Revise GCSE Physics

Question:What is meant by Cosmic Microwave Background Radiation?

The universe has been found to be full of microwave radiation, corresponding to a temperature of about 3 degrees above the coldest temperture that is possible (called absolute zero).

This is called the 'Cosmic Microwave Background Radiation' and it is a key piece of evidence supporting the Big Bang Theory.

Basically, if the Universe used to be very small and hot, and then cooled as it expanded, there should be some small amount of energy everywhere left over from this early time.