Relic Particles from the Early Universe

Abstract

We have seen in Chap. 3 that during the radiation-dominated epoch the cosmic time t is proportional to the inverse square of the temperature, t α T ⁻², except during the annihilation processes which heat up the gas of photons. We can write

$$t = 2.42{{ \times }^{{ - 6}}}{{g}^{{ - 1/2}}}\left( T \right)T_{{GeV}}^{{ - 2}},$$

(7.1)

where kT is measured in GeV, k is set equal to one, and t is measured in seconds.

“The evolution of the world can be compared to a display of fireworks that has just ended: some few red wisps, ashes, and smoke. Standing on a cooled cinder, we see the slow fading of the suns, and we try to recall the vanishing brillance of the origin of the world.”

G. Lemaitre

“Unifit to mend the azure sky, I passed some years to no avail. My life in both worlds written here, whom can I ask to pass it on?”

(Inscription on the jade stone rejected by the goddness Nu Wa when she repaired the sky [from A Dream of Red Mansions by Tsao Hsueh-Chin; Foreign Language Press, Beijing 1987]).