Edwin Hubble’s work provoked a dramatic change in people’s beliefs about the universe, when he proved it is home to other galaxies besides the Milky Way.
Hubble showed we live in a universe of many galaxies separated by immense distances, each an isolated ‘island universe.’ Just as Copernicus caused an epochal change when he removed Earth from the center of the solar system, Hubble did so too when he removed our galaxy from the center of the universe.
Hubble’s Law signals that the farther away another galaxy is, the faster it is moving away from us. Most scientists believe this means we live in an expanding universe, although Hubble was reluctant to accept this interpretation without further experimental proof.
Beginnings
Edwin Powell Hubble was born on November 20, 1889 in the township of Marshfield, Missouri, USA.
His mother was Virginia Lee James. His father was John Powell Hubble, who had a law degree and was an insurance salesman. Edwin was the third of eight children, not all of whom survived childhood.
The Hubble family were financially prosperous. They needed to be mobile because of John Hubble’s insurance career, and they lived in the suburbs of cities including Chicago and Louisville. Their homes were large and prestigious and staffed with servants.
The Hubble children were all given chores to do, because their parents believed this helped them develop better characters.
Edwin began reading when he was an infant, trying to keep up with his elder brother and sister who had started school. His favorite books were adventure stores by Jules Verne and H. Rider Haggard.
When he was seven, his grandfather, who was an enthusiastic amateur astronomer, showed him one of his telescopes. Edwin was so eager to use it that he asked if he could stay up at night studying the heavens rather than have an eighth birthday party.
High School
Edwin seems to have sailed easily through his studies at Wheaton High School near Chicago. His grades in English, Mathematics, Biology, Chemistry, Physics, Latin, and German were usually between 95 and 100. He actually spent more time on sports than study. Encouraged by his father, he worked as a delivery boy during his vacations. He graduated from high school in 1906, age 16, with a scholarship for the University of Chicago.
College
In the fall of 1906, still 16, Hubble enrolled at Chicago. He continued devoting a great deal of time to sport, particularly basketball, athletics, and heavyweight boxing. Records show that on May 6, 1906 he set a new state record for the high jump, clearing 5 feet 8-and-a-half inches. Hubble was six foot two inches tall and strongly built. In 1910, he graduated with a Bachelor’s of Science degree, with credits in sciences including physics and astronomy.
Hubble spent the next three years on the other side of the Atlantic at the University of Oxford on a Rhodes scholarship. He was still enthusiastic about science, particularly astronomy, but he studied Jurisprudence (the theory of law) in deference to his law-graduate father. Hubble graduated with a Bachelor of Arts in 1912. He spent a further year learning Spanish. During his time at Oxford, he spent two summer vacations cycling around Europe, but thoughts about his future direction were never far from his mind, and he was thinking big. He wrote his mother:
“Work, to be pleasant, must be toward some great end, an end so great that dreams of it, anticipation of it overcomes all aversion to labor. If only I find some principle, for whose sake I could leave everything else and devote my life.”
In the fall of 1912, Hubble learned that his father was dying. He asked his father’s permission to leave Oxford and return to see him. His father refused, telling his son to keep working. His father died in January 1913.
Teaching and Graduate School
Hubble returned to the USA in the summer of 1913.
Hubble (left) with friends sometime after his return from Oxford. Image courtesy The Huntington Library.
Hubble exploring a cave sometime after returning from Oxford. Image courtesy The Huntington Library.
He got a job teaching Spanish and Physics at New Albany High School, Indiana. He also coached the school basketball team and did commercial German translation work. He was a very popular teacher, but he did not enjoy it much.
He contacted Forest Ray Moulton, an astronomy professor at the University of Chicago, asking about graduate work. Moulton wrote Edwin Frost, head of the university’s Yerkes Observatory in Wisconsin, saying Hubble:
“…is a man of the finest type. Physically he is a splendid specimen. In his work here, altogether, and especially in science, he showed exceptional ability. I feel sure you would find him just the sort of man you would wish to have.”
And so, age 24, Hubble finally entered the field that had fascinated him since he first looked through his grandfather’s telescope almost two decades earlier. He began a Ph.D. in Astronomy, graduating in 1917 with the thesis Photographic Investigations of Faint Nebulae.
Hubble studied nebulae, which are clouds in space. This one is called ESO 373-8.
World War 1 then intervened and Hubble spent a year in the army and a year at the University of Cambridge carrying out astronomy research work.
In 1919, age 30, he began work at Mount Wilson Observatory in California, renowned for its clear air and excellent viewing conditions. He would remain there for the rest of his life.
Edwin Hubble’s Contributions to Science
Galaxies Beyond Our Own
Hubble studied nebulae for his Ph.D. and he returned to this work at Mount Wilson, where he could make observations using the world’s largest telescope, the 100-inch (2.5 m) Hooker Telescope.
In 1912, Henrietta Leavitt had discovered something remarkable about a type of star known as a Cepheid variable: the rate at which this type of star goes through a dim-bright-dim cycle is highly significant; it offers a way of finding out how far away the star is.
In the early 1920s, benefitting from access to the huge Hooker Telescope, Hubble found Cepheid variable stars located in nebulae. He paid close attention to the Andromeda nebula, and discovered that the Cepheid variables within the nebula are at tremendous distances from the earth, much farther than stars in our own Milky Way galaxy.
Hubble realized that the Andromeda nebula is actually a galaxy. Until then, most astronomers thought the Milky Way and the universe were the same thing. Hubble now knew the universe was considerably bigger than the Milky Way; it contained other galaxies or ‘island universes.’
The Andromeda nebula is actually a galaxy. The idea that some nebulae could be island universes was first suggested by the British astronomer Thomas Wright in 1750, and popularized by the German philosopher Immanuel Kant in 1755. Image courtesy NASA/JPL.
Hubble found:
- His best photographs of the outer parts of the Andromeda and Triangulum nebulae showed “dense swarms of actual stars.”
- Many of the stars were Cepheid variables.
- The nebulae were located almost a million light-years † from Earth – four times farther away than anything observed before.
- The Andromeda nebula’s diameter exceeded 30,000 light-years††, making it bigger than the Milky Way.
- The Andromeda galaxy emitted light of the order of a billion of our suns.
Three days after his thirty-fifth birthday, Hubble’s discovery was announced – not in a scientific journal – but in The New York Times. His results had actually been circulating quietly among America’s astronomers for some time: the official presentation came in a paper he submitted to be read at the January 1, 1925 meeting of the American Astronomical Society.
Hubble had changed our view of the universe forever. Our own vast galaxy, home to our sun and 100 billion other stars, is but one of billions of other galaxies.
In addition to this, Hubble gave us the system we use for classifying galaxies, shown below:
Hubble’s classification of galaxy types.
Red Shift is Directly Related to Distance
The eminent astronomer Vesto Slipher had also studied nebulae. In 1913, he reported that light from nebulae was shifted to the red end of the spectrum.
He interpreted his discovery as a Doppler shift, one of the most familiar examples of which is the pitch of a police car’s siren: if the car is racing towards you the pitch is raised; if it is racing away from you the pitch is lowered.
Light behaves in a similar way. Light emitted by an object racing away from Earth is shifted to the red end of the spectrum.
If the sun were racing away from us at an enormous speed, its light would be shifted to the red end of the spectrum.
Slipher examined a number of nebulae – he did not know they were galaxies – and found light from a large majority of them showed a significant red shift, indicating they were moving away from Earth at prodigious speeds.
In 1929, Hubble took Slipher’s red-shift data and combined it with red-shift observations he and his assistant Milton Humason had made. He plotted the red-shift data against galaxy distance data and found a remarkable correlation.
Hubble obtained convincing evidence that the farther away a galaxy is from us, the faster it moves away from us.
Hubble turned the relationship from his graph into an equation, now called Hubble’s Law, which says:
where v is velocity, r is distance, and H is the Hubble Constant, which Hubble calculated to be 530 km s-1 Mpc-1. Today, with the benefit of much more sophisticated observational data and better distance calibrations, H is believed to be approximately 70 km s-1 Mpc-1.
The Expanding Universe
One interpretation of Hubble’s Law is that we live in an expanding universe. Hubble did not believe there was enough hard evidence to support this interpretation of red-shifts.
In fact, although Hubble brought the scientific world’s attention to Hubble’s Law, the law was in fact discovered two years earlier by Georges Lemaître. Unfortunately for Lemaître, his work received little attention. Lemaître calculated H to be 625 km s-1 Mpc-1.
Not only did Lemaître discover ‘Hubble’s Law,’ his interpretation of it is the one accepted by modern cosmologists. Lemaître used Albert Einstein’s theory of general relativity to show that red-shifts would result naturally if the very fabric of space itself were expanding.
Expanding space is a little bit like rising raisin bread; from the point of view of any single raisin all the other raisins move away from it as the bread expands.
However, Hubble’s point of view was perfectly logical. Although the existence of ‘dark matter’ in the universe often seems a modern concern, Hubble wrote that the red-shifts could only be justified as evidence for an expanding universe if the density of matter in the universe were much larger than had actually been observed. He said the density of matter needed to accept red-shifts as evidence of an expanding universe is:
“…many times greater than even the maximum estimates of the smoothed-out density of material concentrated in nebulae, and we find no evidence of any considerable amount of internebular material which might increase the density.”
Also, if Hubble, for the sake of argument, accepted that red-shifts were caused by an expanding universe, observational data led him to believe that the universe’s rate of expansion was slowing.
“Long ago when the light we now record left the very distant nebulae, the expansion was more rapid than it is today.”
The Expanding Universe – Very Tricky
As an illustration of just how tricky this field is, in 2011, Saul Perlmutter, Brian Schmidt and Adam Riess shared the Nobel Prize in Physics “for the discovery of the accelerating expansion of the Universe through observations of distant supernovae.”
However, in 2016, a joint report by physicists at the Niels Bohr Institute and University of Oxford said that an analysis of more data than used by the Nobel winners indicated the evidence for an accelerating expansion fell short of that required for a discovery of fundamental significance.
No doubt an unchallenged picture of what our universe is doing and why it is doing it will emerge, but it might be some time yet.
Honors
Hubble received a large number of awards in his lifetime, including the Newcomb Cleveland Prize in 1924; the Bruce Medal in 1938; the Franklin Medal in 1939; and the Gold Medal of the Royal Astronomical Society in 1940. For his work in World War 2, when he was chief of ballistics and director of the supersonic wind tunnel laboratory at Aberdeen, Maryland, he was awarded the Legion of Merit in 1946.
Probably the greatest honor Hubble received, albeit posthumously, was the naming of the great space telescope for him. The Hubble Space Telescope has transformed cosmology, provided images of unmatched beauty, and yielded data that has driven both a better understanding of the universe and an ongoing realization that we do not know or understand everything yet.
Some Personal Details and the End
In February 1924, age 34, Hubble married Grace Burke Leib, a graduate of Stanford University. They had no children.
Hubble’s main hobby was book collecting – particularly books relating to the history of science. He became a trustee of the Huntington Library in San Marino.
Hubble gained a reputation for eccentricities. As a young man, he left America as an all-American college graduate and returned from Oxford as a pipe-smoking English gentleman, complete with whimsical turns of phrase that even Bertie Wooster might have hesitated to use. Hubble also became prone to exaggerating some of the experiences of his earlier years, such as his sporting achievements.
Hubble’s discovery of other galaxies made him famous. He featured on the front page of Time magazine in 1948, and he and Grace became close friends with the novelist Aldous Huxley and his wife Maria and met many of Hollywood’s stars.
In 1949, age 59, Hubble suffered a serious heart attack. Grace nursed him back to health, but had to reduce his working hours – no more long cold nights at the telescope were allowed.
Edwin Hubble died, age 63, of a stroke (cerebral thrombosis) on September 28, 1953 in San Marino, California. At his own request, his final resting place is not known and Grace destroyed his personal papers. When Grace died in 1980 she was buried in the same secret resting place.
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Further Reading
Edwin Hubble
The Realm of the Nebulae
Yale University Press, 1936
Edwin Hubble
The Observational Approach to Cosmology
Oxford Clarendon, 1937
W. S. Adams
Obituary: Dr. Edwin P. Hubble
The Observatory, Vol. 74, pp. 32-35, 1954
R. Berendzen and M. Hoskin
Hubble’s Announcement of Cepheids in Spiral Nebulae
Astronomical Society of the Pacific Leaflets, Vol. 10, No. 504, pp. 425-440, 1967
Donald E. Osterbrock, Ronald S. Brashear, Joel A. Gwinn
Self-Made Cosmologist: The Education of Edwin Hubble
ASP Conference Series, Vol. 10, Evolution of the Universe of Galaxies; Proceedings of the Edwin Hubble Centennial Symposium, ed. by Richard G. Kron, pp. 1-18
Alexander S. Sharov, Igor D. Novikov
Edwin Hubble, The Discoverer of the Big Bang Universe
Cambridge University Press, 1993
William H. Cropper
Great Physicists: The Life and Times of Leading Physicists from Galileo to Hawking
Oxford University Press, 2004