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Einstein was not the first to propose all the elements that went into the
special theory of relativity; his contribution lies in having unified important
parts of classical mechanics and Maxwellian electrodynamics. The third of
Einstein's seminal papers of 1905 concerned statistical mechanics, a field of
study that had been elaborated by, among others, Ludwig Boltzmann and Josiah
Willard Gibbs. Unaware of Gibbs' contributions, Einstein extended Boltzmann's
work and calculated the average trajectory of a microscopic particle buffeted by
random collisions with molecules in a fluid or in a gas. Einstein observed that
his calculations could account for brownian motion, the apparently erratic
movement of pollen in fluids, which had been noted by the British botanist
Robert Brown. Einstein's paper provided convincing evidence for the physical
existence of atom-sized molecules, which had already received much theoretical
discussion. His results were independently discovered by the Polish physicist
Marian von Smoluchowski and later elaborated by the French physicist Jean
Perrin. ( http://www.humboldt1.com/~gralsto/einstein/1905.html) General Theory
of Relativity After 1905, Einstein continued working in all three of his works
in the 1905 Papers.
He made important contributions to the quantum theory, but
increasingly he sought to extend the special theory of relativity to phenomena
involving acceleration. The key to an elaboration emerged in 1907 with the
principle of equivalence, in which gravitational acceleration was held a priori
indistinguishable from acceleration caused by mechanical forces; gravitational
mass was therefore identical with inertial mass. Einstein elevated this
identity, which is implicit in the work of Isaac Newton, to a guiding principle
in his attempts to explain both electromagnetic and gravitational acceleration
according to one set of physical laws. In 1907 he proposed that if mass were
equivalent to energy, then the principle of equivalency required that
gravitational mass would interact with the apparent mass of electromagnetic
radiation, which includes light. By 1911, Einstein was able to make preliminary
predictions about how a ray of light from a distant star, passing near the Sun,
would appear to be attracted, or bent slightly, in the direction of the Sun's
mass. At the same time, light radiated from the Sun would interact with the
Sun's mass, resulting in a slight change toward the infrared end of the Sun's
optical range. At this turning point Einstein also knew that any new theory of
gravitation would have to account for a small but persistent anomaly in the
perihelion motion of the planet Mercury. About 1912, Einstein began a new phase
of his gravitational research, with the help of his mathematician friend Marcel
Grossmann, by phrasing his work in terms of the tensor calculus of Tullio Levi-Civita
and Gregorio Ricci-Curbastro.
The tensor calculus greatly facilitated
calculations in four-dimensional space-time, a notion that Einstein had obtained
from Hermann Minkowski's 1907 mathematical elaboration of Einstein's own special
theory of relativity. Einstein called his new work the general theory of
relativity. After a number of false starts, he published the definitive form of
the general theory in late 1915. In it the gravitational field equations were
covariant; that is, similar to Maxwell's equations, the field equations took the
same form in all equivalent frames of reference. To their advantage from the
beginning, the covariant field equations gave the observed perihelion motion of
the planet Mercury. In its original form, Einstein's general relativity has been
verified numerous times in the past 60 years, especially during solar-eclipse
expeditions when Einstein's light-deflection prediction could be tested.
(http://www.humboldt1.com/~gralsto/einstein/relativ.html) Later life When
British eclipse expeditions in 1919 confirmed his predictions about the general
theory of relativity, Einstein was bombarded by the popular press. Einstein's
personal ethics also fired public imagination. Einstein, who after returning to
Germany in 1914 did not reapply for German citizenship, was one of only a
handful of German professors who remained a pacifist and did not support
Germany's war aims. After the war, when the victorious allies sought to exclude
German scientists from international meetings, Einstein--a Jew traveling with a
Swiss passport--remained an acceptable German envoy. Einstein's political views
as a pacifist and a Zionist pitted him against conservatives in Germany, who
branded him a traitor and a defeatist. The public success accorded his theories
of relativity evoked savage attacks in the 1920s by the anti-Semitic physicists
Johannes Stark and Philipp Lenard, men who after 1932 tried to create a
so-called Aryan physics in Germany. Just how controversial the theories of
relativity remained for less flexibly minded physicists is revealed in the
circumstances surrounding Einstein's reception of a Nobel Prize in 1921--awarded
not for relativity but for his 1905 work on the photoelectric effect. With the
rise of hitlerism in Germany, Einstein moved, in 1933 to the United States and
abandoned his pacifism. He reluctantly agreed that the new hazard had to be put
down through force of arms. In this context Einstein sent a letter, in 1939, to
President Franklin D. Roosevelt that urged that the United States proceed to
develop an atomic bomb before Germany did. The letter, composed by Einstein's
friend Leo Szilard, was one of many exchanged between the White House and
Einstein, and it contributed to Roosevelt's decision to fund what became the
Manhattan Project. As much he appeared to the public as a champion of unpopular
causes, Einstein's central concerns always revolved around physics. At the age
of 59, when other theoretical physicists would long since have abandoned
original scientific research, Einstein and his co-workers Leopold Infeld and
Banesh Hoffmann achieved a major new result in the general theory of relativity.
Until the end of his life Einstein sought a unified field theory, whereby the
phenomena of gravitation and electromagnetism could be derived from one set of
equations. After 1920, however, while retaining relativity as a fundamental
concept, theoretical physicists focused more attention on the theory of quantum
mechanics, as elaborated by Max Planck, Niels Bohr, Werner Heisenberg, and
others, and Einstein's later thoughts went somewhat neglected for decades. This
picture has changed in more recent years. Physicists are now striving to combine
Einstein's relativity theory with quantum theory in a theory of everything, by
means of such highly advanced mathematical models as superstring theories.
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