After about 300 seconds (five minutes!), the Universe was mostly hydrogen and helium, and it stayed this way for a long, long time.

Freedman and Kaufmann

In fact, we have to wait about 150 million years for the appearance of the first star!

Only then will the composition of the Universe start to evolve again.

Back Next

Back to Lecture 4 outline

Back to main lectures page

Back to main course page