The question of the end time is a tough one. Big Chill or Big Crunch or Big Boom or Big Something Else? Jim Holt likes Big Questions. If this is (fair & balanced) existentialism, so be it.
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How Will the Universe End?
by Jim Holt
One of my favorite moments in Woody Allen's film Annie Hall is when Alvy Singer (Allen's alter ego) is shown having an existential crisis as a little boy. His mother summons a psychiatrist, one Dr. Flicker, to find out what's wrong.
"Why are you depressed, Alvy?" Dr. Flicker asks.
"The universe is expanding," Alvy says. "The universe is everything, and if it's expanding, some day it will break apart and that will be the end of everything."
"Why is that your business?" interrupts his mother. Turning to the psychiatrist, she announces, "He's stopped doing his homework!"
"What's the point?" Alvy says.
"What has the universe got to do with it!" his mother shouts. "You're here in Brooklyn! Brooklyn is not expanding!"
Dr. Flicker jumps in: "It won't be expanding for billions of years, Alvy, and we've got to enjoy ourselves while we're here, eh? Ha ha ha." (Cut to a view of the Singer house, which happens to be under the Coney Island roller coaster.)
I used to take Dr. Flicker's side in this matter. How silly to despond about the end of everything! After all, the cosmos was born only around 13 billion years ago, when the Big Bang happened, and parts of it will remain hospitable to our descendants for a good hundred billion years, even as the whole thing continues to spread out.
A half-dozen years ago, however, astronomers peering through their telescopes began to notice something rather alarming. The expansion of the universe, their observations indicated, was not proceeding at the stately, ever-slowing pace that Einstein's equations had predicted. Instead, it was speeding up. Some "dark energy" was evidently pushing against gravity, sending galaxies hurtling away from one another at a runaway rate. New measurements earlier this year confirmed this strange finding. Last July 22, the New York Times ran an ominous headline: "ASTRONOMERS REPORT EVIDENCE OF 'DARK ENERGY' SPLITTING THE UNIVERSE." David Letterman found this so disturbing that he mentioned it several consecutive nights in his Late Show monologue, wondering why the Times buried the story on Page A-13.
Until recently, the ultimate destiny of the universe looked a little more hopeful—or remote. Back around the middle of the last century, cosmologists figured out that there were two possible fates for the universe. Either it would continue to expand forever, getting very cold and very dark as the stars winked out one by one, the black holes evaporated, and all material structures disintegrated into an increasingly dilute sea of elementary particles: the Big Chill. Or it would eventually stop expanding and collapse back upon itself in a fiery, all-annihilating implosion: the Big Crunch.
Which of these two scenarios would come to pass depended on one crucial thing: how much stuff there was in the universe. So, at least, said Einstein's theory of general relativity. Stuff—matter and energy—creates gravity. And, as every undergraduate physics major will tell you, gravity sucks. It tends to draw things together. With enough stuff, and hence enough gravity, the expansion of the universe would eventually be arrested and reversed. With too little stuff, the gravity would merely slow the expansion, which would go on forever. So, to determine how the universe would ultimately expire, cosmologists thought that all they had to do was to weigh it. And preliminary estimates—taking account of the visible galaxies, the so-called "dark matter," and even the possible mass of the little neutrinos that swarm though it all—suggested that the universe had only enough weight to slow the expansion, not to turn it around.
Now, as cosmic fates go, the Big Chill might not seem a whole lot better than the Big Crunch. In the first, the temperature goes to absolute zero; in the second, it goes to infinity. Extinction by fire or by ice—what's to choose? Yet a few imaginative scientists, haunted, like Woody Allen, by visions of the end of the universe, came up with formulations of how our distant descendants might manage to go on enjoying life forever, despite these unpleasant conditions. In the Big Chill scenario, they could have an infinity of slower and slower experiences, with lots of sleep in between. In the Big Crunch scenario, they could have an infinity of faster and faster experiences in the run-up to the final implosion. Either way, the progress of civilization would be unlimited. No cause for existential gloom.
So, Letterman had reason to be upset by the dark energy news. It spells inescapable doom for intelligent life in the far, far future. No matter where you are located, the rest of the universe would eventually be receding from you at the speed of light, slipping forever beyond the horizon of knowability. Meanwhile, the shrinking region of space still accessible to you will fill up with a kind of insidious radiation that would eventually choke off information processing—and with it, the very possibility of thought. We seem to be headed not for a Big Crunch or a Big Chill but something far nastier: a Big Crackup. "All our knowledge, civilization and culture are destined to be forgotten," one prominent cosmologist has declared to the press. It looks as if little Alvy Singer was right after all. The universe is going to "break apart," and that will indeed mean the end of everything—even Brooklyn.
Hearing this news made me think of the inscription that someone once said should be on all churches: important if true. Applied to cosmology—the study of the universe as a whole—that is a big "if." Cosmic speculations that make it into the newspapers should often be taken with a pinch of salt. A few years ago, some astronomers from Johns Hopkins made headlines by announcing that the cosmos was turquoise; two months later they made headlines again by announcing that, no, it was actually beige. This may be a frivolous example, but even in graver matters—like the fate of the universe—cosmologists tend to reverse themselves every decade or so. As one of them once told me, cosmology is not really a science at all since you can't do experiments with the universe. It's more like a detective story. Even the term that is sometimes applied to theorizing about the end of the universe, "eschatology" (from the Greek word for "furthest") is borrowed from theology.
Before I was going to start worrying about the extinction of absolutely everything in some inconceivably distant epoch, I thought it would be a good idea to talk to a few leading cosmologists. Just how certain were they that the cosmos was undergoing a disastrous runaway expansion? Was intelligent life really doomed to perish as a result? How could they, as scientists, talk about the ultimate future of "civilization" and "consciousness" with a straight face?
It seemed natural to start with Freeman Dyson, an English-born physicist who has been at the Institute for Advanced Study in Princeton since the 1940s. Dyson is one of the founding fathers of cosmic eschatology, which he concedes is a "faintly disreputable" subject. He is also a fierce optimist about the far future, one who envisions "a universe growing without limit in richness and complexity, a universe of life surviving forever and making itself known to its neighbors across unimaginable gulfs of space and time." In 1979, he wrote a paper called "Time Without End," in which he used the laws of physics to show how humanity could flourish eternally in a slowly expanding universe, even as the stars died and the chill became absolute. The trick is to match your metabolism to the falling temperature, thinking your thoughts ever more slowly and hibernating for longer and longer periods while extraneous information is dumped into the void as waste heat. In this way, Dyson calculated, a complex society could go on perpetually with a finite energy reserve, one equivalent to a mere eight hours of sunlight.
The day I went to see Dyson, it was raining in Princeton. It took me a half-hour to walk from the train station to the Institute for Advanced Study, which sits by a pond in 500 acres of woods. The institute is a serene, otherworldly place. There are no students to distract the eminent scientists and scholars in residence from pursuing their intellectual fancies. Dyson's office is in the same building where Einstein spent the last decades of his career fruitlessly searching for a unified theory of physics. An elfin, courtly man with deep-set eyes and a hawklike nose, Dyson frequently lapsed into silence or emitted snuffles of amusement. I started by asking him whether the evidence that the universe was caught up in an accelerated expansion had blighted his hopes for the future of civilization.
"Not necessarily," he said. "It's a completely open question whether this acceleration will continue forever or whether it will peter out after a while. There are several theories of what kind of cosmic field might be causing it and no observations to determine which of them is right. If it's caused by the so-called 'dark energy' of empty space, then the expansion will keep speeding up forever, which is bad news as far as life is concerned. But if it's caused by some other kind of force field—which, out of ignorance, we label 'quintessence'—then the expansion might well slow down as we go into the future. Some quintessence theories even say that the universe will eventually stop expanding altogether and collapse. Of course, that, too, would be unfortunate for civilization since nothing would survive the Big Crunch."
Well, then, I said, let's stick with the optimistic scenario. Suppose the acceleration does turn out to be temporary and the future universe settles into a nice cruise-control expansion. What could our descendants possibly look like a trillion trillion trillion years from now, when the stars have disappeared and the universe is dark and freezing and so diffuse that it's practically empty? What will they be made of?
"The most plausible answer," Dyson said, "is that conscious life will take the form of interstellar dust clouds." He was alluding to the kind of inorganic life forms imagined by the late astronomer Sir Fred Hoyle in his 1957 science fiction novel, The Black Cloud. "An ever-expanding network of charged dust particles, communicating by electromagnetic forces, has all the complexity necessary for thinking an infinite number of novel thoughts."
How, I objected, can we really imagine such a wispy thing, spread out over billions of light-years of space, being conscious?
"Well," he said, "how do you imagine a couple of kilograms of protoplasm in someone's skull being conscious? We have no idea how that works either."
Practically next door to Dyson at the institute is the office of Ed Witten, a gangly, 50-ish fellow who is widely regarded as the smartest physicist of his generation, if not the living incarnation of Einstein. Witten is one of the prime movers behind superstring theory, which, if its hairy math is ever sorted out, may well furnish the Theory of Everything that physicists have long been after. He has an unnerving ability to shuffle complicated equations in his head without ever writing anything down, and he speaks in a hushed, soft voice. Earlier this year, Witten was quoted in the press calling the discovery of the runaway expansion of the universe "an extremely uncomfortable result." Why, I wondered, did he see it that way? Was it simply inconvenient for theoretical reasons? Or did he worry about its implications for the destiny of the cosmos? When I asked him, he agonized for a moment before responding, "Both."
Yet Witten, too, thought there was a good chance that the runaway expansion would be only temporary, as some of the quintessence theories predicted, rather than permanent, as the dark-energy hypothesis implied. "The quintessence theories are nicer, and I hope they're right," he told me. If the acceleration does indeed relax to zero, and the Big Crackup is averted, could civilization go on forever? Witten was unsure. One cause for concern was the possibility that protons will eventually decay, resulting in the dissolution of all matter within another, oh, 10^33 years or so. Freeman Dyson had scoffed at this when I talked with him, pointing out that no one had ever observed a proton decaying, but he insisted that intelligent beings could persist even if atoms fell to pieces, by re-embodying themselves in "plasma clouds"—swarms of electrons and positrons. I mentioned this to Witten. "Did Dyson really say that?" he exclaimed. "Good. Because I think protons probably do decay."
Back at the Princeton railroad station after visiting Ed Witten and Freeman Dyson, waiting for the train to New York and munching on a vile "veggie" sandwich that I had picked up at the convenience store across the parking lot, I pondered proton decay and Dyson's scenario for eternal life. How would his sentient Black Clouds, be they made up of cosmic dust or of electron-positron plasma, while away the eons in an utterly freezing and dark universe? What passions would engross their infinite number of ever-slowing thoughts? After all (as Alvy Singer's alter ego once observed), eternity is a long time, especially toward the end. Maybe they would play games of cosmic chess, in which each move took trillions of years. But even at that rate they would run through every possible game of chess in a mere 10^(10^70) years—long before the final decay of the burnt-out cinders of the stars. What then? Would they come around to George Bernard Shaw's conclusion (reached by him at the age of 92) that the prospect of personal immortality was an "unimaginable horror"? Or would they feel that, subjectively at least, time was passing quickly enough? After all, as Fran Lebowitz pointed out, once you've reached the age of 50, Christmas seems to come every three months.
It was almost with a sense of relief that I spoke to Lawrence Krauss a few days later. Krauss, a boyish fellow in his late 40s who teaches at Case Western Reserve in Cleveland, is one of the physicists who guessed on purely theoretical grounds, even before the astronomical data came in, that the cosmos might be undergoing a runaway expansion. "We appear to be living in the worst of all possible universes," Krauss told me, clearly relishing the note of anti-Leibnizian pessimism he struck. "If the runaway expansion keeps going, our knowledge will actually decrease as time passes. The rest of the universe will be literally disappearing before our very eyes surprisingly soon—in the next ten or twenty billion years. And life is doomed—even Freeman Dyson accepts that. But the good news is that we can't prove we're living in the worst of all possible universes. No finite set of data will ever enable us to predict the fate of the cosmos with certainty. And, in fact, that doesn't really matter. Because, unlike Freeman, I think that we're doomed even if the runaway phase turns out to be only temporary."
What about Dyson's vision of a civilization of sentient dust clouds living forever in an expanding universe, entertaining an infinite number of thoughts on a finite store of energy? "It turns out, basically for mathematical reasons, that there's no way you can have an infinite number of thoughts unless you do a lot of hibernating," Krauss said. "You sleep for longer and longer periods, waking up for short intervals to think—sort of like an old physicist. But what's going to wake you up? I have a teenage daughter, and I know that if I didn't wake her up, she'd sleep forever. The Black Cloud would need an alarm clock that would wake it up an infinite number of times on a finite amount of energy. When a colleague and I pointed this out, Dyson came up with a cute alarm clock that could actually do this, but then we argued that this alarm clock would eventually fall apart because of quantum mechanics."
So, regardless of the fate of the cosmos, things look pretty hopeless for intelligent life in the long run. But I should remember, Krauss said, that the long run is a very long time. He told me about a meeting he attended at the Vatican a few years back on the future of the universe: "There were about 15 people, theologians, a few cosmologists, some biologists. The idea was to find common ground, but after three days it was clear that we had nothing to say to one another. When theologians talk about the 'long term,' raising questions about resurrection and such, they're really thinking about the short term. We weren't even on the same plane. When you talk about 10^50 years, the theologians' eyes glaze over. I told them that it was important that they listen to what I had to say—theology, if it's relevant, has to be consistent with science. At the same time I was thinking, 'It doesn't matter what you have to say, because whatever theology has to say is irrelevant to science."
At least one cosmologist I knew of would be quite happy to absorb theology into physics, especially when it came to talking about the end of the universe. That's Frank Tipler, a professor at Tulane University in New Orleans. In 1994 Tipler published a strangely ingenious book called The Physics of Immortality, in which he argued that the Big Crunch would be the happiest possible ending for the cosmos. The final moments before universal annihilation would release an infinite amount of energy, Tipler reasoned, and that could drive an infinite amount of computation, which would produce an infinite number of thoughts—a subjective eternity. Everyone who ever existed would be "resurrected" in an orgy of virtual reality, which would correspond pretty neatly to what religious believers have in mind when they talk about heaven. Thus, while the physical cosmos would come to an abrupt end in the Big Crunch, the mental cosmos would go on forever.
Was Tipler's blissful eschatological scenario—which he called "the Omega Point"—spoiled by the news that the cosmos seemed to be caught up in a runaway expansion? He certainly didn't think so when I talked to him. "The universe has no choice but to expand to a maximum size and then contract to a final singularity," he exclaimed in his thick Southern drawl. (He's a native of Alabama and a self-described "redneck.") Any other cosmic finale, he said, would violate a certain law of quantum mechanics called "unitarity." Moreover, "the known laws of physics require that intelligent life persist until the end of time and gain control of the universe." When I mentioned that Freeman Dyson (among others) could not see why this should be so, Tipler shouted in exasperation, "Ah went up to Princeton last November and ah tode him the argument! Ah tode him!" Then he told me, too. It was long and complicated, but the nub of it was that intelligent beings must be present at the end to sort of massage the Big Crunch in a certain way so that it would not violate another law of quantum mechanics, the "Beckenstein bound." So, our eternal survival is built into the very logic of the cosmos. "If the laws of PHEE-ysics are with us," he roared, "who can be against us?"
Tipler's idea of an infinite frolic just before the Big Crunch was seductive to me—more so, at least, than Dyson's vision of a community of increasingly dilute Black Clouds staving off the cold in an eternal Big Chill. But if the universe is in a runaway expansion, both are pipe dreams. The only way to survive in the long run is to get the hell out. Yet how do you escape a dying universe if—as little Alvy Singer pointed out—the universe is everything?
A man who claims to see an answer to this question is Michio Kaku. A theoretical physicist at City College in New York, Kaku looks and talks a bit like the character Sulu on Star Trek. (He can be seen in the recent Michael Apted film about great scientists, Me and Isaac Newton.) He is not the least bit worried about the fate of this universe. "If your ship is sinking," he said to me, "why not get a lifeboat and leave?" We earthlings can't do this just yet, Kaku observed. That is because we are a mere Type 1 civilization, able to marshal the energy only of a single planet. But eventually, assuming a reasonable rate of economic growth and technological progress, we will graduate to being a Type 2 civilization, commanding the energy of a star, and thence to being a Type 3 civilization, able to summon the energy of an entire galaxy. Then space-time itself will be our plaything. We'll have the power to open up a "wormhole" through which we can slip into a brand new universe.
"Of course," Kaku added, "it may take as long as 100,000 years for such a Type 3 civilization to develop, but the universe won't start getting really cold for trillions of years." There is one other thing that the beings in such a civilization will need, Kaku stressed to me: a unified theory of physics, one that would show them how to stabilize the wormhole so it doesn't disappear before they can make their escape. The closest thing we have to that now, superstring theory, is so difficult that no one (with the possible exception of Ed Witten) knows how to get it to work. Kaku wasn't the least bit gloomy that the universe might be dying. "In fact," he said, "I'm in a state of exhilaration, because this would force us, really force us, to crack superstring theory. People say, 'What has superstring theory done for me lately? Has it given me better cable TV reception?' What I tell them is that superstring theory—or whatever the final, unified theory of physics turns out to be—could be our one and only hope for surviving the death of this universe."
Although other cosmologists were rudely dismissive of Kaku's lifeboat scenario—"a good prop for a science fiction story," said one; "somewhat more fantastical than most of Star Trek," remarked another—it sounded good to me. But then I started thinking. To become a Type 3 civilization, one powerful enough to engineer a stable wormhole leading to a new universe, we would have to gain control of our entire galaxy. That means colonizing something like a billion habitable planets. But if this is what the future is going to look like, then almost all the intelligent observers who will ever exist will live in one of these billion colonies. So, how come we find ourselves sitting on the home planet at the very beginning of the process? The odds against being in such an unusual situation—the very earliest people, the equivalent of Adam and Eve—are a billion to one.
My vague qualm about the unlikeliness of Kaku's lifeboat theory was considerably sharpened when I talked to J. Richard Gott III, an astrophysicist at Princeton University. Gott is known for making bold quantitative predictions about the longevity of things—from Broadway shows like Cats to America's space program to intelligent life in the universe. He bases these predictions on what he calls the Copernican Principle, which says, in essence: You're not special. "If life in the universe is going to last a long time, why do we find ourselves living when we do, only 13 billion years after the beginning?" Gott said to me, speaking in an improbable Tennessee accent whose register occasionally leapt up an octave, like Don Knotts'. "And it is a disturbing fact that we as a species have only been around for 200,000 years. If there are going to be many intelligent species descended from us flourishing in epochs far in the future, then why are we so lucky to be the first?" Doing a quick back-of-the-envelope calculation, Gott determined that it was 95 percent likely that humanity would last more than 5,100 years but would die out before 7.8 million years (a longevity that, coincidentally, is quite similar to that of other mammal species, which tend to go extinct around 2 million years after appearing). Gott was not inclined to speculate on what might do us in—biological warfare? asteroid collision? nearby supernova? sheer boredom with existence? But he did leave me feeling that the runaway expansion of our universe, if real, was the least of our worries.
Despite the pessimistic tenor of Gott's line of thought, he was positively chirpy in conversation. In fact, all the cosmologists I had spoken to so far had a certain mirthfulness about them when discussing eschatological matters—even Lawrence Krauss, the one who talked about this being the worst of all possible universes. ("Eschatology—it's a great word," Krauss said. "I had never heard of it until I discovered I was doing it.") Was no one made melancholy or irritable by the prospect of our universe decaying into nothingness? I thought of Steven Weinberg, the Nobel laureate in physics who, in his 1977 book about the birth of the universe, The First Three Minutes, glumly observed, "The more the universe seems comprehensible, the more it also seems pointless." It was Weinberg's pessimistic conclusion in that book—he wrote that civilization faced cosmic extinction from either endless cold or unbearable heat—that had inspired Freeman Dyson to come up with his scenario for eternal life in an expanding cosmos.
I called Weinberg at the University of Texas, where he teaches. "So, you want to hear what old grumpy has to say, eh?" he growled in a deep voice. He began with a dazzling theoretical exposition that led up to a point I had heard before: No one really knows what's causing the current runaway expansion or whether it will continue forever. The most natural assumption, he added, was that it would. But he wasn't really worried about the existential implications. "For me and you and everyone else around today, the universe will be over in less than 10^2 years," he said. In his peculiarly sardonic way, Weinberg seemed as jolly as all the other cosmologists. "The universe will come to an end, and that may be tragic, but it also provides its fill of comedy. Postmodernists and social constructivists, Republicans and socialists and clergymen of all creeds—they're all an endless source of amusement."
It was time to tally up the eschatological results. The cosmos has three possible fates: Big Crunch (eventual collapse), Big Chill (expansion forever at a steady rate), or Big Crackup (expansion forever at an accelerating rate). Humanity, too, has three possible fates: eternal flourishing, endless stagnation, or ultimate extinction. And judging from all the distinguished cosmologists who weighed in with opinions, every combination from Column A and Column B was theoretically open. We could flourish eternally in virtual reality at the Big Crunch or as expanding black clouds in the Big Chill. We could escape the Big Crunch/Chill/Crackup by wormholing our way into a fresh universe. We could face ultimate extinction by being incinerated by the Big Crunch or by being isolated and choked off by the Big Crackup. We could be doomed to endless stagnation—thinking the same patterns of thoughts over and over again, or perhaps sleeping forever because of a faulty alarm clock—in the Big Chill. One distinguished physicist I spoke to, Andrei Linde of Stanford University, even said that we could not rule out the possibility of their being something after the Big Crunch. For all of the fascinating theories and scenarios they spin out, practitioners of cosmic eschatology are in a position very much like that of Hollywood studio heads: Nobody knows anything.
Still, little Alvy Singer is in good company in being soul-sick over the fate of the cosmos, however vaguely it is descried. At the end of the 19th century, figures like Swinburne and Henry Adams expressed similar anguish at what then seemed to be the certain heat-death of the universe from entropy. In 1903 Bertrand Russell described his "unyielding despair" at the thought that "all the labors of the ages, all the devotion, all the inspiration, all the noonday brightness of human genius, are destined to extinction in the vast death of the solar system, and that the whole temple of Man's achievement must inevitably be buried beneath the debris of a universe in ruins." Yet a few decades later, he declared such effusions of cosmic angst to be "nonsense," perhaps an effect of "bad digestion."
Why should we want the universe to last forever, anyway? Look—either the universe has a purpose or it doesn't. If it doesn't, then it is absurd. If it does have a purpose, then there are two possibilities: Either this purpose is eventually achieved, or it is never achieved. If it is never achieved, then the universe is futile. But if it is eventually achieved, then any further existence of the universe is pointless. So, no matter how you slice it, an eternal universe is either a) absurd, b) futile, or c) eventually pointless.
Despite this cast-iron logic, some thinkers believe that the longer the universe goes on, the better it is, ethically speaking. As John Leslie, a cosmological philosopher at the University of Guelph in Canada, told me, "This is true simply on utilitarian grounds: The more intelligent happy beings in the future, the merrier." Philosophers of a more pessimistic kidney, like Schopenhauer, have taken precisely the opposite view: Life is, on the whole, so miserable that a cold and dead universe is preferable to one teeming with conscious beings.
If the current runaway expansion of the cosmos really does portend that our infinitesimal flicker of civilization will be followed by an eternity of bleak emptiness, then that shouldn't make life now any less worth living, should it? It may be true that nothing we do in A.D. 2004 will matter when the burnt-out cinder of our sun is finally swallowed by a galactic black hole in a trillion trillion years. But by the same token, nothing that will happen in a trillion trillion years matters to us now. In particular (as the philosopher Thomas Nagel has observed), it does not matter now that in a trillion trillion years nothing we do now will matter.
Then what is the point of cosmology? It's not going to cure cancer or solve our energy problems or give us a better sex life, obviously enough. Still, it is bracing to realize that we live in the first generation in the history of humanity that might be able to answer the question, How will the universe end? "It amazes me," Lawrence Krauss said, "that, sitting in a place on the edge of nowhere in a not especially interesting time in the history of the universe, we can, on the basis of simple laws of physics, draw conclusions about the future of life and the cosmos," he said. "That's something we should relish, regardless of whether we're here for a long time or not."
So, remember the advice offered by Monty Python in their classic "Galaxy Song." When life gets you down, the song says, and you're feeling very small and insecure, turn your mind to the cosmic sublimity of the ever-expanding universe—"because there's bugger-all down here on Earth."
Jim Holt writes the "Egghead" column for Slate. He also writes for The New Yorker and the New York Times Magazine.
Copyright © 2004 Slate Magazine
