Why Is the Night Sky Dark?

This is not quite as obvious as it sounds. Back in 1576, Thomas Digges did a simple calculation, which brought to light (almost literally as we shall see!) a famous puzzle in the history of science–the dark night sky paradox. Assuming that the intensity of a light source decays by the inverse square law, and that the universe is relatively homogeneous so that the density of stars is roughly constant everywhere, one can calculate that the intensity of light from stars should be blinding. Under these conditions, in fact, the intensity would be infinite , which is contrary to what we know from every day (and “every night”) experience: We would not have a dark night sky!