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

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.

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.

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.

If you walk along the street you will encounter a number of scientific problems. Of these, about 80 per cent are insoluble, while 19½ per cent are trivial. There is then perhaps half a per cent where skill, persistence, courage, creativity and originality can make a difference. It is always the task of the academic to swim in that half a per cent, asking the questions through which some progress can be made.

On the most usual assumption, the universe is homogeneous on the large scale, i.e. down to regions containing each an appreciable number of nebulae. The homogeneity assumption may then be put in the form: 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.

Our most successful theories in physics are those that explicitly leave room for the unknown, while confining this room sufficiently to make the theory empirically disprovable. It does not matter whether this room is created by allowing for arbitrary forces as Newtonian dynamics does, or by allowing for arbitrary equations of state for matter, as General Relativity does, or for arbitrary motions of charges and dipoles, as Maxwell's electrodynamics does. To exclude the unknown wholly as a “unified field theory” or a “world equation” purports to do is pointless and of no scientific significance.

Sir Hermann Bondi once wrote that so-called scientific progress does not consist so much in an advancement in science but rather in taking something that beforehand was not science and making it become a part of science itself.

Sometimes I am a little unkind to all my many friends in education … by saying that from the time it learns to talk every child makes a dreadful nuisance of itself by asking “Why?.” To stop this nuisance society has invented a marvellous system called education which, for the majority of people, brings to an end their desire to ask that question. The few failures of this system are known as scientists.

The fact that stares one in the face is that people of the greatest sincerity and of all levels of intelligence differ and have always differed in their religious beliefs. Since at most one faith can be true, it follows that human beings are extremely liable to believe firmly and honestly in something untrue in the field of revealed religion. One would have expected this obvious fact to lead to some humility, to some thought that however deep one's faith, one may conceivably be mistaken. Nothing is further from the believer, any believer, than this elementary humility. All in his power … must have his faith rammed down their throats. In many cases children are indeed indoctrinated with the disgraceful thought that they belong to the one group with superior knowledge who alone have a private wire to the office of the Almighty, all others being less fortunate than they themselves.

The great physicist von Laue said … a pendulum clock is not the Box you buy in a shop; a pendulum clock is the box you buy in a shop together with the Earth.

The hypothetical character of continual creation has been pointed out, but why is it more of a hypothesis to say that creation is taking place now than that it took place in the past? On the contrary, the hypothesis of continual creation is more fertile in that it answers more questions and yields more results, and results that are, at least in principle, observable. To push the entire question of creation into the past is to restrict science to a discussion of what happened after creation while forbidding it to examine creation itself. This is a counsel of despair to be taken only if everything else fails.

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.

The landscape has been so totally changed, the ways of thinking have been so deeply affected, that it is very hard to get hold of what it was like before… It is very hard to realize how total a change in outlook Isaac Newton has produced.

The public image of the scientist tends to be that of a magician, occasionally benevolent, though more often giving rise to disastrous inventions, or perhaps that of a man shutting himself into a laboratory and, in his lonely way, playing with retorts and test tubes, or perhaps leaning back in a comfortable armchair in a darkened room and thinking.

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.

The test of science is not whether you are reasonable—there would not be much of physics if that was the case—the test is whether it works. And the great point about Newton’s theory of gravitation was that it worked, that you could actually say something about the motion of the moon without knowing very much about the constitution of the Earth.

The true contrast between science and religion is that science unites the world and makes it possible for people of widely differing backgrounds to work together and to cooperate. Religion, on the other hand, by its very claim to know “The Truth” through “revelation,” is inherently divisive and a creator of separatism and hostility.

Time is that which is measured by a clock. This is a sound way of looking at things. A quantity like time, or any other physical measurement, does not exist in a completely abstract way. We find no sense in talking about something unless we specify how we measure it. It is the definition by the method of measuring a quantity that is the one sure way of avoiding talking nonsense about this kind of thing.

We find no sense in talking about something unless we specify how we measure it; a definition by the method of measuring a quantity is the one sure way of avoiding talking nonsense...

What I remember most clearly was that when I put down a suggestion that seemed to me cogent and reasonable, Einstein did not in the least contest this, but he only said, 'Oh, how ugly.' As soon as an equation seemed to him to be ugly, he really rather lost interest in it and could not understand why somebody else was willing to spend much time on it. He was quite convinced that beauty was a guiding principle in the search for important results in theoretical physics.

Sir Hermann Bondi once wrote that so-called scientific progress does not consist so much in an advancement in science but rather in taking something that beforehand was not science and making it become a part of science itself.