The universe is permeated by a universal light. Don't worry, it's not getting esoteric here, and I'm not talking about the cosmic microwave background. It is about a completely different part of the spectrum, on the other side, the ultraviolet range. The so-called Lyman-alpha ultraviolet background was first discovered in the 1960s; its existence was confirmed in 1971. It is formed when light particles of a certain frequency (an excitation frequency of hydrogen) are scattered by neutral hydrogen atoms. Such photons emanate from the Sun in large numbers in the solar system. The light particles are invisible to the eye…