On Tuesday, January 17, 2017 at 1:03:44 AM UTC+2, fil...@gmail.com wrote:   
   > On Tuesday, January 10, 2017 at 5:46:13 PM UTC-8, Nagaraju Palagani wrote:   
   > > Because of gravity, if we drop something, it falls down, instead   
   > > of up. Well everybody knows that! But we do not know the mechanism   
   > > that governs gravity?   
   >   
   > No. We only have a model that tells us how paths of free fall are coupled   
   > to energy-momentum(*). General relativity is a non-quantum theory so this   
   > sort of thing is perhaps not that surprising:   
   > this is a situation similar to where Lagrangian mechanics was with its   
   > least action principle: no mechanism underlying the odd property of nature   
   > choosing extremal paths for particle motions. Then came quantum mechanics   
   > in the Feynman formulation showing how those extremal paths arise from   
   > certain wave reinforcement and cancellation.   
      
   ============================   
   does the Feynman diagram explain why  the change in direction (after collision   
   )   
   is in angle say ''x''   
   and not angle ''y ''   
   iow   
   why just the angle he is suggesting ??   
   ==========================   
      
   TIA   
   Y.P   
   ===============================================   
      
   [[Mod. note --   
   * 9 excessively-quoted lines snipped here.   
   * To answer the poster's question, this depends on how precisely the   
     initial conditions are specified.  If they are specified sufficiently   
     precisely [so that the impact parameter of the incoming particle   
     (i.e., the lateral offset of its incoming trajectory with respect   
     to a collision) is known; obviously the uncertainty principle imposes   
     restrictions on just how well this can be done] then yes, the particle's   
     future trajectory (including the change in direction) can be computed.   
      
     But in the usual case the impact parameter is completely unspecified   
     (we *don't* know the incoming particle trajectory's lateral position   
     to ultra-high accuracy) and in this case even classical mechanics can't   
     do what you ask.   
   -- jt]]   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)