After the Big Bang, the stars and galaxies did not just simply form and begin to shine and expand. After the universe cooled down to about 100,000 degrees Kelvin, the protons and electrons began to combine and create hydrogen. This was so because only the simplest particles were present, protons and electrons, which create the simplest element, hydrogen. This hydrogen began to come together and form clouds. So at first, all that existed in the primeval universe were these clouds of hydrogen. Masses of hydrogen began to come together and form huge hydrogen clouds. These would be the creators of the present universe.