Albert Einstein (March 14, 1879 – April 18, 1955) was a German-born theoretical physicist. He is best known for his theory of relativity and specifically mass-energy equivalence, E = mc2. Einstein received the 1921 Nobel Prize in Physics "for his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect."

Einstein's many contributions to physics include his special theory of relativity, which reconciled mechanics with electromagnetism, and his general theory of relativity, which extended the principle of relativity to non-uniform motion, creating a new theory of gravitation. His other contributions include relativistic cosmology, capillary action, critical opalescence, classical problems of statistical mechanics and their application to quantum theory, an explanation of the Brownian movement of molecules, atomic transition probabilities, the quantum theory of a monatomic gas, thermal properties of light with low radiation density (which laid the foundation for the photon theory), a theory of radiation including stimulated emission, the conception of a unified field theory, and the geometrization of physics.

Works by Albert Einstein include more than fifty scientific papers and also non-scientific books. In 1999 Einstein was named Time magazine's "Person of the Century", and a poll of prominent physicists named him the greatest physicist of all time. In popular culture the name "Einstein" has become synonymous with genius.

Youth and schooling
Albert Einstein was born into a Jewish family in Ulm, Württemberg, Germany. His father was Hermann Einstein, a salesman and engineer. His mother was Pauline Einstein (née Koch). In 1880, the family moved to Munich, where his father and his uncle founded a company, Elektrotechnische Fabrik J. Einstein & Cie that manufactured electrical equipment, providing the first lighting for the Oktoberfest and cabling for the Munich suburb of Schwabing.

The Einsteins were not observant of Jewish religious practices, and Albert attended a Catholic elementary school. Although Albert had early speech difficulties, he was a top student in elementary school.

When Albert was five, his father showed him a pocket compass. Albert realized that something in empty space was moving the needle and later stated that this experience made "a deep and lasting impression". At his mother's insistence, he took violin lessons starting at age six, and although he disliked them and eventually quit, he later took great pleasure in Mozart's violin sonatas. As he grew, Albert built models and mechanical devices for fun, and began to show a talent for mathematics.

In 1889, family friend Max Talmud (later: Talmey), a medical student, introduced the ten-year-old Albert to key science, mathematics, and philosophy texts, including Kant's Critique of Pure Reason and Euclid's Elements (Einstein called it the "holy little geometry book"). From Euclid, Albert began to understand deductive reasoning (integral to theoretical physics), and by the age of twelve, he learned Euclidean geometry from a school booklet. Soon thereafter he began to investigate calculus.

In his early teens, Albert attended the new and progressive Luitpold Gymnasium. His father intended for him to pursue electrical engineering, but Albert clashed with authorities and resented the school regimen. He later wrote that the spirit of learning and creative thought were lost in strict rote learning.

In 1894, when Einstein was fifteen, his father's business failed, and the Einstein family moved to Italy, first to Milan and then, after a few months, to Pavia. During this time, Albert wrote his first scientific work, "The Investigation of the State of Aether in Magnetic Fields". Albert had been left behind in Munich to finish high school, but in the spring of 1895, he withdrew to join his family in Pavia, convincing the school to let him go by using a doctor's note.

Rather than completing high school, Albert decided to apply directly to the ETH Zurich, the Swiss Federal Institute of Technology in Zurich, Switzerland. Without a school certificate, he was required to take an entrance examination, which he did not pass, although he got exceptional marks in mathematics and physics. Einstein wrote that it was in that same year, at age 16, that he first performed his famous thought experiment, visualizing traveling alongside a beam of light (Einstein 1979).

The Einsteins sent Albert to Aarau, Switzerland to finish secondary school. While lodging with the family of Professor Jost Winteler, he fell in love with the family's daughter, Sofia Marie-Jeanne Amanda Winteler, called "Marie". (Albert's sister, Maja, his confidant, later married Paul Winteler.) In Aarau, Albert studied Maxwell's electromagnetic theory. In 1896, he graduated at age 17, renounced his German citizenship to avoid military service (with his father's approval), and finally enrolled in the mathematics program at ETH. On February 21, 1901, he gained Swiss citizenship, which he never revoked. Marie moved to Olsberg, Switzerland for a teaching post.

In 1896, Einstein's future wife, Mileva Marić, also enrolled at ETH, as the only woman studying mathematics. During the next few years, Einstein and Marić's friendship developed into romance. Einstein's mother objected because she thought Marić "too old", not Jewish, and "physically defective". Einstein and Marić had a daughter, Lieserl Einstein, born in early 1902. Her fate is unknown.

Einstein graduated in 1900 from ETH with a degree in physics. That same year, Einstein's friend Michele Besso introduced him to the work of Ernst Mach. The next year, Einstein published a paper in the prestigious Annalen der Physik on the capillary forces of a straw (Einstein 1901).

Light and general relativity
In 1906, the patent office promoted Einstein to Technical Examiner Second Class, but he was not giving up on academia. In 1908, he became a privatdozent at the University of Bern. In 1910, he wrote a paper on critical opalescence that described the cumulative effect of light scattered by individual molecules in the atmosphere, i.e. why the sky is blue.

During 1909, Einstein published "Über die Entwicklung unserer Anschauungen über das Wesen und die Konstitution der Strahlung" ("The Development of Our Views on the Composition and Essence of Radiation"), on the quantization of light. In this and in an earlier 1909 paper, Einstein showed that Max Planck's energy quanta must have well-defined momenta and act in some respects as independent, point-like particles. This paper introduced the photon concept (although the term itself was introduced by Gilbert N. Lewis in 1926) and inspired the notion of wave–particle duality in quantum mechanics.

In 1911, Einstein became an associate professor at the University of Zurich. However, shortly afterward, he accepted a full professorship at the Charles University of Prague. While in Prague, Einstein published a paper about the effects of gravity on light, specifically the gravitational redshift and the gravitational deflection of light. The paper appealed to astronomers to find ways of detecting the deflection during a solar eclipse. German astronomer Erwin Freundlich publicized Einstein's challenge to scientists around the world.

In 1912, Einstein returned to Switzerland to accept a professorship at his alma mater, the ETH. There he met mathematician Marcel Grossmann who introduced him to Riemannian geometry, and at the recommendation of Italian mathematician Tullio Levi-Civita, Einstein began exploring the usefulness of general covariance (essentially the use of tensors) for his gravitational theory. Although for a while Einstein thought that there were problems with that approach, he later returned to it and by late 1915 had published his general theory of relativity in the form that is still used today (Einstein 1915). This theory explains gravitation as distortion of the structure of spacetime by matter, affecting the inertial motion of other matter.

After many relocations, Mileva established a permanent home with the children in Zurich in 1914, just before the start of World War I. Einstein continued on alone to Berlin, where he became a member of the Prussian Academy of Sciences. As part of the arrangements for his new position, he also became a professor at the University of Berlin, although with a special clause freeing him from most teaching obligations. From 1914 to 1932 he was also director of the Kaiser Wilhelm Institute for physics.

During World War I, the speeches and writings of Central Powers scientists were available only to Central Powers academics, for national security reasons. Some of Einstein's work did reach the United Kingdom and the United States through the efforts of the Austrian Paul Ehrenfest and physicists in the Netherlands, especially 1902 Nobel Prize-winner Hendrik Lorentz and Willem de Sitter of the Leiden University. After the war ended, Einstein maintained his relationship with the Leiden University, accepting a contract as an Extraordinary Professor; he travelled to Holland regularly to lecture there between 1920 and 1930.

In 1917, Einstein published an article in Physikalische Zeitschrift that proposed the possibility of stimulated emission, the physical process that makes possible the maser and the laser (Einstein 1917b). He also published a paper introducing a new notion, a cosmological constant, into the general theory of relativity in an attempt to model the behavior of the entire universe (Einstein 1917a).

1917 was the year astronomers began taking Einstein up on his 1911 challenge from Prague. The Mount Wilson Observatory in California, U.S., published a solar spectroscopic analysis that showed no gravitational redshift. In 1918, the Lick Observatory, also in California, announced that they too had disproven Einstein's prediction, although their findings were not published

However, in May 1919, a team led by British astronomer Arthur Stanley Eddington claimed to have confirmed Einstein's prediction of gravitational deflection of starlight by the Sun while photographing a solar eclipse in Sobral northern Brazil and Principe. On November 7, 1919, leading British newspaper The Times printed a banner headline that read: "Revolution in Science – New Theory of the Universe – Newtonian Ideas Overthrown". In an interview Nobel laureate Max Born praised general relativity as the "greatest feat of human thinking about nature"; fellow laureate Paul Dirac was quoted saying it was "probably the greatest scientific discovery ever made".

In their excitement, the world media made Albert Einstein world-famous. Ironically, later examination of the photographs taken on the Eddington expedition showed that the experimental uncertainty was of about the same magnitude as the effect Eddington claimed to have demonstrated, and in 1962 a British expedition concluded that the method used was inherently unreliable. The deflection of light during a solar eclipse has, however, been more accurately measured (and confirmed) by later observations.

There was some resentment toward the newcomer Einstein's fame in the scientific community, notably among German physicists, who later started the Deutsche Physik (German Physics) movement.

Having lived apart for five years, Einstein and Mileva divorced on February 14, 1919. On June 2 of that year, Einstein married Elsa Löwenthal, who had nursed him through an illness. Elsa was Albert's first cousin (maternally) and his second cousin (paternally). Together the Einsteins raised Margot and Ilse, Elsa's daughters from her first marriage.

Nobel Prize
In 1921 Einstein was awarded the Nobel Prize in Physics, "for his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect". This refers to his 1905 paper on the photoelectric effect: "On a Heuristic Viewpoint Concerning the Production and Transformation of Light", which was well supported by the experimental evidence by that time. The presentation speech began by mentioning "his theory of relativity been the subject of lively debate in philosophical circles also has astrophysical implications which are being rigorously examined at the present time." (Einstein 1923) As per their divorce settlement, Einstein gave the Nobel prize money to his first wife, Mileva Marić.

Einstein traveled to New York City in the United States for the first time on April 2, 1921. When asked where he got his scientific ideas, Einstein explained that he believed scientific work best proceeds from an examination of physical reality and a search for underlying axioms, with consistent explanations that apply in all instances and avoid contradicting each other. He also recommended theories with visualizable results (Einstein 1954).

Death
On April 17, 1955, Albert Einstein experienced internal bleeding caused by the rupture of an aortic aneurism. He took a draft of a speech he was preparing for a television appearance commemorating the State of Israel's seventh anniversary with him to the hospital, but he did not live long enough to complete it. He died in Princeton Hospital early the next morning at the age of 76. Einstein's remains were cremated and his ashes were scattered.

Before the cremation, Princeton Hospital pathologist Thomas Stoltz Harvey removed Einstein's brain for preservation, in hope that the neuroscience of the future would be able to discover what made Einstein so intelligent.

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