From: jos.bergervoet@xs4all.nl   
      
   On 1/27/2017 11:35 AM, Nicolaas Vroom wrote:   
   > On Sunday, 8 January 2017 09:38:43 UTC+1, Rich L.  wrote:   
   ...   
   >>   .. that the wave function is something real and represents the   
   >> particle itself, which clearly doesn't work.   
   >   
   > I hope that more readers agree with us.   
      
   You then should tell us *why* it cannot work. Just saying   
   "which clearly doesn't work" is not convincing. Why can't   
   the QM state vector be something real? Why can't it be the   
   complete description of reality?!   
      
   >>  ...  My point is that the wave function actually tells   
   >> you nothing about how the particle gets there.   
   >   
   > Again I agree with you   
      
   How can you be sure particles exist? If we accept that the   
   QM state vector (generalized name for "wave function" in   
   cases of ageneral superposition of multi-particle states)   
   is all of reality, then there is no need to include any   
   other concept. You first need to prove to us that it is   
   necessary.   
      
     ...   
   >>> The first thing you can do is to study the mathematics how water   
   >>> waves propagate through one or two holes.   
   >>   
   >> That can be misleading because the water waves ARE real and show   
   >> locality.   
   >   
   > There is nothing misleading in studying experiments involving water waves.   
      
   Exactly! Just like there is nothing wrong in studying   
   electron fields and photon fields. Your problem (and   
   Rich L's) still is to first convince others that this   
   would "clearly" not work to describe reality. Until   
   then, I would say the case is solved by QM. We know what   
   reality is: it is the state described by quantum field   
   theory (QFT).   
      
   >> QM is inherently non-local, and that is one (of several)   
   >> reasons why we consider the wave function to be a purely mathematical   
   >> entity, and definitely not the particle itself.   
   >   
   > All physical reactions IMO are local.   
      
   "Local" has a meaning in QFT and our theories *are* local   
   in that sense! If Rich (or you) use another meaning it   
   just becomes a game of words.   
      
   >>   ... Study the two slit   
   >> experiment, Stern-Gerlach experiments, photon entanglement experiments   
   >> (e.g. Aspects experiments) for the original experimental basis for the   
   >> thought experiments.   
   >   
   > Non of these experiments can be performed as a thought experiment.   
      
   Yes they can. If you use (e.g.) QFT as your theory, you   
   can do Aspect's experiment as a thought experiment. It   
   would require describing the photons by QFT, together with   
   the measurement setup, and even aspects body and his brain   
   as well. Very complicated of course, but in principle you   
   could do it.   
      
   The system (including Aspect) would end up in a superposition   
   of the different result (and Aspect himself in a superposition   
   of different states of mind, i.e. having observed different   
   results), all with the amplitude ratios that QM gives us for   
   these interactions. In practice it's a lot of work to compute   
   all of it, but doesn't that make it "par excellence" a good   
   case of a thought experiment? (Of course this closely matches   
   the already well-known "Wigners friend" thought experiment. We   
   are too late to invent something new here..)   
      
     ...   
   >>> Along that same line does it make sense to use a concept like   
   >>> the collapse of a wave function?   
   >>   
   >> No, except as a mathematical concept, not a physical one.   
   >   
   > When the 'collapse of the wave function' does not make sense physical,   
   > than the concept also not make sense mathematically.   
      
   Right! The mathematical description should preferably only   
   describe things that are in principle falsifiable, so they   
   should at least have some implications for the physical world.   
   Which could be equated to calling them "physical".   
      
     ...   
   > I get the impression that for some people the action of performing   
   > a measurement involves the 'collapse of the wave function'.   
   > IMO if this is always the case then the concept does not make   
   > sense.   
      
   It doesn't and it never did, because no-one ever answered:   
      "When is an interaction *not* a measurement?"   
   Systems are interacting all the time in our universe and   
   in some cases we call one of them "device under test" and   
   another one "measurement setup". That is purely subjective,   
   so giving any physical meaning to it is pseudo-science.   
      
   And if you try to be fair and say that everything is a   
   measurement, then the wave function of the whole universe   
   collapses at any point in time and it never acts as a wave   
   so you have no QM left..   
      
   Actually it is a disgrace for physics that there is hardly   
   ever a clear statement of the unacceptability of these old   
   QM concepts! (But at least people like Steven Weinberg do   
   occasionally speak out against them   
      
   ).   
      
   --   
   Jos   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)