From: mlfasf@comcast.net   
      
   On 3/20/22 4:44 AM, I (Mike Fontenot) wrote:   
   > On 3/19/22 12:27 PM, Tom Roberts wrote:   
   >>   
   >> Observation implies a physical quantity is being observed. Simultaneity   
   >> at different spatial points is not any kind of physical quantity, it is   
   >> a CONVENTION based on the time coordinate of a particular inertial   
   >> frame   
   >>   
   >   
   > Tom, what is your "take" on the use of an array of clocks, stationary in   
   > some inertial frame, that have been synchronized using only the   
   > assumption that the speed of light is equal to the universal constant   
   > "c" in that frame.  Each of those clocks is attended by a human "helper   
   > friend" (HF), who can observe his immediate local surroundings.  Another   
   > particular observer (whom I'll refer to as "he"), also stationary in   
   > that inertial frame, wants to know (when his watch shows time tau) the   
   > current reading on a particular distant clock which is NOT stationary   
   > with respect to that array of clocks.  It seems reasonable that he is   
   > entitled to say that the current reading on that distant clock is what   
   > the HF, who happens to be colocated with that distant clock at the   
   > instant when the HF's clock reads tau, directly observes it to be.   
   > Doesn't that convey a sense of "meaningfulness", to the observers who   
   > are stationary in that frame?  I think Einstein thought it does.   
      
   Tom hasn't responded yet.  Maybe he will shortly.  But while waiting,   
   I'd like to add a bit to my above argument.   
      
   I think a sizeable number of physicists DO believe that simultaneity at   
   a distance is a meaningless concept, and I've even noticed a trend of   
   trying to de-emphasize talking about simultaneity-at-a-distance in   
   introductory special relativity courses.  But I think that is a big   
   mistake.  It certainly wasn't Einstein's view, at least for inertial   
   observers.  (I've seen a quote from Einstein somewhere where he said he   
   hardly recognizes his theory when he reads some modern descriptions of   
   it.)   
      
   My above question of Tom Roberts was prompted mostly by his use of the   
   word "Convention" in describing simultaneity at a distance for an   
   inertial observer.  To me, the term "Convention" implies that there is   
   more than one possible answer to the question "How old is that distant   
   person (she), right now", when asked and answered by a particular   
   inertial observer.  "Convention" implies that one can pick from among   
   multiple alternatives, all equally good.   
      
   But I don't believe that is true, given my above description of how an   
   array of synchronized clocks (all permanently stationary with respect to   
   the given inertial observer) can be set up, creating a common "NOW"   
   instant for him and for all of the HF's ("helper friends") co-located   
   and co-stationary with the clocks.  At any given instant "tau" in the   
   life of the given inertial observer, it's clear that there is just a   
   single answer to the question "How old is that particular distant person   
   (she) right now (at the given time "tau" in the life of the inertial   
   observer): it is what the particular HF (he) who happens to be   
   momentarily co-located with the distant person (she), says it is, at the   
   instant when he is age "tau".  The only way there could be any other   
   allowable answer is if the synchronization of the clocks isn't valid,   
   and that is impossible if the velocity of light in that inertial   
   reference frame is equal to the universal constant "c".   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)