"What one man can imagine, another can make real," Jules Verne once remarked.
Science fiction has certainly changed men's imaginations. How much it has changed the world as a result is a question that might well be tackled by social scientists. But Donald A. Wollheim, a prominent editor in the field, has gone so far as to say we are "living in a science fiction story." 
And while we must be wary of exaggeration, it is significant that in a world that is so much the product of scientific invention and discovery, Isaac Asimov has observed that at least half the really creative scientists have backgrounds that include reading S.F.
"It could be argued that a scientist's interest in science fiction is merely a reflection of his professional preoccupation," he noted. "I do not believe this is often the case, however, since one rarely begins reading science fiction in adulthood. The habit starts in adolescence, and interest in science is stimulated by the reading, rather than the reverse."
Critics and scholars often argue the sterile issue of whether science fiction "prophesizes" the future. Hugo Gernsback, founder in 1926 of the first science fiction magazine, AMAZING STORIES, even argued that this was the genre's true purpose—"extravagant fiction today, cold fact tomorrow" was his magazine's slogan.
Sober critics like James Blish and Damon Knight have pointed out that no story has ever predicted the details of any development with great accuracy, however—and there have been all kinds of "forecasts" in science fiction that never came true in any sense.
DREAMS COUNT But this is beside the point. Science fiction projects possibilities of things that might be done, given certain scientific advances. It creates dreams. And it is the dreams that count.
When Verne, in 1863, wrote FROM THE EARTH TO THE MOON, he was a poor prophet in the technical sense. His space gun could never have worked. The passengers in his shell would have been reduced to jelly—even if the shell hadn't burned up on its way through the atmosphere.
Yet Verne stimulated men's imaginations because of his realistic attitude towards the future of science. Unlike Cyrano de Bergerac or even Edgar Allan Poe, whose accounts of lunar journeys were really satires or burlesques on obvious "impossibilities," he never doubted that men could go to the Moon—and would.
"I remember well how the thought struck me of making calculations for rockets," wrote space pioneer Konstantin Eduardovich Tsiolkovsky. "I think the first seeds were sown by the imaginative tales of Jules Verne, which assailed my mind. I was assailed with a sense of longing, and this set me to thinking in a specific way." 
Tsiolkovsky was 17 at the time, in 1874. Before the turn of the century, this provincial schoolteacher in Kaluga, Russia, had worked out the theory of liquid fuel rockets that is the basis of space flight today. His work was duplicated in 1919 by Robert H. Goddard and in 1923 by
Hermann Oberth, both of them early readers of Verne and other science fiction writers.
In a remarkable Vernian novel called BEYOND THE EARTH, begun in 1896 and completed in 1916, Tsiolkovsky himself anticipated space walks, lunar rovers, life styles of weightless environments, recycling of air and wastes, and many other aspects of the space program—and he never doubted any of it would come true, either.
Nor did Fritz Lang, the German motion picture director who in 1929 hired Oberth as technical advisor for his FRAU IM MONO, and tried to assist Oberth in the work of the Verein fuer Raumschiffahrt (Society for Space Travel). Some scenes in the film, of a huge two- stage rocket being moved on tracks from its assembly building to the launch site, are uncannily like those at Cape Kennedy. Lang even invented the countdown.
It was only the science fiction readers who took such things seriously in those days. Oberth's work stimulated popular writers like Otto Willi Gail (whose THE SHOT INTO INFINITY used a three-stage rocket very much like the Saturn-Apollo system in 1925) and Hans Dominik. Lang was familiar with both, and with Kurd Lasswitz, whose ON TWO PLANETS (1897) was as popular in Germany as Verne's works were elsewhere and which had much to do with planting the seeds of Oberth's own dreams.
SPACE TRAVEL Publication of Tsiolkovsky's works touched off a similar interest in space travel in the early years of Soviet Russia. Aleksandr Belyaev and others wrote space travel stories—Tsiolkovsky himself wrote the introduction to one of them (another was titled THE STAR KETS, using his initials as an acronym). But the rise of Stalin, like that of Hitler in Germany, killed off early interest in space research—though not in rockets.
America actually lagged behind Russia and Germany in the 1920's as far as space-consciousness was concerned. Goddard's work was even sneered at in the NEW YORK TIMES. Possibly this was a reflection of the fact that science fiction here was still dominated by the Edgar Rice Burroughs school of "scientific romance," which didn't take scientific possibilities very seriously.
In fact, when Gernsback wanted to redress the balance, he had to do so by publishing translations of German science fiction novels by Gail and others, and articles like Hermann Noordung's "Problems of Space Flying." These provided the background for the more realistic space fiction of Robert A. Heinlein and others that was to develop in the 1940's. It was George Pal's DESTINATION MOON (1950), on which Heinlein served as technical advisor and scriptwriter, that finally began to make the American public at large space-conscious.
Space travel is the most obvious science fiction dream come true, but not the only one. Igor Sikorsky, for example, was stimulated by Verne's ROBUR THE CONQUEROR to build the world's first practical helicopters. Simon Lake, who built the first submarine to be navigated in the open sea, also gave credit to Verne. Leo Szilard's interest in splitting the atom came from H.G. Wells' THE WORLD SET FREE.
GENERAL INFLUENCE In most cases, of course, the influence of science fiction is more general—a stimulus to invention and discovery in the broad sense. And if the stimulus of imagination provided by science fiction has helped shape the future, it has also helped in cultural adaptation to a world in change. As Alvin Toffler points out:
"Science fiction has an immense value as a mind-stretching force for the creation of the habit of anticipation. Our children should be studying Arthur C. Clarke, William Tenn, Robert Heinlein, Ray Bradbury and Robert Sheckley, not because these writers can tell them about rocket ships and time machines but, more important, because they can lead young minds through an imaginative exploration of the jungle of political, social, psychological and ethical issues that will confront these children as adults."
While science fiction has traditionally been apolitical in the narrow sense, it has been concerned with the impact of change on society and human institutions. Even in the days of the "pulps," it sometimes fulfilled this role—the original version of Buck Rogers, a story called "Armageddon 2419 A.D.," for example, dealt with the impact of advanced technology on guerrila warfare and was serious (if not literate) speculation.
MIXED BLESSINGS Many of science fiction's dreams have proved mixed blessings—one hardly need mention that atomic energy brought with it the atomic bomb (but S.F. anticipated that too, Wells as far back as 1913), or that technology by itself hasn't cured all our social ills (but then, few science fiction writers thought it would).
And not all dreams have turned out to be worth having in reality. The utopian dreamers, from Plato and More to Bellamy and Wells, had much to do with the rise of collectivism—whether in the form of Communism or the welfare state or the military-industrial complex. Utopia turned out to be a bright cloud with anything but a silver lining.
But perhaps the only cure for bad dreams is better ones. Man seems to evolve only by trying to turn his dreams into reality—a point made much of recently in MAN OF LA MANCHA and elsewhere. Science fiction is almost always humanistic and anti-authoritarian (even in the Soviet Union, where the genre in its postStalinist renaissance was a far cry from the leaden preachments of Socialist Realism), and is today one of the few places where the dignity of man is taken seriously.
Certainly S. F. can popularize social ideas as such—Heinlein's THE MOON IS A HARSH MISTRESS did this so well for libertarianism that a lot of readers didn't even notice what the novel did with artificial intelligence and the biological and social ecology of a new environment.
But it will only be through its imaginative appeal that libertarian science fiction will have any lasting impact. Preachments or lectures disguised as stories preach only to the converted, and science fiction that does not create the same "sense of longing" Tsiolkovsky felt in another sphere is unlikely to have any influence.
Or to put it another way, in the realm of futurism, science fiction provides, not the catechism, but the mythology.
John Pierce's Science Fiction column alternates monthly in REASON with Davis Keeler's Money column.
NOTES AND REFERENCES
 Wollheim, Donald A., THE UNIVERSE MAKERS (Harper & Row 1971), p. 1.
 Asimov, Isaac, IS ANYONE THERE? (Ace Books 1969), p. 301.
 Quoted in Nikolai A. Rynin's INTERPLANETARY FLIGHT AND COMMUNICATION, Vol. Ill, No. 7, "K. E. Tsiolkovskii: Life, Writings and Rockets," Leningrad, 1931 (translated by Israel Program for Scientific Translations on behalf of National Aeronautics and Space Administration, 1971).
 Toffler, Alvin, FUTURE SHOCK (Random House 1970), pp. 376-77.