Murmurs of Earth: The Voyager Interstellar Record
by Carl Sagan, by F.D. Drake, by Ann Druyan, by Timothy Ferris, by Jon Lomberg, by Linda Salzman Sagan
Random House, 273 pp., $15.00
Spaceships of the Mind
by Nigel Calder
Viking, 144 pp., $14.95
In the Center of Immensities
by Bernard Lovell, edited by Ruth Nanda Anshen
Harper & Row, 171 pp., $10.95
“A sad spectacle!” exclaimed Thomas Carlyle, contemplating the possibility that millions of planets circle other suns. “If they be inhabited, what a scope for pain and folly; and if they be not inhabited, what a waste of space!”
Much more is now known about the universe than in Carlyle’s time, but the question of whether ETI (a fashionable new acronym for Extraterrestrial Intelligence) exists is as open as it ever was. However, one incredible new fact has entered the picture. For the first time in history we have the technology for maybe answering the question. This mere possibility is so overwhelming in its implications that a new science called “exobiology” has already been named even though its entire subject matter may not exist.
We do know that our Milky Way galaxy contains more than 200 billion suns, and that there are billions of other galaxies. Are there other planets? Fifty years ago the two most popular theories about the origin of the solar system each made such planetary systems so unlikely that top astronomers believed that ours was the only one in the galaxy. After flaws were found in both theories, astronomers returned to a model proposed by Immanuel Kant (later by Laplace) in which solar systems are so likely that most of the Milky Way’s stars must have them. The wobblings of a few nearby suns suggest big planets close to them, but no one really knows.
If solar systems are plentiful, our galaxy could contain billions of planets earthlike enough to support carbon-based life. Biologists have a strong case for confining life to carbon compounds (silicon and boron are the next best bets), but no one has any notion of how earthlike a planet must be to permit carbon life to arise. Our two nearest neighbors, Venus and Mars, were probably formed the same time the earth was, yet their atmospheres are strikingly different from each other and from ours. Even if a planet goes through an early history exactly like our earth’s, no one knows the probability that life on its surface can get started. If it does start, no one knows the probability that it will evolve anything as intelligent as a fish.
Our probes of Mars have been great disappointments in SETI (Search for ETI). I can still recall the tingling of my spine when as a boy I read on the first page of H.G. Wells’s War of the Worlds:
Yet across the gulf of space, minds that are to our minds as ours are to those of the beasts that perish, intellects vast and cool and unsympathetic, regarded this earth with envious eyes, and slowly and surely drew their plans against us.
Not even Wells guessed how quickly the Martians would vanish from science fiction.
If we can trust recent polls, half of America believes that ETIs are regularly visiting the earth in UFOs, but this is no more than part of the big upsurge of enthusiasm for …