What Redshift & Blueshift Tell Us

Picture of several galaxies. Box and circle show one of the farthest known

galaxies. Photo provided by NASA. Public domain.

Just the idea of redshift/blueshift may (or may not) be interesting to you. But where the idea really starts to become interesting is how it helps explain the Big Bang theory.

As astronomers observed the stars and made measurements they observed that some nearby galaxies were redshifted and some were blueshifted. This discovery puzzled scientists, because if the universe was always the same size, then there shouldn't be any shift. Since the galaxies were redshifted, that means they are moving away from our own Milky Way galaxy. If some galaxies are moving away from us, then they must have been closer in the past. That means the universe would have been smaller long ago. Therefore, scientists believe that redshifting in stars and galaxies is evidence that the Big Bang happened.