From: goldenfieldquaternions@gmail.com   
      
   On Monday, November 20, 2017 at 3:36:35 PM UTC-6, Michael Cole wrote:   
   > Hi all.  I am working with a student who is trying to learn QFT.   
   > Is there a good simple reason why spin 0 can occur for a massive   
   > spin 1 particle but cannot occur for a photon?  I am not asking for   
   > a proof; I have read proofs and believe I understand them.  But   
   > does anyone know a nice simple idea.  I.e. "this is the reason in   
   > a nutshell"?   Thanks in advance for assistance.   
      
   It is because the angular momentum has the projections m = L, L - 1,   
   L - 2, ..., -L + 1, -L along the direction of motion, and for L = 1   
   these states are m = 1, 0, -1. The m = 0 means the angular momentum is   
   perpendicular to the momentum. This can only occur if the particle is   
   in the rest frame of the measuring apparatus. This means it is timelike   
   with a mass and not massless and on a null geodesic like a photon.   
      
   LC   
      
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