The Formative Years of Relativity and a Prejudice on Poincaré’s Conventionalism

The purpose of this piece is to review Hanoch Gutfreund’s and Jürgen Renn’s new book The Formative Years of Relativity: The History and Meaning of Einstein’s Princeton Lectures, Princeton University Press and Oxford University Press. I find two problems in the book the first of which is Poincaré’s influence on Einstein. This is the first part of the review which deals with Poincaré’s influence on Einstein. Since the book has mistakes and also errors in English and Jürgen Renn is considered a notable scholar, I assume that Gutfreund is probably responsible for the mistakes and for the errors in English.

Let us begin with page 26 of the book The Formative Years of Relativity. Gutfreund is apparently much attracted by “the painstaking analysis by the philosopher of science Yemima Ben-Menachem” in her book Conventionalism: From Poincaré to Quine. Cambridge University Press, Cambridge (2006):

Yemima 1921

Gutfreund writes that “Until 1921, Einstein did not mention Poincaré explicitly”.

Einstein obviously mentioned Poincaré before 1921. For instance, after the first Solvay congress in 1911, Einstein wrote to Heinrich Zangger (see the Collected Papers of Albert Einstein, CPAE):




Einstein says that Poincaré was in general simply antagonistic and for all his acuity showed little understanding of the situation.

There was then great excitement among philosophers and historians of science when they discovered, as Gutfreund writes on page 26 above that “We know that he [Einstein] read Science and Hypothesis with his friends in the Akademie Olympia in 1902″.

Poincaré’s publisher Flammarion published La science et l’hypothèse (Science and Hypothesis) in Paris in 1902. How do we know that Einstein read this book in 1902 and not in 1903 or 1904? Take a look at Gutfreund’s words: “We know that he [Einstein] read Science and Hypothesis with his friends in the Akademie Olympia in 1902″. It means that Einstein rushed to the local bookstore in Bern the day the book was out, dodged people in the crowd waiting outside the bookstore and found the first French edition of Poincaré’s book. But maybe Einstein read the 1904 German translation of Poincaré’s 1902 book? This could be quite different from the original 1902 French edition.

Subsequently,  on page 26 Gutfreund writes: “Einstein’s biographer Abraham Pais quotes one of the members, Maurice Solovine, as saying: ‘This book profoundly impressed us and kept us breathless for weeks on end'”:


Gutfreund simply takes the Pais paragraph from Yemima Ben-Menahem’s book, Conventionalism, see footnote 80 below (page 134):


This is a mistake: We cannot cite Einstein’s biographer Abraham Pais quoting one of the members of the Akademie Olympia (Olympia Academy). The biography of Pais is not a primary source. We have to check a primary source and see whether Maurice Solovine himself said: “This book profoundly impressed us and kept us breathless for weeks on end”.

Here is the original primary source:


Lettres à Maurice Solovine. Paris: Gauthier-Villars, 1956.

Here luck plays an important role because in the above book Solovine writes in French that Poincaré’s book “profoundly impressed us and kept us breathless for many weeks”. One should, however, check the original quote in French.

On page 30 Gutfreund tells the story of Einstein who explored “a famous example that goes back Poincaré”. There are several typos in the book.

Poincare typo

It is interesting, however, to look at the following sentence, several sentences below the above one on page 30:

He typo

“Without the distinction between axiomatic Euclidean geometry and practical rigid-body geometry, we arrive at the view advanced by Poincaré”. And then Gutfreund adds an end-note 15: “For an extensive analysis of Poincaré’s conventionalism, see Yemima Ben-Menachem, […]” Her book Conventionalism.

Yemima 1921-2

You might, of course, be tempted to suppose that Ben-Menahem has said the above words in her book. But this is by no means the case. Einstein says this in his 1921 talk, “Geometry and Experience” (see CPAE):

geometry and experience

After the words: “Without the distinction between axiomatic […]” Gutfreund writes: “He suggested that […]”

He typo

Who is “He”? Einstein or Poincaré?

Let us then examine Yemima Ben-Menahem’s book, Conventionalism.

I am quoting from Yemima Ben-Menahem’s book Conventionalism, page 84:

“… as both GR [general relativity] and the special theory of relativity originated in insights about equivalence, an element of conventionality might seem to be built right into the theory.  It is important to recognize, however, that Einstein’s use of equivalence arguments differs fundamentally from that of the conventionalist”.

And on page 134 Ben-Menahem writes: “The preceding discussion should alert us to the traces of Poincaré’s equivalence argument in Einstein’s work on GR as well. […] The centrality of equivalence arguments and their geometric implications is too obvious in Science and Hypothesis to be missed by a reader such as Einstein, who, we know, was familiar with the book. Beginning with the hypothesis of equivalence in 1907, Einstein makes use not only of the general idea of equivalent descriptions, but also of the types of examples Poincaré used”.


and on page 135, Yemima Ben Menahem argues that “Einstein was deeply influenced by the idea of equivalence, and to that extent could concede that Poincaré was right”:

page 135

I have found no historical evidence (primary documents, i.e. correspondence of Einstein with others, manuscripts, and also interviews with Einstein) supporting the claim that Einstein makes use of Poincaré’s equivalent descriptions.

In the 1920 unpublished draft of a paper for Nature magazine, “Fundamental Ideas and Methods of the Theory of Relativity, Presented in Their Development”, Einstein explained how he arrived at the principle of equivalence (see CPAE):

happiest happiest2

(Original in German). “When I (in Y. 1907) [in Bern] was busy with a comprehensive summary of my work on the special theory relativity for the ‘Jahrbuch für Radioaktivität und Elektronik’, I also had to try to modify Newton’s theory of gravitation in such a way that its laws fitted into the theory. Attempts in this direction showed the feasibility of this enterprise, but did not satisfy me, because they had to be based upon unfounded physical hypotheses. Then there came to me the happiest thought of my life in the following form:

The gravitational field is considered in the same way and has only a relative existence like the electric field generated by magneto-electric induction. Because for an observer freely falling from the roof of a house there is during the fall – at least in his immediate vicinity – no gravitational field. Namely, if the observer lets go of any bodies, they remain relative to him, in a state of rest or uniform motion, regardless of their particular chemical and physical nature. The observer is therefore justified in interpreting his state as being ‘at rest’.

The extremely strange experimental law that all bodies fall in the same gravitational field with the same acceleration, immediately receives through this idea a deep physical meaning. If there were just one single thing that fell differently in a gravitational field from the others, the observer could recognize with its help that he was in a gravitational field and that he was falling in the latter. But if such a thing does not exist – as experience has shown with great precision – then there is no objective reason for the observer to regard himself as falling in a gravitational field. Rather, he has the right to consider his state at rest with respect to gravitation, and his environment as field-free.

The experimental fact of independence of the material of acceleration, therefore, is a powerful argument for the extension of the relativity postulate to coordinate systems moving nonuniformly relative to each other”.

Isaac Newton had already recognized that Galileo’s law of free fall was connected with the equality of the inertial and gravitational mass. In approximately 1685, Newton realized that there was an (empirical) equality between inertial and gravitational mass (Newton 1726, Book I, 9). For Newton, however, this connection was accidental. Einstein, on the other hand, said that Galileo’s law of free fall could be viewed as Newton’s equality between inertial and gravitational mass, but for him the connection was not accidental.

Hence, Einstein made use of Newton’s equality (accidental equivalence) between inertial and gravitational mass and Galileo’s law of free fall and in his 1907 paper, “On the Relativity Principle and the Conclusions Drawn from It”, he invoked a new principle, the equivalence principle or hypothesis. He assumed the complete physical equivalence of a homogeneous gravitational field and a corresponding (uniform) acceleration of the reference system. Acceleration in a space free of homogeneous gravitational fields is equivalent to being at rest in a homogeneous gravitational field.

Ernst Mach criticized Newton’s bucket experiment. He said that we cannot know which of the two, the water or the sky, are rotating; both cases produce the same centrifugal force. Mach thus expressed a kind of equivalence principle: Both explanations lead to the same observable effect. Einstein could have been influenced by Mach’s idea that we cannot know which of the two, the water or the sky, are rotating. Indeed Charles Nordmann interviewed Einstein and wrote: “Perhaps even more than Poincaré, Einstein admits to have been influenced by the famous Viennese physicist Mach”.

On page 31, Gutfreund writes in his book:


“Had he [Einstein] instead accepted the conventionalist position […]” and then Gutfreund writes: “This in fact is exactly the situation in which Einstein introduced the mental model of a rotating disk, which he used as early as 1912 to show that the new theory of ravitation requires a new framework for space and time”.

Another typo: it should be the new theory of gravitation.

The rotating disk story starts with a problem in special relativity, with Max Born’s notion of rigidity and not with Poincaré! Einstein never mentioned any influence Poincaré had had on him when inventing the disk thought experiment.

At the annual eighty-first meeting of the German Society of Scientists and Physicians in Salzburg on 21-25 September 1909, Born first analyzed the rigid body problem and showed the existence of a class of rigid motions in special relativity.

John Stachel describes this state of affairs in his seminal paper of 1980: “The Rigidly Rotating Disk as a ‘Missing Link’ in the History of General Relativity”. It seems that Gutfreund is unacquainted with Stachel’s paper.

On September 29, 1909 the Physikalische Zeitschrift received a short note from Paul Ehrenfest. In his note Ehrenfest demonstrated that according to Born’s notion of rigidity, one cannot bring a rigid body from a state of rest into uniform rotation about a fixed axis. Ehrenfest had pointed out that a uniformly rotating rigid disk would be a paradoxical object in special relativity; since, on setting it into motion its circumference would undergo a contraction whereas its radius would remain uncontracted.

Born noted: “Mr. Ehrenfest shows that the rigid body at rest can never be brought into uniform rotation; I have discussed the same fact with Mr. Einstein in the meeting of natural scientists in Salzburg”. Born discussed the subject with Einstein and they were puzzled about how the rigid body at rest could never be brought into uniform motion. Born and Einstein discovered in that discussion that setting a rigid disk into rotation would give rise to a paradox: the rim becomes Lorenz-contracted, whereas the radius remains invariant. This problem was discussed almost simultaneously by Ehrenfest in the above short note.

Later in 1919, Einstein explained to Joseph Petzoldt why it was impossible for a rigid disk in a state of rest to gradually set into rotation around its axis:


On page 32 Gutfreund mentions the 10th German edition of Einstein’s popular book Relativity the Special and General Theory. He says that in a copy of this book there is a sheet of paper in the handwriting of Einstein’s stepdaughter containing a remark:


As you can see this remark is quite similar to Einstein’s letter to Petzoldt. Thus, it is preferable to quote Einstein’s own words, his letter to Petzhold. It seems that Gutfreund is unacquainted with the history of the rotating disk, because according to his book he is unaware of Stachel’s paper and the letter to Petzhold.

At the end of October 1909 Born submitted an extended version of his Salzburg talk to Physikalische Zeitschrift. In December 1909 Gustav Herglotz published a paper in which he noted that according to Born’s notion of rigidity, a “rigid” body with a fixed point can only rotate uniformly about an axis that goes through it, like an ordinary rigid body. Several months later, Einstein mentioned Born’s and Herglotz’s papers in a letter from March 1910 to Jakob Laub, in which he said that he was very much interested in their then recent investigations on the rigid body and the theory of relativity.  A month later, in conversations with Vladimir Varičak Einstein explained that the great difficulty lies in bringing the “rigid” body from a state of rest into rotation. In this case, each material element of the rotating body must Lorentz contract. See my new book Einstein’s Pathway to the Special Theory of Relativity 2Ed for full details.

In his paper from February 1912, Einstein considered a system K with coordinates x, y, z in a state of uniform rotation (disk) in the direction of its x-coordinate and referred to it from a non-accelerated system. Einstein wrote that K‘s uniform rotation is uniform “in Born’s sense”, namely, he considered a rotating disk already in a state of uniform rotation observed from an inertial system and reproduced his conversations with Varičak. Einstein then extended the 1907–1911 equivalence principle to uniformly rotating systems as promised in conversations with Sommerfeld in 1909.

All we know according to primary sources is that the origin of the rotating disk story is in a problem in special relativity, Max Born’s notion of rigidity and Ehrenfest’s paradox, which Einstein mentioned many times before 1912. Einstein never mentioned any influence Poincaré had had on him when inventing the disk thought experiment. Writing that Einstein was influenced by Poincaré’s conventionalism and equivalent arguments is speculating about the influence of the later on the former.

Gutfreund’s mistake about Poincaré’s influence on Einstein and Einstein’s so-called failure to acknowledge Poincaré’s work in connection with the equivalence principle and the rotating disk thought experiment in general relativity comes from Yemima Ben-Menahem’s book, Conventionalism. However, this misconception or prejudice on the part of Ben-Menahem comes from my PhD thesis which was submitted to the Hebrew University of Jerusalem back in 1998. I was a PhD student in the program for the history and philosophy of science and Yemima Ben-Menahem was a professor there. Here for example are several paragraphs from my PhD thesis:




And Poincaré’s disk thought experiment:








I have thus written in my thesis about Poincaré’s disk thought experiment and the equivalence of Euclidean and non-Euclidean geometries. I then mentioned Einstein’s rotating disk thought experiment and said that we eliminate absolute motion of the disk by assuming the equivalence of gravity and inertia. I then spoke about conventionalism and Einstein’s equivalence principle.

After the PhD I corrected and edited my PhD but then I was horrified to discover what looked like a magnification of the prejudice of Poincaré’s conventionalism and equivalence argument and his disk thought experiment influencing Einstein when creating general relativity: In 2006 Yemima Ben-Menahem said exactly the same thing in her book, Conventionalism. You might say that it is even a more unfortunate instance to write about Poincaré’s influence on Einstein in connection with the equivalence principle and the disk thought experiment in general relativity over and over again in a single book… (see now for instance her book, pages 64-65):






Going on to Hanoch Gutfreund, in his new book of 2017, The Formative Years of Relativity, he has simply brought this incidence to the surface when he told the whole story of this prejudice all over again.








Did Einstein ever say “biggest blunder”?

Astrophysicist and author Mario Livio publishes a new book Brilliant Blunders.

George Gamow reports about Einstein telling him: “Einstein’s original gravity equation was correct, and changing it was a mistake. Much later, when I was discussing cosmological problems with Einstein, he remarked that the introduction of the cosmological term was the biggest blunder he ever made in his life. But this ‘blunder,’ rejected by Einstein is still used by cosmologists even today, and the cosmological constant denoted by the Greek letter Λ rears its ugly head again and again and again. (Gamow, George My World Line, 1970, Viking Press, pp. 149-150; see quote in Janssen below).

In his new book “Brillianat Blundders”, Livio doubts that Einstein said “biggest blunder” to Gamow. Livio can find no documentation that Einstein said this. Instead, claims Livio, all references eventually lead back only to Gamow, who reported Einstein’s use of the phrase in two sources: his posthumously published autobiography My World Line (1970) and a Scientific American article from September 1956.

Yet from the reported evidence Livio was unable to demonstrate that Einstein have never  uttered the phrase “biggest blunder.” See reference here. And here.

In an interview with Livio, reporter of the Atlantic writes that Livio “looked at almost every single paper that Einstein ever wrote” including making a trip to the Einstein archive in Jerusalem to look at the collection personally. “And nowhere did I ever find the phrase ‘biggest blunder’” said Livio.

Already in 1999 John Stachel told the authors of this paper that “The comment [‘biggest blunder’] doesn’t appear in Einstein’s writings”.

The phrase “biggest blunder” perfectly suits Einstein’s sense of humor.

On September 30, 1915, Einstein was completely excited. He wrote an astrophysicist friend from Berlin Erwin Freundlich about his 1914 general theory of relativity: He thought the latter might help him:

“I am writing you now  about a scientific matter that electrifies me enormously. I have come upon a logical contradiction of a quantitative nature in the theory of gravitation, which proves to me that there must be a calculational error somewhere within my framework”. Einstein spoke about “a blatant contradiction” [ein flagranter Widerspruch].

Einstein asked for help from Freundlich: “I do not think that I myself am in the  position to find the error, because my mind is locked in the same rut in this matter. Rather, I must depend on a person being with unspoiled brain matter to find the error. If you have time, do not forget to be occupied with the topic”.

On November 28, 1915 Einstein wrote Arnold Sommerfeld: “I realized, namely, that my existing field equations of gravitation were entirely untenable! […] This showed that covariance with respect to ‘adapted’ coordinate system was a flop [ein Schlag ins Wasser war]”. And Einstein explained to Sommerfeld: “Once every last bit of confidence in result and method of the earlier theories had given away, I saw clearly that only through a link with general covariance theory, i.e., with Riemann’s covariant, that a satisfactory solution could be found. Unfortunately, I have immortalized the last error in this struggle in the Academy-papers, which I can send to you soon”.

On April 8, 1915 Einstein wrote Tulio Levi-Civita: “Hoch geehrter und lieber Herr Kollege!” In a long an tiering correspondence with Levi-Civita Einstein stubbornly tried to save his limited covariant gravitational tensor. Einstein was hard to give up, but then finally wrote his “Kollege” Levi-Civita: “My proof of the invariant nature of ΔJ fails with such infinitesimal transformations”, (which he called the sorest spot) “in which the gμν‘s of the original system are constant, because then the quantities Aμν cannot be chosen freely, but vanish altogether”.

On May 23, 1923 Einstein wrote a postcard to Herman Weyl, and towards the end of the postcard he wrote (Archives ETH, Zurich):

“Wenn schon keine-quasistatische Welt, dann fort mit dem kosmologischen Glied.”

Abraham Pais translated this in the following way (Subtle is the Lord, 1983, p. 288): “If there is no quasi-static world, then away with the cosmological term”.


Postcard to Herman Weyl. Archives ETH, Zurich.

Einstein replied to an article by Lemaître (the latter trying to persuade Einstein that the cosmological term is necessary in the equations of gravitation):

“I must admit that these arguments do not appear to me as sufficiently convincing in view of the present state of our knowledge.

The introduction of such a constant implies a considerable renunciation of the logical simplicity of theory, a renunciation which appeared to me unavoidable only so long as one had no reason to doubt the essentially static nature of space. After Hubble’s discovery of the ‘expansion’ of the stellar system, and since Friedmann’s discovery that the unsupplemented equations involve the possibility of the existence of an average (positive) density of matter in an expanding universe, that introduction of such a constant appears to me, from the theoretical standpoint, at present unjustified”.

Indeed Einstein’s main object in the 1916 general theory of relativity was to develop a theory that the chosen path entered to it was psychologically the natural one, and its underlying assumptions would appear to have been secured experimentally.

Einstein abandoned his cosmological constant when he gradually understood that it was untenable; but did he say it was a blunder or his biggest blunder?

In his paper “Mathematical theory of the origin of matter” Fred Hoyle describes cosmologists as “umpires” and he tells the following anecdote: “[Vesto Melvin] Slipher was the first important umpire. In effect, he had the temerity to give Einstein out leg before the wicket. A story tells us that Einstein did not enjoy the experience. For quite a while he glared at the umpire and even complained to the crowd as he walked back to the pavilion. When in later years Martin Ryle, dressed in the umpires white coat, somewhat joyously gave me out caught behind I did not hesitate to follow Einstein’s excellent example, and indeed a TV rerun of the situation has shown that the ball actually hit my boot not my bat”.

In the same paper Hoyle also wrote about Gamow: “would shout from the other end: ‘the elements were made in less time than you could cook a dish of duck and roast potatoes”. Indeed Gamow was known of his sense of Humor.

In 1949, in his paper, “On relativistic Cosmology”, Gamow wrote:

“Another important group of studies based on the general theory of relativity is presented by the work on relativistic cosmology, which is an attempt to understand the development of various characteristic features of our universe as the result of its expansion from the originally homogeneous state. This includes essentially the theory of the origin of atomic species, which presumably took place during the very early epoch when the material forming the universe was in highly compressed and very hot state, and the theory of the formation of galaxies which must have occurred during the later revolutionary period. The neutron-capture theory of the origin of atomic speciaes recently developed by Alpher, Bethe, Gamow, and Delter suggests that different atomic nuclei were formed by the successive aggregation of neutrons and protons which formed the original hot ylem during the early highly compressed stages in the history of the universe”.

And in the footnote the reference appearing are: G. Gamow, Phys. Rev. 70, 572 (1946); Alpher, Bethe, and Gamow, Phys. Rev. 73, 803 (1948); R. A. Alpher, Phys. Rev. 74, 1577 (1948); R.A. Alpher and R. C. Herman, Phys. Rev. 74, 1737 (1948).

The αβγ paper was created by Ralph Alpher under the supervision of Gamow. Livio says, “that if he were to add as a co-author another known astrophysicist, whose name was Hans Bethe, then the three names would be Alpher Bethe Gamow, like alpha beta gamma, even though Hans Bethe had nothing to do with that paper.”

In his 1949 paper Gamow even humorously added a new “Mr. Tompkins” by the name: Deltor…

However, it is possible that Einstein was fond of Gamow’s sense of humor. He owned Gamow’s humorous popular science books in his personal library.

For instance one can find two of Gamow’s popular books in Einstein’s personal library kept in the Einstein Archives:

Gamow, George, Mr. Tompkins in Wonderland: or stories of c, G, and h, illustrated by John Hookham, 1940, New York : Macmillan. Gamow, George, One, two, three… infinity: facts & speculations of science, illustrated by the author, 1947, New York: Viking Press.

George Gamow told the following anecdote in his autobiography My World Line:

“There is very little to say about my consultation work for the armed forces of the United States during World War II. It would have been, of course, natural for me to work on nuclear explosions, but I was not cleared for such work until 1948, after Hiroshima. The reason was presumably my Russian origin and the story I had told freely to my friends of having been a colonel in the field artillery of the Red Army at the age of about twenty.

Thus I was very happy when I was offered a consultantship in the Division of High Explosives in the Bureau of ordnance of the US navy Department.

A more interesting activity during that time was my periodic contact with Albert Einstein, who along with other prominent experts such as John von Neumann, served as a consultant for the High Explosive Division. Accepting this  consultantship, Einstein stated that because of his advanced age he would be unable to travel periodically from Princeton to Washington, D.C., and back, and that somebody must come to his home in Princeton, bringing the problems with him. Since I happened to have known Einstein earlier, on non-military grounds, I was selected to carry out this job. Thus on every other Friday I took a morning train to Princeton, carrying a briefcase tightly packed with confidential and secret Navy projects. […]

After the business part of the visit was over, we had lunch either at Einstein’s home or at the cafeteria of the Institute for Advanced Study, which was not far away, and the conversation would turn to the problems of astrophysics and cosmology. In Einstein’s study there were always many sheets of paper scattered over his desk and on a nearby table, and I saw that they were covered with tensor formulae which seemed to pertain to the unified-field theory, but Einstein never spoke about that. However, in discussing purely physical and  astronomical problems he was very refreshing, and his mind was as sharp as ever”.

Livio discovered an article by a scientist: “I discovered a small article published in some obscure journal of the Navy by somebody named Stephen Brunauer,” a scientist who had recruited both Einstein and Gamow to the Navy. In that article, Brunauer wrote, “Gamow, in later years, gave the impression that he was the Navy’s liaison man with Einstein, that he visited every two weeks, and the professor ‘listened’ but made no contribution—all false [emphasis added]. The greatest frequency of visits was mine, and that was about every two months.” Clearly, Livio says, Gamow exaggerated his relationship with the famous physicist.

It is not surprising. Einstein’s fame led people who knew him to write about their personal acquaintance with him. Brunauer was probably one of them… And indeed Gamow probably also exaggerated his friendship with Einstein. Einstein had a friend, a Hungarian Jewish physician named János Plesch.  Jeremy Bernstein writes of Plesch autobiography, “indicates it was there that he began collecting people both as patients and friends. If we can believe his autobiography, he knew everybody”, and above all Albert Einstein. Plesch starts the chapter of his autobiography presenting Einstein with the following description, “Among the many scientific men who are, or have been, my friends there is one who out-tops all the others in stature, and that is Albert Einstein”. Yet Einstein told him many valuable typical Einstein anecdotes.

How do we know whether Plesch’s reports are authentic or not? We cross-reference them with letters, unpublished talks, etc., written by Einstein himself!

We know from Einstein’s own writings that it was typical of Einstein to tell his friends that he made errors and found blatant contradiction in his work. With his usual sense of humor, Einstein used to laugh about his difficulties in inventing the most beautiful and genius theory ever created: the general theory of relativity.

It is possible that Einstein said something in German to Gamow, and the latter might have translated it to one of the classical apercus attributed to Einstein.

Albert Einstein and Willem de Sitter discussing the Universe.

Further reading:

Michel Janssen, “Why Einstein Introduced the Cosmological Constant”.

John Stachel, Einstein from B to Z.

Abraham Pais, Subtle is the Lord.

Albert Einstein and the Theory of Relativity איינשטיין ותורת היחסות

Age 16. Between 1894 and 1895 Einstein writes an essay and sends it to his uncle Caesar Koch. He believes in the ether. Einstein is also familiar with the principle of relativity in mechanics

A year later, in 1895-1896, while in Aarau, Einstein conceives of a thought experiment: Einstein chases a light beam

In 1899 Einstein studies Maxwell’s electromagnetic theory

Around 1898-1900Einstein invents the magnet and conductor thought experiment

Between 1899 and 1900 Einstein is occupied with the contradiction between the Galilean principle of relativity and the constancy of the velocity of light in Maxwell’s theory

Between 1899 and 1901 Einstein is interested in ether drift experiments, and appears to have designed at least two experiments, the first in 1899

In 1901 Einstein still accepts the Galilean kinematics of space and time, in which the Galileian principle of relativity holds good

In 1902 Einstein reads Hendryk Antoon Lorentz’s 1895 seminal work on electron theory

Between 1901 and 1903 Einstein is working with the Maxwell-Hertz equations for empty space. He tries to find solutions to two problems

Magnet and conductor experiment and Faraday’s induction law lead to a conclusion that there is an asymmetry in the explanation depending on whether the magnet moves or the conductor moves. Einstein analyzed the magnet and conductor thought experiment according to Maxwell’s theory and the Galilean transformations. But covariance of Maxwell equations failed

Einstein confronts a conflict between the principle of Galilean relativity and the constancy of the velocity of light

Between 1901 and 1903 Einstein drops the ether hypothesis and chooses the principle of relativity instead of the postulate of the constancy of the velocity of light, and finds a (temporary) solution for his conflict in the form of an emission theory

Einstein seems to have pondered with this problem for an extra year, from 1903-1904 until almost spring-summer 1904. Einstein discusses Fizeau’s experiment using emission theory. He demonstrates, by using Fizeau’s celebrated experimental result, why this standpoint of emission theories cannot hold true

Towards spring-summer 1904 Einstein dropps emission theory and returns to Lorentz’s theory. He spends almost a year in vain trying to modify the idea of Lorentz in the hope of resolving the above problem. Einstein tries to discuss Fizeau’s experiment in Lorentz’s theory [In 1895 Lorentz managed to derive the Fresnel Formula from the first principles of his theory (stationary ether and moving electrons) without the need of any partial ether drag. Lorentz thus adhered to Fizeau’s original 1851 experimental result, but not to Fresnel’s theoretical interpretation of partial ether drag hypothesis, used to derive his dragging coefficient]. Finally

Age 26. In spring 1905, Einstein found the final solution, the “step”, which solved his dilemma

For footnotes, references, and further details please consult my papers