Richard Feynman on Albert Einstein

“We postulate: It shall be impossible, by any experiment whatsoever performed inside such a box, to detect a difference between an acceleration relative to the nebulae and gravity. That is, an accelerating box in some gravitational field is indistinguishable from a stationary box in some different gravitational field. How much like Einstein this sounds, how reminiscent of his postulate of special relativity! We know the principle of equivalence works for springs, (as we knew special relativity worked for electrodynamics), and we extend it by fiat to all experiments whatsoever. We are used to such procedures by now, but how originally brilliant it was in 1911—what a brilliant, marvelous man Einstein was!”

“Einstein, who thought that he had a unified theory just around the corner, but didn't know anything about nuclei and was unable of course to guess it.”

“Einstein was a giant. His head was in the clouds, but his feet were on the ground. Those of us who are not so tall have to choose!”