At the Edge of Time: Exploring the Mysteries of Our Universe’s First Seconds (Science Essentials Book 32)

by Dan Hooper

During the formation of the cosmic microwave background—about 380,000 years after the Big Bang—each point in space was surrounded by a horizon about a million light years in radius. From our vantage point today, a region of space this size appears to be about one degree in diameter. This means that the background of microwave radiation that we observe across our sky does not originate from one causally connected region, but from many thousands of independent regions that had absolutely no way of influencing each other. But without any way to interact with each other, how did these regions come to have temperatures that are so nearly identical? To return to my earlier analogy, it is as if we found a collection of thousands of nearly perfectly synchronized stopwatches, with no explanation for how they came to be that way in the first place.