🚀 go-pugleaf

Feynman 26 "Is it unitary?"
p.258 from James Gleick's GENIUS: ( March 30, 1948 Poconos Meeting)
""Feynman explained his path integrals, an alien idea, and his positrons
moving backward in time, even more disturbing.  Teller caught the apparent
infringement of the exclusion principle and refused to accept Feynman's
inrigorous justification.  It struck Feynman that everyone had a favorite
principle or theorem and he was violating them all.  When Dirac asked, 'Is
it unitary?' Feynman did not even know what he meant. Dirac explained: the
matrix that carries on from the past to the future had to maintain an exact
bookkeeping of total probability.  But Feynman had no such matrix.  The
essence of his approach was a view of past and future together, with the
freedom to go forward and backward in in time at will. .... Feynman knew he
had failed.  At the time he was in anguish.  Later he  said simply: 'I had
too much stuff.  My machines came from too far away.'"
- indeed, from the future!

PS "A Half-Assedly Thought-Out Pictorial Semi-Vision Thing" p.p. 241-251 is
a superb piece of pop writing on quantum mechanics.