What is redshift?

The term redshift refers to the wavelength of light being stretched; this results in the light being seen as “shifted” towards the red part of the spectrum. This is similar to how sound waves work – if the source and the observer are approaching each other, then the frequency heard by the observer is higher, and if they move away from each other it is lower.

This is known as the Doppler effect and is evident in our everyday life, such as police and ambulance sirens as well as the sound of a loud car passing. Since light is a wave, it behaves similarly to sound waves, therefore, the light from a light emitting object is affected by the Doppler effect.

Redshift can be used to show that the Universe is constantly expanding, and this is because light from distant galaxies is shifted to longer wavelengths (this is the Doppler effect) and this means that the light is shifted to the red side of the visible light spectrum. The fact that light from distant galaxies is shifted to longer wavelengths suggests that the galaxies used to be much closer.

Edwin Hubble made the observation using the Hubble telescope that the redshift of galaxies was directly proportional to the distance of the galaxy from Earth. In 1929, he shared his findings that things further away from Earth were moving away faster and this meant that the universe must be expanding.

It was later discovered that the matter of the universe was not increasing due to the expansion, but rather the space in between. One good way to model this is to think of a balloon with round stickers stuck on the outside, the balloon represents the universe and as someone blows up the balloon this represents the expansion of the universe. As the balloon is blown up, the amount of matter (round stickers) does not increase, but the space between them does. However, there are a few limitations to this model, such as how the area withing the balloon should contain matter and the fact that the balloon cannot expand beyond a certain point as it would burst – unlike the Universe.

How does redshift support the Big Bang Theory?

Redshift states that the Universe is expanding, this idea implies that the Universe began expanding at some point and this point. In the words of Georges Lemaître in 1927, the Big Bang is where the universe started at a single point and has stretched and expanded to get as big as it is now and that it is going to continue expanding. These two ideas compliment each other and show that redshift is evidence for the Big Bang Theory.