Albert Einstein (1879-1955) was a German-American physi­cist who significantly changed the physical and philosophical view of time and space. The special and general theories of relativity are among his most seminal works. He also provided fundamen­tal contributions to early quantum theory. For his quantum theoretical interpretation of the photo­electric effect, he was awarded the Nobel Prize in Physics in 1921. His most lasting contribution, however, is his theory of relativity, which changed our conception of time forever. As a pacifist, Einstein was actively involved with movements for peace, tolerance, and international under­standing all his life.

Early Developments

Albert Einstein was born in Ulm, Germany, on March 14, 1879. His father was a moderately successful salesman in the electrical trade. The South German roots of Einstein’s Jewish family reached back for centuries. Since 1880, the family had lived in Munich. According to Einstein, the experience that aroused his scientific curiosity occurred at the age of 6, when he was wondering about the invisible force aligning a compass nee­dle. The stories often told about Einstein’s under­achievement in school are merely a myth. He earned average marks in most subjects but was excellent in the natural sciences. However, he showed a dismissive attitude toward dull author­ity from his early days on. Beyond school lec­tures, he was able to figure out the infinitesimal calculus on his own.

While his family moved to Milan, Italy, in 1894 for economic reasons, young Albert stayed back in Munich alone to finish grammar school. Ahead of time and without formal graduation, Einstein left school on his own decision when he became at odds with the school’s authorities. “Your sheer presence corrupts the class’s respect for me,” his teacher remarked. On the basis of his attitude as a freethinker, he also resigned from the Jewish reli­gious community. In 1895, he went to the Kantonschule Aarau (Switzerland) where he passed the Matura (the Swiss grammar school diploma), qualifying himself for the Confederate Polytechnical Academy Zurich (today’s ETH). In 1900, he achieved the teacher’s diploma for math and phys­ics. He applied for an assistantship at the Zurich Academy, but his application was rejected, so he eked out a living as a substitute teacher at first. In

• Einstein submitted his dissertation on the theory of thermal equilibrium and the second law of thermodynamics to the University of Zurich; the dissertation was declined.

During his years of study, Einstein fell in love with his Serbian fellow student Mileva Maric. In

• she gave birth to their illegitimate daughter, Lieserl, at Mileva’s parents’ home in Serbia. The subsequent fate of the child is uncertain; it is stated in various sources that she was given up for adop­tion at Einstein’s insistence in order to preserve moral standards; some sources state that she suf­fered from trisomy 21 (Down syndrome) and died at the age of almost 2 years.

Annus Mirabilis: An Explosion of Creativity

In 1902, after a recommendation from his friend Marcel Grossmann, Einstein got employment as “third class expert” at the Swiss patent office in Bern. Half a year later, on January 6, 1903, he married Mileva. Their sons Hans Albert (1904-1973) and Eduard (1910-1965) were born from this marriage.

Along with his time-consuming but nevertheless regular work, Einstein concentrated on theoretical physics and prepared for his graduation at the University of Zurich. With his friends Maurice Solovine and Conrad Habich, he founded a sort of philosophical discussion circle, the Akademie Olympia. After leaving work, they would study and discuss the works of Immanuel Kant, Ludwig Boltzmann, Henri Poincare, or Ernst Mach. Einstein’s wife Mileva was among the intellectual discussion partners.

Einstein’s ambitions, advanced beyond the aca­demic establishment, first culminated in a scientific “eruption of genius” in 1905, often referred to as his annus mirabilis, or miraculous year. Within a few months, the 26-year-old Einstein published four papers of historical relevance in the prestigious journal Annalen der Physik. In mid-March, he explained the photoelectric effect and laid one of the cornerstones of quantum mechanics by ascrib­ing a corpuscular nature to light; in 1921 Einstein would win the Nobel Prize for this work. Two weeks thereafter, he resubmitted a dissertation titled A New Way to Determine Molecular Dimensions. This work contained essential hints on the atomic nature of matter. With this publication, he succeeded in referring the Brownian motion in fluids to the thermal motion of molecules. He thus established the kinetic interpretation of heat.

Foremost, however, the name of Einstein is associated with the idea of relativity. The first and most constitutive work on this topic was the “Electrodynamics of Moving Bodies” paper, which he submitted on June 30, 1905. The paper is par­ticularly remarkable in that it does not contain any academic references, unthinkable for a scientific paper today. Finally, in September, he provided a sort of extension to the electrodynamics paper cul­minating in the equation E = mc², the most famous physical formula in history. Both works set up the special theory of relativity, Einstein’s revolutionary new theory of time and space.

Scientific Reputation

In January 1906, Einstein received his Ph.D. Shortly thereafter he was advanced to a “second-class expert” as a patent office employee. Until 1908, he made his living from passing expert opinions on patents. Later on, his weighty contributions would pave the way for a scientific career. Meanwhile, qualified as a professor and now possessing a cer­tain reputation within the scientific community, Einstein delivered lectures beginning in 1908 and was appointed to an associate professorship at the University of Zurich in October 1909. During the following 5 years, he changed his academic affilia­tion several times. After working in Prague for a short period, he returned to Zurich. Finally, in 1914 he was enticed by his elder colleague, Max Planck, into going to Berlin, and he worked there without teaching commitments. Einstein’s depar­ture from Zurich was impelled by more than scien­tific reasons; his marriage to Mileva was breaking up, and in Berlin, he had begun an extramarital relationship with his second cousin Elsa Löwenthal in 1912.

After the outbreak of World War I on August 1, 1914, Einstein began to care about political con­cerns more intensely. He joined the group Neues Vaterland (New Fatherland), which was based on a decidedly pacifistic attitude. Despite lucrative offers by other German and international universi­ties, he would stay in Berlin until his emigration to the United States in 1933.

Quanta and Relativity

Einstein’s 1905 works provide not only the general basis of his theoretical framework but also, in par­ticular, a radical new view of space and time. Until his death, Einstein would criticize the new quan­tum theory. “God doesn’t play dice”: With these words, he summarizes his pessimistic attitude toward the probabilistic “Copenhagen interpreta­tion” of quantum theory developed by Nils Bohr and Werner Heisenberg in 1926, even though in 1905, Einstein had provided a fundamental contribution to the quantum concept. “On a Heur­istic Aspect Concerning the Creation and Trans­formation of Light” is the bulky title of the very paper postulating the particle character of light. In a letter to his friend Konrad Habicht, Einstein announced his own work to be “revolutionary.”

The quantum concept had been introduced 5 years earlier by the physicist Max Planck, also in the context of electromagnetic radiation. However, Planck was referring only to the radiation energy being emitted and absorbed in discrete packets, denoted as quanta.

Around the mid-19th century, the French phys­icist Alexandre Edmond Becquerel discovered the effect that an ultraviolet-irradiated, negatively charged metal plate emitted negative charge carri­ers in a characteristic manner. The energies of the individual electrons emitted do not depend on the radiation’s intensity, but only on its wavelength. Moreover, the effect sets only in as soon as the radiation wavelength drops below a certain limit. These observations were not compatible with the conventional and established wave picture of elec­tromagnetic radiation.

Einstein took on the challenge and postulated that both light and electromagnetic radiation consist of tiny portions of “light” particles called photons. However, the wave properties of light had been proved experimentally in Newton’s era. In this respect, Einstein introduced the duality of light, which is still considered valid today: Though excluding each other, both natures obviously coex­ist in electromagnetic radiation. Many years after Einstein’s work, the concept of duality was applied to any kind of matter when two beams of elec­trons were observed to interfere. This is considered as conclusive proof of waves acting.

Einstein would apply himself to quantum theory all his life. After the publication of his light-quantum hypothesis, however, his investi­gations on the nature of space and time came to the forefront.

Around 1900, the classical disciplines of physics had been completed in their main features. What one knows as classical mechanics today was provided as a complete theory by Isaac Newton (1643-1727) more than 300 years ago. Meanwhile, it turned out to be a valid border case of Einstein’s theory of rela­tivity. James Clerk Maxwell, on the other hand, united the broad domains of electric and magnetic effects within a single theory of electromagnetism, based on four fundamental equations that provide the undisputed classical frame to this day.

After the turn of the 20th century, insurmount­able problems arose at the borderland between mechanics and electrodynamics. Elegant attempts at solutions were suggested by Hendrik Antoon Lorentz and Henri Poincare, but these turned out to be mathematical gimmicks rather than plausible physical explanations.

Again, it was Albert Einstein who brought about a rebound in 1905. To conserve the univer­sal validity of the principle of relativity (PR, the equivalence of any uniformly moving frame of reference), and without further ado, he ascribed physical reality upon the Lorentz transformations (Lorentz’s mathematical gimmick). At the same time, he declared dispensable the concept of the ether that had been postulated centuries earlier; this substance was believed to pervade all space and bodies though it had never been detected. Light and electromagnetic waves should propagate through this ether like sound waves through the air. Last but not least, ether was to provide an absolute frame of reference in Newtonian space.

Together with the universal validity of the PR, the new ideas called into question the classical Newtonian concepts of space and time. They indi­vidually lose their rigid, absolute characters and turn from passive subjects to active objects depend­ing on the physical circumstances. Simultaneity becomes relative and depends on the observer’s state of motion: Two events, appearing simultaneous to a (say) resting observer A, happen successively to a moving observer B. Following the theory of relativ­ity, clocks run differently for two observers moving with respect to each other; likewise, spatial length measures are different. “From now on space and time apart shall reduce to shadows and only a kind of a union shall keep autonomy,” the German mathematician Hermann Minkowski stated. This bizarre issue is frequently illustrated using the twins paradox. An astronaut says good-bye to his twin brother prior to his interstellar flight. In his space­craft, he would travel through space at 99.5% the speed of light. He returns 10 years later and is greeted by his brother, whereupon both brothers realize they have aged unequally. While the earthling is older by 10 years, there passed only 1 year for the space traveler!

Furthermore, Einstein showed that the new theory implies that the mass and energy content of a body are equivalent. This is expressed in his most famous equation, E = mc². The relativistic effects of length contraction and time dilation are proved by many experiments today.

Starting in 1907, Einstein tried to generalize the PR for accelerated frames of reference. The PR in the special theory of relativity says it is not possible for an observer to distinguish whether he is placed in a resting or a uniformly moving frame of refer­ence. As a generalization, Einstein introduced the principle of equivalence, the “most felicitous idea in [his] life.” An observer in a closed room, such as an elevator or a windowless spaceship, is strictly unable to tell whether he is accelerating in free space or resting in a gravitational field (like on the surface of the earth).

From this principle, Einstein finally over­throws the concept of time and space even more radically than before. Gravitation turns out to be an intrinsic curvature of spacetime. This curva­ture is in principle comparable to a spherical surface but, beyond any human imagination, in three dimensions instead of two. The curvature of spacetime is caused by the presence of mass- afflicted matter. Vice versa, the curvature causes a body to accelerate. A direct and verifiable implication of the general theory of relativity (GTR) is the deflection of a light beam passing near a massive body (like a star). Einstein’s arti­cle “The Foundations of the General Theory of Relativity” was published in the Annalen der Physik on March 20, 1916.

Three years later, following the war’s end, a British expedition led by Sir Arthur Eddington left for West Africa to observe and measure the exact positions of stars appearing close to the obscured sun during a total eclipse. Einstein remarked that his theory would be incorrect if it were not able to correctly predict the deflection of light (and thus the shifted positions of the observed stars). It turned out that the deflection of the starlight pass­ing the gravitational field of the sun was in close agreement with the predictions of the GTR. This verification of Einstein’s theory was the onset of his international fame and myth. One week after the confirmation of his theory, Einstein married his cousin (the daughter of his father’s cousin), Elsa Löwenthal. In December 1919, he published a popular science book titled The Special and General Theory of Relativity, Generally Understandable.

During the following years, many physicists and mathematicians attempted to find solutions for the GTR field equations. Particular sign­ificance in this context was achieved in the works by Georges Edouard Lemaître (1894-1966) and Alexander Friedmann (1888-1925). Their solutions for homogenous and isotropic spaces constitute the foundation of the cosmological standard model to this day.

Berlin and Princeton

Einstein left Switzerland the year before he sub­mitted his GTR. In Berlin, he was accorded respect by the Prussian Academy of Sciences and given a professorship. He would never re-enter Germany after his emigration in 1933, and he expressed disgust with the “brutality and cowardice” of the Nazi Germans. He states about Berlin: “There’s no city ever, I’m more associated to by human and scientific connections.”

Though he was exempted from lecture commit­ments in Berlin, Einstein gave numerous public talks. Sometimes there was such an enormous crowd of attendees that only the largest audito­rium in the university could accommodate it. Among his various leading positions within the academic community, perhaps the most noteworthy was his being the chair of the German Physical Society, a position he held as the successor of Max Planck from 1916 to 1918.

In the year of his move, Einstein was sensitized to politics through the outbreak of the Great War. Contrary to the initial national enthusiasm for the war, he pleaded in public for international under­standing and called for an immediate end to the war. He campaigned for democracy and pacifism and engaged himself for the Bund Neues Vaterland (New Fatherland Alliance), later renamed the League for Human Rights. After the war, he embraced the anti-monarchic German November Revolution and the ensuing Weimar Republic.

In a famous statement that offended many, Einstein expressed his contempt for war and soldierhood:

If someone feels pleasure marching lock-step to music in rank and file, he has already earned my contempt. He has been given a big brain by mis­take, since for him a spinal cord would be quite enough. This disgrace to civilization should be done away with at once. Heroism on command, senseless violence and deplorable “fatherland” blubbering, how passionately I hate it, how mean and ignoble war seems to me. I would rather be torn to shreds than take part in so base an action! It is my convic­tion that killing under the cloak of war is nothing but an act of murder.

Being more in the public eye and as a commit­ted advocate of humanistic values, Einstein more and more became a focal point of anti-Semitic hostilities, which occasionally arose even from his circle of colleagues. In particular, Philipp Lenard and Johannes Stark excelled with subjec­tive debates against “Jewish physics” and declared the theories of relativity “degenerations of com­mon sense.” As anti-Semitism flourished in Germany and elsewhere in Europe, Einstein reflected on his Jewish roots and joined the Zionist movement. Together with its leader Chaim Weizmann, he traveled across the United States for 2 months. In a show of solidarity in the face of hostility and persecution, he rejoined the Jewish religious community, which he had quit in his earlier days. In 1921, Albert Einstein was awarded the Nobel Prize for his light quantum hypothesis (not for his theories of relativity).

Einstein undertook three more extensive, scien­tifically motivated journeys to the United States. During his last one, starting in December 1932, Adolf Hitler came into power; immediately Einstein declared that he would not return to Germany. After a trip to Europe, he moved to his adopted city of Princeton in the United States, where he would work at the Institute for Advanced Studies until the end of his life.

In 1939, alerted by the outbreak of the war in Europe, Einstein wrote a letter to the president of the United States, Franklin D. Roosevelt, and advised him to develop a nuclear bomb, in antici­pation of the Germans’ attempt to do so. Thereupon, Roosevelt initiated the Manhattan Project, culminating in the dropping of two nuclear bombs on the Japanese cities of Hiroshima (August 6, 1945) and Nagasaki (August 9, 1945).

After the end of World War II, shocked by these terrible incidents, Einstein intensively campaigned for armament control and suggested that a world government be established. In November 1952, the Israeli President Chaim Weizmann died. Einstein was immediately offered the presidency, but he declined: “Equations are more significant to me. Policy is for the present but equations are for eter­nity,” he was said to have explained. As one of his last contributions for a peaceful world, he signed a manifesto, written by the British philosopher and mathematician Bertrand Russell, calling for all nations to abstain from nuclear weapons.

On April 15, 1955, Albert Einstein was taken to Princeton Hospital because of internal bleeding. He died on April 18 at the age of 76. In keeping with his wishes, his body was burned to ashes on the same day, but not before a pathologist pur­loined Einstein’s brain during the autopsy.

“God Doesn’t Play Dice”:
Criticism of Quantum Mechanics

In 1926, the young German physicist Werner Heisenberg had published the so-called uncertainty principle. It is the preliminary climax in the evolu­tion of quantum theory, initiated by Max Planck (1900) and Einstein (1905). With the uncertainty principle, Heisenberg expressed the innermost character of quantum mechanics: the turning away from classical strict determinism and the wave-particle duality, which Einstein prepared the ground for with his light-quantum hypothesis. A year later, Heisenberg and his Danish mentor Niels Bohr developed a probabilistic interpretation of the theory (the Copenhagen interpretation), accepted by most physicists today.

Einstein disliked this idea from the beginning. During the Fifth Solvay Meeting, he led a legendary series of lively disputations with his friends and col­leagues Niels Bohr and Max Born, but both of them emerged victorious in each case. Some of Einstein’s objections to quantum theory Bohr could parry using Einstein’s general theory of relativity. But until his death, Einstein was unwilling to accept the dual character of matter, the renunciation of determinism, or the introduction of randomness into physics.

Search for a Unified Theory

The pursuit of structural unity in physical theories arose with the birth of theoretical physics itself. In his historic work Philosophic Naturalis Principia Mathematica (1687), Isaac Newton had devel­oped a single unified theory to explain the fall of an apple and the journey of a planet around the sun. Another great success of theoretical physics was the unification of electric and magnetic phe­nomena, developed around 1864 by the Scottish scientist James Clerk Maxwell.

Of the four fundamental forces that physics now recognizes, only two were known in Einstein’s time: the electromagnetic and, exhaustively inves­tigated by Einstein, the gravitational force. After the publication and experimental confirmation of his GTR, Einstein for the first time addressed the problem of describing both within a common scheme. He provided a first paper in 1922 and a second one in 1929, accompanied by high expecta­tions within the scientific community.

Like his lifelong but unsuccessful criticisms of quantum mechanics, Einstein’s enterprise was to lead to a scientific dilemma that Carl-Friedrich von Weizsacker called the “tragedy of his late years.” Neither Einstein nor any other physicist ever suc­ceeded in unifying gravitation with any other funda­mental force. Three of the four forces known today (including the weak and strong interactions) are so far unified in the so-called grand unified theory. To this day, gravitation, with its completely different mathematical structure, resists any such attempt at being unified with the three other forces.

Nature of Time in Relativity

It is by far the most significant effect of relativity that space and time lose their absolute and inde­pendent character. Absolute means that time intervals do not depend on the observer’s state of motion and the presence of gravitational fields. In particular, the term simultaneity loses its meaning beyond the context of a certain frame of reference (i.e., a certain observer). Because there is nothing like one frame of reference in the universe being superior to any other, there is no absolute, univer­sally valid measure of time, but only some observ­er’s inherent time or proper time. The loss of independence means that time cannot be consid­ered as a physical quantity independent of space. Rather, time and space generate a four-dimen­sional coordinate system called spacetime, provid­ing the stage for any physical phenomena.

The twins paradox in principle demonstrates the possibility of time travel to the future in terms of special relativity. However, this would require technical conditions (far out of reach today) for traveling at almost the speed of light over a sig­nificant period of time. Furthermore, it would not be possible to travel back to the present, which would require superluminal velocities.

Finally, going back to the general theory of rela­tivity, one insight is that time has (at least) one uni­versal border. Within the framework of the big bang cosmological theory, time begins with the big bang event, which is held to have occurred about 13.7 billion years ago. There is no moment “prior” to the big bang, just as, according to Stephen Hawking, there is no point “north of the north pole.” Today, cosmologists maintain that there will be no end to time in the form of a big crunch, as the “reversal big bang” is frequently called. In fact, there are many hints pointing to an eternal, even accelerated, expan­sion of the universe.

Helmut Hetznecker

See also Cosmogony; Einstein and Newton; Galilei, Galileo; Hawking, Stephen; Light, Speed of; Newton, Isaac; Planck Time; Quantum Mechanics; Relativity, General Theory of; Relativity, Special Theory of; Spacetime, Curvature of; Spacetime Continuum Time, Relativity of

Further Readings

Davies, P. (1995). About time: Einstein’s unfinished revolution. New York: Touchstone.

Einstein, A. (1961). The special and general theory (R. W. Lawson, Trans.). New York: Three Rivers Press.

Folsing, A. (1998). Albert Einstein: A biography (E. Osers, Trans.). New York: Penguin.

Greene, B. (2004). The fabric of the cosmos: Space, time, and the texture of reality. New York: Vintage Books.

Hoffman, B., & Dukas, H. (Eds.). (1981). Albert Einstein: The human side. Princeton, NJ: Princeton University Press.

Isaacson, W. (2007). Einstein: His life and universe. New York: Simon & Schuster.

Kaku, M. (2004). Einstein’s cosmos: How Albert Einstein’s vision transformed our understanding of space and time. New York: Norton.

Kaku, M., & Thompson, J. (1995). Beyond Einstein: The cosmic quest for the theory of the universe. New York: Anchor Books.

Neffe, J. (2007). Einstein: A biography (S. Frisch, Trans.). New York: Farrar, Straus, and Giroux.

Richardson, S. (Ed.). (2008, March). The unknown Einstein [Special issue]. Discover.