  The interplay between optical and statistical physics is a rich and exciting
field of study. Black body radiation was the first application of photon
statistics, although it was initially treated as a problem of the cavity
oscillators in equilibrium with the photon field. However Planck surprisingly
resisted the idea that anything physical would be quantized for a long time
after he had solved the problem. We trace this development.
  Then, after the invention of the laser itself, it proved difficult to develop
a theory of laser action that could account for photon statistics, i.e.
fluctuations near threshold. This was accomplished in 1965. After Bose-Einstein
condensation was successfully achieved, the same problem arose in this case.
The fluctuation problem had not been treated adequately even for the ideal Bose
gas. However this problem has now been solved using the same techniques as in
the theory of laser action.
