Hans Bethe: The discoverer of the Sun's secret

Just losing more than a year ago, he was one of the great theoretical physicists of our time, who in the 30s of the last century found nuclear reactions, discovering secrets. classified the huge energy of stars.

With the computation and explanation of Lamb's shift, he is widely regarded as the father of quantum field theory. His life also has many paradoxes. The skinny man with this sickly but humorous smile was the head of the theoretical physics department at Los Alamos during the period of the US deployment of the wartime Manhattan program.

Once an important figure involved in the construction of the first atomic bombs, but after the war, Bethe became a talented orator, fighting against nuclear weapons during the negotiation period. in Geneva to go to the east-west peace treaty, disarmament.

Hans Bethe (1906 - 2005) - (Photo: aapt.org)

Born on July 2, 1906 in Strasburg , the son of a university lecturer, Bethe studied in Munich and Frankfurt and later became a lecturer in Munich and Tubingen in the years 1930-1933. Although Bethe's mother was Jewish, he avoided the Nazi persecution and discrimination. Receiving a scholarship from the Rockefeller Foundation, Bethe and friend Rudolf Peierls went to Rome and Cambridge in turn to escape Hitler's suffocating Germany. In the UK, Bethe became a University of Manchester lecturer for a year, sharing a rented house with the Peierls family and having to travel six miles every day to an old bicycle. Later, he also found a similar position at Bristol University.

At that time, astrophysics still had a difficult problem without a solution. This problem was raised by Arthur Eddington in the 1920s, challenging the physical world. That's how stars can continuously emit enormous energy in billions of years without being turned off? It has been thought that energy can be the kinetic energy produced when matter falls into each other under the effect of a large gravitational field. But calculations have shown that such a source of energy is only enough to provide a star like the Sun within a few million years. So the huge energy source of the stars is still a mystery.

In 1935, Bethe moved Bristol to Cornell University (USA), and he found that the answer was hidden in the complexes of high-energy nuclear processes. Bethe studied thoroughly all that was known about the atomic nucleus. He wrote a series of three articles on nuclear physics. These articles soon became famous and classic works, also known as " Bethe Bible ".

He pointed out that there must be two processes here: at extremely high temperatures, carbon can act as a nuclear catalyst, which promotes the synthesis of hydrogen atoms into helium. and produce enormous energy due to the mass block. The carbon cycle proposed by Bethe was published in 1938, explaining the great life of extremely hot stars. Bethe also showed that, at lower temperatures, under the same pressure and density as the Sun, a series of events could lead to the direct incorporation of hydrogen atoms to form helium and solution. release lots of energy. This mechanism is close to the working principle of H-bombs (people are still looking for ways to control this kind of nuclear fusion to serve energy needs). With thermonuclear reactions, the lifespan of the stars could reach billions of years, and Bethe's solution was actually verified.

In September 1939, Hitler's army attacked Poland, triggering an outbreak of World War II. Many talented physicists have run to America. Bethe was then invited to be an adviser to the US Defense Research Council. He also worked as a researcher at the Radiation Laboratory at the Massachusetts Institute of Technology.

Bethe's most notable activity in the early 1940s was to participate in the summer research program in Berkeley in 1942 . J. Robert Oppenheimer formed a research group on the feasibility of an atomic weapon. In addition to Bethe, the team includes many other talented physicists such as Edward Teller, Felix Bloch and Emil Konopinski. They established a theoretical basis for the construction of the atomic bomb. In the winter of 1942, the US began to deploy the " Medical Program " in Los Alamos under the command of General Leslie R. Groves and Oppenheimer. Teller tried to convince Bethe to join the program. At first Bethe hesitated, but in the end he accepted it. Oppenheimer let him be the head of the theory department, a position that Teller had coveted. This caused Teller 's affection for Bethe for decades.

Physicist Hans Bethe was awarded the Nobel Prize for the discovery of the star's energy source in 1967 (Photo: Cornell.edu)

After the war, Bethe returned to Cornell and became a very enthusiastic participant in community movements. He propagated much about controlling atomic energy for civilian purposes, also writing articles and talking about the dangers of nuclear war. Bethe also continued to pursue her career in basic scientific research. In 1947, he published a theoretical calculation of the Lamb shift, explaining the shift in the energy levels of electrons in hydrogen atoms. This study of Bethe started the field of quantum electrodynamics, which is the first and very classic calculation of quantum field theory.

In 1949, the Soviet Union successfully tested the atomic bomb. The United States urgently promotes the hydrogen bomb program (H bomb). Teller once again tried to convince Bethe to participate in the project of making this extremely dangerous weapon. At first, Bethe refused to refuse, he strongly resisted the construction of destructive weapons, he also sought to argue that the H bomb could not be successfully built. However, when the Korean War broke out, Bethe agreed to participate in the project, he explained: ". my main desire is to prove explicitly that the H bomb will not work . " In fact, Teller's original design was proved impossible. However, in early 1951, Teller and Stan Ulam devised a method of detonating bombs. Bethe was also bewildered: "I was convinced that such a terrible weapon could become. reality, and we are forced to worry that Russians can and will make it. " The first H bomb was detonated on October 1, 1952.

In the 1950s, Bethe was a member of President Eisenhower's Scientific Advisory Council. One of Eisenhower's greatest goals at the time was to come to a pact with the Soviet Union on the ban on nuclear weapons testing, which he had trusted in Bethe. Even after Eisenhower ended his term, Bethe continued her efforts for this goal in the early 1960s. Finally, in 1963, President Kennedy signed a treaty to ban nuclear weapons testing. in the atmosphere. With her deep understanding and persuasion ability, Bethe and the tireless contribution to the agreements between the opposition factions of nuclear weapons in the Cold War.

In 1967, Hans Bethe was awarded the Nobel Prize for his discovery of the energy source of stars. In her acceptance speech, Bethe himself admitted that he was surprised that many people had longer, more basic and more complex contributions that were not awarded while his work was only done in a short time but still selected to award. That's probably Bethe's very modest humility, but we all know that he deserves that Nobel prize. Because the star's answer to the energy source has become one of the most important applications of physics in our time. Moreover, it also brought revolutionary changes in our understanding of the universe.

In addition to the Nobel Prize, Bethe also received many other prestigious awards such as the Max Planck Medal, the Enrico Fermi Award, the Medal of Los Alamos National Laboratory. In 1992, he and Joseph Rotblat were awarded the Albert Einstein Peace Prize.

Bethe retired in 1975, but was still an honorary professor at Cornell. He is active in campaigns to reduce and eliminate weapons of destruction. In an open letter to the scientific community in July 1995, he wrote: "I urgently call on all scientists in all countries to stop and abandon research and development programs. create and develop nuclear weapons, chemical and biological weapons, as well as any other destructive weapons " . In 1999, at the age of 93, Bethe still tried to fight against the Senate's decision to withdraw from the Comprehensive Nuclear Prohibition Treaty.

Hans Bethe died on March 6, 2005. Until his last breath, he continued to pursue his decades-long campaign, a campaign that made this world a safer place for everyone.

Tran Trung