Hans Albrecht Bethe was born in Strassburg, Germany (now part of France), in 1906, the son of two university professors. His father taught physiology, and his mother, medicine. Science was Bethe's passion, but the nature of his work was shaped largely by political events. He is best known for discovering the process of nuclear fusion and for his work on the development of the atomic bomb.
Bethe was a brilliant high school student and went on to study physics at universities in Frankfurt and Munich. In Munich in 1926, Bethe came under the wing of Arnold Sommerfeld, an early pioneer of quantum mechanics, the study of nuclear and atomic particles in motion. He joined Sommerfeld's brilliant group of scientists which included Linus Pauling and Edward Teller. Bethe's main project in the group was to study the structure of atoms and nuclei.
Bethe finished his studies in 1930. A Rockefeller Foundation fellowship enabled him to spend two years as a visiting scholar at the Cavendish Laboratory in Cambridge, England. He then continued his studies in Rome, working with Enrico Fermi. Bethe returned to Germany in 1932 to teach physics at the University of Tübingen.
Just two months later, Adolf Hitler rose to power. Because of his mother's Jewish heritage Bethe was fired from his job and had to leave the country. Many of Germany's finest scientific minds found themselves in a similar predicament, and waves of scholars left for the United States, England, Australia, and other countries.
Bethe went first to England, where he taught for two years. He then went to Cornell University in Ithaca, New York, where he teaches to this day.
Bethe Analyzes Nuclear Fusion
Soon after reaching Cornell, Bethe tackled a question that had baffled scientists for centuries: how do stars produce their energy? To arrive at the answer, Bethe combined what he knew about subatomic physics with theories of the high temperatures of stars. This approach led him to understand the process of nuclear fusion. By May 1938, as the Nazi war effort went into high gear, Bethe announced his answer.
Bethe suggested that deep in a star's core, where the temperature is in the millions of degrees, nuclear fusion takes place. He suggested two ways this can happen. In very hot stars, the nuclei of hydrogen atoms can fuse with carbon nuclei. This process begins a complex chain reaction, ending with the fusion of two hydrogen nuclei into a helium nucleus. One recycled carbon nucleus, and a tremendous amount of energy are also produced. In slightly cooler stars, hydrogen nuclei do not fuse with carbon, but fuse together to produce helium and energy.
Our sun contains so much helium that the fusion of hydrogen to helium must have been going on for billions of years. The sun has enough hydrogen to continue producing energy for many more billions of years.
Bethe and the Manhattan Project
In 1939, as the world was headed for war, several prominent scientists visited Albert Einstein, who was living in New York. They convinced him to write a letter to President Franklin D. Roosevelt urging him to begin work on an atomic bomb to help defeat the Nazis. Einstein, who had always been a pacifist (one opposed to war or violence), later called this letter "the greatest mistake" he ever made.
Nonetheless, Einstein's letter set the wheels in motion. In 1942, one year after the Japanese attacked Pearl Harbor, a program known as the Manhattan Project was created to manufacture the atomic bomb. Robert Oppenheimer, one of the the atomic physicists who worked on the project recruited Bethe to join his research team.
Three years later, the bombs were ready. In July 1945, the United States dropped atomic bombs on the Japanese cities; Hiroshima and Nagasaki, and the world was changed forever. The most destructive weapon devised had been unleashed, killing thousands of civilians and leveling entire cities at once, giving new meaning to the nuclear threat.
After the war, Bethe returned to Cornell and resumed teaching and conducting research into the nature of the physical universe. Bethe received the Fermi Award in 1961 for his part in the development of atomic energy and the Nobel Prize in physics in 1967.