MacDonald (a science-fiction author now transmogrified into one of the most interesting contemporary writers of detective fiction), we find the sentence “and there are traces, in Earth mythology… of great ships and chariots that crossed the sky.” The story
THE INTERWEAVING of science and science fiction sometimes produces curious results. It is not always clear whether life imitates art or vice versa. For example, Kurt Vonnegut, Jr., has written a superb epistemological novel,
The trouble has been that our understanding of the other planets has been changing faster than the science- fiction representations of them. A clement twilight zone on a synchronously rotating Mercury, a swamp-and-jungle Venus and a canal-infested Mars, while all classic science-fiction devices, are all based upon earlier misapprehensions by planetary astronomers. The erroneous ideas were faithfully transcribed into science-fiction stories, which were then read by many of the youngsters who were to become the next generation of planetary astronomers-thereby simultaneously capturing the interest of the youngsters and making it more difficult to correct the misapprehensions of the oldsters. But as our knowledge of the planets has changed, the environments in the corresponding science-fiction stories have also changed. It is quite rare to find a science-fiction story written today that involves algae farms on the surface of Venus. (Incidentally, the UFO-contact mythologizers are slower to change, and we can still find accounts of flying saucers from a Venus populated by beautiful human beings in long white robes inhabiting a kind of Cytherean Garden of Eden. The 900° Fahrenheit temperatures of Venus give us one way of checking such stories.) Likewise, the idea of a “space warp” is a hoary science-fiction standby but it did not arise in science fiction. It arose from Einstein’s General Theory of Relativity.
The connection between science-fiction depictions of Mars and the actual exploration of Mars is so close that, subsequent to the Mariner 9 mission to Mars, we were able to name a few Martian craters after deceased science- fiction personalities. (See Chapter 11.) Thus there are on Mars craters named after H. G. Wells, Edgar Rice Burroughs, Stanley Weinbaum and John W. Campbell, Jr. These names have been officially approved by the International Astronomical Union. No doubt other science-fiction personalities will be added soon after they die.
THE GREAT INTEREST of youngsters in science fiction is reflected in films, television programs, comic books and a demand for science-fiction courses in high schools and colleges. My experience is that such courses can be fine educational experiences or disasters, depending on how they are done. Courses in which the readings are selected by the students provide no opportunity for the students to read what they have not already read. Courses in which there is no attempt to extend the science-fiction plot line to encompass the appropriate science miss a great educational opportunity. But properly planned science-fiction courses, in which science or politics is an integral component, would seem to me to have a long and useful life in school curricula.
The greatest human significance of science fiction may be as experiments on the future, as explorations of alternative destinies, as attempts to minimize future shock. This is part of the reason that science fiction has so wide an appeal among young people: it is
Such ideas, when encountered young, can influence adult behavior. Many scientists deeply involved in the exploration of the solar system (myself among them) were first turned in that direction by science fiction. And the fact that some of that science fiction was not of the highest quality is irrelevant. Ten-year-olds do not read the scientific literature.
I do not know if time travel into the past is possible. The causality problems it would imply make me very skeptical. But there are those who are thinking about it. What are called closed time-like lines-routes in space-time permitting unrestricted time travel-appear in some solutions to the general relativistic field equations. A recent claim, perhaps mistaken, is that closed timelike lines appear in the vicinity of a large, rapidly rotating cylinder. I wonder to what extent general-relativists working on such problems have been influenced by science fiction. Likewise, science-fiction encounters with alternative cultural features may play an important role in actualizing fundamental social change.
In all the history of the world there has never before been a time in which so many significant changes have occurred. Accommodation to change, the thoughtful pursuit of alternative futures are keys to the survival of civilization and perhaps of the human species. Ours is the first generation that has grown up with science-fiction ideas. I know many young people who will of course be interested but in no way astounded if we receive a message from an extraterrestrial civilization. They have already accommodated to that future. I think it is no exaggeration to say that if we survive, science fiction will have made a vital contribution to the continuation and evolution of our civilization.
PART III. OUR NEIGHBORHOOD IN SPACE
CHAPTER 10

Like a shower of stars the worlds whirl, borne along by the winds of heaven, and are carried down through immensity; suns, earths, satellites, comets, shooting stars, humanities, cradles, graves, atoms of the infinite, seconds of eternity, perpetually transform beings and things.
CAMILLE FLAMMARION,
(New York, D. Appleton & Company, 1894)
IMAGINE THE EARTH scrutinized by some very careful and extremely patient extraterrestrial observer: 4.6 billion years ago the planet is observed to complete its condensation out of interstellar gas and dust, the final planetesimals falling in to make the Earth produce enormous impact craters; the planet heats internally from the