- Person
- Hans Bethe
- Lived
- 1906–2005
- Field
- Theoretical physics
- From
- German-born American
The story
In June 1947 leading American physicists met at the Ram's Head Inn on Shelter Island, New York, for the first major physics conference after the Second World War. Sponsored by the National Academy of Sciences, it was a chance to pick up where they had left off before the war and set the direction of new research. Hans Bethe, back at Cornell after leading the Theoretical Division at Los Alamos, was among them.
The talk of the meeting was a new measurement by Willis Lamb and his graduate student Robert Retherford. They had found that one of two energy levels of the hydrogen atom, which Paul Dirac's theory said should be identical, sat slightly higher than the other. The effect became known as the Lamb shift. Explaining it was a serious problem, because quantum electrodynamics, the theory of light and matter, gave infinite answers for such effects. Hans Kramers had suggested a remedy called renormalisation, but nobody knew how to carry out the calculation, and many thought a radical new theory would be needed.
Bethe worked it out on the train from New York to Schenectady, where he was doing work for General Electric. He realised that the main part of the effect could be treated without relativity, which greatly simplified the problem. The infinite part was already contained in the observed mass of the electron and could be removed, leaving a finite answer. He arrived at a value of about 1040 megahertz, extremely close to the figure Lamb and Retherford had measured.
His paper, published in the Physical Review in August 1947, was only three pages long and contained just twelve equations, but it was enormously influential. It showed that the existing theory could be rescued rather than replaced. Richard Feynman called it the most important discovery in the history of the theory of quantum electrodynamics, and Paul Dirac called it the most important calculation in physics for decades.
Bethe's result opened the way for the full theory of quantum electrodynamics developed over the following years by Julian Schwinger, Richard Feynman, Sin-Itiro Tomonaga and Freeman Dyson, one of Bethe's own former students. The Nobel Foundation later wrote that Bethe had laid the foundation for the modern development of quantum electrodynamics.
Why it matters
Bethe's calculation launched the modern era of particle physics, whose precision theories underpin technologies from lasers to semiconductors.
About Hans Bethe
Refugee physicist who explained how the stars shine, led theory at Los Alamos, cracked the Lamb shift and spent half a century campaigning against the nuclear arms race; Nobel Prize 1967.
More about Hans Bethe
- Hans Bethe championed peaceful nuclear energyThroughout the 1980s and 1990s Hans Bethe campaigned for the peaceful use of nuclear energy, calling nuclear electricity 'a necessity, not merely an option'.
- Hans Bethe's 1931 method still solves quantum puzzlesWhile working with Enrico Fermi in Rome in 1931, Hans Bethe devised the Bethe ansatz, a method for exactly solving certain quantum many-body problems.
- 'Bethe's Bible' taught a generation nuclear physicsIn 1936–37 Hans Bethe, with Robert Bacher and Stanley Livingston, wrote three review articles so complete they became known as 'Bethe's Bible'.
- Hans Bethe explained how the stars shineIn 1938–39 Hans Bethe worked out the nuclear reactions that power the Sun and stars, work that won him the 1967 Nobel Prize in Physics.
- The Bethe formula tracks radiation through matterIn 1930 Hans Bethe derived a formula for how fast charged particles lose energy passing through matter, still used across physics today.
- Bethe showed missile defence could be fooled by decoysIn 1968 Hans Bethe and Richard Garwin argued that missile defences could be defeated by simple decoys, an argument that helped lead to the 1972 ABM Treaty.
- Hans Bethe helped secure the 1963 Test Ban TreatyHans Bethe served on the President's Science Advisory Committee from 1956 to 1964 and helped bring about the 1963 treaty banning atmospheric nuclear tests.
- At 85, Hans Bethe helped solve the solar neutrino puzzleAt the age of 85, Hans Bethe wrote an important paper on the solar neutrino problem, helping establish that neutrinos change type on their way from the Sun.
Sources
- Hans Bethe Wikipedia
- Lamb shift Wikipedia
- Hans Bethe – Biographical NobelPrize.org
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