Since the speed of light is finite, we are only able to see as far as light has had time to travel (the age of the universe). Since the universe is approximately 13.7 billion years old, the radius of the visible universe is 13.7 billion light years, which is much smaller than the line of sight we calculated (3 × 1013 billion light years). Most lines of sight, then, will leave the visible universe without reaching any stars.
The size of our visible universe, which is related to its age, is too small to have a star at each point in the night sky. Any starlight outside the visible universe has not had time to reach us, leaving portions of the sky dark. These dark portions indicate that light is emitted from stars at distances greater than the radius of our visible universe. This means the universe has a finite age, providing further evidence for the Big Bang.