恩里科·费米Enrico Fermi

恩里科·费米的父亲是Alberto Fermi，母亲是艾达·德·加蒂斯。艾达是一位杰出的人，是一位军官的女儿。她接受过学校教师培训，一生大部分时间在小学教书。她非常聪明，在1898年与阿尔贝托结婚后，对孩子们产生了主要影响。艾达结婚时27岁，但她的丈夫阿尔贝托41岁。他曾在意大利各地的铁路公司工作，但于1888年搬到了罗马。他在与艾达结婚的那一年被提升为检查员，到职业生涯结束时，他已在当时国有的铁路公司中发挥了重要作用。费米是他父母的第三个孩子，有一个姐姐玛丽亚（生于1899年）和一个哥哥朱利奥（生于1900年）。按照当时的习俗，费米在约30个月大之前由保姆在家庭之外抚养。之后，尽管家庭并不宗教（这使阿尔贝托的家庭感到不安，除了阿尔贝托外，他们都是虔诚的天主教徒），他还是被严格抚养长大。

当他六岁时，费米开始上一所小学，这所学校之所以被选中，是因为它是一所世俗学校。他展现出极大的天赋，尤其是在数学方面，到十岁离开小学时，他已经在琢磨方程$x^{2} + y^{2} = r^{2}$如何表示一个圆。随后他在文科中学学习了五年，又在高中学习了三年，为进入大学做准备。在整个教育过程中，他都是一名杰出的学生，显然是班上最有能力的。他热爱科学，花了很多时间与Maria和Giulio一起制作电动机和机械玩具。1915年1月，当费米14岁时，家庭遭遇了悲剧，Giulio在接受一次咽喉脓肿的小手术时去世。这当然对费米产生了深远而持久的影响，他本来就有些内向，变得更加不爱交际。此时他与同班的费米 Persico成为了朋友。Persico后来也成为了理论物理学教授，他后来写道（例如见[4]）：

我们养成了长时间一起散步的习惯，穿过罗马城从一边走到另一边，以年轻人特有的莽撞讨论各种话题。但在这些青春期的交谈中，费米带来了思想的精确、自信和独创性，不断让我感到惊讶。此外，在数学和物理学方面，他展现出的知识远远超出了学校所教的内容。他了解这些主题不是以学究的方式，而是能够极其自如和熟悉地运用它们。对他来说，即使在这个时候，知道一个定理或定律主要意味着知道如何使用它。

进入比萨高等师范学校是通过竞争性考试。费米于1918年11月14日参加了考试，并就给定的主题Characteristics of sound写了一篇文章。在文章中，费米推导了振动杆的偏微分方程组，然后使用傅里叶分析来求解它们。这篇文章的水平堪比博士论文，而非学校考试。当考官读到费米的答卷时，他如此惊讶，以至于安排了一次与他的会面，告诉他这无疑会赢得竞赛，而且费米毫无疑问会成为一位著名科学家。

费米由物理实验室主任Luigi Puccianti指导。也许我们应该澄清这一说法，因为尽管Puccianti名义上担任这一角色，但他承认自己几乎没有什么可以教给费米的，而且他经常请费米教他一些东西。很快费米就开始发表论文，他的第一篇Sulla dinamica di un sistema rigido di cariche elettriche in moto traslatorio Ⓣ（《论平移运动中刚性电荷系统的动力学》）于1921年发表。1921年的另一篇出版物之后，次年发表了他早期最重要的论文，即Sopra i fenomeni che avvengono in vicinanza di una lina oraria Ⓣ（《论世界线附近发生的现象》）。这篇论文给出了关于广义相对论几何中世界线附近空间欧几里得性质的重要结果。费米向高等师范学校提交了他的博士论文Un teorema di calcolo delle probabilità ed alcune sue applicazioni Ⓣ（《一个概率定理及其某些应用》），并于1922年7月7日接受了答辩。Laura Fermi在[3]中写到这一事件：

十一位身穿黑色长袍、头戴方顶帽的考官庄严地坐在长桌后面。费米也穿着黑色长袍，站在他们面前，他开始讲话，带着冷静、从容的自信。随着他继续，一些考官抑制着哈欠，一些惊讶地扬起眉毛，另一些则放松下来，不再试图跟上。显然，费米的学识超出了他们的理解。费米以优异成绩获得了学位。但考官中没有人与他握手或祝贺他，大学出版论文的传统荣誉也没有授予他。

这篇学位论文于1962年发表在他的Collected Works上。获得博士学位后，费米回到罗马，开始与那里的数学家合作，特别是Castelnuovo、图利奥·列维-齐维塔和费代里戈·恩里克斯。他还与物理实验室主任建立了联系。1922年10月，他获得了政府奖学金，这使他得以在1923年上半年在哥廷根与马克斯·玻恩合作。随后，他被任命在1923-24学年在哥廷根为科学家教授数学。1924年夏天在多洛米蒂山徒步旅行后，他前往莱顿与保罗·埃伦费斯特合作。他回到意大利开始1924-25学年，并在该学年及随后一学年担任佛罗伦萨大学数学物理与力学的临时讲师。此时，费米正试图最大限度地提高自己获得学术职位的机会，因此发表了大量论文。在撒丁岛卡利亚里大学数学物理讲席的竞争中输给Giovanni Giorgi，他感到很失望。值得注意的是，图利奥·列维-齐维塔和维多·沃尔泰拉都支持费米。也许费米落选是件好事，因为1926年又宣布了另一场竞争，这次是罗马大学理论物理讲席。这一次，尽管对于这样的职位来说他还非常年轻，费米仍被委员会任命，委员会认可了他科学工作的卓越质量。

费米 开始建设物理研究所，他刚到任时该研究所小得令人惊讶。费米 于 1928 年 7 月 19 日与 Laura Capon 结婚；他们有一个女儿 Nella，生于 1931 年 1 月 31 日，一个儿子 Giulio，生于 1936 年 2 月 16 日。1929 年，他当选为 Accademia dei Lincei 院士。嗯，这并不完全准确，因为墨索里尼未经选举就任命他为 科学院 院士。当然，从学术角度他理应获得这一荣誉，但不应因此认为他被墨索里尼任命就意味着 费米 支持法西斯主义。也许更可能的是，由于 费米 相当不涉政治，墨索里尼觉得至少他不是在任命一个政治对手。Academy 的任命为 费米 提供了大幅增加的薪水。他于 1930 年首次访问美国，访问了安娜堡的密歇根大学。他与从荷兰搬到那里的 乔治·乌伦贝克 进行了有趣的讨论，保罗·埃伦费斯特 也在夏天加入了他们。费米 讲授了量子理论。

1934年，费米完成了他在中子产生的人工放射性方面最重要的工作。他将此发表在Radioattività indotta dal bombardamento di neutronⓉ（由中子轰击引起的放射性）（1934年）以及Artificial radioactivity produced by neutron bombardment（1934年、1935年）在Proceedings of the Royal Society of London和On the absorption and diffusion of slow neutrons（1936年）上的进一步论文中。这项工作导致了核裂变的发现，实验人员能够利用他的结果创造新元素。费米于1938年被授予诺贝尔物理学奖。授奖词称该奖项是——

……以表彰他证明了由中子辐照产生的新放射性元素的存在，以及他关于慢中子引起的核反应的相关发现。

另一篇重要论文由费米于1935年发表，是Sulla quantizzazione del gas perfetto monoatomicoⓉ（论单原子理想气体的量子化）。在这篇论文中，他提出了费米统计，给出了原子和原子核的统计模型。

1938年夏天，墨索里尼突然效仿德国的希特勒，开始了一场反对犹太人的运动。费米不是犹太人，但他的妻子是，而且尽管他的两个孩子是罗马天主教徒，家庭的处境还是变得不自在。费米决定写信给美国的大学寻找职位。他完全秘密地做这件事，因为担心如果当局知道他的意图，他会被阻止。他写信给各个大学，并把它们全部投递到不同的城镇，以免引起怀疑。他收到了五份聘书，并接受了哥伦比亚大学的那一份。诺贝尔奖的授予证明是这个家庭离开意大利并前往斯德哥尔摩参加颁奖典礼，然后直接前往美国的绝佳机会。有趣的是，费米在获得美国签证之前必须通过一项算术测试。他于1939年1月2日与家人抵达纽约。

费米在哥伦比亚大学的工作，与团队其他成员合作，很快展示了其研究的可能应用。哥伦比亚大学物理学教授George Pegram于1939年3月16日写信给海军部的Hooper海军上将（例如见[4]）：——

哥伦比亚大学物理实验室的实验表明，可以找到某些条件，使化学元素铀能够释放其大量过剩的原子能，这可能意味着铀有可能被用作炸药，每磅释放的能量是任何已知炸药的一百万倍。

铀计划过了一段时间才真正启动，但巧合的是，在1941年12月珍珠港事件的前一天，做出了投入巨大努力的决定。该项目将在芝加哥大学进行，包括费米在哥伦比亚大学的小组在内的多个小组被集中到那里。由于多种原因，这并不太合费米的心意。首先，他在哥伦比亚大学非常愉快；其次，这使他更像一个管理者而不再是科学家；第三，一旦美国与意大利交战，意大利人就被归类为“敌国侨民”，在美国境内受到严格的旅行限制。然而，困难被克服了，到1942年夏天，费米已在芝加哥。1942年12月2日，由费米领导的团队实现了首次受控核能释放——说一个新时代已经开始，这或许并非夸大其词。1944年，费米成为美国公民，并于当年开始全面参与洛斯阿拉莫斯制造炸弹的项目。他在洛斯阿拉莫斯为参与该项目的科学家讲授了多门课程。

战争结束后，费米决定他想回到大学生活。他于1945年接受了芝加哥大学的教授职位。在接下来的几年里，他进行研究，对宇宙射线的起源产生了兴趣，他还研究π介子-核子相互作用，试图在理解强相互作用方面取得进展。他进行了许多研究访问，如洛斯阿拉莫斯，他每年都去，华盛顿大学（1947年），加利福尼亚大学乔治·伯克利分校（1948年）和布鲁克黑文国家实验室（1952年）。他参加了1949年在意大利科莫举行的高能物理会议。这是他十多年前离开欧洲后第一次回到欧洲。在这次旅行中，他还在Accademia dei Lincei演讲，由Castelnuovo主持会议。

1954年夏天，费米回到意大利，在科莫湖畔瓦伦纳的修道院别墅进行了一系列讲座。随后，他前往法国夏蒙尼附近的一所暑期学校。他试图保持一贯精力充沛的生活方式，在山中散步并从事体育运动。然而，他显然正遭受医生未能诊断出的健康问题。回到芝加哥后，医生诊断出胃癌并进行了手术。他挺过了手术并回到家中。他曾告诉朋友，如果他能有足够的时间，他将把自己的核物理课程整理成书，作为对科学的最后贡献。他只来得及为该课程写了一份不完整的内容目录。尤金·维格纳写道：-

在费米去世前十天，他告诉我：“我希望不会太久。”他已完全坦然接受了自己的命运。

E Sergè写道[4]：-

他直到最后都保持着几乎超人的勇气、性格力量和思维清晰。

费米被安葬在芝加哥的橡树林公墓。

Enrico Fermi's father was Alberto Fermi and his mother was Ida de Gattis. Ida was a remarkable person who was the daughter of an army officer. She trained as a school teacher and taught in elementary schools for most of her life. Highly intelligent, she was the major influence on her children after her marriage to Alberto in 1898. Ida was 27 years old when she married but her husband Alberto was 41. He worked for railway companies in various parts of Italy but had moved to Rome in 1888. He was promoted to inspector in the year he married Ida and by the end of his career he had risen to play a major role in what was by that time the state owned railway company. Enrico was the third of his parents' children having an older sister Maria (born in 1899) and older brother Giulio (born in 1900). In line with the custom of the time, Enrico was brought up by a nurse away from the family until he was about 30 months old. He was then strictly brought up although the family were not religious (something which upset Alberto's family who were all devout Catholics except Alberto).

When he was six years old Enrico began to attend an elementary school which was chosen because it was a secular establishment). He showed great talents, especially in mathematics and by the time he left elementary school at the age of ten he was puzzling out how the equation $x^{2} + y^{2} = r^{2}$ represented a circle. He then spent five years at the ginnasio and then a further three years at the liceo preparing to enter university. He was an outstanding student throughout his education being clearly the most able in his class. He enjoyed science and spent much time building electric motors and mechanical toys with Maria and Giulio. In January 1915, when Enrico was 14, tragedy struck the family when Giulio died undergoing a minor operation for a throat abscess. This, of course, had a deep and lasting affect on Enrico who, already somewhat introverted, became even less outgoing. At this time he became friends with Enrico Persico, who was in the same class as school. Persico, who also went on to become a professor of theoretical physics, later wrote (see for example [4]):-

We formed the habit of taking long walks together, crossing the city of Rome from one side to the other, discussing all kinds of subjects with the brashness characteristic of youth. But in these adolescent talks Enrico brought a precision of ideas, a self-assurance, and an originality which continually surprised me. Furthermore, in mathematics and in physics he showed knowledge of many subjects well beyond what was taught at school. He knew these topics not in a scolastic fashion, but in such a way that he could use them with extreme facility and familiarity. For him, even at this time, to know a theorem or law meant chiefly to know how to use it.

Entry to the Scuola Normale Superiore in Pisa was by competitive examination. Fermi sat the exam on 14 November 1918 and wrote an essay on the given theme of Characteristics of sound. In his essay Fermi derived the system of partial differential equations for a vibrating rod, then used Fourier analysis to solve them. It was written at the level of a doctoral thesis rather than a school examination. When the examiner read Fermi's entry he was so amazed that he set up a meeting with him, telling him that it would undoubtedly win the competition and moreover that Fermi would without doubt become a famous scientist.

In Pisa Fermi was advised by the director of the physics laboratory Luigi Puccianti. Perhaps we should clarify this statement, for although Puccianti nominally had this role he acknowledged that there was little that he could teach Fermi, and frequently he asked Fermi to teach him something. Soon Fermi was publishing papers, his first Sulla dinamica di un sistema rigido di cariche elettriche in moto traslatorio Ⓣ being published in 1921. Another publication in 1921 was followed by the most important of his early papers in the following year, namely Sopra i fenomeni che avvengono in vicinanza di una lina oraria Ⓣ. This paper gave an important result about the Euclidean nature of space near a world line in the geometry of general relativity. Fermi submitted his doctoral thesis Un teorema di calcolo delle probabilità ed alcune sue applicazioni Ⓣ to the Scuola Normale Superiore and was examined on 7 July 1922. Laura Fermi writes about this event in [3]:-

The eleven examiners in black togas and square-topped hats were sitting in solemn dignity behind a long table. Fermi, also in a black toga, stood in front of them, and he started talking with cool, deliberate assurance. As he proceeded, some of the examiners repressed yawns, some sent their brows up in wonder, others relaxed and did not try to follow. Clearly Fermi's erudition was above their comprehension. Fermi received his degree magna cum laude. But none of the examiners shook hands with him or congratulated him, and the customary honour of having the thesis published by the university was not conferred upon him.

The thesis was published in his Collected Works in 1962. After the award of his doctorate Fermi returned to Rome and began working with the mathematicians there, particularly Castelnuovo, Levi-Civita and Enriques. He also made contact with the director of the physics laboratory. In October 1922 he was awarded a Government Scholarship which enabled him to work with Max Born in Göttingen in the first half of 1923. He was then appointed to teach mathematics to scientists in Göttingen during the academic year 1923-24. After spending the summer of 1924 hiking in the Dolomites, he went to Leiden to work with Ehrenfest. He returned to Italy for the start of academic year 1924-25 and he spent that academic year and the following one as a temporary Lecturer in Mathematical Physics and Mechanics at the University of Florence. At this point Fermi was trying to maximise his chances of an academic career so he published a large number of papers. He was disappointed to lose out to Giovanni Giorgi in the competition for the chair of mathematical physics at the University of Cagliari in Sardinia. It is worth noting that both Levi-Civita and Volterra supported Fermi. Perhaps it was good that Fermi lost for in 1926 another competition was announced, this time for the chair of theoretical physics at the University of Rome. This time, despite being very young for such a position, Fermi was appointed by the committee which recognised the exceptional quality of his scientific work.

At Rome Fermi began to built up the physics institute, which was surprisingly small when he arrived. Fermi married Laura Capon on 19 July 1928; they had one daughter Nella born 31 January 1931 and one son Giulio born on 16 February 1936. In 1929 he was elected to the Accademia dei Lincei. Well this is not quite accurate since Mussolini appointed him to the Academy without an election. Certainly he deserved the honour on academic grounds but one should not assume that his appointment by Mussolini meant that Fermi supported fascism. Perhaps it is more likely that because Fermi was pretty non-political, Mussolini felt that at least he was not appointing an political opponent. The Academy appointment provided Fermi with a substantially additional salary. He made his first visit to the United States in 1930 when he visited the University of Michigan at Ann Arbor. He had interesting discussions with George Uhlenbeck, who had moved there from Holland, and Ehrenfest joined them over the summer. Fermi gave lectures on quantum theory.

In 1934 Fermi carried out his most important work on the artificial radioactivity produced by neutrons. He published this in Radioattività indotta dal bombardamento di neutron Ⓣ (1934) and in further papers Artificial radioactivity produced by neutron bombardment (1934, 1935) in the Proceedings of the Royal Society of London and On the absorption and diffusion of slow neutrons (1936). This work led to the discovery of nuclear fission and experimentalists were able to use his results to create new elements. Fermi was awarded the Nobel Prize in Physics in 1938. The citation states that the award is:-

... for his demonstrations of the existence of new radioactive elements produced by neutron irradiation, and for his related discovery of nuclear reactions brought about by slow neutrons.

Another important paper, published by Fermi in 1935, was Sulla quantizzazione del gas perfetto monoatomico Ⓣ. In this paper he presented Fermi statistics, giving a statistical model of the atom and nucleus.

In the summer of 1938 Mussolini suddenly followed Hitler in Germany in starting a campaign against Jews. Fermi was not Jewish but his wife was and, although his two children were Roman Catholics, the family's situation became uncomfortable. Fermi decided to write to universities in the United States looking for a position. He did this with complete secrecy for fear that he would be prevented if the authorities learnt of his intentions. He wrote letters to various universities and posted them all in different towns not to arouse suspicions. He received five offers and accepted the one from Columbia University. The award of the Nobel Prize proved a wonderful opportunity for the family to leave Italy and travel to the presentation ceremony in Stockholm, then go straight on to the United States. Amusingly, Fermi had to pass an arithmetic test before being granted a visa for the United States. He arrived with his family in New York on 2 January 1939.

Fermi's work at Columbia University, in collaboration with other members of his team, soon showed possible applications of his research. George Pegram, professor of physics at Columbia, wrote to Admiral Hooper in the Navy Department on 16 March 1939 (see for example [4]):-

Experiments in the physics laboratories at Columbia University reveal that conditions may be found under which the chemical element uranium may be able to liberate its large excess of atomic energy, and that this might mean the possibility that uranium might be used as an explosive that would liberate a million times as much energy per pound as any known explosive.

It took a while for things to get moving on the uranium project but a decision to make a major effort was taken, by coincidence, the day before Pearl Harbour in December 1941. The project was to be carried out at the University of Chicago with various groups, including Fermi's group at Columbia, being brought together there. This was not greatly to Fermi's liking for a number of reasons. First he was very happy at Columbia University, second it made him more of an administrator and less of a scientist, and thirdly once the United States was at war with Italy, Italians were classed as 'enemy aliens' and severe travel restrictions within America were imposed. However, the difficulties were overcome and by the summer of 1942 Fermi was in Chicago. On 2 December 1942 the team, headed by Fermi, achieved the first controlled release of nuclear energy - it is probably not an understatement to say that a new era had begun. In 1944, Fermi became American citizen and in that year he began to take a full part in the Los Alamos project to build a bomb. He taught various courses at Los Alamos for the scientists taking part in the project.

After the war ended Fermi decided that he wanted to return to university life. He accepted the offer of a professorship at the University of Chicago in 1945. Over the next few years he undertook research, becoming interested in the origin of cosmic rays and he also worked on pion-nucleon interaction trying to make progress on understanding strong interactions. He made many research visits such as Los Alamos, which he visited every year, the University of Washington (1947), the University of California at Berkeley (1948) and the Brookhaven National Laboratory (1952). He attended a high-energy physics conference in Como, Italy, in 1949. This was his first trip back to Europe since he left over ten years before. During this trip he also lectured to the Accademia dei Lincei with Castelnuovo chairing the meeting.

In the summer of 1954 Fermi returned to Italy and gave a series of lectures in the Villa Monastero in Varenna on Lake Como. He then went on to a summer school near Chamonix in France. He tried to follow his usual energetic life style with walks in the mountains and playing sports. However, he was clearly suffering from health problems which doctors had failed to diagnose. Back in Chicago doctors diagnosed stomach cancer and an operation was carried out. He survived the operation and returned home. He had told his friends that he would write up his course on nuclear physics as his last service to science if he was spared long enough. He only managed to write an incomplete page of contents for the course. Eugene Wigner wrote:-

Ten days before Fermi died he told me, 'I hope it won't take long.' He had reconciled himself perfectly to his fate.

E Sergè writes [4]:-

He preserved to the last an almost superhuman courage, strength of character, and clarity of thought.

Fermi was buried in Oak Woods Cemetery in Chicago.