Pale Blue Dot - Carl Sagan [134]
Since, in the long run, every planetary society will be endangered by impacts from space, every surviving civilization is obliged to become spacefaring—not because of exploratory or romantic zeal, but for the most practical reason imaginable: staying alive. And once you’re out there in space for centuries and millennia, moving little worlds around and engineering planets, your species has been pried loose from its cradle. If they exist, many other civilizations will eventually venture far from home.*
A MEANS HAS BEEN OFFERED of estimating how precarious our circumstances are—remarkably, without in any way addressing the nature of the hazards. J. Richard Gott III is an astrophysicist at Princeton University. He asks us to adopt a generalized Copernican principle, something I’ve described elsewhere as the Principle of Mediocrity. Chances are that we do not live in a truly extraordinary time. Hardly anyone ever did. The probability is high that we’re born, live out our days, and die somewhere in the broad middle range of the lifetime of our species (or civilization, or nation). Almost certainly, Gott says, we do not live in first or last times. So if your species is very young, it follows that it’s unlikely to last long—because if it were to last long, you (and the rest of us alive today) would be extraordinary in living, proportionally speaking, so near the beginning.
What then is the projected longevity of our species? Gott concludes, at the 97.5 percent confidence level, that there will be humans for no more than 8 million years. That’s his upper limit, about the same as the average lifetime of many mammalian species. In that case, our technology neither harms nor helps. But Gott’s lower limit, with the same claimed reliability, is only 12 years. He will not give you 40-to-1 odds that humans will still be around by the time babies now alive become teenagers. In everyday life we try very hard not to take risks so large, not to board airplanes, say, with 1 chance in 40 of crashing. We will agree to surgery in which 95 percent of patients survive only if our disease has a greater than 5 percent chance of killing us. Mere 40-to-l odds on our species surviving another 12 years would be, if valid, a cause for supreme concern. If Gott is right, not only may we never be out among the stars; there’s a fair chance we may not be around long enough even to make the first footfall on another planet.
To me, this argument has a strange, vaporish quality. Knowing nothing about our species except how old it is, we make numerical estimates, claimed to be highly reliable, about its future prospects. How? We go with the winners. Those who have been around are likely to stay around. Newcomers tend to disappear. The only assumption is the quite plausible one that there is nothing special about the moment at which we inquire into the matter. So why is the argument unsatisfying? Is it just that we are appalled by its implications?
Something like the Principle of Mediocrity must have very broad applicability. But we are not so ignorant as to imagine that everything is mediocre. There is something special about our time—not just the temporal chauvinism that those who reside in any epoch doubtless feel, but something, as outlined above, clearly unique and strictly relevant to our species’ future chances: This is the first time that (a) our exponentiating technology has reached the precipice of self-destruction, but also the first time that (b) we can postpone or avoid destruction by going somewhere else, somewhere off the Earth.
These two clusters of capabilities, (a) and (b), make our time extraordinary in directly contradictory ways—which both (a) strengthen and (b) weaken Gott’s argument. I don’t know how to predict whether the new destructive technologies will hasten, more than the new spaceflight technologies will delay, human extinction. But since never before have we contrived the means of annihilating ourselves, and