How to Predict Everything (1999)

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J. Richard Gott III, the celebrated Princeton astrophysicist, has always been interested in predicting the future of things, but only recently has he got around to forecasting how long Broadway plays will run. Gott started big. In the seventies, he and several colleagues published an influential paper arguing that the universe is geometrically “open”—meaning that it will go on expanding forever. Then, building on research pioneered by Kip Thorne, the eminent black-hole theorist at Caltech, he identified circumstances under which time travel into the past might be possible, inside black holes. This work has held up well, and has contributed to Gott’s growing reputation as a provocateur whose ideas, although sometimes startling, are difficult to dismiss.

Physicists are good at predicting the behavior of simple systems like the universe (which, typically, is modelled as if it were a gas) and black holes (from within which, one may rest assured, no reporter will ever file dispatches). But neither physics nor any other science has had much success in predicting what is to become of the human species, or whether a Broadway musical will make money. Now that Gott has waded into those waters, one naturally wonders whether he has at last gone too far. To find out, I asked him, over dinner, how his predictions were faring.

“Quite well, actually. I’m batting a thousand,” Gott replied, with his customary ebullience. A sunny, moon-faced man with a lilting voice that creaks like an old attic beam and is rounded by a vintage Kentucky accent (he’s from Louisville), Gott, who is fifty-two, is invariably cheerful; in the more than twenty years that I’ve known him, I’ve never heard him utter a discouraging word. He’s exquisitely serious about science, and is given to long-playing discourses—he can spend forty minutes answering a question without wasting a word—but a playful irony is seldom far from the thread of his conversation. Once, when presenting a paper on his time-travel research—work that has led to the discovery of a mechanism by which the universe could, theoretically, have created itself—he claimed to be an emissary from the future, proffering as evidence the consideration that nobody in the present could find a cranberry sports coat as vivid as the one he was wearing. On this occasion, he was, as is his custom, dressed brightly, in a neon-blue sports coat, a green shirt, and a rainbow tie; a collapsible umbrella projected from his hip pocket like a nightstick. He reached into a large brown attaché case and produced a sheaf of papers that he arrayed on the table in front of him, moving aside a Coke he’d ordered in lieu of a cocktail.

“On May 27, 1993, I looked up all the plays that were listed in _The New Yorker—_Broadway and Off Broadway plays and musicals—and called up each of the theatres and asked when each play had opened,” Gott said, drawing my attention to the top sheet of paper. It listed the plays in the order of their longevity, from “Later Life,” which had then been open for four days and was to close after forty-five days, to “The Fantasticks,” which had been running for twelve thousand seventy-seven days and was still open. “I predicted how long each would run, based solely on how long it had been running already. Forty-four shows were playing at the time. So far, thirty-six of them have closed, all in agreement with my predictions of how long they would last. And the others, which are still running, are also within the range I’d predicted. So, as I say, I’m batting a thousand so far. But I should be right ninety-five per cent of the time, since these predictions are made to a ninety-five-per-cent confidence level.”

It must be said that Gott’s predictions are, well, broad. He predicted, for instance, that “Marisol,” which had been open for a week when he called the theatres, would close in less than thirty-nine weeks; it lasted ten more days. To “Cats,” which had then been running for three thousand eight hundred and eighty-five days, Gott assigned a longevity of not less than a hundred days and not more than four hundred and fourteen years. Even theatregoers who took literally the newspaper advertisements proclaiming “ ‘Cats’: Now and Forever” probably do not expect it to be on the boards in the year 2407. The significance of Gott’s approach resides not in any likely improvement in backers’ ability to handicap theatrical productions but in its startling originality and its ability to address issues previously inaccessible to scientific inquiry, such as predicting how long the human species will endure. I asked Gott for some background.

“My approach is based on the Copernican principle, which has been one of the most famous and successful scientific hypotheses in the history of science,” he said. “It’s named after Nicolaus Copernicus, who proved that the earth is not the center of the universe; and it’s simply the idea that your location is not special. The more we’ve learned about the universe, the more non-special our location has looked. The earth is orbiting an ordinary star in an ordinary galaxy. The reason the Copernican principle works is that, of all the places for intelligent observers to be, there are by definition only a few special places and many non-special places. So you’re simply more likely to be in one of the many non-special places.

“The predictions that I make are based on applying this principle to time. I first thought of it in 1969. I’d just graduated from Harvard and was travelling around Europe, and I visited the Berlin Wall. People at that time wondered how long the Wall might last. Was it a temporary aberration, or a permanent fixture of modern Europe? Standing at the Wall in 1969, I made the following argument, using the Copernican principle. I said, Well, there’s nothing special about the timing of my visit. I’m just travelling—you know, Europe on five dollars a day—and I’m observing the Wall because it happens to be here. My visit is random in time. So if I divide the Wall’s total history, from the beginning to the end, into four quarters, and I’m located randomly somewhere in there, there’s a fifty-percent chance that I’m in the middle two quarters—that means, not in the first quarter and not in the fourth quarter.

“Let’s suppose that I’m at the beginning of that middle fifty per cent. In that case, one quarter of the Wall’s ultimate history has passed, and there are three quarters left in the future. In that case, the future’s three times as long as the past. On the other hand, if I’m at the other end, then three quarters have happened already, and there’s one quarter left in the future. In that case, the future is one-third as long as the past.

“Let’s see,” I interjected. “How old was the Wall at that time?”

“Eight years,” Gott replied. “So I said to a friend, ‘There’s a fifty-per-cent chance that the Wall’s future duration will be between two-thirds of a year and twenty-four years.’ Twenty years later, in 1989, the Wall came down, within those two limits that I had predicted. I thought, Well, you know, maybe I should write this up.”

Gott did precisely that, in a paper published in the journal Nature on May 27, 1993—and that was the day he called around to find out how long the plays had been running. “I picked plays because they are subject to all sorts of chaotic effects—the star could get sick, there could be a fire in the Broadway district,” Gott said. “Recently, it’s come to be understood that systems may behave chaotically and therefore be unpredictable. You know, a butterfly in the Amazon can affect the weather thousands of miles away, that sort of thing. This has led some people to say that predicting the future of complex systems is impossible. Which is true if you are concerned with the precise specifics. To predict the name of the President of the United States in the year 2085, for instance, is impossible. But if you ask the right question maybe you can get an interesting answer.”

The question that Gott has been asking lately is how long the human species is going to last. Since scientists generally make predictions at the ninety-five-per-cent confidence level, Gott begins with the assumption that you and I, having no reason to think we’ve been born in a special time, are probably living during the middle ninety-five per cent of the ultimate duration of our species. In other words, we’re probably living neither during the first two and a half per cent nor during the last two and a half per cent of all the time that human beings will have existed.

“Homo sapiens has been around for two hundred thousand years,” Gott said, once we’d finished our entrées. “That’s how long our past is. Two and a half per cent is equal to one-fortieth, so the future is probably at least one-thirty-ninth as long as the past but not more than thirty-nine times the past. If we divide two hundred thousand years by thirty-nine, we get about fifty-one hundred years. If we multiply it by thirty-nine, we get 7.8 million years. So if our location in human history is not special, there’s a ninety-five-per-cent chance we’re in the middle ninety-five per cent of it. Therefore the human future is probably going to last longer than fifty-one hundred years but less than 7.8 million years.

“Now, those numbers are interesting, because they give us a total longevity that’s comparable to that of other species. The predicted total lifetime of the human species is quite similar to the ranges we see for other species—species that have gone extinct. Homo erectus, our ancestor species, lasted for about 1.6 million years. The Neanderthals went extinct after about three hundred thousand years. The mean duration for all mammal species is two million years.”

I remarked that in my experience most people either think we’re going to hell in a handbasket or assume that we’re going to be around for a very long time. Recently, I went on to say, I tested this by E-mailing a dozen friends to ask their predictions. Sure enough, the majority of those who hazarded a guess fell into two camps, clustered around the extremes. Most predicted either that human beings will last less than two hundred years or that we’re good for more than ten million years.

“That’s because people like to think they’re living in special times,” Gott observed. “We like to think of ourselves as near the beginning of things, or in an apocalyptic situation near the end. It’s more dramatic that way. A lot of people might say, ‘Oh, but we are in a special epoch. We’re in the epoch when men first went to the moon, when we discovered genetic engineering, nuclear energy, and so forth.’ My answer to this is that the Copernican principle predicts that you will be living in a high-population century—most people do, just as most people come from cities with higher than average populations, in larger than average nations. It’s people who make discoveries, so if you live when there are more people around, you should expect to live in an age when a lot of interesting discoveries are being made.”

The waiter came with the check. I asked him in what year the Four Seasons had opened. “In 1959,” he answered instantly.

“That’s a good example,” Gott said, whipping out a pocket calculator. “Let’s see, 1959 was thirty-nine years ago. One-thirty-ninth of thirty-nine is one year. Thirty-nine times thirty-nine years is fifteen hundred and twenty-one years. So I predict, at a ninety-five-per-cent confidence level, that this restaurant will still be open in a year but will have closed prior to the year—let’s see-3519! Because, you know, there’s nothing special about our happening to be here this particular evening. We just came here because the restaurant happens to be here now.”

We strolled back to my hotel, and there I turned on a tape recorder, while Gott, who likes to talk late into the night, put his feet up. I asked him about what is, to me, the most disturbing aspect of his theory—the ice water it throws on the optimists who expect human beings to survive pretty much forever.

“People think that, sure, other species go out of business every million or so years, but since we’re smarter than they are we will last longer. Unfortunately, the facts don’t really bear this out,” Gott said. “I mean, Einstein was very, very smart, but he didn’t live longer than the rest of us. Smartness doesn’t seem to be correlated very well with longevity in the animal kingdom, right up to and including very smart species, similar to us. Mammals are smart, but mammals haven’t lasted any longer than other species. The Neanderthals and Homo erectus and the other hominid species, of which there were a number, also went extinct on comparable time scales. And our past track record is right in the same league. If the human race is actually to last for a billion years, we today are in the very, very beginning of it, and it would be quite a coincidence that we were so lucky as to be among the very first humans. It would also be a coincidence that we came along at just the right time to fool us into thinking that our longevity is about the same as other species’. That’s like expecting that your last name falls in the first fortieth of the names in the Manhattan phone book, between Aaron and Antonio. It probably doesn’t.”

Gott, after rummaging around in his attaché case, produced a set of dominoes, which he set up in five stacks of doubling height, starting with one domino and ending with a stack of sixteen. “These dominoes represent the human population over time,” he said. “We’ve gone through a period of exponential growth, so I have one, two, four, eight, and then sixteen dominoes. Now, what’s going to happen in the future? One prospect is that the population will reach a peak, then go back down at a similar rate. This is something that has happened to many species: you have an exponential growth rate that reaches a peak and then something bad happens and you have an exponential decline. In that case, you would expect to be right about here, near the peak. Most people are. And that’s where we are.”

I counted the dominoes. There were sixteen in the stack representing the present and only fifteen in all the preceding four stacks combined. “That’s the non-special place to be—in a population peak, not near the beginning or near the end,” Gott said cheerfully. “It’s like your place of birth. I come from Jefferson County, which happens to be the most populous county of all the hundred and twenty counties in Kentucky. That’s not an accident; it’s just likely. And here we are, having this conversation in New York City, where there are a lot of people. Sometimes people say, ‘Why is it I always find myself in the longest line at the post office?’ But if “the lines have various lengths most people are going to find themselves in the longer of the lines. If there’s any variation in the length of the lines, you’re likely to end up in one of the longer ones simply because there are more people in those lines.”

Gott took out some more dominoes and made several additional stacks, each as tall as the one marking the present. “Now let’s look at a more optimistic model—one in which, following the period of exponential growth, the population reaches equilibrium and stays at something like current levels far into the future,” he said. “What’s wrong with this model? Well, if that’s what’s going to happen, if we’re going to have a global population of, say, five or ten billion for millions of years to come, then almost every human ever to be born lives out here on the long plateau. The Copernican question is: If the future is going to be like that, why don’t you and I live on the plateau? Why don’t we, looking back, see that the world population has remained level for millions of years? We don’t, so if the optimistic prediction is right, then you and I are in a very special place. But one is not likely to be special. Whereas if the population is going to decline, then we’re living in exactly a typical place, just as one would expect.”

I poured myself a Scotch-and-water. This is the part of Gott’s argument that most troubles me—not because I can find fault with it but because I can’t. It ranks as one of the most baleful prognostications of the human fate since Malthus.

Gott went happily on, tapping his right index finger on the domino plateau. “A lot of people say, ‘Well, our species may go out of existence, but we’ll be replaced by smarter, genetically engineered human beings. We’ll have many descendant species, so we shouldn’t mourn if Homo sapiens goes extinct, because we’ll be replaced by something much better.’ But, as Mr. Darwin noted, most species do not leave any descendants. A few do, and they leave a lot: there are sixteen species of rodents. Our genus, Homo, is down to one. We’re like the horse. There used to be several, now there’s only one. There used to be several different hominid species—the Neanderthals and us, for example—and now we’re down to one. This is not a good sign.

“Some say that we are destined to turn ourselves into intelligent computers that live forever. But, if you believe that, you have to ask yourself, ‘Why am I not an intelligent computer? Why am I not genetically engineered?’ If you believe that we are going to venture into space and colonize the galaxy, you have to ask yourself, ‘Why am I not a space colonist?’ Because, if colonization occurs, almost everyone is a colonist. In fact, you and I are continental colonists. We’re living here in North America. People started out in Africa; we’re not from the original continent. Now, travel between continents is pretty easy, but travel between stars, to set up colonies on other star systems, that’s more difficult. So where do you expect to find yourself by the Copernican principle? You expect to find yourself at a niche that’s easily filled up, where the next jump is difficult. And that’s where we are.”

The hour was approaching midnight, and I was feeling a bit fatalistic. Gott, however, has a more upbeat reaction to his conclusions. He thinks that we should improve our survival chances by colonizing Mars, that we need to do it promptly, and that that should be the goal of the space program.

“The manned space program is thirty-eight years old, so it’s been around only a short time,” he said. “Things that haven’t been around a very long time are not likely to be around very long in the future. So there’s a real danger that we will quit it, as the Chinese did in the fifteenth century. They explored Africa, came back with a giraffe that everybody wondered at, and then they just quit. The period of great Egyptian pyramid-building lasted about a century from the first to the biggest; then there was a long, slow decline during which the Egyptians built crummy ones. So there’s a danger that we’ll end up stuck on the earth—that if we wait too long we may have a population that’s too small to respond to an emergency or to do space colonization. Should something bad take us by surprise in a hundred and fifty thousand years—an epidemic, or something like that—we’d be saying, ‘We should have colonized back there in the twenty-first century, while we had the chance.’

“I’m not saying that Mars isn’t dangerous, but colonizing Mars would increase our survival prospects by giving us two chances in the casino of life. It’s often said that people have a wanderlust, but why do we have this wanderlust? Because it’s good biological sense to spread out and multiply, to make copies of yourself. The Greeks had all their books in the Alexandrian library and they guarded it very well, but eventually the thing burned down. The only reason we have seven of Sophocles’ hundred and twenty plays, the rest having been lost, is that somebody copied them and put them elsewhere. So we should copy ourselves. This has been life’s good strategy for 3.8 billion years—to make copies and spread out, because entropy’s trying to cut you down. I think the very first astronauts sent to Mars should be people who are prepared to stay on and start a colony. Why bring them back just to give them a ticker-tape parade in New York City? Leave them there!”

Outside, at the curb, I waved goodbye as Gott’s car headed crosstown, bound for Princeton. That car is about a year old, I thought, so it’s likely to keep running for more than a week but less than thirty-nine more years. New York City was first settled in 1626; that gives it nine and a half to 14,500 years to go. Jupiter stood high in the southern sky, warranteed for at least another hundred and fourteen million years. Science, like art, changes the way one looks at things. ♦

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