The Redshift was the first element to contradict Aristotle’s view of the universe, which is that the universe is static, never changed, and will never change (except on Earth, where things do change).

When American astronomer Edwin Hubble began to observe galaxies, he noticed that their spectra (what types of light do objects emit: mostly X rays, UV, Visible Light, Infrared, Microwave, or Radio?) that the light of these galaxies where all in the red spectrum. Even better, he noticed that the farther the galaxy was, the redder its spectrum was.

Our friend Hubble used the Doppler Effect to interpet the results. A red spectrum meant that galaxies were moving away from each other, and the farther the galaxy was, the faster it was moving away! So the whole universe is expanding. You’re wondering how can an infinite universe be expanding? Read this article about it: An Expanding Universe

This is only true for close galaxies: when galaxies are very far away, it’s the expanding space that actually stretches the light, making the wavelength longer, so visible light is redshifted to infrared, for example.

He found out that our universe was not static like Aristotle and many others still think, but constantly moving. This was the first pillar to come and support an upcoming new theory, first named big bang by one of the people trying to sink it! The big bang was and still is today the only way of explaining why the redshift occured. The universe is thus expanding, and was at some point an extremely hot and dense mixture of elementary particles that interacted with each other, that scientists evaluate at happening 13,7 billion years ago: the famous moment where time was 0… Where matter was infinitely dense, and thus infinitely hot.