The open society, the unrestricted access to knowledge, the unplanned and uninhibited association of men for its furtherance-these are what may make a vast, complex, ever growing, ever changing, ever more specialized and expert technological world, nevertheless a world of human community.

Pragmatism is an intellectually safe but ultimately sterile philosophy.

You can certainly destroy enough of humanity so that only the greatest act of faith can persuade you that what's left will be human.

[About the great synthesis of atomic physics in the 1920s:] It was a heroic time. It was not the doing of any one man; it involved the collaboration of scores of scientists from many different lands. But from the first to last the deeply creative, subtle and critical spirit of Niels Bohr guided, restrained, deepened and finally transmuted the enterprise.

Things which stimulate my curiosity are pretty far removed from the practical and therefore from classification.

When all thermonuclear sources of energy are exhausted a sufficiently heavy star will collapse. Unless fission due to rotation, the radiation of mass, or the blowing off of mass by radiation, reduce the star's mass to the order of that of the sun, this contraction will continue indefinitely.

In a free world, if it is to remain free, we must maintain, with our lives if need be, but surely by our lives, the opportunity for a man to learn anything