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.

We're forever teetering on the brink of the unknowable, and trying to understand what can't be understood.

People think of education as something that they can finish.

He had read much, if one considers his long life; but his contemplation was much more than his reading. He was wont to say that if he had read as much as other men he should have known no more than other men.

The laws of history are as absolute as the laws of physics, and if the probabilities of error are greater, it is only because history does not deal with as many humans as physics does atoms, so that individual variations count for more.

There never can be a man so lost as one who is lost in the vast and intricate corridors of his own lonely mind, where none may reach and none may save.

There is not a discovery in science, however revolutionary, however sparkling with insight, that does not arise out of what went before.