Fine structure of the hydrogen atom by a microwave method. Offprint from: The Physical Review, Vol. 72, No. 3, 1 August 1947.
[Lancaster, PA and New York, NY: American Institute of Physics, 1947]. First edition, very rare offprint, signed by Lamb, who received a half-share of the 1955 Nobel Prize in Physics for this work. The Lamb-Retherford experiment of 1947 was the first to measure what is now known as the Lamb shift—the difference in energy between two energy levels 2S½ and 2P½ of the hydrogen atom—which had not been correctly predicted by the Dirac relativistic wave equation. “The Lamb shift experiment was a landmark in 20th-century physics” (Biographical Memoir, National Academy of Sciences). “After it was reported at Shelter Island, [the Lamb-Retherford experiment] became the point of departure for the renormalization program” (Silvan Schweber). Lamb (1913-2008) received his doctorate at Berkeley in 1938 under the guidance of J. Robert Oppenheimer. “Unlike many of his generation of physicists, Lamb did not follow Oppenheimer into the wartime atom-bomb project. Instead, he concentrated on his specialisms — microwaves and radar — at Columbia University in New York, performing the experiments that culminated in the observation of the Lamb shift. This shift is a tiny difference in energy between two atomic orbitals in hydrogen, denoted 2S and 2P, distinguished only by their angular momenta. Quantum theories of the time predicted that these levels should have identical energies. The discovery that they did not demanded a fundamental theoretical rethink — one that was initiated almost immediately by Hans Bethe. The Lamb shift thus became a cornerstone of the modern edifice of quantum electrodynamics (QED). This, the quantum field theory of the electromagnetic interaction, explains the shift as resulting from energy fluctuations in the vacuum that smear out the position of the electron in a hydrogen atom. This process has a greater effect on the Coulomb energy of the electron’s binding to the central proton at smaller radii (where the 2S state is most likely) than at larger radii (where the 2P state dominates). Today, precise measurements of the Lamb shift have tested QED to an accuracy of better than one part in a million” (Sargent). On Lamb’s 65th birthday, Freeman Dyson wrote, “those years, when the lamb shift was the central theme of physics, were golden years for all the physicists of my generation. You were the first to see that this tiny shift, so elusive and hard to measure, would clarify in a fundamental way our thinking about particles and fields.” Not on OCLC or RBH. Provenance: Willis Lamb (signature on front wrapper). Lamb was born in Los Angeles, the son of a telephone engineer. He entered the University of California at Berkeley in 1930, where he earned a bachelor’s degree in chemistry (1934). Lamb continued at Berkeley as a graduate student in theoretical physics directed by J. Robert Oppenheimer, receiving his doctorate in 1938. In that year Lamb joined the faculty at Columbia University, New York, where he carried out research in microwaves and radar. His defence-related investigations focused on the problem of how to make shorter, higher frequency microwave sources for radar. It was this that would eventually lead to a Nobel prize in 1955. Lamb continued working in atomic spectroscopy and laser physics at Stanford University (1951-56), where he devised microwave techniques for examining the hyperfine structure of the spectral lines of helium, and then as professor at Oxford (1956-62). He returned to the US in 1962 as Henry Ford II professor of physics at Yale, joining the University of Arizona in 1974 until his retirement in 2002. “In the second quarter of the 20th century, quantum theory faced some serious challenges, including unexplained details of atomic spectra and difficulties in calculating basic properties of charged particles. In 1947 Willis Lamb and Robert Retherford of Columbia University discovered an unexpected detail in the hydrogen spectrum, later called the Lamb shift, that became an essential clue in solving both problems. The measurement agreed with new calculations and was the first indication that the theoretical approach called renormalization could resolve the mathematical infinities that had threatened to derail the progress of quantum mechanics. “By the 1940s, theorists understood a variety of phenomena that had small effects on the energies of atomic electrons, such as relativistic corrections and interactions between spin and orbital angular momentum. These effects showed themselves in the so-called fine structure of atomic spectra—the way that many spectral lines, corresponding to jumps between electron energy levels, are seen on close examination to split into groups of closely spaced lines. “Lamb and graduate student Retherford wanted to measure the hydrogen fine structure by investigating two specific electron states. One was a relatively long-lived S state, with a spherically symmetric orbital, and the other was a shorter-lived P state, with less symmetry. Standard theory predicted that the two states should have equal energy but that applying a magnetic field should influence the states in different ways and induce an energy difference between them. “The team sent a stream of electrons at right angles into a beam of hydrogen atoms, exciting a few of them into the S state and also deflecting them slightly from the main beam direction. The excited atoms passed through a region containing both microwave radiation and an adjustable magnetic field and then hit a metal target. The excited atoms would then drop back to the ground state, emitting electrons that the team could detect as a current. The key to the experiment was that if the magnetic-field-induced energy difference between the two states was equal to the energy of the microwave photons, then the long-lived S state would absorb a photon and turn into the short-lived P state. These atoms would drop back to their ground state before reaching the target, and the current in the detector would essentially vanish. “By plotting the critical magnetic-field strength for a variety of microwave frequencies, Lamb and Retherford could determine the energy difference between the two states in the absence of a magnetic field. Contrary to expectation, the difference was not zero. “This departure from theory became known as the Lamb shift and was a prime topic for discussion at the Shelter Island Conference on Quantum Mechanics that took place in June 1947 at the far end of Long Island, New York. Many of the attending theorists argued that the Lamb shift was a result of the ‘self-energy’ problem in quantum electrodynamics. The problem was that calculations of the interaction of an electron’s charge with its own field yielded apparently infinite values for the particle’s energy and mass and also threw off calculations of atomic spectra. “It was Hans Bethe, on the train ride home, who wrote a short paper giving a somewhat sketchy but fairly accurate calculation of the shift. The solution to the self-energy problem, proposed by others, was to think of the ‘bare’ electron as having infinite energy that is mostly cancelled out by the infinitely negative energy of its interaction with its own electric field. This so-called renormalization approach leads to a correction to the classical energy that depends on distance. A P-state electron spends a different amount of time close to the nucleus than an S-state electron, so they require different corrections. Bethe’s estimate for the resulting Lamb shift fit the experimental result remarkably well and demonstrated that renormalization—which is at the core of today’s quantum mechanics—could be verified in experiments” (Lindley). “[Swedish physicist Ivar] Waller, who made the presentation speech when Lamb was awarded the Nobel Prize in 1955, observed that ‘it does not often happen that experimental discoveries exert an influence on physics as strong and invigorating as did your work. Your work led to a re-evaluation and a reshaping of the theory of the interaction of electrons and electromagnetic radiation, thus initiating a development of utmost importance to many of the basic concepts of physics, a development the end of which is not yet in sight’” (Schweber, QED and the Men Who Made It, p. 218). “Speaking at a conference on the history of particle physics in 1980 Lamb, obviously with some pleasure, remarked that he had been in contact with the leading figures in the history of fine structure, Michelson, Sommerfeld, and Dirac. When he was still a high-school student he had met Michelson, who spent his last years at Caltech, at a chess festival in Pasadena. ‘We talked a little about the game, but not about physics, and although I knew that he was famous for the measurement of the velocity of light, I did not know of any other reasons.’ He never met Sommerfeld, but ‘in 1950 he sent me a handwritten note that indicated that he had heard of our measurements, and he mentioned that he was the ‘81-year-old great-grandfather’ of the hydrogen fine-structure theory.’ Lamb met Dirac repeatedly. About one occasion he remembers that Dirac asked him if he had enjoyed participating in the discovery of the fine-structure anomaly. Lamb said he had but added that he would have had much more pleasure if instead he had discovered the Dirac equation. As Lamb recalls, after a brief pause Dirac said gently, ‘Things were simpler then’” (Brandt, Harvest of a Century, p. 306). Lindley, ‘Quantum Milestones, 1947: Lamb Shift Verifies New Quantum Concept,’ Physics 18 (2025), p. 41 (https://physics.aps.org/articles/v18/41). Sargent, ‘Willis E. Lamb Jr (1913–2008),’ Nature 453 (2008), p. 867.
4to (266 x 198 mm), pp. 241-243, [1, blank]. Original printed wrappers (a bit ceased at the foot).
Item #6543
Price: $9,500.00
