In the mid-20th century, the Big Bang and Steady State theories were competing cosmological models. The graph below illustrates how the scale factor, R(t)R(t)R(t), of the Universe varies with time ttt under both models.
Explain how the cosmological red-shift of spectral lines from distant galaxies supports the expansion of space proposed by both theories, and explain why the discovery of the Cosmic Microwave Background (CMB) radiation with a blackbody temperature of approximately 2.7 K2.7\text{ K}2.7 K supports only the Big Bang theory.