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By Allan Franklin, University of Colorado
At this year’s April APS meeting in Salt Lake City, the forum sponsored a session on “Some History You Won’t Find in Physics Textbooks.” The first speaker was Allan Franklin of the University of Colorado, winner of the 2016 Abraham Pais Prize for History of Physics. Franklin’s topic was “Physics Textbooks Don’t Always Tell the Truth.” He noted that there was often a difference between the actual history of physics and that presented in physics textbooks. He remarked that this was not necessarily a bad thing. An inaccurate history may well serve a pedagogic purpose. It may help students to better understand certain concepts. Nevertheless, he stated that physics teachers should be aware of the actual history and that students should learn that the history of physics is not the unbroken string of successes that it appears to be in textbooks.
Franklin discussed two experiments: 1) Robert Millikan’s measurement of Planck’s constant using the photoelectric effect and 2) the measurement of the average energy of electrons emitted in the beta decay of Radium E (210Bi) by Charles Ellis and William Wooster. Virtually all physics textbooks tell us that Millikan’s experiment confirmed and established Einstein’s photon theory of light. As discussed later, the Ellis and Wooster experiment was quite important, but it is not often mentioned in physics textbooks. Franklin noted that Millikan, himself, did not believe in the photon theory either before or after his experiment because it conflicted with the well-established facts of interference. Millikan called the idea of a photon “a bold not to say reckless hypothesis.” The photon theory predicts that the maximum kinetic energy of the electron emitted in the photoelectric effect is given by KEmax = eVstop = hν – W0, where ν is the frequency of the incoming light and W0 is the work function of the metal. Millikan plotted Vstop against the frequency and obtained a straight line, from which, knowing e, the charge of the electron, he could determine h, Planck’s constant. Millikan believed that his result confirmed on Einstein’s equation and not the underlying photon theory. Millikan, along with the physics community did not accept the photon theory until the 1930s.
Franklin also discussed the Ellis-Wooster experiment. In the early 20th century most physicists believed that beta decay was a two-body process. Thus the observation of a spectrum of electron energies by Becquerel, by Kaufmann, and by Chadwick posed a problem because the conservation of energy and momentum required a unique energy for the electron. Physicists believed that the emitted electrons were monoenergetic, but lost energy by various processes in leaving the radioactive source. Ellis and Wooster proposed to solve the problem by measuring the average energy of the electrons using a total-absorption calorimeter. If that energy was the maximum decay energy 1 MeV, then the emitted electrons were monoenergetic and that the spread in energy was caused by energy loss in leaving the source. If the average energy was that of the observed spectrum, about 350 keV, then the observed spectrum was the spectrum of the emitted electrons. Ellis and Wooster found that the average energy was approximately 350 keV, establishing the continuous spectrum A few years later Pauli solved the problem by proposing that a third particle with no charge, very small mass, and spin 1/2 was also emitted in beta decay. This particle, later named by Fermi as the neutrino, was soon incorporated in Fermi’s successful theory of beta decay. Although the Ellis-Wooster is a very important contribution to physics, it is often neglected by textbooks writers.
George Smith, of Tufts University, discussed “Newton’s Principia, Myth and Reality.” He argued against the received view that Newton developed his law of gravity in order to explain Kepler’s laws of planetary motion and that his success in doing so was, for Newton, the principal evidence for his theory. Smith noted that there were, at the time, five other calculations of planetary orbits in addition to that of Kepler; those of Boulliau, Horrocks, Streete, Wing, and Mercator. He also remarked that Newton understood quite well that “the planets neither move exactly in ellipses nor revolve twice in the same orbit.” Smith identifies Newton’s method as finding a robust physical source for each discrepancy between theory and observation, one that had further observational consequences. As Newton stated, “If the sun were at rest and the Planets did not act on one another, the orbits would elliptical.” In addition, Kepler’s other two laws, the equal areas law, and the relation between planetary orbits and their periods, would also be exact. It was the planetary interaction that provided the robust physical source, and hence it was the observation of the deviations from Kepler’s laws, explained by the interaction that provided Newton with the principal evidence for his theory of gravity.
A second myth identified by Smith was, as Euler said, that in order for the discrepancies between calculated and observed motions to be evidence for Newton’s theory, Newton was presupposing that all motions refer to what we call inertial frames. Smith argued that on the contrary, Newton assumed that the planetary system was quasi-insular, “i.e. a system in which, if not all, then at least all of the detectable changes of position and motions of its bodies among themselves result entirely from the actions of those bodies on one another.” Smith outlined the continuing tests of Newton’s counterfactual assumptions. He stated Newton’s method of testing counterfactual conclusions as follows: 1) idealized calculated orbits presupposing theory and principal physical sources; 2) comparison with observations; 3) discrepancy with a clear signature; 4) physical source of the discrepancy, still further physical sources that make a difference; 5) New idealized calculation incorporating the new sources and their further implications. The process would then begin again with comparison with observations. He illustrated this with the discovery of Neptune and the advance of the perihelion of Mercury.
Jed Buchwald, of the California Institute of Technology, was the third speaker. He extended the discussion in his talk, “Historical Examples of Politics, Morality, Innovation and Fraud in Physical Science and Technology.” His first example was Heinrich Hertz’s discovery of electromagnetic radiation. When Hertz published his account of the discovery he claimed that he was relating the actual sequence of experiments and thoughts that resulted in that discovery. Hertz’s notebook, recently found, tells a very different story. It shows that Hertz had considerably altered the true course of events in ways that made his path to discovery seem to be more logical and linear than it was. Buchwald asked whether Hertz’s misrepresentation should be considered fraud, an issue that has been in the news recently. In Buchwald’s view this was not the case. Hertz did not attempt to mislead his readers to enhance their view of his experimental and logical abilities, nor did he have a financial interest in his account. Rather Hertz’s presentation was good pedagogy. Other laboratories soon began to investigate electromagnetic radiation.
Buchwald also discussed the relation between science and technology. He remarked that the cliché, “Science produces, industry consumes,” is occasionally correct, but that more often the interaction is more complex. His example was the work of Marconi and Fleming. Buchwald pointed out that Hertz’s discovery, using a very broadband device, was useless as a practical means of communication. Marconi’s device, which had a narrow bandwidth, was the only possibility. Buchwald argues that the path to a useful Marconi device was quite complex, involving connections to economics, society, and government, even though the science was already known.
Buchwald’s final example was the conflict between Herman Helmholtz and Friedrich Zollner on the virtues of free investigation, unconstituted by ideologies or religious beliefs. This was Helmholtz’s view, one opposed by Zollner. Zollner accused Helmholtz of propagating unGermanic science, primarily because Helmholtz had translated William Thomson’s, later Lord Kelvin, Treatise on Natural Philosophy. Zollner’s opposition to academic freedom dismayed Helmholtz who advocated the free pursuit of scientific research as a model for intellectual freedom and for a tolerant and moral society. Helmholtz’s view was abandoned in Germany in the 1930s as typified by tearing down a statue honoring Hertz, because of his Jewish ancestry.
Pais Prizewinner Allan Franklin (center) with George Smith (right) and Jed Buchwald (left).
The articles in this issue represent the views of their authors and are not necessarily those of the Forum or APS.