THE EXPANDING UNIVERSE
Not even the hardiest lichens grow on the windswept summit of Mauna Kea. But the astronomers who brave the Hawaiian peak’s rarefied atmosphere have other vistas on their minds. Drawn by the Canada-France-Hawaii telescope, they come to probe the cosmos. Among them is the University of Toronto’s Barry Madore, who deep into the night photographs the swirling galaxies millions of light-years away. Madore is one of a growing throng of scientists meticulously accumulating data on the cosmos. And their findings are rapidly revolutionizing man’s traditional view of the universe. Says Carl Sagan, a Pulitzer Prize-winning astronomer: “We will for the first time rigorously determine the nature and fate of the universe.”
That may be an understatement. Accelerating efforts to penetrate the secrets of the cosmos have brought scientists to the brink of the greatest enigma that mortals can contemplate—the very destiny of the universe itself. Within the next few decades, Sagan claims researchers may well find answers to a whole series of profound and shattering issues. Among them: will the galaxies keep flying apart forever until the cosmos ends in utter blackness and everlasting cold as the last star flickers out? Or will the expansion ultimately reverse with a cataclysmic, atom-crunching collapse? No longer is the conventional belief that the universe will expand indefinitely considered fully acceptable. Says astronomer George Mitchell of St. Mary’s University in Halifax: “The powerful arguments for an open universe heard during the mid-’70s just do not seem as strong anymore. We may be at a critical turning point.”
What is rapidly becoming clear is just how close scientists are now to that turning point. In the past year alone, robot probes have measured the mountains of Venus and scanned the icy rings of Saturn. Among the major landmarks in our solar system, only remote Uranus, Neptune and Pluto elude closeup scrutiny. After more than a decade of landmark discoveries, budgetary pragmatism has virtually ended the era of interplanetary missions. And scientists—undaunted—are turning their attention to the new and awesome frontier: the universe at large.
In the past two years an army of researchers has focused its efforts on that most fundamental of questions. While astronomers ponder measurements of distant galaxies, nuclear physicists analyse the behavior of the smallest atomic entities that whirl through particle accelerators. Chemists measure the abundance of chemical elements in meteorites. High-energy physicists decode the message of cosmic X-rays and gamma rays trapped by earth-orbiting observatories. And relativity theorists toil over equations that could elegantly describe the universe’s history.
For more than a decade, few scientists seriously challenged the vision of an ever-ballooning, or open, cosmos. The tide of evidence heavily favored that notion. Galaxies are still being propelled away from each other by the force of the colossal explosion that triggered the universe’s birth about 15 billion years ago. In the time it takes to read this sentence, for example, the universe will expand by 100 trillion cubic light-years. But lately, new findings have rocked the case for continued expansion. Says Sagan: “It would seem that the pendulum is swinging toward a closed universe.”
For sheer imaginative force, that prospect rivals—and perhaps eclipses—the revelation that the world is round. Resolving the current debate will demand no less than the weighing of the entire cosmos, which poets have called “fathomless” and philosophers have labelled “the language of God.” If the total amount of matter in the universe exceeds a _ certain critical mass—and no one has yet determined what g that is precisely—then all that exists will ultimately yank £
itself back into its primordial egg. In the same way that a rocket would plunge back to Earth if it lacked the thrust to reach escape velocity, the galaxies would be pulled back to their origin if the universe were heavy enough to force a complete slowing down. For years the open-universe camp has maintained that the mass of all the known or suspected galaxies totals less than three per cent of that stillelusive critical mass.
But in the past two years—and particularly in the past few months—researchers have accumulated evidence that the universe contains far more than meets the astronomer’s eye. And the quest to reveal the universe’s fate now focuses on the so-called “missing mass”—whatever form it may take. Scientists are seeking it in subatomic particles; in galaxies millions of light-years away; beyond the galaxies in the mysterious quasars; and even in the apparent emptiness of the abyss of space itself.
Estimates of the masses of galaxies have jumped tenfold in the past, with staggering implications. “Less than 10 years ago we were confident that the mass of our own galaxy, the Milky Way, was less than 200 billion times the mass of the sun,” recalls galaxy expert Bart J. Bok of the University of Arizona. “Now the best-accepted estimates are more than 10 times greater—over two trillion solar masses.” Since most stars are less massive than the sun, this means there could be as many as five to 10 trillion stars in the Milky Way
galaxy alone—or a quarter of a million stars for each man, woman and child in Canada. For every one of the billions of known galaxies, the same scenario applies.
What spurred these new estimates were studies of the motions of stars in nearby galaxies. Explains Halifax astronomer Mitchell: “Just as the planets closer to the sun orbit more quickly than those farther away, we would expect that stars nearer the centre of galaxies would orbit faster than those in the spiral arms.” But that is not the case. The speeds are virtually identical. Mitchell’s conclusion: “There must be unseen material there that is adding significantly to the masses of galaxies.” Mitchell and other researchers pondering the problem are convinced that the extra mass is contributed by faint, low-mass stars that swathe the visible parts of galaxies in a vast, unseen halo.
The argument for invisible material intrigues more than one observer—and there is more than one theory as to what it might be. At the University of Toronto’s Scarborough College, astronomer Philipp Kronberg, for one, is combing the void between the galaxies to determine whether the missing mass might be thinly dispersed gas. He is analysing data from astronomical satellites which measure radiation that is completely blocked by the Earth’s atmosphere long before reaching ground level. Though these orbiting sleuths have yet to confirm his hypothesis, Kronberg maintains his experiments indicate that researchers “cannot rule out the possibility that there is gas equivalent in mass to the matter in galaxies.” If the galaxies have 10 times the mass once
assigned to them, and if Kronberg eventually detects the gas he seeks, the total mass would be nearly sufficient to reverse the cosmic expansion—and close the universe.
Still another conundrum surrounds the galaxies, and it too could affect the fate of the universe. About 60 million lightyears away, toward the constellation Virgo, more than 2,000 star cities swarm in a vast cluster. Such clusters are so common that astronomers suspect almost every galaxy is part of one, including our own Milky Way. The very presence of the clusters, however, is vexing scientists. Says Wallace Tucker of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.: “Galaxy clusters should have dispersed long ago. The mutual gravitation of all the galaxies in a cluster isn’t enough to hold it together. There has to be something else there that we can’t see.” Tucker’s is not a renegade view: the motions of individual stars within galaxies also hint that “something else” exists. As Mitchell points out, the mass of a cluster affects a galaxy’s speed within it.
But Mitchell wonders why some clusters contain about 50 times more mass than the visible galaxies would suggest. Once again, the evidence points to missing mass. Determining what it might be has plagued theorists for years. But the shadow of a solution may finally have emerged. According to University of Chicago astrophysicist David Schramm, neug trinos could be producing the massive but invisible webs that 3 keep galaxy clusters gravitationally bound. Neutrinos are ^virtually indifferent to ordinary matter, and they have long sbeen considered massless. Yet recent U.S. and Soviet experi-
ments have produced direct, if controversial, evidence that neutrinos have tiny but perceptible masses. Because these smallest of particles outnumber their subatomic cousins by about 10 billion to one, a mere whisper of mass assigned to each would instantly account for most of the mass in the universe. Neutrinos, says Schramm, are the most promising candidates for the urgently sought missing mass.
The cosmic riddles confronting today’s scientists were undreamed of just decades ago. Unravelling the true extent of the cosmos has been almost entirely a 20th-century enterprise (page 39). For thousands of years, the prevailing view placed the Earth at the centre of a finite universe. The night sky seemed a crystalline dome, and the stars merely phantom lights on its surface. Upstarts who challenged this view were quickly silenced. In 1600, the Italian philosopher Giordano Bruno was burned at the stake when he dared to suggest that our sun is only one of an infinite number of stars strewn throughout space and the Earth only one world among many. Even a scant three generations ago, conjectures about the grand design of all that exists were as much the province of philosophy as of science. The galaxies that preoccupy contemporary researchers were barely understood when telescopes first detected them. Were those puzzling objects distant congregations of stars, observers wondered, or nearby puffs of gas? Even the size of our own system, the Milky Way galaxy, was only crudely known at the turn of the century,
with estimates of its size varying by a factor of 100.
The path to the present debate has been circuitous indeed. To comprehend the universe, scientists had first to place Earth within it. Harvard astronomer Harlow Shapley met that challenge just after the First World War. He found that the largest star clusters associated with our galaxy are distributed in a roughly spherical pattern, the centre of which is thousands of light-years from the sun. Shapley boldly— and correctly—predicted that this focus pinpoints the Milky Way’s centre. By 1924, his picture of the galaxy met few detractors.
Meanwhile, American astronomer Edwin Hubble was approaching a revelation: the first proof of the universe’s expansion. Armed with the new 2.5-m telescope at Mt. Wilson, Calif., Hubble proved conclusively that the galaxies are continents of stars like the Milky Way and that all but the very nearest galaxies are hurtling away from the Earthsome as rapidly as several thousand kilometres a second. Hubble saw one possible conclusion: the universe is growing ever more vast. Like dots on an inflating transparent plastic balloon, each galaxy sees all its neighbors moving away. The farther apart the galaxies, the faster their separation.
That epochal discovery raised questions about the vast distances involved. Astronomers soon learned to gauge the speed of a galaxy’s journey into space through measuring a shift in the spectrum of light it leaves behind. This shift resembles the change in pitch of a passing train’s horn—higher during approach than in recession. As a galaxy plunges away from the Earth, the light it emits shifts measurably toward the red end of its spectrum—the greater the “red shift,” the faster its speed (see diagram). But it turned out that measurements of departing galaxies’ speed were far more precise than estimates of their distance from the Earth, which still confounded scientists. They based their crude reckonings on comparing bright stars in other galaxies with similar stars in our own—until 1949, when Walter Baade took the controls of the powerful new five-metre telescope at Mt. Palomar, Calif. Baade’s refined classification of the types of stars in galaxies led to the serendipitous discovery that the galaxies themselves are actually two or three times farther away than previously believed. This placed the Milky Way’s nearest counterpart, the Andromeda galaxy, about two million light-years away.
With the universe’s expansion confirmed and the galaxy distance scale established, astronomers then considered how the cosmos began. The expansion, they reasoned, was triggered by a monstrous explosion (prosaically dubbed the Big Bang), whose 100-billion-degree fury hurled matter in all directions with such force that it still flies apart today. In 1948, two Johns Hopkins University physicists, Ralph Alpher and Robert Herman, showed mathematically that some evidence of the Big Bang should still be detectable. They calculated that it might reveal itself vastly red-shifted because the galaxy is receding from the site of its birth at near-light speed. Seventeen years later Arno Penzias and Robert Wilson of Bell Laboratories in Holmdel, N.J., were testing a new microwave telescope when they noticed the precise signal Alpher and Herman had predicted. The pair eventually collected a Nobel Prize for their chance confirmation that the Big Bang happened. They had heard its echo 15 billion years later.
In the years spanning Shapley’s visionary prediction and the Bell researchers’ discovery, scientists solved one mystery after another. But toward the end of that period, in the early ’60s, they came upon a new enigma that now plays a key role in the universe-destiny debate. To the cosmic zoo they added quasars. They offer powerful clues to the universe’s past and consequently can illuminate its future. Bizarre objects that
look like stars, quasars are enormously distant and pour out radiation rivalling what a hundred galaxies can produce. Most have huge red shifts indicating awesome distances up to 12 billion light-years from the Earth. Because their light has taken billions of years to reach inquiring astronomers, these compact sources of energy are seen today as they were—not as they are. If the universe was indeed created about 15 billion years ago, then the quasars, thought to be the precursors of galaxies, open a window to the beginnings of the cosmos.
Among those probing the secrets of quasars are University of Toronto astronomers Robert Roeder and Charles Dyer. They have uncovered evidence that quasars have colossal masses, which bolsters the argument that the basic components of the universe (galaxies and their presumed ancestors) are far more massive than astronomers once suspected. Behind this conclusion is their observation of a pair of quasars—the nearer about three billion light-years away, the more remote about three times farther off. “The light from the distant quasar has been distorted into an ellipse by the gravitational ‘lens’ effect of the nearer quasar,” explains Roeder. He has deduced from this distortion that the intervening quasar must have a mass at least 100 times greater than the entire Milky Way galaxy. This finding follows
research by Princeton astronomers, who, using a different method, have come up with a similar figure for the mass of the nearest quasar.
Yet the quasars still pose as many questions as they promise to answer. Using the 3.6-m Canada-France-Hawaii telescope, astronomer John Hutchings, of Victoria’s Dominion Astrophysical Observatory, has found a hazy envelope, or “fuzz,” surrounding the brilliant pinpoint core of all 29 quasars he has examined so far. He suspects the centres of quasars are energized by enormous gravity whirlpools—black holes—
that constitute the supreme powerhouses of the known universe. Half the potential energy of matter that swirls into a black hole is released as radiation, making a prodigiously efficient cosmic beacon. Says Hutchings of the quasars: “We may be looking at galaxies in formation-
stars being born around super-massive black holes.” Hutchings’ findings offer strong support for the theory that galaxies evolve over time. If that is the case, scientists must grapple with a complex of new riddles they will have to answer before reaching a verdict on the destiny of the cosmos. Do the galaxies become fainter and more sedate in their old age? Was the Milky Way galaxy once a quasar? Do galaxies evolve gradually or in bursts? Faced with such unknowns, astronomers cannot put their faith in the critical distance estimates because almost all of these values are based on apparent brightnesses that could well change with time. Contends Madore: “We just don’t know enough about galaxy evolution to be able to make sweeping statements about strong evidence that favors either an open or a closed universe.”
Yet another bothersome is-
Milestones in space
1543: Nicolaus Copernicus argues that the sun, not the Earth, is the centre of the universe.
1784: William Herschel uses his telescope to determine that the sun is part of a vast disc-shaped system of stars. 1900: Cornelis Easton conjectures that the Milky Way is a spiral galaxy and that the sun is located in the region of the spiral arms.
1920: Harlow Shapley statistically proves that the sun is located off toward the edge of a massive spiral galaxy (the Milky Way).
1929: Edwin Hubble publishes measurements of receding galaxies—the discovery of the expanding universe.
1952: Walter Baade uses five-metre telescope to establish the currently accepted distance scale to the galaxies.
1963: Quasars discovered by Maarten Schmidt.
1965: Microwave-radiation evidence of Big Bang detected-proof of the origin of the expanding universe.
sue also demands attention—the possibility that the red shift might be due to something other than recession. Halton Arp, of California’s Mt. Wilson Observatory, points to certain quasars that seem to be arranged around nearby galaxies as if they were explosively ejected like shrapnel. Mere coincidence, answer most astronomers, insisting that the quasars are indeed as distant as their red shifts indicate. But while only a small band of astronomers takes Arp’s idea seriously, its consequences are devastating. If Arp is right,
almost all current ideas about thé universe’s evolution and destiny would be shattered. As a result, scientists are anxious to dispel the mists of doubt surrounding red shift.
Equally important to any universe-destiny scenario will be wrestling an unequivocal verdict from respected conservatives such as Allan Sandage of the California Institute of Technology. After a lifetime spent measuring and compar-
ing the recessional velocities and properties of galaxies and quasars, the reclusive Sandage still believes the evidence to date supports an open universe, although he admits the case has weakened in the past five years. Says James Gunn, a Sandage associate: “Maybe the rest of us are working under the delusion that we think we can comprehend the - universe.”
Delusion or not, approaching technological advances promise to clarify the picture. The 2.4-m Space Telescope, due to be launched by the Space Shuttle in 1985, “will be capable of observing objects 100 times fainter than any existing Earth telescopes,” says an optimistic George Field of the Harvard-Smithsonian Center for Astrophysics. It should detect the suspected stellar halos of galaxies and yield detailed pho£ tographs of galaxies 2 and quasars that will I allow refined distance § estimates. The $500% million Space Telex scope is raising hopes for new evidence in the unresolved puzzles of
both missing mass and galaxy-quasar relationships.
Says Madore: “Sometimes I wonder where it will all lead, if the big picture will ever come into focus.” His mind drifts while the great telescope plows through interstellar dust and devours galaxies. “But then, it’s just over 50 years since we found out that other galaxies exist. Now we’re tracking down how it will all end.” He turns back to the guiding eyepiece. £>