Albert Einstein is probably the only 20th-century scientist whose name would be recognized by a majority of the population. This is, of course, a strong indictment of scientific education in an age of science, but there is a rough justice in it, because Einstein was, beyond doubt, the greatest scientist of the era. His greatness was acknowledged by his scientific peers before World War I, and he achieved overnight public fame immediately after the war with the experimental confirmation of the general theory of relativity. In the succeeding half century, countless books and articles on the man and his theories have been written, both popular and technical, but the full picture of Einstein's impact remains to be told.
In the last two years, three books have been published which attempt to take the measure of the man from the present vantage point, eighteen years after his death and almost seven decades since his first epochal contributions burst upon the world. One of the books is a full-scale biography by Ronald W. Clark,1 a professional biographer of science, who attempts not only to comment on Einstein's work but also to relate in great detail the story of his long life, both as private citizen and public figure. The other two are less ambitious, aiming mainly to convey the outline of his major contributions to physics and to give some idea of Einstein the man. Of these, one is written by the physicist Jeremy Bernstein,2 known for his urbane articles on scientific topics in the New Yorker, and is a volume in the “Modern Masters” series; the other is by Banesh Hoffman, in collaboration with Helen Dukas.3 Mr. Hoffman is a well-known popularizer of science, a mathematician and one-time assistant of Einstein, while Miss Dukas was Einstein's secretary and is literary trustee of his estate.
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I
The basic story of Einstein's life is easily sketched. He was born in Ulm in 1879, but his family moved to Munich while he was still a baby. Though he appeared to be a slow developer, not learning to speak until he was three years old, as a young child he developed a passionate interest in the phenomena of the physical world, and by the time he entered his teens he had acquired a thirst for mathematical knowledge, as well as a precocious taste for Kant. When his father's business failed and the family transplanted itself to Milan, the fifteen-year-old Einstein, temperamentally unsuited to the rigid atmosphere of 19th-century Germany in general, and to that of his gymnasium in particular, rebelled against being left behind to finish high school. Joining his family in Italy, he enlisted his father's help in renouncing his German nationality. Without a high-school diploma, he took the entrance examination for the Zurich Polytechnic, but failed in the general subjects, although he did well in the mathematical part; after a year's further study in the free atmosphere of a progressive Swiss high school he was able to enter the Polytechnic.
Once again, he failed to fit in with a rigid academic environment; though he studied physics intensively on his own, he relied on the lecture notes taken by a more diligent fellow student to pass his examinations. By the time he graduated in 1900, he had made such a negative impression that he was unable to find any reasonable academic post, much less one at the Polytechnic itself. He had to scratch around for various temporary teaching jobs until he was able in 1901 to obtain a position in the Swiss Patent Office in Berne, this time through the help of a friend's well-placed father. About a year later he married Mileva Maric, a Serbian girl who had been a classmate of his. Isolated from any contact with professional physicists, and able to discuss his ideas only with a group of philosophically inclined friends, Einstein set about his scientific work in the time not taken up by his duties in the patent office or by his growing family responsibilities.
In 1905 he published four papers. One of these was his doctoral dissertation, concerned with the diffusion of sugar molecules in solution; the other three were his explanation of Brownian motion, his explanation of the photoelectric effect via the quantum concept, and his introduction to the theory of special relativity. The production of three such significant pieces of work in one year was the most astonishing feat performed by any physicist since a similar period two-hundred-forty years earlier when Newton had discovered the dispersion of light by a prism, invented the calculus, formulated his laws of motion, and discovered his law of gravitation.
In the following years, Einstein published further developments of these themes, and his name became well known among a select group of physicists of the highest ability, but not until 1908 was he to obtain even the minor academic post of privatdozent at Berne University. That same year, the noted mathematician, Minkowski, who had been one of the Zurich professors singularly unimpressed by Einstein the student, made a major address highlighting the significance of relativity. By 1909, Einstein was sufficiently well recognized to be awarded an honorary doctorate at the 350th anniversary celebrations of the University of Geneva, together with Marie Curie and others of similar eminence; when he gave an invited paper at a scientific meeting in Salzburg, he found himself for the first time in the company of world-class physicists.
During the next five years, his rise was meteoric; he was appointed professor at the University of Zurich, where he stayed only a year and a half before moving to Prague. A year later, he returned once more to Zurich, this time to the Polytechnic, thus fulfilling an old ambition. In 1913 he was offered, and could not refuse, a position at the pinnacle of world science, as director of the newly established Kaiser Wilhelm Institute of Physics in Berlin and a full member of the Prussian Academy of Sciences, with no teaching or other official duties to interfere with his research.
The outbreak of World War I, soon after Einstein's arrival in Berlin, was greeted by a famous manifesto, signed by ninety-three of Germany's leading intellectuals, which loudly and belligerently asserted the correctness of Germany's activities in the war. A counter-manifesto, opposing the war and calling for a united Europe, was signed by Einstein and three others.
Isolated in his position, Einstein nevertheless made no secret of his pacifist views, though he was more circumspect in expressing his hopes for a German defeat, which he voiced on his visits to neutral Switzerland. His researches on relativity culminated in the publication of his General Theory in 1916; in 1917 he returned to the quantum theory and published a new derivation of the Planck formula of 1901—of which more below—in which he formulated the idea of stimulated emission of radiation, a concept that more than forty years later would produce the laser.
Early in 1919, Einstein was divorced. His wife and two sons had been in Zurich since before the war; the marriage had not been a happy one, although the couple parted on good terms, and his wife retained her famous married name and was even given the money to come from a Nobel prize which was not to be awarded him for another three years. A few months later, Einstein married his widowed cousin Elsa, who had taken care of him during a serious illness in wartime. This year did not mark a change in his personal status alone. The predictions made in his 1916 paper had aroused much interest in England, and preparations had been made for an astronomical expedition to test them during the eclipse of 1919. When the results of the expedition were released, the long established Newtonian picture of the world had been replaced by that of Einstein, who became world-famous overnight on a scale unmatched before or since by any other scientist.
While before this date Einstein's signing of the 1914 anti-war manifesto marked an unusual departure from his immersion in the world of physics, he now took on a public role. He was an outspoken supporter of pacifism, campaigner for international cooperation, and a champion of the Weimar republic. He had also become a convinced Zionist, and in 1921 visited the U.S. together with Chaim Weizmann to publicize the movement and to raise funds. He had a particular interest in the Hebrew University, where he gave the inaugural address in 1923. All these activities served to make him a focus of nationalist and anti-Semitic attack at home, as a symbol of the alien forces that were said to be keeping Germany from attaining its proper position in the world.
As the 20s passed, Einstein spent his time trying to generalize his theories still further by formulating a unified field theory that would include electromagnetism as well as gravitation, developing one branch of quantum statistical mechanics, and arguing against the “Copenhagen interpretation” of quantum mechanics. Yet while he was hailed in the outside world, his position in Germany was never secure, and by the early 30's Einstein had arranged to spend part of his working time outside Germany. He was to pass a segment of each year in residence at Oxford, a segment in Pasadena at the California Institute of Technology, and the rest in Berlin. He was at Caltech in 1933, when Hitler came to power. He wasted no time in publicly announcing that he would not return to Germany. After short stays in Belgium and England, he accepted a position at the newly established Institute for Advanced Study in Princeton, his taste for Caltech having soured as a result of disputes over remuneration4 and opposition to his presence voiced by conservative alumni and contributors who disapproved of his radical reputation.
In Princeton, Einstein settled down. Becoming a widower in 1936, he continued his search for a unified field theory, and made his last notable contributions to the debate over quantum mechanics. Having abandoned pacifism with Hitler's accession to power, he urged collective action against Nazi Germany, and used whatever personal influence he had to help refugees from Europe reestablish themselves.
In the 30's, nuclear physics had advanced by leaps and bounds, its study being mainly carried out by physicists a generation younger than Einstein. In 1939, the uranium nucleus had been split in Berlin, and physicists in Western Europe became aware of the possibility of producing an atom bomb. News of this possibility spread rapidly via refugee scientists to the U.S., where two such refugees, Leo Szilard and Eugene Wigner, informed Einstein of the potential import of the new developments. They persuaded him to write a letter to President Roosevelt drawing his attention to the possibility that a bomb could be built, and pointing out that the Germans were probably also aware of the possibility. This letter led to the establishment of a committee to study the prospects of building a bomb; progress was slow and Einstein later wrote another letter to urge more speed. Apart from this early advocacy, Einstein played no part in the Manhattan Project itself, partly because of a concern for security on the part of leading figures in the project who were unaware of his role in initiating it. However, he did serve as a technical consultant to the navy on problems involving conventional explosives.
After the war, with the menace of Nazism removed from the scene, Einstein returned to his traditional concern with the problem of avoiding war, now buttressing his arguments by appealing to the dangers inherent in the existence of nuclear weapons. Though his health was failing, he continued his search for a unified field theory while remaining a public figure. After Weizmann's death in 1952, he was offered the presidency of Israel, but declined, citing his temperamental unsuitability and physical frailty. His final public activities included preparing a statement on Israel's seventh anniversary, and signing a declaration, originated by Bertrand Russell, which led to the establishment of the Pugwash movement, dedicated to the problems of world peace and limiting nuclear weapons.
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II
A measure of the greatness of Einstein's achievements is that they cannot be described without first summarizing the history of physics since Sir Isaac Newton. Newton's law of motion explained how, given a knowledge of the forces acting on a body and its initial position and velocity, its future motion could be predicted completely; his law of universal gravitation described the fundamental force acting in the universe. For the next two hundred years, one of the major tasks of physicists and mathematicians was applying Newton's laws to ever more complicated situations, and reformulating these laws in ever more abstract fashion.
Gravitation was not the only force which was known to exist, however, and by the middle of the 19th century the second great triumph of classical physics had been achieved by Maxwell, who was able to formulate a set of equations which unified the laws of electricity and magnetism previously discovered by Faraday, Ampère, and other experimenters. The most outstanding results of Maxwell's theory were the identification of light as a form of electromagnetic radiation, and the prediction that other forms of this radiation should exist, a prediction whose fruition gave the world radio and television.
But Newton's mechanics and Maxwell's electromagnetism were not enough by themselves to explain the behavior of matter, because the sheer magnitude of the number of molecules present in even the smallest macroscopic quantity of matter made it impossible to perform the calculations necessary to solve the equations involved. Statistical mechanics was developed in the last third of the 19th century, most notably by Boltzmann and Gibbs, to make this application possible and to provide a fundamental explanation of the laws of thermodynamics, which had been empirically discovered by engineers. With the synthesis of mechanics, electromagnetism, and statistical mechanics, physicists were able to set about their program of explaining the workings of the physical world.
The heyday of classical physics was short. By the end of the 19th century, a number of problems were seen which defied solution in terms of an otherwise eminently successful theory. By the time these problems had been solved, about the middle of the 1920's, physics had passed through two revolutions, and the Newtonian view of the world had been superseded. The first revolution was brought about almost singlehandedly by Einstein, with his special and general theories of relativity; by rejecting those of Newton's axioms which asserted the absolute nature of time and space, he was able to reconcile contradictions between classical mechanics and electromagnetism which had become inescapable, and thereby to bring a new unity to the description of the physical world. The second revolution, made necessary by the failure of classical theory to account for many phenomena occurring on an atomic scale, culminated in the mid-1920's when a new picture of the world emerged with the development of quantum mechanics—a development that was helped immeasurably by the major contributions made by Einstein to the old quantum theory which preceded it.
According to traditional Newtonian ideas, two people moving with respect to each other, who measure the velocity of the same object, should obtain different results, as indeed they do in general. Experiment shows, however, that no matter how fast we are moving, we always find the same value for the speed of light. It is therefore clear that we cannot rely on common sense to tell us how to relate measurements taken by observers in relative motion. Others (notably Poincare and Lorentz) had realized this before Einstein (though unknown to him); what Einstein did was to show that the constancy of the speed of light with respect to differently moving observers (which had previously only been looked at from the point of view of electromagnetic theory) was really quite consistent with a fundamental concept of Newtonian mechanics, that observers in constant relative motion with respect to each other observe the same laws of motion.5 As a natural result of this perception, the special theory of relativity follows logically, with all its consequences. These consequences include the paradoxical fact that identical clocks run at different rates when they are moving at different speeds.6 Perhaps the most startling result, however, is that mass is a form of energy.
No one before Einstein had been able to follow through the internal logic of the relationship between the laws of mechanics and electromagnetism which produced the theory of special relativity, although it is widely believed that the time was ripe for the theory to emerge then, even had Einstein not been the one responsible. The same is not true of his further extension of the logic. Driven by his compulsion to unify the laws of nature, which had already led him to show that the linkage of space and time implied a relation between mass and energy, he postulated that the very structure of space-time was connected with the presence of matter and energy. His theory of general relativity presented the mathematical expression of this reduction of gravitation to geometry. Using this theory he was able not only to account for an astronomical effect (the anomalous advance of the perihelion of Mercury) which Newton's gravitational theory could not explain, but also to predict that light should follow a curved path in a gravitational field, a prediction subsequently verified by observation. Tests of this prediction of the general theory are made every time a solar eclipse occurs, when it is possible to see that stars whose light passes close to the sun appear in positions slightly different from where we know they are.
The theory of special relativity removed the inconsistency between the laws of mechanics and electro-magnetism, so it was no longer a puzzle why the speed of light appeared the same to observers moving at different speeds. But there were other discrepancies between the laws of classical physics and the observed laws of nature. In 1901, Planck had managed to describe the distribution of radiation emitted by a hot object7 by an equation which could not be derived by classical arguments, by postulating that radiation could be emitted and absorbed only in fixed amounts (“quanta”). This hypothesis was generally ignored because of its radical nature, until Einstein in 1905 made an even more radical assumption, that electromagnetic radiation itself existed in the form of quanta (which was completely in contradiction to the well-established picture of radiation as a wave phenomenon) and used it to explain another puzzling phenomenon, the photoelectric effect.8 In the same year, Einstein demonstrated his mastery of statistical mechanics by deriving a quantitative description of Brownian motion.9 and two years later he combined statistical mechanics and the quantum concept to describe the internal thermal vibration of solids, and to explain more anomalous results inexplicable by classical arguments.
In 1913, Niels Bohr gave the old quantum theory its greatest triumph when he used it to explain the structure of the spectrum of light emitted by the hydrogen atoms. However, the foundations of the theory were unsatisfactory, and further progress with it was limited. In the early 20's, Louis de Broglie suggested that just as light, which under most circumstances behaves like a wave, can sometimes behave like a particle, so matter might have a wave-length aspect. The new theory of quantum mechanics, developed independently in two different forms by Schrö-dinger and Heisenberg, showed that this was indeed the case, and thus the old Newtonian equation of motion was replaced by an equation which predicts not the exact future position and velocity of a particle, but only its probability of being in a certain state, which cannot be specified to arbitrary accuracy in both position and velocity.10 It is impossible in principle to know both the position and velocity to an accuracy better than that given by Heisenberg's uncertainty principle, according to quantum mechanics. Only by performing a measurement on a system are we able to see what state it is in, and as long as the measurement has not been performed, we can only talk about its relative probability of being in various states.
The dominant school of thought in modern physics accepts this “Copenhagen interpretation” which was developed most fully by Bohr and his followers and which tells us that we can never know more about a physical system than the uncertainty principle allows us. Einstein objected vigorously to this interpretation, maintaining that it must be possible to describe reality in strictly deterministic terms, and that the probabilistic language of quantum mechanics was merely evidence of our inability as yet to obtain an adequate description. The incredible physical insight which had enabled him to formulate his theories of relativity was accompanied by a self-confidence that led him on several occasions to ignore experiments which seemed to contradict his theories. Just as it was the experimental results which had finally been proved false, he remained confident that the claims of the ultimate truth of quantum mechanics would eventually be rejected. He stated his intuitive conviction aphoristically: “God does not play dice with the world.”
The long debate between Bohr and Einstein, notable for its profundity, ingenuity, and the mutual respect of the two opponents, was probably the most important contribution in this century to the long-standing philosophical puzzle of the nature of reality. Einstein threw out suggestion after suggestion of thought experiments which would disprove the uncertainty principle, and Bohr managed each time to find some factor Einstein had neglected. Bohr tried to appeal to Einstein's philosophical side by suggesting a principle of complementarity, whereby the alternative description of nature in terms of concrete particle and diffuse wave involved such non-scientific dual concepts as justice and mercy, but Einstein remained unmoved.
The reason that Bohr's interpretation generally prevailed is that quantum mechanics is an amazingly successful theory, and enables us to describe phenomena taking place in environments as different as stars, magnets, and transistor radios. Physicists do not spend too much time justifying themselves philosophically (a well-known joke is that they spend three days of the week considering the electron as a particle, three days considering it as a wave, while the Sabbath is devoted to sermons on duality) and until someone comes up with a better theory, quantum mechanics gives us the best picture we have of the physical world.
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III
Einstein lived for three-quarters of a century, and his own thought was one of the dominating intellectual influences for two-thirds of that time. Any biography of the man must be selective in what it chooses to say about his work and his influence. In the case of books as short as those of Bernstein and Hoffman, the biographer must concentrate on those aspects he considers central. In both of these books, an account in simple and non-technical language of Einstein's contributions to physics is accompanied by a description of his character, which combined nobility and simplicity with a humble awareness of his limited place in a universe of complex and beautiful construction which his own mind had sought to explain. The description is accomplished using Einstein's own words, the words of those who knew him, and by anecdotes. In Hoffman's case, we are also given a number of photographs, showing Einstein at work, at play, alone, with his friends both famous and obscure, as well as a large number of memorabilia.
In a volume as long as that by Clark, the problems are greater. In general, a massive accumulation of detail might be expected to make us lose interest in the subject, unless the details are addressed to some major thesis; in Clark's case, the thesis he himself suggests in his foreword, that Einstein was “one of the greatest tragic figures of our time,” is hardly borne out by the account of the life which follows. In fact, the motivating influence of his book seems to be a reaction to what he sees as a tendency to hagiolatry in earlier biographies. As a result, while reaffirming his subject's greatness Clark tends to stress little-emphasized aspects of Einstein: his unreliability as a reporter of his own history (which was due mainly to his playful nature and delight in a good story), his ability to negotiate the most favorable working conditions for himself, and the like. Clark accentuates the ironies he perceives in Einstein's life: the dedicated scientist forced into the public spot-light; the pacifist who urges the building of the atomic bomb; the Zionist who believed in peaceful accommodation with the Arabs but finally acknowledged the necessity to fight. While there may be paradox here, it is hardly the stuff of tragedy.
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The unique position Einstein held insures that his biography tells us much about the world of physics in the 20th century, and casts much light on the social history of science. The exploration of Einstein's role in physics is such an awesome project that it has as yet only been attempted piecemeal, most notably in the collection of essays assembled twenty-five years ago by Paul Arthur Schilpp, and it is hardly fair to expect it in a general biography. What we could reasonably ask from a biography of Einstein, however, is a more convincing psychological portrait than that given by Clark. One topic in particular where we could wish for more insight is Einstein's relationship to Jewishness and Judaism.
Hoffman points out that as a child Einstein went through a religious stage, when he was upset at his parents' non-observance, followed by his discovery of the world of science, when he became violently anti-religious. Once past adolescence, he adopted a more tolerant attitude to the foibles of others. Both Hoffman and Bernstein make his later Zionism seem a natural reaction to anti-Semitism. From the more detailed account given by Clark, a somewhat more complex picture emerges.
While it may now, thirty years after Auschwitz and twenty-five after the establishment of a Jewish state, seem that Zionism was an inevitable choice for Einstein, the picture looked quite different immediately after World War I. The non-inevitability of Zionism is more easily seen by looking at the paths chosen by contemporaries of Einstein, such as that of the chemist Fritz Haber, whose process for the synthesization of ammonia had been vital to Germany's war effort, and who was an ardent German patriot and an assimilationist who had even been baptized together with his family. Haber was to be forced out of Germany when the Nazis came to power and to die in Switzerland, on his way to take up a position in the Sieff (later Weizmann) Institute in Palestine. An even more dramatic contrast was Paul Ehrenfest, who was one of Einstein's closest friends. The Viennese-born Ehrenfest had, like Einstein, made significant contributions to statistical mechanics and quantum theory. Married, like Einstein, to a non-Jewish wife who was a physicist, Ehrenfest was offered the chair in Prague vacated by Einstein in 1912, but was unable to take it because he insisted on proclaiming his atheism. Under the same circumstances, Einstein had bowed to Emperor Franz Josef's rule that all professors must affirm some religion, and had declared himself a Jew.
If we want to know why Einstein voluntarily identified himself as a Jew rather than waiting for external circumstances to force the identification; we need greater insight than any of our authors has given us. Clark devotes some attention to Einstein's stay in Prague. The city was polarized between Germans and Czechs, and so Einstein, with his immersion in a German cultural world but his intense distaste for German nationalism, found himself compelled to associate almost exclusively with the Jewish community. He could also not fail to be impressed by the inescapable atmosphere of a rich Jewish past which pervaded the city.
While the Prague atmosphere may have begun to awaken dormant instincts in Einstein which were eventually to bring him to Zionism some years later, a more fundamental cause may well have been his deep-rooted attachment to his family. Very soon after his father's death in 1902, which he described as the deepest shock he had ever experienced, he married his first wife; his father had disapproved of the relationship. It was during his mother's terminal illness after World War I that he was divorced, married his second wife, who was the daughter of his mother's sister and his father's cousin, and became a convinced Zionist. He subsequently referred to his relationship to the Jewish people as “my strongest human bond.” It is difficult to believe that an attachment described in such a fashion could be created by anti-Semitism, as he himself believed.
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It is of interest in this connection to pay some attention to what Clark calls Einstein's “cosmic religion,” his strong philosophical conviction of a world with a mysterious underlying order which he expressed in religious terms. This attitude was held even more strongly by Newton, the only figure in the history of physics with whom Einstein may really be compared. Bernstein illustrates the mysticism of Newton's thought by quoting from an essay by John Maynard Keynes who called him “the last of the Babylonians and Sumerians, the last great mind which looked out on the visible and intellectual world with the same eyes as those who began to build our intellectual inheritance rather less than 10,000 years ago.” Einstein, in turn, compared his own world outlook with that of Spinoza, the philosopher generally considered the first modern thinker, the outsider, a type Isaac Deutscher has called the non-Jewish Jew. Einstein spoke of his personal religious belief as a belief in “Spinoza's God, who reveals himself in the orderly harmony of what exists, not in a God who concerns himself with the fates and actions of human beings.”
The Midrash contains many accounts of how the patriarch Abraham came to monotheism by a rational investigation of natural and astronomical phenomena. But while Abraham was the first Jew, he was not the first monotheist. The rabbis relate how the secrets of the universe were known to a select few even before Abraham, whose distinction lay in his assertion that monotheism eventually implied a vital concern with the “fates and actions of human beings.” The best known of the earlier monotheists, who ascribed to the Deity power only over the heavens, a concern with “the orderly harmony of what exists,” was Noah's son Shem, and Shem, of course, was the ancestor of the Babylonians and Sumerians.
1 Einstein: The Life and Times, World, 718 pp., $15.00.
2 Einstein, Viking, 242 pp., $6.95.
3 Albert Einstein: Creator and Rebel, Viking, 272 pp., $8.95.
4 Still, he had to be persuaded to accept a salary of $15,000 at the Institute rather than the $3,000 he himself suggested.
5 According to Newton, the acceleration of a body is proportional to the force acting on it; the acceleration appears the same to all observers moving with constant velocity relative to each other.
6 Because of the huge value of the speed of light (18,000 miles per second) the relativistic slowing of clocks is not noticed under everyday circumstances.
7 Actually, a so-called “black body,” an idealization which can be modeled theoretically and well approximated experimentally.
8 When light shines on certain metals, electrons are emitted. If the frequency of the light is changed, the energy of these “photo-electrons” is changed also, but not the number emitted. This cannot be explained if one assumes that light acts as a wave.
9 Microscopic particles suspended in a liquid undergo a rapid jerky motion as they are buffeted by the sub-microscopic molecules of the liquid.
10 The velocity of a particle (or, more precisely, its momentum) is given by the wavelength of the wave. A pure wave, not made up of a mixture of wavelengths, must extend forever, and so the particle's position is completely uncertain if its velocity is precisely defined. Similarly, to obtain a highly localized disturbance, we must superimpose a large number of waves, so that the better defined the position, the less accurately we know the velocity. Because the number (Planck's constant. denoted by h) which tells us the magnitude of the uncertainty is so small, the uncertainty principle is useful only in dealing with submicroscopic systems, and in everyday life we are able to get along happily with Newtonian mechanics.
