Chapter 15 Alone on the Mountain
George Ellery Hale was the director of the Mount Wilson Observatory, located high in the San Gabriel Mountains near Pasadena, California. Hale, a leading American astronomer, was responsible for the construction in 1917 of the 100-inch Hooker telescope. Michelson was one of its earliest users; and in 1919, he fitted it out with an auxiliary optical system and used interferometry to make the first measurement of a star’s diameter.43 The star Betelgeuse turned out to be about as big as our entire solar system! Mount Wilson was at the center of American observational astronomy, and Hale and his colleagues were keenly interested in the role of astronomy in testing Dr. Einstein’s relativity.
Hale’s own principal interest was the study of the sun. He built a solar observatory and developed a device he called a spectro-heliograph with which he could photograph lines of the solar spectrum. His goal was to understand the environment, composition, and movements of atoms in the chaotic solar atmosphere. Hale was the first to detect the strong magnetic fields associated with storms on the sun that result in sun spots.
From 1915 on, studies of the solar spectrum related to more than just solar weather reports: they could possibly provide a second test of general relativity. In addition to predicting the bending of light passing near the sun, Einstein maintained that light coming from the sun, or even more so, light from a very dense star, would have to fight its way against gravity, losing some of its energy on the way. This would result in a “gravitational redshift,” and this too might be looked for by astronomers. Furthermore, Einstein proposed a third
43 Michelson and his collaborator,
Francis Pease, were the first to apply this technique. They blocked off the
main mirror and placed a twenty-foot-long beam in front of the telescope. The
beam carried two narrow slits and mirrors which redirected two pencils of
star-light into the telescope where they produced an interference pattern. The spacing
of the resulting fringes depended on the tiny angular spread of the light
coming from the star, and thus on the star’s diameter.
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astronomical test of general relativity: the precession of the orbit of Mercury. Planetary astronomers were able to use Newtonian physics to calculate the rate at which the inner planet’s orbit shifted with time, but their very precise measurements showed that the calculated rate was too small by a bit less than 1 percent. Einstein asserted that general relativity accounts for this difference.
In summary, there were four ways to test relativity :
1 look for ether-drift;
2 measure the tiny bending of starlight as it passes by the sun;
3 measure the tiny shifts in wavelengths of spectral lines in emissions from dense stars;
4 measure tiny changes in Mercury’s orbit.
Many, perhaps most, in the world’s physics community in 1920 considered Einstein’s relativity to be incomprehensible and counter-intuitive. They expected that the theory would be falsified. For two decades, testing relativity would be the number one challenge. Three of the four tests belonged to the realm of the astronomers, who tackled them with enthusiasm. The earlier ether-drift searches, in the opinion of many, had not been conclusive, either way.
In the spring of 1920, Miller contacted Hale with a proposal that he should come out to Mount Wilson and give the ether-drift experiment another try, this time at an elevation of 5700 feet.44 Surely that would reduce ether-drag—if there were such a thing. Hale had in fact been discussing a possible repetition of the experiment with both Michelson and the eighty-two-year-old Morley. Although each had serious doubts about the claims of a 6 to 10-kilometer-per-second drift, they agreed that it was worth another try. So in the summer of 1920, Hale wrote to Miller inviting him to set up his interferometer at the Mount Wilson complex.
Mount Wilson was not just a “higher hill”; it was the place
where the “action” was, where physics and astronomy were coming together to
achieve a better understanding of the universe. Hale was determined to create a
vital center for cutting-edge research at Pasadena, Caltech, and Mount Wilson.
He lured Robert Millikan from the University of Chicago to take over as
president of Caltech. (Millikan would later be awarded a Nobel Prize for
measuring the electron’s charge.)
44 This
exchange of letters is preserved among the G. E. Hale papers at the Archives of
the American Institute of Physics, courtesy Roberto Lalli
of the University of Milan.
In August, Miller and his wife took the train out to Oakland, California, on a previously planned trip to spend three weeks with his siblings and their families. They had left the family home in Ohio years earlier. Miller took advantage of his visit to the Bay Area to give a lecture at the University of California, Berkeley, describing his Sandy Hook artillery work. He then traveled south, on September 10, to visit Mount Wilson and to meet with Michelson, Hale, and Hale’s new young assistant, Edwin Hubble. They drove the ten miles up the breathtaking twists of the Mount Wilson Toll Road to check out the site proposed for a new ether-drift laboratory. Returning to Cleveland, Miller had to look into the logistics of moving the equipment and to identify sources of funds.
The road up Mount Wilson
The steel-based interferometer was shipped to California; and in March of 1921, Miller arrived to set it up. He was accompanied by his former Case student and invaluable assistant, Ralph Hovey. Hovey had been Miller’s right-hand man for over a decade in the sound analysis work. Another traveling companion was CSAS treasurer, Eckstein Case, who clearly had some financial interest in the endeavor. Eventually, Miller would receive additional funding from the Carnegie Institution for Science, which provided the funds for essentially all of the Mount Wilson Observatory. Not one to miss an opportunity to give a public lecture, Miller entertained audiences with his phonodeik sound demonstrations at Caltech, UCLA, and USC.
Within the month, the interferometer was installed on concrete piers in a tar paper and canvas tent, and Miller began accumulating data. Once again there were signs of an ether-drift, indicating an earth-ether relative speed of about 10 km/sec, but Miller decided that the setup had to be improved before making any public announcement. (Remember, extraneous effects of one part in a hundred million would invalidate the experiment.) To eliminate possible magnetostriction caused by motion of the interferometer through the earth’s magnetic field, the steel base was replaced by one made of concrete reinforced with brass. The steel base eventually proved to be more reliable and was restored for subsequent runs. In addition, construction of a new and more substantial enclosure was begun at another location on Mount Wilson, one better protected from wind and weather.
“Ether-house” on Mount Wilson
In May, Miller returned to Cleveland to close out the semester and participate in the 1921 graduation ceremonies. On that very weekend, Miller welcomed a surprise visitor, someone who had come to Case expressly to meet him and to discuss his work. His guest book, now part of the Library of Congress D. C. Miller Collection, contained one line in small, neat handwriting: “Albert Einstein Berlin (Haberlandstr. 5) 25 Mai 21.” The world-famous theorist was travelling with Chaim Weizmann, the future president of Israel, on a tour to raise money for the establishment of an independent Zionist state of Israel. At their meeting in Miller’s Rockefeller Hall, Einstein expressed admiration for the great effort Miller was putting into getting unambiguous results from the ether-drift experiment. It was in Einstein’s interest for someone, somewhere, to get the experiment done properly and presumably put an end to the ether idea once and for all. For starters, data should be collected at different times of the year. Miller’s German was excellent, thanks to his undergraduate studies at the Baldwin school and the two men spent an interesting afternoon together.
Einstein signs Miller’s guest book (line 6)
Einstein, being a polite and diplomatic gentleman, probably did not repeat to Miller, that day, a remark which he had made at Princeton a few days earlier. Having been informed that Miller was continuing to claim a non-zero ether effect, the father of relativity made what has become a frequently quoted observation: Raffiniert ist der Herr Gott, aber boshaft ist Er nicht. Subtle is the Lord, but malicious He is not.
California was too far away, and the facilities on the mountaintop too primitive for any systematic search for improvements that might be made. Besides, Miller did have a full-time commitment to his duties as chairman of the Case physics department. By the end of 1921, he decided to ship everything back to Cleveland. For a full two years, he worked on optimizing every aspect of the experiment, working conveniently and comfortably in his first-floor lab in the Rockefeller building. He tried arc lights, automobile headlights, sunlight, and other light sources. He experimented with different telescopes and mirrors. He tried photographing the fringes. He used electrical heaters in a systematic study of temperature effects. He replaced the moving telescope with a simple eyepiece attached to a moving arm and a large objective lens fixed to the center of the interferometer. This magnified the fringes by a factor of fifty “so that direct reading with the eye was very satisfactory.” 45
45 Quotation from the “final” Miller paper: The Ether-Drift Experiment
and the Determination of the Absolute Motion of the Earth” Reviews of Modern
Physics 5 203-242 (1933).
In April, 1922, Miller, recently elected to the National Academy of Sciences, received a second distinguished visitor at Case. This time it was the 1902 Nobel Laureate, Hendrik A. Lorentz , who had for thirty years been at the center of the ether-relativity debate. He was on his way back to the Netherlands after spending two months lecturing at Caltech as a guest of Hale. (Miller’s guest book entry: H. A. Lorentz Haarlem, Netherlands April 5, 1922, and a note in Miller’s hand “Lectured in my Lecture Room, Case and WRU auspices. 400 present.”) Lorentz was keenly supportive of what Miller was trying to do at Mount Wilson. It has been reported that when Miller invited Lorentz to take a look at the fringes in his interferometer, the famous theorist confessed that he had never before seen white-light optical interference patterns. That makes three Nobel laureates (Michelson, Einstein, and Lorentz) who, each for his own reasons, encouraged Miller to persevere!
Interferometer set up at Case in 1922
Miller welcomes H. A. Lorentz to Case
Sensationalist press coverage