From: mlfasf@comcast.net   
      
   Inertial observers can legitimately use the famous time-dilation result   
   of special relativity to determine simultaneity at a distance. Observers   
   who are currently accelerating can't.   
      
   To be an inertial observer during some period of your life, do you have   
   to be a PERPETUALLY inertial observer? I.e., is it required that you   
   must NEVER have accelerated in the past, and that you can guarantee that   
   you will NEVER accelerate in the future?   
      
   Or, can you be an inertial observer if it has been long enough since you   
   stopped accelerating, and if you can guarantee that you will not   
   accelerate for some period of time into the future?   
      
   Or, can you be an inertial observer for some period of time, provided   
   that you don't accelerate during that period?   
      
   The question matters, because the answer specifies WHO is entitled to   
   use the famous time-dilation result, and WHEN can they use it, in order   
   to determine simultaneity at a distance.   
      
   Different answers to that question have produced several different   
   published procedures for answering the question, "How old is that   
   particular distant person, who is moving with respect to me, RIGHT NOW?".   
      
   Dolby and Gull, in their "Radar Simultaneity", say that an observer is   
   an inertial observer if he has not accelerated too recently, and will   
   not accelerate too far into the future (and they exactly specify how   
   much is too much). Dolby and Gull's method is clearly non-causal.   
      
   Minguzzi says that an observer is an inertial observer if he hasn't   
   accelerated too recently, but there is no requirement that he can't   
   accelerate at any time in the future.   
      
   The "Momentarily Co-Moving Inertial Frames Montage" (MCMIFM) says that   
   an observer is an inertial observer if he isn't CURRENTLY accelerating,   
   even if he has accelerated infinitesimally-recently in the past, or will   
   accelerate infinitesimally-soon in the future ... i.e., he can use the   
   time dilatation result throughout any period of time in which he is not   
   accelerating.   
      
   What say you?   
      
   [[Mod. note -- It would be useful if you were to provide references   
   for the statements you attribute to Dolby and Gull, and to Minguzzi.   
   Expecting readers to guess which of the possibly many works these   
   authors have written is the one you're referring to, wastes everyone's   
   time (and leads to further confusion if readers guess incorrectly).   
   -- jt]]   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)