From: PointedEars@web.de   
      
   Please repair your From header field value.  There has to be an actual   
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   jojo wrote:   
   > Thomas 'PointedEars' Lahn wrote:   
   >> While it is correct to say that zero proper time elapses along lightlike   
   >> geodesics (ds^2 = +- c^2 (d tau)^2 = 0 ==> (d tau) = 0 ==> Delta tau = 0),   
   >> we also know that *a photon has no inertial rest frame* as that would   
   >> contradict the postulate of the constancy of c, one of two postulates which   
   >> make up the special principle of relativity which special relativity is   
   >> based on, *and* the Planck--Einstein relation E = p c = h f.   
   >>   
   >> Curiously, special relativity fails to describe *completely* a motion at the   
   >> speed c that it is based on.   
   >   
   > because of the dividing by zero happening?   
      
   Put simply: Yes.  The Lorentz factor and equivalent terms [e.g. the rapidity   
   w = artanh(v/c)] are singular at v = c.   
      
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   PointedEars   
      
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