Hans Bethe, RIP

Oh, this is sad. The greatest physicist of the 20th Century has passed away:

Hans Bethe, the nuclear physicist whose elegant calculations explained how stars shine and laid the foundation for development of both the atomic and hydrogen bombs, has died. He was 98. Bethe, who received the Nobel Prize in Physics in 1967, died Sunday at his home in Ithaca, N.Y., Cornell University announced Monday.

A reluctant but crucial participant in the World War II effort to develop nuclear weapons, Bethe subsequently became one of the country's most passionate and persuasive proponents of disarmament. He argued that the use of such weapons would cost not only countless lives, but "liberties and human values as well."

...Bethe (pronounced Bay-ta) was the lone survivor of the remarkable group of mostly German physicists of the early 20th Century — a group that included Einstein, Dirac, Fermi and Heisenberg — that deciphered the fundamental laws of matter and energy and set the stage for the remarkable technological developments of the last half of the century."

... Given the known temperature of the core of the sun — about 20,000,000 degrees Celsius — and the proportions of carbon, hydrogen and other elements in its interior, he deduced which nuclear reactions could be responsible for its radioactive fire.

He ultimately developed a six-step cycle in which carbon and nitrogen atoms act as catalysts for the conversion of four hydrogen nuclei (protons) into one helium nucleus. The very slight mass lost in the process is converted into large amounts of energy according to Albert Einstein's famous equation, E = mc2.

Bethe later remarked with typical modesty that he found the answer by "looking through the periodic table [of elements] step by step. So you see, this was a discovery by persistence, not by brains."

One oft-told story about Bethe recounts the evening after he discovered the secrets of starlight. During a late-night stroll, his fiance, Rose — daughter of theoretical physicist Paul Ewald — remarked on how beautiful the stars looked. He responded: "Yes, darling, and I'm the only one on Earth who knows how they do it."

Bethe and his Cornell colleagues then verified five of the six steps in the laboratory; the sixth was reproduced by researchers at Cambridge University. The entire six-step cycle takes 5.4 million years to complete.

With the coming of World War II and by then a naturalized citizen, Bethe joined the war effort, first at MIT's Radiation Laboratory and later as the chief theoretical physicist for the Manhattan Project at Los Alamos, N.M., even though he felt development of the bomb was morally wrong, and that the United States — and the world — would be far more secure without it."

...Bethe's solid, plow-through-the-problem approach earned him the nickname The Battleship; in contrast, his close colleague and office-mate physicist Richard Feynman became known as the Mosquito Boat because he skittered around a problem from all sides at once.Together, they were a formidable pair; the formula for calculating the efficiency of nuclear weapons became known as the Bethe-Feynman formula

...Despite his moral qualms about the bomb, Bethe considered it a necessary evil. He felt that its use in Japan was justified because many more Japanese and American lives would have been lost in an invasion of the island nation.

After the war, he became a prominent spokesman against proliferation — arguing without success that atomic bombs should be placed under strict international controls. He made countless public speeches throughout the country arguing his case.

He initially opposed Edward Teller's plans to build the hydrogen bomb, arguing that it was unnecessary. "We had enough A-bombs to kill the world," he said later. "Why add an H-bomb and kill the other half? So I said no to Teller.... I would not join him at Los Alamos."He became the spokesman for 12 physicists who opposed the project, a group which later developed the idea that the United States should publicly declare that it would not be the first to use the H-bomb "since it was not a weapon of war but a means of exterminating entire populations."

Bethe initially thought the point was moot because none of Teller's ideas for producing the bomb seemed likely to work. But in 1951, physicist Stanislaw Ulam conceived a new way to make fission bombs and Teller saw how this could be used to make a fusion bomb — using an A-bomb to trigger the H-bomb.Bethe recognized that the bomb could be built and could undoubtedly be built by the Russians as well. "If I didn't work on the bomb, somebody else would — and I had the thought that if I were around Los Alamos, I might still be a force for disarmament," he later said.

...Interestingly, after the H-bomb was made, reporters started to call Teller the father of the H-bomb," he said. "For the sake of history, I think it is more precise to say that Ulam is the father, because he provided the seed, and Teller is the mother, because he remained with the child. As for me, I guess I am the midwife."

While Bethe did not achieve many of his arms reduction goals, he believed that all scientists should take an active role in influencing public policy."Whether or not their governments respond to their advice, scientists have an obligation to speak out publicly when they feel there are dangers ahead," he wrote.

Bethe was an advisor to presidents from Truman to Clinton, and served on dozens of advisory committees When the idea of anti-ballistic missile systems became popular under President Johnson in 1967, Bethe and Garwin published an article in Scientific American arguing that such systems would add to the insecurity of the U.S. as well as the world — a position he held until his death.

Even with the best system, he wrote, there would be too many incoming targets to stop, and it would be too easy for an enemy to avoid our missiles and destroy our satellites. "Even quite feeble blows against orbiting battle stations ... could render them useless."

On Aug. 6, 1995, the 50th anniversary of the bombing of Hiroshima, Bethe called on scientists all over the world to stop working on all weapons of mass destruction, and appealed to all nuclear powers to slash arsenals to less than 100 bombs each. That way, he argued, even if political leaders went crazy, (he used Hitler as an example), at least they couldn't destroy all of civilization.

Bethe also worried that the U.S. would be seen as hypocritical for urging nuclear nonproliferation while continuing to design and build bombs, and argued that funds should go instead for improved stewardship of the weapons we already have.

Throughout his life and despite the potential distractions of his forays into the politics of arms control, Bethe continued to produce first-rate physics in an unusually wide range of disciplines. He worked on theories of metals, developed important insights into such exotica as neutron stars, and speculated how neutrinos that appeared to be missing from the sun's nuclear output could be eluding detectors because they were changing into different forms en route to Earth."

...In the 1970s, Bethe returned to his first love: astrophysics. While his earlier work explained how stars lived, he turned after his retirement to the fireworks produced when they die.

When massive stars run out of fuel, they eventually collapse under their own gravitation weight, then explode in colossal fireworks. Physicists knew most of the energy was carried away by wispy neutrinos, but the mechanism was a mystery.

Bethe's insights helped cut through complexities that had stumped much younger minds."Other people were cranking out large computer codes and reams of output, but they weren't cranking out understanding," Kolb said. "Hans came in with a pencil and paper and made more sense of what was coming out of the computer than the people who wrote the code."

His style of working never changed. "It was wonderful to watch him write a scientific paper," said Morrison. "He would write steadily, sentence after sentence, without looking anything up. When he got to a place that was hard, he'd go very slowly, but he wouldn't stop. Then he'd give those pages to a typist, and they'd be published as a book. Without any correction whatsoever. Hans didn't know about mistakes."

After his retirement in 1975, Bethe became a strong advocate for the development of peaceful nuclear power — along with drastic conservation efforts — as the only realistic short-term alternative to fossil fuels. "The country has to realize that the energy problem is terribly serious and is likely to be permanent," he wrote.

But he never lost his interest in science. At the age of 83, he apprenticed himself to Gerald E. Brown of the State University of New York at Stony Brook to learn lattice gauge theory, which predicts how nuclear matter is transformed at extremely high temperatures into a plasma of particles called quarks and gluons. "I'm interested in learning new things," Bethe explained.