What's New in the Universe?

In the beginning, God created the singularity.

And the singularity was infinitely dense, and all that was and all that will be was compressed into that singularity; and darkness was upon the face of the universe.

And God said, Let there be a big bang; and there was a big bang; and from the big bang emerged matter and radiation.

And God saw the big bang, that it was one hell of an explosion; and the evening and the morning were the first billion years, 16 billion years ago.

And God said, Let there be hydrogen and helium and let them swirl randomly; and let some of the gas swirl into regions of greater density; and let those regions of greater density contract themselves into protogalaxies; and let the protogalaxies contract themselves further into galaxies.

And when they had done so, God said, Let there be stars.

And the first stars began to form within the galaxies; and when the gases whereof they were made had sufficiently compressed, there began thermonuclear burning and, lo, there was starlight. And the evening and the morning were the third billion years, 14 billion years ago.

And to assure that man would not quickly understand His great works, God gave to the speed of light a finite limit of 300,000 kilometers a second, and to the atmosphere of the earth, when He got around to creating it, five billion years ago, He gave turbulence and distortion, and opacity to many kinds of radiation; and further to confound man's understanding, He placed throughout the universe quasars, neutron stars, black holes and other kinky peculiarities.

And He looked upon the work of His singularity approvingly and said, Lo, it is a puzzlement. And it was a puzzlement.

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Was, still is. We could hardly have expected a universe with anything so strange as men in it to be simple, could we? God the mathematician, God the astrophysicist, moves in mysterious ways. So, necessarily, does modern astronomy.

The science of an expanding and truly cosmic universe began in 1922, when the American astronomer Edwin Hubble discovered that the nebulous, cometlike clouds that previously had been cataloged all over the sky were, in fact, galaxies, huge assemblages of stars far distant from our own. In the decade between 1923 and 1934, Hubble and his Mount Wilson colleague Milton Humason demonstrated that the universe was expanding and that the distribution of galaxies beyond our own was everywhere much the same. The distinguished astronomer Allan Sandage of the Carnegie Institution of Washington at Pasadena has compared Hubble's contribution to Copernicus', and with good reason: Copernicus removed the earth from the center of the universe; Hubble expanded the universe from our galaxy out to the edge of time.

"Do you know," Sandage asked me, "that astronomy has solved the ancient question of the universe--the question of how the universe was formed?"

I didn't know, and not all of Sandage's peers agree, but the assertion itself is a taste of astronomy's keen pleasures and keener ambitions. In a civilization of practical experiments and practical results, astronomy is the last purely observational science, and astronomers are men who unaccountably decide to spend their lives studying objects of extraordinary beauty and mystery that they can never touch or manipulate. They work with objects that are far removed from the earth, from the solar system, even from the huge wheeling galaxy itself; objects, many of them, so distant and information poor that they are no more than point sources of light, small black spots collected among other black spots on glass negative plates. Some objects, among them the most interesting in the universe, can't be seen at all by the human eye, and certainly one of the reasons for the recent explosion of astronomical theory and discovery has been the development since Hubble's time of new and wider ways of seeing: the great 200-inch Hale telescope on Mount Palomar first of all, the new telescopes on Kitt Peak in Arizona, the balloon, aircraft, rocket and satellite systems that sample radiation that the earth's atmosphere has screened from view.

The single most fertile invention of modern astronomy may have been the radio telescope. The heavens shine at radio frequencies as well as at optical frequencies. Until recently, even the largest radio telescopes were unable to produce any but the fuzziest images of radio objects in the sky. Today, by using radio telescopes thousands of miles apart in concert, they see better than the best of optical telescopes: 1000 times better, in fact. To locate bright radio sources, radio astronomers took advantage of the blocking effect of the moon, the same effect that kept the astronauts out of communication with the earth when they orbited to the moon's dark side. The moon served the astronomers as a knife edge, occluding interesting radio sources as it passed between them and the earth. With this technique, they could be located far more precisely and optical astronomers could search a smaller area of their photographic plates for objects in the same location that also radiated light.

In 1960, searching one such radio area with the 200-inch telescope, Sandage found a quasar, 3C 273, one of the first to be identified, a starlike object tnat radiated in both the visible and the radio portion of the spectrum. By any standards, it was peculiar: a distant, starlike point of light that also radiated radio waves (most stars don't) with a strange spectrum and what looked like a glowing jet of matter coming out one side. No one knew what to make of it. No one realized that it would open the cosmic Pandora's box.

Lacking any more direct means of measuring the distance from the earth to the farther stars and galaxies, astronomers study their spectra, the rainbows of light and other radiation that are revealed when their images are broken down with a prism or a diffraction grating. Hubble and Humason's second great demonstration, that the universe is expanding, depended on the interpretation of spectra. The spectrum of a star, a thin, fuzzy band on a glass photographic plate no bigger than a postage stamp, reveals bright vertical lines that are the characteristic signatures of various chemical elements burning within the star. Among the most frequently encountered lines are the Balmer series, the lines that make up the visible spectrum of hydrogen. When produced in a laboratory on earth, the characteristic spectral lines for any element occupy a definite and unchanging place in the spectrum. But the spectral lines from galaxies and stars are always shifted. For some stars, the lines are shifted to the left, toward the blue end of the spectrum. For other stars and almost all galaxies, the lines are shifted to the right, toward the red end of the spectrum.

Wave lengths are shorter--higher in pitch--toward the blue, longer--lower in pitch--toward the red. Astronomers make a basic assumption about such blue shifts and red shifts by analogy with a common experience: A jet engine, for example, sounds higher in pitch when it's approaching us, lower in pitch when it's going away. The change in pitch is caused by the overlapping of sound waves as the jet approaches, the stretching out of sound waves as the jet goes away. By analogy, a blue shift means that a star is approaching us, a red shift that a star or a galaxy is receding from us. Once this assumption is accepted, the shifts can be used with a standard formula to compute the object's velocity.

What Hubble and Humason did, in 1929, was demonstrate that there is a clear relation between an object's velocity and its distance from the earth. The two men measured the distance to a representative selection of galaxies by other means and compared the distances with the red shifts. They found that the greater the distance, the greater the red-shift velocity. The greater the distance, the faster the galaxies were receding from us. The only model of the universe that fits these conclusions is an expanding model (inflate a toy balloon and mark it with dots of ink, then inflate it some more: From the point of view of any one dot, the other dots will all seem to be moving away, the nearer dots more slowly, the farther dots more rapidly).

Quasar 3C 273's spectrum was peculiar, with spectral lines in places where spectral lines ought not to be. Astronomer Maarten Schmidt of the California Institute of Technology sat puzzling over 3C 273's spectrum one late December day in 1963 and had a vision. "I couldn't understand the spectral lines," he remembers today. "The spectra of several other quasars had already been taken, and they were all mysteries and they'd all been laid aside. I was looking at 3C 273's spectrum again, because I was writing an article, and for some reason, I noticed some regularity in it. The stronger lines were to the right and the weaker lines to the left, and the spacing also gradually decreased as I went to the left, to the blue, which is the way the Balmer series of hydrogen occurs. I thought I saw a regular pattern, so I attempted to make an energy diagram. In hindsight, that was totally meaningless, but, you know, do something.

"I must have made an error, because the numbers I got weren't regular at all, and I looked again at the spectrum and it was regular, and in order to convince myself that it was, I took the ratio of the wave length of those lines to the nearest Balmer lines, which, you know darn well, are regular. Well, I took the ratio of the first line and found 1.158, and then I took the ratio of the next line to the next Balmer line and found 1.158, and I did it again, and suddenly I realized that I had a constant ratio and therefore that it could be the Balmer spectrum shifted to the red by 15.8 percent. It was an intuitive moment and actually took only a short while, about ten minutes."

It was an intuitive moment that almost didn't occur. Quasars may be the most distant objects in the universe, with red shifts of as much as 453 percent, more than 90 percent of the speed of light. "The reason I succeeded with 3C 273," Schmidt says, "is that the red shift was fairly small. The lines were shifted only--only!--within the visible portion of the spectrum. When you have a red shift of 453 percent, the shift comes from a portion of the spectrum that's invisible, which makes it very difficult to observe. A relatively small shift was, in hindsight, the most promisings Still incredibly big for a star. In our own galaxy, for example, you never see red shifts greater than .2 percent, because .2 percent corresponds to 600 kilometers per second, which is the escape velocity for our galaxy. Any star (continued on page 158)The Universe?(continued from page 142) with a red shift greater than .2 percent would have escaped from our galaxy long ago. The step from .2 percent to almost 16 percent was the big hurdle."

Schmidt's discovery of the quasars' enormous red shifts was important far beyond the fact that it added a new animal to the stellar zoo, as one astronomer I talked with calls it. It also opened astronomers' minds to exotic possibilities. "Quasars," says Schmidt, "were essentially the first discovery of the new type of exotic objects--pulsars, X-ray binaries, black holes, everything. The quasar was the first. Before that time, things were fairly conventional. We thought we knew most of the things that were happening in the universe, and we thought especially that we knew what could not be the case. We knew what could not happen, and one thing that could not happen was that a star couldn't have a big red shift. Once we found a starlike object that did have a big red shift, our attitude changed completely. We were soon completely open-minded."

There were problems with quasars in 1963; there are problems with quasars still. If they are as far away as their red shifts indicate, then they are among the brightest objects in the universe, too bright to be explained as normal thermonuclear processes that generate energy in stars. All sorts of theories have been devised to account for quasars' energy, most of which assume that they aren't stars at all but energetic cores of galaxies, cores so bright that the rest of the galaxy is lost in their glare: the simultaneous and continuing explosion of hundreds of supernovae, vast collisions between matter and antimatter, the gravitational collapse of an entire galaxy in upon itself, and more. No one knows which theory, if any, is valid. About the only thing the theories have going for them is that they more or less account for the quasars' energy output. The simplest solution to the problem of the quasars is to assume that they aren't so distant as their red shifts say they are, which would mean they aren't so energetic as they appear to be; but to accept that solution is to conclude that nearby red shifts work as Hubble and Humason said they did but that faraway red shifts do not, and not many astronomers are prepared to throw their most cherished baby out with the quasi-stellar bath water.

To look out into the distance of space is to look back into the past: All vision is history. We see each other not as we are but as we were a fraction of a fraction of a second ago, when the light reflected off our bodies began its flight to our eyes. We see the sun as it was eight minutes ago, when the light it generates started its journey outward toward the earth. And because the velocity of light is finite, is 300,000 kilometers per second, there is an absolute limit to our vision: In an expanding universe, we can never see farther than 18 billion light-years in any direction, because light from that horizon, if there is light, is red shifted to zero velocity and does not reach us at all. That is, objects out there were moving so fast that the light they gave off never reached us. We live inside a huge bubble, and what is outside the bubble we will never know. If we commissioned an astronaut to travel to the edge of the observable universe and report back what he saw, his report would never arrive. Our vision is eternally limited, though a bubble 36 billion light-years across ought to be room enough, even for a race so diabolically curious as Homo sapiens.

If quasars are the most distant objects known, they are also the oldest. A quasar with a red shift of 453 percent represents the state of the universe more than 13 billion years ago, perhaps no more than three billion years after the singularity exploded with the big bang. A quasar that began shining when the universe exploded would have a red shift of infinity. But it turns out that after thorough search, no quasar has been found--there are estimated to be at least 1,000,000 of them in the sky--with a red shift greater than 453 percent. Beyond these most distant visible objects there appears to be--nothing at all. Sandage, who, with Gustav Tammann, has recently reported on 20 years of work calculating the age of the universe, believes that the cutoff of quasars at 13 to 14 billion years means we are seeing, in quasars, the very leading edge of creation, the first galaxies taking fire after coalescing out of the hot gases of the big bang itself. Working along the same lines, Schmidt has produced statistical studies that indicate that there were far more quasars in the universe in that distant past than there are today, perhaps 1000 times as many, which is further evidence that they are special types of objects that formed more frequently under the severe conditions near the beginning of the universe than they do in the less dense universe of today. It's as if there's a shell of quasars out there beyond which we see nothing at all, because, maybe, there's nothing to see, the lights weren't turned on yet, and nearer than which conditions weren't drastic enough to produce objects of such excessive energy. Adjusting their apparent brightness for distance, it is calculated that many quasars are 50 to 100 times brighter than entire galaxies.

One quasar named BL Lacertae appears to be less than one light-year in diameter. The mechanism that powers an object this small but as bright as 50 or 100 entire galaxies remains unknown, but the likelihood increases that quasars are old galaxies and possibly the first ones formed. "That we can, in principle, see the edge of the world is amazing," Sandage has written. "That we may have done so already would be unique."

Distinguished though their ancestry, quasars are far from the strangest of stellar objects. It used to be easy to say which stellar objects were strange, but there are objects known or surmised today whose strangeness almost surpasses ranking. A walk through the stellar zoo will prepare us for a visit to the vast, if still somewhat wobbly, cathedral of cosmology, the science of the universe itself.

Most of the objects are stars in various stages of birth, aging and death. Consider the sun, our own local star, an average-sized yellow star about six billion years old and halfway through its life. It coalesced out of gas, mostly hydrogen and helium, in one of the outer arms of the galaxy, probably in response to density waves that move through the galaxy creating spiral arms (you can make every kind of galaxy model by stirring your coffee and then pouring in a little cream--you'll see irregulars, spirals, S curves, you name it). A little greater density in one place than another and the gas particles were squeezed close enough together that their gravitational interaction took effect and they began to fall toward one another. As they got closer together, they bumped into one another more often, which is to say they began to heat up. When they got close enough together, they got hot enough for thermonuclear fusion to begin, the same process that powers the hydrogen bomb. The energy produced by the fusion of hydrogen into helium pushed back against the particles until they found an equilibrium between attraction and repulsion, and the sun settled down to be the congenial star it is.

When most of the hydrogen in the cores of sunlike stars has been converted by fusion into helium, then helium fusion will begin. When most of the helium has been fused into carbon, then carbon fusion will begin. Eventually, the fusion reactions will work their way all the way up to iron, which is at the mid-point in the periodic table of elements and the most stable element around. Fusion can't take sunlike stars any farther than that; when it ceases, when the energy pushing outward fades, gravity will cause them to collapse.

The sun has an amount of matter in it that we can conveniently call one solar mass. Because of its particular size, the sun when it collapses will probably become the first strange object in our zoo: a white dwarf, a small, extremely economical star about the size of the earth, inside of which matter is compressed until a lump the size of a martini olive would weigh more than a fleet of Mercedes-Benzes. The white dwarf is kept from further collapse by the motion of its electrons, which move faster the closer they come to one another. The more squeeze, the more motion: Nothing material in the universe can collapse completely. The white dwarf slowly cools; the sun's light slowly goes out; the sun finally becomes a black dwarf, a cinder blowing through space, forever keeping its appointed rounds.

Stars up to something less than two or three solar masses could die another way: They could collapse until they were only about 15 miles in diameter, at which point they would have a density as great as if all the people in the world were squeezed into a single raindrop, and they would stabilize in size because of forces that normally operate in the nuclei of atoms. They would then be superdense. Their interiors might contain a supercooled neutron fluid, but what they might look like is not so interesting to us here as what they do: They spin, some of them, at up to 30 revolutions per second (the earth, which isn't exactly a sluggard, spins at one revolution per day, right?). Spinning so fast, with such a load of superdense matter inside, they evolve an intense magnetic field around them. They also produce beams of radio waves and, in one known case, even visible light waves, and because they are revolving, their beams reach us as pulses, like the flashes of light from a lighthouse: pulsars.

As a theoretical object, the neutron star has been around for a long time. The late Fritz Zwicky of Caltech predicted as far back as 1934 that such objects could exist. But it wasn't until the first pulsar was discovered, in 1967, and its amazingly regular pulses measured (and the possibility that they were signals from some distant civilization discounted), that anyone seriously believed in the existence of neutron stars, which were the only structures that could account for the pulses.

Neutron stars produce delightful numbers. A teaspoonful of neutron-star material would weigh a billion tons; dropped onto the ground, it would fall all the way through the earth as easily as an ordinary rock falls through the air. Mountains on the crust of a neutron star couldn't be more than a few centimeters high; a groundquake, a neutron-starquake, would produce a noticeable jiggle in the star's pulse, and astronomers think they may have detected such jiggles and therefore, such quakes. From the point of view of physics, neutron stars are, in effect, gigantic atomic nuclei. The lightest atomic nucleus is that of hydrogen; helium is next, and so on up the periodic table to uranium, the last element that occurs naturally on the earth. After uranium come the transuranium elements, and then nature takes a great leap: The next nuclei are neutron stars. The pulses of neutron stars are accurate to within a few millionths of a second, better than all but the best of earthly clocks. The energy for the radiation of neutron stars comes not from thermonuclear fusion but from the rotation of the star. As the star radiates, its rotation slows. A few million years after its birth, the star has slowed so much that it can no longer generate radiation: There may be millions of "dead" neutron stars in the universe that don't wink at us anymore.

The pulsar with the fastest pulse, 30 times per second--the youngest known pulsar--is one in the Crab nebula, a beautiful structure of glowing gases in the constellation Taurus in the northern sky that can be seen with a small telescope as a fuzzy patch. The pulsar in the Crab nebula claims several other distinctions that make it what one radio astronomer calls "a marvelous astrophysical laboratory": It's the only known pulsar that radiates not only radio waves but also visible light and X rays as well (radiates, this small object less than 15 miles across, as much energy as 100,000 suns); and it's almost certainly the collapsed remnant of a supernova--an exploding star--seen by Chinese astronomers in 1054, when it appeared in the sky as a star so bright that it could even be seen by daylight. Its brightness persisted by daylight for weeks, and by night for several years, before it faded away. A star collapsed to become a rotating neutron star and the glowing gases of the Crab blew off, more than 900 years ago as the light flies. (Some stars explode entirely and blow away, and out of their vacuous remains the earth was made. There was only hydrogen and helium in the aftermath of the big bang; the heavier elements got manufactured in stars that have long since died and drifted away. So the visionaries and the crackpots are right: We came from the stars, but not in little silvery ships.)

The most bizarre animal in the stellar zoo is the third kind of collapsed star. If a star is larger than about three solar masses, and if too much of its envelope doesn't expand away, it can begin a catastrophic collapse that doesn't end in a white dwarf or even in a neutron-star stage but keeps on going until the star disappears from the observable universe. It disappears when its matter, falling together, becomes so compressed, and therefore its gravitational pull so strong, that anything trying to escape from it would have to exceed the speed of light to get away. Since nothing can exceed the speed of light, nothing can leave such a collapsed star, not even light itself. In place of the star then appears a black hole.

A black hole is a wondrously simple thing. The standard black hole, the type formed by the collapse of massive stars, has only two physical properties: mass and (assuming it is rotating) angular momentum. "All the properties of the black hole," writes astrophysicist Kip Thorne of Caltech, "are determined completely by Einstein's laws for the structure of empty space." A typical standard black hole has a diameter of from 12 to 200 miles, into which have fallen from 3 to 50 solar masses (the sun, by comparison, has a diameter of 865,000 miles). "It's conceivable," Thorne told me, "but highly unlikely, that half the mass of the universe is down black holes. But it's much more likely that maybe one part in 1000 is down black holes."

Black holes were proposed theoretically in the Thirties, but not until recently did anyone seriously believe they existed. Astronomers are now about 80 percent sure they've found one, Cygnus X-1, in the constellation Cygnus, orbiting a star designated HDE 226868. How do you find an object that emits no light or any other kind of radiation, whose two effects on the rest of the universe are effects of an immensely powerful gravitational field and an extremely rapid rotation? Astronomers have searched the sky for double, or binary, star systems, one star of which isn't visible but can be calculated by its gravitational effect on its companion to have a mass of at least three solar masses (the object in Cygnus is about 12 solar masses) and that produces X rays. The X rays result from a black hole's tendency to pull gas off its companion star. Before the gas disappears into the black hole, it is heated enough by friction to produce radiation. Cygnus X-1 is the leading black-hole candidate; astronomers won't be certain it's a black hole until information from the new generation of X-ray satellites is analyzed, before the end of the Seventies.

Why pursue black holes? Because they may be far more important in the universe than anyone has suspected. But before we get to that, we ought to get nonstandard black holes out of the way.

Theory often precedes discovery in modern astronomy, and a small group of scientists led by Stephen Hawking of Cambridge has been theorizing while (continued on page 212)The Universe?(continued from page 160) observers search. By combining the laws of quantum mechanics with Einstein's theory of gravitation, Hawking has proved that black holes should leak, which would mean they weren't completely black. "Maybe we should call them gray holes," Hawking told me. "The bigger the black hole, the smaller the leak; a big black hole leaks very slowly. A standard black hole would take about 1064 years to empty itself [1064 is the figure 1 followed by 64 zeros--10,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 years--a very slow leak]. But there may be very small black holes that were formed during the rather chaotic first days of the universe." How small? As small as the nucleus of an atom but with a mass of 1015 grams. "Most small holes would have evaporated by now," Hawking says, "and as they evaporated, they would have emitted gamma rays. So it might be possible to detect them by detecting their gamma radiation--the radiation coming from holes now in the last stages of evaporation or the radiation left behind from holes now evaporated away."

If black holes, large and small, leak, then a second possibility suggests itself to Hawking. Theory predicts that inside every black hole there must be a singularity, a region of infinite density and gravitation that is fundamentally unpredictable, like the singularity from which the universe itself is believed to have been formed. As long as the singularity stays inside the black hole, the universe is still the universe according to Newton and Einstein. Where the universe is concerned, the one we live in, whatever is inside a black hole doesn't exist, because nothing can come out of it, and therefore we can have no information of it and it can't affect us. But if black holes leak, then it's possible that a singularity could leak out. "At that point," says Hawking, "all physics breaks down. If a black hole evaporates, then you might be able to see a naked singularity and the breakdown would be a fundamental breakdown in physics, a new level of uncertainty in physics in the sense of uncertainty about what's going to come out of the singularity. It seems to be completely random."

Thorne elaborates: "It turns out that if you could find a naked singularity, then you'd have a real problem analyzing how the universe would behave. We don't know the laws that would govern the region of a singularity. And it even seems likely, according to Hawking, that precise governing laws don't exist, that a naked singularity can spew out anything it wishes and will spew out all things conceivable--electrons, protons, television sets--all with equal probability. This is what Hawking calls the 'principle of randomicity'--and he has even succeeded in proving it mathematically in special situations. If the principle of randomicity is correct, it may be our first clue to unlocking the mystery of the big-bang singularity, as well as our only clue to the behavior of naked singularities, if they exist."

Nobody knows if naked singularities do or can exist. For the present, the operant rule remains the one that physics borrowed from The Once and Future King novelist T. H. White, who deciphered it as the governing rule of a colony of ants. It's called the totalitarian principle of physics, and it says that "everything not forbidden is compulsory."

Black holes produce such fierce gravitational effects that they have begun to be looked at as possible sources of some of the universe's more extreme violence. With the exception of such exotic processes as collisions between matter and antimatter, black holes are the most efficient systems yet found for converting mass into energy. "Black holes may play important roles in various key places in the universe," Thorne says. "It's quite likely--50 percent likely--that the central nuclei of many galaxies have black holes in them and that the activity that one sees in the nuclei of some galaxies may be associated with the interaction of in-falling matter with black holes. That includes our own galaxy. There's one very bright compact region in the center of our galaxy--bright to radio and infrared radiation [but not to light, because clouds of dust completely obscure our optical view of the center of the galaxy]. Bruce Balick of the University of Washington and Robert Brown of the National Radio Astronomy Observatory have shown that there's at least one very bright object down there that is smaller than about .01 light-year in size. This object might weigh as much as 107 solar masses. Donald Lynden-Bell of Cambridge suggested seven years ago that the object down in the center of our galaxy may be a black hole. He pointed out that the total energies coming from the centers of some galaxies are so large that whatever kind of machine one invents to explain them, it always has to involve a large amount of mass contained within a very compact region. Whatever system is involved, Lynden-Bell argued, with so much mass it would have to evolve rapidly, so that even if black holes weren't presently there, they would very likely be the end point of that activity. So on statistical grounds, he said, we can conclude that a very large fraction of all the galaxies in the universe might have huge black holes at their centers."

Black holes are closely related to the singularity that began the universe. Thorne again: "When matter is compacted smaller than black-hole size, then according to Einstein's theory of gravitation, it's in either a collapsed state or an explosion state. If it's collapsing, that collapse can't be reversed short of reaching infinite density. If it's exploding, that explosion can't be reversed until the matter gets bigger than black-hole size. Which means you have two types of condensed or compact objects, the type that is compact and collapsing and the type that is compact and exploding. Black holes represent the first type. The universe represents the second type. The universe began very compact, much smaller than black-hole size for its mass--it has a mass of at least 1050 tons--and it began exploding. What this general feature of gravity says is that until the universe got bigger than black-hole size, it couldn't turn around and start recollapsing. We don't know that it ever will. The predominance of the evidence at the moment suggests that it won't. But there's an intimate relationship between the universe and black holes. The same features of gravity that describe black holes also help govern the fate of the universe."

There's another intimate relationship as well. At some unbelievably distant time, most of the universe will be swallowed up by black holes, one of whose quainter properties is that they can only get bigger, never smaller, as they swallow the mass of the matter outside their edges. The process is slow because black holes get bigger so slowly. Our own galaxy contains about 100 billion stars spread out over a region about 100,000 light-years in size. If you stuffed half those stars down a black hole at the center of the galaxy, it would still be no larger than about a tenth of a light-year, far away from the remaining stars in the galaxy, its gravitational field attenuated by great distance. Nevertheless, someday most of the matter in the universe will disappear down black holes, returning, in effect, to the condition of matter before the big bang. Two of astronomy's generous limits, then: a limit to the observable universe, an edge beyond which our observation can't go, and a limit to the eternity of the universe as we know it, a time beyond which few stars will shine and few cinders of black dwarfs wander.

One more bizarre creature deserves notice in our stellar zoo. This one can't be caged, because it's everywhere at once, and it may be, historically, at least, the most important of them all, and to see it you have only to turn on your television set. Some of the "snow" on your screen is produced by what remains of the immense heat generated in the fireball of the big bang. If the universe began with an explosion, as it almost certainly did, then the temperature of that explosion was likely to have been at least ten billion degrees. By now, billions of years later, that temperature should have dropped to about three degrees above absolute zero--three degrees Kelvin--and to have spread out so that if it could be detected on earth as microwave radiation, it ought to be detectable in every direction equally. In 1965, scientists at the Bell Labs in New Jersey first, and scientists down the road at Princeton almost immediately thereafter, detected the three-degree background radiation coming in uniformly from every direction. Since then, their findings have been all but universally accepted as valid: The microwaves in their horns and some of the snow on your TV are left over from the big bang. The cosmological theory that the universe is "steady state"--that it has always existed as it is now and that matter within it is continually created out of nothing to keep it expanding--is today effectively disproved. The universe began with an explosion from which it's still expanding.

These vast formulations lead us properly to the cathedral of cosmology, the science of the universe itself. Cosmology, by definition, is the most ambitious of all sciences, and its practitioners are few. I talked with two of the leading cosmologists in the United States, Sandage and James Gunn of Caltech. Both men have recently published major papers discussing the probable origin and age of the universe and the likelihood that it is a once-around, one-way system, and both men's work generally agrees. Gunn feels less certain of his conclusions--"Nature always has tricks up her sleeve"--but Sandage is ebullient, a mature man at the full reach of his powers and as confident as an astronomer can be.

Sandage points to the agreement of several different time scales to demonstrate the age of the universe. The age of the chemical elements can be calculated by counting back from their state of radioactive decay, and this method gives about 15 billion years ago as the time of their creation in the first stars formed after the big bang. The age of the oldest stars in the galaxy gives another measure. The oldest stars, metal poor and containing about the same amount of helium as estimates indicate the big bang itself created, are the stars of the globular clusters, small spherical groupings that revolve not in the plane of the galactic spiral but in plunging orbits in and out of the galactic center from above and below, orbits that look as if the clusters blew out of the galaxy when it first coalesced. Their age is also about 15 billion years. The expansion of the universe figured from the Hubble Constant--the number that turns red-shift velocity into distance and therefore into age--gives 15 billion years. These three age scales, Sandage argues, constitute one proof of the universe's probable age. A second proof is the three-degree background radiation, because it would have taken about 15 billion years for the primeval fireball to cool to that temperature.

Taking these proofs together, and allowing in the case of some of the numbers for the slowing down of the universe's expansion by the gravitational attraction among the objects in the universe, Sandage concludes that the universe began about 16 billion years ago and the galaxies turned on two billion years after that. Sandage believes that astronomy's discovery of this time scale, and its increasingly detailed knowledge of how the universe has evolved since, constitutes as important a contribution to human knowledge as Darwin's, and for similar reasons: Darwin found a rational system of organic evolution that operates independent of any miraculous interference; astronomy may have found a rational system of cosmic evolution that also operates independent of any miraculous interference. If God created anything, He created the singularity; the universe followed as certainly as a fireball follows the assembling of a critical mass inside an atomic bomb.

Gunn, for his part, has at least tentatively concluded that the universe doesn't have enough mass in it to stop expanding. "The universe is mostly empty space," he says. "Even doubling its mass wouldn't do much. It appears there's less than ten percent enough mass in the universe to cause it to fall back in on itself."

"It looks," says Sandage with impressive awe, "as if the universe happened only once." Which leaves it, this starlit shell that we so tenuously inhabit, spreading out almost forever, suffering only the excruciatingly slow demolition of being nibbled to death by black holes.

•

I saw the stars one moonless night in East Africa a few years ago, saw them as we almost never see them in North America anymore, undimmed by city lights, thousands of them shining down on the Serengeti Plain, where the last Pleistocene animals left on earth still graze and hunt and wander. That view of the equatorial constellations seemed as antique to me as the animals did: To travel in the East African bush is to travel back in time 10,000 years, when the only light at night was moonlight and starshine, when those points of light were as familiar to men, and as mysterious, as the beings who moved beside them across the plain.

There was death on the plain, change, mire, passionate intensity, imperfection. It isn't hard to see how men divided the firmaments--the waters below, the heavens above: Even the sun could be eaten, blotted out in eclipse, even the moon, but never the stars. Imagine waking at the beginning of the world and seeing the stars. Leaves fall; children grow to manhood; the animal is opened and its strange interior plumbed; the sun's light fails and the stars come out; the sun's light increases and the stars fade away. They glow in patterns too complicated to discern. They disappear north and south as the seasons change but return more certainly than the herds of wildebeest return, more certainly than the long rains. Fathers fail at hunting; mothers bear dead twins; the stars appear and fade and appear and fade again. Only the rocks that in places marked the plain had such endurance, and over a man's lifetime even they suffered weather and change. The stars suffered nothing at all.

The old order, the religious order, saw eternity and perfection in the stars and asked why and heard only the whistling of the wind. The new order, the scientific order, sees violence and change and asks how and the cards fill the bins. When, in 1054, the supernova that would become the Crab nebula appeared in the sky, the one the Chinese astronomers saw, no one in Europe dared endanger his immortal soul by recording that he had noticed it--had noticed less than unchanging perfection in the sky--and only Asian records of its appearance survive; today astronomers catalog such supernovae as enthusiastically as ornithologists catalog the arrival of rare birds. Once we talked to God; now we attempt to talk to alien civilizations out along the Milky Way. Once we counted 6000 stars in the night sky; now we count billions, stars and galaxies both, and billions beyond that, most of them forever unresolvable from the other billions through which they swing. Most of the universe is empty space: The stars burn not from love but from thermonuclear fusion. If 100 billion races occupy planets like our own, the common state of matter is still not flesh but gas, and between the gas is emptiness.

Now at the beginning of our second evolution, we are not necessarily more sophisticated, despite our tools, but our expectations have changed, and with them, perhaps, our hopes. We know more now and hope for less, because we have learned there are barriers to our understanding that nature itself throws up: distances beyond which we cannot see, predictions we cannot make, interiors we cannot enter or, having entered, from which we can never return. If religious belief, our companion through the long millennia of our first evolution, is faltering everywhere in the world, and it is, it is not faltering because knowledge has disproved it but because a method of knowledge has displaced it: because we have made an exchange, how for why, vastness for certitude, the dance of time for the perfection of the timeless.

To know with reasonable certainty the few things that we know is priceless, but it has meant giving up all the possibilities that could not be. On that rock we have built our new church, for better or worse. The galaxy has turned only 50 times since time began, organizing itself from insignificance into light: How many times, organizing ourselves, and through how much pain and through how much exaltation, have we, and will we how many more, and still the holy mire?

"We see each other not as we are but as we were a fraction of a fraction of a second ago."

"Where the universe is concerned, the one we live in, whatever is inside a black hole doesn't exist."