How is the Universe Expanding?

Illustration representing the mesh used to describe gravity.

Create An Expanding Universe

You have likely heard about the Universe expanding. Or that redshift can tell us about the movements of galaxies. Both are difficult ideas to imagine and understand.

Cartoon of a person blowing up a balloon. The balloon is covered with galaxies.


Most galaxies appear to be moving away from us. This means that the light from them is "stretched" slightly and appears a bit redder than it would otherwise do.

This is similar to what happens to sound. Imagine that a fire engine is driving past you with its siren on. When it is moving towards you, the siren it quite high-pitched. When it is moving away from you, the pitch drops, and it sounds lower. With light, "lower" means more red and "higher" means more blue.