We are taught that the probability of detecting a particle is <ψ*|ψ>. I understand it is a postulate of QM and required by the maths, but have often wondered as to why it seems to represent a joint probability. For a while it seemed to make some sense to me in the time symmetric QM interpretation, namely two halves making a whole so to speak. Today I read this on the Relativity Forum which suggests time has no particular significance and arrives a the Born probability another way. http://uk.arxiv.org/pdf/gr-qc/0306059v1 My question is, can it be said that this formulation represents a joint probability and if so of what.