so that for the radiation in equilibrium
ϵ = Λ 4 3 E { 1 + 2 c 2 + v 2 c 2 − v 2 } = Λ 4 3 c 2 + v 2 3 ( c 2 − v 2 ) E . {\displaystyle \epsilon ={\frac {\Lambda ^{4}}{3}}E\left\{1+2{\frac {c^{2}+v^{2}}{c^{2}-v^{2}}}\right\}=\Lambda ^{4}{\frac {3c^{2}+v^{2}}{3\left(c^{2}-v^{2}\right)}}E.}
Thus
p = Λ 4 P = 1 3 Λ 4 E = c 2 − v 2 3 c 2 + v 2 ϵ . {\displaystyle p=\Lambda ^{4}P={\frac {1}{3}}\Lambda ^{4}E={\frac {c^{2}-v^{2}}{3c^{2}+v^{2}}}\epsilon .}
This is the same equation as that obtained in § 3. Exactly in the same way for the momentum is found the result
g = 4 3 Λ 4 v c 2 − v 2 E = 4 v 3 c 2 + v 2 ϵ . {\displaystyle g={\frac {4}{3}}{\frac {\Lambda ^{4}v}{c^{2}-v^{2}}}E={\frac {4v}{3c^{2}+v^{2}}}\epsilon .}
