(1879-1955) German/American Theoretical Physicist, Relativist, Quantum Theorist, Philosopher of Science
Albert Einstein’s extraordinary life in physics was a quest for nothing less than to “know how God created this world,” to uncover the fundamental, unifying laws of the universe. In this he succeeded more than any scientist before him, with the possible exception of sir isaac newton. His theories of special and general relativity grew out of the paradoxes facing physicists as the 20th century began: the cracks in the seemingly solid walls of the house of classical mechanics that Newton and his successors had built. Revolutionary ideas about the nature of space, time, and matter were in the air that turn-of-the-century physicists breathed, but only a daring leap of intuition and imagination would unify and transform them into a new vision of physical reality. This astounding insight into the workings of nature was the essence of Einstein’s genius. Early in his career, it led him to discoveries that confirmed the existence of atoms, launched quantum mechanics, demolished classical Newtonian notions of absolute space and time, redefined gravitation, and revolutionized cosmology. In Einstein’s later years, however, the same sense of inner rightness that guided him to these discoveries led him to reject quantum mechanics and to search futilely for a theory that would unify electromagnetic and gravitational forces.
Little in Einstein’s early years presaged his future greatness. Born in Ulm, in Wurttemberg, Germany, on March 14, 1879, into a Jewish family, he moved to Munich six weeks after his birth, when his father’s business ventures failed. Late in speaking, he talked slowly, pausing to consider what he would say. When he was four or five, his father showed him a magnetic compass, which convinced him that there was “something behind things, something deeply hidden.” As a boy, he sang hymns praising God, which he had composed himself, on his way to school. But at 12, reading a book on Euclidean plane geometry, his religious impulse took the form it would retain all his life: a sense of profound wonder before the natural universe. Young Albert did not extend this sense of awe to secular authorities, however. He was a rebellious, disruptive student at his Munich gymnasium, where successful students learned by memorizing and doing what they were told. Albert preferred to study at home and, at 15, quit school and rejoined his family, who had moved once again, in Italy. The following year he failed the entrance examination to the Swiss Federal Polytechnic in Zurich, Switzerland, and was obliged to beef up his math knowledge at a preparatory school in Arrau, Switzerland.
It was in Arrau, walking along the river, that Albert began the relentless questioning of nature’s laws that he would pursue all his life. He asked himself an almost childlike question, What would he see if he were to chase a beam of light at the velocity of light? He knew that Newtonian physics would say that he could catch up with the beam of light and would then observe it as a spatially oscillatory electromagnetic field at rest. But experience told him that no such thing could ever be observed, an assertion verified by the great james clerk maxwell, whose famous equations for a unified electromagnetic field indicated that velocity is inherent in light. Albert’s gedanken experiment (thought experiment) led him to a fork in the road: he must give up either Maxwell’s equations or Newton’s laws of motion. For the moment, he would live with this paradox.
The next year, he passed his entrance exams and began his studies at the polytechnic. When his physics professor, Heinrich Weber, an old-fashioned classical physicist, ignored the giants of electromagnetic field theory, Maxwell and michael faraday, Albert began skipping Weber’s classes and reading physics on his own. When he was not hanging out in coffee houses, playing his violin, or spending time with one of the few women physics students, Mileva Maric, he conducted experiments in the polytechnic’s laboratories, one of which ended in an explosion that almost cost him a hand. He managed to pass his exams and graduate in 1900 with unexceptional grades.
Having failed to impress his professors, who might have eased his way into the university system, he floundered at first, taking low-paying teaching jobs. When he was offered a well-paid post as a patent clerk in the Swiss Patent Office in Bern, in 1901, he grabbed it and became a Swiss citizen. By 1903, he was in a position to marry Mileva, who had, meanwhile, given birth to an illegitimate daughter, Lieserl, and entrusted her to the care of relatives in Serbia. Albert never knew his daughter, whose fate has remained a mystery. Over the next few years, Mileva and Albert would have two sons, Hans Albert and Edward. Albert would work as a technical expert at the patent office until 1909, years he would later remember as “my best time of all.” In his friend and coworker Michael Besso he had an ideal sounding board for the physics theories he dreamed up in his spare time. It was Besso who steered him to the work of ernst mach, one of the few leading scientists to question the Newtonian paradigm that underlay the belief in an ether, the mysterious fluid pervading all of space, in which electromagnetic waves were said to propagate. To Mach, the ether was a “metaphysical obscurity.” Observation, he insisted, was the only way for scientists to know. As a corollary, he held that space was no abstract thing, but an expression of interrelationships among events: “All masses and all velocities, and consequently all forces, are relative.” Although Mach would later deny his role as the progenitor of relativity, his influence on the young Einstein was profound. By 1905, Albert’s thoughts began to crystallize. That year he obtained a doctoral degree from the University of Zurich and published three papers—on Brownian motion, the photoelectric effect, and special relativity. Each unraveled a mystery that had stumped the best scientific minds.
Albert Einstein’s theories of special and general relativity demolished classical Newtonian notions of absolute space and time, redefined gravitation, and revolutionized cosmology.
Einstein’s first paper had a major impact on the running debate between physicists of the atomist and energeticist schools. In 1827, Robert Brown had observed through a microscope the random motion of small particles in a fluid: the motion of the particles increases when the temperature increases but decreases if larger particles are used. Since then physicists had been trying to explain the phenomenon. To the energeticists, who rejected the concept of atoms and thought of all matter as continuous, Brownian motion, with its discrete bumps, was disturbing. Einstein only increased their consternation when he explained the phenomenon as the effect of large numbers of molecules bombarding the particles. His assumptions allowed him to predict the movement and size of the particles, values that were later verified experimentally by the French physicist jean-bap-tiste perrin. Experiments based on this work were used to obtain an accurate value of the Avo-gadro number, which is the number of atoms in one mole of a substance, and the first accurate values of atomic size. Einstein had struck a decisive blow in favor of the theory that matter is composed of atoms.
In his second classic paper, Einstein addressed himself to a puzzle surrounding the so-called photoelectric effect, the ejection of electrons from the surface of a substance by radiation. In the classical theory of electromag-netism, light was viewed as a wave. Maxwell’s equations for the electromagnetic field predicted that when light waves fall on a metal surface, the energy of the electrons that are ejected depends on the intensity as well as the frequency of the light. But the experiment that produced the photoelectric effect showed that the energy of the electrons ejected is quantized according to the frequency and not the intensity of the light.
In 1900 max ernest ludwig planck, while studying blackbodies (objects that do not reflect surface light and are thus perfect emitters and absorbers of radiation at all frequencies), had discovered a formula that related the energy of the radiation to its frequency. This was his famous blackbody radiation law, which predicted that E = hv, where E is the energy, h is a number known as Planck’s constant, and v is the frequency of radiation. He was led to the realization that a sound derivation of his law could only be based on the postulate that the energy of radiation is emitted and absorbed, not continuously, but in discrete packets, which he called quanta. Planck postulated that the material oscillators in the walls of the blackbody had units of energy that were quantized in terms of the frequency of light, but he did not quantize the light itself.
It was Einstein who took that step, generalizing from Planck’s quantum postulate. Suppose, he said, the light itself is quantized according to its frequency. Light then would consist of particles, which he called light quanta or photons. He used Planck’s constant as a way to determine the energy of these light particles, suggesting that the kinetic energy of each electron is equal to the difference in the incident energy and the light energy needed to overcome the threshold of emission. The equation expressing this is known as Einstein’s photoelectric law. This work would earn him the Nobel Prize in physics 16 years later, in 1921. It would also mark the beginning of his long friendship with Planck, who disliked the quantum idea he himself had fathered as much as Einstein had. For years Einstein would struggle in vain to understand how the classical Maxwell’s equations could consistently produce his light quanta. The key to this enigma would be found 30 years later by richard phillips feyn-man, julian seymour schwinger, and others, in the form of quantum electrodynamics, a theory that Einstein never accepted.
Although solving the enigma of Brownian motion and discovering that light has a particle property were no small achievements, they paled next to the sweeping discoveries enunciated in Einstein’s third 1905 paper, “On the Electrodynamics of Moving Bodies,” which unveiled the theory of special relativity. Nineteenth-century physicists had amassed a growing body of knowledge indicating that the behavior of light and other electromagnetic radiation regularly contradicts classical Newtonian physics. Since 1881, they had been living with the results of the Michelson-Morley experiment, which conclusively demonstrated that the velocity of light is constant and does not vary with the motion of either the source or the observer. Designed to measure the effect of the ether, the mysterious medium pervading the universe, in which light waves were thought to be propagated, the Michelson-Morley experiment appeared to disprove the ether’s very existence. A number of theories arose, attempting to rescue this pillar of the Newtonian universe, including the brash idea, arrived at independently by hendrik anton lorentz and george francis fitzgerald, that objects moving through the ether contract slightly in the direction of their motion and thereby hide the effect of the change in the velocity of light.
As for Einstein, the lack of an ether was not a problem but an opportunity to propose the central tenet of special relativity: since there is no frame of reference against which absolute motion can be measured, all motion can only be measured as relative to the observer. He further proposed that the velocity of light is constant and does not depend on the motion of the observer. From these two postulates and some elementary algebra, he concluded that when an object is in uniform motion relative to an observer, length decreases and time slows by the amount postulated by Lorentz, while the inertial mass of particles increases. At ordinary velocities, the magnitude of these effects is negligible and Newton’s laws still apply. But at velocities approaching that of light, they become substantial. To quantify this strange state of affairs, Einstein found that he could use the Lorentz transformations, a group of equations that mathematically predict the increase of mass, shortening of length, and dilation of time for an object traveling at near the speed of light, while the velocity of light is always the same. Many years later, Einstein’s conclusions on time dilation, length contraction, and mass increase would be confirmed by observations of fast-moving subatomic particles and cosmic rays.
Since an object moving at the velocity of light would appear to an observer to have zero length and infinite mass, while time would stand still, Einstein concluded that an object cannot move at a velocity equal to or greater than the velocity of light. Answering the question he had asked himself in Arrau, at age 16, he concluded that one could never catch up with a beam of light. Maxwell’s equations, which stated that the velocity of light was constant, were correct, whereas the ether and Newton’s absolute space were superfluous. There was no need for any preferred universal frame of reference. What matter are observable events, and no event can be observed until the light that communicates it reaches the observer. If space and time had been the absolutes in Newton’s universe, the speed of light was the only absolute in Einstein’s. Indeed, no velocity greater than that of light has ever been detected.
In the process of exploring the further implications of special relativity, Einstein was led, in 1907, to the discovery that mass is equivalent to energy, which he expressed in what is undoubtedly the most famous equation ever written: E = mc2, or energy equals mass times the square of the speed of light. Given the magnitude of the speed of light, Einstein’s equation revealed that an enormous amount of energy is stored as mass. It would provide the key to both nuclear power and nuclear weapons, although such applications were far from Einstein’s mind at the time.
Special relativity would undergo a vital evolution in 1908 when Einstein’s former professor at the polytechnic, the brilliant mathematician Herbert Minkowski, expressed Einstein’s ideas in terms of a geometric form: a four-dimensional continuum made up of three dimensions of space and one of time: Minkowski space or spacetime. If this interpretation helped make relativity acceptable to most physicists, it led Einstein himself to remark, “Since the mathematicians have invaded the theory of relativity, I do not understand it myself anymore.”
With the lay public, not to mention a good many scientists, confounded by special relativity, recognition was not immediate. Einstein was brusquely rejected when he applied for an academic job at the University of Bern. But by 1909 his discoveries were gaining appreciation in the scientific community. Einstein was offered a junior professorship at the University of Zurich. As his reputation grew, in 1911 he became a full professor, first in Prague, and, in 1912, in Zurich. Then in 1914, just as war was breaking out in Europe, Einstein moved his family to Berlin, where he had been offered a post, without teaching duties, as director of the Kaiser Wilhelm Institute.
By this time, Einstein was nearing the end of his eight-year struggle to make the theory of relativity generally applicable by considering not only systems that are in uniform motion but also those that are accelerating. The special theory dealt with inertial mass, which is the resistance objects offer to change in their state of motion. Inertial mass is what you feel when you glide a bowling ball along the floor. Gravitational mass is what you feel when you lift it. Yet, for some reason, the inertial and gravitational masses of any given object are equivalent. Moreover, because they are equivalent, they cancel each other out. Since galileo galilei’s discovery that an apple and a cannon-ball fall at the same velocity, scientists had been aware of this. But what had struck Galileo and Newton as mere coincidence appeared to Einstein in a different light.
He had begun his relentless pursuit of a relativistic theory of gravity in 1907. In his famous elevator gedanken experiment, he had shown that people in a sealed elevator would be unable to determine whether they were in a real gravitational field or just feeling the inertial forces due to acceleration. Einstein would later call this idea, known as the principle of equivalence, “the happiest thought of my life.” Einstein reasoned that if the effects of gravity are identical to those of acceleration, gravitation itself might be regarded as locally equivalent.
In this context he investigated the effect of gravitation on light and in 1911 concluded that light rays would be bent in a gravitational field. He realized, however, that if gravitation were a form of acceleration, the new theory would require something other than the four-dimensional Euclidean geometry that underlay the spacetime continuum of special relativity. Moreover, to prevent reintroducing the concept of the ether, the mathematical formalism had to be expressed in a covariant manner, that is, one in which the physical laws seen by observers are not tied to a preferred frame of reference. In 1912, Einstein enlisted his friend Marcel Grossman to find a way of expressing the new theory in terms of a new mathematical language called covariant tensor calculus.
Despite many setbacks, by 1915, Einstein had developed these ideas into the general theory of relativity, which states that masses distort the structure of spacetime and that this distortion produces the effects of gravitation. Matter curves space, and what we call gravitation is only the acceleration of objects as they fall along their trajectories in curved spacetime. The ability of this new formulation to account for a phenomenon that Newton’s theory could not—the anomalous part of the perihelion in Mercury’s orbit—convinced Einstein himself that his theory was correct. He had only a handful of supporters, however, during the chaotic years of World War I. When not involved in scientific research, Einstein was embroiled in pacifist activities and a bitter separation from Mileva, who returned to Zurich with their two sons. When his divorce was finalized in 1919, Einstein married his cousin and longtime mistress Elsa Einstein.
That same year, his theory of general relativity would achieve spectacular recognition. The English astronomer Arthur Eddington traveled to Brazil to observe a solar eclipse, hoping to confirm general relativity’s prediction that the apparent position of stars would shift when they are seen near the Sun because its intense gravity would bend the light rays from the stars as they pass the Sun. When Eddington announced that the apparent bending of the light rays seen from the stars was offset to just the degree predicted by general relativity, Einstein became an overnight international celebrity. General relativity was further confirmed in 1925, when its prediction that a red shift is produced if light passes through a strong gravitational field was observed.
General relativity gave an exciting new answer to the age-old question, What exists beyond the edge of the universe? Since gravity is linked to the geometry of a curved four-dimensional space-time, the universe can be both infinite in four dimensions and bounded in three, to those who observe it from a three-dimensional universe. Since matter warps three-dimensional space, the total of the mass in all the galaxies in the universe may be sufficient to cause three-dimensional space to close around them.
Despite burgeoning recognition of his relativity theory, the conservative Nobel Prize committee awarded Einstein the 1921 prize for his work on the photoelectric effect. Einstein would spend the next decade traveling widely—within Europe, to the United States, to Palestine, and to South America—explaining his theories to mostly rapt audiences. The 20s was also the time when Einstein would commence his lifelong debate with the adherents of the new quantum mechanics. As early as 1909 Einstein had pointed to the need to reconcile the particle and wave theories of light. It would be louis-victor-pierre, prince de broglie, who in 1923, using Einstein’s mass-energy equation and Planck’s quantum theory, would find a way to describe the wave nature of a particle. Whereas Einstein was supportive of de Broglie’s work, he rejected its further development by erwin schrodinger, werner heisenberg, niels henrick david bohr, and others, into a theory expressed in terms of probabilities, which essentially banished microscopic causality in space-time. For Einstein the revolutionary, this was one revolution too many, signaling the end of physics itself. His meeting with Bohr in 1927 at the Solvay Conference marked the beginning of a famous series of debates between the two giants, in which Einstein would present a gedanken experiment designed to debunk quantum theory, which Bohr would then proceed to demolish. For Einstein, the great stumbling block was the principle of indeterminacy: “God does not play dice,” he told Bohr, who replied, “Einstein, stop telling God what to do.” To this day the conceptual and mathematical incompatibility of relativity and quantum mechanics has not been resolved.
With Hitler’s ascendance to power in 1933, the heady period of discovery and unfettered debate in European physics came to an end. That year Einstein emigrated to the United States, accepting a position at Princeton University’s Institute for Advanced Study, where he would remain for the rest of his life. His second wife, Elsa, died in 1936, and he never remarried. In 1939, with the Hungarian physicist Leo Szi-lard, he wrote to President Roosevelt, informing him that Hitler had the ability to build an atomic bomb, an admonition that led to the establishment of the Manhattan Project. When World War II ended, Einstein was tormented by his role in the development of the American atomic bomb and campaigned actively to abolish nuclear weapons. In 1952, Einstein, who had helped establish the Hebrew University of Jerusalem, was offered the presidency of Israel. He refused, believing he was temperamentally unsuited for the job. He eloquently described the two poles of his nature:
My passionate sense of social justice and social responsibility has always contrasted oddly with my pronounced lack of need for direct contact with other human beings and human communities. I am truly a “lone traveler” and have never belonged to my country, my home, my friends, or even my immediate family, with my whole heart; in the face of all these ties, I have never lost a sense of distance and a need for solitude.
In the solitude of his later years, believing that “God is subtle, but he is not malicious,” Einstein labored tirelessly to plumb that subtlety, seeking a theory that would unify gravity and electromagnetism. This time the mystery did not yield to him.
Albert Einstein died in Princeton on April 18, 1955, when an aneurysm in his abdominal aorta burst. He was cremated that day at 4 p.m. in Trenton, New Jersey. His ashes were scattered at a nearby river.
After Einstein, the mathematical language of relativity became the stuff of which all the laws of physics would have to be constructed. From then on, one of the key tests of any new physical law would be whether it could be written in a “relativistic form,” capable of satisfying the fundamental structure of space and time that Einstein had revealed.
