Robert Millikan

Robert Millikan

Date of Birth: 22.03.1868
Country: USA

  1. Biography of Robert A. Millikan
  2. Education and Early Career
  3. Research on the Charge of the Electron
  4. Other Contributions and Later Career
  5. Research on Cosmic Rays and Personal Life

Biography of Robert A. Millikan

Robert Andrews Millikan was an American physicist born in Morrison, Illinois. He was the second son of Silas Franklin Millikan, a Congregationalist Church minister, and Mary Jane Andrews Millikan, a former dean of the women's department at Olivet College in Michigan. In 1875, the Millikan family moved to Maquoketa, Iowa, a small town near the Mississippi River, where Robert grew up with two brothers and three younger sisters.

Education and Early Career

After graduating from high school in Maquoketa, Millikan attended Oberlin College in Ohio, where his mother had studied. He focused his interests on mathematics and ancient Greek language. Although he took only a twelve-week physics course, which he later considered a waste of time, Millikan was asked to teach physics at the college's preparatory school. He accepted the offer to earn money and taught physics for two years after receiving his bachelor's degree in 1891. He prepared for his teaching using textbooks he managed to obtain. As a reward, Oberlin College awarded him a master's degree in physics in 1893 and sent his lecture notes to Columbia University, which appointed Millikan a research fellow. At Columbia University, Millikan worked under the guidance of renowned physicist and inventor Michael I. Pupin. He also spent one summer at the University of Chicago, where he worked under the supervision of renowned experimental physicist Albert A. Michelson. It was during this time that he became convinced that physics was his true calling. In 1895, he defended his dissertation on the polarization of light to obtain his doctoral degree from Columbia University. The following year, Millikan traveled to Europe, visiting Jena, Berlin, Göttingen, and Paris, where he met Henri Becquerel, Max Planck, Walther Nernst, and Henri Poincaré. Upon his return to the United States in 1896, he became an assistant professor of physics under Michelson at the University of Chicago. Over the next twelve years, Millikan wrote several physics textbooks, which were the first books written for American students rather than translations of French or German textbooks. These books became standard textbooks in colleges and high schools and remained so for over half a century. In 1907, Millikan was appointed assistant professor of physics, and in 1910, he became a full professor.

Research on the Charge of the Electron

In 1908, Millikan stopped working on textbooks to dedicate more time to original research. Like many physicists of the time, he was interested in the newly discovered electron, particularly its electric charge, which had not yet been measured. English physicist G.A. Wilson attempted to do so by studying the influence of an electric field on a charged cloud of ether vapor. However, his calculations were based on the average behavior of microscopic ether droplets since Wilson could not develop a method to measure each individual droplet. Wilson's results varied widely, and some scientists began to suspect that different electrons had different charges, suggesting that the electron was not an indivisible charged particle. Millikan decided to determine if all electrons had the same charge and accurately measure it. He developed a method involving charged droplets, which became a classic example of an elegant physical experiment and one of Millikan's achievements for which he was awarded the Nobel Prize. Millikan improved Wilson's experimental setup by building a powerful battery that created a much stronger electric field. He also managed to isolate several charged water droplets between metal plates in free space. With the field turned on, the droplet moved slowly upward due to electric attraction. With the field turned off, the droplet fell due to gravity. By turning the field on and off, Millikan could study each droplet suspended between the plates for 45 seconds before they evaporated. By 1909, Millikan had determined that the charge of any droplet was always a whole multiple of the fundamental unit of charge, e (the charge of an electron). This was compelling evidence that electrons were fundamental particles with identical charge and mass. Millikan faced experimental challenges on his path to measuring the precise value of the electron charge, but he patiently overcame them. By replacing water droplets with nearly non-volatile oil droplets, he extended the observation time to 4.5 hours. In 1913, after eliminating possible sources of error one by one, Millikan published his first definitive value for the electron charge: e = (4.774 ± 0.009) x 10^-10 electrostatic units. This value remained unchanged for over 70 years until recent advances in high-sensitivity instrumentation made a slight adjustment. The new value for the electron charge is e = 4.80298 x 10^-10 electrostatic units. During his work on textbooks, Millikan also conducted research on the photoelectric effect, which is the ejection of electrons from a metal surface by incident light. In 1905, Albert Einstein attempted to explain some aspects of the photoelectric effect with his hypothesis that light consists of particles called photons. Einstein's hypothesis was an extension of Max Planck's earlier hypothesis that energy is emitted in discrete quantized units, or quanta. Since Einstein's idea contradicted the prevailing notion of light as a wave (wave nature of light was confirmed by convincing experimental data), most physicists did not believe in it. In 1912, Millikan decided to test the relationship derived by Einstein for the photoelectric effect, which related the energy of ejected electrons to the frequency of the incident light. Through a complex experimental setup that eliminated many sources of error, Millikan proved, to his own surprise, that Einstein's relationship was correct. Furthermore, as a result of his experiment, he was able to determine the value of Planck's constant (a fundamental constant of quantum theory) much more accurately than his predecessors. Millikan's findings, published in 1914, helped convince scientists of the validity of quantum theory. Millikan was awarded the Nobel Prize in Physics in 1923 for his work on determining the elementary electrical charge and the photoelectric effect. In his Nobel lecture, Millikan expressed his belief that "science walks forward on two feet, namely theory and experiment...Sometimes the foot of theory goes forward, sometimes the foot of experiment, but unceasing progress is only made by the use of both."

Other Contributions and Later Career

Among Millikan's other important work at the University of Chicago were his studies of various parts of the electromagnetic spectrum using spark spectroscopy and his research on Brownian motion in gases, which helped confirm the tenets of molecular theory. His works gained international recognition, and the results of his research were implemented in industry. In 1913, he became a consultant for Western Electric on vacuum devices and worked as an expert in the patent office from 1916 to 1926. In 1917, at the invitation of astronomer George Ellery Hale, Millikan traveled to Washington, D.C., where he held positions as the vice chairman and head of scientific research at the National Research Council, a special organization created by the U.S. government during World War I under the National Academy of Sciences. Millikan also served in the Signal Corps, where he coordinated the work of scientists and engineers, especially in the crucial area of submarine communication. After the war, Millikan returned to the University of Chicago, but only for a short time. Hale, a trustee of the California Institute of Technology (Caltech) in Pasadena, invited Millikan to California in 1921 to lead a new laboratory with an annual fund of $90,000. Millikan was appointed the director of the new Norman Bridge Laboratory of Physics and the chairman of the executive committee of Caltech, essentially making him the president of the institute. During his tenure, Millikan dedicated his efforts to transforming Caltech into one of the world's premier research and engineering institutions. However, his most significant accomplishment was attracting top faculty and talented students to Caltech. Even after stepping down as the head of the executive committee in 1946, Millikan continued his work as an outstanding administrator until his death.

Research on Cosmic Rays and Personal Life

Millikan's first project at Caltech was the investigation of radiation coming from space and reaching the Earth (which had been first detected by Austrian physicist Victor F. Hess). Millikan called this radiation cosmic rays, a term that quickly gained acceptance among scientists and the general public. To unravel the nature of these mysterious rays, Millikan and his assistants took their instruments to mountain peaks, launched them on balloons, and lowered them to the depths of deep lakes. In the course of these investigations, one of Millikan's students, Carl D. Anderson, discovered the positron and the muon.

In 1902, Millikan married Greta Irvin Blanchard, a classics graduate from the University of Chicago whose specialization was ancient Greek language. They had three sons, all of whom became renowned scientists. Millikan passed away on December 19, 1953, in San Marino, California.

In politics, Millikan held conservative views and was opposed to President Franklin D. Roosevelt's New Deal policies. He believed that the best way for the United States to recover from the Great Depression was through collaboration between science and industry. However, like many conservatives of the time, Millikan was also against isolationism and actively contributed to redirecting Caltech's research programs towards military needs during World War II. Millikan was a religious modernist and wrote several books on the relationship between science and religion. In his leisure time, he enjoyed playing tennis and golf.

Millikan received numerous awards, including the Hughes Medal from the Royal Society of London (1923) and the Faraday Medal from the British Chemical Society (1924). He was a Commander of the Legion of Honor and a Knight of the Order of the Amber, awarded by the Chinese government. Twenty-five universities granted him honorary doctorates. At various times, he served as the president of the American Association for the Advancement of Science and the American Physical Society, and he was a member of the American Philosophical Society. From 1903 to 1916, he served as the associate editor of the American Physical Review. By the end of his life, Millikan was a member of twenty-one foreign scientific academies.