Pale Blue Dot - Carl Sagan [143]
In the next few decades we have a real chance of examining the layout and something of the composition of many other mature planetary systems around nearby stars. We will begin to know which aspects of our system are the rule and which the exception. What is more common—planets like Jupiter, planets like Neptune, or planets like Earth? Or do all other systems have Jupiters and Neptunes and Earths? What other categories of worlds are there, currently unknown to us? Are all solar systems embedded in a vast spherical cloud of comets? Most stars in the sky are not solitary suns like our own, but double or multiple systems in which the stars are in mutual orbit. Are there planets in such systems? If so, what are they like? If, as we now think, planetary systems are a routine consequence of the origin of suns, have they followed very different evolutionary paths elsewhere? What do elderly planetary systems, billions of years more evolved than ours, look like? In the next few centuries our knowledge of other systems will become increasingly comprehensive. We will begin to know which to visit, which to seed, and which to settle.
Imagine we could accelerate continuously at 1 g—what we’re comfortable with on good old terra firma—to the midpoint of our voyage, and decelerate continuously at 1 g until we arrive at our destination. It would then take a day to get to Mars, a week and a half to Pluto, a year to the Oort Cloud, and a few years to the nearest stars.
Even a modest extrapolation of our recent advances in transportation suggests that in only a few centuries we will be able to travel close to the speed of light. Perhaps this is hopelessly optimistic. Perhaps it will really take millennia or more. But unless we destroy ourselves first we will be inventing new technologies as strange to us as Voyager might be to our hunter-gatherer ancestors. Even today we can think of ways—clumsy, ruinously expensive, inefficient to be sure—of constructing a starship that approaches light speed. In time, the designs will become more elegant, more affordable, more efficient. The day will come when we overcome the necessity of jumping from comet to comet. We will begin to soar through the light-years and, as St. Augustine said of the gods of the ancient Greeks and Romans, colonize the sky.
Such descendants may be tens or hundreds of generations removed from anyone who ever lived on the surface of a planet. Their cultures will be different, their technologies far advanced, their languages changed, their association with machine intelligence much more intimate, perhaps their very appearance markedly altered from that of their nearly mythical ancestors who first tentatively set forth in the late twentieth century into the sea of space. But they will be human, at least in large part; they will be practitioners of high technology; they will have historical records. Despite Augustine’s judgment on Lot’s wife, that “no one who is being saved should long for what he is leaving,” they will not wholly forget the Earth.
But we’re not nearly ready, you may be thinking. As Voltaire put it in his Memnon, “our little terraqueous globe is the madhouse of those hundred thousand millions* of worlds.” We, who cannot even put our own planetary home in order, riven with rivalries and hatreds, despoiling our environment, murdering one another through irritation and inattention as well as on deadly purpose, and moreover a species that until only recently was convinced that the Universe was made for its sole benefit—are we to venture out into space, move worlds, re-engineer planets, spread to neighboring star systems?
I do not imagine that it is precisely we, with