XPost: sci.electronics.design   
   From: ram@zedat.fu-berlin.de   
      
   john larkin  wrote or quoted:   
   >Two gamma rays (zero mass total) can collide to produce a particle   
   >pair (which has mass.)   
      
     Let's call the momenta of the two photons p0 and p1.   
      
     We may assume p1 = -p0 as the two photons are moving towards   
     each other from opposite directions. Let's call the momentum   
     of the system of these two photons "p", then we have:   
      
   p = p0 + p1 = p0 +( -p0 )= p0 - p0 = 0   
      
     . Let's call the energy of this pair "E" and its mass "m". From   
      
   E^2 = m^2 + p^2   
      
     (in units with c=1) and   
      
   p = 0   
      
     , we get,   
      
   E^2 = m^2   
      
     for the pair. I.e., all its energy is mass. And this is the   
     mass the particle pair has after the collision.   
      
   Newsgroups: sci.electronics.design,sci.physics   
   Followup-To: sci.physics   
   Subject changed.   
      
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