From Strelno to the gold fields
Albert Abraham Michelson was born on 19 December 1852 in Strelno, a small town in the Prussian province of Posen, today Strzelno in Poland. His family were Polish Jews. In 1855, when Albert was two, his parents emigrated to the United States, joining the great migration to California in the years after the gold rush.
He grew up in mining country. The family lived first at Murphy’s Camp in the Sierra Nevada foothills of California and later in Virginia City, Nevada, the boom town of the Comstock silver lode, where his father, Samuel Michelson, kept a store selling goods to miners. The household was not religious, and Albert himself would be an agnostic all his life. For his high-school years he was sent to San Francisco to live with an aunt, Henriette Levy, where he finished his schooling. The Michelsons were a talented family: his younger sister Miriam Michelson became a novelist and journalist, and his cousin Harriet Lane Levy was a writer.
An appointment from the President
In 1869 the young Michelson competed for a congressional appointment to the United States Naval Academy at Annapolis. When the place went to another candidate, he took a letter of recommendation from his congressman, travelled across the continent to Washington and went to see President Ulysses S. Grant. Grant gave him a special appointment to the Academy.
Michelson graduated in 1873, and after two years at sea he returned to Annapolis in 1875 as an instructor in physics and chemistry. It was there, preparing a classroom demonstration, that he became absorbed by the problem that would occupy him for the rest of his life: the speed of light.
Measuring the speed of light
Michelson began experimenting in 1877, refining the rotating-mirror method devised by the French physicists Léon Foucault and Hippolyte Fizeau. In June and July 1879 he carried out a series of formal measurements at the Naval Academy, sending a beam of light from a rapidly spinning mirror to a distant fixed mirror and measuring the tiny angle by which the returning beam was displaced. His result was far more accurate than any before, and it made the twenty-six-year-old naval officer famous. He then worked with the astronomer Simon Newcomb at the Nautical Almanac Office in Washington.
He returned to the problem again and again. In 1926, using a light path of some 22 miles (35 kilometres) between Mount Wilson and Mount San Antonio in southern California, he obtained 299,796 kilometres per second, plus or minus 4. In his last years he began an even more ambitious measurement inside a mile-long evacuated tube; it was unfinished at his death and its result, 299,774 kilometres per second, was published by his colleagues in 1935. The value accepted today is 299,792.458 kilometres per second.
The interferometer and the missing aether
In 1880 Michelson went to Europe to study, working in Berlin in the laboratory of Hermann von Helmholtz and later in Heidelberg and Paris. Helmholtz directed his attention to a great open question: whether the Earth’s motion through the luminiferous aether, the invisible medium through which light was thought to travel, could be detected. Michelson designed a new instrument for the purpose, the interferometer, which splits a beam of light in two, sends the halves along perpendicular paths and recombines them, so that the smallest difference in their travel shows up as a shift in a pattern of light and dark fringes. Built with support arranged through Alexander Graham Bell, it was so sensitive that street traffic in Berlin disturbed it, and in April 1881 he moved it to the astrophysical observatory at Potsdam. He found no sign of the aether. He resigned from the Navy that year.
In 1883 he became professor of physics at the Case School of Applied Science in Cleveland, Ohio, and there, with the chemist Edward Morley of neighbouring Western Reserve University, he repeated the experiment with far greater precision. Their apparatus, mounted on a heavy stone slab floating in mercury so that it could be rotated smoothly, should have revealed the Earth’s motion through the aether. In 1887 Michelson and Morley reported that it did not: whichever way the instrument was turned, and at whatever time of day, the fringes stayed essentially where they were, with any shift far smaller than the aether theory required. The Michelson–Morley experiment is perhaps the most famous null result in the history of science.
How a null result changed physics
Michelson himself was disappointed and continued to believe in some form of aether for years. But his result could not be explained away. Physicists including George FitzGerald and Hendrik Lorentz proposed that moving bodies contract in the direction of motion, and in 1905 Albert Einstein’s special theory of relativity did away with the aether altogether, taking the constancy of the speed of light as a basic principle. The experiment became one of the classic empirical foundations of relativity.
The interferometer, meanwhile, became one of the most important instruments in physics. In 1892–93, in Paris, Michelson used it to measure the length of the international prototype metre in terms of the wavelength of the red light emitted by cadmium, about 1.55 million wavelengths, showing that a unit of length could be defined by nature rather than by a metal bar. Interferometry today underlies precision engineering, optical testing and spectroscopy, and the giant laser interferometers of LIGO, which detected gravitational waves for the first time in 2015, are direct descendants of Michelson’s design.
Chicago and the Nobel Prize
In 1889 Michelson moved to Clark University in Worcester, Massachusetts, and in 1892 he became the first head of the physics department at the newly founded University of Chicago, where he remained until his retirement in 1929. He built the department into one of the leading centres of physics in America and continued to invent instruments, including the echelon spectroscope and, with S. W. Stratton, a mechanical harmonic analyser for working with Fourier series.
In 1907 he received the Nobel Prize in Physics “for his optical precision instruments and the spectroscopic and metrological investigations carried out with their aid”. He was the first American to win a Nobel Prize in any of the sciences. That same year the Royal Society awarded him its Copley Medal. He served as president of the American Physical Society in 1900, of the American Association for the Advancement of Science in 1910–11 and of the National Academy of Sciences from 1923 to 1927.
Measuring a star
Michelson saw that interferometry could reach far beyond the laboratory. In 1920, with Francis Pease at the Mount Wilson Observatory in California, he mounted an interferometer on the 100-inch Hooker telescope and measured the diameter of the red supergiant Betelgeuse, the first time the size of a star other than the Sun had been measured. Astronomical interferometry, which links telescopes to achieve the resolving power of a much larger instrument, now allows astronomers to image the surfaces of stars and, on a planetary scale, produced the first images of the shadows of black holes.
During the First World War, now in his sixties, he returned to the Navy as an officer in the Naval Reserve, working on optical instruments for the Bureau of Ordnance until 1921.
The man behind the instruments
Michelson married Margaret Hemingway in 1877; they had two sons and a daughter. After that marriage ended he married Edna Stanton in 1899, and they raised three daughters. He was reserved and exacting, happiest alone with his apparatus, and colleagues remembered him as a perfectionist who could make an instrument do more than anyone thought possible.
He was also a serious amateur artist. He sketched and painted all his life, above all watercolours of California landscapes in his later years, and some of them were exhibited at the Pasadena Art Institute shortly before his death. Of his Jewish background he made little in public; he grew up in a non-observant family and was an agnostic, but he never denied his origins. Already in his lifetime he was counted among the notable Jews of America: the Jewish Encyclopedia, published in New York between 1901 and 1906, gave him an entry of his own, at a time when his Nobel Prize still lay in the future. His story, from a small Prussian town to the gold fields to the summit of American science, was in many ways the story of the immigrant generation itself.
Death and legacy
After retiring from Chicago, Michelson moved to Pasadena to continue his final speed-of-light measurement. He died there on 9 May 1931, at the age of seventy-eight, with only a fraction of the planned series of measurements complete; his collaborators Francis Pease and Fred Pearson finished the work.
His name lives on in the interferometer that bears it, in a crater on the Moon, in the Michelson Laboratory at the Naval Air Weapons Station China Lake and in Michelson Hall at the Naval Academy. More than any single number, his legacy is a standard of precision. He showed that patient measurement, pushed to its limits, could overturn the foundations of physics, and the experiment he hoped would find the aether opened the way to the physics of the twentieth century.
Sources & further reading
Albert A. Michelson, Wikipedia · Michelson, Albert Abraham, Encyclopedia.com (Dictionary of Scientific Biography) · Albert Michelson, Nimitz Library, U.S. Naval Academy · Michelson, Albert A., Jewish Encyclopedia (1906) · Researched from the sources above and checked against them. Spotted an error? Tell us.
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