I'll have struggle on how to get started on this problem. I don't have a clue on how to start, somebody give me some tips on how to figure this problem out. Thanks Experiments has shown that for the quantum of radiation(a photon), the energy and momentum are related by E=pc, corresponding to a particle with mass m=0. Suppose that in the observation of a supernova 170,000 light-years away, the first bursts of photons with an energy range of E= 10 eV to 10^4 eV arrive within 10^-8 s of each other. What limits does this set on the mass of the photon? Anybody have a clue on how to do this?