Tech UPTechnologyThe man who knew why the stars shine

The man who knew why the stars shine

In April 1938, two of the giants of modern physics , the Ukrainian Georgi Gamow and the American Edward Teller, organized a conference at the Carnegie Institution in Washington. His goal: to solve the problem of why stars shine. Among the participants was a refugee from Nazi Germany, an expert in nuclear processes and a professor at Cornell University: Hans Bethe . An effervescent thinker, he had an innate talent for physics and mathematics ; it seemed that he was playing with numbers and letters.

At the meeting in Washington, astronomers told physicists everything they knew about the internal constitution of stars, which was a lot, and that without really knowing how the energy inside them was generated . One of the classic texts of astrophysics, On the Constitution of the Stars , written by the Englishman Arthur Eddington, perfectly described the internal structure of stars without mentioning anything about the nature of their energy engine. Now it was the turn of the physicists to get to work.

Back at Cornell, Bethe attacked and solved the problem so quickly that Gamow would go so far as to say that he had calculated the answer before the train reached the destination station. Bethe sent the paper describing her finding to Physical Review but was then told by one of her students that the New York Academy of Sciences was offering a $500 prize for the best unpublished paper on energy production in stars . Bethe asked the magazine to return the article, submitted it to the contest, and, of course, won.

The physicist had his reasons for doing so. His mother was still in Germany and although the Nazis agreed to let her out, they asked for $250 if she also wanted to take her furniture. Bethe earmarked half the prize money for it. Only later did he allow his article to be published, for which he won the Nobel Prize in 1967 . Of course, this story would not be complete if we did not mention its controversy . That same year the German Carl Friedrich von Weizsäcker solved the carbon cycle independently. As German physicists recall with some distaste, Bethe’s article reached the Physical Review editorial office on September 7 , while Weizsäcker’s did the same to Zeitschrift für Physik on July 11 , then, strictly speaking, it was Weizsäcker the first to discover it. It is true that Bethe and her collaborator Charles Critchfield had sent on June 23 a paper containing the most important part of their work. However, the Nobel should not have been exclusively for Bethe, but shared with Weizsäcker.

Hans Albrecht Bethe was born on July 2, 1906 in Strasbourg, then in Germany . The son of a physiology professor, he was a sensitive child who escaped loneliness thanks to fairy tales and numbers. His love for the latter turned into a passion, to such an extent that he compulsively memorized train schedules and boarding lists. During his adolescence he was torn between mathematics and physics until he finally forgot about the former because “they seemed to prove things that were obvious”. It should come as no surprise: Bethe’s mathematical ability is legendary . It is said that he worked for hours sitting at a table, with a pile of blank pages on one side and a pile of finished pages on the other, while he filled out a spreadsheet with infinite calm, without making any corrections. When her friend Victor Weisskopf asked her one day how long it would take her to do certain calculations, Bethe replied:

― It would take three days, but it would take you three weeks!

According to Weisskopf, it actually took him three weeks.

In 1928 he obtained his doctorate in theoretical physics under the supervision of Arnold Sommerfeld and after passing through the universities of Frankfurt and Stuttgart, he finished Privatdozent of the University of Munich at the age of 24. Meanwhile, in Germany the anti-Semitic atmosphere was becoming more and more oppressive . Einstein was advised, for his own safety, not to make any public appearances; Sommerfeld smashed a blackboard in class upon discovering that someone had written “Damn Jews!” in it, and Bethe found herself teaching students wearing swastikas. With Hitler’s rise to power, a law was enacted prohibiting Jews and children or grandchildren of Jews from holding public office . Bethe didn’t think of herself as such, but her mother was and she lost her job . Like many others, he left his country, went to England and finally landed in the United States , more specifically in Cornell , in February 1935.

Over the next four years he built an excellent reputation as a nuclear physicist , largely motivated by three monumental articles published in Reviews of Modern Physics known since as “the Bible of Bethe” and, above all, by his exquisite and detailed calculations on nuclear reactions inside stars.

During the Second World War he heard about the atomic bomb construction project : “I considered it something so remote that I completely refused to have anything to do with it”. However, he was willing to contribute to the fight against the Nazis, especially after the fall of France. So in 1942, when Robert Oppenheimer assembled a group of physicists in Berkeley to prepare the design of the bomb, Bethe accepted the invitation . Together with his wife Rose – the daughter of a former professor of his and whom he married in 1939 – they crossed the entire United States by car, from Cornell to California, stopping in Chicago to pick up their great friend Edward Teller and his wife Mici. When Bethe saw the atomic pile built by Fermi, she became convinced that the bomb could work. However, the deep friendship between the two physicists suffered. Oppenheimer had called Bethe to run the theoretical division at Los Alamos—perhaps the most important position within that place “reminiscent of a concentration camp,” according to Fermi’s Jewish wife—and Teller was upset because he thought that position it must have been for him. The tension between the two increased when Teller, who was supposed to lead the group in charge of the implosion calculations, began to focus on the feasibility of a hydrogen bomb.

At the end of the war, Bethe – who earned the nickname ‘The Warship’ at Los Alamos – returned to Cornell. In August 1949 the Soviets made their first nuclear test and Teller asked him to come back to work on the H-bomb. Bethe refused and since then he has been a staunch advocate of peace , opposing the Anti-Ballistic Missile System (ABM) in the 1960s. ABM), in the 1980s to the Star Wars program, and in the 1990s by addressing a letter to President Clinton urging him to stop, not only all nuclear tests, but all “calculations and ideas aimed at producing new types of weapons nuclear”.

This physicist who laid the foundations for quantum electrodynamics by explaining the Lamb shift of the hydrogen spectrum, who had brilliant ideas in collision theory and solid state physics, who predicted the discovery of the pi meson, and who in 1948, as part of a joke devised by Gamow, was listed with Gamow and Ralph Alpher as the author of the famous “alpha-beta-gamma” article on the origin of chemical elements at the time of the Big Bang, died March 6, 2005 at Cornell .

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