Show that the number of photons sn in equilibrium at temperature in a cavity of volume V is N 2 40 2V( hc)3 From (23) the entropy is (42V 45)( hc)3, whence N ( 3 602 It is believed that the total number of photons in the universe is 108 larger than the total number of nucleons (protons, neutrons) B...

We need n n where w The L u TLn The sum is converted to wn an integ ...

Show that the number of photons < sn > in equilibrium at temperature in a

Question:

Show that the number of photons ∑< sn > in equilibrium at temperature τ in a cavity of volume V is
N = 2.40π-2V(τ/hc)3

From (23) the entropy is σ (4π2V/45)(τ/hc)3, whence σ/N ( 3.602. It is believed that the total number of photons in the universe is 108 larger than the total number of nucleons (protons, neutrons). Because both entropies are of the order of the respective number of particles, the photons provide the dominant contribution to the entropy of the universe, although the particles dominate. The total energy. We believe that the entropy of the photons is essentially constant so that the entropy of the universe is approximately constant with time.