利奥波德·英费尔德Leopold Infeld

利奥波德·英费尔德出生在克拉科夫的犹太聚居区卡齐米日。他的父亲Salomon Infeld是一名皮革商人，尽管家境比周围许多人要好，但生活条件仍然很差。在生命的最初十八年里，他与两个姐妹同睡一间房里的沙发，这间房也是全家白天生活和吃饭的地方。他最初在一所犹太宗教学校接受教育，但随着长大，他反抗宗教，也反抗父母在家说的意第绪语。英费尔德迫切想要逃离，能够上大学，于是他恳求父母允许他上一所文理中学（Gymnasium），为大学入学做准备。然而，他的父亲希望儿子进入家族生意，于是把他送到了一所商业学校。

英费尔德当然不会轻易放弃自己的抱负，所以他自学以参加“matura”考试。商业学校根本不教授拉丁语等科目，因此他不得不在没有任何教师支持的情况下学习这些内容。1916年，当他以极高的成绩通过“matura”考试时，他的父亲让步了，允许他进入克拉科夫的雅盖隆大学。由于当时欧洲正处于第一次世界大战之中，英费尔德先被征入奥地利军队，但他的犹太背景和学术兴趣意味着他的士兵生涯绝不会顺利。他尽快离开了军队，开始在雅盖隆大学学习数学和物理。由于波兰的理论物理不强，英费尔德决定需要出国留学，以获得攻读博士学位的研究经验[8]：-

感到需要更广泛的学术联系，他在1920—21年在柏林度过了一年，在那里他遇到了阿尔伯特·爱因斯坦，并发表了他的第一篇论文，题为“相对论中的光波”。

可以说阿尔伯特·爱因斯坦充当了他的学位论文导师，因为他在返回克拉科夫后将在柏林完成的工作提交给了雅盖隆大学。他于1921年被授予博士学位——这是波兰大学授予的第一个理论物理博士学位。他实现了童年的抱负，现在站在学术生涯的边缘。然而，他寻找学术职位的尝试失败了，他毫不怀疑原因；他觉得，这肯定是因为他是一个犹太人在反犹大学寻找职位。然而，据他自己估计，他的麻烦比这更深，因为在犹太学校当老师似乎同样困难。他写道[2]：-

对波兰世界来说，我是个犹太人。对波兰犹太人来说，我不够犹太。

终于，在1922年，他被任命为科宁一所犹太男女同校高中的校长。在这个小镇上，他极度不快乐。他在[2]中写道：-

当我在那里时，我的世界被分成两部分：孤立的科宁，我想我可能会死在那里，以及我永远见不到的世界的其他地方。

他在那里的生活条件比克拉科夫犹太人聚居区还要差。他在1中写道：-

我们的外屋离房子大约220码。我至今还记得那些夜晚，我手里拿着蜡烛，心中充满绝望，去那里方便的情景。

这样的条件不利于他继续进行研究2：-

当我回到家时，我无法忍受去看那些多年学习期间收集的科学书籍。我不相信我此生还会再打开其中任何一本。

在科宁待了两年后，英费尔德被任命为华沙一所犹太女子中学的物理教师。这份工作不算好，但至少他在华沙。然而，他意识到，一个科学家本应最富有成效的岁月正在被浪费2：-

任何科学家一生中最好的岁月，想象力达到顶峰的岁月。那些岁月已经一去不复返了……

1928年，他遇到了Halina；他们同年结婚。1930年，他终于设法获得了一个学术职位，在Lwów（现乌克兰利沃夫）担任理论物理学的高级助理。这正是他八年前就期望得到的职位，但尽管如此，他非常高兴，并很快被提升为讲师（Docent） [2]：-

一切都变了，一切似乎都美丽而充满希望……

1932年，他访问了莱比锡，在那里与维尔纳·海森堡和巴特尔·伦德特·范德瓦尔登合作，与他们合写了论文Spinors in Riemannian geometry。然而，这一年悲剧降临，因为Halina在长期遭受消耗性疾病后去世。因悲伤而无法工作，并意识到在Lwów取得进展几乎不可能，英费尔德决定接受洛克菲勒基金会资助，前往英国剑桥学习。1933-35年，他在剑桥度过了两年，在学术环境中茁壮成长。在此期间，他与马克斯·玻恩合写了六篇论文——他们在Proceedings of the Royal Society上的论文例子有Foundations of the new Field Theory（1934）和On the Quantization of the New Field Equations（1935）。Bialynicki-Birula写道[3]：-

六十五年前，英费尔德作为洛克菲勒基金会会士前往英国。在剑桥，他遇到了卢瑟福和保罗·狄拉克，并与刚刚抵达英国的马克斯·玻恩合作。这次合作的结果是马克斯·玻恩-英费尔德电动力学。

从科学上讲，这些年是美好的，但他在英国的社交生活却不太成功。他与一位英国表亲私奔并结婚，但婚姻并不成功。1935年，他回到Lwów，但此时纳粹威胁已显而易见。他与阿尔伯特·爱因斯坦通信，后者建议他申请资助访问普林斯顿高等爱德华·斯图迪研究所。在阿尔伯特·爱因斯坦的支持下，他的申请成功了，他于1936年前往美国。离开前，他最后一次回到克拉科夫，他在[2]中描述了这次访问：-

我漫步穿过我所在城镇的犹太人区。在一个夏日早晨，透过学校敞开的窗户，我听到犹太男孩们齐声唱着《托拉》的话语。他们中也许有人像我一样憎恨这个地方，梦想着去上中学。我走近了些。学校的窗户开着，一座沉闷房屋的一楼窗户。我闻到房间里污浊的空气。那是同样的空气，同样的洋葱和土豆的气味，三十多年前我就闻到过。我看到疲惫、瘦削、营养不良的面孔，燃烧着黑色的眼睛，我一生中第一次意识到，在这悲伤的犹太人区场景中，有一丝诗意。

英费尔德与阿尔伯特·爱因斯坦合作撰写了一部通俗读物Evolution of Physics（1938年）。Gajewski写道[5]：-

英费尔德喜欢写作。他的大部分文学作品都是用英语写的。（他会带着自嘲式的谦逊说，在世界文学史上，有两位用英语写作的波兰作家；另一位是Joseph Conrad。）作为他两本书的译者，我有机会近距离欣赏他文学技艺的精湛：句子简短、节奏富有韵律，最重要的是表达极为清晰。与阿尔伯特·爱因斯坦合著的《物理学的发展》是一部真正的杰作。它为后世如何普及前沿科学树立了标准。

1938年，英费尔德收到了约翰·L·辛格提供的多伦多大学教授职位。他满怀对在加拿大新生活的希望，欣然接受了邀请。然而，他确实对世界以及自己在其中的位置感到不安。他写道[2]：-

但我能否消除那迄今为止从我童年岁月起就不断滋长的躁动不安？也许我会怀念我呼吸了这么多年的那种战斗与斗争的氛围。我真的已经斩断了我出生之岛通往外部世界的所有桥梁吗？如果黑暗与仇恨蔓延到全世界，也许我将被迫退却，重新开始我的漂泊。被动地等待未来，就意味着认可今天的世界，并分担其命运的责任。我在世界上的位置在哪里？

1939年，英费尔德与Helen结婚，Helen是美国人，毕业于康奈尔大学数学专业。英费尔德已经作为阿尔伯特·爱因斯坦的合作者而闻名，在接下来的几年里发表了许多重要论文。例如，他（与阿尔伯特·爱因斯坦和B Hoffmann共同）发表了The gravitational equations and the problem of motion（1938年），两年后又与阿尔伯特·爱因斯坦共同发表了第二部分。正如霍华得·帕西·罗伯特森所写，在第一篇论文中，作者们表明：-

……在无物质区域中满足的引力场方程，意味着对包围着包含产生该场的粒子的空间区域的二维曲面所取的某些面积分消失。在得到这一结果时，作者们利用了一个限制坐标选择的归一化条件；借助它，他们能够表明面积分的消失导出了粒子的运动方程。

第二篇论文表明，同样的结果可以在没有归一化条件的情况下得到证明。他在这段时间前后发表的其他论文包括（与他的博士生之一 P R Wallace 合作）The equations of motion in electrodynamics（1940年）、On the Theory of Brownian Motion（1940年）、On a new treatment of some eigenvalue problems（1941年）、A generalization of the factorization method for solving eigenvalue problems（1942年）和Clocks, rigid rods and relativity theory（1943年）。1945年，他与他的博士生之一 A Schild 发表了两篇论文，即A note on the Kepler problem in a space of constant negative curvature和A new approach to kinematic cosmology。

战后，英费尔德的妻子 Helen 在抚养他们的两个孩子 Eric 和 Joan 的同时给工程师们讲课，这两个孩子都出生在多伦多。英费尔德一生都是和平主义者。这在20世纪40年代后期的北美成了一个麻烦，而英费尔德并不是一个把自己的政治观点藏在心里的人。莫里茨·亚伯拉罕·斯特恩[10]讲述了这样一件事：-

1948年4月16日晚上，加拿大皇家骑警“特别科”的一名成员参加了在蒙特利尔麦吉尔大学举行的一场公开讲座。特别科充当国内间谍机构，是加拿大安全情报局的前身。在这个春夜，这名特工混在听众中，很可能假扮成学者或学生，听众大多与麦吉尔大学神学系有关。这名特工被指派汇报特邀演讲者英费尔德博士的情况，此人当时是加拿大最伟大的物理学家。英费尔德是多伦多大学的教授，作为阿尔伯特·爱因斯坦的亲密合作者而广为人知。10年前，英费尔德博士离开美国北上，这对加拿大科学界来说是一件了不起的大事。与阿尔伯特·爱因斯坦一样，英费尔德也是一位和平活动家。

两年后，加拿大政府对英费尔德及其家人采取了行动[10]：-

……议会谴责英费尔德是叛徒，策划——如果还没有付诸行动的话——向俄罗斯提供原子机密。……对英费尔德的指控是基于谣传。即便如此，他的照片还是被登在全国各地的报纸上，他的家人受到骚扰，1950年他移居到他的出生国波兰。他的加拿大公民身份以及他在加拿大出生的年幼子女的加拿大公民身份都被撤销了。

G de B Robinson在[8]中写道：-

英费尔德于1950年回到华沙，成为新成立的波兰科学院的主席团成员，并担任理论物理研究所所长以及大学中同一研究所的主任。战前被忽视的他，如今被授予最高荣誉。1950年至1968年间，他的科学活动十分活跃，出版了四十多篇论文，并于1960年与J Plebanski合著了《运动与相对论》一书。……但是，他两个在多伦多出生的孩子被取消[加拿大]公民身份，对他是一个残酷的打击。

这段引文中提到的重要著作Motion and relativity是一部重要的专著。以下是F A E Pirani的书评中的一小段摘录：-

这不是一本普通教科书，而是一部面向专家的专著。书中汇集了英费尔德于1938年在普林斯顿与阿尔伯特·爱因斯坦和Hoffmann开始、并在过去十年中与他在华沙的学生继续进行的关于广义相对论引力理论中运动问题的研究的“最终结果”。“运动问题”是确定具有给定结构的引力粒子在彼此场中的运动的问题。这个问题意义重大，因为场方程是非线性的，并且它们由微分恒等式相联系。……

他以这样的话结束书评：-

整本书带有资深作者有力而热情的风格印记。作为广义相对论理论这一部分的权威性、详尽论述，它将在任何该主题的严肃图书馆中具有永久价值。

英费尔德回到波兰曾受到极大欢迎，但在共产党政权下的生活变得越来越困难。Gajewski是他在华沙的学生，在[5]中讲述了波兰安全警察对英费尔德的调查。他写到了英费尔德的最后岁月[5]：-

当英费尔德处于政治权力的巅峰时，我没有和他谈论政治。在他生命的最后阶段，我谈了。他对政权彻底失望，对其科学和文化政策感到失望，对猖獗的官方反犹主义感到厌恶。尽管健康状况不佳，并冒着相当大的个人风险，他愿意公开加入抗议政府政策的重大倡议。这些倡议是工人防卫委员会形成的前身，而工人防卫委员会又是团结工会的前身。其余的事，正如他们所说，就是历史了。

加耶夫斯基将英费尔德描述为一位老师[5]：-

英费尔德是一位富有灵感、鼓舞人心的老师。他讲课时大多不用笔记，会用书法般的公式一丝不苟地写满黑板。他当时使用张量记号，这对我来说很新奇。（英费尔德喜欢开玩笑说，人类可以分为两类：知道张量是什么的人，以及其他所有人；他还会加上一句“我不太关心那些其他人”。）

Leopold Infeld was born in Kazimierz, the Jewish ghetto of Kraków. His father, Salomon Infeld, was a leather merchant and although the family was better off than many others around them, their living conditions were still poor. For the first eighteen years of his life he slept on a sofa in the same room as his two sisters, the room in which the family lived and ate during the day. His first education was at a Jewish religious school, but as he grew up he rebelled against the religion and against the Yiddish language which his parents spoke at home. Infeld wanted desperately to escape and be able to go to university, so he begged his parents to allow him to attend a gymnasium which would prepare him for university entrance. His father, however, wanted his son to enter the family business so he sent him to a commercial school.

Infeld certainly was not going to give up his ambitions that easily, so he studied on his own to enable him to take the 'matura' exams. Subjects like Latin were not covered at all at the commercial school so he had to learn that without any support from teachers. When he passed his 'matura' exams in 1916 with very high grades his father relented and allowed him to enter the Jagiellonian University in Kraków. Since Europe was, at this time, in the middle of World War I, Infeld was first drafted into the Austrian Army but his Jewish background and academic interests meant that his career as a soldier was never going to go well. As soon as possible he left the army behind and began his study of mathematics and physics at the Jagiellonian University. Since theoretical physics was not strong in Poland, Infeld decided that he needed to study abroad to gain experience in research for his doctorate [8]:-

Feeling the need for wider academic contacts, he spent the year 1920 - 21 in Berlin, where he met Einstein and produced his first paper entitled "Light waves in the theory of relativity."

One could say that Einstein acted as his thesis advisor, for he submitted the work he had carried out in Berlin to the Jagiellonian University on his return to Kraków. He was awarded his doctorate in 1921 - the first in theoretical physics to be awarded by a Polish university. He had achieved his childhood ambitions and now stood on the brink of an academic career. However his attempts to find an academic post failed and he was left in little doubt as to the reasons; it was, he felt, certainly because he was a Jew looking for a post in anti-Semitic universities. However, in his own estimation, his troubles went deeper than that for becoming a teacher in a Jewish school seemed equally hard. He wrote [2]:-

To the Polish world I was a Jew. To the Polish Jews I was not sufficiently Jewish.

At last, in 1922, he was appointed headmaster at a Jewish co-educational high school in Konin. He was desperately unhappy in this small town. He wrote in [2]:-

While I was there my world was divided into two parts: isolated Konin in which, I thought, I should probably die, and the rest of the world which I should never see.

His living conditions there were worse than they had been in the Jewish ghetto of Kraków. He wrote in [1]:-

Our outhouse was about 220 yards from the house. I still remember my visits there at night with a candle in my hand and despair in my heart.

These were not conditions conducive to carrying on with his research [2]:-

When I returned home I could not bear to look at my scientific books, collected during years of study. I did not believe that I would ever open one of them again in my life.

After two years spent in Konin, Infeld was appointed as a physics teacher at a Jewish gymnasium for girls in Warsaw. The job was not great but at least he was in Warsaw. He was aware, however, that the years which should be the most productive for a scientist were being wasted [2]:-

The best years in the life of any scientist, the years in which imagination reaches its peak. Those years were gone ...

In 1928 he met Halina; they married in the same year. In 1930 he at last managed to get an academic appointment, a senior assistantship in theoretical physics in Lwów (now Lviv in Ukraine). This was the sort of position he had expected to get eight years earlier, but despite this he was very happy and soon promoted to Docent [2]:-

Everything was changed, everything seemed beautiful and full of hope ...

In 1932 he visited Leipzig where he worked with Heisenberg and van der Waerden, with whom he wrote the paper Spinors in Riemannian geometry. Tragedy struck in this year, however, for Halina died after suffering a long drawn out wasting disease. Unable to work through grief, and realising that progress in Lwów would be well nigh impossible, Infeld decided to accept a Rockefeller Foundation Grant to study in Cambridge, England. He spent two years 1933-35 in Cambridge where he thrived in the academic environment. During this time he wrote six joint papers with Max Born - examples of their papers in the Proceedings of the Royal Society are Foundations of the new Field Theory (1934) and On the Quantization of the New Field Equations (1935). Bialynicki-Birula writes [3]:-

Sixty-five years ago Leopold Infeld went to England as a Fellow of the Rockefeller Foundation. In Cambridge he met Rutherford and Dirac and entered into the collaboration with Max Born, who has just arrived in England. The result of this collaboration was the Born-Infeld electrodynamics.

Scientifically these were good years but his social life in England proved less successful. He eloped with, and married, one of his English cousins but the marriage was not a success. He returned to Lwów in 1935 but by this time the Nazi threat was evident. He corresponded with Einstein who suggested he apply for a grant to visit the Institute for Advanced Study at Princeton. His application, with Einstein's support, was successful and he left in 1936 for America. Before he left he returned to Kraków for a final visit which he describes in [2]:-

I wandered through the ghetto of my town. On a summer morning the voices of Jewish boys singing in chorus the words of the Torah reached me through the open window of the school. There may be among them someone who hates this place as I hated it and who dreams of going to a gymnasium. I went nearer. The school windows were open, the first-floor windows of a dreary house. I smelt the foul air of the room. It was the same air, the same smell of onions and potatoes, which I had smelled over thirty years before. I saw the tired, thin, badly nourished faces with burning dark eyes and for the first time in my life I was conscious of a touch of poetry in this sad ghetto scene.

In Princeton, Infeld collaborated with Einstein writing a popular text Evolution of Physics (1938). Gajewski writes [5]:-

Infeld enjoyed writing. Most of his literary output was in English. (He would remark with mocking modesty that in the history of world literature there were two Polish writers who wrote in the English language; the other one was Joseph Conrad.) As a translator of two of his books I had the opportunity to admire from up close the mastery of his literary craft: short sentences, rhythmic cadences and, above all, utter clarity of exposition. 'The Evolution of Physics', co-authored with Einstein, is a true masterpiece. It set a standard for generations to come on how to popularize cutting-edge science.

In 1938 Infeld received an offer from J L Synge of a professorship at the University of Toronto. He gladly accepted the invitation full of hope for a new life in Canada. However, he did fell uneasy about the world and his place in it. He wrote [2]:-

But will I be able to destroy the restlessness which up to now has grown from the years of my childhood? Perhaps I will miss the atmosphere of fight and struggle which I have breathed for so many years. Have I really crossed all the bridges leading to the outside world from the island on which I was born? Perhaps I will be forced to retreat and to start my wanderings again if darkness and hate spread over the world. Passively to await the future means to approve the world of today and to share the responsibility for its fate. Where is my place in the world?

In 1939 Infeld married Helen, an American who was a graduate from Cornell in mathematics. Already famed as a collaborator of Einstein, Infeld published many important papers over the next few years. For example he published (jointly with A Einstein and B Hoffmann) The gravitational equations and the problem of motion (1938) and a second part, jointly with Einstein, two years later. In the first paper the authors showed, as H P Robertson wrote, that:-

... the gravitational field equations, satisfied in regions free of matter, imply the vanishing of certain surface integrals taken over 2-dimensional surfaces enclosing spatial regions containing the particles responsible for the field. In obtaining this result the authors made use of a normalizing condition restricting the choice of coordinates; with it they were able to show that the vanishing of the surface integrals led to equations of motion for the particles.

The second paper showed that the same results could be proved without the normalizing condition. Other papers he published around this time include (with P R Wallace, one of his doctoral students) The equations of motion in electrodynamics (1940), On the Theory of Brownian Motion (1940), On a new treatment of some eigenvalue problems (1941), A generalization of the factorization method for solving eigenvalue problems (1942), and Clocks, rigid rods and relativity theory (1943). He published two papers with A Schild, one of his doctoral students, in 1945, namely A note on the Kepler problem in a space of constant negative curvature, and A new approach to kinematic cosmology.

After the war Infeld's wife Helen lectured to engineers while bringing up their two children Eric and Joan who had both been born in Toronto. Infeld had all his life been a pacifist. This became a problem in North America in the later 1940s and Infeld was not one to keep his political views to himself. Stern [10] relates one incident:-

On the evening of April 16, 1948, a member of the Royal Canadian Mounted Police's "special branch" attended a public lecture at McGill University in Montreal. The special branch served as a domestic spy agency, forerunner to the Canadian Security Intelligence Service. On this spring night the operative mingled in the audience, probably posing as a scholar or student, most of whom were associated with McGill's theology department. The agent had been assigned to report on guest speaker Dr Leopold Infeld, then Canada's greatest physicist. A professor at the University of Toronto, Infeld was well known as a close collaborator of Albert Einstein. It was a great prize for Canada's scientific community when, 10 years earlier, Dr Infeld left the United States to come north. Like Einstein, Infeld was a peace activist.

Two years later the Canadian government acted against Infeld and his family [10]:-

... Parliament denounced Infeld as a traitor who planned, if he hadn't done so already, to provide Russia with atomic secrets. ... the allegations against Infeld were based on rumour. Even so, his photograph was splashed across the nation's newspapers, his family was harassed, and in 1950 he moved to Poland, his country of birth. His Canadian citizenship and that of his young Canadian-born children were revoked.

G de B Robinson writes in [8]:-

Infeld returned to Warsaw in 1950 as a member of the Praesidium of the newly formed Polish Academy and Head of the Institute of Theoretical Physics as well as Director of the same Institute in the University. He who had been ignored before the war was now accorded the highest honours. The years 1950 - 68 were full of scientific activity as evidenced by the publication of more than forty papers and the book with J Plebanski 'Motion and relativity' in 1960. ... but the withdrawal of [Canadian] citizenship of his two children, born in Toronto, came as a cruel blow.

The important book Motion and relativity referred to in this quote is an important monograph. Here is a short extract from F A E Pirani's review:-

This is not a general textbook, but a monograph for specialists. In it are collected "final results" of the study, begun by Infeld with Einstein and Hoffmann in Princeton in 1938, and carried on by him with his students in Warsaw during the last decade, of the problem of motion in the general relativity theory of gravitation. The "problem of motion" is the problem of determining the motion, in their mutual fields, of gravitating particles of given structure. The problem is a substantial one, because the field equations are non-linear, and because they are connected by differential identities. ...

He end his review with the words:-

The whole book bears the marks of the senior author's vigorous and enthusiastic style. It will have permanent value, in any serious library of the subject, as a definitive, detailed account of this part of general relativity theory.

Infeld's return to Poland had been greatly welcomed but life under the Communist regime became increasingly difficult. Gajewski, who was his student in Warsaw, tells in [5] of investigations by the Polish security police into Infeld. He writes of Infeld's final years [5]:-

I did not talk politics with Infeld when he was at the height of his political power. I did toward the end of his life. He was utterly disillusioned with the regime, disappointed in its policies towards science and culture, disgusted with the raging official anti-Semitism. Despite failing health, and at a considerable personal risk, he was willing to publicly join in major initiatives protesting the policies of the government. Those initiatives were the precursors to the formation of the Worker's Defence Committee which, in turn, was the precursor to Solidarity. And the rest, as they say, is history.

Gajewski describes Infeld as a teacher [5]:-

Infeld was an inspired, and inspiring, teacher. Lecturing mostly without notes, he would meticulously cover the blackboard with calligraphic formulas. He used tensor notation at that time a novelty to me. (Infeld liked to quip that mankind can be classified into two categories: those who knew what a tensor was, and all the rest; and he would add "I don't much care about that rest".)