From: richalivingston@gmail.com   
      
   On Saturday, September 3, 2022 at 7:15:37 PM UTC-5, ju...@diegidio.name wrote:   
   > On Saturday, 3 September 2022 at 15:50:03 UTC+2, Thomas Koenig wrote:   
   > > Julio Di Egidio  schrieb:   
   > > >   
   > > > And *reversibility* itself is already present in classical physics,   
   > > > namely since the Hamiltonian/Lagrangian approaches, where the dynamics   
   > > > of a system are described in terms of the evolution of a *system state*   
   > > > in a state space: *that* evolution has to be reversible, indeed lack of   
   > > > reversibility would simply not be a state space: IOW, given a "law of   
   > > > motion", there must be one and only one next state, and one and only one   
   > > > previous state, or the whole state-space based approach becomes simply   
   > > > meaningless.   
   > >   
   > > And yet, the Second Law of Thermodynamics holds.   
   > I did say except for the "measurement problem" and thermodynamics.   
   > Thermodynamics is indeed another story: the laws of thermodynamics   
   > are not exact laws, in fact thermodynamics is not deterministic, while,   
   > to the point, the laws of quantum mechanics *are* exact and   
   > deterministic: the fact that we measure probabilities has again to do   
   > with "the problem of measurement", i.e. how we go from the quantum   
   > state to a classical outcome, but, to reiterate, the evolution of the wave   
   > function, as expressed by the Schroedinger equation, is per se indeed   
   > deterministic.   
   >   
   > Julio   
   Julio,   
      
   Thank you for your detailed response.  I have to debate some points where   
   I think you are being inconsistent.  You say that QM wave function is   
   reversible because it evolves by a unitary operator.  This is true, but the   
   wave function calculated is not real.  I admit that it is simulating something   
   that is real, as proven by interference patterns, but that is not the same   
   thing.   
      
   The difference is "collapse".  Take the two slit experiment with a single   
   photon.  When a photon is detected on the screen at one of several   
   predicted interference spots, the physical situation is now a photon   
   (or its packet of energy-momentum) in one specific atom/molecule.   
   If you try to start from this state and compute backwards you do NOT   
   get that the photon had to come from the single point light source  on   
   the other side of the screen.  The backward computed wave function   
   includes many possible sources, including the one that photon   
   actually came from.   
      
   QM is not deterministic in that at any given moment   
   there are several possible mutually exclusive future outcomes.  It seems   
   to me that this means that information is not conserved in the actual   
   physics, despite what the math appears to say.  The disconnect is that   
   the math only predicts probabilities of multiple outcomes, while the   
   actual physics, in many but not all cases, has only one specific future.   
      
   In other words, knowing the exact present state does not tell you which   
   of many future states the system may evolve to, nor which of several   
   states it evolved from.  It seems to me that this precludes any   
   conservation of information.   
      
   Is there an error in my reasoning here?   
      
   Rich L.   
      
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