Question

In the early universe, pairs of photons collide to create fermion and antifermion pairs and the fermions also annihilate into photon pairs. As the universe expands and cools (there might be more than one correct answer):a). This process continues to the present day b). Massive hadrons are produced and the light nuclei are formed c). Photons start to ionize new atoms d). Photons eventually cannot even ionize atoms and stream through the universe forever e). Photons eventually cannot even ionize atoms and disappear

Answer 1

In option a, the process of annihilation and pair production is still possible and mostly observed by the photons emitted from the unstable nucleus (radioactive nucleus).

Thus, option a is correct.

In option b, as with the help of heat light nuclei can be produced but they destroy immediately.

Hence, option b is not correct.

In option c, the photons emitted from the nucleus do have very large energy and can easily ionize an atom.

Hence, option c is correct.

In option d, the photons can ionize the atoms.

Hence, option d is incorrect.

In option e, the photons can ionize the atoms.

Thus, option e is incorrect.

Hence, options a and c are correct.