Electromagnetic radiation is (packets/quanta) or waves of energy that propagates throughout the universe. Some of the most distant radiation we can detect is that of the Cosmic Microwave Background Radiation (CMBR). It is leftover heat from the The Big Bang that is red shifting away from us via to the expansion of the universe. It appears to be largely uniform and random. Several surveys have been performed of the CMBR and can be found online.