Evidence for the Big Bang theory
Hubble’s law supports the Big Bang theory in that it is evidence of the universe is ever-expanding. Edwin Hubble founded this law by measuring the redshifts of different faraway galaxies. Just as when wavelength increases as a siren goes past you, and the pitch/frequency decreases, the same happens with the red shift of light. As the galaxies are further away (and are continuing to get further away because the universe is expanding) light waves from those galaxies to Earth should be stretched further and further apart. Long wavelengths of visible light are red, which is why it is called the red shift of light. Going back to Hubble’s law, he found the velocities (relative to Earth) of faraway galaxies using redshift, and compared that information with how far away those galaxies were from Earth. The result was the following: Hubble’s findings said that the further away a galaxy is from a point in space, the faster the galaxy moves further away. That mean everything was moving away from everything, so this proved that the universe is expanding. Cosmic background radiation was discovered in the 1960s when a satellite picked up huge radio frequencies from every direction. This electromagnetic radiation fills the universe, and is radiation from the early growth of the universe. The Big bang theory also states that the early universe was very hot, so there should be radiation that is the leftover heat from the Big Bang. And that is what CMB is, and why it is evidence of the Big Bang.
The spots in this picture are related to the gravitational pull of the universe (after the Big Bang).