Unit 13 Albert EAinstein
Albert Einstein's Early Life
Einstein
was born in Ulm, Germany on Mar. 14,
1879. Einstein's parents, who were non
observant Jews, moved from Ulm to Munich
when Einstein was an infant. The family
business was the manufacture of electrical
parts. When the business failed, in
1894, the family moved to Milan, Italy.
At this time Einstein decided officially
to relinquish his German citizenship.
Within a year, still without having
completed secondary school, Einstein
failed an examination that would have
allowed him to pursue a course of study
leading to a diploma as an electrical
engineer at the Swiss Federal Institute
of Technology. He spent the next year
in nearby Aarau at the cantonal secondary
school, where he enjoyed excellent teachers
and first-rate facilities in physics.
Einstein returned in 1896 to the Swiss
Federal Institute of Technology, where
he graduated, in 1900 as a secondary
school teacher of mathematics and physics.
After two years he obtained a post
at the Swiss patent office in Bern.
The patent-office work required Einstein's
careful attention, but while employed
(1902-09) there, he completed an astonishing
range of publications in theoretical
physics. For the most part these texts
were written in his spare time and without
the benefit of close contact with either
the scientific literature or theoretician
colleagues. Einstein submitted one of
his scientific papers to the University
of Zurich to obtain a Ph.D. degree in
1905. In 1908 he sent a second paper
to the University of Bern and became
a lecturer there. The next year Einstein
received a regular appointment as associate
professor of physics at the University
of Zurich.
By 1909, Einstein was recognized throughout
German-speaking Europe as a leading
scientific thinker. In quick succession
he held professorships at the German
University of Prague and at the Swiss
Federal Institute of Technology. In
1914 he advanced to the most prestigious
and best-paying post that a theoretical
physicist could hold in central Europe,
professor at the Kaiser-Wilhelm Gesellschaft
in Berlin.
ith the rise of fascism in Germany, Einstein moved, in 1933 to the United States and abandoned his pacifism. He reluctantly agreed that the new menace 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 super string theories.
The 1905 Papers
In
the first of three seminal papers that
were published in 1905, Einstein examined
the phenomenon discovered by Max Planck,
according to which electromagnetic energy
seemed to be emitted from radiating
objects in quantities that were ultimately
discrete. The energy of these emitted
quantities, the so-called light-quanta,
was directly proportional to the frequency
of the radiation. This circumstance
was perplexing because classical electromagnetic
theory, based on Maxwell's equations
and the laws of thermodynamics, had
assumed that electromagnetic energy
consisted of waves propagating in a
hypothetical, all-pervasive medium called
the aluminiferous ether, and that the
waves could contain any amount of energy
no matter how small. Einstein used Planck's
quantum hypothesis to describe visible
electromagnetic radiation, or light.
According to Einstein's heuristic viewpoint,
light could be imagined to consist of
discrete bundles of radiation. Einstein
used this interpretation to explain
the photoelectric effect, by which certain
metals emit electrons when illuminated
by light with a given frequency. Einstein's
theory, and his subsequent elaboration
of it, formed the basis for much of
quantum mechanics.
The second of Einstein's 1905 papers
proposed what is today called the special
theory of relativity. At the time Einstein
knew that, according to Hendrik Antoon
Lorentz's theory of electrons, the mass
of an electron increased as the velocity
of the electron approached the velocity
of light. Einstein also knew that the
electron theory, based on Maxwell's
equations, carried along with it the
assumption of aluminiferous ether, but
that attempts to detect the physical
properties of the ether had not succeeded.
Einstein realized that the equations
describing the motion of an electron
in fact could describe the nonaccelerated
motion of any particle or any suitably
defined rigid body. He based his new
kinematics on a reinterpretation of
the classical principle of relativity,
that the laws of physics had to have
the same form in any frame of reference.
As a second fundamental hypothesis,
Einstein assumed that the speed of light
remained constant in all frames of reference,
as required by classical Maxwellian
theory. Einstein abandoned the hypothesis
of the ether, for it played no role
in his kinematics or in his reinterpretation
of Lorentz's theory of electrons. As
a consequence of his theory Einstein
recovered the phenomenon of time dilatation,
wherein time, analogous to length and
mass, is a function of the velocity
of a frame of reference. Later in 1905,
Einstein elaborated how, in a certain
manner of speaking, mass and energy
were equivalent. 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
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 Perrinelectrodynamics.
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 equivalence 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 spectrum. At this
juncture 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.