It shouldn’t be so surprising that *unitarity *survives completely while *causality *doesn’t. After all, the basic postulates of quantum mechanics, including *unitarity*, the probabilistic interpretation of the amplitudes, and the linearity of the operators representing observables, seem to be universally necessary to describe physics of any system that agrees with the basic insights of the quantum revolution.

On the other hand, *geometry *has been downgraded into an effective, approximate, emergent aspect of reality. The metric tensor is just one among many fields in our effective field theories including gravity.

— Black hole information puzzle

— Lubos Motl

2012.04.25 Wednesday ACHK