Are probabilities always and necessarily positive-definite?
I'm asking this because there is a thread, started by Dirac
and Feynman, saying the only difference between the classical
and quantum cases is that in the former we assume the probabilities
Thus, speaking of MWI, we could also ask: what is the joint
probability of finding ourselves in a universe alpha and of
finding ourselves in a universe beta, which is 180 degrees
out of phase with the first one (whatever that could mean)?