Edwin Hubble

Hubble's studies at the University of Chicago were concentrated on mathematics, astronomy and philosophy, which resulted in a bachelor of science degree by 1910. Hubble also became a member of the Kappa Sigma Fraternity. A Rhodes Scholar, he spent three years at The Queen's College, Oxford studying jurisprudence instead of science (as a promise to his dying father),[17] and later added studies in literature and Spanish,[17] eventually earning his master's degree.[18]

In 1909, Hubble's father moved his family from Chicago to Shelbyville, Kentucky, so that the family could live in a small town, ultimately settling in nearby Louisville. His father died in the winter of 1913, while Edwin was still in England. In the following summer, Edwin returned home to care for his mother, two sisters, and younger brother, along with his brother William. The family moved once more to Everett Avenue, in Louisville's Highlands neighborhood, to accommodate Edwin and William.[19]

Hubble was also a dutiful son, who despite his intense interest in astronomy since boyhood, acquiesced to his father's request to study law, first at the University of Chicago and later at Oxford. In this time, he also took some math and science courses. After the death of his father in 1913, Edwin returned to the Midwest from Oxford but did not have the motivation to practice law. Instead, he proceeded to teach Spanish, physics and mathematics at New Albany High School in New Albany, Indiana, where he also coached the boys' basketball team. After a year of high-school teaching, he entered graduate school with the help of his former professor from the University of Chicago to study astronomy at the university's Yerkes Observatory, where he received his Ph.D. in 1917. His dissertation was titled "Photographic Investigations of Faint Nebulae".[20] In Yerkes, he had access to one of the most powerful telescopes in the world at the time, which had an innovative 24 inch (61 cm) reflector.[21]

Hubble's identity card in the American Expeditionary Forces.

After the United States declared war on Germany in 1917, Hubble rushed to complete his Ph.D. dissertation so he could join the military. Hubble volunteered for the United States Army and was assigned to the newly created 86th Division, where he served in 2nd Battalion, 343 Infantry Regiment. He rose to the rank of Major,[22] and was found fit for overseas duty on July 9, 1918, but the 86th Division never saw combat. After the end of World War I, Hubble spent a year at Cambridge University, where he renewed his studies of astronomy.[23]

The 100-inch Hooker telescope at Mount Wilson Observatory that Hubble used to measure galaxy distances and a value for the rate of expansion of the universe.

Edwin Hubble's arrival at Mount Wilson Observatory, California, in 1919 coincided roughly with the completion of the 100-inch (2.5 m) Hooker Telescope, then the world's largest. At that time, the prevailing view of the cosmos was that the universe consisted entirely of the Milky Way Galaxy.

Using the Hooker Telescope at Mount Wilson, Hubble identified Cepheid variables, a standard candle discovered by Henrietta Leavitt.[7] Comparing their apparent luminosity to their intrinsic luminosity gives their distance from Earth.[25][26] Hubble found Cephieds in several nebulae, including the Andromeda Nebula and Triangulum Nebula. His observations, made in 1924, proved conclusively that these nebulae were much too distant to be part of the Milky Way and were, in fact, entire galaxies outside our own, thus today they are no longer considered nebula.

This was first hypothesized as early as 1755 when Immanuel Kant's General History of Nature and Theory of the Heavens appeared. This hypothesis was opposed by many in the astronomy establishment of the time, in particular by Harvard University-based Harlow Shapley. Despite the opposition, Hubble, then a thirty-five-year-old scientist, had his findings first published in The New York Times on November 23, 1924,[27] then presented them to other astronomers at the January 1, 1925 meeting of the American Astronomical Society.[28] Hubble's results for Andromeda were not formally published in a peer-reviewed scientific journal until 1929.[29]

Hubble's classification scheme

Hubble's findings fundamentally changed the scientific view of the universe. Supporters state that Hubble's discovery of nebulae outside of our galaxy helped pave the way for future astronomers.[30] Although some of his more renowned colleagues simply scoffed at his results, Hubble ended up publishing his findings on nebulae. This published work earned him an award titled the American Association Prize and five hundred dollars from Burton E. Livingston of the Committee on Awards.[16]

Hubble also devised the most commonly used system for classifying galaxies, grouping them according to their appearance in photographic images. He arranged the different groups of galaxies in what became known as the Hubble sequence.[31]

Hubble went on to estimate the distances to 24 extra-galactic nebulae, using a variety of methods. In 1929 Hubble examined the relationship between these distances and their radial velocities as determined from their redshifts. His estimated distances are now known to all be too small, by up to a factor of about 7. This was due to factors such as the fact that there are two kinds of Cepheid variables or confusing bright gas clouds with bright stars.[32] However, his distances were more or less proportional to the true distances, and combining his distances with measurements of the redshifts of the galaxies by Vesto Slipher, and by his assistant Milton L. Humason, he found a roughly linear relationship between the distances of the galaxies and their radial velocities (corrected for solar motion),[11] a discovery that later became known as Hubble's law.

This meant that the greater the distance between any two galaxies, the greater their relative speed of separation. If interpreted that way, Hubble's measurements on 46 galaxies lead to a value for the Hubble constant of 500 km/s/Mpc, which is much higher than the currently accepted values of 74 km/s/Mpc[33][34] (cosmic distance ladder method) or 68 km/s/Mpc[35][36] (CMB method) due to errors in their distance calibrations.

Yet the reason for the redshift remained unclear. Georges Lemaître predicted on theoretical grounds based on Einstein's equations for general relativity the redshift-distance relation, and published observational support for it, two years before the discovery of Hubble's law.[37] Although he used the term "velocities" in his paper (and "apparent radial velocities" in the introduction), he later expressed doubt about interpreting these as real velocities. In 1931 he wrote a letter to the Dutch cosmologist Willem de Sitter expressing his opinion on the theoretical interpretation of the redshift-distance relation:[32]

"Mr. Humason and I are both deeply sensible of your gracious appreciation of the papers on velocities and distances of nebulae. We use the term 'apparent' velocities to emphasize the empirical features of the correlation. The interpretation, we feel, should be left to you and the very few others who are competent to discuss the matter with authority."

Today, the "apparent velocities" in question are usually thought of as an increase in proper distance that occurs due to the expansion of the universe. Light travelling through an expanding metric will experience a Hubble-type redshift, a mechanism somewhat different from the Doppler effect (although the two mechanisms become equivalent descriptions related by a coordinate transformation for nearby galaxies).

In the 1930s, Hubble was involved in determining the distribution of galaxies and spatial curvature. These data seemed to indicate that the universe was flat and homogeneous, but there was a deviation from flatness at large redshifts. According to Allan Sandage,

"Hubble believed that his count data gave a more reasonable result concerning spatial curvature if the redshift correction was made assuming no recession. To the very end of his writings, he maintained this position, favouring (or at the very least keeping open) the model where no true expansion exists, and therefore that the redshift "represents a hitherto unrecognized principle of nature."[38]

There were methodological problems with Hubble's survey technique that showed a deviation from flatness at large redshifts. In particular, the technique did not account for changes in luminosity of galaxies due to galaxy evolution. Earlier, in 1917, Albert Einstein had found that his newly developed theory of general relativity indicated that the universe must be either expanding or contracting. Unable to believe what his own equations were telling him, Einstein introduced a cosmological constant (a "fudge factor") to the equations to avoid this "problem". When Einstein learned of Hubble's redshifts, he immediately realized that the expansion predicted by general relativity must be real, and in later life, he said that changing his equations was "the biggest blunder of [his] life." In fact, Einstein apparently once visited Hubble and tried to convince him that the universe was expanding.[39]

Hubble also discovered the asteroid 1373 Cincinnati on August 30, 1935. In 1936 he wrote The Observational Approach to Cosmology and The Realm of the Nebulae which explained his approaches to extra-galactic astronomy and his view of the subject's history.

In December 1941, Hubble reported to the American Association for the Advancement of Science that results from a six-year survey with the Mt. Wilson telescope did not support the expanding universe theory. According to a Los Angeles Times article reporting on Hubble's remarks, "The nebulae could not be uniformly distributed, as the telescope shows they are, and still fit the explosion idea. Explanations which try to get around what the great telescope sees, he said, fail to stand up. The explosion, for example, would have had to start long after the earth was created, and possibly even after the first life appeared here."[40][41] (Hubble's estimate of what we now call the Hubble constant would put the Big Bang only 2 billion years ago.)

Hubble had a heart attack in July 1949 while on vacation in Colorado. He was cared for by his wife and continued on a modified diet and work schedule. He died of cerebral thrombosis (a blood clot in his brain) on September 28, 1953, in San Marino, California. No funeral was held for him, and his wife never revealed his burial site.[45][46][47]

In 2011, the journal Nature reported claims that Hubble had played a role in the redaction of key parts of the translation of Lemaître's 1927 paper, which stated what is now called Hubble's Law and also gave observational evidence for it. Historians quoted in the article were skeptical that the redactions were part of a campaign to ensure Hubble retained priority. However, the observational astronomer Sidney van den Bergh published a paper[48] suggesting that while the omissions may have been made by a translator, they may still have been deliberate.

In November 2011, the astronomer Mario Livio reported in Nature that documents in the Lemaître archive demonstrated that the redaction had indeed been carried out by Lemaître himself, who apparently saw little point in including scientific content which had already been reported by Hubble.[37] This, however, does not detract from the fact that Lemaître published[49] in French, without such omissions, two years prior to Hubble.

At the time, the Nobel Prize in Physics did not recognize work done in astronomy. Hubble spent much of the later part of his career attempting to have astronomy considered an area of physics, instead of being its own science. He did this largely so that astronomers—including himself—could be recognized by the Nobel Prize Committee for their valuable contributions to astrophysics. This campaign was unsuccessful in Hubble's lifetime, but shortly after his death, the Nobel Prize Committee decided that astronomical work would be eligible for the physics prize.[16] However, the prize is not one that can be awarded posthumously.

• Newcomb Cleveland Prize in 1924;[50]
• Bruce Medal in 1938;[51]
• Franklin Medal in 1939;[52]
• Gold Medal of the Royal Astronomical Society in 1940;[53]
• Legion of Merit for outstanding contribution to ballistics research in 1946;[54]

• Asteroid 2069 Hubble;
• The crater Hubble on the Moon;
• Orbiting Hubble Space Telescope;
• Edwin P. Hubble Planetarium, located in the Edward R. Murrow High School, Brooklyn, NY.;[55]
• Edwin Hubble Highway, the stretch of Interstate 44 passing through his birthplace of Marshfield, Missouri;[56]
• Hubble Middle School, a public school in Wheaton, Illinois, where he lived from 11 years old and up.[57]

On March 6, 2008, the United States Postal Service released a 41-cent stamp honoring Hubble on a sheet titled "American Scientists" designed by artist Victor Stabin.[46] His citation reads:[58]

Often called a "pioneer of the distant stars," astronomer Edwin Hubble (1889–1953) played a pivotal role in deciphering the vast and complex nature of the universe. His meticulous studies of spiral nebulae proved the existence of galaxies other than our own Milky Way. Had he not died suddenly in 1953, Hubble would have won that year's Nobel Prize in Physics.

(Note that the assertion that he would have won the Nobel Prize in 1953 is likely false, although he was nominated for the prize that year.[59])

The other scientists on the "American Scientists" sheet include Gerty Cori, biochemist; Linus Pauling, chemist, and John Bardeen, physicist.

• Hall of Famous Missourians 2003[60]
• 2008 "American Scientists" US stamp series, $0.41.[61]
• 2017 Indiana Basketball Hall of Fame[62]