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Physics Today
Mystery Error in Gamow’s Tompkins Reappears John D. Hey
Published May 1, 2001 • 1 citation
Abstract The review by Daniel M. Greenberger of Russell Stannard’s The New World of Mr. Tompkins (Physics Today, June 2000, page 57) intrigued me sufficiently that I obtained a copy of this revised and extended version of George Gamow’s (now dated) three classic works for the general reader. I agree with much of what Greenberger writes. Stannard has “done a remarkable job of preserving the mood and feeling of the original,” and I hope that at least some of the few small slips will be edited out before this commendable book is reprinted.One error, however, struck me rather forcibly. In the diagram on page 159, the professor is lecturing to his evening audience, which contains the (as usual) dozing Mr. Tompkins. A slide of the Bohr-Sommerfeld orbits for principal quantum numbers n = 2,3 has been projected onto the screen. Unfortunately, the orbits with highest azimuthal quantum number (orbital angular momentum quantum number l) are shown as ellipses with the highest eccentricity, while the s-orbits (l = 0) are shown as circles. This confusion of “penetrating” with “nonpenetrating” orbits is common, occasioned perhaps by the recollection that in the wave-mechanical picture, the s-orbitals are spherically symmetrical, albeit with the important property that their probability densities peak at the origin. This property is of vital importance, for example, for the Lamb shift and the Fermi contact interaction in hyperfine structure, quite apart from the fact that the quantum defects are therefore largest for the s-orbitals in many-electron atoms. For comparison purposes, excellent diagrams of these two distinctly different forms of representation may be found in reference 11. H. E. White, Introduction to Atomic Spectra, McGraw-Hill, New York, (1934), pp. 47–71..How did this unfortunate mistake occur in the new work? On turning to its predecessor, 2 2. G. Gamow, Mr. Tompkins in Paperback, Cambridge U. Press, (1965) pp. 132–133. one finds on page 132 a picture containing the same Bohr–Sommerfeld orbits and, in addition, the quantization rules in the “old quantum theory” and formulas for the energies. (A keen-eyed reader will spot that the electronic charge e is raised to the wrong power in two places.) Moreover, in this diagram by Gamow himself, the orbitals are labeled in exactly the same incorrect fashion: The s- and d-labels should be interchanged.This brought to mind the amusing account in Gamow’s delightful “informal autobiography” My World Line (I write from memory of a book read well over two decades ago), in which he describes his initial difficulties on arrival from Russia at the University in Göttingen, home of the “new quantum theory,” around 1928. The easier problems having already been solved, his contemporaries were then working on aspects of atomic theory requiring considerable dexterity in advanced special function theory, and the sort of heavy algebraic manipulation (“exerei”) that Gamow disliked, topology and group theory being more appealing to him. On a certain day, the frustrated young Gamow was sitting on a park bench, wondering what to do. His eye fell on the description by Ernest Rutherford, in the Philosophical Magazine that he happened to be carrying, of a now rather implausible idea invoked to explain the escape of alpha particles from the atomic nucleus. In a flash of inspiration, Gamow sketched out in his mind the correct explanation, involving “quantum tunneling” and the now famous “Gamow factor.” When one considers the author’s age of barely 24 years, the ensuing paper 3 3. G. Gamow, Z. Phys. 51, 204 (1928) https://doi.org/10.1007/BF01343196. makes an astonishing impression of both maturity and unusual clarity, attributes that of course lent themselves admirably in due course to writing the “Tompkins” books.Making a hypothesis of my own, I surmised that his inattention to detail regarding the electron orbitals was perhaps a consequence of this early predilection for nuclear, rather than atomic, physics. But no—on turning to my last source, 4 4. G. Gamow, Mr. Tompkins Explores the Atom, Cambridge U. Press, (1946), pp. 72–74. I found not only the best drawing of all three (again by Gamow), but the orbits correctly labeled! No doubt the professor himself could comment most aptly on this mutilation of his original over time.REFERENCESSection:ChooseTop of pageREFERENCES <<1. H. E. White, Introduction to Atomic Spectra, McGraw-Hill, New York, (1934), pp. 47–71. Google Scholar2. G. Gamow, Mr. Tompkins in Paperback, Cambridge U. Press, (1965) pp. 132–133. Google Scholar3. G. Gamow, Z. Phys. 51, 204 (1928) https://doi.org/10.1007/BF01343196. Google ScholarCrossref, CAS4. G. Gamow, Mr. Tompkins Explores the Atom, Cambridge U. Press, (1946), pp. 72–74. Google Scholar© 2001 American Institute of Physics.
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The review by Daniel M. Greenberger of Russell Stannard’s The New World of Mr. Tompkins (Physics Today, June 2000, page 57) intrigued me sufficiently that I obtained a copy of this revised and extended version of George Gamow’s (now dated) three classic works for the general reader. I agree with much of what Greenberger writes. Stannard has “done a remarkable job of preserving the mood and feeling of the original,” and I hope that at least some of the few small slips will be edited out before this commendable book is reprinted.One error, however, struck me rather forcibly. In the diagram on page 159, the professor is lecturing to his evening audience, which contains the (as usual) dozing Mr. Tompkins. A slide of the Bohr-Sommerfeld orbits for principal quantum numbers n = 2,3 has been projected onto the screen. Unfortunately, the orbits with highest azimuthal quantum number (orbital angular momentum quantum number l) are shown as ellipses with the highest eccentricity, while the s-orbits (l = 0) are shown as circles. This confusion of “penetrating” with “nonpenetrating” orbits is common, occasioned perhaps by the recollection that in the wave-mechanical picture, the s-orbitals are spherically symmetrical, albeit with the important property that their probability densities peak at the origin. This property is of vital importance, for example, for the Lamb shift and the Fermi contact interaction in hyperfine structure, quite apart from the fact that the quantum defects are therefore largest for the s-orbitals in many-electron atoms. For comparison purposes, excellent diagrams of these two distinctly different forms of representation may be found in reference 11. H. E. White, Introduction to Atomic Spectra, McGraw-Hill, New York, (1934), pp. 47–71..How did this unfortunate mistake occur in the new work? On turning to its predecessor, 2 2. G. Gamow, Mr. Tompkins in Paperback, Cambridge U. Press, (1965) pp. 132–133. one finds on page 132 a picture containing the same Bohr–Sommerfeld orbits and, in addition, the quantization rules in the “old quantum theory” and formulas for the energies. (A keen-eyed reader will spot that the electronic charge e is raised to the wrong power in two places.) Moreover, in this diagram by Gamow himself, the orbitals are labeled in exactly the same incorrect fashion: The s- and d-labels should be interchanged.This brought to mind the amusing account in Gamow’s delightful “informal autobiography” My World Line (I write from memory of a book read well over two decades ago), in which he describes his initial difficulties on arrival from Russia at the University in Göttingen, home of the “new quantum theory,” around 1928. The easier problems having already been solved, his contemporaries were then working on aspects of atomic theory requiring considerable dexterity in advanced special function theory, and the sort of heavy algebraic manipulation (“exerei”) that Gamow disliked, topology and group theory being more appealing to him. On a certain day, the frustrated young Gamow was sitting on a park bench, wondering what to do. His eye fell on the description by Ernest Rutherford, in the Philosophical Magazine that he happened to be carrying, of a now rather implausible idea invoked to explain the escape of alpha particles from the atomic nucleus. In a flash of inspiration, Gamow sketched out in his mind the correct explanation, involving “quantum tunneling” and the now famous “Gamow factor.” When one considers the author’s age of barely 24 years, the ensuing paper 3 3. G. Gamow, Z. Phys. 51, 204 (1928)
https://doi.org/10.1007/BF01343196 . makes an astonishing impression of both maturity and unusual clarity, attributes that of course lent themselves admirably in due course to writing the “Tompkins” books.Making a hypothesis of my own, I surmised that his inattention to detail regarding the electron orbitals was perhaps a consequence of this early predilection for nuclear, rather than atomic, physics. But no—on turning to my last source, 4 4. G. Gamow, Mr. Tompkins Explores the Atom, Cambridge U. Press, (1946), pp. 72–74. I found not only the best drawing of all three (again by Gamow), but the orbits correctly labeled! No doubt the professor himself could comment most aptly on this mutilation of his original over time.REFERENCESSection:ChooseTop of pageREFERENCES <<1. H. E. White, Introduction to Atomic Spectra, McGraw-Hill, New York, (1934), pp. 47–71. Google Scholar2. G. Gamow, Mr. Tompkins in Paperback, Cambridge U. Press, (1965) pp. 132–133. Google Scholar3. G. Gamow, Z. Phys. 51, 204 (1928)
https://doi.org/10.1007/BF01343196 . Google ScholarCrossref, CAS4. G. Gamow, Mr. Tompkins Explores the Atom, Cambridge U. Press, (1946), pp. 72–74. Google Scholar© 2001 American Institute of Physics.
Although I have neither an objection to nor an endorsement of David Mermin’s major premise in his Quick Study, “There is no quantum measurement problem” (Physics Today, June 2022, page 62), I would like to make several contextual points.Mermin’s argument has an extensive history, along with a comparable history of rebuttal. Five decades ago Max Jammer wrote that “measurements in quantum mechanics are no more or less problematic than in classical physics, for the Hilbert space vector is only a purely formal device for relating the statistics associated with these arrangements to the physics of observations in classical physics.” That seems like a condensed version of the argument Mermin presents. On the following page, however, Jammer notes that a “problematic aspect whose serious implications were only gradually understood was the fact that as long as a quantum mechanical one-body or many-body system does not interact with macroscopic objects, as long as its motion is described by the deterministic Schrödinger time-dependent equation, no events could be considered to take place in the system.”11. M. Jammer, The Philosophy of Quantum Mechanics: The Interpretations of Quantum Mechanics in Historical Perspective, Wiley (1974), pp. 473, 474.Niels Bohr giving a lecture in Copenhagen in April 1929. (Photograph by Samuel Goudsmit, courtesy of the AIP Emilio Segrè Visual Archives, Goudsmit Collection.)PPT|High resolutionRegarding the quotations from Niels Bohr, Mermin’s point is entirely valid and represents Bohr’s position accurately, but Bohr’s thought is always subtle and difficult to capture completely. Another quotation from Bohr, which is consistent with everything else he wrote, is, “The decisive point is that in neither case does the appropriate widening of our conceptual framework imply any appeal to the observing subject, which would hinder unambiguous communication of experience.”22. N. Bohr, Essays 1958–1962 on Atomic Physics and Human Knowledge, Ox Bow Press (1987), p. 7. That quotation seems inconsistent with Mermin’s paragraph that includes the passage “Why should I insist that my interpretation of science, which I use to make sense of the world that I experience, should never make any mention of me?” Bohr always insisted that his framework was a rational “generalization” of classical objectivity.The last and most conceptually important point concerns the ontological status of probability. I don’t necessarily disagree with Mermin and Bruno de Finetti, but it is by no means obvious that they are correct either. David Hawkins, for example, begins 50 pages of rigorous analysis with a brief statement of a major premise.The obvious and natural interpretation of probability in this context is that it introduces, not something that has to do with the nature of the physical system, but something that has to do with the incompleteness of our knowledge….But this opinion turns out to be false. Ignorance of dynamical regularity may be a motive for resorting to probabilities, but it does not explain the probabilities to which we resort.33. D. Hawkins, The Language of Nature: An Essay in the Philosophy of Science, W. H. Freeman (1964), p. 135.Another example can be found in Jammer’s well-known historical account of quantum theory: “For Einstein the notion of probability … was the traditional conception of classical physics, a mathematical objectivization of the human deficiency of complete or exact knowledge but ultimately a creation of the human mind…. For Born probability, as far as it was related to the wave function, was not merely a mathematical fiction but something endowed with physical reality.”44. M. Jammer, The Conceptual Development of Quantum Mechanics, McGraw-Hill (1966), p. 286.Of course, such examples don’t mean that Mermin’s position is incorrect, but I do think that they demand a better argument than a comparison to “Fairies and Witches.” I am confident that Mermin has such an argument, and I look forward to reading it as I continue working toward a coherent position on the unresolved interpretational issues of quantum theory.ReferencesSection:ChooseTop of pageReferences <<CITING ARTICLES1. M. Jammer, The Philosophy of Quantum Mechanics: The Interpretations of Quantum Mechanics in Historical Perspective, Wiley (1974), pp. 473, 474. Google Scholar2. N. Bohr, Essays 1958–1962 on Atomic Physics and Human Knowledge, Ox Bow Press (1987), p. 7. Google Scholar3. D. Hawkins, The Language of Nature: An Essay in the Philosophy of Science, W. H. Freeman (1964), p. 135. Google Scholar4. M. Jammer, The Conceptual Development of Quantum Mechanics, McGraw-Hill (1966), p. 286. Google Scholar© 2022 American Institute of Physics.
The old quantum theory of Bohr and Sommerfeld was abandonned for the wrong reason. Its contradictions were caused not by the orbit concept but by a mental barrier—the inconceivability that an electron might collide with the atomic nucleus. Removing that barrier resolves the theory’s main failures—incorrect orbital momenta, He atom, H + 2 molecule ion. The inclusion of electron oscillations through the nucleus—a concept called “Coulomb oscillator”—renders the old quantum theory consistent with quantum mechanics (although devoid of wave character). The triple success of the Bohr-Sommerfeld model is its correct description of the H atom (and one-electron ions) concerning (1) the energy levels Enl, (2) the orbital angular momenta Lnl—if corrected as L 2 = l(l + 1)~ 2 and with the Coulomb oscillator included—and (3) the orbits’ space quantization—with (Lnl)z = ml~. These achievements are succinctly represented by the principal, angular and magnetic quantum numbers (n, l, ml) and visualized by orbital ellipse geometry—major axis, vertex curvature, and tilt angle, respectively. Orbit geometry also accounts for the average orbit size. Moreover, the Coulomb oscillator provides a natural explanation of (isotropic) hyperfine interaction. The shortcomings of the old quantum theory lie in its neglect of three properties of particles—their spin, their wave nature and their quantum statistics. These deficiencies notwithstanding, the visual appeal of the Bohr-Sommerfeld model remains a pedagogical asset to complement the abstract character of quantum mechanics.
The old quantum theory of Bohr and Sommerfeld was abandonned for the wrong reason. Its contradictions were caused not by the orbit concept but by a mental barrier--the inconceivability that an electron might collide with the atomic nucleus. Removing that barrier resolves the theory's main failures--incorrect orbital momenta, He atom, H2+ molecule ion. The inclusion of electron oscillations through the nucleus--a concept called "Coulomb oscillator"--renders the old quantum theory consistent with quantum mechanics (although devoid of wave character). The triple success of the Bohr-Sommerfeld model is its correct description of the H atom (and one-electron ions) concerning (1) the energy levels Enl, (2) the orbital angular momenta Lnl--if corrected as Lnl^2 = l(l+1) hbar^2 and with the Coulomb oscillator included--and (3) the orbits' space quantization--with (Lnl)z = ml hbar. These achievements are succinctly represented by the principal, angular and magnetic quantum numbers (n, l, ml) and visualized by orbital ellipse geometry--major axis, vertex curvature, and tilt angle, respectively. Orbit geometry also accounts for the average orbit size. Moreover, the Coulomb oscillator provides a natural explanation of (isotropic) hyperfine interaction. The shortcomings of the old quantum theory lie in its neglect of three properties of particles--their spin, their wave nature and their quantum statistics. These deficiencies notwithstanding, the visual appeal of the Bohr-Sommerfeld model remains a pedagogical asset to complement the abstract character of quantum mechanics.
Anatoly Svidzinsky, Marlan Scully, and Dudley Herschbach have illustrated well how the molecular theory might have looked had quantum mechanics not been invented. It’s worth noting that Niels Bohr was not alone in his attempts to extend semiclassical mechanics to systems more complex than the hydrogen atom. From 1913 to 1925, many semiclassical models of two-electron systems were proposed.As we see from the authors’ figure 3a, Bohr assumed that electrons in hydrogen molecules move around the molecular axis out of phase. It is a remarkable fact that Werner Heisenberg put forward in 1922 a two-electron atomic model that had electrons moving similarly out of phase and that ascribed a fractional quantum number (½) to the bending mode of the configuration.11. G. Tanner, K. Richter, J.-M. Rost, Rev. Mod. Phys. 72, 497 (2000). https://doi.org/10.1103/RevModPhys.72.497 Although Heisenberg’s model predicted the ground-state helium level, which was in excellent agreement with the spectroscopic data, Bohr opposed the model, since a noninteger quantum number was considered sacrilege. For the same reason, Bohr never published his own results. However, the asynchronous two-electron atomic model turned out to be the fertile one, though the corresponding classical configurations can have very complex structure.22. P. Grujic, N. Simonovic, J. Phys. B 28, 1159 (1995). https://doi.org/10.1088/0953-4075/28/7/011REFERENCESSection:ChooseTop of pageREFERENCES <<1. G. Tanner, K. Richter, J.-M. Rost, Rev. Mod. Phys. 72, 497 (2000). https://doi.org/10.1103/RevModPhys.72.497, Google ScholarCrossref, ISI2. P. Grujic, N. Simonovic, J. Phys. B 28, 1159 (1995). https://doi.org/10.1088/0953-4075/28/7/011, Google ScholarCrossref, ISI© 2014 American Institute of Physics.
Writing about what is usually termed the Aharonov-Bohm (AB) effect, Peter Sturrock and Timothy Groves argue (Physics Today, April 2010, page 8) that the same physics was discovered a decade earlier 1 1. W. Ehrenberg, R. E. Siday, Proc. Phys. Soc. B 62, 8 (1949). and should rightly be called the Ehrenberg-Siday effect. I agree that Werner Ehrenberg and Raymond Siday deserve recognition for their anticipation of AB. Indeed, in recent talks celebrating the 50th anniversary of AB, I began by describing the unfairly neglected paper by Ehrenberg and Siday. Nevertheless, I have come to a different conclusion from Sturrock and Groves: The expression “Aharonov-Bohm effect” is justified, for two reasons.First, although there is no doubt that the work by Ehrenberg and Siday anticipated how inaccessible magnetic flux can influence electron interference, that was as a curiosity, at the end of a paper whose main emphasis was the Hamiltonian analysis of electron optics. By contrast, Yakir Aharonov and David Bohm emphasized from the start, as an essential and general aspect of quantum mechanics, the physical influence of inaccessible fields that act nonlocally through the vector potential.Second, Ehrenberg and Siday’s semi-classical approximation—essentially applying the Dirac magnetic phase factor to electrons traveling on either side of the flux—implies a wavefunction that is multivalued and therefore not the correct solution of Schrödinger’s equation. The lack of a single-valued wavefunction leaves their prediction open to doubt. By contrast, Aharonov and Bohm derived the exact single-valued solution for waves scattered by a flux line. Recently, it was shown that the Ehrenberg-Siday approximation corresponds to the first terms in a “many-whirls” representation that treats the exact AB wavefunction as a topological sum over paths circling the flux. 2 2. M. V. Berry, J. Phys. A (in press). Attribution of credit is a delicate matter. It tends to excite strong feelings, and I write about it reluctantly. But the Ehrenberg-Siday paper does seem to exemplify the unfortunate phenomenon identified by Alfred North White-head in a 1916 address to the British Association for the Advancement of Science: “Everything of importance has been said before, by someone who did not discover it.”In a companion letter in the April 2010 issue, Alexander Ershkovich correctly points out that the AB effect is present in classical Hamiltonian mechanics, even though remote magnetic fields cannot influence Newtonian trajectories. He advocates a “search for experiments that might prove … a classical analogue of the Aharonov-Bohm effect.” Such an experiment exists already. In the classical physics of waves on a moving medium, the flow velocity acts like the vector potential in quantum mechanics, so the flow vorticity acts like the magnetic field; the analogy is precise. Fine details of the AB wavefunction were observed in ripples on the surface of water swirling irrotationally into a bathtub vortex, 3 3. M. V. Berry, R. G. Chambers, M. D. Large, C. Upstill, J. C. Walmsley, Eur. J. Phys. 1, 154 (1980). whose core is the analogue of inaccessible magnetic flux. REFERENCESSection:ChooseTop of pageREFERENCES <<CITING ARTICLES1. W. Ehrenberg, R. E. Siday, Proc. Phys. Soc. B 62, 8 (1949). Google ScholarCrossref2. M. V. Berry, J. Phys. A (in press). Google Scholar3. M. V. Berry, R. G. Chambers, M. D. Large, C. Upstill, J. C. Walmsley, Eur. J. Phys. 1, 154 (1980). Google ScholarCrossref© 2010 American Institute of Physics.
With considerable interest I read the article “Bohr’s molecular model, a century later” by Anatoly Svidzinsky, Marlan Scully, and Dudley Herschbach (Physics Today, January 2014, page 33). It is always interesting to see how our current understanding sheds new light on the revolutionary scientific ideas of the past. I agree with the authors that although quantum mechanics is the real basis for atomic- and molecular-physics computations, the old Bohr model that treats electrons in atoms like tiny planets moving around the sun-nucleus is intuitively clear and very attractive.As I see it, the aim of the article is to show how to use Bohr’s approach to treat not only simple atoms but molecules. An important point in that approach is reconciliation of quantum mechanics with Bohr’s ideas. The authors claim that in infinite dimensions, quantum mechanics “morphs into classical mechanics.”I cannot say, however, that the infinite-dimension system is a clarifying model to describe physical or chemical objects. I do not see that the reference to chromodynamics (and to Edward Witten’s article in Physics Today, July 1980, page 38) is a clarifying one. Far from convincing are statements like “Hence the large-D limit, where 1/D → 0, is closer to the real world (1/D = 1/3) than is the oft-used D = 1 regime. Indeed, results obtained at large D usually resemble those for D = 3.” I confess it sounds too lacking in rigor to be convincing.But the large-D limit per se is not what bothers me. Of great concern is the assumption that the radial part of the D-dimensional Schrödinger equation in Hartree units looks like this:(1)where Z is the nuclear charge and l is the angular momentum.Equation (1) has no sense for D = 1. Indeed, in one dimension, a finite angular momentum requires infinite speed of a rotating particle. Therefore, for D = 1, the correct equation is(2)which does not follow from equation (1) at D = 1.But most important is that equation (1) implies that the Coulomb potential does not depend on D. That could have been considered correct before it became clear that the Coulomb law follows from Maxwell’s equations when one considers a field generated by a point-like electric charge. So to obtain the Coulomb law for a two-dimensional space, one has to consider Maxwell equations in a two-dimensional world. For a point-like charge, those equations lead to a 1/(ln r) instead of 1/r dependence. If one takes into account the D-dependence of the Coulomb potential, derivations performed in the Physics Today article become meaningless. Indeed, when using an unrealistic equation (1), how can one believe that it illuminates Bohr’s quite realistic and physical postulates?© 2014 American Institute of Physics.