From: richalivingston@gmail.com   
      
   On Monday, September 5, 2022 at 12:03:11 AM UTC-5, ju...@diegidio.name wrote:   
   > On Sunday, 4 September 2022 at 19:54:28 UTC+2, richali...@gmail.com wrote:   
   > > On Saturday, September 3, 2022 at 7:15:37 PM UTC-5, ju...@diegidio.name   
   wrote:   
   >    
   > > but the wave function calculated is not real.   
   > That *depends* on your ontological stance: and your choice,   
   > which is the standard one, is the one that is *most* problematic.   
      
   This clarifies a difference of opinion between us.  I don't understand   
   why you say that is *most* problematic?  Can you elaborate?  I'm   
   curious.   
      
   > > The difference is "collapse". Take the two slit experiment with   
   > > a single photon. When a photon is detected on the screen [...]   
   > > If you try to start from this state and compute backwards [...]   
   > > The backward computed wave function includes many   
   > > possible sources   
   > When the photon is detected, that is a *measurement*, i.e.   
   > (standardly) you have *collapsed* the wave function, aka   
   > the state: and *that* operation is not reversible, not QM!!   
   > Conversely, do not collapse the wave function (consider   
   > the joint system observer/observed) and you stay quantum   
   > and have reversibility.   
      
   Are you saying that measurement is not part of QM?  Isn't it part of the   
   physics?  Aren't there some events that permanently refine the wave   
   function down to a subset of possible outcomes?   
      
   For what it is worth,  I distinguish the physics of QM from the math of   
   QM.  The math is a model of our understanding that may be imperfect. I   
   believe there is a reality where the actual physics happens.   
      
   > > QM is not deterministic in that at any given moment there   
   > > are several possible mutually exclusive future outcomes.   
   > Yes, it is: you are still conflating classical outcomes with   
   > the evolution of the wave function, aka the quantum state.   
   > > to me that this means that information is not conserved   
   > Sure, but it's *collapse* that destroys information.   
   > > Is there an error in my reasoning here?   
   > Only if you'll insist... :)   
      
   Oh!  I insist!   
      
   Seriously, isn't collapse a part of reality, or required by reality?   
   For example, back to the photon detected in the two slit experiment,   
   once the photon is detected there is now a new reality that differs from   
   the previous wave function.   
      
   It sounds like you may follow the many worlds concept.  If so I can see   
   your point being that the wave function describes all the possible   
   worlds and then no information would be lost.  However we live in just   
   one of those many worlds, and it seems to me that we need a QM theory   
   that includes the random selection (aka "measurement" or "collapse")   
   down to just one of the many worlds.  Therefore it seems to me that in   
   our world there is a loss of information every time there is a   
   measurement.   
      
   Or so I believe!   
      
   Thanks Julio for responding, this is clarifying these ideas for me.   
      
   Rich L.   
   >   
   > HTH,   
   >   
   > Julio   
      
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