Edwin Hubble was an American astronomer who, in 1925, was the first to demonstrate the existence of other galaxies besides the Milky Way, profoundly changing the way we look at the universe. Later, in 1929, he also definitively demonstrated that the universe was expanding, (considered by many as one of the most important cosmological discoveries ever made), and formulated what is now known as Hubble’s Law to show that the other galaxies are moving away from the Milky Way at a speed directly proportionate to their distance from it. He has been called one of the most influential astronomers since the times of Galileo, Kepler and Newton.
Edwin Powell Hubble was born on 20 November 1889 in Marshfield, Missouri, U.S.A., although the family moved to Wheaton, Illinois soon after his birth. At school he earned good grades in most subjects, although he was more noted for his athletic prowess than his intellectual abilities (in 1906, he won seven first places and a third place in a single high school track meet, and set a state record for high jump). He was also a keen fisherman, basketball player and an amateur boxer.
From 1907 to 1910, he studied mathematics, astronomy and philosophy at the University of Chicago, leading to a BSc degree in 1910. He spent the next three years as one of the first Rhodes Scholars at Oxford University, where he studied jurisprudence before switching his major to Spanish and receiving an MA degree. On returning to the United States in 1913, he taught Spanish, physics and math (and coached the basketball team) at a high school in New Albany, Indiana, and also practiced law half-heartedly for a year in Louisville, Kentucky.
Hubble’s arrival at Mount Wilson in 1919 coincided roughly with the completion of the 100-inch Hooker Telescope, then the world’s largest telescope, which allowed him to observe hitherto unheard of distances into the universe. During the period from 1922 to 1923, he was able to identify Cepheid variables (a class of variable stars notable for a tight correlation between their period of variability and their absolute luminosity, which makes them useful as a “standard candle” to determine distances) in several spiral nebulae, including the Andromeda Nebula.
His meticulously documented observations, announced at the beginning of 1925, proved conclusively that these nebulae were nearly a million light years away, much too distant to be part of the Milky Way, and were in fact entire galaxies outside our own. At that time, this was a revolutionary idea, the prevailing view being that the universe consisted entirely of the Milky Way, and it was opposed vehemently by many in the astronomy establishment, particularly by Harvard-based Harlow Shapley, who had made his reputation by measuring the size of the Milky Way.
Hubble went on to devise the most commonly used system for classifying galaxies, grouping them according to their appearance in photographic images, in what became known as the Hubble sequence. But an even more dramatic and important discovery was still to come.
Using the recently discovered concept of the redshift of galaxies (a measure of recession speed, based on the idea that visible light emitted or reflected by an object is shifted towards the less energetic red end of the electromagnetic spectrum as it moves away from the observer), and combining his own measurements with those of Vesto Slipher, Hubble and his assistant, Milton Humason, discovered a rough proportionality of the objects’ distances with their redshifts. This led to the statement in 1929 of the “redshift distance law of galaxies”, now better known as Hubble’s Law, which states that the greater the distance between any two galaxies, the greater their relative speed of separation.
Hubble’s initial estimate of the rate of expansion (the constant term in his equation linking the recession velocity of galaxies and their distance, known as Hubble’s constant) was perhaps ten times too great due to measurement errors, and its exact value still remains a contentious subject. However, the general concept of an expanding universe was consistent with the solutions to Einstein’s equations of general relativity for a homogeneous, isotropic expanding space. Thus, it provided the first observational support for the expanding universe theory which had been proposed in theory by Alexander Friedmann in 1922 and Georges Lemaître in 1927, and for the Big Bang explanation of the birth of the universe.
Albert Einstein, whose general relativity equations had seemed to indicate that the universe must be either expanding or contracting, had introduced a compensatory “cosmological constant” into his equations back in 1917 because he could not believe that the universe was anything but static and infinite. When he heard of Hubble’s discovery, however, he said that changing his equations was “the biggest blunder” of his life, and he was grateful to Hubble for negating the need for such a fudge factor in his equations. Einstein travelled to Mount Wilson to see the telescope and to thank Hubble personally for delivering him from folly.
During World War II, from 1942 to 1946, he served in the U.S. Army as head of ballistics at the Aberdeen Proving Ground, for which he received the Legion of Merit decoration. He remained active in astronomy research until his death, both at Mount Wilson Observatory and also at Palomar Observatory, where he had a central role in the design and construction of the 200-inch Hale Telescope. When the Hale Telescope was completed in 1948, Hubble was the first to use it.
However, soon after that, he suffered a major heart attack, and he never fully regained the stamina needed to spend all night in a freezing-cold observatory. Hubble died of a cerebral thrombosis on 28 September 1953, in San Marino, California. No funeral was held, and his wife, Grace, never revealed what happened to his body.
Although he had been awarded the Bruce Medal in 1938, the Gold Medal of the Royal Astronomical Society in 1940 and the Medal of Merit for outstanding contribution to ballistics research in 1946, Hubble, as an astronomer, was inelegible for the Nobel Prize in Physics (a rule which always irked him, although it was changed just after his death). He was, however, honoured posthumously in other ways, including the naming of an asteroid and a crater on the Moon and, most famously, the orbiting Hubble Space Telescope, which was launched in 1990 and which continues to provide us with astounding pictures of deep space.