“Asimov: Science fiction always bases its future visions on changes in the levels of science and technology. And the reason for that consistency is simply that—in reality—all other changes throughout history have been irrelevant and trivial. For example, what difference did it make to the people of the ancient world that Alexander the Great conquered the Persian Empire? Obviously, that event made some difference to a lot of individuals. But if you look at humanity in general, you'll see that life went on pretty much as it had before the conquest.
On the other hand, consider the changes that were made in people's daily lives by the development of agriculture or the mariner's compass… and by the invention of gunpowder or printing. Better yet, look at recent history and ask yourself, "What difference would it have made if Hitler had won World War II?" Of course, such a victory would have made a great difference to many people. It would have resulted in much horror, anguish, and pain. I myself would probably not have survived.
But Hitler would have died eventually, and the effects of his victory would gradually have washed out and become insignificant—in terms of real change—when compared to such advances as the actual working out of nuclear power, the advent of television, or the invention of the jet plane.”

Locus interview (2000)
Context: Why do so many people dislike science fiction? The answer goes like this: You have to think of science fiction in contrast to its nearest competitor, heroic fantasy. In heroic fantasy, by and large, things are pretty stable, and then some terrible evil comes along that's going to take over the world. People have to fight it. In the end they win, of course, so the earth is restored to what it was. The status quo comes back. Science fiction's quite different. With science fiction, the world's in some sort of a state, and something awful happens. It may not be evil, it may be good or neutral, just an accident. Whatever they do in the novel, at the end the world is changed forever. That's the difference between the two genres — and it's an almighty difference! And the truth is science fiction, because we all live in a world that's changed forever. It's never going to go back to what it was in the '60s or the '70s or the '30s, or whatever. It's changed.

Source: Shadow Kiss

The Paris Review interview (2010)
Context: Science Fiction is the fiction of ideas. Ideas excite me, and as soon as I get excited, the adrenaline gets going and the next thing I know I’m borrowing energy from the ideas themselves. Science fiction is any idea that occurs in the head and doesn’t exist yet, but soon will, and will change everything for everybody, and nothing will ever be the same again. As soon as you have an idea that changes some small part of the world you are writing science fiction. It is always the art of the possible, never the impossible.

A Conversation With Neal Stephenson http://www.sfsite.com/10b/ns67.htm

Technology and Justice (Notre Dame: 1986), p. 13

From Hawking's article A Brief History of Relativity http://www.time.com/time/magazine/article/0,9171,993018-6,00.html, in Time magazine (31 December 1999)

The Twilight Zone, "The Fugitive" (1962).
The Twilight Zone

Source: The Social Function of Science (1939), p. 246 : How such a method of teaching could become an integral part of general education is sketched by H. G. Wells' British Association address, "The Informative Content of Education," reprinted in World Brain (Mathuen, 1938).

p, 125
Physics and Philosophy (1958)