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.