Earlier today, Professor York took us on a trip back to the very beginnings of the universe. We knew that the basic building blocks of space were stars and galaxies, but what came before them? At the very beginning, there was only dark matter and one basic force we experience every day: gravity.
Because dark matter has mass, its gravity affected the dark matter around it, clumping together. These clumps grew and grew and eventually pulled in atoms to make clusters we describe as galaxies. The earliest galaxies became breeding grounds for stars.
Thus, from the basic combination of matter and a simple physical force, the universe has grown to become what we see today.