There are theoretical physicists who imagine, deduce, and guess at new laws, but do not experiment; and then there are experimental physicists who experiment, imagine, deduce, and guess.

A great deal more is known than has been proved.

We find that the statements of science are not of what is true and what is not true, but statements of what is known with different degrees of certainty: "It is very much more likely that so and so is true than that it is not true".

From a long view of the history of mankind, seen from, say, ten thousand years from now, there can be little doubt that the most significant event of the 19th century will be judged as Maxwell's discovery of the laws of electrodynamics. The American Civil War will pale into provincial insignificance in comparison with this important scientific event of the same decade.

Some people think Wheeler's gotten crazy in his later years, but he's always been crazy.

I have a limited intelligence and I've used it in a particular direction.

We absolutely must leave room for doubt or there is no progress and no learning. There is no learning without having to pose a question. And a question requires doubt. People search for certainty. But there is no certainty.