Noncorporeal life is hypothetical life that exists without material bodies. The idea has been extensively explored in science fiction (see Childhood's End) but, from the viewpoint of science itself, the concept of life based on "pure energy," such as electromagnetic radiation, poses significant difficulties. A being made only of photons, for example, could not move slower than the speed of light and would essentially exist outside of the normal time stream of the rest of the universe. Artificial life represents a possible alternative form of noncorporeal life with a basis in information.