Scientific knowledge is a body of statements of varying degrees of certainty -- some most unsure, some nearly sure, none absolutely certain.

Fall in love with some activity, and do it! Nobody ever figures out what life is all about, and it doesn't matter.

Our freedom to doubt was born out of a struggle against authority in the early days of science. It was a very deep and strong struggle: permit us to question - to doubt - to not be sure. I think that it is important that we do not forget this struggle and thus perhaps lose what we have gained.

The principle of science, the definition, almost, is the following: The test of all knowledge is experiment. Experiment is the sole judge of scientific "truth." But what is the source of knowledge? Where do the laws that are to be tested come from? Experiment, itself, helps to produce these laws, in the sense that it gives us hints. But also needed is imagination to create from these hints the great generalizations--to guess at the wonderful, simple, but very strange patterns beneath them all, and then to experiment to check again whether we have made the right guess.

There is enough energy in a single cubic meter of space to boil all the oceans in the world.

As usual, nature's imagination far surpasses our own, as we have seen from the other theories which are subtle and deep.

Once we were driving in the midwest and we pulled into a McDonald's. Someone came up to me and asked me why I have Feynman diagrams all over my van. I replied, "Because I am Feynman!" The young man went, "Ahhhhh!"