Some corrections. The link in the sentence
TheCanadian said:
is to a hyperphysics page. The explanation on that page requires a correction. The Bose-Einstein distribution is not the 'probability' of a particle having the energy but the thermodynamic average number of particles having the energy E.
Why is probability incorrect? well, for Bose-Einstein distribution, the value can be larger than 1 if E is sufficiently small. Probability cannot be larger than one, ever.
TheCanadian said:
is A = 1 for photons? Does this not imply that photons will have an increasingly high probability of being present as E approaches 0?
It means that as we approach zero energy, the number of photons in the given energy state approaches to infinity, i.e. infinite number of photons at zero energy.
TheCanadian said:
I am wondering if there is any minimum to a photon's energy (i.e. frequency).
This is actually a very interesting question.
Let's consider a one dimensional case, think of a cavity of length L. Then the lowest mode of electromagnetic wave (photon) will have the wavelength of 2L, That gives the energy ## E = \frac{hc}{2L}##. This is the lowest energy of a photon confined in one dimension to a cavity of length L. In 3D, if the cavity is a cube of the same length, the minimum photon energy is ##\sqrt 3## times larger.
So, as L goes to infinity, the minimum energy for a photon goes to zero.
However, if you confined photons to a finite volume, the minimum energy is inversely proportional to the dimension of the volume.
This leads to observable effect, such as Casimir effect
Henryk