William Duncan MacMillan

William Duncan MacMillan (July 24, 1871 – November 14, 1948) was an American mathematician and astronomer on the faculty of the University of Chicago. He published research on the applications of classical mechanics to astronomy, and is noted for pioneering speculations on physical cosmology.[1] For the latter, Helge Kragh notes that "the cosmological model proposed by MacMillan was designed to lend support to a cosmic optimism which he felt was threatened by the world view of modern physics."[2]

He was born in La Crosse, Wisconsin to D. D. MacMillan, who was in the lumber business, and Mary Jane MacCrea. His brother, John H. MacMillan, headed the Cargill Corporation from 1909 to 1936. MacMillan graduated from La Crosse High School in 1888. In 1889 he attended Lake Forest College, then entered the University of Virginia. Later in 1898 he earned an A.B. degree from Fort Worth University. He performed his graduate work at the University of Chicago, earning a master's degree in 1906 and a PhD in 1908. In 1907, prior to completing his PhD, he joined the staff of the University of Chicago as a research assistant in geology. In 1908 he became an associate in mathematics, then in 1909 he began instruction in astronomy at the same institution. His career as a professor began in 1912 when he became an assistant professor. In 1917 the U.S. declared war on Germany, and Dr. MacMillan served as a major in the U.S. army's ordnance department during World War I. Following the war he became associate professor in 1919, then full professor in 1924.[3]

He made noted contributions in mathematics and astronomy, and ultimately wrote a three-volume treatise on classical mechanics that remained in print for decades. In the 1920s, he proposed a cosmology that presumed a static universe, which was uncontroversial until Hubble's later observations suggesting an expanding universe. More controversially, he avoided the conclusion of a "heat death" of the universe due to constantly increasing entropy. In particular, he proposed a version of a mechanism later known as the "tired-light hypothesis" to explain how the light emitted by stars might re-create matter in its travels through space.[2] In a published debate, Macmillan also invoked "postulates of normal intuition" to argue against Einstein's relativity theories, which don't allow for an absolute scale of time independent of an observer.[4]

In an Associated Press report Dr. MacMillan speculated on the nature of interstellar civilizations, believing that they would be vastly more advanced than our own. "Out in the heavens, perhaps, are civilizations as far above ours as we are above the single cell, since they are so much older than ours."

The crater MacMillan on the Moon is named in his honor.[5]