Until now in world's history, whenever we've had a dark age, its been temporary and local. And other parts of the world have been doing fine. And eventually, they help you get out of the dark age. We are now facing a possible dark age which is going to be world-wide and permanent! That's not fun. That's a different thing. But once we have established many worlds, we can do whatever we want as long as we do it one world at a time.

The greatest weapons in the conquest of knowledge are an understanding mind and the inexorable curiosity that drives it on.

Scientists derive satisfaction from figuring out the puzzle. It's about the quest, not the grail.

You must keep sending work out; you must never let a manuscript do nothing but eat its head off in a drawer. You send that work out again and again, while you're working on another one. If you have talent, you will receive some measure of success - but only if you persist.

It's humbling to think that all animals, including human beings, are parasites of the plant world.

Early in my school career, I turned out to be an incorrigible disciplinary problem. I could understand what the teacher was saying as fast as she could say it, I found time hanging heavy, so I would occasionally talk to my neighbor. That was my great crime, I talked in school.

No one can possibly have lived through the Great Depression without being scarred by it. No amount of experience since the depression can convince someone who has lived through it that the world is safe economically.