I now want to tell three stories about advances in twentieth-century physics. A curious fact emerges in these tales: time and again physicists have been guided by their sense of beauty not only in developing new theories but even in judging the validity of physical theories once they are developed. Simplicity is part of what I mean by beauty, but it is a simplicity of ideas, not simplicity of a mechanical sort that can be measured by counting equations or symbols.

It is positively spooky how the physicist finds the mathematician has been there before him or her.

If history is any guide at all, it seems to me to suggest that there is a final theory. In this century we have seen a convergence of the arrows of explanation, like the convergence of meridians toward the North Pole.

Alas, Islam turned against science in the twelfth century. The most influential figure was the philosopher Abu Hamid al-Ghazzali, who argued in The Incoherence of the Philosophers against the very idea of laws of nature, on the ground that any such laws would put God's hands in chains. According to al-Ghazzali, a piece of cotton placed in a flame does not darken and smoulder because of the heat, but because God wants it to darken and smoulder. After al-Ghazzali, there was no more science worth mentioning in Islamic countries.

If there is no point in the universe that we discover by the methods of science, there is a point that we can give the universe by the way we live, by loving each other, by discovering things about nature, by creating works of art. And that — in a way, although we are not the stars in a cosmic drama, if the only drama we're starring in is one that we are making up as we go along, it is not entirely ignoble that faced with this unloving, impersonal universe we make a little island of warmth and love and science and art for ourselves. That's not an entirely despicable role for us to play.

A theorist today is hardly considered respectable if he or she has not introduced at least one new particle for which there is no experimental evidence.

It appears that anything you say about the way that theory and experiment may interact is likely to be correct, and anything you say about the way that theory and experiment must interact is likely to be wrong.