- Astron. low-intensity, multidimensional microwave radiation present in space: its existence is used to support the validity of the big-bang theory since it is thought to be a remnant of the original explosion
- Physics low levels of natural radiation existing on earth as a result of high-energy cosmic rays, the radioactive decay of rock, etc.
background radiationbackground radiation
(plural background radiations)
- ionizing radiation that is naturally present in the environment.