From: dan131riley@gmail.com   
      
   John Heath  writes:   
   > I would like it if you start a thread on neutrinos as I have a beef with   
   > kids today going on and on about what a neutrino is while ignoring   
   > flavor change problem. A tauon neutrino mass is in the 18 MeV range so   
   > how could a neutrino going through flavor changes be clocked at almost c   
   > with a massive 18 MeV boat anchor on it?   
      
   There are no (reliable) direct measurements of any neutrino mass.  18.2   
   MeV is an upper bound, meaning it should very likely have been measured   
   if it were heavier than that, so it's likely lighter, with no prejudice   
   as to how much lighter.  There are arguments from nucleosynthesis bounds   
   that the tau neutrino mass must be less than 1 MeV, and arguments from   
   CMB constraints that the sum of all the neutrino masses must be around 1   
   eV or less.   
      
   You are correct that an 18 MeV neutrino mass would be inconsistent with   
   flavor changing--for mixing to occur as observed, the neutrino masses   
   need to be around 1 eV or less, and close together.   
      
   -dan   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)