Albert Einstein
Albert Einstein (
/ /;
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 large-scale structure of the
universe.
[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 an
American citizen in 1940.
[7] On the eve of World War II, he endorsed a
letter to President Franklin D. Roosevelt
alerting him to the potential development of "extremely powerful bombs
of a new type" and recommending that the U.S. begin similar research.
This eventually led to what would become the
Manhattan Project. Einstein supported 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]
Biography
Early life and education
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 (now known as the Albert Einstein
Gymnasium) where he received advanced primary and secondary school
education until he left Germany seven years later.
[11]
Contrary to popular suggestions that he had struggled with early speech
difficulties, the Albert Einstein Archives indicate 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. 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 1895, at the age of sixteen, Einstein sat the entrance examinations for the
Swiss Federal Polytechnic in
Zurich
(later the Eidgenössische Technische Hochschule ETH). He failed to
reach the required standard in the general part of the examination,
[22] but obtained exceptional grades in physics and mathematics.
[23] 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. (Albert's sister
Maja later married Wintelers' son Paul.)
[24] In January 1896, with his father's approval, he renounced his
citizenship in the German Kingdom of Württemberg to avoid
military service.
[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 Zurich Polytechnic. 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
With the discovery and publication in 1987 of an early correspondence
between Einstein and Marić it became known that they had a daughter
they called
"Lieserl" in their letters, born in early 1902 in
Novi Sad
where Marić was staying with her parents. Marić returned to Switzerland
without the child, whose real name and fate are unknown. Einstein
probably never saw his daughter, and the contents of a letter he 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. He acquired Swiss citizenship in February
1901,
[37] but was not
conscripted for medical reasons. With the help of
Marcel Grossmann's father Einstein secured a job in Bern at the
Federal Office for Intellectual Property, the patent office,
[38] as an assistant
examiner.
[39] 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".
[40]
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.
[41]
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 Capillaritätserscheinungen" ("Conclusions from the Capillarity Phenomena") was published in the prestigious
Annalen der Physik.
[42][43] 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."
[44][45] This paper included Einstein's initial estimates of
Avogadro constant as
2.2×1023 based on diffusion coefficients and viscosities of sugar solutions in water.
[46] 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[47] at the University of Zurich. He became a full professor at
Charles-Ferdinand University
in Prague in 1911. Also in 1911, corrections of algebraic errors in his
thesis brought Einstein's Avogadro constant estimate to
6.6×1023. In 1914, he returned to Germany after being appointed director of the
Kaiser Wilhelm Institute for Physics (1914–1932)
[48] 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).
[49][50]
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".
[51]
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.
[52]
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.
[53][54] Eddington's selection from the data seems valid and his team indeed made astronomical measurements verifying the theory.
[55]
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 in New York, 1921, his first visit to the United States
Einstein visited New York City for the first time on 2 April 1921, where he received an official welcome by Mayor
John Francis Hylan, 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.
[56]
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:
[57]: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."
[57]: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.[58]: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, Adolf Hitler.
[59][60] 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.
[58] A few years later, the Nazis sold his boat and turned his cottage into an Aryan youth camp.
[61]
In early April 1933, he learned that the new German government had
passed laws barring Jews from holding any official positions, including
teaching at universities.
[58] 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."
[58] Einstein also learned that his name was on a list of assassination targets, with a "$5,000 bounty on his head."
[58] One German magazine included him in a list of enemies of the German regime with the phrase, "not yet hanged".
[58]
He resided in Belgium for some months, before temporarily living in England.
[62][63] 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."
[58]
Portrait taken in 1935 in Princeton
In October 1933 he returned to the U.S. and took up a position at the
Institute for Advanced Study (in
Princeton, New Jersey), that required his presence for six months each year.
[64][65] 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.
[66][67]
His affiliation with the Institute for Advanced Study would last until his death in 1955.
[68] 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 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."
[58]
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.
[69] 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."
[57]:630[70] On July 12, 1939, a few months before the beginning of World War II in Europe, Szilárd and Wigner visited Einstein
[71] and they explained the possibility of atomic bombs, to which
pacifist Einstein replied:
Daran habe ich gar nicht gedacht (I had not thought of that).
[72] 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".
[73] In addition to the letter, Einstein used his connections with the
Belgian Royal Family[74] and the Belgian queen mother
[69] to get access with a personal envoy to the White House's Oval Office.
[69]
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." By signing the letter to Roosevelt he went against his pacifist
principles.
[75] 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 ..."
[76]
US citizenship
Einstein became an American citizen in 1940. Not long after settling
into his career at the Institute for Advanced Study (in Princeton, New
Jersey), 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.[58]:432
As a member of the
National Association for the Advancement of Colored People (NAACP) in 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".
[77]
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".
[78]
During the final stage of his life, Einstein transitioned to a vegetarian lifestyle,
[79]
arguing that "the vegetarian manner of living by its purely physical
effect on the human temperament would most beneficially influence the
lot of mankind".
[80]
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.
[81] 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".
[57]: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.[57]:522[81][82]
Death
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.
[83]
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.
[84]
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."
[85] 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.
[86] Einstein's remains were
cremated and his ashes were scattered at an undisclosed location.
[87][88]
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."
[89]
Scientific career
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.
[90]
1905 – Annus Mirabilis papers
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).[91] This idea was pivotal to the early development of quantum theory.[92] |
| 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.[93] Discredited the concept of a "luminiferous ether."[94] |
| 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
Albert Einstein's first paper
[95] submitted in 1900 to
Annalen der Physik was on
capillary attraction.
It was published in 1901 with the title "Folgerungen aus den
Capillaritätserscheinungen," 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.
[95]
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
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.
[96]
In his paper on
mass–energy equivalence Einstein produced
E =
mc2 from his special relativity equations.
[97]
Einstein's 1905 work on relativity remained controversial for many
years, but was accepted by leading physicists, starting with
Max Planck.
[98][99]
Photons and energy quanta
Main articles:
Photon and
Quantum
In a 1905 paper,
[100] 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.
[101]
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.
[102]
Adiabatic principle and action-angle variables
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.
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.
[103] 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.
Einstein saw this wave-particle duality in radiation as concrete
evidence for his conviction that physics needed a new, unified
foundation.
Theory of 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
Rayleigh scattering, which is what happens when the fluctuation size is much smaller than the wavelength, and which explains why the sky is blue.
[104]
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
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
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.
[105] Consequently, 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.
[106]
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.
[107]
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
Einstein was displeased with quantum theory and mechanics, despite
its acceptance by other physicists, stating "God doesn't play with
dice." As Einstein died at the age of 76 he still would not accept
quantum theory.
[108] 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.
[109]
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
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.
[110] 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.
[111] 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.
[90]
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
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".
[112]
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
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
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
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
Einstein conducted other investigations that were unsuccessful and abandoned. These pertain to
force,
superconductivity,
gravitational waves, and other research.
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
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.
[113]
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.
[114] 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.
[115]
Bohr versus Einstein
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.
[116][117][118]
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
Einstein's political view was in favor of
socialism and critical of capitalism, which he detailed in his essays such as "
Why Socialism?".
[119][120]
Einstein offered to and was called on to give judgments and opinions on
matters often unrelated to theoretical physics or mathematics.
[121]
Einstein's views about religious belief have been collected from interviews and original writings.
He called himself an
agnostic, while disassociating himself from the label
atheist.
[122] He said he believed in the
"pantheistic" God of
Baruch Spinoza, but not in a
personal god, a belief he criticized.
[123][124]
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.
[125]
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 without "ever practicing systematically", adding that
"Love is a better teacher than a sense of duty."
[125] 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."
[125]
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.
[126][127] 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."
[125]
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
[128]). 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.
[129]
Corbis, successor to
The Roger Richman Agency, licenses the use of his name and associated imagery, as agent for the university.
[130]
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."
[131][dead link]
Einstein has been the subject of or inspiration for many novels, films, plays, and works of music.
[132] 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".
[133]
Awards and honors
Einstein received numerous awards and honors, including the
Nobel Prize in Physics.
