There were timelines branching and branching, a mega-universe of universes, millions more every minute. Billions? Trillions? The universe split every time someone made a decision. Split, so that every decision ever made could go both ways. Every choice made by every man, woman, and child was reversed in the universe next door.

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

Never fire a laser at a mirror.

Spray a book with insect spray, drop it in a bag, add some mothballs and seal it. Put it in another bag and seal it. Another. The packages piled up on the floor, each a book sealed in four plastic envelopes.

Fear is the brother of hate.

One mark of a good officer, he remembered, was the ability to make quick decisions. If they happen to be right, so much the better

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.

Psi and/or magical powers, if real, are nearly useless.

Never tell a computer to forget it.

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

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 value of a thing is what that thing will bring. -Legal Maxim

Ethics change with technology.

Each nugget of information was fascinating. The world was full of new-found marvels and he wanted to share the excitement with everybody. They all did. They had a certain sense. It wasn't a sense of ennui or cynicism. It was . . . A sense of wonder.That was it. A sense of wonder, in the fine old original meaning of the word. They wondered at their world. Because when you did that, everything was wonder-full.

On a world built to ordered specification, there was no logical reason for such a mountain to exist. Yet every world should have at least one unclimbable mountain.

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!