Before another century is done it will be hard for people to imagine a time when humanity was confined to one world, and it will seem to them incredible that there was ever anybody who doubted the value of space and wanted to turn his or her back on the Universe.

After years of finding mathematics easy, I finally reached integral calculus and came up against a barrier. I realized that this was as far as I could go, and to this day I have never successfully gone beyond it in any but the most superficial way.

The whole world might know you and acclaim you, but someone in the past, forever unreachable, forever unknowing, spoils it all.

If knowledge can create problems, it is not through ignorance that we can solve them.

Working ten hour days allows you to fall behind twice as fast as you could working five hour days.

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

The essential building block is...the true love that is impossible to define for those who have never experienced it and unnecessary to define for those who have.