Clarke's First Law: When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong.

Clarke's Law of Evolution: It has yet to be proven that intelligence has any survival value.

Clarke's Second Law: The only way of discovering the limits of the possible is to venture a little way past them into the impossible.

Clarke's Third Law:. Any sufficiently advanced technology is indistinguishable from magic.

A hundred years ago, the electric telegraph made possible—indeed, inevitable—the United States of America. The communications satellite will make equally inevitable a United Nations of Earth; let us hope that the transition period will not be equally bloody.

Anything that is theoretically possible will be achieved in practice, no matter what the technical difficulties are, if it is desired greatly enough.

As our own species is in the process of proving, one cannot have superior science and inferior morals. The combination is unstable and self-destroying.

As three laws were good enough for Newton, I have modestly decided to stop there.
Commenting on Clarke's own three laws.

At the present rate of progress, it is almost impossible to imagine any technical feat that cannot be achieved, if it can be achieved at all, within the next five hundred years.

Deep beneath the surface of the Sun, enormous forces were gathering. At any moment, the energies of a million hydrogen bombs might burst forth in the awesome explosion…. Climbing at millions of miles per hour, an invisible fireball many times the size of Earth would leap from the Sun and head out across space.

Human judges can show mercy. But against the laws of nature, there is no appeal.

I sometimes wonder how we spent leisure time before satellite television and Internet came along…and then I realise that I have spent more than half of my life in the ‘dark ages’!

I'm sure we would not have had men on the Moon if it had not been for Wells and Verne and the people who write about this and made people think about it. I'm rather proud of the fact that I know several astronauts who became astronauts through reading my books.

If there are any gods whose chief concern is man, they cannot be very important gods.

If we have learned one thing from the history of invention and discovery, it is that, in the long run—and often in the short one—the most daring prophecies seem laughably conservative.

In physics, mathematics, and astronautics [elderly] means over thirty; in the other disciplines, senile decay is sometimes postponed to the forties. There are, of course, glorious exceptions; but as every researcher just out of college knows, scientists of over fifty are good for nothing but board meetings, and should at all costs be kept out of the laboratory!
Defining 'elderly scientist' as in Clarke's First Law.

Information is not knowledge, knowledge is not wisdom, and wisdom is not foresight. Each grows out of the other, and we need them all.

It is a good principle in science not to believe any “fact”—however well attested—until it fits into some accepted frame of reference. Occasionally, of course, an observation can shatter the frame and force the construction of a new one, but that is extremely rare. Galileos and Einsteins seldom appear more than once per century, which is just as well for the equanimity of mankind.

It may be that the old astrologers had the truth exactly reversed, when they believed that the stars controlled the destinies of men. The time may come when men control the destinies of stars.

It will be possible in a few more years to build radio controlled rockets which can be steered into such orbits beyond the limits of the atmosphere and left to broadcast scientific information back to the Earth. A little later, manned rockets will be able to make similar flights with sufficient excess power to break the orbit and return to Earth. (1945) [Predicting communications satellites.]

I’m sure the universe is full of intelligent life. It’s just been too intelligent to come here.

Mars is the next frontier, what the Wild West was, what America was 500 years ago. It’s time to strike out anew. Mars is where the action is for the next thousand years. The characteristic of human nature, and perhaps our simian branch of the family, is curiosity and exploration. When we stop doing that, we won’t be humans anymore. I’ve seen far more in my lifetime than I ever dreamed. Many of our problems on Earth can only be solved by space technology. The next step is in space. It’s inevitable.

Mathematics is not only one of the most valuable inventions—or discoveries—of the human mind, but can have an aesthetic appeal equal to that of anything in art. Perhaps even more so, according to the poetess who proclaimed, “Euclid alone hath looked at beauty bare.”

Microprocessors are getting into everything. We won’t be able to pick up a single piece of equipment in the near future, except maybe a broom, that hasn’t got a microprocessor in it.

One of the biggest roles of science fiction is to prepare people to accept the future without pain and to encourage a flexibility of the mind. Politicians should read science fiction, not westerns and detective stories.

One orbit, with a radius of 42,000 kilometers, has a period of exactly 24 hours. A body in such an orbit, if its plane coincided with that of the Earth’s equator, would revolve with the Earth and would thus be stationary above the same spot on the planet. It would remain fixed in the sky of a whole hemisphere ... [to] provide coverage to half the globe, and for a world service three would be required, though more could be readily utilized. (1945) [Predidicting geosynchronous communication satellites]

Our lifetime may be the last that will be lived out in a technological society.

Perhaps a species that has accumulated ... tons of explosive per capita has already demonstrated its biological unfitness beyond any further question.

Politicians should read science fiction, not westerns and detective stories.

Science can destroy religion by ignoring it as well as by disproving its tenets. No one ever demonstrated, so far as I am aware, the nonexistence of Zeus or Thor—but they have few followers now.

Sometimes I think we’re alone in the universe, and sometimes I think we’re not. In either case, the idea is quite staggering.

The earth is simply too small and fragile a basket for the human race to keep all its eggs in.

The Earth would only have to move a few million kilometers sunward—or starward—for the delicate balance of climate to be destroyed. The Antarctic icecap would melt and flood all low-lying land; or the oceans would freeze and the whole world would be locked in eternal winter. Just a nudge in either direction would be enough.

The inspirational value of the space program is probably of far greater importance to education than any input of dollars... A whole generation is growing up which has been attracted to the hard disciplines of science and engineering by the romance of space.

The moon is the first milestone on the road to the stars.

The only way of finding the limits of the possible is by going beyond them into the impossible.

The realization that our small planet is only one of many worlds gives mankind the perspective it needs to realize sooner that our own world belongs to all of its creatures, that the Moon landing marks the end of our childhood as a race and the beginning of a newer and better civilization.

There is hopeful symbolism in the fact that flags do not wave in a vacuum.

Using material ferried up by rockets, it would be possible to construct a “space station” in ... orbit. The station could be provided with living quarters, laboratories and everything needed for the comfort of its crew, who would be relieved and provisioned by a regular rocket service. (1945)

Clarke's First Law - Corollary: When, however, the lay public rallies round an idea that is denounced by distinguished but elderly scientists and supports that idea with great fervor and emotion—the distinguished but elderly scientists are then, after all, probably right.