Transcript: The big bang model predicts that the universe is evolving, that it was smaller, hotter, and denser in the past. Astronomers would like to test this basic prediction. One test involves spectral lines in distant quasi-stellar objects or quasars where the cosmic microwave background radiation excites the line. Observations and comparisons at different redshifts show that the temperature of the microwave background radiation, which is currently 2.7 Kelvin, was indeed hotter in the past, varying as one plus the redshift as predicted by the big bang model. Also, there are many observations to show that galaxies themselves have evolved, being smaller and having been assembled from pieces so they grow bigger and brighter with time and redshift to the present day. The universe is indeed evolving.