Professor Robert Andrews Millikan
|Born||March 22, 1868 |
Morrison, Illinois, USA
|Died||December 19, 1953 |
San Marino, California, USA
|Institution||University of Chicago |
California Institute of Technology
|Alma mater||Oberlin College |
|Academic advisor||Michael Pupin |
|Notable students||William Pickering|
|Known for||Charge on the electron & advanced work on cosmic ray physics|
|Notable prizes||Nobel Prize for Physics (1923)|
Professor Robert Andrews Millikan (March 22, 1868 – December 19, 1953) was an American experimental physicist who won the 1923 Nobel Prize for his measurement of the charge on the electron and for his work on the photoelectric effect. He later studied cosmic rays.
Millikan received a Bachelor's degree in the classics from Oberlin College in 1891 and his doctorate in physics from Columbia University in 1895 – he was the first to earn a Ph.D. from that department.
Millikan's enthusiasm for education continued throughout his career, and he was the coauthor of a popular and influential series of introductory textbooks, which were ahead of their time in many ways. Compared to other books of the time, they treated the subject more in the way in which it was thought about by physicists. They also included many homework problems that asked conceptual questions, rather than simply requiring the student to plug numbers into a formula.
Starting in 1909, while a professor at the University of Chicago, Millikan and Harvey Fletcher worked on his oil-drop experiment (since repeated, with varying degrees of success, by generations of physics students) in which he measured the charge on a single electron. After a publication on his first results in 1910, contradictory observations by Felix Ehrenhaft started a controversy between the two physicists. After improving his setup he published his seminal study in 1913.
The so-called elementary charge is one of the fundamental physical constants and accurate knowledge of its value is of great importance. His experiment measured the force on tiny charged droplets of oil suspended against gravity between two metal electrodes. Knowing the electric field, the charge on the droplet could be determined. Repeating the experiment for many droplets, Millikan showed that the results could be explained as integer multiples of a common value (1.592 × 10−19 coulomb), the charge on a single electron. That this is somewhat lower than the modern value of 1.602 176 53(14) x 10−19 coulomb is probably due to Millikan's use of an inaccurate value for the viscosity of air.
Although at the time of Millikan's oil drop experiments it was becoming clear that there exist such things as subatomic particles, not everyone was convinced. Experimenting with cathode rays in 1897, J.J. Thomson had discovered negatively charged 'corpuscles', as he called them, with a mass about 1000 times smaller than that of a hydrogen atom. Similar results had been found by George FitzGerald and Walter Kaufmann. Most of what was then known about electricity and magnetism, however, could be explained on the basis that charge is a continuous variable; in much the same way that many of the properties of light can be explained by treating it as a continuous wave rather than as a stream of photons.
The beauty of the oil drop experiment is that as well as allowing quite accurate determination of the fundamental unit of charge Millikan's apparatus also provides a 'hands on' demonstration that charge is actually quantised. It demonstrates this simply and elegantly. Thomas Edison, who had previously thought that charge is a continuous variable, became convinced after having a go with Millikan's apparatus.
There is some controversy over the use of selectivity in Millikan's results of his second experiment measuring the electron charge. This work was done by Allan Franklin, a former high energy experimentalist and current philosopher of science at the University of Colorado. Franklin contends that, while Millikan's exclusions of data do not affect the final value of the charge of an e− that he obtained, there was substantial "cosmetic surgery" that Millikan performed which had the effect of reducing the statistical error on the charge of an e−. This enabled Millikan to quote the figure that he had calculated the charge of e− to better than one half of one percent; in fact, if Millikan had included all of the data he threw out, it would have been to within 2%. While this would still have resulted in Millikan having measured the charge of e− better than anyone else at the time, the slightly larger uncertainty might have allowed more disagreement with his results within the physics community, which Millikan likely tried to avoid.
When Einstein published his seminal 1905 paper on the particle theory of light, Millikan was convinced that it had to be wrong, because of the vast body of evidence that had already shown that light was a wave. He undertook a decade-long experimental program to test Einstein's theory, which required building what he described as "a machine shop in vacuo" in order to prepare the very clean metal surface of the photo electrode. His results confirmed Einstein's predictions in every detail, but Millikan was not convinced of Einstein's radical interpretation, and as late as 1916 he wrote, "Einstein's photoelectric equation... cannot in my judgment be looked upon at present as resting upon any sort of a satisfactory theoretical foundation," even though "it actually represents very accurately the behavior" of the photoelectric effect. In his 1950 autobiography, however, he simply declared that his work "scarcely permits of any other interpretation than that which Einstein had originally suggested, namely that of the semi-corpuscular or photon theory of light itself."
Since Millikan's work formed some of the basis for modern particle physics, it is ironic that he was rather conservative in his opinions about 20th century developments in physics, as in the case of the photon theory. Another example is that his textbook, as late as the 1927 version, unambiguously states the existence of the ether, and mentions Einstein's theory of relativity only in a noncommittal note at the end of the caption under Einstein's portrait, stating as the last in a list of accomplishments that he was "author of the special theory of relativity in 1905 and of the general theory of relativity in 1914, both of which have had great success in explaining otherwise unexplained phenomena and in predicting new ones." He is also credited with measuring the value of Planck's constant by using photoelectric emission graphs of various metals.
In 1917, solar astronomer George Ellery Hale convinced Millikan to begin spending several months each year at the Throop College of Technology, a small academic institution in Pasadena, California that Hale wished to transform into a major center for scientific research and education. A few years later Throop College became the California Institute of Technology (Caltech), and Millikan left the University of Chicago in order to become Caltech's "chairman of the executive council" (effectively its president). Millikan would serve in that position from 1921 to 1945. At Caltech most of his scientific research focused on the study of "cosmic rays" (a term which he coined). In the 1930s he entered into a debate with Arthur Compton over whether cosmic rays were composed of high-energy photons (Millikan's view) or charged particles (Compton's view). Millikan thought the cosmic ray photons were the "birth cries" of new atoms continually being created by God to counteract entropy and prevent the heat death of the universe. Compton would eventually be proven right by the observation that cosmic rays are deflected by the Earth's magnetic field (and so must be charged particles).
In his private life, Millikan was an enthusiastic tennis player. He was married and had three sons, the eldest of whom, Clark B. Millikan, became a prominent aerodynamic engineer.
In his later life he became interested in the relationship between Christian faith and science, his own father having been a minister. He dealt with this in his Terry Lectures at Yale in 1926–7, published as Evolution in Science and Religion. A more controversial belief of his was eugenics. This led to his association with the Human Betterment Foundation and his praising of San Marino, California for being "the westernmost outpost of Nordic civilization . . . [with] a population which is twice as Anglo-Saxon as that existing in New York, Chicago or any of the great cities of this country." 
In 1938, he wrote a short passage to be placed in the Westinghouse time capsule .
AT this moment, August 22, 1938, the principles of representative ballot government, such as are represent- ed by the governments of the Anglo-Saxon, French, and Scandinavian countries, are in deadly conflict with the principles of despotism, which up to two centuries ago had controlled the destiny of man throughout practically the whole of recorded history. If the rational, scientific, progressive principles win out in this struggle there is a possibility of a warless, golden age ahead for mankind. If the reactionary principles of despotism triumph now and in the future, the future history of mankind will repeat the sad story of war and oppression as in the past.
He died at his home in San Marino, California in 1953 and was interred in the "Court of Honor" at Forest Lawn Memorial Park Cemetery in Glendale, California. Millikan Middle School (formerly Millikan Junior High School) in the suburban Los Angeles neighborhood of Sherman Oaks is named in his honor, as is Robert A. Millikan High School in Long Beach, California. The Millikan Library, the tallest building on the Caltech campus, and Caltech's Millikan Auditorium, are also named for him.
Robert Millikan is widely believed to have been denied the 1920 prize for physics owing to Felix Ehrenhaft's claims to have measured charges smaller than Millikan's elementary charge. Ehrenhaft's claims were ultimately dismissed and Millikan was awarded the prize in 1923.