Quantum Man: Richard Feynman's Life in Science by Lawrence M. Krauss Page A
Authors: Lawrence M. Krauss
Tags: Science / Physics
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accord with some biblical estimates of the age of the universe. Later in the century, two famous physicists, Heinrich Helmholtz and Lord Kelvin, estimated that the sun could be powered by the energy released during gravitational contraction, and this energy source could power the sun for perhaps 100 million years. However, even this estimate was far too low to explain what was by then the inferred age of the solar system—namely, billions, not hundreds of millions, of years.
The mystery persisted through the 1920s, when the famous British astrophysicist Sir Arthur Stanley Eddington argued that there must be some unknown source of energy powering the solar interior. The problem was that model calculations of the sun’s profile suggested that the interior was no more than 10 million degrees in temperature, which is hot, but not that hot. In other words, the physical processes associated with the energies available at these temperatures were thought to be fairly well understood, with no room for new exotic physics. As a result, Eddington’s assertion was met with skepticism, leading him to utter his famous rebuke: “To those that think the temperature in the center of the Sun is not hot enough for some new physical process to take place, I say: Go and find a hotter place!”
Bethe, who had studied with the greatest theoretical physicists in Europe, including Arnold Sommerfeld, Paul Dirac, and Enrico Fermi, had, by the early 1930s, established himself as perhaps the world’s foremost authority on the emerging field of nuclear physics. He wrote the definitive set of reviews in this field, which Feynman had studied while an undergraduate. If anyone was prepared to find the new process that powered the sun, it was Bethe, and in 1939 he made his great discovery. He realized that newly discovered nuclear reactions (similar in spirit to those later exploited in building the fission bomb, but instead of being based on breaking up heavy nuclei such as uranium and plutonium, these involved fusing light nuclei such as hydrogen into heavier nuclei) provided the key to releasing tremendous amounts of energy. Moreover, he showed that there was a series of reactions starting with protons, which make up the nuclei of hydrogen, and ultimately producing the nuclei of the next lightest element, helium, that would release more than twenty million times as much energy as comparable chemical reactions between hydrogen would release. While at a temperature of only 10 million degrees the average hydrogen nucleus might take over a billion years to experience a collision energetic enough to initiate such a reaction, over a hundred thousand tons of hydrogen could nevertheless convert to helium each second, providing enough energy to power the sun at its current luminosity for about 10 billion years.
For this important theoretical discovery, Bethe was awarded the Nobel Prize in Physics in 1969, four years after Feynman would share the prize for his own work on quantum electrodynamics (QED). And the nuclear “fusion” reactions Bethe exploited in his explanation of the workings of the sun would be re-created seven years after the end of World War II, in the development of “thermonuclear explosives,” otherwise known as hydrogen bombs.
Oppenheimer had recruited Bethe in 1942 and wisely chose him to head the Theoretical Division, which contained the biggest brains and the biggest egos that would reside at Los Alamos. Not only was Bethe their intellectual equal, but also his calm yet persistent strength of character would be essential in helping to guide them, put out fires, and, above all, put up with their idiosyncrasies.
In Feynman, Bethe had found just the foil he needed to bounce ideas off of, just as Feynman had found the perfect mentor to help steer his active imagination. That they both loved their work didn’t hurt either. Bethe, to his credit, recognized Feynman’s talent quickly and made what might seem the unorthodox decision to
The mystery persisted through the 1920s, when the famous British astrophysicist Sir Arthur Stanley Eddington argued that there must be some unknown source of energy powering the solar interior. The problem was that model calculations of the sun’s profile suggested that the interior was no more than 10 million degrees in temperature, which is hot, but not that hot. In other words, the physical processes associated with the energies available at these temperatures were thought to be fairly well understood, with no room for new exotic physics. As a result, Eddington’s assertion was met with skepticism, leading him to utter his famous rebuke: “To those that think the temperature in the center of the Sun is not hot enough for some new physical process to take place, I say: Go and find a hotter place!”
Bethe, who had studied with the greatest theoretical physicists in Europe, including Arnold Sommerfeld, Paul Dirac, and Enrico Fermi, had, by the early 1930s, established himself as perhaps the world’s foremost authority on the emerging field of nuclear physics. He wrote the definitive set of reviews in this field, which Feynman had studied while an undergraduate. If anyone was prepared to find the new process that powered the sun, it was Bethe, and in 1939 he made his great discovery. He realized that newly discovered nuclear reactions (similar in spirit to those later exploited in building the fission bomb, but instead of being based on breaking up heavy nuclei such as uranium and plutonium, these involved fusing light nuclei such as hydrogen into heavier nuclei) provided the key to releasing tremendous amounts of energy. Moreover, he showed that there was a series of reactions starting with protons, which make up the nuclei of hydrogen, and ultimately producing the nuclei of the next lightest element, helium, that would release more than twenty million times as much energy as comparable chemical reactions between hydrogen would release. While at a temperature of only 10 million degrees the average hydrogen nucleus might take over a billion years to experience a collision energetic enough to initiate such a reaction, over a hundred thousand tons of hydrogen could nevertheless convert to helium each second, providing enough energy to power the sun at its current luminosity for about 10 billion years.
For this important theoretical discovery, Bethe was awarded the Nobel Prize in Physics in 1969, four years after Feynman would share the prize for his own work on quantum electrodynamics (QED). And the nuclear “fusion” reactions Bethe exploited in his explanation of the workings of the sun would be re-created seven years after the end of World War II, in the development of “thermonuclear explosives,” otherwise known as hydrogen bombs.
Oppenheimer had recruited Bethe in 1942 and wisely chose him to head the Theoretical Division, which contained the biggest brains and the biggest egos that would reside at Los Alamos. Not only was Bethe their intellectual equal, but also his calm yet persistent strength of character would be essential in helping to guide them, put out fires, and, above all, put up with their idiosyncrasies.
In Feynman, Bethe had found just the foil he needed to bounce ideas off of, just as Feynman had found the perfect mentor to help steer his active imagination. That they both loved their work didn’t hurt either. Bethe, to his credit, recognized Feynman’s talent quickly and made what might seem the unorthodox decision to
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