Otherwise your games with the “definition” of initial and final states and with the sign of *t *are completely immaterial. “Initial” and “final” states are, according to logic, qualitatively different things, and the usual convention for the sign of *t *is that *t_{initial} < t_{final}*. But I have never even used this convention.

Even if I had, it wouldn’t matter. One can easily rewrite all proofs to the opposite convention by replacing *t* with −*t*; all those things are physically vacuous. The non-vacuous claim is that the future and past don’t play symmetric roles in logic.

— Physics Stack Exchange

— Jan 25 ’12 at 9:49

— Lubos Motl

2013.09.26 Thursday ACHK