Robert Andrews Millikan

Robert Andrews Millikan (White) (USA: /ˈɹɑbəɹt ˈænˌdɹuz ˈmɪləkən/; Morrison, Illinois, March 22, 1868-San Marino, California, December 19, 1953) was an American experimental physicist who won the Nobel Prize Physics in 1923 primarily for his work to determine the value of the charge of the electron and the photoelectric effect. He also investigated cosmic rays.

Biography

Robert A. Millikan graduated from Oberlin College in 1891 and received his Ph.D. from Columbia University in 1895. In 1896 he became an assistant at the University of Chicago, where he would become a professor in 1910, a post which he retained until 1921. In 1907 he began a series of works aimed at measuring the charge of the electron, studying the effect of electric and gravitational fields on a drop of water (1909). The results suggested that the electric charge of the droplets were multiples of an elementary electric charge, but the experiment with water droplets was not precise enough to be convincing, they had a tendency to evaporate too quickly. The definitive results came in 1910 when he replaced the water drops in his experiment with drops of oil, deducing from his observations the first precise value of the "elementary electrical" constant.

In 1916 Robert A. Millikan used his skills in the experimental verification of the equation introduced by Albert Einstein in 1905 to describe the photoelectric effect and evaluating the constant "h" of Planck. In 1921 Millikan changed his position at the University of Chicago to Director of the Norman Bridge Physics Laboratory at the California Institute of Technology (Caltech) in Pasadena. There he specialized in the study of the radiation that the physicist Victor Hess had detected coming from outer space. Robert A. Millikan proved that this radiation was extraterrestrial and named it "cosmic rays." As chairman of Caltech's Executive Board (the center's governing body at the time) from 1921 until his retirement in 1945, Robert A. Millikan built the center into one of the leading research institutions in the United States. He also participated from 1921 to 1953 in the patronage of the Science Service, now known as the Society for Science and the Public...

He initially studied the radioactivity of uranium ores and the discharge in gases. He later carried out research on ultraviolet radiation.

Education

Robert A. Millikan was born on March 22, 1868, in Morrison, Illinois. He went to high school in Maquoketa, Iowa. He received his BA in Classics from Oberlin College in 1891 and earned his Ph.D. in Physics from Columbia University in 1895, the first to do so in his department.

At the end of my second year [...] my Greek teacher [...] asked me to impart [...] the course of elementary physics during the next course. To my answer saying that he knew nothing about physics at all, his answer was "whoever knows well Greek can teach physics." "Without problems," I said, "it will have to face the consequences, but I will try and see what I can do." Then I bought the text. Elements of Physics of Avery, and I dedicated part of the summer vacation of 1889 at home - trying to dominate the matter [...] I doubt if I ever taught better physics in my life than in my first course in 1889. I was so deeply interested in acquiring more knowledge of what is necessary for the classes that they could be told of my own interest and enthusiasm.

Robert A. Millikan

Milikan's enthusiasm for education continued throughout his career, and he co-authored an influential and popular series of texts that were ahead of their time in many ways. Compared to the other books of the time, they treated the subject more in the way that it was thought by physicists. They also included many problems that included conceptual questions, rather than requiring students to simply plug numbers into the formulas.

In 1902, he married Greta Ervin Blanchard. They had three children: Clark Blanchard, Glenn Allen, and Max Franklin.

Scientific work

Charge of the Electron

Millikan designed fitting for his experiment with oil drop (1909-1910).

Beginning in 1909, while he was a professor at the University of Chicago, Millikan began working on his experiment with a drop of oil in order to measure the charge of the electron. J.J. Thomson had discovered the charge-mass relationship of the electron, but none of them separately. Therefore, if one of these two values could be determined, the other could easily be calculated. Robert A. Millikan and his undergraduate student Harvey Fletcher used the oil drop experiment to measure the electron's charge (and thus its mass) and Avogadro's Number.

Although the discovery was double authored, Millikan, knowing that determining the charge of the electron would build him a reputation in the scientific community, made a deal with Harvey Fletcher to list Robert A. Millikan as the sole author of the discovery. article on the determination of the charge of the electron, and as compensation would allow Fletcher to be the sole author of the article on the determination of Avogadro's Number, which could well be used as a doctoral thesis. The deal was obviously not to Fletcher's liking, but considering that Robert A. Millikan was his mentor, he had no choice but to accept it. Following the defense of his doctorate in 1911, Harvey Fletcher did not continue to work with Robert A. Millikan; however, and despite the determination of the charge of the electron being one of the fundamental reasons for receiving the Nobel Prize in Physics in 1923, the two maintained good relations for the rest of his life and the story was not made public until his death. from both.

After the publication of his results in 1910, the Austrian physicist Felix Ehrenhaft trying to reproduce the oil drop experiment, obtained contradictory results and this started a battle that would last for years, until Robert A. Millikan published his data in 1913 definitive.

Elementary charge is one of the fundamental constants of physics and its precise determination is of great importance to science. The experiment measured the force of a small charged drop suspended against the gravitational force by an electric field created between two electrodes. Knowing the electric field, the accumulated charge on the drop could be determined. The experiment was repeated many times, and it was determined that the results obtained could be explained if there was a single elementary charge (1.592 x10^-19 coulomb) and the charges identified were integer multiples of this number. The current value associated with it is 1.602176487|(40) x 10^-19 C and there are various reasons to justify this deviation, among them possibly the inappropriate estimate of the value of the viscosity of the air.

Although it was clear at the time that subatomic particles must exist, not everyone was convinced of this. J. J. Thomson in 1897, experimenting with cathode rays, had discovered negatively charged corpuscles (this is what he called them) with a mass 1840 times less than that of the hydrogen ion. Similar results were found by George FitzGerald and Walter Kaufmann. And since everything that was known at that time about electricity and magnetism was associated with fluidity, charge was also considered a continuous variable; similarly many of the properties of light could be explained by treating it as a continuous wave rather than a stream of individual particles.

The beauty of the oil drop experiment is that at the same time that it accurately determined the fundamental charge, Millikan's apparatus also showed that the charge was quantized.

Controversy over data selection

There is controversy over the selection process of data chosen by Millikan to determine the charge of the electron. This has been studied by Allan Franklin, a former high-energy experimenter and current scholar of the history of science at the University of Colorado, who after painstakingly analyzing each and every drop that Robert A. Millikan omitted in his article of 1913, showed that almost all the omissions had been due to solid reasons of experimental error. And perhaps even more important, even if Millikan had included all this data, the end result would not have changed much.

The best study of Millikan's experiment is arguably Subelectrons, Presuppositions, and the Millikan-Ehrenhaft Dispute by Gerald Holton, who goes so far as to say that Robert A. Millikan's 1909 paper describing his method is notable for the honesty of its presentation, in a "rare gesture in the scientific literature." Millikan included personal judgments about the reliability and validity of each of the 38 drop observations. As noted by the philosopher and historian of science Robert P. Crease:

The examination that Holton made of Millikan's lab notebooks with the annotations on the work on which his 1913 article was based reveals that Milikan had actually studied 140 drops and not the 58 that he mentioned in it [...] This author suggests two partial explanations. One is the controversy with Ehrenfaft; Millikan, convinced of being right, did not want to give the Austrian ammo, which in his opinion could only create more confusion. The second reason Millikan failed to mention the other drops is clear when the sources of error that Holton found in the notebooks are examined. "The voltage of the battery has fallen; the nanometer is stuck; the convection often interferes; the distance has to remain constant; there has been an error in the chronometer; the atomizer has been damaged." The American, in sum, did not believe that these 82 "disappeared" drops of the article could be considered data.

Robert P. Crease, at the The prism and the pendulum (2003)

The photoelectric effect

Robert A. Millikan (1923).

When Einstein published his groundbreaking paper on the corpuscular nature of light: "A Heuristic View on the Production and Transformation of Light," Millikan was convinced something had to be wrong. Scientists had been convinced for 50 years that light was a wave, and Millikan was one of them. So he set out to prove Einstein's theory wrong.

For a decade he experimented, for which he had to build a "vacuum mechanical workshop" in order to have a very clean metal surface to act as a photo-electrode.

The experiment measured the energy of the electrons that were emitted by a metal plate that was struck by a ray of light. However, to his surprise, the results seemed to confirm Einstein's theory of the corpuscular nature of light. But not only that, the experiment allowed the most precise determination to date of the value of Planck's constant. Decades later, when Millikan described his work, a point of frustration still loomed: "I spent ten years of my life proving Einstein's theory of 1905 and, against all my expectations, I was forced to assert its verification outright to despite how unreasonable it was." In his 1950 autobiography, he would state that his work "hardly permitted any other interpretation than that which Einstein had originally suggested, namely the semi-corpuscular theory or the photonic theory of light."

Michelson, Einstein and Robert A. Millikan, (Caltech, 1931).

However, at the time of his experiments Millikan did not accept that his experiment proved that light was composed of quanta; he would only admit that Einstein's mathematics matched his experiments. In his paper on the photoelectric effect, Millikan wrote: "Einstein's photoelectric equation...seems to accurately predict in all cases the observed results...Yet the semi-corpuscular theory by which Einstein arrived at his equation now seems completely untenable." Millikan also described Einstein's theory of light particles as a "daring, not to call it foolish hypothesis." Millikan knew that without Einstein's equations the phenomenon of photoelectricity could not be explained using the classical view of light, so he knew that something had to change, but the arbitrary introduction of photons was not, to his liking., the answer. In addition, Millikan worked with Michelson (his thesis director), who believed all his life in the existence of an ether through which light waves traveled (despite the fact that his own experiments demonstrated its non-existence), for which reason he they mutually reinforced their belief in the wave nature of light as the only possible one.

But while his results confirmed Einstein's theoretical predictions in every detail, Robert A. Millikan maintained a very conservative spirit about the new discoveries being made in physics. Even in a 1927 version of his textbooks, he would still state the existence of the ether and present the theory of relativity cautiously. So much so that in his lecture on the occasion of receiving the Nobel Prize in Physics in 1923, Millikan once again mentioned that "the concept of localized light quanta from which Einstein got his equation must still be considered far from being established." ».

Main recognitions

• Nobel Prize in Physics in 1923.
• He was awarded in 1910 with the Hughes medal, granted by the Royal Society "for his determination of the charge of the electron and other physical constants".
• Moon crater Millikan bears this name in his memory.