THE first lights in the sky of the early universe didn’t switch on suddenly. Instead, the brightening of the cosmos was much more tentative, unfolding gradually or perhaps in successive waves, according to scientists studying the light from distant quasars. The discovery is “quite surprising”, says Abraham Loeb, one of the scientists who reached the conclusion.
When the heat of the big bang subsided, the primordial plasma of ions and electrons cooled enough to form clouds of hydrogen and helium atoms that absorbed ultraviolet light. During the subsequent era, dubbed the “cosmic dark ages”, the glow from the hot primordial…
