“Mother Nature doesn't care if you're having fun. ”

“In the world of words the imagination is one of the forces of nature.”

“There had been a popular joke on Freedom, started by a man named Calder. Looking down from space, he had said, the dominant life forms on Earth were obviously the cereals and other grasses. They occupied all the most desirable and fertile land; and they had tamed insects and animals to care for them. In particular, they had domesticated the bipeds to nurture and cultivate them and to save and plant their seed. Now, watching the farmers, Alex could easily imagine that they were worshiping and genuflecting before their masters.”

“The dinosaurs became extinct because they didn't have a space program. And if we become extinct because we don't have a space program, it'll serve us right!”

“It's very difficult for a black man to get out of South-Central Los Angeles, and get out civilized....The only men I know who have escaped, all began reading Robert Heinlein at age ten.”

“I myself have dreamed up a structure intermediate between Dyson spheres and planets. Build a ring 93 million miles in radius - one Earth orbit - around the sun. If we have the mass of Jupiter to work with, and if we make it a thousand miles wide, we get a thickness of about a thousand feet for the base.And it has advantages. The Ringworld will be much sturdier than a Dyson sphere. We can spin it on its axis for gravity. A rotation speed of 770 m/s will give us a gravity of one Earth normal. We wouldn't even need to roof it over. Place walls one thousand miles high at each edge, facing the sun. Very little air will leak over the edges.Lord knows the thing is roomy enough. With three million times the surface area of the Earth, it will be some time before anyone complains of the crowding.”

“The gods do not protect fools. Fools are protected by more capable fools.”