XPost: sci.physics.relativity, alt.atheism, sci.physics   
   From: PointedEars@web.de   
      
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   Jack Sovalot wrote:   
   > Thomas 'PointedEars' Lahn wrote:   
   >> On the other hand, in quantum electrodynamics a photon cannot be   
   >> understood as a point particle with a position (not even an uncertain   
   >> one) in the first place, but must be understood as a non-local   
   >> excitation state of the quantum-electromagnetic field.  It therefore   
   >> exists everywhere (and at all times) from the outset.  The   
   >> semi-classical photon is merely where the peak of that state, so to   
   >> speak, is largest, where and when it has a high probability to be   
   >> found.  In Feynman's (path integral) interpretation, it takes all   
   >> paths between two points simultaneously.  Both correspond nicely to   
   >> the naive interpretation that a photon is everywhere at the same time   
   >> as for it the rest of the universe is infinitely length-contracted,   
   >> and the purely mathematical result that zero proper time elapses   
   >> along its worldline.  But I do not understand what that could mean.   
   >   
   > Are you able to tell us any more about the Feynman path itegral   
   > interpretation?   
      
   At best partially (I know basically the Feynman rules, i.e. how to calculate   
   an n-point function for a Feynman diagram; but I have not studied QED yet),   
   but the mathematics is still too difficult to explain in a Usenet posting.   
   For that you have to take classes in quantum field theories.   
      
   However, good simplified graphical illustrations have been done by Don   
   Lincoln (experimental particle physicist at Fermilab) and Science Asylum   
   (theoretical particle physicist, real name and place of work unknown),   
   respectively:   
      
      
   pp.   
      
      
      
   And, of course, Feynman's lectures can be found online, e.g. at   
      
      
      
   and on various channels on YouTube.  He also wrote a popular-scientific   
   textbook about the subject: "QED: The Strange Theory of Light and Matter".   
   (I have not read it yet.)   
      
   HTH.   
      
      
   F'up2 sci.physics   
      
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   PointedEars   
      
   Twitter: @PointedEars2   
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