How does red shift lead to the big bang theory?

Answer 1

The red shift is a Doppler effect for visible light that implies an object is moving away from you. The blue shift is a Doppler effect for visible light that implies an object is moving towards you. Stars are distrbuted within galactic clusters. If a star is red-shifted, the distance between us and that galaxy is increasing. If it is blue-shifted, the distance between us and the galaxy is decreasing.

All galaxies outside our local galactic cluster produce light that is red-shifted; and the greater the distance between us and these outside galaxies, the greater the red shift. That the size of the red shift depends on the distance is considered isotropic (or the same in all directions), meaning the distance between our local galactic cluster and all other galactic clusters is increasing at the same ratio based on distance from us. These distant galactic clusters, demonstrating red shift, are supportive evidence that these outside galaxies are moving further apart consistent with the Big Bang Theory.

While the red shifted starlight is considered supportive evidence of an expanding universe, there are a few examples of blue shifted starlight within our Local galactic cluster. The Andromeda Galaxy is moving towards within the Milky Way galaxy, so when it is observed from Earth, its light is blue shifted. Any even within our own Milky Way galaxy, the Barnard Star is also moving towards Earth and appears to have a slight blue shift.

Answer 2

Red shift is the phenomenon where light waves from distant galaxies are stretched, causing a shift towards longer (redder) wavelengths. This supports the Big Bang theory as it suggests that the universe is expanding, with galaxies moving away from each other. The further away a galaxy is, the more pronounced the red shift, indicating a faster rate of expansion in the past.