It is no longer possible to know everything there is to know

Physicists are ontological detectives. We think of scientists as wholly rational, open to all possible arguments. But to begin with a conviction and then to use one's intellectual prowess to establish support for that conviction is a methodology that really has worked for scientists, including Deutsch. One could argue that he dreamed up quantum computing because he was devoted to the idea that science can explain the world. Deutsch would disagree. In "The Fabric of Reality," Deutsch writes, "I remember being told, when I was a small child, that in ancient times it was still possible to know everything that was known. I was also told that nowadays so much is known that no one could conceivably learn more than a tiny fraction of it, even in a long lifetime. The latter proposition surprised and disappointed me. In fact, I refused to believe it."

--Rivka Galchen
"Dream Machine," a profile of physicist David Deutsch
in The New Yorker, May 2, 2011