During the Roaring ’20s, an intrepid astronomer blazed a trail with the world’s largest telescope to the edge of an ever-expanding universe.
On an October night in 1923, at the Mount Wilson Observatory north of Los Angeles, the view of the night sky was unparalleled. Down in the valley, Hollywood was booming, but the population of the city was still less than a million, and the tide of smog and city lights had not yet crept up the mountain. On its 5,700-foot peak stood the largest telescope in the world, a reflecting telescope with a 100-inch-wide mirror. At the eyepiece that night, guiding the mammoth white tube as it tracked the Andromeda Nebula across the sky, sat a 33-year-old astronomer named Edwin Hubble.
He was about to redefine our concept of the universe.
Hubble would have been wearing loose knickers and smoking a pipe that October night, two habits he had picked up while a Rhodes Scholar at Oxford. But everything else about this story— the story of how he discovered our universe is vast beyond imagining, and always growing vaster—is quintessentially American. The red-white-and-blue starts with Hubble himself. Born near Springfield, Mo., to God-fearing Baptists, Hubble was a star athlete. Alonzo Stagg wanted him for the University of Chicago football team, but his parents forbade him that violent sport, so he stuck with track and field. “An Olympian, tall, strong, and beautiful,” his widow Grace later wrote, recalling her first sight of him; he had been silhouetted against a window on Mount Wilson, examining one of his glass plates. He could have been the subject of a Hollywood biopic. In later years, after he became famous as a cosmic explorer, he would appear on the cover of Time, and would consort with movie people as much as with astronomers.
The telescope was the second American thing about this story. It’s not just that it was the world’s largest, and thus the instrument that could see the farthest into what Hubble would later call “the realm of the nebulae”—it’s that it was paid for, not by the government, but by wealthy philanthropists. John D. Hooker, a local businessman, footed the bill for the mirror, which was cast in France from greenish wine-bottle glass and then shipped to Pasadena for grinding and polishing. The rest of the money came from Andrew Carnegie, who through his Carnegie Institution supported science by supporting “exceptional” individuals like himself. The brains behind the telescope, George Hale, fit that bill, and so did Hubble, whom Hale recruited.
And finally there was Hubble’s method: It was pure American, just-the-facts-ma’am empiricism. Over in Germany a few years earlier, Einstein had revolutionized physics and cosmology in a very German way, from his desk. The intricate equations of his general theory of relativity had raised the unsettling possibility that the whole universe might be expanding. At first it was too unsettling even for Einstein; to keep the universe constant and stable, the way it always had been, he added a fudge factor to the equations. But the question really wasn’t one you could settle at a desk with pen and paper and long hours of strenuous ratiocination. Someone needed instead to spend long hours in a cold, darkened telescope building, its roof open to the heavens, its interior lit only by the glow of his pipe. Someone needed to measure the universe—and that’s what Hubble did. What he discovered, that night in October, was his first measuring stick.
Astronomers at that time could not decide, even roughly, how big the universe was, let alone whether it was expanding. There were basically two camps. According to one, the universe was no bigger than our own galaxy, the Milky Way. The sun, like most stars we can see, is embedded in that flat disk of stars, which appears as a band of light bisecting the night sky. But above and below the disk float the nebulae: faint clouds of light that, according to the first camp, were just that—clouds of luminous gas, studded perhaps with a few stars. They were part of our galaxy too; nothing we could see was not. It was anywhere from 20,000 to 200,000 light years across, depending on which astronomer you talked to.
According to the other camp, how – ever, those nebulae were not intrinsically faint and wispy—they only looked faint because they were very far away. They were other galaxies just like our own, floating in a much bigger sea of empty space. “Island universes,” Immanuel Kant had called them when he first proposed the theory in the 18th century. The debate between the two camps wasn’t new—but it had heated up in the 20th century, as new telescopes made it possible to see the nebulae more clearly. Hubble had devoted his doctoral work at Chicago to observing nebulae with a 24- inch reflecting telescope; that’s what brought him to the attention of Hale, who offered him a job at Mount Wilson, then held it for him for two years while Hubble went off to join World War I.
On his return to the United States, in August 1919, Hubble wasted no time. He had not seen action in France, much to his chagrin, and he was champing at the bit. According to his biographer Gale Christianson, he stopped in Chicago for one day to visit his mother and siblings; according to other sources, they had moved to Madison by then and Hubble did not bother to make the short detour. “I sometimes feel there is within me to do what the average man would not do,” he had once written to his mother, while a Rhodes Scholar at Oxford, “if only I could find some principle for whose sake I could leave everything else and devote my life.” He had found that principle now; he would never again have much contact with his family. He would spend his life in California, with the stars.
The timing of his arrival on Mount Wilson—still in military uniform—was perfect. After a prolonged gestation the 100-inch telescope had begun normal operations just a few weeks earlier. Hubble soon started observing with it— and soon revealed an uncommon knack for finding his way around the sky, and for noticing small but significant changes in it from one observation to the next. Back then, astronomers still actually looked through telescopes, at least to select the field of view. Then they sat and waited for the photo graphic plate at the focus of the telescope to collect enough light to reveal objects too faint to see through the eyepiece.
The Andromeda Nebula itself was not too faint—indeed it is visible without a telescope, to the naked eye, “an elongated cigar about half the size of the full moon,” as Hubble put it. The individual stars in it were what you could see only with a telescope, and the 100-inch reflector revealed more than ever. On the night of Oct. 5, 1923, Hubble noticed a faint star he had not seen before. Back in his office in Pasadena, though, he found the same star on earlier plates—it was a regularly pulsing star called a Cepheid variable. Astronomers had studied Cepheids in the Milky Way, and dis – covered that the period of the pulsations was a reliable measure of the star’s intrinsic brightness. Comparing that with how bright the star appeared on their photographs, they could calculate how far away it was. Hubble did that right away with his first Cepheid. He found that it and, thus, the Andromeda Nebula were 1 million light-years away— a distance five times greater than the largest estimate of the Milky Way’s diameter. Clearly Andromeda was not part of the Milky Way.
To prove that, Hubble had to collect many more dots, of course. But astronomers were quick to recognize the end of the long-running debate. When Hubble’s first results were presented at a scientific meeting at the end of 1924, one astronomer pulled out a slide rule to calculate how much the volume of the universe had just grown: a hundredfold, he said. When Harlow Shapley, the leader of the our-galaxy-is-the-whole-shebang camp, received a letter from Hubble in 1924, announcing the Cepheids in Andromeda and another nebula, he is reported to have said to a colleague, “Here is the letter that has destroyed my universe.”
Hubble destroyed everyone’s universe, everyone but Einstein’s, and replaced it with a new one, a universe populated not just by one but by millions— billions, we now know—of galaxies. By 1929, he and a colleague named Milton Humason had showed that light waves from most of the nebulae were stretched longer and reddened—presumably by the same “Doppler shift” phenomenon that stretches the sound waves of a passing race car, deepening the roar of its engine. Without Hubble’s meticulous observations, no one would have believed the bizarre implication of Einstein’s theory, not even Einstein: that the other galaxies were hurtling away from us because new empty space is always popping up between them, and has been ever since the universe was first created, billions of years ago, in the Big Bang. “The history of astronomy is a history of receding horizons,” Hubble said in one of a series of popular lectures at Yale in 1935, later published as The Realm of the Nebulae. The double meaning was surely intentional.
Yet Hubble himself never fully committed to the expanding-universe theory—never even used the word “galaxy” to describe the nebulae he had proved were galaxies like our own. His original papers are noteworthy for his refusal to acknowledge the most interesting implications of his work, and for his almost fetishistic commitment to the data and nothing but. He was an enigmatic man in other ways as well. Christianson tracked down witnesses from grade school on who testified to his standoffishness and arrogance—yet he was also apparently insecure enough to feel the need to affect a British accent while at Oxford. In his new life in California, he told bold lies about his old one, claiming falsely to have practiced as a lawyer, and to have been wounded in the war. He seemed in many ways a hard and brittle man—and yet he cried in the theater, and teared up even at the sound of old cowboy songs, which he would sometimes sing to while away the long nights at the telescope. When you look at photos of Hubble, early and late, he is ever handsome and manly. But the most disconcerting feature is the soft, slightly drooping, melancholy eyes.
The creator of our modern universe died childless in 1953, and left behind no memoir. His ashes were buried in the presence of five people, all of whom have since died; the site is unknown. Today a famous space telescope named after him has seen more than 10 billion light years out, 20 times farther than Hubble could with the 100-inch. It has produced far more precise estimates of distances and of the cosmic expansion rate than Hubble himself was able to do. But the basic structure of our universe remains the one he determined.
“The stellar system is a swarm of stars isolated in space,” he said at the beginning of his Yale lectures, referring to the Milky Way. “It drifts through the universe as a swarm of bees drifts through the summer air. From our position somewhere within the system, we look out through the swarm of stars, past the borders, into the universe beyond.” Thanks to Hubble, we know there is a beyond. And we know we’ll never see the end of it.
Robert Kunzig is the author of Fixing Climate and Mapping the Deep.
Originally published in the August 2009 issue of American History. To subscribe, click here.