XPost: sci.electronics.design   
   From: ram@zedat.fu-berlin.de   
      
   john larkin  wrote or quoted:   
   >If e and m are the same thing, why do people use two symbols?   
      
     Energy and mass are not the same thing. For one example, a photon   
     has energy, but not mass. (I already gave this example before.)   
      
     The capital "E" is mass, the small "e" is an electron.   
      
   >Do photons attract one another? Do they bounce off one another?   
      
     There is photon-photon scattering in QED (virtual charged particle   
     loops), but it is a very weak effect that rarely matters in practice.   
      
     In general relativity, photons should attract each other, but   
     this effect should be very weak and should hardly be observable.   
      
     Both effects are so small they have never been measured directly.   
      
   >If you apply Newton's law of gravitation to photons, the force will be   
   >enormous when they get in a close intersection. Wouldn't that fuzz up   
   >images at cosmological distances?   
      
     Photons are usually not that localized like tiny balls that   
     have a sharp distance. They are being described by quantum   
     electrodynamics, which does not take gravity into account.   
     On the other hand, general relativity does not take quantum effects   
     into account. We do not yet have a theory of everything.   
      
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