If as in (11) is the average occupancy of a single orbital of a boson system, then from (5.83) show that
<(∆N)2> = (1 + M).
Thus if the occupancy is large, with >> 1, the fractional fluctuations are of the order of unity: <(∆N)2> / 2 ≈ 1, so that the actual fluctuations can be enormous. It has been said that “bosons travel in flocks.” The first edition of this text has an elementary discussion of the fluctuations of photons.