Extraterrestrial Civilizations - Isaac Asimov [104]
*It always yields ludicrously short intervals of time when we try to calculate how long it would take a virus, a bacterium, a pair of flies, a pair of mice, a pair of human beings, even a pair of elephants, to produce offspring equal in mass to the entire Earth-assuming free reproduction, unlimited food, and no deaths but by old age. In the case of human beings, if we start with one pair and multiply them at an overall rate of 3.3 percent a year-easily within human capacity the descendants of that one pair will be equal in mass to the entire Earth in 1,600 years
* Even if we accept tales such as that of Atlantis, we would be dealing with only a slightly earlier version of human civilization.
* I will discuss the difllcultles of interstellar travel in some detail in the next chapter.
* This was the central motif of the science fiction movie 2001: A Space Odyssey.
CHAPTER 11
Space Exploration
THE NEXT TARGETS
If the key to the paradox of the existence of many civilizations in a Universe in which to all appearances we are alone, rests with the presumed difficulty of space exploration, let us examine that problem more closely.
After all, human beings managed to place the first object in orbit, thus initiating the “Space Age,” only on October 4, 1957. Before the Spage Age was a dozen years old, human beings stood on the Moon. That is a rather promising beginning. Surely we can go farther now.
In a way, we already have. Instruments have been soft-landed on the surface of Venus and Mars, and photographs and other data have been sent back to Earth. Probes have, without landing, skimmed by the surfaces of Mercury and Jupiter and have, again, returned photographs and other data. As I write, probes are on the way to Saturn and beyond.
This far penetration of human instruments without the involvement of human beings themselves does not, however, have the glorious ring of accomplishment that we associate with the mystique of exploration. Can human beings themselves, as distinct from their inanimate instruments, move to worlds beyond the Moon?
Unfortunately, the Moon is not a particularly hopeful precedent. It is so close to Earth that it can’t help but give us a false confidence; it lures us on to underestimate the distances involved in space exploration.
The Moon, after all, is so close to Earth that it takes only 3 days to reach it, as compared with the 7 weeks it took Columbus to cross the Atlantic Ocean.
In reaching the Moon, we have made only the most microscopic dent in the true vastness of space. Indeed, we have not really left Earth, since the Moon is as much a slave to Earth’s gravitational influence as an apple on a tree—something Isaac Newton perceived three centuries ago.
To be sure, there are small bodies that occasionally come to within a few million kilometers of the Earth, 10 to 50 times the distance of the Moon—an occasional asteroid or comet. The nearest sizable body other than the Moon, however, is the planet Venus.
Even when Venus is at its closest to Earth, it is 40 million kilometers (25 million miles) away in a straight line, and is 105 times the distance of the Moon.
We cannot expect a space vessel to move straight across the gap between the planetary orbits. The most economical route for a space vessel to follow is an elliptical orbit of its own that begins at Earth and intersects the orbit of Venus just as that planet approaches the intersection point.
The probes that we have sent out to Venus take 7 months to cover the distance. Those probes, however, are given one burst of acceleration at the start of their journey and are then allowed to coast the rest of the way. Time is of little importance to an inanimate object.
In the case of a manned vessel, time is of importance. The journey must be carried through quickly, and the easiest way of doing that is to build up greater speeds.
Human beings have more than once cancelled distance by increasing speed. I have already said that the astronauts take three days to reach the Moon, while Columbus took