Just read Feynmen's QFT and been wondering the difference between photon reflection by a perfect mirror and photon scatter by say a rough surface. In both cases, photons are said to be absorbed by electrons and re-emitted. But in reflection case, photons get to "preserve" its wave information (wavefunction never collapse, phase increase by pi/2). I think in QFT, photons are said to have virtual interaction with all the electrons on the mirror? In scattering case, photon is absorbed by a specific electron and re-emitted, destroying all wave information. So what decide photon when to be reflected when to be scattered? Thanks for the help, just a curious laymen here.