The crossover point from radiation to matter domination occurred:
A) when the strong force separated from the other two forces.
B) with the emission of the cosmic background radiation.
C) about 50,000 years after the Big Bang, at a temperature of about 16,000 K.
D) with the creation of neutrons and protons, at about 10¹³ K.
E) with the creation of electrons and positrons at about 6 × 10⁹ K.

Question

Quizplus · Accepted Answer

The crossover point from radiation to matter domination occurred about 50,000 years after the Big Bang, at a temperature of about 16,000 K. This is known as the recombination era, during which protons and electrons combined to form neutral hydrogen atoms, leading to a decrease in the scattering of photons and the emission of the cosmic background radiation. Prior to this era, the universe was dominated by radiation (photons and other particles), whereas afterwards it was dominated by matter (protons, neutrons, and dark matter).

The Crossover Point from Radiation to Matter Domination Occurred