Edwin Hubble

• 1. Introduction

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  Edwin Hubble grew up in Marshfield, Missouri, known more for his athletic prowess than his intellect, a boy who won seven first places and a third in a single high school track meet in 1906. He earned good grades in every subject except spelling. Today his name circles the Earth on a telescope, and a model of that telescope stands in his hometown. How did an insurance executive's son, pushed toward law by a dying father's wish, become the man who proved the universe is far larger than anyone imagined? This is the story of an astronomer who looked at smudges of light called nebulae and saw entire galaxies. It is also the story of an interpretation he never fully accepted, a Nobel he never received, and a French priest whose claim to the same discovery still stirs argument.

• 2. The Reluctant Lawyer

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  John Powell Hubble, an insurance executive, asked his son to study law, and Edwin obeyed despite an interest in astronomy he had carried since boyhood. He took a Bachelor of Science degree from the University of Chicago by 1910, concentrating on mathematics, astronomy and philosophy. For a year he assisted the physicist Robert Millikan, a future Nobel Prize winner. As a Rhodes Scholar he spent three years at The Queen's College, Oxford, studying jurisprudence rather than science, a promise made to his dying father, and later adding literature and Spanish for a master's degree. His father died in the winter of 1913 while Edwin was still in England. The following summer Edwin returned home to care for his mother, two sisters, and younger brother. Without the motivation to practice law, he taught Spanish, physics and mathematics at New Albany High School in New Albany, Indiana, and coached the boys' basketball team. After a single year of teaching, he entered graduate school to study astronomy at the University of Chicago's Yerkes Observatory, where he received his Ph.D. in 1921. His dissertation carried the title "Photographic Investigations of Faint Nebulae."

• 3. Soldier And Ballistician

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  After the United States declared war on Germany in 1917, Hubble rushed to finish his dissertation so he could enlist. He volunteered for the United States Army and was assigned to the newly created 86th Division, serving in the 2nd Battalion, 343rd Infantry Regiment. He rose to the rank of major and was found fit for overseas duty on the 9th of July 1918, though the 86th Division never saw combat and its personnel were used as replacements elsewhere. A second war pulled him from the stars again. During World War II he worked as a civilian for the United States Army at Aberdeen Proving Ground in Maryland, serving as Chief of the External Ballistics Branch of the Ballistic Research Laboratory. There he directed a large volume of research that increased the effective firepower of bombs and projectiles. He personally developed instrumentation, most notably a high-speed clock camera that made it possible to study bombs and low-velocity projectiles in flight. His studies were credited with improving the design and military effectiveness of bombs and rockets, work that earned him the Legion of Merit.

• 4. Beyond The Milky Way

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  In 1919, George Ellery Hale offered Hubble a staff position at the Carnegie Institution for Science's Mount Wilson Observatory near Pasadena, California, where he would remain until his death. His arrival coincided roughly with the completion of the 100-inch Hooker Telescope, then the world's largest. At that time the prevailing view held that the universe consisted entirely of the Milky Way galaxy. Using the Hooker Telescope, Hubble identified Cepheid variables, a standard candle whose luminosity and pulsation period were linked by Henrietta Swan Leavitt's 1908 discovery. Comparing a Cepheid's apparent brightness to its intrinsic brightness yields its distance from Earth. Hubble found these stars in several nebulae, including the Andromeda Nebula and the Triangulum Nebula. His observations, made in 1924, proved that these objects lay far too distant to belong to the Milky Way and were themselves entire galaxies. The idea that other worlds of stars might exist had been hypothesized as early as 1755, when Immanuel Kant's General History of Nature and Theory of the Heavens appeared. Hubble's findings drew opposition from the astronomy establishment, particularly Harvard-based Harlow Shapley. The thirty-five-year-old scientist saw his results first published in The New York Times on the 23rd of November 1924, then presented them to the American Astronomical Society at its meeting on the 1st of January 1925. His work earned him the American Association Prize and five hundred dollars from Burton E. Livingston of the Committee on Awards.

• 5. Sorting The Galaxies

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  Hubble devised the most commonly used system for classifying galaxies, grouping them by how they appeared in photographic images. He arranged these groups into what became known as the Hubble sequence. His broader views reached a wide readership in 1936, when he wrote The Observational Approach to Cosmology and The Realm of the Nebulae, both explaining his methods in extra-galactic astronomy and his sense of the field's history. His attention was not fixed on distant galaxies alone. On the 30th of August 1935, he discovered the asteroid 1373 Cincinnati. His formal recognition gathered through these years, beginning with the Newcomb Cleveland Prize in 1924 and his election to the United States National Academy of Sciences in 1927.

• 6. The Stretching Cosmos

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  Hubble estimated the distances to 24 extra-galactic nebulae using a variety of methods, then in 1929 compared those distances against radial velocities drawn from their redshifts. His distance estimates are now known to be too small, by up to a factor of about 7, partly because there are two kinds of Cepheid variables. Yet his distances stayed roughly proportional to the true ones. Combining them with redshift measurements by Vesto Slipher and by his assistant Milton L. Humason, he found a roughly linear relationship between a galaxy's distance and its velocity, a finding that became Hubble's law. The greater the distance between two galaxies, the greater their speed of separation. His measurements on 46 galaxies yielded a Hubble constant of 500 km/s/Mpc, far above the currently accepted values of 74 or 68 km/s/Mpc, a gap traced to errors in his distance calibrations. A decade earlier, Vesto Slipher had supplied the first evidence that light from many of these nebulae was strongly red-shifted, pointing to high recession velocities. The meaning of that redshift would divide Hubble from the very implication his data carried.

• 7. The Doubter Of Expansion

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  Hubble himself resisted the conclusion others drew from his measurements. In a 1931 letter to the Dutch cosmologist Willem de Sitter, he wrote that he and Humason used the term "apparent" velocities "to emphasize the empirical features of the correlation," adding that interpretation "should be left to you and the very few others who are competent to discuss the matter with authority." According to Allan Sandage, Hubble favored a model in which no true expansion exists, holding that the redshift might "represent a hitherto unrecognized principle of nature." His survey work in the 1930s, on the distribution of galaxies and spatial curvature, suggested a flat and homogeneous universe with a puzzling deviation at large redshifts, a deviation traced to his technique ignoring changes in galaxy luminosity from evolution. In December 1941, he told the American Association for the Advancement of Science that a six-year survey did not support the expanding universe theory. A Los Angeles Times article reported his view that the nebulae "could not be uniformly distributed, as the telescope shows they are, and still fit the explosion idea." Others embraced what Hubble would not. In 1917, Albert Einstein's general relativity had indicated a universe that must expand or contract, and he had inserted a cosmological constant to avoid the problem. Learning of Hubble's redshifts, Einstein called that move "the biggest blunder of his life." He visited Mount Wilson in 1931, met Hubble, and announced there that "the visit had changed his mind."

• 8. Priority And The Missing Prize

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  Georges Lemaitre had predicted the redshift-distance relation on theoretical grounds from Einstein's equations, and published observational support for it two years before Hubble's law was established. His paper appeared in French. In 2011, the journal Nature reported claims that Hubble might have played a role in redacting key parts of the 1931 English translation of Lemaitre's 1927 paper. That November, the astronomer Mario Livio reported in Nature that a letter from the Lemaitre archive showed the redaction had been made by Lemaitre himself, who saw no point in republishing content already reported by Hubble in 1929. A different recognition eluded Hubble entirely. During his life the Nobel Prize in Physics did not cover astronomy, and he spent much of his later career arguing that astronomy belonged within physics, partly so that astronomers, himself included, could be honored by the Nobel Committee. The campaign failed in his lifetime. Shortly before his death he became the first astronomer to use the 200-inch Hale Telescope at the Palomar Observatory near San Diego. He died of cerebral thrombosis on the 28th of September 1953, in San Marino, California. No funeral was held, and his wife, Grace, whom he had married on the 26th of February 1924, never revealed his burial site. Shortly after his death, the Nobel Committee decided astronomical work would be eligible for the physics prize.