You can use the concepts in this chapter to obtain an estimate of the number
of atoms in the universe. These steps
will guide you through this calculation.
(a) Begin by calculating the number of atoms in the sun.
Assume that the sun is pure hydrogen with a density
of 1.4 g>cm3
. The radius of the sun is 7 * 108 m, and
the volume of a sphere is V = 4
3pr3
.
(b) The sun is an average-sized star, and stars are
believed to compose most of the mass of the visible
universe (planets are so small they can be ignored),
so we can estimate the number of atoms in a galaxy
by assuming that every star in the galaxy has the
same number of atoms as our sun. The Milky Way
galaxy is believed to contain 1 * 1011
stars. Use your
answer from part a to calculate the number of atoms
in the Milky Way galaxy
(c) Astronomers estimate that the universe contains
approximately 1 * 1011
galaxies. If each of these
galaxies contains the same number of atoms as the
Milky Way galaxy, what is the total number of atoms
in the universe?