From: tjroberts137@sbcglobal.net   
      
   On 10/21/20 11:23 PM, rockbrentwood@gmail.com wrote:   
   > On Saturday, September 5, 2020 at 3:36:26 AM UTC-5, PengKuan Em   
   > wrote:   
   >> a)	Material clock What is time? This question is tricky because in   
   >> relativity time-rate changes when frame of reference changes.   
   >> Time-rate changing is puzzling because it is in conflict with our   
   >> intuition that time is the flow of ticks of clocks of which the   
   >> mechanical structure does not change. Then how to clearly explain   
   >> the contradiction between the constant flow of ticks delivered by   
   >> clocks and the relativistic time dilation?   
      
   The answer to this is simple and straightforward: "time dilation" does   
   not affect any clock or any "time rate"; it only affects how a moving   
   clock is OBSERVED/MEASURED from an inertial frame. The "conflict" and   
   "contradiction" here are PengKuan Em's alone, in misunderstanding what   
   "time dilation" actually is.   
      
        [As I said earlier: It is best to avoid such wishy-washy   
         phrases as "time rate". Talk instead about definite,   
         unambiguous, and directly measurable quantities such as   
         clock tick rates.]   
      
   > We can fix that. Make it both. A coordinate time (t) and historical   
   > time (s), which we'll identify as proper time. Throw it in as another   
   > coordinate too.   
      
   That is nonsense. Attempting to use FIVE coordinates on a 4-D spacetime   
   is useless. And why didn't you add a SIXTH "coordinate" in an attempt to   
   deal with "length contraction"? -- after all that is essentially the   
   same as "time dilation" (both are simple geometrical projections,   
   differing only in orientation).   
      
   Moreover, you use an unacknowledged PUN on "coordinate": your s, which   
   you identify as proper time, is not a coordinate, and can never be one   
   -- coordinates are a 1-to-1 map from a region of an N-dimensional   
   manifold to a region of R^N. Proper time is path dependent and cannot   
   possibly participate in such a map.   
      
        [FYI: I put "time dilation" and "length contraction" in   
         "scare quotes", because they are rather poor names for   
         the actual phenomena, fostering the mistake PengKuan Em   
         made above. No time actually dilates, and no length ever   
         contracts, only measurements and relationships do so.]   
      
   > [...ignored: long, involved elaboration of that basic mistake]   
      
   Tom Roberts   
      
   --- SoupGate-Win32 v1.05   
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