From: fortunati.luigi@gmail.com   
      
   Tom Roberts alle ore 05:20:38 del 06/08/2017 ha scritto:   
   >> The "surprising causal effect" (real not apparent) [...]   
   >   
   > This is NOT "real" in the sense that it is part of a valid model   
   > of the world.  Causality is not involved, as at the instant the   
   > traveling twin measures (or computes) the home twin's age they are   
   > separated by a spacelike interval.   
   >   
   > Consider how the traveling twin would measure the home twin's age:   
   > there would have to be an assistant at rest in the traveling twin's   
   > inertial frame pre- positioned to be co-located with the home twin   
   > at the instant of the measurement, who observes the home twin's   
   > clock; this assistant would then send the measurement data to the   
   > traveling twin. Do this immediately before and immediately after   
   > the traveling twin turns around, and the assistants are located and   
   > moving very differently -- it's no surprise that their measurements   
   > are very different, as the assistants' clocks are synchronized very   
   > differently with the traveling twin's clock. It is, of course, that   
   > change in clock synchronization that is the underlying effect.   
   >   
   > The home twin, of course, is completely unaffected and notices   
   > nothing (except the traveling twin's assistants, who pass by in   
   > opposite directions many years apart).   
   >   
   > The whole notion of "what does the traveling twin measure" is highly   
   > artificial, requiring outrageously impractical assistants; Fontenot's   
   > "CADO frame" is merely a way to compute the highly artificial value   
   > that such assistants would measure.  As "all physics is local"   
   > [Einstein and others], this is not part of any valid model of the   
   > world; it is a measurement over a spacelike interval. The aspect   
   > of this that proves its artificiality is the fact that it is   
   > coordinate dependent -- coordinates are arbitrary human constructs   
   > which Nature does not use, and no natural phenomenon can possibly   
   > depend on such an arbitrary human choice....   
   >   
   > What is real (i.e. unambiguous) is the comparison of the twins'   
   > ages when they reunite. That is both independent of coordinates and   
   > very non-local.   
   >   
   > Tom Roberts   
      
     The TS distance between Earth T and Space Station S is perfectly=20   
   measurable without the need for assistants and more.   
   =A0=A0   
   =A0=A0From the ground just send electromagnetic signals and wait for the=20   
   return.   
   =A0=A0   
   =A0=A0The twin (or who for him) has already done so and knows that the=20   
   "measurement" of the TS distance is almost 40 years-light.   
   =A0=A0   
   =A0=A0Then the twin starts and arrives at Space Station S where he does=20   
   another measure with his watch marking the 5-year time.   
   =A0=A0   
   =A0=A0This other measure guarantees that the journey lasted 5 years and=20   
   therefore the actual real distance traveled was almost 5 years-light=20   
   (it could not be otherwise because in 5 years you can not travel 40=20   
   light years!).   
   =A0=A0   
   =A0=A0The two "measurements" (before and after acceleration) unambiguously=   
   =20   
   document that the Earth-StazioneSpaziale distance was close to 40=20   
   years-light before acceleration and reduced to nearly five years-light=20   
   after acceleration.   
   =A0=A0   
   =A0=A0No appearance, no "model" and no need for assistants, only "real=20   
   measures" and nothing else.   
   =A0=A0   
   =A0=A0Why did the TS distance remain unchanged for the earth twin (40=20   
   year-light) and decreased (40 to 5 years-light) for the traveling twin?   
   =A0=A0   
   =A0=A0What did the other one do that did not do?   
      
   Luigi Fortunati   
      
   --=20   
   Luigi Fortunati   
      
   Credere e' piu' facile che pensare   
   Believing is easier than thinking   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)