How do scientists know the universe is expanding?

Three studies of supernovae conducted between 1997 and 1998—the Superova Cosmology Project, the Supernova Legacy Survey, and the Superova Search Team—found evidence of an increasing rate of expansion for the universe.

According to the inverse square relationship, the further away the light source, the less luminosity; therefore, by comparing the red shift of the light from a supernova to the luminosity, calculations could be made as to the velocity of the object relative to the observer. These studies treated supernovas as a standard candle. The supernova is assumed to give a standard total luminosity.

It was significant that all three of these studies found empirical evidence supporting the theory that the universe is expanding at an increasing rate, despite the expectation that the studies would find evidence supporting the opposite theory.

The supernova studies disproved the theory of an oscillating universe, which held that the universe was eternal, self-existent, and oscillated between periods of expansion and contrition. The evidence of an increasing rate of expansion of the universe suggests that the universe is not eternal, self-existent, or a closed system.

Cosmologists track far-off galaxies by measuring their redshift, which shows how far away they are from us. They also find evidence for the expanding universe theory in cosmic microwave background radiation.