Infinite/Eternal Universe Problems

l Paradox of the Dark Night Sky

Slide 10 of 22

Many scientists had originally thought that the universe might be infinite and eternal. However, there was a major problem with the theory. If the universe were infinite, the amount of light falling on the earth would also be infinite (assuming an approximately uniform density of galaxies throughout the universe. The reason for this is that the volume of the universe increases 8-fold with doubling of distance, while the decrease of light is only 4-fold with the doubling of the distance. The result is that the amount of light falling in the earth would double every time the size of the universe is doubled. Therefore, if the universe were infinite, we would not expect the sky to be dark at night. Since the night sky is dark, we know that the universe could not be infinite.