The Year of Dr. Einstein
He was a modern Merlin, conjuring up astonishing new notions of space and time, changing forever man's perception of his universe --and of himself. He fathered relativity and heralded the atomic age with his famed formula E=mc2. Yet his formidable reputation never undermined his simple humanity. He spoke out courageously against social injustice. In his later years, dressed in baggy clothes, his white hair as unkempt as a sheep dog's, he helped yourgsters with their geometry homework, still loved to sail, play Mozart melodies on the violin and scribble reams of doggerel. Though he has been dead nearly a quarter of a century, there are few people who do not recognize the face or name of Albert Einstein.
Scientists share that adulation, for Einstein was the most eminent among them in this century and, in the eyes of some, the greatest scientist of all time. Says Nobel Laureate I.I. Rabi: "There are few ideas in contemporary physics that did not grow out of his work." Adds M.I.T.'s Irwin Shapiro: "He makes me proud to call myself a physicist."
This year marks the centennial of Einstein's birth on March 14, 1879, in Ulm, Germany, and all the world seems to be joining the party. In the U.S. and Europe, in Asia and Latin America, even in the Soviet Union, where Einstein's ideas were once considered heresy, academic institutions are vying to outdo each other with special tributes.
The largest commemorations will be held next month at the Institute for Advanced Study in Princeton, N.J., where Einstein spent his last 22 years, and at the Hebrew University in Jerusalem, which he helped found. "It's an avalanche effect," says Relativist Peter G. Bergmann of Syracuse University, one of Einstein's old collaborators. "Everyone wants to snatch a bit of reflected glory." Says Cambridge University's Martin Rees: "Einstein is the only scientist who has become a cult figure, even among scientists."
But the centennial fever has spread far beyond academe. The U.S., West Germany and other countries are issuing special Einstein stamps. There is a spate of new books on Einstein, including two volumes of his writings published in China. Museums such as the Smithsonian Institution in Washington and the Pompidou Center in Paris are mounting Einstein exhibits. In New York City, the American Institute of Physics is assembling Einstein memorabilia for a traveling show. The East Germans are sprucing up Einstein's old summer cottage at Caputh, near Berlin. Japanese Einstein buffs are planning a pilgrimage to some of his European haunts. Television too is paying homage with several Einstein specials, including the BBC-WGBH two-hour Einstein's Universe, starring Peter Ustinov as a wide-eyed student of relativity, and PBS's 60-minute Nova documentary Einstein. Above it all is the "Einstein Observatory," an astronomical satellite launched in November to investigate stars and other celestial objects that radiate high-energy X rays.
Some of Einstein's old associates are appalled by the hoopla. Says Helen Dukas, his longtime secretary, who lovingly watches over the Einstein archives in Princeton and still places flowers in the study of his white clapboard house on Mercer Street: "Do you know what he would say? 'You see, they are still taking pieces out of my hide.' " Philosopher Paul Schilpp, who is helping arrange a centennial symposium at Southern Illinois University, acknowledges that Einstein "would hate all this uproar."
What has aroused Einsteinophiles especially is a 12-ft.-high bronze statue of the physicist that will be unveiled in April by the National Academy of Sciences on Washington's Constitution Avenue. Critics have attacked Sculptor Robert Berks for his "bubble gum" style, the astrological connotation of the star-studded base and the statue's cost (at least $1.6 million). Others insist that no statue could really be appropriate; Einstein, after all, was so opposed to posthumous veneration that he willed his ashes to be scattered at an undisclosed place. Constantly called upon to pose for photographers, painters and sculptors (including Berks), he once gave his occupation as "artist's model."
Perhaps the most meaningful tribute to Einstein is entirely unplanned: the renaissance of interest in his scientific work. Before his death in 1955 at 76, Einstein had called himself a "museum piece," a fossil who had long since slipped out of the mainstream of physics. Indeed, his greatest work, general relativity, fell into an intellectual limbo. Explains University of Texas Physicist John Wheeler: "For the first half-century of its life, general relativity was a theorist's paradise but an experimentalist's hell. No theory was more difficult to test." Physicists turned to other concepts, mostly concerning atomic structure, that could be more easily verified and had more applications.
Now that view has undergone a dramatic change. Says West German Physicist Carl Friedrich von Weizsacker: "Einstein's true greatness lies in the fact that he remains relevant today, in spite of the breakthroughs that have occurred since his death." Indeed, it is many of those breakthroughs that have contributed to the Einstein revival.
Since the early 1960s, astronomers have been opening up an entirely new universe, aided by technology only vaguely dreamed of in Einstein's day: giant radio antennas that can "see" hitherto unknown sources of energy in space, orbiting satellites that scan the heavens high above the obscuring atmosphere, and atomic clocks so accurate they lose or gain barely a billionth of a second in a month.
This unexpected world includes enigmatic objects called quasars.
Radiating prodigious amounts of energy, they are visible on earth despite the fact that they may be the most distant objects in the universe. Pulsars, or neutron stars, have also been detected; these highly compressed cadavers of massive stars usually signal their existence by their highly regular radio beeps. Even stranger are the giant stars that may have in effect gone down the cosmic drain: those elusive black holes, with gravitational fields so powerful that not even light can escape them. Astronomers have also picked up what may be the echo of the Creation. Coming from everywhere in the skies, and in a sense from nowhere at all, these faint microwaves appear to be the lingering reverberations of the Big Bang, the cataclysmic explosion in which the universe was apparently born 15 billion to 20 billion years ago.
Einstein, in his time, could have had little inkling of this astronomical revolution. Yet to understand phenomena of such cosmic proportions, scientists must rely on his theoretical masterwork: the general relativity theory. Unfolded in 1916 to an astonished and largely uncomprehending scientific community, it is Einstein's complex and subtle yet beautifully elegant mathematical explanation of nature's most pervasive--and paradoxically, its weakest--force: gravity.
As a direct consequence of the recent astronomical discoveries and a host of new and precise measuring techniques, general relativity is finally enjoying boom times. Thus Einstein, a genius in his own age, remains a powerful intellectual force in this time as well. The number of learned papers on general relativity has risen from only a handful a few years ago to some 600 or 700 a year. The relativistic revival can also be seen in the spirited competition by scientists around the world to be the first to detect the gravity waves, which, Einstein said, are the vehicle by which gravitational force is transmitted, just as light or radio waves are the carriers of electromagnetic force.
Scientists are also conducting ever more sensitive tests of Einstein's theory. M.I.T.'s Shapiro and his colleagues have been sending radio signals past the rim of the sun, bouncing them off other planets and clocking their return to earth to an accuracy of better than a millionth of a second. The object: to see if solar gravity slows the signals down by the amount forecast by Einstein. So far, general relativity has passed these and other tests without exception. Says Yale Physicist Feza Gursey: "Einstein's theories tend to become stronger with time."
In his earliest years, Einstein showed no obvious sign of genius; he did not begin talking until the age of three. At Munich's Luitpold Gymnasium (high school), he bridled at the inflexible system of rote learning and the drill-sergeant manner of his teachers, annoying them with his rebellious attitude. Said one: "You will never amount to anything."
Yet there were also some hints of the man to be. At five, when he was given a compass, he was fascinated by the mysterious force that must be influencing its needle. He went through a deeply religious period before adolescence, berating his freethinking father, a manufacturer of electrochemical products, for straying from the path of Jewish orthodoxy. But this phase passed soon after he began studying science, math and philosophy on his own. He was especially enamored of a basic math text--his "holy geometry booklet." At 16, he devised one of his first "thought experiments." These can only be done in the mind, not in a laboratory, and would eventually lead him to his stunning theories. In this case, he imagined what a light wave would look like to an observer riding along with it.
Within a year after his father's business failed and the family moved to Northern Italy to start anew, Einstein dropped out of school and renounced his German citizenship. To shake off the bitter memories of the Munich school, he spent a year hiking in the Apennines, visiting relatives and touring museums. He then decided to enroll in the famed Swiss Federal Institute of Technology in Zurich. Though he failed the entrance exam--because of deficiencies in botany and zoology, as well as in languages other than German--he was admitted after a year's study at a Swiss high school.
(Eventually he became a Swiss citizen.)
Yet Einstein's rebelliousness continued. He cut lectures, read what he pleased, tinkered in school labs and incurred the wrath of his teachers.
Mathematician Hermann Minkowski, who later made valuable contributions to Einstein's new physics, called him a "lazy dog." Only scrupulous notes kept by a classmate, Marcel Grossmann, enabled Einstein to cram successfully for his two major exams and to graduate in 1900.
Having antagonized his professors, Einstein failed to obtain a university teaching post. He eked out a living by doing calculations for an astronomer, tutoring and substituting as a teacher. At 23 he got a job as an examiner with the Swiss Patent Office in Bern. His title: technical expert, third class. His pay: a modest 3,500 francs, then about $675, a year.
Still, as Einstein said, the post "in a way saved my life." It enabled him to marry a fellow physics student Mileva Marie, from Serbia. In reviewing patent applications, he also learned to get to the heart of a problem and to decide quickly if ideas were valid. That left him time to think about physics.
There was plenty to ponder. For more than two centuries, the basic laws of motion and gravitation postulated by Isaac Newton had prevailed. They were more than adequate tc describe planetary movements, the behavior of gases and other everyday physical phenomena. But by the end of the 19th century serious cracks had developed in the Newtonian edifice. For example, Newton had regarded light as a stream of particles ("corpuscles"). Experiments had already shown that light was wavelike. Perhaps more significant, the English scientist Michael Faraday and the Scot James Clerk Maxwell had demonstrated that electromagnetism, which includes light, comprised a class of phenomena that did not fit easily into the Newtonian system.
If light consisted of waves, however, how were they transmitted? Scientists realized that space was largely empty of conventional matter. So, to carry light over such vast distances as that between sun and earth, they postulated the existence of a tenuous, invisible substance called the ether. To detect the ether, the Americans Albert Michelson and Edward Morley performed a clever experiment in 1887. As the earth moved around the sun at about 30 km (19 miles) per second, the motion-would generate an ether "wind" in the opposite direction, just as a bicyclist pedaling on a calm day creates a wind that blows into his face. Thus the velocity of light should be greater when light moves with this wind, or across it, than against it. To test the ether theory, Michelson and Morley constructed an ingenious rotating apparatus with a light source and mirrors. To their amazement, they found that no matter in what direction light was beamed, its velocity remained exasperatingly constant. Could it be that the ether did not exist?
In an attempt to preserve the ether, Irish Physicist George FitzGerald offered a novel theory: perhaps motion through the ether causes an object to shrink slightly in the direction of its travels. Indeed, by his argument, the contraction would be just enough to compensate for the change in the velocity of light caused by the ether wind. Thus the wind would be impossible to detect. Putting the theory into elegant mathematical form, the Dutch physicist Hendrik Lorentz added another idea: permeating the structure of all matter, the ether would also slow down clocks traveling through it--in fact, just enough so light's speed would always seem constant.
Even to scientists of the day, these theories seemed patchwork: they dealt with nagging questions, but in an artificial and contrived way. Yet they contained seeds of truth. Science was groping toward the answer to the ether dilemma and the limitations of Newtonian physics. And even without Einstein, someone eventually would have solved the puzzle.
Still, the intuitive flash did not occur to any of the scientific greats of the day, but to the 26-year-old patent examiner on the fringes of physics. That insight was shown in two remarkable papers that appeared during 1905 in the German scientific journal Annalen der Physik. The title of the first -- "On the Electrodynamics of Moving Bodies" -- did not begin to reflect its eventual significance. Later it would become known as Einstein's special theory of relativity.
Einstein boldly disregarded the notion of the ether. Then he went on to state two postulates: 1) An experiment can detect only relative motion, that is, the motion of one observer with respect to an other. 2) Regardless of the motion of its source, light always moves through emp ty space at a constant speed (this seems to violate common sense, which suggests that light projected forward from a moving spacecraft, like a bullet fired from a plane, would travel at a speed equal to its velocity plus that of the craft). From these statements, using thought experiments and simple mathematics, Einstein made deductions that shook the central ideas of Newtonian physics.
In demolishing New ton's basic assumption that time is absolute, that it is universally the same, and that it flows steadily from the past toward the future, Einstein used the following thought experiment: an observer standing next to a railroad embankment sees two bolts of lightning strike the tracks at the same time and thus concludes that they occurred simultaneously, one far to the east, the other an equal distance to the west. Just as the bolts hit, a second observer passes directly 'in front of him on a train moving at high speed from east to west.
To the second observer, the bolts do not seem to strike simultaneously. Rea son: because he is moving away from the bolt in the east, its light takes slightly longer to reach him. Similarly, because he is moving toward the bolt in the west, its light reaches him earlier. Thus what the stationary observer sees as simultaneous lightning strikes, the moving observer sees as a flash in the west followed by one in the east. If, on the other hand, the bolts had struck at different times, it could well have been the moving observer who saw them simultaneously and the man along the tracks who thought that they did not occur at the same time.
In any case, the question remains:
Which of these views is wrong? Nei ther, said Einstein. Measurements of time depend on the choice of the reference frame -- in this case, the train or the point along the tracks.
By similar reasoning, Einstein also showed that the Newtonian concept of ab solute length was obsolete.
In Einstein's new relativistic world, both time and distance are equally fickle and depend on the relative motion of observers. The only absolute remaining is the speed of light. Out of this theorizing emerged some bizarre conclusions about the effect of so-called relativistic speeds, those near the velocity of light. As an observer on earth, for example, watches a spacecraft move away at about 260,000 km (160,-000 miles) per second, time aboard the ship (assuming he is able to see the ship's clock) seems to him to move at only half the rate that it would on earth. The mass of the ship and everything on it appear to dou ble relative to what their mass was on earth, while all dimensions in the direction of travel seem to contract to half their earth lengths. Strangely enough, a ship board observer notices no changes aboard his craft. He thinks that it is time back on earth that is slowing, and that the masses and lengths there are changing.
These seemingly contradictory effects lead to a famous brain teaser called the Twin Paradox: If one twin goes off into space, which twin will be the older (if either is) when the brothers are reunited?
Einstein says there is a definitive answer and, therefore, no paradox. Be cause of other relativistic effects that stem from leaving and returning to earth, if one twin departs on a high-velocity space journey, he will be younger than the earth-bound brother when he returns.
Astonishing as these effects seem, they have all been verified. In designing nuclear accelerators, for example, scientists must take into account the fact that subatomic particles whipped to speeds approaching the velocity of light will appear to increase in mass. Furthermore, particles called muons, which at rest exist for only very short spans of time before decaying into other particles, are found to live far longer at high velocities.
Einstein published two other landmark reports in Annalen der Physik during 1905. One paper explained a laboratory curiosity called the photoelectric effect, which occurs when a light beam hits a metallic target and causes it to give off electrons. (This phenomenon makes possible a host of today's electronic gadgetry, ranging from electric-eye devices to TV picture tubes and solar panels for spacecraft.) In this paper Einstein borrowed from a theory by German Physicist Max Planck, who had solved a vexing problem about the radiation of heat and light from hot objects by proposing that this radiant energy is carried off or absorbed in tiny packets, or quanta. Planck himself was dissatisfied with the theory, believing it contrary to nature, but Einstein enthusiastically seized it. He introduced the very revolutionary idea that light at times has the characteristics of particles (later named photons). These particles were knocking the electrons from the metal.
Before the scientific world could even begin to digest these assertions, the journal published still another communique from the young patent examiner. Einstein had devised an equation that accounted for Brownian motion, the random, zigzagging movements of microscopic particles within liquids (named after the Scottish botanist Robert Brown, who first observed it in 1827). Einstein suggested that the specks were being jostled by molecules in the liquid, an idea that finally convinced many early 20th century skeptics of the atomic nature of matter.
In his second relativity paper, the final report published in 1905, Einstein used relativity's mathematics as well as ideas from his photoelectric paper to make a historic deduction: if a body gives off an amount of energy (E) in the form of light, its mass will be reduced by that amount divided by the speed of light spuared (m = E/c2), From there was only one short algebraic step, but a giant intellectual leap, to a more daring conclusion: that mass and energy are not only equivalent but interchangeable.
That idea was contained in a far more famous equation published two years later: E=mc2. This said in effect that even a small amount of matter held the ex plosive power of tons of TNT, which opened the door to the nu clear age. It also eventually ex plained why the sun could burn for so many billions of years while not shrinking appreciably in size.
Einstein's awesome output in that miracle year of 1905 was as astounding as its implications In fact, nothing quite like it had occurred since 1666, when New ton, at 23, had left Cambridge and taken refuge in Lincolnshire from the bubonic plague and in that isolation studied the spectrum of light, invented calculus and aid the groundwork for his universal theory of gravitation and motion.
After seven years Einstein at last merged from the patent office and won a succession of academic posts in Prague and Zurich. Finally, on the ve of World War I, in spite of his distaste for Germany's pervasive militarism, he accepted a professorship at the University of Berlin and an appointment to the Kaiser Wilhelm Institute as head of a newly created center for theoretical physics.
The move had some bitter consequences. After the outbreak of hostilities, Einstein, a socialist and pacifist, was one of four German intellectuals who signed a manifesto condemning the war. His wife and their two sons had returned to Switzerland. Within a few years the separation led to divorce. In a characteristic gesture of generosity, Einstein had agreed to give the money from his anticipated Nobel Prize to his family. (The $30,000 prize was finally announced in 1922--for his photoelectric theory. Relativity, still not universally accepted among scientists, was only hinted at in the Nobel citation.) Shortly after the divorce, Einstein married his widowed cousin Elsa.
Meanwhile, Einstein's restless mind had turned from special relativity's uniform motion to the greater complexities of accelerated movements. These are motions involving changes in velocity: as when the earth's gravity draws an object toward the ground, the object's velocity increases by 9.8 meters (32 ft.) per second each second. Einstein took an approach entirely different from Newton. The 17th century master had noted what seemed to be a remarkable coincidence: gravity acted in the same way on all bodies, regardless of their mass. That could be shown by an apocryphal experiment of Galileo's in which objects of different weight dropped from the Tower of Pisa were said to strike the ground at virtually the same instant (any difference being due to air resistance). Einstein offered an explanation. Acceleration caused by gravity, he said, is indistinguishable from that caused by other forces. I That proposition is Einstein's 1 principle of equivalence. As usual, Einstein gave a graphic example. I Consider a scientist riding in an elevator in space, far from the earth. 1 The elevator is accelerating "upward" at a rate of 9.8 meters per second each second. As a result of his body's resistance to change in velocity (his inertia), the scientist's feet press against the floor just as they would if the elevator were at rest on the earth's surface. He has no way of telling whether the pull from below is gravitational or inertial.
Then what is gravity, this mysterious force that Newton believed exerted its influence instantaneously over the greatest distances? According to Einstein, it really is not a force at all, but a property of what came to be called spacetime. In this world picture, the universe is shaped by the three spatial dimensions of ordinary experience, plus the added dimension of time--one that cannot be described by the sacred Euclidean geometry of Einstein's youth. In his search for a new "metric" to describe spacetime, Einstein again turned to his old friend Grossmann, now a distinguished mathematician. Grossmann provided the necessary mathematical tool: an obscure non-Euclidean geometry (developed by the 19th century German mathematician Bernhard Riemann) that could accommodate Einstein's new four-dimensional world.
Tying everything neatly together in ten complex "field" equations, Einstein in 1916 published his general relativity theory. Unlike the special thepry, it had almost no immediate intellectual predecessors. Even today, scientists marvel at the mental processes Einstein used to develop it. Says Nobel Laureate Physicist Richard Feynman of Caltech: "I still can't see how he thought of it."
' Hard as it is to visualize, Einstein's curved four-dimensional space-time "continuum" is often likened to a suspended rubber sheet stretched taut but deformed wherever heavy objects--stars, galaxies or any other matter--are placed on it. Thus, according to Einstein, a massive body like the sun curves the space-time around it. The planets, instead of being held in their elliptical orbits around the sun by the force of gravity, move along the curved pathways of spacetime.
To prove his dumbfounding theories, Einstein first used the field equations to clear up a puzzling anomaly in the orbital motion of the planet Mercury. Over a century, the point closest to the sun in Mercury's elliptical orbit moves 43 seconds of arc more than Newtonian mechanics dictated that it should. Scientists had been unable to explain this difference. But when the Einstein equations were applied to Mercury's orbit, they precisely accounted for the extra 43 seconds of arc.
In another thought experiment, Einstein imagined that his hypothetical elevator, accelerating at a tremendous rate, was traveling at close to the speed of light. In that case, a beam of light entering through a hole in the wall would appear to a scientist inside the elevator to bend down in an arc and exit at a lower point on the opposite wall. Reason: even as the light moves across the elevator, the elevator is moving "up." But the scientist inside, aware only that his feet are pressing on the floor (because of the acceleration), assumes that gravity is bending the beam.
The experiment suggested--and Einstein's equations showed--that gravity would indeed curve light.
It was a test of this effect, expanded from the hypothetical elevator into a global picture by his field equations, that finally brought Einstein worldwide attention. General relativity indicated that when light from a distant star passes very close to the sun on its way to earth, it should be deflected by solar gravity, thereby shifting the star's position in the sky. The amount of shift, Einstein calculated, should be 1.75 seconds of arc--a small variation, but one discernible by astronomers of the day. But how could astronomers photograph a star nearly in line with the sun when it would certainly be obscured by sunlight? Answer: during a total eclipse. On May 29, 1919, during an eclipse expedition to the island of Principe off the West African coast, the British astronomer Arthur Eddington found deflections in starlight that almost matched Einstein's prediction. Later, when Einstein was asked what he would have concluded if no bending had been detected, he replied: "Then I would have been sorry for the dear Lord--the theory is correct."
In a world still reeling from a bloody war, the thought that a single man, working only with mathematical scribblings, could reorder the universe seemed just short of miraculous. Newspapers and magazines clamored for interviews. Einstein was besieged by lecture invitations, received by presidents and kings and given tumultuous welcomes by throngs from Tokyo to Manhattan. Popular books were written to explain the mysteries of relativity. Still, the theory was difficult, its mathematics decipherable by only a tiny part of the scientific priesthood. Asked if it were true that only three people understood the subject, Eddington jokingly countered, "I'm trying to think who the third person is."
Einstein soon found himself embroiled in controversy. Some churchmen perceived his theory, which did not rely on the old Newtonian absolutes, as an attack on religion. Boston's Cardinal O'Connell charged that relativity was "cloaked in the ghastly apparition of atheism." For a rabbi who asked him frankly if he believed in God, Einstein recalled a famous Jewish apostate: "I believe in Spinoza's God, who reveals himself in the orderly harmony of all that exists, not in the God who concerns himself with fates and actions of human beings."
It was easy to see why Einstein aroused ire. Revolutionary in nature, his ideas about space and time collided directly with ancient prejudices and seemed to contradict everyday experience. In ad dition, there were his outspoken antinationalism and, ironically in light of his own lack of belief in formal religion, the fact that he was a Jew. But criticism abroad was muted compared with that in Germany, where Jews were being made the scapegoats for loss of the war and Einstein's pacifism was bitterly remembered. Einstein and his "Jewish physics" became the object of increasingly scurrilous denunciations. Fellow German scientists turned their backs on him--with the notable exception of a few men like Planck. Shortly after Hitler took over in 1933, Einstein, who was abroad at the time, accepted a post at the newly created Institute for Advanced Study in Princeton and never returned to Germany.
Despite his public activities, Einstein managed to push ahead with his scientific work. In 1917 he completed a paper of considerable import for all of physics: it not only laid down the basic principle of the laser some 40 years before the first such device was made but, more broadly, also advanced quantum theory. In addition, Einstein contributed significantly to the rebirth of cosmology, the study of the origin, history and shape of the universe. The Dutch astronomer Willem de Sitter and later the Russian scientist Alexander Friedmann had concluded that Einstein's equations pointed to an unstable universe --possibly an expanding one. Because such a changing, dynamic universe was totally at odds with the popular picture of the heavens portrayed by most astronomers, Einstein had opted for a stable, unchanging universe; he had managed that feat with a mathematical sleight of hand that involved what he called the cosmological constant. A decade later, after the American astronomer Edwin Hubble had shown that the distant galaxies were all receding from one another and that the universe was indeed expanding, Einstein reversed himself and accepted the fact toward which his original equations had pointed. The cosmological constant, he allowed, was the worst mistake of his scientific career.
But he was stubborn on other scientific issues. As he admitted in his later years: "I have become an obstinate heretic in the eyes of my colleagues. In Princeton, they consider me an old fool." He had earned this new reputation by his continued objections to what had become the basic conceptual tool for studying atomic structure: quantum mechanics, a statistical way of looking at the atom that Einstein himself had helped develop by using Planck's quanta to explain the nature of light.
Nowadays physicists rank quantum mechanics alongside relativity as one of the twin pillars of their science. But at its heart is an almost philosophical aspect that deeply troubled Einstein. It is the uncertainty principle, which says, for example, that it is impossible to tell both the exact position and the momentum of a single atomic particle--an electron, say--because the very act of observing disturbs it. Only by statistical means (like those used to determine probability in dice or poker) can a scientist predict what the results of such an experiment will be.
Einstein, who had helped revolutionize 20th century physics, now was resisting the revolution's latest turn. To him, quantum mechanics was fundamentally incomplete. Nature, he was sure, operated by strict rules that scientists : could uncover. But because of the role of probability in quantum mechanics, Einstein felt that it failed to meet his crucial standard. The universe, he insisted, could not operate on chance. Causality had to exist. Again and again, he would say such things as "God does not play dice." Exasperated, the Danish physicist Niels Bohr, Einstein's friendly adversary, finally replied, "Stop telling God what to do."
Einstein, however, was determined to go his own way. Despite criticism he spent much of the second half of his life pursuing the development of what scientists call a unified field theory. In Einstein's time, this meant an all encompassing mathematical construct that would unite under a single set of equations not only gravity but also electromagnetism. Since then the task has become even more difficult, with the discovery of two other basic forces: the nuclear forces. Most physicists thought Einstein's lonely quest was hopeless, and in fact he never succeeded. But Einstein was convinced such a basic harmony and simplicity existed in nature.
Even after the pace of Einstein's career slowed and his resistance to quantum mechanics earned him the scorn of some scientists, he still epitomized science in the public eye. As Carl Sagan notes, his example inspired numerous Depression-era youngsters to choose scientific careers. His persona and pronouncements became legends. Asked why he used one soap for washing as well as shaving, he replied, "Two soaps? That is too complicated." Even when receiving visitors like David Ben-Gurion (who later offered him the presidency of Israel), Einstein often would be tieless and sockless. Recalls Physicist-Biographer Banesh Hoffmann, who worked with Einstein: "He never tried to show you how clever he was. He always made you feel comfortable."
Einstein had enormous powers of concentration. When the wind died down while he was out sailing, he would whip out his notebook and do his calculations. Stymied by a thorny problem, he would tell his colleagues in accented English, "Now I will a little tink," pace slowly up and down, while twirling a lock of his unruly hair, or perhaps puff on his pipe, then suddenly erupt in a smile and announce a solution. Interrupted by parades of visitors to his Mercer Street house, he could resume his work almost as soon as they stepped out of his second-floor study. Recalls British Author C.P. Snow: "Meeting him in old age was rather like being confronted by the Second Isaiah--even though he retained traces of a rollicking, disrespectful common humanity and had given up wearing socks."
In 1939, when Einstein's fellow refugees Leo Szilard and Eugene Wigner learned that German scientists had managed to split the atom, they sought Einstein's help. Einstein himself may have had only the faintest idea of the recent progress in nuclear physics, but after a briefing by Szilard and Wigner he agreed to write a letter to President Roosevelt alerting him to the possibility that the Nazis might try to make an atomic bomb. That letter is popularly credited (though its precise effect is unclear) with helping to persuade Roosevelt to order up the Manhattan Project, which produced the first atomic weapons.
Later, when A-bombs exploded over Hiroshima and Nagasaki, Einstein expressed deep regret. After the war, he apologized personally --and in tears--to visiting Japanese Physicist Hideki Yukawa. On another occasion, he said, "Had I known that the Germans would not succeed in developing an atomic bomb, I would have done nothing for the bomb."
In his final years Einstein was an outspoken foe of McCarthyism, which he felt was an echo of the turbulent events that had preceded the downfall of Germany's Weimar Republic. He urged intellectuals to defy what he considered congressional inquisitions, even at the risk of "jail and economic ruin." He was widely denounced, and Senator Joseph McCarthy called him "an enemy of America." In his last public act, Einstein joined Bertrand Russell and other scholars in a desperate plea for a ban on all warfare.
British Science Writer Nigel Calder says that "the Einstein honored in later generations expired long before--in 1919." That is, to some extent, true, although work by Physicists Steven Weinberg of Harvard and Abdus Salam of London's Imperial College of Science and Technology suggests that Einstein's dream of a unified field theory may some day be realized. There is also a glimmer in the esoteric new work on such baffling mathematical concepts as "supergravity" and "twistors" of possibly achieving a union of Einstein's beloved relativity and the quanta that he so distrusted.
However that quest may turn out, the father of relativity remains a moving figure, a 20th century Newton who set physics aflame and left an intellectual legacy so rich and profound that its depth is still a source of amazement and discovery. Yet Einstein, for his part, never lost sight of the humanity that new knowledge should serve. Says Einstein's executor, Economist Otto Nathan: "Even if he had never done science at all, he would have been one of the memorable figures of the century." That may be the exaggeration of a loyal friend. But as a centennial assessment, it is, relatively speaking, not entirely off the mark.
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