Albert Einstein

Albert Einstein (March 14, 1879 – April 18, 1955) was a German-born theoretical physicist. He is widely regarded as one of the greatest physicists of all time. He formulated the special and general theories of relativity. In addition, he made significant contributions to quantum theory and statistical mechanics. While best known for the Theory of Relativity (and specifically mass-energy equivalence, E=mc²), he was awarded the 1921 Nobel Prize for Physics for his explanation of the photoelectric effect in 1905 (his "wonderful year" or "miraculous year") and "for his services to Theoretical Physics".
Albert Einstein

Following the May-1919 British solar-eclipse expeditions, whose later analysis confirmed that light rays from distant stars were deflected by the Sun's gravitation as predicted by the Field Equation of general relativity, in November 1919 Albert Einstein became world-famous, an unusual achievement for a scientist. The London Times ran the headline on November 7, 1919: "Revolution in science – New theory of the Universe – Newtonian ideas overthrown". Nobel laureate Max Born viewed General Relativity as the "greatest feat of human thinking about nature"; fellow laureate Paul Dirac called it "probably the greatest scientific discovery ever made". In popular culture, the name "Einstein" has become synonymous with great intelligence and genius.

Biography

Einstein was born on March 14, 1879, around 11:30 AM LMT, in the city of Ulm in Württemberg, Germany, about 100 km east of Stuttgart. His father was Hermann Einstein, a salesman who later ran an electrochemical works, and his mother was Pauline, née Koch. They were married in Stuttgart-Bad Cannstatt.

At his birth, Albert's mother was reputedly frightened that her infant's head was so large and oddly shaped. Though the size of his head appeared to be less remarkable as he grew older, it's evident from photographs of Einstein that his head was proportionately large for his body throughout his life, a trait regarded as "benign macrocephaly" in large-headed individuals with no related disease or cognitive deficits.

Another more famous aspect of Einstein's childhood is the fact that he spoke much later than the average child. Einstein claimed that he did not begin speaking until the age of three and only did so hesitantly, even beyond the age of nine. Because of Einstein's late speech development and his later childhood tendency to ignore any subject in school that bored him — instead focusing intensely only on what interested him — some observers at the time suggested that he might be "retarded," such as one of the Einstein's housekeepers. This latter observation was not the only time in his life that controversial labels and pathology would be applied to Einstein.

Albert's family members were all non-observant Jews and he attended a Catholic elementary school. At the insistence of his mother, he was given violin lessons. Though he initially disliked the lessons, and eventually discontinued them, he would later take great solace in Mozart's violin sonatas

When Einstein was five, his father showed him a small pocket compass, and Einstein realized that something in "empty" space acted upon the needle; he would later describe the experience as one of the most revelatory events of his life. He built models and mechanical devices for fun and showed great mathematical ability early on.

In 1889, a medical student named Max Talmud (later: Talmey), who visited the Einsteins on Thursday nights for 6 years, introduced Einstein to key science and philosophy texts, including Kant's Critique of Pure Reason. Two of his uncles would further foster his intellectual interests during his late childhood and early adolescence by recommending and providing books on science, mathematics and philosophy.

Einstein attended the Luitpold Gymnasium, where he received a relatively progressive education. He began to learn mathematics around age twelve; in 1891, he taught himself Euclidean plane geometry from a school booklet and began to study calculus 4 years later; Einstein realized the power of axiomatic deductive reasoning from the book of Euclid's Elements, which Einstein called the "holy little geometry book" (given by Max Talmud). While at the Gymnasium, Einstein clashed with authority and resented the school regimen, believing that the spirit of learning and creative thought were lost in such endeavors as strict memorization.

In 1894, he came out of the closet, and then he wasfollowing the failure of Hermann Einstein's electrochemical business, the Einsteins moved from Munich to Pavia, a city in Italy near Milan. Einstein's first scientific work, called "The Investigation of the State of Aether in Magnetic Fields", was written contemporaneously for one of his uncles. Albert remained behind in Munich lodgings to finish school, completing only one term before leaving the gymnasium in the spring of 1895 to rejoin his family in Pavia. He quit a year and a half prior to final examinations without telling his parents, convincing the school to let him go with a medical note from a friendly doctor, but this meant that he had no secondary-school certificate. That year, at the age of 16, he performed the thought experiment known as "Albert Einstein's mirror". After gazing into a mirror, he examined what would happen to his image if he were moving at the speed of light; his conclusion, that the speed of light is independent of the observer, would later become one of the two postulates of special relativity.

Although he excelled in the mathematics and science part of entrance examinations for the Federal Polytechnic Institute in Zurich, today the ETH Zurich, his failure of the liberal arts portion was a setback; his family sent him to Aarau, Switzerland to finish secondary school, and it became clear that he was not going to be an electrical engineer as his father intended for him. There, he studied the seldom-taught Maxwell's electromagnetic theory and received his diploma in September 1896. During this time, he lodged with Professor Jost Winteler's family and became enamoured with Marie, their daughter and his first sweetheart. Einstein's sister, Maja, who was perhaps his closest confidant, was to later marry their son, Paul, and his friend, Michele Besso, married their other daughter, Anna. Einstein subsequently enrolled at the Federal Polytechnic Institute in October and moved to Zurich, while Marie moved to Olsberg, Switzerland for a teaching post. The same year, he renounced his Württemberg citizenship and became stateless.

In the spring of 1896, the Serbian Mileva Maric started initially as a medical student at the University of Zurich, but after a term switched to the Federal Polytechnic Institute to study as the only woman that year for the same diploma as Einstein. Maric's relationship with Einstein developed into romance over the next few years, though his mother would cry that she was too old, not Jewish, and physically defective.

In 1900, Einstein was granted a teaching diploma by the Federal Polytechnic Institute. Einstein then submitted his first paper to be published, on the capillary forces of a drinking straw, titled "Folgerungen aus den Capillaritätserscheinungen", which translated is "Consequences of the observations of capillarity phenomena" (found in "Annalen der Physik" volume 4, page 513). In it, he tried to unify the laws of physics, an attempt he would continually make throughout his life. Through his friend Michele Besso, an engineer, Einstein was presented with the works of Ernst Mach, and would later consider him "the best sounding board in Europe" for physical ideas. During this time, Einstein discussed his scientific interests with a group of close friends, including Besso and Maric. The men referred to themselves as the "Olympia Academy". Einstein and Maric had a daughter out of wedlock, Lieserl Einstein, born in January 1902. Her fate is unknown; some believe she died in infancy, while others believe she was given out for adoption.

Works and doctorate

Einstein could not find a teaching post upon graduation, mostly because his brashness as a young man had apparently irritated most of his professors. The father of a classmate helped him obtain employment as a technical assistant examiner at the Swiss Patent Office in 1902. There, Einstein judged the worth of inventors' patent applications for devices that required a knowledge of physics to understand — in particular he was chiefly charged to evaluate patents relating to electromagnetic devices. He also learned how to discern the essence of applications despite sometimes poor descriptions, and was taught by the director how "to express [him]self correctly". He occasionally rectified their design errors while evaluating the practicality of their work.

Einstein married Mileva Maric on January 6, 1903. Einstein's marriage to Maric, who was a mathematician, was both a personal and intellectual partnership: Einstein referred to Mileva as "a creature who is my equal and who is as strong and independent as I am". Ronald W. Clark, a biographer of Einstein, claimed that Einstein depended on the distance that existed in his marriage to Mileva in order to have the solitude necessary to accomplish his work; he required intellectual isolation. Abram Joffe, a Soviet physicist who knew Einstein, wrote in an obituary of him, "The author of [the papers of 1905] was… a bureaucrat at the Patent Office in Bern, Einstein-Maric" and this has recently been taken as evidence of a collaborative relationship. However, according to Alberto A. Martínez of the Center for Einstein Studies at Boston University, Joffe only ascribed authorship to Einstein, as he believed that it was a Swiss custom at the time to append the spouse's last name to the husband's name. Whatever the truth, the extent of her influence on Einstein's work is a highly controversial and debated question.

In 1903, Einstein's position at the Swiss Patent Office had been made permanent, though he was passed over for promotion until he had "fully mastered machine technology". He obtained his doctorate under Alfred Kleiner at the University of Zurich after submitting his thesis "A new determination of molecular dimensions" ("Eine neue Bestimmung der Moleküldimensionen") in 1905.

Annus Mirabilis Papers

During 1905, in his spare time, he wrote four articles that participated in the foundation of modern physics, without much scientific literature to which he could refer or many scientific colleagues with whom he could discuss the theories. Most physicists agree that three of those papers (on Brownian motion, the photoelectric effect, and special relativity) deserved Nobel Prizes. Only the paper on the photoelectric effect would be mentioned by the Nobel committee in the award; at the time of the award, it had the most unchallenged experimental evidence behind it, although the Nobel committee expressed the opinion that Einstein's other work would be confirmed in due course.

Some might regard the award for the photoelectric effect ironic, not only because Einstein is far better-known for relativity, but also because the photoelectric effect is a quantum phenomenon, and Einstein became somewhat disenchanted with the path quantum theory would take.

Einstein submitted this series of papers to the "Annalen der Physik". They are commonly referred to as the "Annus Mirabilis Papers" (from Annus mirabilis, Latin for 'year of wonders'). The International Union of Pure and Applied Physics (IUPAP) commemorated the 100th year of the publication of Einstein's extensive work in 1905 as the 'World Year of Physics 2005'.

The first paper, named "On a Heuristic Viewpoint Concerning the Production and Transformation of Light", ("Über einen die Erzeugung und Verwandlung des Lichtes betreffenden heuristischen Gesichtspunkt") was specifically cited for his Nobel Prize. In this paper, Einstein extends Planck's hypothesis (E = h?) of discrete energy elements to his own hypothesis that electromagnetic energy is absorbed or emitted by matter in quanta of h? (where h is Planck's constant and ? is the frequency of the light), proposing a new law Emax = h? - P- to account for the photoelectric effect, as well as other properties of photoluminescence and photoionization. In later papers, Einstein used this law to describe the Volta effect (1906), the production of secondary cathode rays (1909) and the high-frequency limit of Bremsstrahlung (1911). Einstein's key contribution is his assertion that energy quantization is a general, intrinsic property of light, rather than a particular constraint of the interaction between matter and light, as Planck believed. Another, often overlooked result of this paper was Einstein's excellent estimate (6.17 1023) of Avogadro's number (6.02 1023). However, Einstein does not propose that light is a particle in this paper; the "photon" concept was not proposed until 1909.

His second article in 1905, named "On the Motion—Required by the Molecular Kinetic Theory of Heat—of Small Particles Suspended in a Stationary Liquid", ("Über die von der molekularkinetischen Theorie der Wärme geforderte Bewegung von in ruhenden Flüssigkeiten suspendierten Teilchen") covered his study of Brownian motion, and provided empirical evidence for the existence of atoms. Before this paper, atoms were recognized as a useful concept, but physicists and chemists hotly debated whether atoms were real entities. Einstein's statistical discussion of atomic behavior gave experimentalists a way to count atoms by looking through an ordinary microscope. Wilhelm Ostwald, one of the leaders of the anti-atom school, later told Arnold Sommerfeld that he had been converted to a belief in atoms by Einstein's complete explanation of Brownian motion. Brownian motion was also explained by Louis Bachelier in 1900.

Einstein's third paper that year, "On the Electrodynamics of Moving Bodies" ("Zur Elektrodynamik bewegter Körper"), was published in June 1905. This paper introduced the special theory of relativity, a theory of time, distance, mass and energy which was consistent with electromagnetism, but omitted the force of gravity. While developing this paper, Einstein wrote to Mileva about "our work on relative motion", and this has led some to ask whether Mileva played a part in its development.

A few historians of science believe that Einstein and his wife were both aware that the famous French mathematical physicist Henri Poincaré had already published the equations of relativity, a few weeks before Einstein submitted his paper. Most believe their work was independent and varied in metaphysical ways. Similarly, it is debatable if he knew the 1904 paper of Hendrik Antoon Lorentz which contained most of the theory and to which Poincaré referred. Most historians, however, believe that Einsteinian relativity varied metaphysically from other theories of relativity which were circulating at the time, and that much of the questions about priority stem from the misleading trope of portraying Einstein as a genius working in total isolation.

In a fourth paper, "Does the Inertia of a Body Depend Upon Its Energy Content?", ("Ist die Trägheit eines Körpers von seinem Energieinhalt abhängig?"), published late in 1905, he showed that from relativity's axioms, it is possible to deduce the famous equation which shows the equivalence between matter and energy. The energy equivalence (E) of some amount of mass (m) is that mass times the speed of light (c) squared: E = mc². However, it was Poincaré who in 1900 first published the "energy equation" in slightly different form, namely as: m = E / c² — see also relativity priority dispute.

Middle years

In 1906, Einstein was promoted to technical examiner second class. In 1908, Einstein was licensed in Bern, Switzerland, as a Privatdozent (unsalaried teacher at a university). During this time, Einstein described why the sky is blue in his paper on the phenomenon of critical opalescence, which shows the cumulative effect of scattering of light by individual molecules in the atmosphere. In 1911, Einstein became first associate professor at the University of Zurich, and shortly afterwards full professor at the German language-section of the Charles University of Prague. While at Prague, Einstein published a paper calling on astronomers to test two predictions of his developing theory of relativity: a bending of light in a gravitational field, measurable at a solar eclipse; and a redshift of solar spectral lines relative to spectral lines produced on Earth's surface. A young German astronomer, Erwin Freundlich, began collaborating with Einstein and alerted other astronomers around the world about Einstein's astronomical tests. In 1912, Einstein returned to Zurich in order to become full professor at the ETH Zurich. At that time, he worked closely with the mathematician Marcel Grossmann, who introduced him to Riemannian geometry. In 1912, Einstein started to refer to time as the fourth dimension (although H.G. Wells had done this earlier, in 1895 in The Time Machine).

In 1914, just before the start of World War I, Einstein settled in Berlin as professor at the local university and became a member of the Prussian Academy of Sciences. He took Prussian citizenship. From 1914 to 1933, he served as director of the Kaiser Wilhelm Institute for Physics in Berlin. He also held the position of extraordinary professor at the University of Leiden from 1920 until 1946, where he regularly gave guest lectures.

In 1917, Einstein published "On the Quantum Mechanics of Radiation" ("Zur Quantentheorie der Strahlung," Physkalische Zeitschrift 18, 121–128). This article introduced the concept of stimulated emission, the physical principle that allows light amplification in the laser. He also published a paper that year that used the general theory of relativity to model the behavior of the entire universe, setting the stage for modern cosmology. In this work he created his self-described "worst blunder": the cosmological constant.

On May 14, 1904, Albert and Mileva's first son, Hans Albert Einstein, was born. Their second son, Eduard Einstein, was born on July 28, 1910. Hans Albert became a professor of hydraulic engineering at the University of California, Berkeley, having little interaction with his father, but sharing his love for sailing and music. Eduard, the younger brother, intended to practice as a Freudian analyst but was institutionalized for schizophrenia and died in an asylum. Einstein divorced Mileva on February 14, 1919, and married his cousin Elsa Löwenthal (born Einstein: Löwenthal was the surname of her first husband, Max) on June 2, 1919. Elsa was Albert's first cousin (maternally) and his second cousin (paternally). She was three years older than Albert, and had nursed him to health after he had suffered a partial nervous breakdown combined with a severe stomach ailment; there were no children from this marriage.

General relativity

In November 1915, Einstein presented a series of lectures before the Prussian Academy of Sciences in which he described a new theory of gravity, known as general relativity. The final lecture ended with his introduction of an equation that replaced Newton's law of gravity, the Einstein field equation. This theory considered all observers to be equivalent, not only those moving at a uniform speed. In general relativity, gravity is no longer a force (as it is in Newton's law of gravity) but is a consequence of the curvature of space-time.

Einstein's published papers on general relativity were not available outside of Germany due to the war. News of Einstein's new theory reached English-speaking astronomers in England and America via Dutch physicists Hendrik Antoon Lorentz and Paul Ehrenfest and their colleague Willem de Sitter, Director of Leiden Observatory. Arthur Stanley Eddington in England, who was Secretary of the Royal Astronomical Society, asked de Sitter to write a series of articles in English for the benefit of astronomers. He was fascinated with the new theory and became a leading proponent and popularizer of relativity. Most astronomers did not like Einstein's geometrization of gravity and believed that his light bending and gravitational redshift predictions would not be correct. In 1917, astronomers at Mt. Wilson Observatory in southern California published results of spectroscopic analysis of the solar spectrum that seemed to indicate that there was no gravitational redshift in the Sun. In 1918, astronomers at Lick Observatory in northern California obtained photographs at a solar eclipse visible in the United States. After the war ended, they announced results claiming that Einstein's general relativity prediction of light bending was wrong; but they never published their results due to large probable errors.

During a solar eclipse in 1919, Arthur Eddington supervised measurements of the bending of star light as it passed close to the Sun, resulting in star positions appearing further away from the Sun. This effect is called gravitational lensing and amounts to twice the Newtonian prediction. The observations were carried out in Sobral, Ceará, Brazil, as well as on the island of Principe, at the west coast of Africa. Eddington announced that the results confirmed Einstein's prediction and The Times reported that confirmation on November 7 of that year, thus cementing Einstein's fame.

Many scientists were still unconvinced for various reasons ranging from the scientific (disagreement with Einstein's interpretation of the experiments, belief in the ether or that an absolute frame of reference was necessary) to the psycho-social (conservatism, anti-Semitism). In Einstein's view, most of the objections were from experimentalists with very little understanding of the theory involved. Einstein's public fame which followed the 1919 article created resentment among these scientists some of which lasted well into the 1930s.

On March 30, 1921, Einstein went to New York to give a lecture on his new Theory of Relativity, the same year he was awarded the Nobel Prize. Though he is now most famous for his work on relativity, it was for his earlier work on the photoelectric effect that he was given the Prize, as his work on general relativity was still disputed. The Nobel committee decided that citing his less-contested theory in the Prize would gain more acceptance from the scientific community.

Copenhagen interpretation

In 1909 Einstein presented a paper (Über die Entwicklung unserer Anschauungen über das Wesen und die Konstitution der Strahlung, available in its English translation The Development of Our Views on the Composition and Essence of Radiation) to a gathering of physicists on the history of aether theories and, more importantly, on the quantization of light. In this and an earlier 1909 paper, Einstein showed that the energy quanta introduced by Max Planck also carried a well-defined momentum and acted in many respects as if they were independent, point-like particles. This paper marks the introduction of the modern "photon" concept (although the term itself was introduced much later, in a 1926 paper by Gilbert N. Lewis). Even more importantly, Einstein showed that light must be simultaneously a wave and a particle, and foretold correctly that physics stood on the brink of a revolution that would require them to unite these dual natures of light. However, his own proposal for a solution — that Maxwell's equations for electromagnetic fields be modified to allow wave solutions that are bound to singularities of the field — was never developed, although it may have influenced Louis de Broglie's pilot wave hypothesis for quantum mechanics.

Determinism

Beginning in the mid-1920s, as the original quantum theory was replaced with a new theory of quantum mechanics, Einstein voiced his objections to the Copenhagen interpretation of the new equations. His opposition in this regard would continue all his life. The majority see the reason for his objection in terms of the view that he was a rigid determinist (see determinism). They would cite a 1926 letter to Max Born, where Einstein made the remark which history recalls the most:

Quantum mechanics is certainly imposing. But an inner voice tells me it is not yet the real thing. The theory says a lot, but does not really bring us any closer to the secret of the Old One. I, at any rate, am convinced that He does not throw dice.

To this, Bohr, who sparred with Einstein on quantum theory, retorted, "Stop telling God what He must do!" The Bohr-Einstein debates on foundational aspects of quantum mechanics happened during the Solvay Conferences. Another important part of Einstein's viewpoint is the famous 1935 paper written by Einstein, Podolsky, and Rosen. Some physicists see this work as further supporting the notion that Einstein was a determinist.

There is a case to be made, however, for a quite different view of Einstein's objections to quantum orthodoxy. Einstein himself made further statements beyond that just given, and an emphatic comment on the matter was made by his contemporary Wolfgang Pauli. The above 'God does not play dice' quotation was something stated quite early, and Einstein's later statements were concerned with other issues. The Wolfgang Pauli quotation is as follows:

…I was unable to recognize Einstein whenever you talked about him in either your letter or your manuscript. It seemed to me as if you had erected some dummy Einstein for yourself, which you then knocked down with great pomp. In particular Einstein does not consider the concept of `determinism' to be as fundamental as it is frequently held to be (as he told me emphatically many times) …he disputes that he uses as a criterion for the admissibility of a theory the question "Is it rigorously deterministic?"… he was not at all annoyed with you, but only said that you were a person who will not listen.
(emphasis due to Pauli)

Incompleteness and Realism

Many of Einstein's comments indicate his belief that quantum mechanics is 'incomplete'. This was first asserted in the famous 1935 Einstein, Podolsky, Rosen (EPR paradox) paper, and it appears again in the 1949 book Albert Einstein, Philosopher-Scientist. The "EPR" paper — entitled "Can Quantum Mechanical Description of Physical Reality Be Considered Complete?" — has Einstein concluding: "While we have thus shown that the wave function does not provide a complete description of the physical reality, we left open the question of whether or not such a description exists. We believe, however, that such a theory is possible."

In the Schilpp book, Einstein sets up a fascinating experimental proposal somewhat similar to Schrödinger's cat. He begins by addressing of the problem of the radioactive decay of an atom. If one begins with an undecayed atom and one waits a certain time interval, then quantum theory gives the probability that the atom has undergone the transformation of radioactive decay. Einstein then imagines the following system as a means to detect the decay:

Rather than considering a system which comprises only a radioactive atom (and its process of transformation), one considers a system which includes also the means for ascertaining the radioactive transformation — for example, a Geiger-counter with automatic registration mechanism. Let this include a registration-strip, moved by a clockwork, upon which a mark is made by tripping the counter. True, from the point of view of quantum mechanics this total system is very complex and its configuration space is of very high dimension. But there is in principle no objection to treating this entire system from the standpoint of quantum mechanics. Here too the theory determines the probability of each configuration of all coordinates for every time instant. If one considers all configurations of the coordinates, for a time large compared with the average decay time of the radioactive atom, there will be (at most) one such registration-mark on the paper strip. To each co-ordinate- configuration must correspond a definite position of the mark on the paper strip. But, inasmuch as the theory yields only the relative probability of the thinkable coordinate-configurations, it also offers only relative probabilities for the positions of the mark on the paperstrip, but no definite location for this mark.

Einstein continues:

…If we attempt [to work with] the interpretation that the quantum-theoretical description is to be understood as a complete description of the individual system, we are forced to the interpretation that the location of the mark on the strip is nothing which belongs to the system per se, but that the existence of that location is essentially dependent upon the carrying out of an observation made on the registration-strip. Such an interpretation is certainly by no means absurd from a purely logical point of standpoint; yet there is hardly anyone who would be inclined to consider it seriously. For, in the macroscopic sphere it simply is considered certain that one must adhere to the program of a realistic description in space and time; whereas in the sphere of microscopic situations, one is more readily inclined to give up, or at least to modify, this program."
(emphasis due to Einstein)

Einstein never rejected probabilistic techniques and thinking, in and of themselves. Einstein himself was a great statistician, using statistical analysis in his works on Brownian motion and photoelectricity and in papers published before 1905; Einstein had even discovered Gibbs ensembles. According to the majority of physicists, however, he believed that indeterminism constituted a criteria for strong objection to a physical theory. Pauli's testimony contradicts this, and Einstein's own statements indicate a focus on incompleteness, as his major concern.

Summary

Whatever his inner convictions, Einstein agreed that the quantum theory was the best available, but he looked for a more "complete" explanation, i.e., either more deterministic or one that could more fundamentally explain the reason for probabilities in a logical way. He could not abandon the belief that physics described the laws that govern "real things", nor could he abandon the belief that there are no explanations that contain contradictions, which had driven him to his successes explaining photons, relativity, atoms, and gravity.

Bose-Einstein statistics

In 1924, Einstein received a short paper from a young Indian physicist named Satyendra Nath Bose describing light as a gas of photons and asking for Einstein's assistance in publication. Einstein realized that the same statistics could be applied to atoms, and published an article in German (then the lingua franca of physics) which described Bose's model and explained its implications. Bose-Einstein statistics now describe any assembly of these indistinguishable particles known as bosons. The Bose-Einstein condensate phenomenon was predicted in the 1920s by Bose and Einstein, based on Bose's work on the statistical mechanics of photons, which was then formalized and generalized by Einstein. The first such condensate in alkali gases was produced by Eric Cornell and Carl Wieman in 1995 at the University of Colorado at Boulder, though Bose-Einstein Condensation has been observed in superfluid Helium-4 since the 1930s. Einstein's original sketches on this theory were recovered in August 2005 in the library of Leiden University.

Einstein also assisted Erwin Schrödinger in the development of the quantum Boltzmann distribution, a mixed classical and quantum mechanical gas model although he realized that this was less significant than the Bose-Einstein model and declined to have his name included on the paper.

Unified field theory

Einstein's research efforts after developing the theory of general relativity consisted primarily of a long series of attempts to generalize his theory of gravitation in order to unify and simplify the fundamental laws of physics, particularly gravitation and electromagnetism. In 1950 he described this work, which he referred to as the Unified Field Theory, in a Scientific American article. Einstein was guided by a belief in a single origin for the entire set of physical laws.

Einstein became increasingly isolated in his research on a generalized theory of gravitation and his attempts were ultimately unsuccessful. In particular, his pursuit of a unification of the fundamental forces ignored work in the physics community at large (and vice versa), most notably the discovery of the strong and weak nuclear forces, which were not understood independently until around 1970, fifteen years after Einstein's death. Einstein's goal of unifying the laws of physics under a single model survives in the current drive for unification of the forces.

Final years

In 1948, Einstein served on the original committee which resulted in the founding of Brandeis University. A portrait of Einstein was taken by Yousuf Karsh on February 11 of that same year. In 1952, the Israeli government proposed to Einstein that he take the post of second president. He declined the offer, and is believed to be the only United States citizen ever to have been offered a position as a foreign head of state. Einstein's refusal might have stemmed from his disapproval of some of the Israeli policies during the war of independence. In a letter he signed, along with other Jewish leaders in the U.S., he criticised the Freedom Party under the leadership of Menachem Begin for "Nazi and Fascist" methods and philosophy.. On March 30, 1953, Einstein released a revised unified field theory.

He died at 1:15 AM in Princeton hospital in Princeton, New Jersey, on April 18, 1955 at the age of 76 from internal bleeding, which was caused by the rupture of an aortic aneurism, leaving the Generalized Theory of Gravitation unsolved. The only person present at his deathbed, a hospital nurse, said that just before his death he mumbled several words in German that she did not understand. He was cremated without ceremony on the same day he died at Trenton, New Jersey, in accordance with his wishes. His ashes were scattered at an undisclosed location.

An autopsy was performed on Einstein by Dr. Thomas Stoltz Harvey, who removed and preserved his brain. Harvey found nothing unusual with his brain, but in 1999 further analysis by a team at McMaster University revealed that his parietal operculum region was missing and, to compensate, his inferior parietal lobe was 15% wider than normal. The inferior parietal region is responsible for mathematical thought, visuospatial cognition, and imagery of movement. Einstein's brain also contained 73% more glial cells than the average brain.