Albert Einstein (pron.: /ˈælbərt ˈaɪnstaɪn/; German: [ˈalbɐt
ˈaɪnʃtaɪn] ( listen); 14 March 1879 – 18 April 1955) was a German-born
theoretical physicist who developed the general theory of relativity, one of
the two pillars of modern physics (alongside quantum mechanics).[2][3] While
best known for his mass–energy equivalence formula E = mc2 (which has been
dubbed "the world's most famous equation"),[4] he 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".[5]
The latter was pivotal in establishing quantum theory.
Near the beginning of his career, Einstein thought that
Newtonian mechanics was no longer enough to reconcile the laws of classical
mechanics with the laws of the electromagnetic field. This led to the
development of his special theory of relativity. He realized, however, that the
principle of relativity could also be extended to gravitational fields, and
with his subsequent theory of gravitation in 1916, he published a paper on the
general theory of relativity. He continued to deal with problems of statistical
mechanics and quantum theory, which led to his explanations of particle theory
and the motion of molecules. He also investigated the thermal properties of
light which laid the foundation of the photon theory of light. In 1917,
Einstein applied the general theory of relativity to model the structure of the
universe as a whole.[6]
He was visiting the United States when Adolf Hitler came to
power in 1933, and did not go back to Germany, where he had been a professor at
the Berlin Academy of Sciences. He settled in the U.S., becoming a citizen in
1940.[7] On the eve of World War II, he helped alert President Franklin D.
Roosevelt that Germany might be developing an atomic weapon, and recommended
that the U.S. begin similar research; this eventually led to what would become
the Manhattan Project. Einstein was in support of defending the Allied forces,
but largely denounced using the new discovery of nuclear fission as a weapon.
Later, with the British philosopher Bertrand Russell, Einstein signed the
Russell–Einstein Manifesto, which highlighted the danger of nuclear weapons.
Einstein was affiliated with the Institute for Advanced Study in Princeton, New
Jersey, until his death in 1955.
Einstein published more than 300 scientific papers along
with over 150 non-scientific works.[6][8] His great intellectual achievements
and originality have made the word "Einstein" synonymous with
genius.[9]
Einstein at the age of three in 1882
Albert Einstein in 1893 (age 14)
Einstein's matriculation certificate at the age of 17,
showing his final grades from the Aargau Kantonsschule (on a scale of 1-6, with
6 being the best mark).
Albert Einstein was born in Ulm, in the Kingdom of
Württemberg in the German Empire on 14 March 1879.[10] 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
Elektrotechnische Fabrik J. Einstein & Cie, a company that manufactured
electrical equipment based on direct current.[10]
The Einsteins were non-observant Jews. Albert attended a
Catholic elementary school from the age of five for three years. At the age of
eight, he was transferred to the Luitpold Gymnasium where he received advanced
primary and secondary school education until he left Germany seven years
later.[11] Although it has been thought that Einstein had early speech
difficulties, this is disputed by the Albert Einstein Archives, and he excelled
at the first school that he attended.[12] He was right handed;[12][13] there
appears to be no evidence for the widespread popular belief[14] that he was
left handed.
His father once showed him a pocket compass; Einstein
realized that there must be something causing the needle to move, despite the
apparent "empty space".[15] As he grew, Einstein built models and
mechanical devices for fun and began to show a talent for mathematics.[10] When
Einstein was ten years old, Max Talmud (later changed to Max Talmey), a poor
Jewish medical student from Poland, was introduced to the Einstein family by
his brother, and during weekly visits over the next five years, he gave the boy
popular books on science, mathematical texts and philosophical writings. These
included Immanuel Kant's Critique of Pure Reason, and Euclid's Elements (which
Einstein called the "holy little geometry book").[16][17][fn 1]
In 1894, his father's company failed: direct current (DC)
lost the War of Currents to alternating current (AC). In search of business,
the Einstein family moved to Italy, first to Milan and then, a few months
later, to Pavia. When the family moved to Pavia, Einstein stayed in Munich to
finish his studies at the Luitpold Gymnasium. His father intended for him to
pursue electrical engineering, but Einstein clashed with authorities and
resented the school's regimen and teaching method. He later wrote that the
spirit of learning and creative thought were lost in strict rote learning. At
the end of December 1894, he travelled to Italy to join his family in Pavia,
convincing the school to let him go by using a doctor's note.[19] It was during
his time in Italy that he wrote a short essay with the title "On the
Investigation of the State of the Ether in a Magnetic Field."[20][21]
In late summer 1895, at the age of sixteen, Einstein sat the
entrance examinations for the Swiss Federal Polytechnic in Zurich (later the
Eidgenössische Polytechnische Schule). He failed to reach the required standard
in several subjects, but obtained exceptional grades in physics and
mathematics.[22] On the advice of the Principal of the Polytechnic, he attended
the Aargau Cantonal School in Aarau, Switzerland, in 1895-96 to complete his
secondary schooling. While lodging with the family of Professor Jost Winteler,
he fell in love with Winteler's daughter, Marie. (His sister Maja later married
the Wintelers' son, Paul.)[23] In January 1896, with his father's approval, he
renounced his citizenship in the German Kingdom of Württemberg to avoid
military service.[24] (He acquired Swiss citizenship five years later, in
February 1901.)[25] In September 1896, he passed the Swiss Matura with mostly
good grades (including a top grade of 6 in physics and mathematical subjects,
on a scale of 1-6),[26] and, though only seventeen, enrolled in the four-year
mathematics and physics teaching diploma program at the ETH Zurich. Marie
Winteler moved to Olsberg, Switzerland for a teaching post.
Einstein's future wife, Mileva Marić, also enrolled at the
Polytechnic that same year, the only woman among the six students in the
mathematics and physics section of the teaching diploma course. Over the next
few years, Einstein and Marić's friendship developed into romance, and they
read books together on extra-curricular physics in which Einstein was taking an
increasing interest. In 1900, Einstein was awarded the Zurich Polytechnic
teaching diploma, but Marić failed the examination with a poor grade in the
mathematics component, theory of functions.[27] There have been claims that
Marić collaborated with Einstein on his celebrated 1905 papers,[28][29] but
historians of physics who have studied the issue find no evidence that she made
any substantive contributions.[30][31][32][33]
Marriages and children
In early 1902, Einstein and Marić had a daughter they named
Lieserl, born in Novi Sad where Marić was staying with her parents. Her fate is
unknown, but the contents of a letter Einstein wrote to Marić in September 1903
suggest that she was either adopted or died of scarlet fever in
infancy.[34][35]
Einstein and Marić married in January 1903. In May 1904, the
couple's first son, Hans Albert Einstein, was born in Bern, Switzerland. Their
second son, Eduard, was born in Zurich in July 1910. In 1914, Einstein moved to
Berlin, while his wife remained in Zurich with their sons. They divorced on 14
February 1919, having lived apart for five years.
Einstein married Elsa Löwenthal on 2 June 1919, after having
had a relationship with her since 1912. She was his first cousin maternally and
his second cousin paternally. In 1933, they emigrated to the United States. In
1935, Elsa Einstein was diagnosed with heart and kidney problems and died in
December 1936.[36]
Patent office
Left to right: Conrad Habicht, Maurice Solovine and
Einstein, who founded the Olympia Academy
After graduating, Einstein spent almost two frustrating
years searching for a teaching post, but Marcel Grossmann's father helped him
secure a job in Bern,[37] at the Federal Office for Intellectual Property, the
patent office, as an assistant examiner.[38] He evaluated patent applications
for electromagnetic devices. In 1903, Einstein's position at the Swiss Patent
Office became permanent, although he was passed over for promotion until he
"fully mastered machine technology".[39]
Much of his work at the patent office related to questions
about transmission of electric signals and electrical-mechanical
synchronization of time, two technical problems that show up conspicuously in
the thought experiments that eventually led Einstein to his radical conclusions
about the nature of light and the fundamental connection between space and
time.[40]
With a few friends he met in Bern, Einstein started a small
discussion group, self-mockingly named "The Olympia Academy", which
met regularly to discuss science and philosophy. Their readings included the
works of Henri Poincaré, Ernst Mach, and David Hume, which influenced his
scientific and philosophical outlook.
Academic career
Einstein's official 1921 portrait after receiving the Nobel
Prize in Physics.
In 1901, his paper "Folgerungen aus den Kapillarität
Erscheinungen" ("Conclusions from the Capillarity Phenomena")
was published in the prestigious Annalen der Physik.[41] On 30 April 1905,
Einstein completed his thesis, with Alfred Kleiner, Professor of Experimental
Physics, serving as pro-forma advisor. Einstein was awarded a PhD by the
University of Zurich. His dissertation was entitled "A New Determination
of Molecular Dimensions".[42][43] That same year, which has been called
Einstein's annus mirabilis (miracle year), he published four groundbreaking
papers, on the photoelectric effect, Brownian motion, special relativity, and
the equivalence of mass and energy, which were to bring him to the notice of
the academic world.
By 1908, he was recognized as a leading scientist, and he
was appointed lecturer at the University of Bern. The following year, he quit
the patent office and the lectureship to take the position of physics
docent[44] at the University of Zurich. He became a full professor at
Karl-Ferdinand University in Prague in 1911. In 1914, he returned to Germany
after being appointed director of the Kaiser Wilhelm Institute for Physics
(1914–1932)[45] and a professor at the Humboldt University of Berlin, with a
special clause in his contract that freed him from most teaching obligations.
He became a member of the Prussian Academy of Sciences. In 1916, Einstein was
appointed president of the German Physical Society (1916–1918).[46][47]
During 1911, he had calculated that, based on his new theory
of general relativity, light from another star would be bent by the Sun's
gravity. That prediction was claimed confirmed by observations made by a
British expedition led by Sir Arthur Eddington during the solar eclipse of 29
May 1919. International media reports of this made Einstein world famous. On 7
November 1919, the leading British newspaper The Times printed a banner
headline that read: "Revolution in Science – New Theory of the Universe –
Newtonian Ideas Overthrown".[48] Much later, questions were raised whether
the measurements had been accurate enough to support Einstein's theory. In 1980
historians John Earman and Clark Glymour published an analysis suggesting that
Eddington had suppressed unfavorable results.[49] The two reviewers found
possible flaws in Eddington's selection of data, but their doubts, although
widely quoted and, indeed, now with a "mythical" status almost
equivalent to the status of the original observations, have not been
confirmed.[50][51] Eddington's selection from the data seems valid and his team
indeed made astronomical measurements verifying the theory.[52]
In 1921, Einstein was awarded the Nobel Prize in Physics for
his explanation of the photoelectric effect, as relativity was considered still
somewhat controversial. He also received the Copley Medal from the Royal
Society in 1925.
Travels abroad
Einstein visited New York City for the first time on 2 April
1921, where he received an official welcome by the Mayor, followed by three
weeks of lectures and receptions. He went on to deliver several lectures at
Columbia University and Princeton University, and in Washington he accompanied
representatives of the National Academy of Science on a visit to the White
House. On his return to Europe he was the guest of the British statesman and
philosopher Viscount Haldane in London, where he met several renowned
scientific, intellectual and political figures, and delivered a lecture at
King's College.[53]
In 1922, he traveled throughout Asia and later to Palestine,
as part of a six-month excursion and speaking tour. His travels included
Singapore, Ceylon, and Japan, where he gave a series of lectures to thousands
of Japanese. His first lecture in Tokyo lasted four hours, after which he met
the emperor and empress at the Imperial Palace where thousands came to watch.
Einstein later gave his impressions of the Japanese in a letter to his sons:[54]:307
"Of all the people I have met, I like the Japanese most, as they are
modest, intelligent, considerate, and have a feel for art."[54]:308
On his return voyage, he also visited Palestine for 12 days
in what would become his only visit to that region. "He was greeted with
great British pomp, as if he were a head of state rather than a theoretical
physicist", writes Isaacson. This included a cannon salute upon his
arrival at the residence of the British high commissioner, Sir Herbert Samuel.
During one reception given to him, the building was "stormed by throngs
who wanted to hear him". In Einstein's talk to the audience, he expressed
his happiness over the event:
I consider this the greatest day of my life. Before, I have
always found something to regret in the Jewish soul, and that is the
forgetfulness of its own people. Today, I have been made happy by the sight of
the Jewish people learning to recognize themselves and to make themselves
recognized as a force in the world.[55]:308
Emigration to U.S. in 1933
Cartoon of Einstein, who has shed his "Pacifism"
wings, standing next to a pillar labeled "World Peace." He is rolling
up his sleeves and holding a sword labeled "Preparedness" (circa
1933).
In February 1933 while on a visit to the United States, Einstein
decided not to return to Germany due to the rise to power of the Nazis under
Germany's new chancellor.[56][57] He visited American universities in early
1933 where he undertook his third two-month visiting professorship at the
California Institute of Technology in Pasadena. He and his wife Elsa returned
by ship to Belgium at the end of March. During the voyage they were informed
that their cottage was raided by the Nazis and his personal sailboat had been
confiscated. Upon landing in Antwerp on 28 March, he immediately went to the
German consulate where he turned in his passport and formally renounced his
German citizenship.[55]
In early April, he learned that the new German government
had passed laws barring Jews from holding any official positions, including
teaching at universities.[55] A month later, Einstein's works were among those
targeted by Nazi book burnings, and Nazi propaganda minister Joseph Goebbels
proclaimed, "Jewish intellectualism is dead."[55] Einstein also
learned that his name was on a list of assassination targets, with a
"$5,000 bounty on his head."[55] One German magazine included him in
a list of enemies of the German regime with the phrase, "not yet
hanged".[55]
He resided in Belgium for some months, before temporarily
living in England.[58][59] In a letter to his friend, physicist Max Born, who
also emigrated from Germany and lived in England, Einstein wrote, ". . . I
must confess that the degree of their brutality and cowardice came as something
of a surprise."[55]
Portrait taken in 1935 at Princeton
In October 1933 he returned to the U.S. and took up a
position at the Institute for Advanced Study at Princeton, New Jersey, that
required his presence for six months each year.[60][61] He was still undecided
on his future (he had offers from European universities, including Oxford), but
in 1935 he arrived at the decision to remain permanently in the United States
and apply for citizenship.[62][63]
His affiliation with the Institute for Advance Studies would
last until his death in 1955.[64] He was one of the four first selected (two of
the others being John von Neumann and Kurt Gödel) at the new Institute, where
he soon developed a close friendship with Gödel. The two would take long walks
together discussing their work. His last assistant was Bruria Kaufman, who
later became a renowned physicist. During this period, Einstein tried to
develop a unified field theory and to refute the accepted interpretation of
quantum physics, both unsuccessfully.
Other scientists also fled to America. Among them were Nobel
laureates and professors of theoretical physics. With so many other Jewish
scientists now forced by circumstances to live in America, often working side
by side, Einstein wrote to a friend, "For me the most beautiful thing is
to be in contact with a few fine Jews—a few millennia of a civilized past do
mean something after all." In another letter he writes, "In my whole
life I have never felt so Jewish as now."[55]
World War II and the Manhattan Project
In 1939, a group of Hungarian scientists that included
emigre physicist Leó Szilárd attempted to alert Washington of ongoing Nazi
atomic bomb research. The group's warnings were discounted.[65] Einstein and
Szilárd, along with other refugees such as Edward Teller and Eugene Wigner,
"regarded it as their responsibility to alert Americans to the possibility
that German scientists might win the race to build an atomic bomb, and to warn
that Hitler would be more than willing to resort to such a
weapon."[54]:630[66] In the summer of 1939, a few months before the
beginning of World War II in Europe, Einstein was persuaded to lend his
prestige by writing a letter with Szilárd to President Franklin D. Roosevelt to
alert him of the possibility. The letter also recommended that the U.S. government
pay attention to and become directly involved in uranium research and
associated chain reaction research.
The letter is believed to be "arguably the key stimulus
for the U.S. adoption of serious investigations into nuclear weapons on the eve
of the U.S. entry into World War II".[67] President Roosevelt could not
take the risk of allowing Hitler to possess atomic bombs first. As a result of
Einstein's letter and his meetings with Roosevelt, the U.S. entered the
"race" to develop the bomb, drawing on its "immense material,
financial, and scientific resources" to initiate the Manhattan Project. It
became the only country to successfully develop an atomic bomb during World War
II.
For Einstein, "war was a disease . . . [and] he called
for resistance to war." But in 1933, after Hitler assumed full power in
Germany, "he renounced pacifism altogether . . . In fact, he urged the
Western powers to prepare themselves against another German
onslaught."[68]:110 In 1954, a year before his death, Einstein said to his
old friend, Linus Pauling, "I made one great mistake in my life — when I
signed the letter to President Roosevelt recommending that atom bombs be made;
but there was some justification — the danger that the Germans would make
them..."[69]
U.S. citizenship
Einstein accepting U.S. citizenship, 1940
Einstein became an American citizen in 1940. Not long after
settling into his career at Princeton, he expressed his appreciation of the
"meritocracy" in American culture when compared to Europe. According
to Isaacson, he recognized the "right of individuals to say and think what
they pleased", without social barriers, and as result, the individual was
"encouraged" to be more creative, a trait he valued from his own
early education. Einstein writes:
What makes the new arrival devoted to this country is the
democratic trait among the people. No one humbles himself before another person
or class. . . American youth has the good fortune not to have its outlook
troubled by outworn traditions.[55]:432
As a member of the National Association for the Advancement
of Colored People (NAACP) at Princeton who campaigned for the civil rights of
African Americans, Einstein corresponded with civil rights activist W. E. B. Du
Bois, and in 1946 Einstein called racism America's "worst
disease".[70] He later stated, "Race prejudice has unfortunately
become an American tradition which is uncritically handed down from one
generation to the next. The only remedies are enlightenment and
education".[71]
Einstein in 1947
During the final stage of his life, Einstein transitioned to
a vegetarian lifestyle,[72] arguing that "the vegetarian manner of living
by its purely physical effect on the human temperament would most beneficially
influence the lot of mankind".[73]
After the death of Israel's first president, Chaim Weizmann,
in November 1952, Prime Minister David Ben-Gurion offered Einstein the position
of President of Israel, a mostly ceremonial post.[74] The offer was presented
by Israel's ambassador in Washington, Abba Eban, who explained that the offer
"embodies the deepest respect which the Jewish people can repose in any of
its sons".[54]:522 However, Einstein declined, and wrote in his response
that he was "deeply moved", and "at once saddened and ashamed"
that he could not accept it:
All my life I have dealt with objective matters, hence I
lack both the natural aptitude and the experience to deal properly with people
and to exercise official function. I am the more distressed over these
circumstances because my relationship with the Jewish people became my
strongest human tie once I achieved complete clarity about our precarious
position among the nations of the world.[54]:522[74][75]
Death
The New York World-Telegram announces Einstein's death on 18
April 1955.
On 17 April 1955, Albert Einstein experienced internal
bleeding caused by the rupture of an abdominal aortic aneurysm, which had
previously been reinforced surgically by Dr. Rudolph Nissen in 1948.[76] He
took the 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.[77] Einstein refused
surgery, saying: "I want to go when I want. It is tasteless to prolong
life artificially. I have done my share, it is time to go. I will do it
elegantly."[78] He died in Princeton Hospital early the next morning at
the age of 76, having continued to work until near the end.
During the autopsy, the pathologist of Princeton Hospital,
Thomas Stoltz Harvey, removed Einstein's brain for preservation without the
permission of his family, in the hope that the neuroscience of the future would
be able to discover what made Einstein so intelligent.[79] Einstein's remains
were cremated and his ashes were scattered at an undisclosed location.[80][81]
In his lecture at Einstein's memorial, nuclear physicist
Robert Oppenheimer summarized his impression of him as a person: "He was
almost wholly without sophistication and wholly without worldliness . . . There
was always with him a wonderful purity at once childlike and profoundly
stubborn."[68]
Scientific career
Albert Einstein in 1904
The photoelectric effect. Incoming photons on the left
strike a metal plate (bottom), and eject electrons, depicted as flying off to
the right.
Throughout his life, Einstein published hundreds of books
and articles.[8][10] In addition to the work he did by himself he also
collaborated with other scientists on additional projects including the
Bose–Einstein statistics, the Einstein refrigerator and others.[82]
1905 – Annus Mirabilis papers
Main articles: Annus Mirabilis papers, Photoelectric effect,
Special theory of relativity, and Mass–energy equivalence
The Annus Mirabilis papers are four articles pertaining to
the photoelectric effect (which gave rise to quantum theory), Brownian motion,
the special theory of relativity, and E = mc2 that Albert Einstein published in
the Annalen der Physik scientific journal in 1905. These four works contributed
substantially to the foundation of modern physics and changed views on space,
time, and matter. The four papers are:
Title (translated) Area
of focus Received Published Significance
On a Heuristic Viewpoint Concerning the Production and
Transformation of Light Photoelectric
effect 18 March 9 June Resolved an unsolved puzzle by suggesting that energy is exchanged
only in discrete amounts (quanta).[83] This idea was pivotal to the early
development of quantum theory.[84]
On the Motion of Small Particles Suspended in a Stationary
Liquid, as Required by the Molecular Kinetic Theory of Heat Brownian motion 11 May 18 July Explained empirical
evidence for the atomic theory, supporting the application of statistical
physics.
On the Electrodynamics of Moving Bodies Special relativity 30 June 26 September Reconciled
Maxwell's equations for electricity and magnetism with the laws of mechanics by
introducing major changes to mechanics close to the speed of light, resulting
from analysis based on empirical evidence that the speed of light is
independent of the motion of the observer.[85] Discredited the concept of a
"luminiferous ether."[86]
Does the Inertia of a Body Depend Upon Its Energy Content? Matter–energy equivalence 27 September 21 November Equivalence
of matter and energy, E = mc2 (and by implication, the ability of gravity to
"bend" light), the existence of "rest energy", and the
basis of nuclear energy.
Thermodynamic fluctuations and statistical physics
Main articles: Statistical mechanics, thermal fluctuations,
and statistical physics
Albert Einstein's first paper[87] submitted in 1900 to
Annalen der Physik was on capillary attraction. It was published in 1901 with
the title "Folgerungen aus den Kapillarität Erscheinungen," which
translates as "Conclusions from the capillarity phenomena". Two
papers he published in 1902–1903 (thermodynamics) attempted to interpret atomic
phenomena from a statistical point of view. These papers were the foundation
for the 1905 paper on Brownian motion, which showed that Brownian movement can
be construed as firm evidence that molecules exist. His research in 1903 and
1904 was mainly concerned with the effect of finite atomic size on diffusion
phenomena.[87]
General principles
He articulated the principle of relativity. This was
understood by Hermann Minkowski to be a generalization of rotational invariance
from space to space-time. Other principles postulated by Einstein and later
vindicated are the principle of equivalence and the principle of adiabatic
invariance of the quantum number.
Theory of relativity and E = mc²
Main article: History of special relativity
Einstein's "Zur Elektrodynamik bewegter Körper"
("On the Electrodynamics of Moving Bodies") was received on 30 June
1905 and published 26 September of that same year. It reconciles Maxwell's
equations for electricity and magnetism with the laws of mechanics, by
introducing major changes to mechanics close to the speed of light. This later
became known as Einstein's special theory of relativity.
Consequences of this include the time-space frame of a
moving body appearing to slow down and contract (in the direction of motion)
when measured in the frame of the observer. This paper also argued that the
idea of a luminiferous aether – one of the leading theoretical entities in
physics at the time – was superfluous.[88]
In his paper on mass–energy equivalence Einstein produced E
= mc2 from his special relativity equations.[89] Einstein's 1905 work on
relativity remained controversial for many years, but was accepted by leading
physicists, starting with Max Planck.[90][91]
Photons and energy quanta
Main articles: Photon and Quantum
In a 1905 paper,[92] Einstein postulated that light itself
consists of localized particles (quanta). Einstein's light quanta were nearly
universally rejected by all physicists, including Max Planck and Niels Bohr.
This idea only became universally accepted in 1919, with Robert Millikan's
detailed experiments on the photoelectric effect, and with the measurement of
Compton scattering.
Einstein concluded that each wave of frequency f is
associated with a collection of photons with energy hf each, where h is Planck's
constant. He does not say much more, because he is not sure how the particles
are related to the wave. But he does suggest that this idea would explain
certain experimental results, notably the photoelectric effect.[93]
Quantized atomic vibrations
Main article: Einstein solid
In 1907 Einstein proposed a model of matter where each atom
in a lattice structure is an independent harmonic oscillator. In the Einstein
model, each atom oscillates independently – a series of equally spaced
quantized states for each oscillator. Einstein was aware that getting the
frequency of the actual oscillations would be different, but he nevertheless
proposed this theory because it was a particularly clear demonstration that
quantum mechanics could solve the specific heat problem in classical mechanics.
Peter Debye refined this model.[94]
Adiabatic principle and action-angle variables
Main article: Old quantum theory
Throughout the 1910s, quantum mechanics expanded in scope to
cover many different systems. After Ernest Rutherford discovered the nucleus
and proposed that electrons orbit like planets, Niels Bohr was able to show
that the same quantum mechanical postulates introduced by Planck and developed
by Einstein would explain the discrete motion of electrons in atoms, and the
periodic table of the elements.
Einstein contributed to these developments by linking them
with the 1898 arguments Wilhelm Wien had made. Wien had shown that the
hypothesis of adiabatic invariance of a thermal equilibrium state allows all
the blackbody curves at different temperature to be derived from one another by
a simple shifting process. Einstein noted in 1911 that the same adiabatic
principle shows that the quantity which is quantized in any mechanical motion
must be an adiabatic invariant. Arnold Sommerfeld identified this adiabatic
invariant as the action variable of classical mechanics. The law that the
action variable is quantized was a basic principle of the quantum theory as it
was known between 1900 and 1925.[citation needed]
Wave–particle duality
Einstein during his visit to the United States
Main article: Wave–particle duality
Although the patent office promoted Einstein to Technical
Examiner Second Class in 1906, he had not given up on academia. In 1908, he
became a privatdozent at the University of Bern.[95] In "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, 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 name photon
was introduced later by Gilbert N. Lewis in 1926) and inspired the notion of
wave–particle duality in quantum mechanics.
Theory of critical opalescence
Main article: Critical opalescence
Einstein returned to the problem of thermodynamic
fluctuations, giving a treatment of the density variations in a fluid at its
critical point. Ordinarily the density fluctuations are controlled by the
second derivative of the free energy with respect to the density. At the
critical point, this derivative is zero, leading to large fluctuations. The
effect of density fluctuations is that light of all wavelengths is scattered,
making the fluid look milky white. Einstein relates this to Raleigh scattering,
which is what happens when the fluctuation size is much smaller than the
wavelength, and which explains why the sky is blue.[96] Einstein quantitatively
derived critical opalescence from a treatment of density fluctuations, and
demonstrated how both the effect and Rayleigh scattering originate from the
atomistic constitution of matter.
Zero-point energy
Main article: Zero-point energy
Einstein's physical intuition led him to note that Planck's
oscillator energies had an incorrect zero point. He modified Planck's
hypothesis by stating that the lowest energy state of an oscillator is equal to
1⁄2hf, to half the energy spacing between levels. This argument, which was made
in 1913 in collaboration with Otto Stern, was based on the thermodynamics of a
diatomic molecule which can split apart into two free atoms.
General relativity and the Equivalence Principle
Main article: History of general relativity
See also: Principle of equivalence, Theory of relativity,
and Einstein field equations
Eddington's photograph of a solar eclipse.
General relativity (GR) is a theory of gravitation that was
developed by Albert Einstein between 1907 and 1915. According to general
relativity, the observed gravitational attraction between masses results from
the warping of space and time by those masses. General relativity has developed
into an essential tool in modern astrophysics. It provides the foundation for
the current understanding of black holes, regions of space where gravitational
attraction is so strong that not even light can escape.
As Albert Einstein later said, the reason for the
development of general relativity was that the preference of inertial motions
within special relativity was unsatisfactory, while a theory which from the
outset prefers no state of motion (even accelerated ones) should appear more
satisfactory.[97] So in 1908 he published an article on acceleration under special
relativity. In that article, he argued that free fall is really inertial
motion, and that for a freefalling observer the rules of special relativity
must apply. This argument is called the Equivalence principle. In the same
article, Einstein also predicted the phenomenon of gravitational time dilation.
In 1911, Einstein published another article expanding on the 1907 article, in
which additional effects such as the deflection of light by massive bodies were
predicted.
Hole argument and Entwurf theory
Main article: Hole argument
While developing general relativity, Einstein became
confused about the gauge invariance in the theory. He formulated an argument
that led him to conclude that a general relativistic field theory is
impossible. He gave up looking for fully generally covariant tensor equations,
and searched for equations that would be invariant under general linear
transformations only.
In June 1913 the Entwurf ("draft") theory was the
result of these investigations. As its name suggests, it was a sketch of a
theory, with the equations of motion supplemented by additional gauge fixing
conditions. Simultaneously less elegant and more difficult than general
relativity, after more than two years of intensive work Einstein abandoned the
theory in November 1915 after realizing that the hole argument was
mistaken.[98]
Cosmology
Main article: Cosmology
In 1917, Einstein applied the General theory of relativity
to model the structure of the universe as a whole. He wanted the universe to be
eternal and unchanging, but this type of universe is not consistent with
relativity. To fix this, Einstein modified the general theory by introducing a
new notion, the cosmological constant. With a positive cosmological constant,
the universe could be an eternal static sphere.[99]
Einstein in his office at the University of Berlin.
Einstein believed a spherical static universe is
philosophically preferred, because it would obey Mach's principle. He had shown
that general relativity incorporates Mach's principle to a certain extent in
frame dragging by gravitomagnetic fields, but he knew that Mach's idea would
not work if space goes on forever. In a closed universe, he believed that
Mach's principle would hold. Mach's principle has generated much controversy
over the years.
Modern quantum theory
Main article: Schrödinger equation
Einstein was displeased with quantum theory and mechanics,
despite its acceptance by other physicists, stating "God doesn't play with
dice." As Einstein passed away at the age of 76 he still would not accept
quantum theory.[100] In 1917, at the height of his work on relativity, 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.[101] This article showed that the statistics of absorption and
emission of light would only be consistent with Planck's distribution law if
the emission of light into a mode with n photons would be enhanced
statistically compared to the emission of light into an empty mode. This paper
was enormously influential in the later development of quantum mechanics,
because it was the first paper to show that the statistics of atomic
transitions had simple laws. Einstein discovered Louis de Broglie's work, and supported
his ideas, which were received skeptically at first. In another major paper
from this era, Einstein gave a wave equation for de Broglie waves, which
Einstein suggested was the Hamilton–Jacobi equation of mechanics. This paper
would inspire Schrödinger's work of 1926.
Bose–Einstein statistics
Main article: Bose–Einstein condensation
In 1924, Einstein received a description of a statistical
model from Indian physicist Satyendra Nath Bose, based on a counting method
that assumed that light could be understood as a gas of indistinguishable
particles. Einstein noted that Bose's statistics applied to some atoms as well
as to the proposed light particles, and submitted his translation of Bose's
paper to the Zeitschrift für Physik. Einstein also published his own articles
describing the model and its implications, among them the Bose–Einstein
condensate phenomenon that some particulates should appear at very low
temperatures.[102] It was not until 1995 that the first such condensate was
produced experimentally by Eric Allin Cornell and Carl Wieman using
ultra-cooling equipment built at the NIST–JILA laboratory at the University of
Colorado at Boulder.[103] Bose–Einstein statistics are now used to describe the
behaviors of any assembly of bosons. Einstein's sketches for this project may
be seen in the Einstein Archive in the library of the Leiden University.[82]
Energy momentum pseudotensor
Main article: Stress-energy-momentum pseudotensor
General relativity includes a dynamical spacetime, so it is
difficult to see how to identify the conserved energy and momentum. Noether's
theorem allows these quantities to be determined from a Lagrangian with
translation invariance, but general covariance makes translation invariance
into something of a gauge symmetry. The energy and momentum derived within
general relativity by Noether's presecriptions do not make a real tensor for
this reason.
Einstein argued that this is true for fundamental reasons,
because the gravitational field could be made to vanish by a choice of coordinates.
He maintained that the non-covariant energy momentum pseudotensor was in fact
the best description of the energy momentum distribution in a gravitational
field. This approach has been echoed by Lev Landau and Evgeny Lifshitz, and
others, and has become standard.
The use of non-covariant objects like pseudotensors was
heavily criticized in 1917 by Erwin Schrödinger and others.
Unified field theory
Main article: Classical unified field theories
Following his research on general relativity, Einstein entered
into a series of attempts to generalize his geometric theory of gravitation to
include electromagnetism as another aspect of a single entity. In 1950, he
described his "unified field theory" in a Scientific American article
entitled "On the Generalized Theory of Gravitation".[104] Although he
continued to be lauded for his work, Einstein became increasingly isolated in
his research, and his efforts were ultimately unsuccessful. In his pursuit of a
unification of the fundamental forces, Einstein ignored some mainstream
developments in physics, most notably the strong and weak nuclear forces, which
were not well understood until many years after his death. Mainstream physics,
in turn, largely ignored Einstein's approaches to unification. Einstein's dream
of unifying other laws of physics with gravity motivates modern quests for a
theory of everything and in particular string theory, where geometrical fields
emerge in a unified quantum-mechanical setting.
Wormholes
Main article: Wormhole
Einstein collaborated with others to produce a model of a
wormhole. His motivation was to model elementary particles with charge as a
solution of gravitational field equations, in line with the program outlined in
the paper "Do Gravitational Fields play an Important Role in the
Constitution of the Elementary Particles?". These solutions cut and pasted
Schwarzschild black holes to make a bridge between two patches.
If one end of a wormhole was positively charged, the other
end would be negatively charged. These properties led Einstein to believe that
pairs of particles and antiparticles could be described in this way.
Einstein–Cartan theory
Main article: Einstein–Cartan theory
In order to incorporate spinning point particles into
general relativity, the affine connection needed to be generalized to include
an antisymmetric part, called the torsion. This modification was made by
Einstein and Cartan in the 1920s.
Equations of motion
Main article: Einstein–Infeld–Hoffmann equations
The theory of general relativity has a fundamental law – the Einstein equations which describe how
space curves, the geodesic equation which describes how particles move may be
derived from the Einstein equations.
Since the equations of general relativity are non-linear, a
lump of energy made out of pure gravitational fields, like a black hole, would
move on a trajectory which is determined by the Einstein equations themselves,
not by a new law. So Einstein proposed that the path of a singular solution,
like a black hole, would be determined to be a geodesic from general relativity
itself.
This was established by Einstein, Infeld, and Hoffmann for
pointlike objects without angular momentum, and by Roy Kerr for spinning
objects.
Other investigations
Main article: Einstein's unsuccessful investigations
Einstein conducted other investigations that were
unsuccessful and abandoned. These pertain to force, superconductivity,
gravitational waves, and other research. Please see the main article for
details.
Collaboration with other scientists
The 1927 Solvay Conference in Brussels, a gathering of the
world's top physicists. Einstein in the center.
In addition to longtime collaborators Leopold Infeld, Nathan
Rosen, Peter Bergmann and others, Einstein also had some one-shot
collaborations with various scientists.
Einstein–de Haas experiment
Main article: Einstein–de Haas effect
Einstein and De Haas demonstrated that magnetization is due
to the motion of electrons, nowadays known to be the spin. In order to show
this, they reversed the magnetization in an iron bar suspended on a torsion
pendulum. They confirmed that this leads the bar to rotate, because the
electron's angular momentum changes as the magnetization changes. This
experiment needed to be sensitive, because the angular momentum associated with
electrons is small, but it definitively established that electron motion of
some kind is responsible for magnetization.
Schrödinger gas model
Einstein suggested to Erwin Schrödinger that he might be
able to reproduce the statistics of a Bose–Einstein gas by considering a box.
Then to each possible quantum motion of a particle in a box associate an
independent harmonic oscillator. Quantizing these oscillators, each level will
have an integer occupation number, which will be the number of particles in it.
This formulation is a form of second quantization, but it
predates modern quantum mechanics. Erwin Schrödinger applied this to derive the
thermodynamic properties of a semiclassical ideal gas. Schrödinger urged
Einstein to add his name as co-author, although Einstein declined the
invitation.[105]
Einstein refrigerator
Main article: Einstein refrigerator
In 1926, Einstein and his former student Leó Szilárd
co-invented (and in 1930, patented) the Einstein refrigerator. This absorption
refrigerator was then revolutionary for having no moving parts and using only
heat as an input.[106] On 11 November 1930, U.S. Patent 1,781,541 was awarded
to Albert Einstein and Leó Szilárd for the refrigerator. Their invention was
not immediately put into commercial production, as the most promising of their
patents were quickly bought up by the Swedish company Electrolux to protect its
refrigeration technology from competition.[107]
Bohr versus Einstein
Main article: Bohr–Einstein debates
Einstein and Niels Bohr, 1925
The Bohr–Einstein debates were a series of public disputes
about quantum mechanics between Albert Einstein and Niels Bohr who were two of
its founders. Their debates are remembered because of their importance to the
philosophy of science.[108][109][110]
Einstein–Podolsky–Rosen paradox
Main article: EPR paradox
In 1935, Einstein returned to the question of quantum
mechanics. He considered how a measurement on one of two entangled particles
would affect the other. He noted, along with his collaborators, that by
performing different measurements on the distant particle, either of position
or momentum, different properties of the entangled partner could be discovered
without disturbing it in any way.
He then used a hypothesis of local realism to conclude that
the other particle had these properties already determined. The principle he
proposed is that if it is possible to determine what the answer to a position
or momentum measurement would be, without in any way disturbing the particle,
then the particle actually has values of position or momentum.
This principle distilled the essence of Einstein's objection
to quantum mechanics. As a physical principle, it was shown to be incorrect
when the Aspect experiment of 1982 confirmed Bell's theorem, which had been
promulgated in 1964.
Political and religious views
Main articles: Albert Einstein's political views and Albert
Einstein's religious views
Albert Einstein, seen here with his wife Elsa Einstein and
Zionist leaders, including future President of Israel Chaim Weizmann, his wife
Dr. Vera Weizmann, Menahem Ussishkin, and Ben-Zion Mossinson on arrival in New
York City in 1921.
Albert Einstein's political view was in favor of
socialism;[111][112] his political views emerged publicly in the middle of the
20th century due to his fame and reputation for genius. Einstein offered to and
was called on to give judgments and opinions on matters often unrelated to
theoretical physics or mathematics.[113]
Einstein's views about religious belief have been collected
from interviews and original writings. These views covered Judaism, theological
determinism, agnosticism, and humanism. He also wrote much about ethical
culture, opting for Spinoza's god over belief in a personal god.[114]
Love of music
Einstein developed an appreciation of music at an early age.
His mother played the piano reasonably well and wanted her son to learn the
violin, not only to instill in him a love of music but also to help him
assimilate German culture. According to conductor Leon Botstein, Einstein is said
to have begun playing when he was five, but did not enjoy it at that age.[115]
When he turned thirteen, however, he discovered the violin
sonatas of Mozart. "Einstein fell in love" with Mozart's music, notes
Botstein, and learned to play music more willingly. According to Einstein, he
taught himself to play by "ever practicing systematically," adding
that "Love is a better teacher than a sense of duty."[115] At age
seventeen, he was heard by a school examiner in Aarau as he played Beethoven's
violin sonatas, the examiner stating afterward that his playing was
"remarkable and revealing of 'great insight.'" What struck the
examiner, writes Botstein, was that Einstein "displayed a deep love of the
music, a quality that was and remains in short supply. Music possessed an
unusual meaning for this student."[115]
Botstein notes that music assumed a pivotal and permanent
role in Einstein's life from that period on. Although the idea of becoming a
professional himself was not on his mind at any time, among those with whom
Einstein played chamber music were a few professionals, and he performed for
private audiences and friends. Chamber music also became a regular part of his
social life while living in Bern, Zurich, and Berlin, where he played with Max
Planck and his son, among others. In 1931, while engaged in research at
California Institute of Technology, he visited the Zoellner family conservatory
in Los Angeles and played some of Beethoven and Mozart's works with members of
the Zoellner Quartet, recently retired from two decades of acclaimed touring
all across the United States; Einstein later presented the family patriarch
with an autographed photograph as a memento.[116][117] Near the end of his
life, when the young Juilliard Quartet visited him in Princeton, he played his
violin with them; although they slowed the tempo to accommodate his lesser
technical abilities, Botstein notes the quartet was "impressed by
Einstein's level of coordination and intonation."[115]
Non-scientific legacy
While travelling, Einstein wrote daily to his wife Elsa and
adopted stepdaughters Margot and Ilse. The letters were included in the papers
bequeathed to The Hebrew University. Margot Einstein permitted the personal
letters to be made available to the public, but requested that it not be done
until twenty years after her death (she died in 1986[118]). Barbara Wolff, of
The Hebrew University's Albert Einstein Archives, told the BBC that there are
about 3,500 pages of private correspondence written between 1912 and 1955.[119]
Einstein bequeathed the royalties from use of his image to
The Hebrew University of Jerusalem. Corbis, successor to The Roger Richman
Agency, licenses the use of his name and associated imagery, as agent for the
university.[120]
In popular culture
Main article: Albert Einstein in popular culture
In the period before World War II, Einstein was so well
known in America that he would be stopped on the street by people wanting him
to explain "that theory". He finally figured out a way to handle the
incessant inquiries. He told his inquirers "Pardon me, sorry! Always I am
mistaken for Professor Einstein."[121]
Einstein has been the subject of or inspiration for many
novels, films, plays, and works of music.[122] He is a favorite model for
depictions of mad scientists and absent-minded professors; his expressive face
and distinctive hairstyle have been widely copied and exaggerated. Time
magazine's Frederic Golden wrote that Einstein was "a cartoonist's dream
come true".[123]
Awards and honors
Main article: Einstein's awards and honors
Einstein received numerous awards and honors, including the
Nobel Prize in Physics.
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