Professor Einstein, Relativity, and Mt. Wilson

A FEW years ago scant attention was paid by the public in general to scientific work except to such as could be promptly commercialized. Scientific news was not popular news and the vast amount of research work which went on in the different fields of natural science was regarded with indifference or with the traditional suspicion that money was somehow being wasted. Realization of what the new physics and the new astronomy might mean to human life and thought came only slowly and doubtfully.

The marked change which has taken place of late in this attitude toward men of science and their mysterious pursuits is nowhere better illustrated than in the case of Professor Einstein. Although his name is now a household word, his original theories were put forth many years ago and for a time attracted the attention only of fellow workers in physical science. By slow degrees the public awoke to the fact that a revolution in the fundamental conceptions of science was in progress led by a genius comparable to Newton. Although but imperfectly realized, it is probably the philosophical necessity for a wider and more adequate view of the physical world that has unconsciously given the theory of relativity its tremendous hold on the public mind

There were two reasons for Professor Einstein's original visit to Pasadena. In the first place he wished to renew his acquaintance and discuss his work with a number of old friends at the California Institute of Technology, mostly mathematical physicists whom he had known in Europe. Secondly, the observational contributions of the Mount Wilson Observatory to the theory of relativity and to the exploration of outer space were naturally of extreme interest to him, since they had a direct bearing upon his own investigations. The operation of a modern observatory whose aim may be defined as the attempt to join the physics of the laboratory to the physics of the stars is fascinating even to the layman. To Professor Einstein it offered a more or less novel experience since he is professionally a theoretical physicist and has had little contact with the machinery of present day astronomy. He therefore had the satisfaction so dear to the scientist of watching the methods by which his own predictions were checked against actual observations.

Professor and Mrs. Einstein arrived in Pasadena at about the time of the annual Tournament of Roses and duly settled themselves in a house in the southern part of the city. At once there arose a situation which called for the exercise of all the patience and sense of humor of which any man might be possessed. He was besieged on all sides by reporters, publicity bureaus, photographers, potential hosts and hostesses and lion hunters of every description. His appearance upon the street was the signal for the arrival of crowds of small boys, invitations to all sorts of public and private affairs were poured upon him and he was even consulted as to his special tastes by caterers and provision stores. Through all this he moved with a quiet dignity and a quizzical smile which endeared him to everyone. As one observer ex- pressed it, "If lion hunting must occur, it is seldom that the lion acts with such universal approbation as he has in the present case."

This extraordinary interest in a man whose work is quite beyond the comprehension of the average layman is in itself a very interesting phenomenon. Professor Einstein received much publicity but publicity is only successful in proportion to the public demand. The explanation seems to lie in a genuine appreciation and admiration for the great products of human thought and a racial pride in what the mind of man can bring forth. Almost mystical in quality, it is a strong and active force which distinguishes unfailingly the great figures in the intellectual life of the world.

The first few weeks of his stay in Pasadena were spent by Professor Einstein in discussions with physicists and astronomers at the California Institute and the Observatory, and in familiarizing himself with the observational work in progress. Himself an experimentalist in earlier years, he showed an extraordinary ability to grasp the essential features of a complicated piece of apparatus in the laboratory, and more than one ingenious experiment bearing on processes within the atom has been undertaken on his advice and with his suggestive criticism.

II A BOUT the middle of February the first trip up the winding road to Mount Wilson was undertaken. Professor Einstein was accompanied by Dr. Mayer, the celebrated Vienna mathematician, and several members of the Observatory staff. On arrival the party went to the Monastery, the name applied to the Observatory living quarters, where tentative plans were made for the day. The first visit was to the 150foot tower telescope, which is used exclusively for the study of the sun, and where much of the work confirmatory of the third prediction of the theory of relativity has been carried on during recent years. After examining the 17-inch image of the sun formed by this telescope Professor Einstein calmly climbed into an open steel box, operated by cables on the side of the tower and somewhat resembling a miniature elevator, and was carried to the top. Here he saw the mechanism of the telescope in operation, admired the view of nearly the whole of Southern California and was duly photographed, a strong breeze giving especial prominence to the well-known and most characteristic Einstein hair.

After luncheon and a short visit at the Monastery in which the Observatory cat Jupiter figured prominently, the party visited the 60-inch and 100-inch telescope building and domes. Here Professor Einstein displayed an extraordinary interest in the details of mechanism and operation, climbing over the instruments and showing an understanding of the purpose and use of every appliance remarkable even in a trained physicist. This was his first view of a very large modern reflecting telescope and his appreciation of the problems which enter into the construction and operation of these great instruments of research was surprisingly quick and intelligent.

Following various encounters with representatives of the press and photographers and after an early dinner the party returned to the 100-inch telescope. With occasional interruptions by clouds but under reasonably good conditions Professor Einstein was able to make observations of Jupiter, Mars, Eros, several ring and spiral nebulae and the faint companion of the bright star Sirius. This last object was of particular interest to him because photographs of its spectrum with the 100-inch telescope had confirmed one of his predictions from the theory of relativity and had led to remarkable inferences regarding the density of matter as it may exist among the stars. He remained in the dome until after one o'clock, finally retiring under protest and with the stipulation that he must be called in time to see the sunrise. The party returned to Pasadena at about ten o'clock on the same morning.

A second very interesting expedition made by Professor Einstein during his stay in Pasadena was to the apparatus with which Dr. Michelson was measuring the velocity of light. In a level field about forty miles south of Pasadena a straight steel pipe three feet in diameter and one mile in length had been set up with its joints carefully sealed so that the air could be pumped out and the pressure maintained at a few thousandths of its normal value. At either end of the pipe was a system of mirrors by which light could be reflected back and forth through the pipe as many times as desired. Usually a total distance of eight or ten miles was used. The most interesting part of the instrument was the small rotating mirror, a block of glass with 32 sides carefully polished and figured so that the angles of all the faces were accurate to about one part in a million. The faces were silvered and the mirror was mounted to rotate around a vertical axis at very high speed, being driven by a blast of compressed air striking on small vanes. A brilliant source of light was focused on one of the faces of the mirror and reflected by it into the interior of the pipe line where the light passed forward and backward by multiple reflections. The problem was to adjust the speed of the mirror so that the light after travelling over its long path would fall on the face of the mirror adjoining that by which it was reflected originally. That is, the mirror should rotate one thirtysecond of its circumference while light travels eight or ten miles. Since the velocity of light is about one hundred and eighty-six thousand miles a second a simple computation shows that the mirror must rotate at a speed of about 730 revolutions a second for a lightpath of eight miles, and 580 revolutions for a path of ten miles. The remarkably ingenious methods developed by Dr. Michelson for measuring with high accuracy the speed of rotation of the mirror, the problem of precision timing of measurement of the optical image and the length of light-path all form interesting stories in themselves. The final result is an accuracy approaching one part in two hundred thousand, or about one mile in the required velocity.

The velocity of light is one of the most fundamental constants of nature and according to the theory of relativity is the limiting velocity in the physical world. Naturally Professor Einstein's reaction to this intricate and spectacular investigation was immediate and profound. His visit was made on a dark winter evening when the glare of the powerful arc lamp, the shriek of the high-speed mirror and the long length of pipe stretching out to be lost in the darkness combined to lend an unusual air of mystery to the lonely place in which these two great scientists had come together to discuss their work. Dr. Michelson's death occurred about two months later so that this meeting proved to be the last between the American master of experimental physics and the famous European mathematician.

III THE chief interests of Professor Einstein as related to the work of the Mount Wilson Observatory naturally centered about two types of observations, those bearing on the astronomical evidences for the theory of relativity, and those dealing with the exploration of space and the nature of the universe. The fundamental contribution of relativity to physical science is the generalization it has introduced into conceptions of time and space and its elimination of any selected and absolute system of reference with peculiar properties of its own. Time and space are not fixed invariable entities but express relations between an observer and the thing observed. If the time standard of one world makes two events simultaneous, the time standard of some other world in motion with reference to the first would place a distinct interval between them. Similarly with measures of length. A transfer to another world changes both systems of measures, the change in time being bound up with the change in distance. As a result we have to have recourse to a union of the two, what may be called space-time. As the well-known Dutch astronomer Professor de Sitter has stated:

"In classical mechanics and physics space and time play no other part than as a sort of background on which the physical reality is projected, or at the utmost a neutral framework by which it is supported. . . . The theory of relativity brought the insight that space and time are not merely the stage on which the piece is produced, but are themselves actors playing an essential part in the plot. The relations between space, time, matter and energy are determined by the equations of (mathematical) theory, and consequently we can only admit such kinds of space as are consistent with these equations."

Since observers on the earth never move very rapidly with reference to each other and are subject to the same influences of gravitation their time and distance measurements agree very closely. It is only when relative motions become very large or we deal with great masses such as the sun or stars that the effects predicted by the theory of relativity become appreciable. Three such predictions have been made which can be tested by observation, the motion of the planet Mercury, the bending of the rays of light from stars as they pass the sun, and a systematic displacement of the lines in the spectrum of the sun and other stars of great mass. In every case observations have confirmed the predicted numerical values and the theory has met the test not only of logical and mathematical reasoning but of crucial physical examination. The laws of nature are valid for every observer without regard to the particular physical conditions surrounding him.

IV A FUNDAMENTAL purpose of the investigations both of physicists and astronomers is a better understanding of the universe, using the word in its widest sense. During the past few years it has been necessary to revise our estimates of the size of this comprehensive universe and the revisions have all been upward. Our own system of stars, numbering many billions of suns and extending outward tens of thousands of light-years into space, is but one of an immense number of similar systems, many of them removed to an almost inconceivable distance. The nebulae beyond the boundaries of the Milky Way are undoubtedly great systems of stars, island universes dotted throughout the depths of space. The nearest of them and the only one visible to the naked eye is the Great Nebula in Andromeda which is about one million light-years away, and is seen by light which left it probably before man existed on the earth. The limit of observation for the 100-inch telescope on Mount Wilson is about three hundred million light-years. An examination of these systems between the limits of one and three hundred million light-years shows that they are fairly uniformly distributed and that there is no appreciable falling off in their number as the search is carried farther and farther into space. The study of these objects affords our only observational clue to physical conditions the outer portions of the universe.

If the light of these faint nebulae is analyzed with the spectroscope we find immediate evidence of the existence in the stars composing them of the same elements which are familiar to us upon the earth, a striking illustration of the uniformity of nature. The spectral lines of iron, calcium, hydrogen and many other elements are as clear and definite in the light of these inconceivably remote systems of stars as in that of our own sun. But there is another very important discovery which has resulted from this analysis. This is the systematic displacement of the spectral lines toward the red end of the spectrum, the "red-shift" as it has come to be known. If a star is approaching us more light-waves of a definite length will be encountered by us in a second than if the distance were not changing. So the observed frequency of the light-vibrations will be slightly greater than its normal value, or the wave-length slightly less. Hence the spectral lines will be shifted in the direction of shorter wave-length or toward the violet end of the spectrum. The converse is true if the star is receding from us, and the lines are shifted toward the red. The displacements are small since the amount depends upon the ratio of the velocity of the star to the enormously high velocity of light, but they are well measurable and the motions toward or away from us of thousands of stars in our own system are known with a high degree of accuracy.

An examination of the spectra of the distant nebulae shows the remarkable fact that almost without exception the spectral lines are displaced toward the red and by amounts far beyond any which we find among the stars of our own system. Interpreted as motion, and we know of no other adequate explanation for such displacements of spectral lines, these red-shifts indicate that the distant stellar systems are moving away from us at tremendous rates of speed. Further examination shows that the farther off these systems are the faster they are receding, the relation being nearly a linear one. For an increase in distance of a million light-years there is an increase in the speed of recession of about 100 miles a second. Recently the faintest and most distant nebula yet observed with the spectroscope at Mount Wilson was found to be going away from us at the rate of 15,000 miles a second. Its distance is estimated at 135 million light-years.

V THE conclusion that these red-shifts represent real motions of recession is in harmony with the general equations of relativity and leads to the view of an expanding universe, a theory at least provisionally accepted by most of the leaders in this field of research. This universe, however, is not static and in equilibrium but its radius changes with the time. We may compare our systems of stars, as Professor de Sitter has done, to specks of dust on the surface of a toy balloon. As the balloon is blown up more and more the distances between these specks increases in proportion to the radius of the balloon, and each will ascribe to all the others a velocity of recession proportional to the distance. When this expansion began in the case of the universe is still uncertain but it cannot have been more than a few billion years ago, a time rather short for the evolution of stars and stellar systems. There are many questions connected with this new and difficult but fascinating subject which must await for an answer the accumulation and refinement of observations, and the completion of instruments capable of penetrating still farther into the outer regions of space.

Professor Einstein's interest in these great problems of the physical universe has been profound and he has devoted to their consideration the finest resources of his extraordinary mathematical talents. But this is only one of his principal activities during his second relatively peaceful visit to Pasadena. The problem of a unified field theory, an attempt to bring into complete harmony the general equations of gravitational and electromagnetic fields, is also engaging his attention. At present he is steering his way through what may be defined as mathematical five-dimensional space and there we may leave our kindly mariner in the full assurance that the harbor is not far distant.

PROFESSOR EINSTEIN Photographed at the top of the 150-foot tower telescope at Mt. Wilson Observatory, of which Dr. Adams '98 is the Director

NOTED ASTRONOMERS (Left to right) Dr. Walter S. Adams, Sir James Jeans, and Edwin P. Hubble on Mount Wilson

ON MT. WILSON Professor Einstein, Dr. Walter S. Adams, Dr. W. W. Campbell, President Emeritus of the University of California

AIRPLANE VIEW OF THE MOUNT WILSON OBSERVATORY At Pasadena, California. The observatory was established and is maintained by the Carnegie Institution of Washington, Dr. Walter S. Adams '98 has directed the work of the observatory since 1923