The Cosmic Microwave Background (CMB) is a form of electromagnetic radiation dating from an early stage of the Universe. It is the oldest known form of electromagnetic radiation. With a traditional optical telescope, the space between stars and galaxies is completely dark but a sufficiently sensitive radio telescope reveals the CMB as a faint glow not associated with any star, galaxy, or other objects.
- The glow of the cosmic microwave background is strongest in the microwave region of the electromagnetic spectrum.
- The CMB is an emission of uniform thermal energy coming from all parts of the sky. As a result, it is often described as being homogeneous and isotropic.
- The CMB is considered to provide demonstrable evidence for the Big Bang theory.
- The CMB appears in the microwave region of the spectrum today because the gamma waves emitted at the start have been stretched by the continuing expansion of the universe over time.