decoupling eraSee Big Bang theory.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006
decoupling era[dē′kəp·liŋ ‚ir·ə]
The time about 300,000 years after the big bang when matter and radiation, which had previously been strongly coupled, practically ceased to interact, electrons were able to attach to nuclei and form atoms, and photons could propagate freely.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.