Reply to Hans C. Ohanian
A response to Hans C. Ohanian’s review of
Kinematics: The Lost Origins of Einstein’s Relativity,
in the journal Physics in Perspective, vol.12 (2010), pp.236-238.
Alberto A. Martínez
To start, Hans C. Ohanian notes that my history of kinematics “is incomplete—it leaves out how nineteenth-century mathematicians developed the description of motion by general curvilinear coordinates, on curved surfaces, and in curved spaces, and the description of geodesic curves, all of which later proved crucial for Einstein’s general relativity.” With any book, it is easy to point out things that the author did not do. As I noted in my Preface: “Not everything about the history of kinematics is in this book.” I chose to research developments in the history of kinematics that contributed to the rise of Einstein’s special theory of relativity of 1905. Hopefully someone else will trace the history of kinematics that contributed to Einstein’s theory of gravity, his so-called “general relativity,” published in 1916.
Next, Ohanian expresses gratitude for the “rich selection of recollections” that I assembled about Einstein. I certainly appreciate that, but Ohanian questions the reliability of some such sources. He gives just one example: that I quoted a sentence by Aylesa Forsee about the key night when Einstein was struggling to solve the puzzle of simultaneity in 1905: “That night when he went to bed, he lay awake tossing and turning.” Ohanian calls this “excessively imaginative.” Actually, we don’t know if it is imaginative. Ohanian did not mention why I quoted Forsee. What matters is that Forsee’s account is based on interviews with Einstein’s son, Hans Albert, who knew his father well. This book is among several that are routinely neglected by nearly all writers on the history of relativity; we do not know which parts of it echo anything that Einstein, Maric, or Besso told Hans Albert, or what Hans Albert in turn told Forsee, or clearly which parts are merely imaginative. Accordingly, what I wrote in my book is:
“Maybe that one night was different. As one biographer claimed, ‘That night when he went to bed, he lay awake tossing and turning.’”
The words ‘Maybe’ and ‘claimed’ show that I am conveying an indirect account; these words clearly convey that I am not attributing truth or falsehood to Forsee’s sentence, but that I wish to share with the reader excerpts from some interesting accounts that are plausible—not as speculations—but because they are found in works that to some extent echo the historical actors. Sources are not equally reliable, of course, so to that end I systematically used brief qualifiers to convey various degrees of credibility: for example, some of my sentences involve words such as “reportedly,” “allegedly,” “claimed,” etc. The most important point is that my account brings together an unparalleled wealth of both well-known and neglected “new” sources, by: Einstein, Besso, Solovine, Marić, Ehrat, Leich, Byland, Kollros, Niggli, Talmud, Niewenhuis, Ries, Paul Habicht, Ishiwara, Sauter, Moszkowski, Wertheimer, Reichinstein, Koch, Kayser, Frank, Franck, Marianoff, Seelig, Tucci, Shankland, Vallentin, Kornitzer, Hoffmann, Cohen, Michelmore, Forsee, etc. In the immensely popular, mature, and expansive field of the history of Einstein’s path to special relativity, no other work, none, uses even half as many relevant sources as Kinematics. (For evidence read this.)
Moreover, no other work in this field cites quotations more accurately. To illustrate the latter point, let me comment on Ohanian’s own book, Einstein’s Mistakes: The Human Failings of Genius (2008). It is perplexing that Ohanian complains about my use of Forsee, who at least did interview Hans Albert Einstein and who did write what I quoted Forsee as writing—while, at the same time, Ohanian consciously includes in his own book quotations that he recognizes as apocryphal. He quotes Einstein as saying: “The secret of creativity is knowing how to hide your sources.” There is no evidence that Einstein ever said that; it is a false quotation that arose in English in the 1990s, and has no source in Einstein’s writings in German. Also, Ohanian echoes the apocryphal quotation: “When does Baden-Baden stop at this train?” These words, really, are just the title of a work of art from 1989, by German artist Klaus Rinke, a clock mounted on a base with wheels, titled: “Albert Einstein! Wann halt Baden-Baden an diesem Zug?” Also, Ohanian’s book includes alleged anecdotes that are simply fiction. For example, he claims that in 1905 Einstein “reviewed patent applications for electromagnetic devices used for the operation of citywide networks of synchronized clocks,” and that Einstein pointed to a clock tower in Bern and to another in Muri to exemplify to Besso his crucial idea about synchronizing clocks. This is all just wrong, it is speculative fiction based on misreadings of historical sources, as I explained in my article: “Material History and Imaginary Clocks: Poincaré, Einstein, and Galison on Simultaneity,” Physics in Perspective, vol. 6 (2004), 224-240.
Let me take this opportunity to debunk also another cute, false quotation that nowadays spreads. When I wrote Kinematics, I collected and painstakingly inspected many alleged quotations and traced their origins in order to determine whether or not to include them in my book. One of the quotations I discarded happens to be the title of Ohanian’s Chapter 4, his account of how Einstein formulated special relativity. Ohanian titled it: “A storm broke loose in my mind,” and he described these words as: “Einstein, in a letter to his son, describing the sudden inspiration that led him to the invention of special relativity.” This is just another mistake, there exists no such letter from Einstein to either of his sons, and there is no evidence that anyone ever claimed that Einstein ever told this to them. The roots of this apocryphal quotation begin in 1921, when Alexander Moszkowski published his book Einstein: Einblicke in seine Gedankenwelt. Moszkowski had various conversations with Einstein at around 1916. In his book, in addition to paraphrasing some of Einstein’s statements, Moszkowski also included abundant literary hyperboles and metaphorical turns of phrase. Thus on p. 227, Moskowski wrote:
“Mitten in seiner Praxis, 1905, brach es in ihm hervor, in Sturm und Drang, geradezu blitzartig. In dichter Folge entband sich sein Geist von einer in mehrjähriger Vorarbeit aufgespeicherten Gedankenfülle, die uns mehr zu bedeuten hat, als nur ein bestimmtes Stadium in der Entwicklung eines Einzelnen.”
Very literally translated, the key sentence reads: “In the midst of his praxis, 1905, it broke out in him, in Storm and Urge, almost in a flash.” This is a literary expression: “Sturm und Drang,” the name given to a movement in German literature and music from the 1760s to the 1780s in which extremes of individual emotion burst out against the constraints of Enlightenment rationalism. The expression is often translated as “Storm and Stress.” Regardless, in 1921, Moszkowski’s book was translated into English by Henry L. Brose, who rendered the lines above as (Einstein, The Searcher, p. 229):
“In 1905, in the midst of his work, the storm broke loose in him with the suddenness of a hurricane. In quick succession his mind disburdened itself of the abundance of ideas that has stored themselves up in the work of the preceding years, and these ideas signify more to us than a definite stage in the development of an individual.”
Next, in 1935, the British writer John William Sullivan wrote a brief biographical sketch of Einstein, based on the translation of Moszkowski’s book and on Rudolf Kayser’s book Albert Einstein: A Biographical Portrait (which Kayser published under the pseudonym Anton Reiser). There, Sullivan wrote: “The young genius had come alive. Einstein has said of that wonderful time, “it was as if a storm had broken loose in my mind.” In just fourteen years, a mistranslation became a quotation. This minor mistake, echoing Moszkowski’s words as if they were a quotation from Einstein, was rarely echoed again (one instance is the Manchester Guardian Weekly, Vol. 70 (1953), p.21), that is, until the British writer Denis Brian published a new biography, Einstein: A Life, in 1996. In that book, Brian wrote:
“There is no record of how late he went to bed that night, what he had for supper, or whether his sleep was disturbed by nightmares. He woke next morning in great agitation, as if, he said, ‘a storm broke loose in my mind.’ With it came the answers.”
Like Sullivan, Brian simply confused his notes from his sources, so he attributed the quotation in question to Anton Reiser’s book. He did not cite the page number because, actually, Reiser’s book includes no such expression at all. Still, “Reiser” was actually Einstein’s stepson-in-law, Rudolf Kayser. Anyone who does not keep track of sources carefully, or who just is not familiar with the individuals in question, could readily recollect, mistakenly, that the quotation in question came from Einstein’s “son-in-law,” or just his “son.” Thus, by 2007, at the latest, colorful bookmarks were being sold by a company called Literary Luminaries featuring a cartoon of Einstein along with a brief biographical sketch, including the claim: “The whirlwind of these breakthroughs was remarkable. In a letter to his son, he said of that period: ‘a storm broke loose in my brain.’” No such letter exists. In 2008, Hans Ohanian likewise claimed that a letter by Einstein to his son referred to that “storm,” and he cited Denis Brian as his source. Ohanian is not alone, several other writers also echo the false quotation, including: Michio Kaku (2004), Michio Kaku in NOVA (2005), John S. Rigden (2005), Jennifer Oulette (2005), George Will (2008), Manjit Kumar (2010).
I don’t want to seem too critical by pinpointing defects in Ohanian’s book. Despite its defects (it’s a popular book, not a scholarly work of history), it is an interesting and entertaining book and I’ve published a positive review of it. I explain the evolution of this one quotation because my recent work (Science Secrets) focuses on that: the evolution of myths in history of science, and this is an interesting, small example of how fiction (literary embellishments) become misconstrued as history. My point is just that when Ohanian insinuates that my handling of sources leaves something to be desired, well, he is just barking up the wrong tree.
Moving on, consider another tree. Ohanian praises my analysis of Einstein’s first relativity paper as “valuable” but complains that it is insufficiently critical. He claims that I am “Blinded by partiality” by following Einstein “into several bad conceptual mistakes.” Specifically, he complains that I follow Einstein’s account of how clocks synchronized by out-and-back light signals require a convention: the assumption that the speeds of light in opposite directions are equal. Ohanian claims that “Einstein took this procedure from Poincaré’s Science and Hypothesis.” But Ohanian’s claim is mistaken. Ohanian footnotes the English translation (1905) of Poincaré’s book. The problem is that Einstein did not read English at all. As I explained in my book, Einstein read either the original French edition of Poincaré’s book (1902), or its German translation (1904), and neither of these editions says anything about how to synchronize clocks using out-and-back light signals. Ohanian’s confusion arises because he did not use primary sources, he just looked at the English translation which includes an Appendix: Poincaré’s article on “The Principles of Mathematical Physics,” which was absent in the original editions of the book because it was a later address which he presented to the International Congress of Arts and Science in St. Louis, in 1904. Notwithstanding Ohanian’s confusion, we just don’t know where Einstein learned the procedure he described for synchronizing clocks. As I show in my Kinematics, it is conceivable that Einstein learned it from a paper by Poincaré from 1900, which we know Einstein had read by 1906, or perhaps from someone who had read it, or perhaps from Poincaré’s book La Valeur de la Science, which was published in 1905 (Einstein read it in 1905, but we do not know if he read it before writing his first paper on relativity), or perhaps from another source; we just don’t know.
Anyhow, Ohanian claims that when Einstein argued that the equality of the speeds of light in opposite directions is a stipulation, that that “was a gross conceptual mistake.” Ohanian claims that I make “the wild claim that theorists have sought to find an experimental method to test or verify the equality of one-way speeds in different directions but failed to find any.” But really, this is not a “wild claim.” Many proposals have been advanced to make such measurements and none have been generally accepted as valid. At the bottom of this reply, as evidence, I have included a list of more than a hundred articles and books, throughout more than a century, in many journals, in which various theorists and experimenters have proposed ways to measure the one-way speed of light and others have systematically refuted such proposals. For example, Ohanian himself formulated such a proposal in 2004 which promptly generated a flurry of submissions to the American Journal of Physics arguing that Ohanian was mistaken. Among these submissions were articles by Robert Klauber, Alan Macdonald, and myself, and the AJP published the latter replies. The search for one-way measurements of the speed of light has been so full of rebuttals and retractions that in 1986 John D. Norton compared it to the old quest for a perpetual motion machine.
Now, in his review of my book, Ohanian alludes to several methods for measuring the speed of light. To start, he claims that, in 1676, Ole Roemer’s astronomical observations constitute one-way measurements. Ohanian notes that I did not discuss Roemer in my book, so let me do so here. Roemer saw that at one point in the year, one of Jupiter’s moons, Io, took a certain time to reappear once it had moved behind Jupiter. Later in the year, Roemer saw that the same moon took longer to reappear. He therefore inferred (correctly) that the additional delay arose because Earth, orbiting the sun, had moved farther away from Jupiter, and therefore, sunlight reflected from Io had to travel a greater distance to reach Earth then. By comparing both delays before Io’s reappearance, Roemer roughly calculated the speed of light from Io to Earth. This might seem to be a one-way measurement because there is no clock on Jupiter or Io, and light is not sent from Earth to Io and back. Therefore, various writers, including Z. Augustynek (1960), G. B. Brown (1967), L. Essen (1969), and now Ohanian, have claimed that Roemer indeed measured the one-way speed of light. Such claims have been criticized, for example, by Reichenbach (1925), Scott-Iversen (1944), Kerlov (1970), Salmon (1977), Torretti (1983), and others, and more recently by Max Jammer (2006).
To calculate the speed of light by using Jupiter’s moons, we need to know the orbital speed of the Earth. Thus we are confronted with an equivalent problem: how do we measure the speed of the Earth? Ohanian knows this (Einstein’s Mistakes, p. 344), so he proposes that Earth’s speed “can be measured by merely timing the orbital period with a single (hypothetical) stationary clock, provided we assume (as Einstein did) that Newtonian mechanics is applicable for low-speed motion.” Now notice how an actual astronomical procedure, by Roemer, becomes an imaginary and impossible thought experiment. Ohanian wants us to set up a stationary clock in space, and have it mark an orbital departure time of Earth and its return, to give us its speed. First problem: the Earth moves not only around the sun, it moves with the solar system, so when Earth completes an orbit around the sun, it will not return to the “stationary” clock that has, in the meantime, been left behind. So, suppose that we can rigidly attach the clock to the sun, so that it remains at rest relative to Earth’s orbit. Second problem, the sun spins on its axis, so we cannot attach the clock rigidly to the sun because it would move the clock away from its initial position in Earth’s orbit. But still, suppose we could somehow overcome that problem too, after all, Ohanian is merely talking about an imaginary clock, not any real experiment. But then we reach the main problem: using one clock, we then know only the average round trip orbital speed of Earth—how do we know the speeds of Earth in different directions? If we assume a constant speed, then we have adopted a similar convention as assuming the equality of light speeds in opposite directions. But now the situation is worse, because we know that Earth travels at different speeds throughout the year, and in different directions. Ohanian disregards any such complications because he claims that since Newton’s mechanics is valid for low speeds, we can use the average orbital speed of Earth as given by Newton’s mechanics as a non-conventional value. Problem: that value is not a measurement.
An odd aspect of Ohanian’s arguments is that they can be answered with very old explanations. In 1898, Henri Poincaré explained how the assumption of the equality of light speeds related to Roemer’s measurements. He explained:
“This postulate assumed, let us see how the velocity of light has been measured. You know that Roemer used eclipses of the satellites of Jupiter, and sought how much the event fell behind its prediction. But how is this prediction made? It is by the aid of astronomic laws, for instance Newton’s law.”
“Could not the observed facts be just as well explained if we attributed to the velocity of light a little different value from that adopted, and supposed Newton’s law only approximate? Only this would lead to replacing Newton’s law by another more complicated. So for the velocity of light a value is adopted, such that the astronomic laws compatible with this value may be as simple as possible.”
Poincaré acknowledged that it is possible, though inconvenient, to assume different speeds of light along with more complicated versions of Newton’s laws. Ohanian claims that Newton’s laws must have their usual form and that therefore the speed of light is constant. Ohanian rejects any unusual formulations of mechanics, but as I stated in my 2004 article, “such equations do not predict any differences whatsoever in the actual material behavior of physical systems. They constitute an unusual but entirely consistent way of representing and accounting for empirical relations.” This is explained further in the papers by Macdonald and Klauber.
Next, Ohanian mentions that Arthur Stanley Eddington was more meticulous than Einstein inasmuch as Eddington acknowledged that in principle it is possible to synchronize clocks by transporting chronometers. Ohanian does not mention, however, that Eddington recognized that such a procedure involves a convention equivalent to that of assuming that light speeds are equal in opposite directions. In 1923, Eddington explained:
“a convention is introduced as to the reckoning of the time differences at different places; this convention takes in the two methods the alternative forms: (1) A clock moved with infinitesimal velocity from one place to another continues to read the correct time at its new station, or (2) the forward velocity of light along any line is equal to the backward velocity. Neither statement is by itself a statement of observable fact, nor does it refer to any intrinsic property of clocks or of light; it is simply an announcement of the rule by which we propose to extend fictitious time-partitions through the world.”
I spare myself the effort of replying to the various other alleged measurements of the one-way speed of light that Ohanian mentions, instead, I leave it to interested readers to reflect on such matters and to look at the extensive literature I cite below in order to find refutations of such schemes. If the topic of the one-way speed of light is new to any reader, I recommend beginning with Salmon’s engaging survey article of 1977, and then proceeding to the more accurate and encompassing work by Jammer (2006). Incidentally, I am not partial to the “conventionality” thesis. I would be glad to learn of a way to measure the one way speed of light, and in my Kinematics book I even describe a proposal. But until any such proposal has been executed in an actual experiment, I just cannot say that the isotropy of light rays is a matter of experimental fact.
It is unusual that Ohanian wants to ground relativity physics on dynamics rather than kinematics. As I showed in my book, it was precisely the transition from explanations based on forces to explanations based instead on possible and actual measurements of spaces and times that led physicists to develop and accept relativity theory. Physicists realized that calculations of force presuppose measurements of positions, displacements, and time intervals, that dynamics depends on kinematics. Ohanian wishes to reverse that, so it is fitting that he has proposed to abandon the law of inertia or to replace it as a corollary of Newton’s force law. He insists also on defining inertial systems in terms of Newton’s force law. He wishes to ground Einstein standard synchrony on Newton’s force law as well. Ohanian portrays Einstein as a stubborn “mystic” who danced “blindly” around his silly mistakes, cherry-picking experimental data, leading sometimes to inspired success but often to mediocre results and delusional failure. His disagreements with Einstein have led Ohanian to endorse H. A. Lorentz’s old theory that a privileged reference frame exists in the universe and there are dynamical causes for relativistic effects of length contraction and time dilation. Ohanian is welcome to cultivate such theoretical preferences, but I do not think that experiments make such views necessary, and I know of no physicists who have yet adopted his views.
Moving on, Ohanian finally complains that in my accounting of Einstein’s first derivation of the Lorentz transformations I did not explain “why Einstein’s calculation is such a mess.” Ohanian suggests a simpler way in which Einstein could have proceeded. Indeed, there are multiple simpler ways in which Einstein could have proceeded. My task was not to blame Einstein for not knowing shortest paths when he first formulated the Lorentz transformations, but only to trace what he actually did. Ohanian further criticizes Einstein as “silly” for replacing variables for infinitesimals, and he complains that I was mistaken by elaborating this by using a series expansion and neglecting higher order terms. I thank Ohanian for commenting on this, as I agree that the ends should not justify the means, and as I noted in my book, “Einstein did not really need to employ the differential calculus but could have obtained the same result more simply, purely by means of linear algebra.”
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