Ordinarily it would take me about fifteen minutes to get a hallucination going," wrote Feynman, "but on a few occasions, when I smoked some marijuana beforehand, it came very quickly.

I believe that a scientist looking at nonscientific problems is just as dumb as the next guy.

If all of mathematics disappeared, physics would be set back by exactly one week.

There is nothing in biology yet found that indicates the inevitability of death. This suggests to me that it is not at all inevitable and that it is only a matter of time before biologists discover what it is that is causing us the trouble.

I don't feel frightened by not knowing things, by being lost in the mysterious universe without any purpose - which is the way it really is, as far as I can tell. Possibly. It doesn't frighten me.

A scientist is never certain. ... We absolutely must leave room for doubt or there is no progress and there is no learning.

Philosophy of science is about as useful to scientists as ornithology is to birds.