汉斯·贝特Hans Bethe

汉斯·贝特于1906年出生在斯特拉斯堡，当时这里是德皇威廉二世的德意志帝国的一部分。如今，斯特拉斯堡作为阿尔萨斯的一部分属于法国，尽管它与德国巴登地区接壤。贝特的父母是阿尔布雷希特，一位医生，和埃拉，她的父亲是斯特拉斯堡大学的医学教授。贝特是独生子，父亲是新教徒，母亲从犹太教改信路德宗，不过宗教在他童年时期绝非主要影响。他的母亲是一位有造诣的音乐家，遗憾的是，就在第一次世界大战前夕，她失去了大部分听力。

可以肯定地说，贝特小时候的数学能力远超他的年龄。他本人和亲戚的回忆包括：他四岁时就能计算平方根，五岁时完全理解分数，七岁时就能找出素数。后者的证据是他能够计算并记住一张包含$2^{14} - 3$和$3^{10} + 2$的素数表。到十四岁时，他已自学了微积分。

但数学和数字的世界并不是他唯一的特长。他很早就学会了写字，不久之后便开始在笔记本上写满故事。一个不寻常之处是，他在一行上从左到右写，然后在下一行从右到左写，他很久以后才知道，古希腊人在他们的一些泥板上也采用这种书写方式。

1924年完成高中学业后，他进入法兰克福大学学习理论物理，因为他觉得：——

……数学似乎能证明那些显而易见的事情。

他的兴趣和能力超出了法兰克福所能提供的范围，有人建议他去慕尼黑，1926年，他在那里开始师从传奇的阿诺·索末菲。到1928年，他以一篇关于晶体中电子衍射的学位论文获得了最优等成绩的博士学位。这篇卓越的学位论文是他最持久、最重要的著作之一。

通过将电子视为波，他意识到波函数必须包含某些与晶体晶格结构具有相同周期性的项。这意味着对于某些入射角，晶格中的电子不存在波函数。这不仅是对固体物理学的重大贡献，也是对量子力学基础的重大贡献，因为它进一步展示了物质波状特性的不寻常后果。

1929年，贝特获得了洛克菲勒基金会奖学金，这使他得以在剑桥与拉尔夫·福勒共事，并在罗马与恩里科·费米共事。在剑桥期间，他与同为访问学者的吉多·贝克和沃尔夫冈·里茨勒合写了一篇关于绝对零度量子理论的论文，结果证明这是一个骗局，目的是让另一位剑桥物理学家（也是拉尔夫·福勒的好友）亚瑟·爱丁顿难堪。亚瑟·爱丁顿刚刚发表了一个精细结构常数的“推导”，而精细结构常数被认为是一个无法推导的实验值。贝特、贝克和里茨勒的这篇论文后来被正式撤回。

那年他在罗马时，贝特发现那里的氛围比剑桥更加不拘礼节。他相当喜欢剑桥，尤其是拉尔夫·福勒，但他与恩里科·费米的关系可以说更加有机，不那么机械。恩里科·费米教会了贝特定性推理的价值，以及物理学不必——事实上should not——是苦差事，而是令人愉快的。在罗马逗留之后，他回到德国，在蒂宾根大学担任讲师直到1933年。

随着1933年希特勒上台和种族法律的颁布，贝特因母亲的犹太血统而失去了工作。阿诺·索末菲确实设法为他争取到了慕尼黑的一个暑期奖学金，但起初几乎没有长期机会。阿诺·索末菲试图为他在曼彻斯特的威廉·劳伦斯·布拉格那里谋得一个职位，但由于一系列不寻常的情况，他最终去了别处。碰巧的是，布拉格访问康奈尔大学的时候，正是贝特在寻找职位的时候，也正是曾与贝特在慕尼黑学习的劳埃德·P·史密斯推荐他填补康奈尔大学一个空缺的理论物理职位的时候。布拉格对贝特评价极高，也转达了阿诺·索末菲的赞扬，于是这份工作就归他了。贝特此后一生都留在康奈尔大学。

贝特的工作逐渐主要集中于核研究。尽管如此，只是在他的朋友Edward Teller一再敦促下，他才参加了1938年专门讨论恒星核心能量产生问题的华盛顿会议。这将成为他一生中的分水岭，因为他终于能够通过将核合成的理论工具应用于该领域迄今收集的数据来解决能量产生问题。正是由于这项工作，他于1967年获得了诺贝尔物理学奖。

这项工作的最高成就是在1939年，当时他在Physical Review上发表了一篇论文，基本上展示了恒星如何发光。然而奇怪的是，他在质子-质子反应方程中省略了中微子。这是因为五年前他与鲁道夫·佩尔斯一起得出结论，认为这样的过程是不可观测的。尽管如此，他的结论——CNO循环驱动了比太阳质量大得多的恒星的能量产生，而$p-p$反应驱动了较轻恒星的能量产生——几乎是每本天文学入门教材的基本内容。

凭借他在固态晶格量子力学方面的工作和在恒星核合成方面的工作，他已经是多个子领域中成就卓著的物理学家。然而，他仍然能够对另一个不同的子领域做出重大贡献：量子电动力学（QED）。

贝特于1931年在访问罗马时从恩里科·费米那里学习了QED，当时他是经由剑桥来的。就在这之后，他为Handbuch der Physik Ⓣ（物理学百科全书）发表了一篇评论，大量涉及氢和氦的量子理论。他在恒星核合成方面工作的种子可以在这里看到，因为这些原子在恒星过程中起着基本作用。他在QED方面的工作包括与Walther Heitler一起计算bremsstrahlung Ⓣ（带电粒子在穿过原子核的电场和磁场后加速或特别是减速时产生的电磁辐射），这也许是20世纪30年代QED中最重要的结果之一。但QED一直是一个有争议的理论，直到1947年，在参加Shelter Island会议后，贝特能够成功地表明QED（特别是源自保罗·狄拉克的电子理论）实际上可以对真实氢原子中的电子跃迁做出准确预测。特别是，他能够成功计算这些原子中的精细结构能级（这似乎与他嘲笑亚瑟·爱丁顿的论文有些矛盾，尽管亚瑟·爱丁顿的方法不寻常且完全错误）。

除了贝特对物理学的理论贡献之外，他还是第二次世界大战期间曼哈顿计划的主要贡献者。在美国参战前后成为美国公民后，他能够参与国防相关项目，并开始在麻省理工学院辐射实验室从事雷达项目。1942年，他说服参加了J Robert Oppenheimer组织的一次夏季研究，这导致1943年成立了洛斯阿拉莫斯实验室，贝特担任理论部主任。他的小组成员中有Edward Teller，当时仍然是他最好的朋友之一。但Teller对开发热核装置（氢弹或H弹）的独特痴迷导致他们的关系冷却（用贝特自己的话来说）。

贝特在他余生中不仅通过直接发表论文，还通过指导康奈尔大学的年轻教职员工，继续为物理学做出贡献。他经常就许多主题（尽管主要是核武器问题）向政府成员提供建议，包括多位总统。他是关注科学家联盟（UCS）的最早成员之一，该联盟部分是为了反对开发反弹道导弹（ABM）而成立的。

弗里曼·戴森记得他总是喜欢被称为“贝特”，并且他有一种不寻常的幽默感，这不仅体现在他与Beck和Reizler的恶作剧出版物中，还体现在他将自己的名字借给一篇他几乎无关的论文（而且是一篇严肃的论文），只是为了让一贯爱开玩笑的George Gamow能够与他的学生Ralph Alpher发表一篇论文，其作者行将写着：R Alpher, H 贝特, and G Gamow。这就是现在著名的（臭名昭著的？）$\alpha, \beta, \gamma$ paper。

贝特在晚年仍然相当活跃，最近参加了几个关于Michael Frayn获奖戏剧Copenhagen的组织论坛。他对物理学界的巨大影响的一个明显迹象是，在他于2005年初去世后，美国物理学会出版的Physics Today整期都献给了他。贝特于1955年荣获马克斯·普朗克奖章，并于1961年获得美国原子能委员会的恩里科·费米奖。1957年，他当选为伦敦皇家学会会士，以及华盛顿特区的国家科学院（美国）成员。

Hans Bethe was born in Strasburg in 1906 which, at the time, was part of the German Empire of Kaiser Wilhelm II. Today, Strasbourg, as part of Alsace, is in France, though it borders the German region of Baden. Hans' parents were Albrecht, a physician, and Ella whose father was a professor of medicine at the university in Strasbourg. Hans was an only child whose father was a protestant and whose mother had converted from Judaism to Lutheranism, though religion was by no means a major force in his childhood. His mother was an accomplished musician who, sadly, lost much of her hearing just prior to World War I.

Hans, it is safe to say, was well above his age in mathematical ability as a child. Recollections of both his own and of relatives include his ability to compute square roots at the age of four, a full understanding of fractions by the age of five, and the ability to find prime numbers by the age of seven. The latter is evidenced by the fact that he was able to compute and memorize a table of primes that included $2^{14} - 3$ and $3^{10} + 2$. By the age of fourteen he had taught himself calculus.

But mathematics and the word of numbers was not his only forte. He learned to write very early and, soon after, began to fill notebooks with stories. In an unusual twist, he wrote first from left to right on one line, and then from right to left on the following line, a manner of writing he much later learned was employed by the ancient Greeks on some of their tablets.

Upon completion of his high school education in 1924, he began attending the University of Frankfurt, studying theoretical physics because he felt:-

... mathematics seemed to prove things that are obvious.

His interest and ability were beyond what Frankfurt could offer and he was advised to go to Münich where, in 1926, he began studying with the legendary Arnold Sommerfeld. By 1928 he had completed his doctorate summa cum laude with a thesis on the diffraction of electrons in crystals. This remarkable thesis was one of his most enduring and important works.

By treating the electrons as waves he realized that the wavefunction had to contain certain terms with the same periodicity as the crystal's lattice structure. This meant that for certain angles of incidence, no wavefunctions existed for an electron in a lattice. This was a major contribution not only to solid state physics but also to the foundations of quantum mechanics as it further demonstrated the unusual consequences of the wave-like properties of matter.

In 1929 Hans was awarded a Rockefeller Foundation fellowship that allowed him to spend time in Cambridge working with Ralph Fowler and time in Rome working with Enrico Fermi. While in Cambridge he coauthored a paper on the quantum theory of absolute zero with fellow visitors Guido Beck and Wolfgang Riezler that turned out to be a hoax concocted to embarrass another Cambridge physicist (and good friend of Fowler's), Arthur Eddington. Eddington had just published a 'derivation' of the fine structure constant which is thought to be an underivable experimental value. The paper by Bethe, Beck, and Riezler was later officially retracted.

While in Rome that year, Hans found the atmosphere even more informal than Cambridge. He enjoyed Cambridge, and particularly Fowler, quite a bit but his relationship with Fermi might be described as having been more organic and less mechanistic. Fermi taught Bethe the value of qualitative reasoning and that physics need not -- in fact should not -- be drudgery, but rather enjoyable. After his stay in Rome, he returned to Germany and served as a lecturer at the University of Tübingen until 1933.

With Hitler's rise to power in 1933 and the enactment of the racial laws, Hans lost his job due to his mother's Jewish heritage. Sommerfeld did manage to secure for him a summer fellowship in Münich but initially few long-term possibilities were forthcoming. Sommerfeld made an attempt to obtain a post for him in Manchester with William Lawrence Bragg, but, thanks to an unusual set of circumstances he was to end up elsewhere. As it happened, Bragg was visiting Cornell at the very time that Hans was searching for a position and at the very time Lloyd P Smith, who had studied with Hans in Münich, recommended him for a vacant theorist position at Cornell. Bragg spoke very highly of Hans, passing along Sommerfeld's praise as well, and the job was his. Hans was to remain at Cornell for the rest of his life.

Hans' work grew to be focused primarily on nuclear research. Despite this it was only after repeated urging on the part of his friend Edward Teller that he attended the 1938 Washington Conference that was dedicated to the problem of energy generation in the cores of stars. It would be a watershed moment in his life for he was able to finally solve the problem of energy generation by applying the theoretical tools of nucleosynthesis to the data that had been so far collected in this field. It was for this work that he won the Nobel Prize in Physics in 1967.

The crowning achievement in this work came in 1939 when he published a paper in Physical Review that essentially showed how stars shine. Oddly, though, he left the neutrino out of the proton-proton reaction equation. This was because he had, with Rudolf Peierls five years earlier, concluded that such a process would be unobservable. Nonetheless, his conclusion -- that the CNO cycle drove energy generation in stars much more massive that the sun while the $p-p$ reaction drove energy production in lighter stars -- is a staple of nearly every introductory textbook on astronomy.

With his work on quantum mechanics in solid state crystal lattices and his work on stellar nucleosynthesis, he was already a highly accomplished physicist in more than one subfield. And yet, he was still able to make significant contributions to yet another distinct subfield: quantum electrodynamics (QED).

Hans had learned QED from Fermi in 1931 while he was visiting Rome, having come by way of Cambridge. It was just after this that he published a review for the Handbuch der Physik Ⓣ dealing heavily with the quantum theory of hydrogen and helium. The seeds of his work in stellar nucleosynthesis can be seen here since these atoms play a fundamental role in stellar processes. His work in QED included the calculation of bremsstrahlung Ⓣ with Walther Heitler, perhaps one of the most important results in QED in the 1930s. But QED was a controversial theory until, in 1947, after attending the Shelter Island Conference, Hans was able to successfully show that QED (particularly as descended from Dirac's theory of the electron) could, in fact, make accurate predictions of electron transitions in real hydrogen atoms. In particular, he was able to successfully calculate the fine structure levels in these atoms (this seems somewhat at odds with his paper mocking Eddington, though Eddington's approach was unusual and not at all correct).

Outside of Hans' theoretical contributions to physics, he was also a major contributor to the Manhattan Project during World War II. Having become a US citizen around the time America entered the war, he was able to participate in defense-related projects and began working on the radar project at MIT's radiation laboratory. He was convinced to participate in a summer study organized by J Robert Oppenheimer in 1942 which led to the creation of Los Alamos Laboratory in 1943 with Hans as head of the theoretical division. Among the members of his group was Edward Teller who was, at the time, still one of his best friends. But Teller's singular obsession with developing a thermonuclear device (the hydrogen or H-bomb) led to a cooling off in their relationship (in Hans' own words).

Hans continued to make contributions to physics not only through direct publication but through his mentoring of younger Cornell faculty members throughout the remainder of his life. He often advised members of the government, including a number of presidents, on numerous topics (though mostly nuclear weapons issues). He was one of the first members of the Union of Concerned Scientists (UCS) founded partly to oppose the development of anti-ballistic missiles (ABMs).

Freeman Dyson remembers he always preferred to be called 'Hans' and that he had an unusual sense of humour, not only evident in his hoax publication with Beck and Reizler, but also in his lending his name to a paper (a serious one at that) he had virtually nothing to do with, simply so the ever-jocular George Gamow could publish a paper with his student Ralph Alpher, whose author line would read: R Alpher, H Bethe, and G Gamow. This is now known as the famous (infamous?) $\alpha, \beta, \gamma$ paper.

Hans remained fairly active well into his later years, most recently participating in several organized forums regarding Michael Frayn's award-winning play Copenhagen. A telling sign of his immense influence on the world of physics was the dedication of an entire issue of Physics Today, published by the American Physical Society, to him after his death in early 2005. Bethe was honoured with the award of the Max Planck Medal in 1955 and the United States Atomic Energy Commission's Enrico Fermi Award in 1961. In 1957 he was elected a fellow of the Royal Society of London, as well as a member of the National Academy of Sciences (United States) in Washington, D.C.