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An insightful tome recounts the heady early days of general relativity

The Formative Years of Relativity: The History and Meaning of Einstein's Princeton Lectures

Hanoch Gutfreund and Jürgen Renn
Princeton University Press,
2017
430 pp.
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On the centenary of general relativity, physicist Hanoch Gutfreund and historian Jürgen Renn published The Road to Relativity, a facsimile of Albert Einstein’s 1915–1916 German manuscript with an English translation and page-by-page commentary placing this seminal work in its historical and scientific context. Their new book, The Formative Years of Relativity, discusses in detail—yet deliberately without mathematics—general relativity’s development up to the early 1930s, focusing mainly on Einstein’s lectures at Princeton in May 1921.

The authors begin by quoting a London lecture given by Einstein in June 1921. “The abandonment of certain notions connected with space, time, and motion hitherto treated as fundamentals must not be regarded as arbitrary, but only as conditioned by observed facts,” he explained, stressing the origin of relativity not in philosophical speculation but in physical observation.

No doubt Einstein had in mind the May 1919 solar eclipse that confirmed general relativity’s exact prediction of the gravitational bending of starlight. So instant was the public reaction to this announcement in November of that year that the first nonmathematical English-language account of relativity, Oxford University physicist Henry Brose’s booklet The Theory of Relativity: An Introductory Sketch Based on Einstein’s Original Writings, was reprinted four times between December 1919 and March 1920. (Einstein’s own best-selling book, published in German in 1917, would not appear in English until August 1920.)

Relativity undoubtedly had a profound influence on cosmology, despite the fact that cosmology “scarcely played a role” in its genesis. In 1915, for example, it was employed to explain the perihelion motion of Mercury; it predicted gravitational waves in 1916, which were finally detected in 2016; and it introduced the cosmological constant in 1917, which helped to facilitate our understanding of the structure of the universe (although not the existence of black holes, which Einstein puzzlingly rejected). It also played a role in the quest for a unified field theory, which preoccupied Einstein until his dying day.

The authors also consider relativity’s relationship with philosophy, notably the work of Ernst Mach and Moritz Schlick, and with politics, including the books that emerged from the antirelativity movement. These include the notorious 100 Authors Against Einstein (which contains only 28 contributions), published in German shortly before the Nazis’ rise to power.

The book refers extensively to The Meaning of Relativity, Einstein’s summary of the Princeton lectures intended for mathematically sophisticated listeners. Indeed, this book is reprinted in The Formative Years of Relativity, along with, for the first time, an English translation of a stenographic record of two lectures intended for a nonprofessional audience.

This record is intriguing, because it allows the reader to “hear” an enthusiastic Einstein, but frustrating, because crucial words are missing or were misunderstood by the stenographer. “Part of the theory he explained on the blackboard,” noted a watching journalist. “The rest he explained out in space, with the chalk drawing imaginary lines … balanced between his fingers like the baton … of an orchestra leader (1).”

In his 1917 book, Einstein tried to make relativity comprehensible by including dialogues with the reader, examples from daily life, and only a few mathematical formulae. But, as Gutfreund and Renn validly note, “it does not compromise on scientific rigor, and the reader soon discovers that an intellectual effort is required to follow the flow of Einstein’s thoughts and arguments.”

Einstein himself called the original German edition “quite wooden” in a letter to Michele Besso (2). He liked to quote Max Planck’s shrewd remark: “Einstein believes his books will become more readily intelligible if every now and again he drops in the words ‘Dear reader’” (3).

No such criticism can be leveled at Gutfreund and Renn, who combine years of Einstein scholarship with readability and insight. However, they cannot rival Einstein’s flair for witty simplification. In April 1921, Einstein offered this—admittedly half-joking—distillation of relativity to a hungry press: “It was formerly believed that if all material things disappeared out of the universe, time and space would be left. According to relativity theory, however, time and space disappear together with the things” (4).

References

  1. J. Illy, Ed., Albert Meets America (John Hopkins Univ. Press, Baltimore, MD, 2006)

  2. Einstein to Michele Besso, 9 March 1917, Collected Papers of Albert Einstein, vol. 8, doc. 306

  3. A. Robinson, Einstein: A Hundred Years of Relativity (Princeton Univ. Press, Princeton, NJ, 2015). A. Robinson, Einstein: A Hundred Years of Relativity (Princeton Univ. Press, Princeton, NJ, 2015)

  4. R. W. Clark, Einstein: The Life and Times (HarperCollins, New York, 2011)

About the author

The reviewer is the author of Einstein: A Hundred Years of Relativity (Princeton Univ. Press, Princeton, NJ, 2015).

  • Pentcho Valev

    Unlike special relativity, general relativity was not deduced from postulates. It is an empirical compilation – a malleable combination of ad hoc equations and fudge factors allowing Einsteinians to predict anything they want. Here Michel Janssen describes the anti-deductive approach of Einstein and his mathematical friends – endlessly adjusting and amending the model until “excellent agreement with observation” is reached:

    Michel Janssen: “But – as we know from a letter to his friend Conrad Habicht of December 24, 1907 – one of the goals that Einstein set himself early on, was to use his new theory of gravity, whatever it might turn out to be, to explain the discrepancy between the observed motion of the perihelion of the planet Mercury and the motion predicted on the basis of Newtonian gravitational theory. […] The Einstein-Grossmann theory – also known as the “Entwurf” (“outline”) theory after the title of Einstein and Grossmann’s paper – is, in fact, already very close to the version of general relativity published in November 1915 and constitutes an enormous advance over Einstein’s first attempt at a generalized theory of relativity and theory of gravitation published in 1912. The crucial breakthrough had been that Einstein had recognized that the gravitational field – or, as we would now say, the inertio-gravitational field – should not be described by a variable speed of light as he had attempted in 1912, but by the so-called metric tensor field. The metric tensor is a mathematical object of 16 components, 10 of which independent, that characterizes the geometry of space and time. In this way, gravity is no longer a force in space and time, but part of the fabric of space and time itself: gravity is part of the inertio-gravitational field. Einstein had turned to Grossmann for help with the difficult and unfamiliar mathematics needed to formulate a theory along these lines. […] Einstein did not give up the Einstein-Grossmann theory once he had established that it could not fully explain the Mercury anomaly. He continued to work on the theory and never even mentioned the disappointing result of his work with Besso in print. So Einstein did not do what the influential philosopher Sir Karl Popper claimed all good scientists do: once they have found an empirical refutation of their theory, they abandon that theory and go back to the drawing board. […] On November 4, 1915, he presented a paper to the Berlin Academy officially retracting the Einstein-Grossmann equations and replacing them with new ones. On November 11, a short addendum to this paper followed, once again changing his field equations. A week later, on November 18, Einstein presented the paper containing his celebrated explanation of the perihelion motion of Mercury on the basis of this new theory. Another week later he changed the field equations once more. These are the equations still used today. This last change did not affect the result for the perihelion of Mercury. Besso is not acknowledged in Einstein’s paper on the perihelion problem. Apparently, Besso’s help with this technical problem had not been as valuable to Einstein as his role as sounding board that had earned Besso the famous acknowledgment in the special relativity paper of 1905. Still, an acknowledgment would have been appropriate. After all, what Einstein had done that week in November, was simply to redo the calculation he had done with Besso in June 1913, using his new field equations instead of the Einstein-Grossmann equations. It is not hard to imagine Einstein’s excitement when he inserted the numbers for Mercury into the new expression he found and the result was 43″, in excellent agreement with observation.”

    Pentcho Valev