LONDON — “You would hope that from this point on,” said Jim Van Laak, manager of the space station Alpha, on Friday, “we will never have a period when humans are not living in space.”

I hope so, too, and I actually know how long “never” is.

It’s much longer away than the year 2085, which is closer to us than the outbreak of World War I. It’s farther away than the year 2507, which is already closer to us than the year of Columbus’s first voyage. It’s even farther away than the year 4054, which is still not as distant as the year Julius Caesar conquered Britain. “Never” is a very, very long time.

Van Laak’s comment probably wasn’t really looking forward to what the situation will be in the year 13271, as far ahead of us as the first villages are behind us. He was probably just saying he hoped that the International Space Station has overcome its teething problems and will be continuously occupied from now on. (On the other hand, he’s in the space business, and they’re all incurable romantics, so maybe . . .)

The point is that he’s either right, and we’ll find ways of making ourselves a wider future that takes us into the universe, or he’s wrong, and we’ll turn back upon the Earth and make our futures only here. There is no way of guessing which it will be because the choice depends on scientific and technological constraints we do not yet know. If it’s easy, we’ll do it, but who knows?

Each of these options, go or stay, also has two possible outcomes. If we do move into the wider universe, we may thrive and spread, and 10,000 years from now humans will live on 1,000 planets. Or we may run into something so big and horrible that it does us in.

Only in the past five years has it finally become clear that planets are as common as dirt in the universe, accompanying many if not most stars. We still do not have hard evidence that Earth-like planets are common (because they are still too small to see at interstellar distances), but that too seems very likely, as does the widespread presence of life. The basic chemical building-blocks of life, after all, abound even in the hard vacuum of interstellar space.

So, our long-term future may resemble one of those two staples of science fiction: an exclusively human “empire” spreading through the star systems of our galactic neighborhood, or an encounter with some truly nasty and dangerous neighbors, if we discover that we are not alone out there.

Again, we have no way of knowing yet, though our inability to detect the kind of electromagnetic radiations you would expect from other advanced civilizations suggests that (a) we’re all alone around here, or (b) that everybody else is hiding — which makes you wonder: What from?

If we stay behind, the same stark division of potential outcomes applies. Either we manage to turn the planet into a sustainable suburban garden (with 9 or 10 billion people by the time population growth slides to a halt, one or two generations from now, it certainly isn’t going to be a wildlife park). Or, we mess things up so badly that there is a drastic human population crash, down to a small fraction of the present population.

On these questions, too, there is simply not enough evidence to make even an educated guess. We do not know enough about the stability and resilience of the current environmental balance under the mounting pressures created by human numbers and activities. Neither do we know what degree of planetary cooperation we can hope for from a traditionally warlike species like ourselves that is only a generation or so away from truly planet-killing weapons.

These two sets of outcomes — the “home” and “away” models — are not mutually exclusive, by the way. We could end up with a future that included both interstellar colonization and Garden Earth, or no human expansion beyond this planet and catastrophe on it.

Common sense says that all these imagined outcomes for the relatively brief experiment of human civilization are too extreme, too dramatic by far. But common sense simply does not apply to domains as large as history (or physics, for that matter).

Common sense is distilled wisdom about how little things work, drawn from many observations of things that repeat all the time. Neither quantum physics nor history on the larger scale is that kind of phenomenon. So far as human history is concerned, radical change and apparently extreme outcomes are likelier than a perpetual prolongation of the present. And if this frightens or depresses you, then you have misunderstood the nature of the experiment.

Human intelligence is astonishingly high in evolutionary terms: far higher than would be needed merely to domesticate plants and animals and create some sort of stable agrarian civilization. We do not have the option of recapitulating the history of ancient Egypt endlessly in safe but boring cycles. We are evolutionary high-rollers, headed for boom or bust in the most dramatic terms.

Which is why one must hope that Jim Van Laak’s wish comes true. If we are not now getting into space for good, all of our extreme outcomes will take place on this single small planet. For some reason or other, that would worry me.

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