How does red-shift provide evidence for the expanding universe?

Red-shift provides evidence for the expanding universe by showing that distant galaxies are moving away from us.

When we observe light from distant galaxies, we notice that the light is shifted towards the red end of the spectrum. This phenomenon is known as red-shift. According to the Doppler effect, when an object emitting light moves away from an observer, the light waves stretch out, increasing their wavelength and shifting the light towards the red part of the spectrum. This red-shift indicates that these galaxies are moving away from us.

The more distant a galaxy is, the greater its red-shift. This relationship was first observed by Edwin Hubble in the 1920s and is now known as Hubble's Law. Hubble found that the further away a galaxy is, the faster it appears to be moving away. This suggests that the universe is expanding uniformly, with galaxies moving away from each other in all directions.

Red-shift is crucial evidence for the Big Bang theory, which proposes that the universe began from an extremely hot and dense state and has been expanding ever since. By analysing the red-shift of galaxies, scientists can estimate the rate of expansion of the universe, known as the Hubble constant. This helps us understand the age and size of the universe.

In summary, red-shift is a key piece of evidence for the expanding universe because it shows that distant galaxies are receding from us, supporting the idea that the universe is growing larger over time.