Stefan-Boltzmann law

This Is How We Know The Cosmic Microwave Background Comes From The Big Bang

If all you see is low-energy light in a myriad of directions, you can’t be sure. But this light comes from the Big Bang.

Ethan Siegel

There are a lot of things that generate an observable signal in the Universe. Astronomically, the primary way we search for those signals is through some form of light. Either the physical phenomenon we’re trying to learn about generates some form of light, which we collect with a telescope or other instrument, or it absorbs light, which means there’s a gap in an otherwise predictable background signal./.../