Question

Why did fusion cease only about 5 minutes after the Big Band (at the end of the era of nucleosynthesis)

a) Gravitational collapse
b) Lack of suitable elements
c) Expansion and cooling
d) Excessive radiation

Answer 1

Fusion ceased about 5 minutes after the Big Bang due to the expansion and cooling of the universe. The temperature dropped too low for the fusion of helium nuclei into heavier elements to occur, limiting the formation of new elements to stars and supernovae.

Step-by-step explanation:

The reason fusion ceased only about 5 minutes after the Big Bang (at the end of the era of nucleosynthesis) was due to the expansion and cooling of the universe.

As the universe was still expanding and cooling down, the temperature dropped so low that the fusion of helium nuclei into heavier elements could not occur anymore. Only elements up to lithium could form in the first few minutes.

This marked the end of the time when the entire universe was a fusion factory, and today, the fusion of new elements is limited to the centers of stars and supernovae explosions.