Albert Abraham Michelson (; December 19, 1852 – May 9, 1931) was an American experimental physicist known for his work on measuring the speed of light and especially for the Michelson–Morley experiment. In 1907, he received the Nobel Prize in Physics, becoming the first American to win the Nobel Prize in a science. He was the founder and the first head of the physics departments of the Case School of Applied Science and the University of Chicago.
Biography Early life Albert Abraham Michelson was born on December 19, 1852, in Strelno (now Strzelno, Poland), Prussia, into a Polish-Jewish family.National Academy of Sciences, Washington, DC, 1938, Vol. XIX) quotes (on p. 128) Michelson's sister, the novelist Miriam Michelson, as having written of her parents in a letter to Millikan that "both Albert Michelson's father and mother were born of Jewish parents ..." He moved to the United States with his parents in 1855, at the age of 2. He grew up in the mining towns of Murphy's Camp, California, and Virginia City, Nevada, where his father was a merchant. His family was non-religious, and Michelson himself was a lifelong agnostic. He spent his high school years in San Francisco in the home of his aunt, Henriette Levy (née Michelson), who was the mother of author Harriet Lane Levy.Levy, 920 O'Farrell Street, 47. His sister was the novelist Miriam Michelson.
Education and career President Ulysses S. Grant awarded Michelson a special appointment to the United States Naval Academy in 1869.Nimitz Library's Virtual Exhibits – LibExhibits During his four years as a midshipman at the Academy, he excelled in optics, heat, climatology and technical drawing. After graduating in 1873 and two years at sea, he returned to the Naval Academy in 1875 to become an instructor in physics and chemistry until 1879, when he was posted to the Nautical Almanac Office, Washington (part of the United States Naval Observatory) to work with Simon Newcomb. The following year, he took a leave of absence to continue his studies in Europe; he visited the universities of Berlin and Heidelberg in Germany, and the Collège de France and École polytechnique in Paris, France.
Michelson was fascinated with the sciences, in particular the problem of measuring the speed of light. While in Annapolis, he conducted his first experiments on the speed of light as part of a class demonstration in 1877. His Annapolis experiment was refined, and in 1879,In 1879 a letter from James Clerk Maxwell to the astronomer David Peck Todd came to the attention of Michelson, possibly giving him considerable motivation. See the book 2012 e-book. he measured the speed of light in air to be kilometres per second, and estimated the speed of light in vacuum as , or . After two years of studies in Europe, he resigned from the Navy in 1881. In 1883, he was appointed Professor of Physics at the Case School of Applied Science in Cleveland, Ohio, and concentrated on developing an improved interferometer. In 1887, he and Edward Morley carried out the famous Michelson–Morley experiment, which failed to detect evidence of the existence of the luminiferous ether. He later moved on to use astronomical interferometers in the measurement of stellar diameters and in measuring the separations of binary stars.
In 1890, Michelson became a professor at Clark University in Worcester, Massachusetts. In 1892, he was appointed Professor and the first head of the Department of Physics at the newly-organized University of Chicago, where he remained until his retirement in 1929.
Michelson returned to military service in the closing months of World War I as a Lieutenant Commander in the Naval Reserve, serving in the Bureau of Ordnance. He was promoted to Commander in the reserve in May 1919 and was recalled briefly to active duty in the 9th Naval District before being released from service on September 30, 1921.
Michelson died on May 9, 1931, in Pasadena, California, at the age of 78.In November 1929, at the French Academy of Sciences, Michelson's death was erroneously announced, see http://cnum.cnam.fr/CGI/fpage.cgi?4KY28.118/97/100/598/5/588 and http://cnum.cnam.fr/CGI/fpage.cgi?4KY28.118/183/100/598/5/588
Speed of light
Early measurements Michelson was fascinated by light all his life. Once asked why he studied light, he reputedly said, "because it's so much fun".
As early as 1869, while serving as an officer in the United States Navy, Michelson started planning a repeat of the rotating-mirror method of Léon Foucault for measuring the speed of light, using improved optics and a longer baseline. He conducted some preliminary measurements using largely improvised equipment in 1878, about the same time that his work came to the attention of Simon Newcomb, director of the Nautical Almanac Office who was already advanced in planning his own study.
Michelson's formal experiments took place in June and July 1879. He constructed a frame building along the north sea wall of the Naval Academy to house the machinery.Michelson, Albert A. "Experimental Determination of the Velocity of Light Made at the U.S. Naval Academy, Annapolis". Michelson published his result of 299,910 ± 50 km/s in 1879 before joining Newcomb in Washington DC to assist with his measurements there. Thus began a long professional collaboration and friendship between the two.
Simon Newcomb, with his more adequately funded project, obtained a value of 299,860 ± 30 km/s, just at the extreme edge of consistency with Michelson's. Michelson continued to "refine" his method and in 1883 published a measurement of 299,853 ± 60 km/s, rather closer to that of his mentor.
Mount Wilson and Lookout Mountain In 1906, a novel electrical method was used by E. B. Rosa and the National Bureau of Standards to obtain a value for the speed of light of 299,781 ± 10 km/s. Though this result has subsequently been shown to be severely biased by the poor electrical standards in use at the time, it seems to have set a fashion for rather lower measured values.
From 1920, Michelson started planning a definitive measurement from the Mount Wilson Observatory, using a baseline to Lookout Mountain, a prominent bump on the south ridge of Mount San Antonio ("Old Baldy"), some 22 miles distant.
In 1922, the United States Coast and Geodetic Survey began two years of painstaking measurement of the baseline using the recently available invar tapes. With the baseline length established in 1924, measurements were carried out over the next two years to obtain the published value of 299,796 ± 4 km/s.
Famous as the measurement is, it was beset by problems, not least of which was the haze created by the smoke from forest fires which blurred the mirror image. It is also probable that the intensively detailed work of the geodetic survey, with an estimated error of less than one part in 1 million, was compromised by a shift in the baseline arising from the Santa Barbara earthquake of June 29, 1925, which was an estimated magnitude of 6.3 on the Richter scale.
The now-famous Michelson–Morley experiment also influenced the affirmation attempts of peer Albert Einstein's theory of general relativity and special relativity, using similar optical instrumentation. These instruments and related collaborations included the participation of fellow physicists Dayton Miller, Hendrik Lorentz, and Robert Shankland.
Michelson, Pease, and Pearson The period after 1927 marked the advent of new measurements of the speed of light using novel electro-optic devices, all substantially lower than Michelson's 1926 value.
Michelson sought another measurement, but this time in an evacuated tube to avoid difficulties in interpreting the image owing to atmospheric effects. In 1929, he began a collaboration with Francis G. Pease and Fred Pearson to perform a measurement in a 1.6 km tube 3 feet in diameter at the Irvine Ranch near Santa Ana, California. In multiple reflections the light path was increased to 5 miles. For the first time in history the speed of light was measured in an almost perfect vacuum of 0.5 mm of mercury. Michelson died with only 36 of the 233 measurement series completed and the experiment was subsequently beset by geological instability and condensation problems before the result of , consistent with the prevailing electro-optic values, was published posthumously in 1935.
Application of basic statistical principles in Michelson's study of speed of light During June and early July 1879, Michelson refined experimental arrangements from those developed by Hippolyte Fizeau and Léon Foucault. The experimental setup was as follows: Light generated from a source is directed towards a rotating mirror through a slit on a fixed plate; the rotating mirror reflects the incoming light and at a certain angle, towards the direction where another fixed flat mirror is placed whose surface is perpendicular to the incoming ray of light; the rotating mirror should have rotated by an angle α by the time the ray of light travels back and is reflected again towards the fixed plate (the distance between the fixed mirror and the rotating one is recorded as D); a displacement from the slit is detected on the plate which measures d; the distance from the rotating mirror to the fixed plate is designated as the radius r while the number of revolutions per second of the mirror is recorded as ω. In this way, ; ; speed of light can be derived as .
While at plain sight, four measured quantities are involved: distance D, radius r, displacement d and rotating mirror revolution per second ω, which seems simple; yet based on the limitation of the measurement technology at that time, great efforts were made by Michelson to reduce systematic errors and apply subsequent corrections. For instance, he adopted a steel measuring tape with a said length of 100 feet and he intended to measure tens of times across the distance; still, he measured its length against a copy of the official standard yard to find out it as 100.006 feet, thus eliminating a systematic error, albeit small.
Aside from the efforts to reduce as much as possible the systematic errors, repeated measurements were performed at multiple levels to obtain more accurate results. As R.J. MacKay and R.W. Oldford remarked in their article, 'It is clear that Michelson appreciated the power of averaging to reduce variability in measurement', it is clear that Michelson had in mind the property that averages vary less which should be formally described as: the standard deviation of the average of n independent random variables is less than that of a single random variable by a factor of the square root of n. To realize that, he also strived to have each measurement not influencing each other, thus being mutually independent random variables.
A statistical model for repeated measurements with the assumption of independence or identical distributions is unrealistic. In the case of light speed study, each measurement is approached as the sum of quantity of interest and measurement error. In the absence of systematic error, the measurement error of speed of light can be modeled by a random sample from a distribution with unknown expectation and finite variance; thus, the speed of light is represented by the expectation of the model distribution and the ultimate goal is to estimate the expectation of the model distribution on the acquired dataset. The law of large numbers suggests to estimate the expectation by the sample mean.
Michelson–Morley experiment