Red Shift

Basics

Red Shift is a phenomenon in astrophysics where the light from an object moving away from an observer is shifted to the red end of the visible light spectrum.
It’s an effect of the Doppler Effect, which also applies to sound waves. The frequency of the waves change based on the movement of the source relative to the observer.
Doppler Effect can result in either an increase (blue shift) or a decrease (red shift) in frequency.
The term ‘red shift’ was chosen because red light has the lowest frequency of all visible light.

When we observe distant galaxies, we see a red shift in the light they emit.
This red shift increases for galaxies that are farther away, which indicates that they are moving away from us at increasing speeds.
It’s important to note that the galaxies themselves aren’t moving, rather the space between the galaxies is expanding.
This discovery was key evidence for the Big Bang Theory, indicating that the universe is expanding from an initial small and dense state.

The amount of red shift can be measured by comparing the spectral lines of light from a distant galaxy to those of the same elements on Earth.
The further towards the red end of the spectrum these lines are, the faster the galaxy is moving away from us.
Hubble’s Law states that the further away a galaxy is, the faster it is moving away from us, which supports an expanding universe.
The cosmological red shift is used to estimate the rate at which the Universe is expanding, known as the Hubble Constant.

The cosmic microwave background radiation (CMBR) provides further evidence for the Big Bang theory and an expanding universe.
The CMBR is the afterglow from the Big Bang, which has stretched out over time due to the expansion of the Universe, causing it to red shift into the microwave part of the spectrum.
It can be detected in all directions, suggesting that the Big Bang was a uniform event that occurred everywhere in space.