During the Middle Ages there were all kinds of crazy ideas, such as that a piece of rhinoceros horn would increase potency. Then a method was discovered for separating the ideas - which was to try one to see if it worked, and if it didn't work, to eliminate it. This method became organized, of course, into science.

The electron is a theory we use; it is so useful in understanding the way nature works that we can almost call it real.

Words can be meaningless. If they are used in such a way that no sharp conclusions can be drawn.

To do any important work in physics a very good mathematical ability and aptitude are required. Some work in applications can be done without this, but it will not be very inspired. If you must satisfy your "personal curiosity concerning the mysteries of nature" what will happen if these mysteries turn out to be laws expressed in mathematical terms (as they do turn out to be)? You cannot understand the physical world in any deep or satisfying way without using mathematical reasoning with facility.

All theoretical chemistry is really physics; and all theoretical chemists know it.

I have the advantage of having found out how hard it is to get to really know something. How careful you have to be about checking your experiments. How easy it is to make mistakes and fool yourself. I know what it means to know something.

We are lucky to live in an age in which we are still making discoveries.