Review: The Cambridge Companion to Einstein

I recommend this recent publication, The Cambridge Companion to Einstein, edited by Michel Janssen and Christoph Lehner.

It is a real good book: The scholarly and academic papers contained in this volume are authored by eminent scholars within the field of Einstein studies.

The first paper introduces the term “Copernican process”, a term invented by scholars to study scientists’ and Einstein’s achievements. The Copernican process describes a complex revolutionary narrative and the book’s side of the divide.

First, Einstein did not consider the relativity paper a revolutionary paper, but rather a natural development of classical electrodynamics and optics; he did regard the light quantum paper a revolutionary paper.

Carl Seelig wrote, “As opposed to several interpreters, Einstein would not agree that the relativity theory was a revolutionary event. He used to say: ‘In the [special] relativity theory it is no question of a revolutionary act but of a natural development of lines which have been followed for centuries'”.

Why did Einstein not consider special relativity a revolutionary event? The answer was related to Euclidean geometry and to measuring rods and clocks. In his special theory of relativity Einstein gave a definition of a physical frame of reference. He defined it in terms of a network of measuring rods and a set of suitable-synchronized clocks, all at rest in an inertial system.

The light quantum paper was the only one of his 1905 papers Einstein considered truly revolutionary. Indeed Einstein wrote Conrad Habicht in May 1905 about this paper, “It deals with the radiation and energy characteristics of light and is very revolutionary”.

A few years ago Jürgen Renn introduced a new term “Copernicus process”: […] “reorganization of a system of knowledge in which previously marginal elements take on a key role and serve as a starting point for a reinterpretation of the body of knowledge; typically much of the technical apparatus is kept, inference structures are reversed, and the previous conceptual foundation is discarded. Einstein’s achievements during his miracle year of 1905 can be described in terms of such Copernican process” (p. 38).

For instance, the transformation of the preclassical mechanics of Galileo and contemporaries (still based on Aristotelian foundations) to the classical mechanics of the Newtonian era can be understood in terms of a Copernican process. Like Moses, Galileo did not reach the promised land, or better perhaps, like Columbus, did not recognize it as such. Galileo arrived at the derivation of results such as the law of free fall and projectile motion by exploring the limits of the systems of knowledge of preclassical mechanics (p. 41).

Einstein preserved the technical framework of the results in the works of Lorentz and Planck, but profoundly changed their conceptual meaning, thus creating the new kinematics of the theory of special relativity and introducing the revolutionary idea of light quanta. Copernicus as well had largely kept the Ptolemaic machinery of traditional astronomy when changing its basic conceptual structure.

Although Einstein did not consider his relativity paper a revolutionary paper, he explained the new feature of his theory just before his death: “the realization of the fact that the bearing of the Lorentz transformation transcended its connection with Maxwell‘s equations and was concerned with the nature of space and time in general. A further new result was that the ‘Lorentz invariance’ is a general condition for any theory. This was for me of particular importance because I had already previously recognized that Maxwell‘s theory did not represent the microstructure of radiation and could therefore have no general validity”.

Planck assumed that oscillators interacting with the electromagnetic field could only emit and/or absorb energy in discrete units, which he called quanta of energy. The energy of these quanta was proportional to the frequency of the oscillator.

Planck believed, in accord with Maxwell’s theory that, the energy of the electromagnetic field itself could change continuously. Einstein first recognized that Maxwell’s theory did not represent the microstructure of radiation and could have no general validity. He realized that a number of phenomena involving interactions between matter and radiation could be simply explained with the help of light quanta.

Using Renn and Rynasiewicz phraseology, Planck “did not reach the promised land”, the light quanta. Moreover, he even disliked this idea. Einstein later wrote about Planck, “He has, however, one fault: that he is clumsy in finding his way about in foreign trains of thought. It is therefore understandable when he makes quite faulty objections to my latest work on radiation”.

In an essay on Johannes Kepler Einstein explained Copernicus’ discovery (revolutionary process): Copernicus understood that if the planets moved uniformly in a circle round the stationary sun (one frame of reference), then the planets would also move round all other frames of reference (the earth and all other planets): “Copernicus had opened the eyes of the most intelligent to the fact that the best way to get a clear group of the apparent movements of the planets in the heavens was to regard them as movements round the sun conceived as stationary. If the planets moved uniformly in a circle round the sun, it would have been comparatively easy to discover how these movements must look from the earth”.

Therefore Einstein’s revolutionary process was the following: Einstein was at work on his light quanta paper, but he was busily working on the electrodynamics of moving bodies too. Einstein understood that if the equation E = hf holds in one inertial frame of reference, it would hold in all others. Einstein realized that the ‘Lorentz invariance’ is a general condition for any theory, and then he understood that the Lorentz transformation transcended its connection with Maxwell’s equations and was concerned with the nature of space and time in general.






Centenary of the Death of Poincaré – Einstein and Poincaré 2012 פואנקרה ואיינשטיין

לרגל מאה שנה למותו של פואנקרה, פרסמתי בשלושה חלקים מחקר על הנרי פואנקרה, תרומתו בתחום של תורת האלקטרון והאלקטרודינמיקה של הגופים בתנועה והשאלה האם פואנקרה הגיע לתורת יחסות ולגילויים שאותם אנו מוצאים בתורת היחסות הפרטית לפני או במקביל לאיינשטיין. כמובן שהשאלה היא מעט יותר מורכבת ולא פשטנית כפי שהצגתי אותה כאן. בנושא זה כתבתי את עבודת הדוקטורט שלי והמאמרים הם סיכום ועדכון של הדוקטורט שלי שנכתב לפני 14 שנה.

A Biography of Poincaré  – Researcher in dynamics of the electron and electrodynamics –  2012 Centenary of the Death of Poincaré. Here

On January 4, 2012 (the centenary of Henri Poincaré’s death) a colloquium was held in Nancy, France the subject of which was “Vers une biographie d’Henri Poincaré”. Scholars discussed several approaches for writing a biography of Poincaré


I present a personal and scientific biographical sketch of Poincaré and his contributions to electrodynamics of moving bodies, which does not in any way reflect Poincaré’s rich personality and immense activity in science. When Poincaré traveled to parts of Europe, Africa and America, his companions noticed that he knew well everything from statistics to history and curious customs and habits of peoples. He was almost teaching everything in science. He was so encyclopedic that he dealt with the outstanding questions in the different branches of physics and mathematics; he had altered whole fields of science such as non-Euclidean geometry, Arithmetic, celestial mechanics, thermodynamics and kinetic theory, optics, electrodynamics, Maxwell’s theory, and other topics from the forefront of Fin de Siècle physical science

As opposed to the prosperity of biographies and secondary papers studying the life and scientific contributions of Albert Einstein, one finds much less biographies and secondary sources discussing Poincaré’s life and work. Unlike Einstein, Poincaré was not a cultural icon. Beginning in 1920 Einstein became a myth and a world famous figure. Although Poincaré was so brilliant in mathematics, he mainly remained a famous mathematician within the professional circle of scientists. He published more papers than Einstein, performed research in many more branches of physics and mathematics, received more prizes on his studies, and was a member of more academies in the whole world. Despite this tremendous yield, Poincaré did not win the Nobel Prize

Most famous is Poincaré’s philosophy of conventionalism, which sprang out of his research into geometry during a period (the end of the 1880’s) when non-Euclidean geometries were a matter of a consistent possibility. Poincaré developed two kinds of conventionalism, conventionalism applicable to geometry and conventionalism for the principles of physics. Both sprang from Poincaré’s mathematical group theory

In addition to the geometries of Euclid, Lobachewski, and Riemann, Poincaré proposed another geometry, the truth of which was not incompatible with the other geometries; he called it the “fourth geometry”. The first time that Poincaré’s fourth geometry appeared in print was in 1891

Einstein did not feel at ease with Poincaré’s standpoint. In 1992 Michel Paty commented on Einstein’s presentation of Poincaré’s conventionalism in 1921, “Actually this is not exactly Poincaré’s point of view, but a translation of it made by Einstein in his own perspective, that is according to his conception of physical Geometry”. See

Scott Walter’s papers here

And Peter Galison’s book Einstein’s Clocks, Poincare’s Maps here

Review by John Stachel: here and by Alberto Martínez here

Scientific contributions in electrodynamics: Before 1905, Poincaré stressed the importance of the method of clocks and their synchronization, but unlike Einstein, magnet and conductor (asymmetries in Lorentz’s theory regarding the explanation of Faraday’s induction) or chasing a light beam and overtaking it, were not a matter of great concern for him

In 1905 Poincaré elaborated Lorentz’s electron theory from 1904 in two papers entitled “On the Dynamics of the Electron”. Poincaré’s theory was a space-time mathematical theory of groups at the basis of which stood the postulate of relativity; Einstein’s 1905 theory was a kinematical theory of relativity

Poincaré did not renounce the ether. He wrote a new law of addition of velocities, but he did not abandon the tacit assumptions made about the nature of time, simultaneity, and space measurements implicit in Newtonian kinematics

Although he questioned absolute time and absolute simultaneity, he did not make new kinematical tacit assumptions about space and time. He also did not require reciprocity of the appearances, and therefore did not discover relativity of simultaneity

These are the main hallmarks of Einstein’s special theory of relativity. Nevertheless, Poincaré had arrived at many novel findings that went way beyond Fin de Siècle physics. here


Read other point of views: Olivier Darrigol’s papers here and here

Darrigol, Olivier, “Henri Poincaré’s criticism of fin de siècle electrodynamics”, Studies in History and Philosophy of Modern Physics 26, 1995, pp. 1-44. here

Darrigol, Olivier, Electrodynamics from Ampère to Einstein, 2000, Oxford: Oxford University Press. Here

Mass-energy equivalence: In 1900 Poincaré considered a device creating and emitting electromagnetic waves. The device emits energy in all directions. As a result of the energy being emitted, it recoils. No motion of any other material body compensates for the recoil at that moment. Poincaré found that as a result of the recoil of the oscillator, in the moving system, the oscillator generating the electromagnetic energy suffers an “apparent complementary force”. In addition, in order to demonstrate the non-violation of the theorem of the motion of the centre of gravity, Poincaré needed an arbitrary convention, the “fictitious fluid”

Einstein demonstrated that if the inertial mass E/c2 is associated with the energy E, and on assuming the inseparability of the theorem of the conservation of mass and that of energy, then – at least as a first approximation – the theorem of the conservation of the motion of the centre of gravity is also valid for all systems in which electromagnetic processes take place

Before 1905 (and also afterwards) Poincaré did not explore the inertial mass-energy equivalence

Einstein was the first to explore the inertial mass-energy equivalence. In 1905 Einstein showed that a change in energy is associated with a change in inertial mass equal to the change in energy divided by c2


For a different point of view: Darrigol, Olivier, “Poincaré, Einstein, et l’inertie de l’énergie”, Comptes rendus de l’Académie des sciences IV 1, 2000, pp. 143-153. Here

See also this paper by Stephen Boughn and  Tony Rothman. A report of the paper here


Did Poincaré influence Einstein on his way to the Special theory of relativity? One differentiates two kinds of questions here

  1What was the effect of Poincaré’s studies on the development of the Special Theory of relativity? and

 2What was the effect Poincaré’s research may have had on the development of Einstein’s own pathway towards the Special Theory of Relativity? hence

Poincaré did contribute to the theory of relativity a great deal. His 1905 space-time theory of groups greatly influenced Minkowski on his way to reformulate and recast mathematically the special theory of relativity. In addition, he arrived at many interesting ideas. However, it appears from examining the primary sources that Poincaré did not influence Einstein on his route to the special theory of relativity. See my papers here