朱利安·施温格Julian Seymour Schwinger

朱利安·施温格在纽约市的公立学校系统中迅速进步。他在纽约市立大学读本科，16岁时发表了他的第一篇物理学论文。当时在哥伦比亚大学领导分子束实验室的教授Isidor I Rabi说服施温格在哥伦比亚攻读博士学位。他于1939年21岁时获得物理学学位论文的博士学位On the Magnetic Scattering of Neutrons。然而，他的论文在获得学位前两三年就已写成，完成正式手续存在问题。乔治·乌伦贝克 [4]解释了施温格获得博士学位的问题：-

我在1938年在哥伦比亚，施温格遇到了麻烦；他无法获得博士学位，因为他没有去听数学家的讲座，也没有足够的学分。所以Rabi告诉施温格，他必须去哥伦比亚听我的讲座；当然，他没有去，因为讲座在清晨，我问Rabi，‘我该怎么办？’。我当然完全愿意给他课程‘A’，因为他需要学分。……他显然和我一样了解——我们像完全平等的人一样交谈。……Rabi说，‘不，你不应该那样做，你应该给他考试，并让它很难。’所以我做了。我们约定了时间，当然他什么都知道。他不知怎么得到了笔记。

获得博士学位后，施温格于1939年至1941年在乔治·伯克利的加利福尼亚大学工作。第一年他是国家研究委员会会士，然后成为J Robert Oppenheimer的助理。1941年，他被任命为普渡大学物理学讲师，次年晋升为助理教授。

在第二次世界大战期间，从1943年开始，施温格从普渡大学请假，被派往麻省理工学院的辐射实验室。后来他被派往芝加哥大学的冶金实验室（原子弹项目），尤金·维格纳在那里工作。施温格不喜欢原子弹的工作，所以他开车去了波士顿，乔治·乌伦贝克在那里从事雷达工作，在辐射实验室。施温格问乔治·乌伦贝克他是否可以在那里工作，并达成了协议。乔治·乌伦贝克说[4]：-

他喜欢这个；他在我的小组里，做了所有这些关于波导的数学问题，这当然非常好。……他是一台真正的计算机，真的非常了不起。他在数学和技术方面真的非常出色。

施温格从[4]开始夜间工作：-

……晚上大约4点钟。我终于让他在4点30分做了一个讨论班。施温格进来时总是上气不接下气，但那时我对他有一定的影响，所以他做了，而且非常认真。

1961年，施温格被普渡大学授予荣誉博士学位。在提名他获得这一学位时，Hubert M James于1960年12月6日写到了施温格的贡献。谈到他在辐射实验室的时光，James写道：-

在辐射实验室期间，施温格发明了电磁场理论中的重要方法，这些方法在波导理论的发展中被广泛采用。他发展了变分技术，在数学物理的几个领域产生了重大进展。更重要的是他对量子电动力学现代形式发展的贡献，通过引入“重整化”技术。由于这项工作，他获得了国家科学院的光之本质奖，并与Kurt 库尔特·弗雷德里希·哥德尔共同获得了首届15000美元的阿尔伯特·爱因斯坦自然科学成就奖。

尽管在普渡大学休假，他还是被提升为那里的理论物理学研究教授。然而，当他完成战时工作后，他辞去了普渡大学的职位，去哈佛大学任职。他从1945年到1972年在哈佛大学工作，先是担任副教授，但在1947年被提升为正教授。他成为正教授的那一年，他与波士顿的Clarice Carrol结婚。

施温格是20世纪40年代上述重整化理论的发明者之一。这一理论允许从远处的视角考虑单个粒子。虚粒子对不是单独考虑的，而是周围的虚粒子影响原粒子的外观。1951年，他提出了今天在量子电动力学中称为施温格效应的东西，即电子-正电子对被电场从真空中吸出。这尚未被实验证实。

1957年，他的理论工作使他得出结论：有两种不同的中微子，一种与电子相关，一种与μ子相关。后来的实验工作证实了这些理论结论。他发明了源理论，统一处理强相互作用粒子、光子和引力子。他对这些思想的发展为所有物理现象提供了一个普遍框架。

施温格因在表述量子电动力学从而调和量子力学与阿尔伯特·爱因斯坦的狭义相对论方面的工作，共同获得了诺贝尔物理学奖（1965年）。这一主题起源于保罗·狄拉克的工作，由共同获得该奖的理查德·费曼独立研究。

在施温格获得诺贝尔奖的场合，伊瓦尔·沃勒所作的介绍演讲将他的工作置于如下背景中：-

原子的电子按照1925年及随后几年建立的量子力学定律运动。对于氢原子，它只有一个电子，因此是理论上研究的最简单原子，计算电子在原子核电场中的运动所得结果如此精确，以至于20年后才在实验上发现该理论的任何误差。然而，这发生在1947年，当时兰姆和他的合作者雷瑟福发现，理论上应当重合的某些氢能级实际上彼此略有偏移。今年诺贝尔奖得主的工作的一项重要成果……是对兰姆位移的解释。……

Almost simultaneously with the discovery of the Lamb-shift another peculiarity was found by Kusch and his collaborator Foley, which made it clear that the magnetic moment of the electron is somewhat larger than had been assumed before. Using the method of renormalization which he also developed Schwinger was able to prove that a small anomalous contribution should be added to the value of the magnetic moment accepted until then. His calculation agreed with the experiments. Schwinger's calculation was indeed earlier than and very important for the proper interpretation of these measurements。

施温格在几篇基础性论文中发展了新量子电动力学的形式体系……他还使这一形式体系更便于实际计算。

从1972年到1994年去世，施温格在加利福尼亚大学洛杉矶分校工作。他备受尊敬，是一位极具天赋的讲师，并指导了一系列令人印象深刻的研究生。在他的职业生涯中，他指导了70多名博士生，其中3人获得了诺贝尔奖。

施温格给予学生的远不止研究上的指导。他给予他们深刻的理解和对该领域的精通，使每个人都能成为独立的科学家，而不是施温格的追随者。

尽管取得了如此显著的成就，随着年龄增长，他在工作中变得越来越孤独。这意味着他对后来的发展没有产生人们所期望的那样大的影响。

2的封面说明对他的贡献作了如下概述：-

施温格是二十世纪最重要、最有影响力的科学家之一。他的贡献清单令人惊叹，从早期导致施温格作用原理、欧几里得量子场论和标准模型起源的工作，到后来关于磁荷和卡西米尔效应的有价值工作。

在[5]中，他被描述如下：-

施温格的遗产远远超出他发表的工作。他的讲座优雅、清晰且富有原创性（他从不以同样的方式做两次同样的事），既是艺术作品也是物理学作品。

诺贝尔物理学奖当然不是施温格获得的唯一荣誉。相反，他获得了许多荣誉，其中一些我们已在上文提到，包括首届阿尔伯特·爱因斯坦奖（1951年）、国家科学奖章（1964年）、普渡大学（1961年）和哈佛大学（1962年）的名誉博士学位，以及美国国家科学院的光之本质奖（1949年）。

Julian Schwinger progressed rapidly through the public school system of New York City. He was an undergraduate at the City College of New York where he published his first physics paper at the age of sixteen. Isidor I Rabi, the professor who led the molecular beam laboratory at Columbia University at this time, persuaded Schwinger to study for his doctorate at Columbia. He received his doctorate in 1939 at the age of 21 for a dissertation in physics On the Magnetic Scattering of Neutrons. However, his thesis had been written two or three years before he was awarded the degree, there being problems in completing the formalities. Uhlenbeck [4] explained about Schwinger's problems in obtaining his doctorate:-

I was in Columbia in 1938 and Schwinger was in trouble; he couldn't get his Ph.D. because he didn't go to lectures of the mathematicians and he didn't have enough credits. So Rabi had told Schwinger that he had to go to my lectures at Columbia; of course, he didn't because it was early in the morning, and I asked Rabi, 'What shall I do?'. I was of course perfectly willing to give him an 'A' on the course because he needed the credits. ... He clearly knew as much as I did - we talked as complete equals. ... Rabi said, 'No, you shouldn't do that, you should give him an exam and make it a tough one.' So I did. We made an appointment, and of course he knew everything. He somehow had got the notes.

After the award of his doctorate Schwinger worked at the University of California, Berkeley from 1939 to 1941. During the first year he was a National Research Council Fellow and then he became J Robert Oppenheimer's assistant. In 1941 he was appointed as an instructor in physics at Purdue University and the following year he was promoted to Assistant Professor.

During World War II, beginning in 1943, Schwinger was given leave of absence from Purdue and was sent to the Radiation Laboratory in the Massachusetts Institute of Technology. Later he was sent to the Metallurgical Laboratory (atom-bomb project) of the University of Chicago where Wigner was working. Schwinger did not like the work on atomic bombs so he got in his car and drove to Boston where Uhlenbeck was working on radar at the Radiation Laboratory. Schwinger asked Uhlenbeck if he could work there and it was agreed. Uhlenbeck said [4]:-

And that he liked; he was in my group and he did all these mathematical problems on wave guides which was very good, of course. ... He was a real computer, really remarkable. He was mathematically and technically really remarkably good.

Schwinger worked at night beginning [4]:-

... in the evening at about 4 o'clock. I finally got him to give a seminar at 4.30. Julian was always out of breath when he came in, but then I had a certain influence on him so he did it and very conscientiously.

In 1961 Schwinger was awarded an honorary doctorate from Purdue. In nominating him for this degree Hubert M James wrote on 6 December 1960 about Schwinger's contributions. Speaking of his time in the Radiation Laboratory James wrote:-

While at the Radiation Laboratory Schwinger invented important methods in electromagnetic field theory, which were extensively employed in the development of the theory of wave guides. He developed variational techniques that produced major advances in several fields of mathematical physics. Still more important were his contributions to the development of the modern form of quantum electrodynamics, through introduction of the "renormalization" technique. For this work he received the Nature of Light Award of the National Academy of Sciences, and shared with Kurt Gödel the first award of the $15 000 Albert Einstein Prize for achievement in Natural Science.

Despite being on leave of absence at Purdue he was promoted to Research Professor in Theoretical Physics there. However, when he had finished his war work he resigned his position at Purdue to take up a post at Harvard. He worked at Harvard University from 1945 to 1972, first as an Associate Professor but being promoted to full Professor in 1947. The year he became a full professor he married Clarice Carrol of Boston.

Schwinger was one of the inventors in the 1940s of the theory of renormalization, mentioned above. This theory allows individual particles to be considered from a distant viewpoint. Virtual particle pairs are not considered individually but rather surrounding virtual particles influence the appearance of the original particle. In 1951 he proposed, what is today called the Schwinger effect in quantum electrodynamics, where electron-positron pairs are sucked out of a vacuum by an electric field. This has not yet been confirmed by experiment.

In 1957 his theoretical work led him to conclude that there were two different neutrinos one associated with the electron and one with the muon. Later experimental work has verified these theoretical conclusions. He invented source theory, which deals uniformly with strongly interacting particles, photons, and gravitons. His development of these ideas provided a general framework for all physical phenomena.

Schwinger was joint winner of the Nobel Prize for Physics (1965) for his work in formulating quantum electrodynamics and thus reconciling quantum mechanics with Einstein's special theory of relativity. This topic, originating with the work of Dirac, was independently studied by Feynman who was a joint winner of the prize.

The Presentation Speech given by Ivar Waller on the occasion when Schwinger received the Nobel Prize put his work in context as follows:-

The electrons of an atom move according to the laws of quantum mechanics established in 1925 and the next following years. For the hydrogen atom, which has only one electron and consequently is the simplest atom to investigate theoretically, the calculation of the motion of the electron in the electric field of the nucleus led to results of such accuracy that 20 years elapsed until any error of the theory could be found experimentally. This occurred, however, in 1947 when Lamb and his collaborator Retherford discovered that some energy levels of hydrogen which should coincide theoretically were in fact somewhat shifted relative to each other. One important result of the work of this year's Nobel Prize winners ... was the explanation of the Lamb-shift. ...

Almost simultaneously with the discovery of the Lamb-shift another peculiarity was found by Kusch and his collaborator Foley, which made it clear that the magnetic moment of the electron is somewhat larger than had been assumed before. Using the method of renormalization which he also developed Schwinger was able to prove that a small anomalous contribution should be added to the value of the magnetic moment accepted until then. His calculation agreed with the experiments. Schwinger's calculation was indeed earlier than and very important for the proper interpretation of these measurements.

Schwinger had developed the formalism of the new quantum electrodynamics in several fundamental papers .... He has also made this formalism more useful for practical calculations.

From 1972 until his death in 1994 Schwinger worked at the University of California, Los Angeles. He was enormously respected, was a highly gifted lecturer, and supervised a string of impressive graduate students. Over his career he supervised over 70 doctoral students, 3 of whom have received Nobel prizes.

Schwinger gave his students much more than guidance on their research. He gave them a depth of understanding and a mastery of the field which permitted each to become not a Schwinger disciple, but an independent scientist.

Despite this remarkable record of achievements, he tended to become more and more solitary in his work as he grew older. This meant that he did not have as much impact on the later developments as one would have expected.

The cover notes of [2] give this summary of his contributions:-

Schwinger was one of the most important and influential scientists of the twentieth century. The list of his contributions is staggering, from his early work leading to the Schwinger action principle, Euclidean quantum field theory, and the genesis of the standard model, to later valuable work on magnetic charge and the Casimir effect.

In [5] he is described as follows:-

Julian Schwinger's legacy goes far beyond his published work. His lectures were elegant, lucid and original (he never did anything the same way twice), works of art and physics both.

The Nobel Prize for Physics was certainly not the only honour Schwinger received. On the contrary he received many honours, some of which we have already mentioned above, including the first Einstein Prize (1951), the National Medal of Science (1964), honorary doctorates from Purdue University (1961) and Harvard University (1962), and the Nature of Light Award of the National Academy of Sciences of the United States (1949).