The Most Influencial People in the World: JOHANNES KEPLER (1571-1630)

Johannes Kepler, the discoverer of the laws of planetary motion, was born in 1571, in the town of Weil der Stadt, Germany. That was just twenty-eight years after the publication of De revolution bus orbit coelestium, the great book in which Copernicus set forth his theory that the planets revolved about the sun rather than the earth. Kepler studied at the University of Tubingen, obtaining a bachelor’s degree in 1588 and a master’s degree three years later. Most scientists of the day refused to accept the heliocentric theory of Copernicus; but while Kepler was at Tubingen he heard the heliocentric hypothesis intelligently ex-pounded, and he soon came to believe in it.

After leaving Tubingen, Kepler was for several years a professor at the Academy in Graz. While there he wrote his first book on astronomy (1596). Although the theory which Kepler propounded in that book turned out to be completely incorrect, the book so clearly revealed Kepler’s mathematical ability and originality of thought, that the great astronomer Tycho Brahe invited him to become his assistant at his observatory near Prague.

Kepler accepted the offer and joined Tycho in January 1600. Tycho died the following year; however, Kepler had made such a favorable impression in the intervening months that the Holy Roman Emperor, Rudolph II, promptly appointed him to succeed Tycho as Imperial Mathematician. Kepler was to hold that post for the rest of his life.

As the successor to Tycho Brahe, Kepler inherited the voluminous records of the careful observations of the planets that Tycho had made over many years. Since Tycho, who was the last great astronomer before the invention of the telescope, was also the most careful and accurate observer the world had yet seen, those records were invaluable. Kepler believed that a careful mathematical analysis of Tycho’s records would enable him to determine conclusively which theory of planetary motion was correct: the heliocentric theory of Copernicus; the older, geocentric theory of Ptolemy; or perhaps a third theory propounded by Tycho himself. However, after years of painstaking numerical calculation, Kepler found to his dismay that Tycho’s observations were not consistent with any of those theories!

Eventually, Kepler realized what the problem was: he, like Tycho Brahe and Copernicus, and like all the classical astronomers, had assumed that planetary orbits consisted of circles, or combinations of circles. In fact, however, planetary orbits are not circular, but rather elliptical.

Even after discovering the basic solution, Kepler still had to spend many months in complicated and tedious calculations to make sure that his theory satisfied in 1609, presented his first two laws of planetary motion. The first law states that each planet moves around the sun in an elliptical orbit, with the sun at one focus. The second law states that a planet moves more quickly when it is closer to the sun; the speed of a planet varies in such a way that the line joining the planet and the sun sweeps out equal areas in equal lengths of time. Ten years later, Kepler published his third law: the more distant a planet is from the sun, the longer it takes to complete its revolution, with the square of the period of revolution being proportional to the cube of the distance from the sun.

Kepler’s laws, by providing a basically complete and correct description of the motions of the planets around the sun, solved one of the basic problems of astronomy, one whose solution had eluded even such geniuses as Copernicus and Galileo. Of course, Kepler had not explained why the planets moved in the orbits they do; that problem was solved later in the century by Isaac Newton. But Kepler’s laws were a vital prelude to Newton’s grand synthesis. (“If I have seen further than other men,” Newton once said, “it is because I stood on the shoulders of giants.” Doubtless, Kepler was one of the giants to whom he was referring.)

Kepler’s contribution to astronomy is almost comparable to that of Copernicus. Indeed, in some ways Kepler’s achievement is even more impressive. He was more original, and the mathematical techniques were not as well developed in those times as they are today, and there were no calculating machines to ease Kepler’s computational tasks.

In view of the importance of Kepler’s achievements, it is surprising that his results were almost ignored at first, even by so great a scientist as Galileo. (Galileo’s neglect of Kepler’s laws is particularly surprising since the two men had corresponded with each other, and since Kepler’s results would have helped Galileo to refute the Ptolemaic theory.) But if others were slow to appreciate the magnitude of his achievement, Kepler understood it himself. In a burst of exultation he wrote:

I give myself up to divine ecstasy…My book is written. It will be read either by my contemporaries or by posterity—I care not which. It may well wait a hundred years for a reader, as God has waited 6,000 years for someone to understand his work.

Gradually though, over the course of a few decades, the significance of Kepler’s laws became apparent to the scientific world. In fact, later in the century, a major argument in favor of Newton’s theories was that Kepler’s laws could be deduced from them. Conversely, given Newton’s laws of motion, it is possible to rigorously deduce Newton’s law of gravitation from Kepler’s laws. To do so, however, would require more advanced mathematical techniques than were available to Kepler. Even without such techniques, Kepler was perspicacious enough to suggest that planetary motions were controlled by forces emanating from the sun.

In addition to his laws of planetary motion, Kepler made various minor contributions to astronomy. He also made significant contributions to the theory of optics. His later years, unfortunately, were clouded by personal problems. Germany was descending into the chaos of the Thirty Years’ War, and it was a rare individual that could escape serious difficulties.

One problem he had was in collecting his salary. The Holy Roman emperors had been slow payers even in comparatively good times. In the chaos of war, Kepler’s salary fell far in arrears. Since Kepler had married twice and had twelve children, such financial difficulties were serious indeed. Another problem concerned his mother, who in 1620 was arrested as a witch. Kepler spent much time in an eventually successful attempt to have her released without being tortured.

Kepler died in 1630, in Regensburg, Bavaria. In the turmoil of the Thirty Years’ War, his grave was soon destroyed. But his laws of planetary motion have proven a more enduring memorial than any made of stone.

The Most Influencial People in the World: ENRICO FERMI (1901-1954)

Enrico Fermi, the man who designed the first nuclear reactor, was born in 1901, in Rome, Italy. He was a remarkably brilliant student and received a Ph.D. in physics from the University of Pisa before he was twenty-one years old. By the time he was twenty-sic, he was a full professor at the University of Rome. By then he had already published his first major paper, one which concerned an abstruse branch of physics called quantum statistics. In that paper, Fermi developed the statistical theory used to describe the behavior of large aggregations of particles of the type today referred to as fermions. Since electrons, protons, and neutrons—the three “building blocks” of which ordinary matter is composed—are all fermions, Fermi’s theory is of considerable scientific importance. Fermi’s equations have enabled us to gain a better understanding of the nucleus of the atoms, of the behavior of degenerate matter (such as occurs in the interior of certain types of stars), and of the properties and behavior of metals—a topic of obvious practical utility.

In 1933, Fermi formulated a theory of beta decay (a type of radioactivity) which included the first quantitative discussion of the neutrino and of weak interactions, both important topics in present-day physics. Research of that kind, though not readily comprehensible by layman, established Fermi as one of the world’s leading physicists. However, Fermi’s most important accomplishments were yet to come.

In 1932, the British physicist James Chadwick had discovered a new subatomic particle, the neutron. Starting in 1934, Fermi proceeded to bombard most of the known chemical elements with neutrons. His experiments showed that many types of atoms were able to absorb neutrons, and that in many cases the atoms resulting from such a nuclear transformation were radioactive. One might have expected that it would be easier for a neutron to penetrate an atomic nucleus if the neutron were moving very rapidly. But Fermi’s experiments showed that the reverse was true, and that if fast neutrons were first slowed down by making them pass through paraffin or water, they could then be more readily absorbed by atoms. This discovery of Fermi’s has a very important application in the construction of nuclear reactors. The material which is used in reactors to slow down the neutrons is referred to as a moderator.

In 1938, Fermi’s important research on the absorption of neutrons resulted in his being awarded a Nobel Prize in physics. Meanwhile, however, he was having trouble in Italy. In the first place, Fermi’s wife was Jewish, and the Fascist government in Italy had promulgated a set of harshly anti-Semitic laws. In the second place, Fermi was strongly opposed to Fascism—a dangerous attitude under Mussolini’s dictatorship. In December 1938, when he went to Stockholm to accept his Nobel Prize, Fermi did not return to Italy. Instead, he went to New York, where Columbia University, delighted to add one of the world’s greatest scientists to its staff, had offered him a position. Fermi became a United States citizen in 1944.

In early 1939, it was reported by Lise Meitner, Otto Hahn, and Fritz Strassmann that the absorption of neutrons sometimes caused uranium atoms to fission. When that report came out, Fermi (like several other leading physicists) promptly realized that a fissioning uranium atom might release enough neutrons to start a chain reaction. Furthermore, Fermi (again like several others) soon foresaw the military potentialities of such a chain reaction. By March 1939, Fermi had contacted the United States navy and tried to interest them in the development of atomic weapons. However, it was not until several months later, after Albert Einstein had written a letter on the subject to President Roosevelt, that the United States government became interested in atomic energy.

Once the American government did become interested, the scientists’ first task was to construct a prototype atomic pile in order to see whether a self-sustaining chain reaction was indeed feasible. Since Enrico Fermi was the world’s leading authority on neutrons, and since he combined both experimental and theoretical talents, he was chosen to head the group attempting to construct the world’s first nuclear reactor. He worked first at Columbia University and then at the University of Chicago. It was in Chicago, on December 2, 1942, that the nuclear reactor which had been designed and constructed under Fermi’s supervision first went into successful operation. That was the true beginning of the atomic age, for that was the first time that mankind succeeded in setting off a nuclear chain reaction. Notice of the successful test was promptly sent back East with the cryptic but prophetic words,” The Italian navigator has entered the new world.” Following this successful test, it was decided to go ahead at full speed with the Manhattan Project. Fermi continued to play an important role in that project as a leading scientific advisor.

After the war, Fermi became a professor at the University of Chicago. He died in 1954. Fermi was married and had two children. Chemical element number 100, fermium, is named in his honor.

Fermi is an important figure for several reasons. In the first place, he was indisputably one of the greatest scientist of twentieth century, and one of the very few who was outstanding both as a theoretician and as an experimenter. Only a few of his most important scientific achievements have been described in this article, but Fermi actually wrote well over 250 scientific articles during his career.

In the second place, Fermi was a very important figure in the creation of the atomic bomb, though several other persons played equally important roles in that development.

Fermi’s chief importance, however, derives from the leading role he played in the invention of the nuclear reactor. That Fermi deserves the principal credit for that invention is quite clear. He first made major contributions to the underlying theory, and then actually supervised the design and construction of the first reactor.

Since, 1945, no atomic weapons have been used in warfare, but a large number of nuclear reactors have been built to generate energy for peaceful purposes. Reactors are likely to be an even more important source of energy in the future. Furthermore, some reactors are used to produce useful radioisotopes, with applications in medicine and in scientific research. Reactors are also—and more ominously—a source of plutonium, a substance which can be used to build atomic weapons. There are understandable fears that the nuclear reactor may pose great hazards to humanity, but nobody claims that it is an insignificant invention. For better or worse, Fermi’s work is likely to have a large influence on the world in the years to come.