Mathematical physics represents the purest image that the view of nature may generate in the human mind; this image presents all the character of the product of art; it begets some unity, it is true and has the quality of sublimity; this image is to physical nature what music is to the thousand noises of which the air is full...
But this same process of the old teaching the young can also cause errors and false conclusions to accumulate with the passage of time. One should therefore study ancient writings, not so much in the hope of finding lost wisdom as in the hope of locating the origin of errors that have been, and still are, accepted truths.
At any one time there is a natural tendency among physicists to believe that we already know the essential ingredients of a comprehensive theory. But each time a new frontier of observation is broached we inevitably discover new phenomena which force us to modify substantially our previous conceptions. I believe this process to be unending, that the delights and challenges of unexpected discovery will continue always.