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How is the Expansion of the Universe Related to the Doppler Effect?
Have you ever wondered why the pitch of a siren drops while an ambulance passes by? Or wondered how scientists discovered that the universe was expanding? Well, believe it or not, the answers to those two questions are deeply related through something called the Doppler effect.
The Doppler effect can be observed for all types of waves, sound, light, even ocean waves. Both sound and light waves travel at a finite speed, though light is significantly faster and is the fastest thing that can move through space.
Born on November 29, 1803, in Salzburg, Austria, Christian Doppler was the person to first person describe how the relative motion of a source and the observer affects observed frequency of sound and light waves. Accordingly, the phenomenon was given the name “the Doppler effect.”
How it all works
Let’s use an example. Waves emitted by an object traveling toward an observer get compressed, resulting in a higher frequency as the source approaches the observer. In contrast, waves emitted by a source traveling away from an observer get stretched out, resulting in a lower frequency. High frequency waves are blue shifted while low frequency waves are redshifted.
