Chapter 34, Problem 14RQ

The universe is about $25\%$ helium. From where did most of the helium come?

To determine

The process that helium is created in the universe.

Answer to Problem 14RQ

The helium in the universe was created many years ago in the Big Bang and it is the product of hydrogen fusion in stars.

Explanation of Solution

After the Big Bang, much less than a second, the universe was both too hot and too dense for elements to form. Hydrogen was not formed until the universe had spread out. A few seconds later, after the Big Bang, neutrinos, quarks, and electrons form.

After 3 minutes, conditions got cooled enough for these protons and neutrons to form hydrogen nuclei. Some of these nuclei combined to form helium as well, though in much smaller quantities.

Most of the helium in the universe was created in the Big Bang, but also, it is the product of hydrogen fusion in stars. Most of the Helium in the universe is helium-4, the vast majority of which was formed during the Big Bang. Large amounts of new helium were created by nuclear fusion of hydrogen in stars.

Conclusion:

Therefore, the helium in the universe was created many years ago in the Big Bang and it is the product of hydrogen fusion in stars.