Albert Einstein 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.
Einstein is revered by the physics community, and in 1999 Time magazine named him the Person of the Century.
In wider culture the name Einstein has become synonymous with genius.
Light and general relativity
One of the 1919 eclipse photographs taken during Arthur Stanley Eddington's expedition,
which confirmed Einstein's predictions of the gravitational bending of light.
In 1906, the patent office promoted Einstein to Technical Examiner Second Class, but he had not given 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 Finlay-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 Humboldt 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, the 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 Príncipe.
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.