Tenderly, as though bidding farewell to a loved one, the veteran astronaut reached out and touched the giant Hubble Space Telescope. He would be the last human to make direct contact with the orbiting observatory that had captured the hearts of the public since it was first launched in 1990. An attempt to abandon Hubble—to cut funding for its shuttle servicing missions in the wake of the Challenger disaster—caused such a public uproar that NASA had to back down and authorize a fifth and final servicing mission. So in May 2009, spacewalking astronauts installed a Wide Field Camera and other advanced technology. Then the Hubble was released from the space station and launched back into space to continue taking its incredibly sharp pictures of the universe—until it is brought down in the 2020s and dropped into the sea.
But the giant space telescope’s real mission was not just to take ever more dazzling pictures of the cosmos. It was to find an exact value for the Hubble Constant, which describes how fast the universe is expanding. Since Isaac Newton’s time, conventional wisdom had held that the universe was static, unchanging. It was the visionary astronomer Edwin Hubble who proved in 1929 that the universe was expanding. So it is fitting that the most magnificent space telescope yet created should be named for the stellar pioneer who for the first time saw beyond our nearby galaxies to a vaster universe.
Edwin Hubble—an athletic Midwestern youth, son of an insurance executive who had wanted his son to be a lawyer—but who followed his heart into physics and astronomy—had spent his entire career after World War I at the Mount Wilson Observatory outside of Los Angeles. Using the new 100” Hooker telescope—at the time the largest in the world—he looked deeper into the night sky than anyone before him. Beyond our Milky Way galaxy, with its billions of stars, there lie countless other galaxies with their billions of stars. As Hubble continued his patient, meticulous measurement of the more distant galaxies, he was astonished to realize that Isaac Newton—and established astronomical doctrine—were wrong! The universe, far from being static, was expanding—and the rate of expansion was expanding! The more distant a galaxy, the faster it was receding.
The clue that caused a completely new view of the universe was Hubble’s discovery of the “redshift.” Light coming from galaxies beyond our own, which he was the first to observe, showed that they were moving away from us. We have all had the experience of hearing a train whistle or an ambulance siren become louder as it approaches, then fainter as it recedes—the familiar Doppler effect. Similarly, light is shifted on the visual spectrum—the light that we can see—toward the red when it is receding, while light approaching us is shifted toward the blue.
The law known as Hubble’s Constant, which was derived from his observation of the redshift, tells us how fast are receding those galaxies whose redshifted light arrives to our telescopes from distances so vast that our minds cannot comprehend them.
Actually, a Belgian priest, cosmologist, and professor of physics named Georges Lemaitre had earlier derived the same law from Einstein’s general relativity equations. In a 1927 article, Lemaitre, who had earlier been exposed to the ideas of Edwin Hubble at the Massachusetts Institute of Technology, proposed that the universe is expanding and suggested an estimated value of the rate of expansion. His work laid the foundation for what we now call the big bang. Two years later in 1929, the breakthrough results of Hubble’s decade of work confirmed those observations and determined a more accurate value for the constant that now bears his name.
Science continues to refine the constant, using, among others, the invaluable results of the Hubble Space Telescope’s observations since its launch in 1990. Aiming for a 2018 launch, if the politicians do not kill it, the new James Webb Space Telescope, operating mostly in the infrared, will see so far into the past that we may be able to detect light coming from only a few million years after the birth of our universe.
Throughout history, most people had believed that the universe is infinite, with no beginning or end. So Hubble’s 1929 discovery shocked the astronomical community. He had shown that the universe is finite —that it had been born some 15 billion years ago in a tremendous explosion that we now call the big bang, and has been expanding ever since. According to Einstein’s general theory of relativity, the expansion is likened to dots on a balloon; as the balloon inflates, the dots move further and further away from each other. So everything in the universe is moving away from everything else.
However, as noted earlier, the exact value of the Hubble Constant is uncertain, which is why the Hubble Telescope and after it the James Webb are tasked with refining it. It is generally thought to be about 70 kilometers per second for every megaparsec in distance. A megaparsec is an incomprehensibly big number, given our earthly sense of distance. We all know the speed of light: 186,000 miles per second, or 300,000 kilometers per second. It takes 8 minutes for light from the sun to reach us. So traveling at the rate of 300,000 kilometers per second, light from the nearest star, Alpha Centauri, takes more than four years to reach us. And that’s the nearest star!
In January 2011, the Hubble Telescope discovered the most distant object in the observable universe. It has taken 13.2 billion years for light from the newly discovered galaxy traveling at 300,000 kilometers per second to reach the earth. That light is from a galaxy born a mere 480 million years after the big bang. We are getting close to the birth of the universe!
Hubble’s discovery of the expanding universe stemmed from one of the most famous scientific rivalries of the time—between Hubble and Harlow Shapley of Harvard, who had already made his name by measuring the size of the Milky Way, our own galaxy. His result of 300,000 light-years for the width of the galaxy, measured by using Cepheids—young stars whose luminosity is variable—was roughly 10 times the previously accepted value. However Shapley, like most astronomers of the time, believed that the fuzzy patches on his photographic plates called “nebulae”—Latin for “mist”—were relatively nearby objects, merely patches of dust and gas.
And then the game-changing breakthrough. After years of bitterly cold nights at the 100’ telescope (his seat can still be seen today by the many pilgrims to Mount Wilson), in October 1923 Hubble spotted what he first thought was a nova flaring up dramatically in the M31 “nebula” in the constellation of Andromeda—one of the galaxies nearest to our own Milky Way, part of what astronomers call the “Local Group.” But after painstakingly examining photographic plates of the same area taken earlier by other astronomers, including Shapley, Hubble realized that what he thought was part of a local galaxy was actually a million light-years away, far beyond the Milky Way. It was itself a galaxy containing millions of stars. That day, Hubble forever changed our understanding of the universe.
Edwin Hubble’s observations had a huge impact on Albert Einstein. Between 1907 and 1913, Einstein was developing his general theory of relativity, which expanded his special theory to include the effect of gravitation on the shape of space and the flow of time. It proposed that matter causes space to curve. Einstein had to invent a “cosmological constant” to make the equations of his new theory come out right because he—along with other scientists of the day—was still convinced that the universe was static, unchanging. His “cosmological constant” gave him a way to balance the gravitational contraction caused by matter.
When Hubble first announced his revolutionary findings, Einstein realized that if the universe was expanding, the cosmological constant was not needed. His beautiful equations had been right all along! So in 1931, Einstein traveled to Mount Wilson to shake Hubble’s hand and thank him for saving General Relativity from what he lamented as “the greatest blunder of my life.” Of course, we know now that Einstein’s “cosmological constant” was not an error of mathematics, but an error based on the static thinking of the time.
Strangely enough, Hubble himself at first did not accept the conclusion of most scientists as to the way the universe was expanding! Six years after his monumental discovery, he still questioned whether the “redshift” really meant that the rate of expansion was increasing, or whether the redshift was merely the familiar Doppler effect—the train whistle or the fire engine siren.
In addition to the Hubble Constant, the great astronomer’s name is attached to the Hubble Time or “expansion timescale”—13.8 billion years since the birth of the universe—and to the Hubble Length, or the distance by which the galaxies are receding from us at the speed of light. The Hubble Volume is generally understood as the volume of the observable universe.
Having your name writ large in the cosmos is not bad for a Midwestern boy, son of an insurance executive who wanted him to become a lawyer! Born in 1889 in a small Missouri town, Hubble spent most of his life in Chicago. A big, strong athletic youth, Hubble was a standout in college sports at the University of Chicago. He had to work his way through school, so while he was taking physics and astronomy courses, he worked in the laboratory of the legendary Robert Millikan, winner of the 1923 Nobel Prize in Physics for his measurement of the charge on the electron and for his work on the photoelectric effect. Graduating in 1910, Hubble was one of the first to win a Rhodes scholarship to Oxford. In accordance with his father’s dying wish, he studied law in England.
On return to the United States, Hubble passed the Bar and desultorily practiced law in Louisville, Kentucky, for a year. But his heart was not in it; in 1914, he “chucked it up” and returned to the University of Chicago to pursue a doctorate in his true love—astronomy. His PhD thesis on “Photographic Investigations of Faint Nebulae” already foreshadowed the life’s work that would open the universe to a new generation of astronomers.
After serving in France during World War I, rising to the rank of major, Hubble joined the staff of the Mount Wilson Observatory, which had earlier tried to lure him, but he had made the choice to go to war for his country. He was to remain at the observatory for the rest of his life, with time out in 1942 to do war work at the Aberdeen Proving Ground for which he was awarded the Medal of Merit, at the time the highest U.S. civilian decoration. In 1924, he married Grace Burke. There were no children.
Hubble’s brilliant work on the Mount Wilson 100” telescope provided strong evidence to the astronomical community of the need for a much larger telescope. He was influential in the design of the 200” Hale telescope on Mount Palomar in Northern San Diego County, California. From its inception in 1930 via a $6,000,000 grant from the Rockefeller Foundation, it took nearly 20 years—interrupted by World War II—for the Mount Palomar Observatory to be completed—to see “first light,” in astronomy’s poetic terminology. Thirteen years alone were required for the huge mirror—the largest in the world to date—to be polished to the required specifications. And it was Edwin Hubble who in 1949 was given the honor of taking the first photographic exposure with the 200”. Asked what he expected to find with the new telescope, he replied simply: “We hope to find something we hadn’t expected.” Exactly. Just as he had done 20 years earlier with the 100” on Mount Wilson!
In addition to the revolutionary new vision of our universe that Hubble brought to humanity—a vision that earned him to sobriquet “father of cosmology”—he wrote two scientific books: The Realm of the Nebulae (1936) and The Observational Approach to Cosmology (1937).
Hubble had long hoped to win the Nobel Prize; he lobbied for it to be awarded to astronomy as a separate category. But he died in 1953, shortly before the Nobel Committee decided that astronomical work would be eligible for the physics prize. Since the prize cannot be awarded posthumously, it is a sad irony that this great explorer of the universe would have won the prize had he lived just a little longer.
Indeed, it is tantalizing to speculate what Hubble would have made of late-20th-century and early-21st-century developments in the study of the expanding universe. By the early 1990s, it was assumed that gravity—the force that pulls all matter together—would eventually slow the expansion that Hubble had discovered. But in 1998, the Hubble Space Telescope’s observation of supernovae whose light was reaching us over an unimaginable gulf of time stunned astronomers by showing that the expansion of the universe is not only not slowing, but it is also accelerating! Theorists have given a name to the mysterious force that is tearing galaxies apart: dark energy. Though it cannot be observed, scientists have compared their theoretical models to cosmological observations and have concluded that dark energy comprises 70% of the universe and dark matter (which does not emit enough radiation to be directly observed) constitutes 25%. So what’s left? “Normal” matter—all the galaxies, all the constellations, all the stars with their planets—everything we have been able to directly observe—amounts to a mere 5% of the universe.
To paraphrase the poet Wordsworth: “Hubble, thou shouldst be living at this hour!”
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Mayall, N. U. Edwin Powell Hubble. Washington, D.C.: National Academies Press, 1970. www.nap.edu/html/biomems/ehubble.pdf
Sharov, Aleksandr Sergeevich, and Igor Dmitrievich Novikov. Edwin Hubble, the Discoverer of the Big Bang Universe. Cambridge: Cambridge University Press, 1993.
White, Martin. The Hubble Expansion. astro. berkeley.edu/ˆmwhite/darkmatter/hubble.html.