On John von Neumann. Why is there no definitive biography of this man?
I have known a great many intelligent people in my life. I knew Planck, von Laue and Heisenberg. Paul Dirac was my brother in law; Leo Szilard and Edward Teller have been among my closest friends; and Albert Einstein was a good friend, too. But none of them had a mind as quick and acute as Jansci [John] von Neumann. I have often remarked this in the presence of those men and no one ever disputed me.
... But Einstein's understanding was deeper even than von Neumann's. His mind was both more penetrating and more original than von Neumann's. And that is a very remarkable statement. Einstein took an extraordinary pleasure in invention. Two of his greatest inventions are the Special and General Theories of Relativity; and for all of Jansci's brilliance, he never produced anything as original.
On Einstein and quantum mechanics.
Einstein plainly saw that the statistical view was a quite novel way of interpreting physical events; he realized, perhaps even before many of its backers, that accepting the statistical view implied a need to reexamine a great many things, including human volition and desire. Einstein did not want to reexamine all that. So he made light of the statistical view. "How about the sun," he would say, "Is that also a probability amplitude?"
[Contrast with Hawking's observation that many worlds is "trivially true" once we assume that quantum mechanics applies to each and every component of the universe.]
On quantum mechanics and the limits of human intelligence.
Until 1925, most great physicists, including Einstein and Planck, had doubted that man could truly grasp the deepest implications of quantum theory. They really felt that man might be too stupid to properly describe quantum phenomena. ...the men at the weekly colloquium in Berlin wondered "Is the human mind gifted enough to extend physics into the microscopic domain ...?" Many of those great men doubted that it could.
But it is sad to lose touch with whole branches of physics, to see scientists cut off from each other. Dispersion theorists do not know axiomatic field theory; cosmologists do not know nuclear physics. Quantum mechanics is hard to explain to a chemist ... and yet the best theoretical chemists really ought to know quantum mechanics.
Specialization of science also robbed us of much of our passion. We wanted to grasp science whole, but by then the whole was something far too vast and complex to master. Only rarely could we ask the deep questions that had first drawn us to science.