Use the concepts in this chapter to obtain an estimate for the number of atoms in the universe. Make the following assumptions:

(a) All of the atoms in the universe are hydrogen atoms in stars. (This is not a ridiculous assumption because over threefourths of the atoms in the universe are in fact hydrogen. Gas and dust between the stars represent only about 15% of the visible matter of our galaxy, and planets compose a far tinier fraction.)

(b) The sun is a typical star composed of pure hydrogen with a density of 1.4 g/cm³ and a radius of 7 * 10⁸ m.

(c) Each of the roughly 100 billion stars in the Milky Way galaxy contains the same number of atoms as our sun. 

(d) Each of the 10 billion galaxies in the visible universe contains the same number of atoms as our Milky Way galaxy.