Why were galaxies so active in the early universe? We may be getting close to the answer

In its infancy, the universe had a bit of an identity crisis. For the first few hundred million years, the vast cosmic gas between galaxies was primarily a chilly, dense affair. But then, it seemed to wake up, deciding to get all warm and fuzzy. This strange shift in the cosmos’ early disposition is a crucial clue to how the very first galaxies burst into being, shaping everything we see today. …