All science is full of statements where you put your best face on your ignorance, where you say: ... we know awfully little about this, but more or less irrespective of the stuff we don't know about, we can make certain useful deductions.

The kind of lecture which I have been so kindly invited to give, and which now appears in book form, gives one a rare opportunity to allow the bees in one's bonnet to buzz even more noisily than usual.

An observer situated in a nebula and moving with the nebula will observe the same properties of the universe as any other similarly situated observer at any time.

The scientist … must always be prepared to deal with the unknown. It is an essential part of science that you should be able to describe matters in a way where you can say something without knowing everything.

[Science doesn't deal with facts; indeed] fact is an emotion-loaded word for which there is little place in scientific debate.

[Newton's calculations] entered the marrow of what we know without knowing how we know it.

A theory is scientific only if it can be disproved. But the moment you try to cover absolutely everything the chances are that you cover nothing.