1. I found a nice site. http://math.ucr.edu/home/baez/photon/schmoton.htm 2. I also found a nice quote. "All the fifty years of conscious brooding have brought me no closer to the answer to the question, "what are light quanta?" Of course today every rascal thinks he knows the answer, but he is deluding himself." Einstein (1951) 3. Then, I also have a question. Is it true that due to time-energy uncertainty only a photon that lived for a very long time has (almost) definite energy and momentum? 4. Matter fact, i have a second question. Do a atoms that had been longer in an excited state produce photons with more precise energy?