I have read that "Information is conserved", or at least that it should be. I read this in some discussion about whether or not black holes destroy information. (ref: Leonard Susskind, Stephen Hawking, The Black Hole War, etc..) It is believed systems in distinct states evolve into distinct states, so that from a current state we can deduce uniquely the previous state. OK. But how does this fit with the wavefunction collapse in quantum mechanics? When the wave function collapse, information is lost, isn't it?. If a particle's spin is measured and collapse along z+, we can not from z+ deduce the previous orientation. So, does the wavefunction collapse violate the conservation of information?