My book: Einstein’s Pathway to the Special Theory of Relativity

2015 marks several Albert Einstein anniversaries: 100 years since the publication of Einstein’s General Theory of Relativity, 110 years since the publication of the Special Theory of Relativity and 60 years since his passing.


What is so special about this year that deserves celebrations? My new book on Einstein: Einstein’s Pathway to the Special Theory of Relativity has just been returned from the printers and I expect Amazon to have copies very shortly.


The Publisher uploaded the contents and intro.


I hope you like my drawing on the cover:


Einstein, 1923: “Ohmmm, well… yes, I guess!”



The book is dedicated to the late Prof. Mara Beller, my PhD supervisor from the Hebrew University of Jerusalem who passed away ten years ago and wrote the book: Quantum Dialogue (Chicago University Press, 1999):


Have a very happy Einstein year!


100 GTR: Uniformly Rotating Disk and the Hole Argument

The “Ehrenfest paradox“: Ehrenfest imagined a rigid cylinder set in motion from rest and rotating around its axis of symmetry. Consider an observer at rest measuring the circumference and radius of the rotating cylinder. The observer arrives at two contradictory requirements relating to the cylinder’s radius:

  1. Every point in the circumference of the cylinder moves with radial velocity ωR, and thus, the circumference of the cylinder  should appear Lorentz contracted to a smaller value than at rest, by the usual “relativistic” factor γ: 2πR‘ < 2πR.
  2. The radius R’ is always perpendicular to its motion and suffers no contraction at all; it should therefore be equal to its value R: R’ = R.

Einstein wrote to Vladimir Varićak either in 1909 or in 1910 (Febuary 28): “The rotation of the rigid body is the most interesting problem currently provided by the theory of relativity, because the only thing that causes the contradiction is the Lorentz contraction”.  CPAE 5, Doc. 197b.

Ehrenfest imagined a rigid cylinder gradually set into rotation (from rest) around its axis until it reaches a state of constant rotation.

In 1919 Einstein explained why this was impossible: (CPAE 9, Doc. 93)

“One must take into account that a rigid circular disk at rest would have to snap when set into rotation, because of the Lorentz shortening of the tangential fibers and the non-shortening of the radial ones. Similarly, a rigid disk in rotation (made by casting) would have to shatter as a result of the inverse changes in length if one attempts to bring it to the state of rest. If you take these facts fully into consideration, your paradox disappears”.

Assuming that the cylinder does not expand or contract, its radius stays the same. But measuring rods laid out along the circumference 2πR should be Lorentz-contracted to a smaller value than at rest, by the usual factor γ. This leads to the paradox that the rigid measuring rods would have to separate from one another due to Lorentz contraction; the discrepancy noted by Ehrenfest seems to suggest that a rotated Born rigid disk should shatter. According to special relativity an object cannot be spun up from a non-rotating state while maintaining Born rigidity, but once it has achieved a constant nonzero angular velocity it does maintain Born rigidity without violating special relativity, and then (as Einstein showed in 1912) a disk riding observer will measure a circumference.

Hence, in 1912, Einstein discussed what came to be known as the uniformly rotating disk thought experiment in general relativity. Thinking about Ehrenfest’s paradox and taking into consideration the principle of equivalence, Einstein considered a disk (already) in a state of uniform rotation observed from an inertial system.

We take a great number of small measuring rods (all equal to each other) and place them end-to-end across the diameter 2R and circumference 2πR of the uniformly rotating disk. From the point of view of a system at rest all the measuring rods on the circumference are subject to the Lorentz contraction. Since measuring rods aligned along the periphery and moving with it should appear contracted, more would fit around the circumference, which would thus measure greater than 2πR. An observer in the system at rest concludes that in the uniformly rotating disk the ratio of the circumference to the diameter is different from π:

circumference/diameter = 2π(Lorentz contracted by a factor…)/2R = π (Lorentz contracted by a factor….).

According to the equivalence principle the disk system is equivalent to a system at rest in which there exists a certain kind of static gravitational field. Einstein thus arrived at the conclusion that a system in a static gravitational field has non-Euclidean geometry.

Soon afterwards, from 1912 onwards, Einstein adopted the metric tensor as the mathematical respresentation of gravitation.

Indeed Einstein’s first mention of the rotating disk in print was in his paper dealing with the static gravitational fields of 1912; and after the 1912 paper, the rotating-disk thought experiment occurred in Einstein’s writings only in a 1916 review article on general relativity: “The Foundation of the General Theory of Relativity”.

He now understood that in the general theory of relativity the method of laying coordinates in the space-time continuum (in a definite manner) breaks down, and one cannot adapt coordinate systems to the four-dimensional space.


My new paper deals with Einstein’s 1912 and 1916 rotating disk problem, Einstein’s hole argument, the 1916 point coincidence argument and Mach’s principle; a combined-into-one deal (academic paper) for the readers of this blog.


Sitting: Sir Arthur Stanley Eddington and Hendrik Antoon Lorentz. Standing: Albert Einstein, Paul Ehrenfest and Willem de Sitter. September 26, 1923.

Further reading: Ehrenfest paradox

My new paper on Einstein and Schwarzschild

My new paper on General Relativity: Einstein and Schwarzschild.

Sometime in October 1915 Einstein dropped the Einstein-Grossman theory. Starting on November 4, 1915, Einstein gradually expanded the range of the covariance of his field equations. On November 11, 1915 Einstein was able to write the field equations of gravitation in a general covariant form, but there was a coordinate condition (there are no equations here so I cannot write it down here).

On November 18, 1915, Einstein presented to the Prussian Academy his paper, “Explanation of the Perihelion Motion of Mercury from the General Theory of Relativity”. Einstein reported in this talk that the perihelion motion of Mercury is explained by his theory. In this paper, Einstein tried to find approximate solutions to his November 11, 1915 field equations. He intended to obtain a solution, without considering the question whether or not the solution was the only possible unique solution.

Einstein’s field equations are non-linear partial differential equations of the second rank. This complicated system of equations cannot be solved in the general case, but can be solved in particular simple situations. The first to offer an exact solution to Einstein’s November 18, 1915 field equations was Karl Schwarzschild, the director of the Astrophysical Observatory in Potsdam. On December 22, 1915 Schwarzschild wrote Einstein from the Russian front. Schwarzschild set out to rework Einstein’s calculation in his November 18 1915 paper of the Mercury perihelion problem. He first responded to Einstein’s solution for the first order approximation from his November 18, 1915 paper, and found another first-order approximate solution. Schwarzschild told Einstein that the problem would be then physically undetermined if there were a few approximate solutions. Subsequently, Schwarzschild presented a complete solution. He said he realized that there was only one line element, which satisfied the conditions imposed by Einstein on the gravitational field of the sun, as well as Einstein’s field equations from the November 18 1915 paper.

“Raffiniert ist der Herrgott, aber boshaft ist er nicht” (Einstein might have already said….), because the problem with Schwarzschild’s line element was that a mathematical singularity was seen to occur at the origin! Oh my, Einstein abhorred singularities.

Actually, Schwarzschild “committed another crime”: he did not satisfy the coordinate condition from Einstein’s November 11 or November 18, 1915 paper. Schwarzschild admitted that his coordinates were not “allowed” coordinates, with which the field equations could be formed, because these spherical coordinates did not have determinant 1. Schwarzschild chose then the non-“allowed” coordinates, and in addition, a mathematical singularity was seen to occur in his solution. But Schwarzschild told Einstein: Don’t worry, “The equation of [Mercury’s] orbit remains exactly as you obtained in the first approximation”! See my paper from 2012.

Einstein replied to Schwarzschild on December 29, 1915 and told him that his calculation proving uniqueness proof for the problem is very interesting. “I hope you publish the idea soon! I would not have thought that the strict treatment of the point- problem was so simple”. Subsequently Schwarzschild sent Einstein a manuscript, in which he derived his solution of Einstein’s November 18, 1915 field equations for the field of a single mass. Einstein received the manuscript by the beginning of January 1916, and he examined it “with great interest”. He told Schwarzschild that he “did not expect that one could formulate so easily the rigorous solution to the problem”. On January 13, 1916, Einstein delivered Schwarzschild’s paper before the Prussian Academy with a few words of explanation. Schwarzschild’s paper, “On the Gravitational Field of a Point-Mass according to Einstein’s Theory” was published a month later.


Karl Schwarzschild

In March 1916 Einstein submitted to the Annalen der Physik a review article on the general theory of relativity, “The Foundation of the General Theory of Relativity”. The paper was published two months later, in May 1916. The 1916 review article was written after Schwarzschild had found the complete exact solution to Einstein’s November 18, 1915 field equations. Even so, in his 1916 paper, Einstein preferred NOT to base himself on Schwarzschild’s exact solution, and he returned to his first order approximate solution from his November 18, 1915 paper.

A comment regarding Einstein’s calculations in his November 18, 1915 paper of the Mercury perihelion problem and Einstein’s 1916 paper. In his early works on GTR, in order to obtain the Newtonian results, Einstein used the special relativistic limit and the weak field approximation, and assumed that space was flat (see my paper). Already in 1914 Einstein had reasoned that in the general case, the gravitational field was characterized by ten space-time functions of the metric tensor. g were functions of the coordinates. In the case of special relativity this reduces to g44 = c2, where c denotes a constant. Einstein took for granted that the same degeneration occurs in the static gravitational field, except that in the latter case, this reduces to a single potential, where g44 = c2 is a function of spatial coordinates, x1, x2, x3. 

Later that year David Hilbert (with a vengeance from 1915?…) arrived at a line-element similar to Schwarzschild’s one, and he concluded that the singularity disappears only if we accept a world without electricity. Such an empty space was inacceptable by Einstein who was apparently much attracted by Mach’s ideas! (later termed by Einstein “Mach’s Principle”). Okay, Einstein, said Hilbert: If there is matter then another singularity exists, or as Hilbert puts it: “there are places where the metric proves to be irregular”…. (See my paper from 2012).








Strange Days at Blake Holsey High: a student is sucked into the black hole…


Einstein’s pathway to his General Theory of Relativity

Einstein thought that when dealing with gravity high velocities are not so important. So in 1912 he thought about gravity in terms of the principle of relativity and not in terms of the constant-speed-of-light postulate (special relativity). But then he engaged in a dispute with other scholars who claimed that he gave up the central postulate of his special theory of relativity. x

File:Max abraham.png

Max Abraham

File:Gunnar Nordström.jpg

Gunnar Nordström

Einstein’s Pathway to his Equivalence Principle 1905-1907


1912 – 1913 Static Gravitational Field Theory


1913 – 1914 “Entwurf” theory


Berlin “Entwurf” theory 1914


The Einstein-Nordström Theory


Dawn of “Entwarf theory”


1915 Relativity Theory


1916 General Theory of Relativity


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

Einstein’s Pathway to the Special Theory of Relativity and the General Theory of Relativity

Einstein’s Pathway to the Special Theory of Relativity

Einstein’s Pathway to the Special Theory of Relativity

Einstein’s discovery of Special Relativity

Einstein Believes in the Ether

Einstein Chases a Light Beam

Einstein recounts the Aarau thought experiment in his Autobiographical Notes, 1949

Magnet and Conductor Thought Experiment, Faraday’s magneto-electric induction

Föppl’s book on Maxwell’s theory

Ether drift and Michelson and Morley’s experiment

The Role of the Michelson-Morley Experiment on the Discovery of Relativity

The Dayton Miller Experiments

Emission theory and ether drift experiments

Paul Ehrenfest and Walter Ritz. Ritz’s Emission Theory

“The Step”

Einstein defined distant simultaneity physically; relativity of simultaneity

The Kyoto lecture notes – Einstein could have visited and consulted his close friend Michele Besso, whom he thanked at the end of his relativity paper. The Patent Office brought them together – their conversations on the way home. Besso was always eager to discuss the subjects of which he knew a great deal – sociology, medicine, mathematics, physics and philosophy – Einstein initiated him into his discovery

Joseph Sauter – Before any other theoretical consideration, Einstein pointed out the necessity of a new definition of synchronization of two identical clocks distant from one another; to fix these ideas, he told him, “suppose one of the clocks is on a tower at Bern and the other on a tower at Muri (the ancient aristocratic annex of Bern)” – synchronization of clocks by light signals.

Did Poincaré have an Effect on Einstein’s Pathway toward the Special Theory of Relativity? Einstein’s reply to Carl Seelig


Einstein’s pathway to the General Theory of Relativity

Entwurf theory – Einstein-Grossmann theory, Hole argument, field equations and the Einstein-Besso manuscript


Gunnar Nordström develops a competing theory of gravitation to Einstein’s 1912-1913 gravitation theory. Einstein begins to study Nordström’s theory and develops his own Einstein-Nordström theory. In a joint 1914 paper with Lorentz’s student Adrian Fokker – a generally covariant formalism is presented from which Nordström’s theory follows if the velocity of light is constant Here


The three problems that led to the fall of the entwurf theory –

The gravitational field on a uniformly rotating system does not satisfy the field equations.

Covariance with respect to adapted coordinate system was a flop.

In the Entwurf theory the motion of Mercury’s perihelion came to 180 rather than 450 per century

The General Theory of Relativity – 1915

David Hilbert Enters the Game, the priority dispute – Einstein and Hilbert

In November 18 1915 Einstein calculated rapidly the precession of Mercury’s


Geodesic Equation. Metric tensor. Einstein’s November 4, 11, and 25 field equations.The Riemann-Christoffel Tensor; the Ricci tensor; the Einstein tensor

von Deinem zufriedenen aber ziemlich kaputen

General Theory of Relativity – 1916

Mid December to Mid January 1915: Exchange of letters between Einstein and Ehrenfest

The disk thought experiment; coordinates have no direct physical meaning Euclidean Geometry breaks down; two Globes Thought Experiment; Mach’s Principle; the principle of general relativity; the Equivalence Principle; the principle of general covariance

The Summation Convention

Motion of the Perihelion of the Planetary Orbit; Redshift; Deflection of light in a gravitational field of the sun

Einstein in the Patent Office:

Michele Besso, Joseph Sauter, and Lucian Chavan – Patent Office, Maurice Solovine and Conrad Habicht – the Olympian Academy

Annus mirabilis papers

On a Heuristic Viewpoint Concerning the Generation and Transformation of Light – It argues a heuristic manner for the existence of light quanta and derives the photoelectric law

On a New Determination of Molecular Dimensions – doctoral thesis submitted to the mathematical and natural science branch of Zürich University

On the Movement of Particles Suspended in Fluids at Rest, as Postulated by the Molecular Theory of Heat. The Brownian motion paper

On the Electrodynamics of Moving Bodies. The Relativity Paper

Does the Inertia of a Body Depend on its Energy Content? The first derivation of the mass energy equivalence

German Scientists Responded to Einstein’s Relativity Paper – Max Planck wrote Einstein. Max von Laue met Einstein

Einstein teaches his 3 friends from the Patent Office at the University of Bern

Finally Einstein leaves the Patent Office to his first post in the University of Zürich

Further reading: Stachel, John, Einstein from ‘B’ to ‘Z’, 2002, Washington D.C.: Birkhauser

אלברט איינשטיין – דרכו ליחסות Albert Einstein – pathway to theory of relativity

My Einstein and Relativity Papers – Gali Weinstein

Einstein’s Pathway to the Special Theory of Relativity

Einstein’s Pathway to the General Theory of Relativity

The papers describe the genesis and history of special relativity and the discovery and history of general relativity – Einstein chases a light beam, the magnet and conductor thought experiment, Michelson-Morley experiment, emission theory, ether superfluous, Fizeau water-tube experiment, the principle of relativity and the principle of the constancy of the velocity of light (light postulate), The Step, Besso-Einstein meeting, Relativity 1905 paper. 1907 equivalence principle, lift experiments, Galileo principle, coordinate-dependant theory of relativity, Zurich Notebook, Einstein-Grossmann theory (Entwurf theory), deflection of light near the sun, Einstein’s struggles with Entwurf theory, hole argument, 1915 General Theory of Relativity: Hilbert – Einstein, precession or advance of Perihelion of Mercury, how Einstein found the generally covariant field equations, and Einstein’s 1916 general theory of relativity – Mach’s principle, rotating disk thought experiment, and point coincidence argument. These papers do not discuss the affine connection. For a discussion of the affine connection please consult Prof. John Stachel’s works

Philosophyof physics andof Special Relativity – papers discussing philosophical questions about space and time and interpretations of Special Relativity. A rigid body does not exist in the special theory of relativity, distant simultaneity defined with respect to a given frame of reference without reference to synchronized clocks, Einstein synchronization, challenges on Einstein’s connection of synchronization and Lorentz contraction, a theory of relativity without light – Ignatowski, Einstein’s composition of relative velocities – addition theorem for relative velocities, and space of relative velocities, Max Born and rigid body problem, Paul Ehrenfest’s paradox, relativity of simultaneity, Einstein’s clocks: Einstein’s 1905 Clock Paradox, Paul Langevin and the Twin Paradox

Poincaré and EinsteinThe inertial mass-energy equivalence, Lorentz’s theory of the electron violated the principle of action and reaction, Henri Poincaré trying to mend this violation, 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. Einstein and Poincaré– Method of clocks and their synchronization, Sur la dynamique de l’electron, Dynamics of the Electron, Einstein’s 1905 letter to Conrad Habicht, Poincaré’s 1905 letters to Lorentz, Poincaré’s spacetime mathematical theory of groups, As opposed to Einstein, before 1905 Poincaré stressed the importance of the method of clocks and their synchronization by light signals. Poincaré’s Lorentz group, Poincaré’s La Science et l’hypothèse  – Science and Hypothesis 

Innovation never comes from the established institutions… – Eric Schmidt

מאמרי איינשטיין והיחסות שלי – גלי וינשטיין

דרכו של איינשטיין ליחסות הפרטית.

דרכו של איינשטיין ליחסות הכללית.

אני מתכננת לפרסם ספר ולכן המאמרים הם טיוטא ולא גרסא סופית.

“חידוש אף פעם לא מגיע ממוסדות מוכרים” – אריק שמידט.

Einstein Archives – Jerusalem and Einstein Papers Project – Caltech

ארכיון איינשטיין

פרויקט איינשטיין

התמונה מכאן