strong interaction (I mean thepowerful kind of interaction of nuclear energy). These are called leptons, andthey are the following: there is the electron, which has a very small mass onthis scale, only 0.510 MeV. Then there is that other, the muon, which has a mass muchhigher, 206 times as heavy as an electron. So far as we can tell, by all experimentsso far, the difference between the electron and the muon is nothing but themass. Everything works exactly the same for the muon as for the electron,except that one is heavier than the other. Why is there another one heavier;what is the use for it? We do not know. In addition, there is a lepton which isneutral, called a neutrino, and this particle has zero mass. In fact, it is nowknown that there are two different kinds of neutrinos, one related toelectrons and the other related to muons.
门捷列夫周期表，确实很好，除了一些地球上很稀有的元素，并不在其中；与此相同，我们也有一些东西，并不在在那个粒子表上，就是那些在原子核中交互作用不强的粒子，及与原子核交互作用没有任何关系的粒子，或者，没有很强交互作用的粒子（我的意思是说，那种原子核能量的强有力的交互作用）。它们被称为轻子，包括电子，在这个水平上，其质量只有0.510 MeV。然后，就是其他的，比如μ介子，它的质量要高得多，是电子重量的256倍。目前为止，通过所有实验，我们所能知道的就是，μ介子与电子的区别，只有质量。μ介子与电子相比，所有的表现都相同，除了比电子重。为什么会有另外一个比较重的粒子呢？其用途为何？我们不得而知。另外，有一个轻子，是中性的，被称为中微子，这个粒子的质量为零。事实上，现在知道有两种不同的中微子，一个与电子有关，另一个与μ介子有关。

Finally, we have two other particles whichdo not interact strongly with the nuclear ones: one is a photon, and perhaps,if the field of gravity also has a quantum-mechanical analog (a quantum theoryof gravitation has not yet been worked out), then there will be a particle, agraviton, which will have zero mass.
最后，我们有另外两个粒子，它们与原子核的交互，并不强烈，一个是光子，或许，如果万有引力领域，有一个量子力学的类比的话（关于万有引力的量子理论，还没有研究出），那么，将会有一个粒子，即引力子，其质量为零。
What is this “zero mass”? The masses givenhere are the masses of the particles at rest. The fact that a particlehas zero mass means, in a way, that it cannot be at rest. A photonis never at rest, it is always moving at 186,000 miles a second. We will understand more what mass means when weunderstand the theory of relativity, which will come in due time.
这个“零质量”是什么意思？这里所给的粒子的质量，是粒子静止时的质量。一个离子具有零质量，就是以某种方式意味着，该粒子不可能是静止的。一个光子永远也不会静止，它总是在以186，000英里/每秒移动。当我们理解了相对论的时候，我们对零质量，就会理解更深；在合适的时候，相对论就会到来。

Thus we are confronted with a large numberof particles, which together seem to be the fundamental constituents of matter.Fortunately, these particles are not all different in their interactionswith one another. In fact, there seem to be just four kinds ofinteraction between particles which, in the order of decreasing strength, arethe nuclear force, electrical interactions, the beta-decay interaction, andgravity. The photon is coupled to all charged particles and the strength of theinteraction is measured by some number, which is 1/137 . The detailed law of this coupling is known, that is quantumelectrodynamics. Gravity is coupled to all energy, but its coupling isextremely weak, much weaker than that of electricity. This law is also known.Then there are the so-called weak decays—beta decay, which causes the neutron todisintegrate into proton, electron, and neutrino, relatively slowly. This lawis only partly known. The so-called strong interaction, the meson-baryon interaction,has a strength of 1 in this scale, and the law is completely unknown, although there are anumber of known rules, such as that the number of baryons does not change inany reaction.
这样，我们就面对了大量的粒子，它们可能共同构成了物质的基础构成分。幸运的是，这些粒子间的交互作用，并非完全不同。事实上，粒子间的交互作用，似乎只有四种，它们按照强度的降序，就是原子核力，电子的交互作用，贝塔衰减交互作用，和万有引力。所有充电的粒子，都伴有光子，交互的强度，是通过一个数值来衡量的，就是1/137。这种陪伴的详细规律，是知道的，那就是量子电动力学。万有引力陪伴着所有的能量，但其陪伴，极其微弱，比电子的陪伴弱得多。电子的规律也是知道的。然后，就有所谓的弱衰减，即贝塔衰减，它引起了中子分裂成质子、电子、和中微子，相对比较慢。这个规律只是部分地知道。所谓的强交互作用，即介子-重子间的交互作用，在这个标准中的强度是1，其规律完全不知道，虽然有一系列不知道的规则，但是，有些还是知道的，比如重子的数量，在任何反应中都不变。

表 2–3 基础交互作用
陪伴 强度* 规律
光子对充电粒子 ∼10−2 规律未知
有引力对所有能量 ∼10−40 规律未知
弱衰减 ∼10−5 规律部分知道
介子对重子 ∼10−20 规律未知(有些规则知道)
* “强度”是每个交互作用中、与维度无关的陪伴常数的度量值。

This then, is the horrible condition of ourphysics today. To summarize it, I would say this: outside the nucleus, we seemto know all; inside it, quantum mechanics is valid—the principles of quantummechanics have not been found to fail. The stage on which we put all of our knowledge,we would say, is relativistic space-time; perhaps gravity is involved inspace-time. We do not know how the universe got started, and we have never madeexperiments which check our ideas of space and time accurately, below some tinydistance, so we only know that our ideas work above that distance. Weshould also add that the rules of the game are the quantum-mechanicalprinciples, and those principles apply, so far as we can tell, to the newparticles as well as to the old. The origin of the forces in nuclei leads us tonew particles, but unfortunately they appear in great profusion and we lack acomplete understanding of their interrelationship, although we already knowthat there are some very surprising relationships among them. We seem graduallyto be groping toward an understanding of the world of subatomic particles, butwe really do not know how far we have yet to go in this task.
因此，我们今天的物理条件{情况}，就是这么恐怖。总结一下，我要这样说：原子核外面，我们似乎都理解了，在其里面，量子力学是有效的，量子力学的原理，还没被发现有失败的情况。我们把我们所有的知识，都放在了一个平台上，这个平台，就是相对的空间-时间；或许万有引力，被卷入了空间-时间。宇宙是如何开始的，我们并不知道，我们从来没有在小的距离下面{？}，做过实验，以准确地检查我们关于空间和时间的想法，所以，我们只知道我们的想法在那个距离上是有效的。我们还应该说，游戏的规则，就是量子力学的原理，这些原理，就我们所知，对于新老粒子，都同样适用。原子核中的力的起源，把我们引向新的粒子，但不幸的是，它们大量地出现，而对它们之间的相互关系，我们缺乏全面的了解，虽然我们已经知道了它们之间的一些令人吃惊的关系。对于亚原子世界，我们似乎正在往前摸索，逐渐理解，但是，我们确实不知道，我们要在这个任务中走多远。

1 Chapter3. TheRelation of Physics to Other Sciences物理学与其他科学的关系
(There was no summary for this lecture.)本讲座没有总结。
3–1Introduction 介绍
Physics is the most fundamental andall-inclusive of the sciences, and has had a profound effect on all scientificdevelopment. In fact, physics is the present-day equivalent of what used to becalled natural philosophy, from which most of our modern sciences arose.Students of many fields find themselves studying physics because of the basicrole it plays in all phenomena. In this chapter we shall try to explain what thefundamental problems in the other sciences are, but of course it is impossiblein so small a space really to deal with the complex, subtle, beautiful mattersin these other fields. Lack of space also prevents our discussing the relationof physics to engineering, industry, society, and war, or even the mostremarkable relationship between mathematics and physics. (Mathematics is not ascience from our point of view, in the sense that it is not a naturalscience. The test of its validity is not experiment.) We must, incidentally,make it clear from the beginning that if a thing is not a science, it is notnecessarily bad. For example, love is not a science. So, if something is saidnot to be a science, it does not mean that there is something wrong with it; itjust means that it is not a science.
物理学是最基础的科学，包罗万象，它对所有科学的发展，都有着深远的影响。事实上，物理学在今天，等价于被称为自然哲学的学科，我们大多数的现代科学，都从中产生。很多领域的学生，发现他们自己学物理，是因为物理在所有现象中所扮演的基本角色。在这章中，我们将尝试解释，其他科学中的基础问题是什么，但是当然，在这么小的空间中，去处理这些其他领域中的复杂的、精细的、和漂亮的事情，是不可能的。缺乏空间，也将会妨碍我们去讨论物理学与工程、工业、社会、战争等的关系，甚至包括最值得注意的数学与物理之间的关系。（从我们的观点看，数学不是一门科学，意义就是，它不是一门自然科学。其有效性的测试，并不是实验。）顺便说说，从一开始，我们就要清楚一点，如果一个事情不是科学，并不意味着它必然就是坏事情。例如，爱就不是科学。所以，如果某事被说成不是一门科学，并不意味着这件事情有什么错；它只意味着，该事不是一门科学。

3–2Chemistry 化学
The science which is perhaps the mostdeeply affected by physics is chemistry. Historically, the early days of chemistrydealt almost entirely with what we now call inorganic chemistry, the chemistry ofsubstances which are not associated with living things. Considerable analysiswas required to discover the existence of the many elements and their relationships—howthey make the various relatively simple compounds found in rocks, earth, etc.This early chemistry was very important for physics. The interaction between thetwo sciences was very great because the theory of atoms was substantiated to alarge extent by experiments in chemistry. The theory of chemistry, i.e., of thereactions themselves, was summarized to a large extent in the periodic chart ofMendeleev, which brings out many strange relationships among the variouselements, and it was the collection of rules as to which substance is combinedwith which, and how, that constituted inorganic chemistry. All these rules wereultimately explained in principle by quantum mechanics, so that theoreticalchemistry is in fact physics. On the other hand, it must be emphasized thatthis explanation is in principle. We have already discussed thedifference between knowing the rules of the game of chess, and being able to play.So it is that we may know the rules, but we cannot play very well. It turns outto be very difficult to predict precisely what will happen in a given chemicalreaction; nevertheless, the deepest part of theoretical chemistry must end up inquantum mechanics.
化学可能是被物理学影响最深的科学。从历史上看，早期的化学，只处理我们今天称为无机化学的东西，即与生物没有联系的实质体的化学。要发现很多元素和它们之间的关系，需要相当数量的分析，它们之间的关系是指，它们是如何构成岩石、土壤中的各种相对简单的复合物的。早期阶段的这种化学，对物理很重要。这两门科学之间的交互非常大，因为原子理论，在很大程度上，是被化学实验所证实的。化学理论，亦即它们自己的反应的理论，在很大程度上，在门捷列夫周期表中被总结了，该表带出了各种元素之间的很多奇怪的关系，它也是规则的收集，比如那一种实质体将与那一种结合，及这种结合，是如何组成无机化学的。所有这些规则，最终都被量子力学中的原理给解释了，所以，理论上讲，化学事实上就是物理学。另一方面，必须强调这个解释，是原理上的。理解象棋的规则，与能下棋之间的差别，我们已经讨论过了。所以情况就是，我们可能知道这些规则，但是，我们不可能玩的很好。结果就是，在一个给定的化学反应中，要精确地预测会发生什么，非常困难；尽管如此，理论化学的最深部分，应该是在量子力学。

There is also a branch of physics andchemistry which was developed by both sciences together, and which is extremelyimportant. This is the method of statistics applied in a situation in whichthere are mechanical laws, which is aptly called statistical mechanics.In any chemical situation a large number of atoms are involved, and we haveseen that the atoms are all jiggling around in a very random and complicatedway. If we could analyze each collision, and be able to follow in detail themotion of each molecule, we might hope to figure out what would happen, but themany numbers needed to keep track of all these molecules exceeds so enormouslythe capacity of any computer, and certainly the capacity of the mind, that it wasimportant to develop a method for dealing with such complicated situations. Statisticalmechanics, then, is the science of the phenomena of heat, or thermodynamics.Inorganic chemistry is, as a science, now reduced essentially to what arecalled physical chemistry and quantum chemistry; physical chemistry to studythe rates at which reactions occur and what is happening in detail (How do themolecules hit? Which pieces fly off first?, etc.), and quantum chemistry tohelp us understand what happens in terms of the physical laws.
还有一门物理和化学的分支，是由是两门科学共同发展出来的，且极端重要。这是一种统计方法，适用于有力学规律的情况，所以，它可以被很合适地称为统计力学。任何化学情况，都会牵扯到大量的原子，我们已经看到，原子是以一种非常随机的和复杂的方式，在摇动。如果我们可以分析每一次碰撞，且可以详细地跟踪每个分子的运动，我们或许可以希望找出，究竟发生了什么，但是，面对这么多的分子，要全部跟踪其路径，超出了任何计算机的容量，当然也超出了大脑的容量，所以，找出一种方法，处理这种复杂的情况，就非常重要。因此，统计力学，就是热或热现象的科学。无机化学，作为一门科学，现在基本被归于物理化学和量子化学；物理化学，研究反应发生的比率为何，以及发生的细节是什么？（分子是如何撞击的？哪一部分先飞出去？，等等）量子化学，依据物理规律，帮助我们理解所发生的事情。