# How is the formation of the first atoms related to the cosmic microwave background? [duplicate]

Common atoms formed when the universe finally got cool enough for electrons to bind with atomic nuclei around the year 380,000. From what I understand this shift in state from plasma to discrete atoms allowed light to escape.

How does this event relate to the baby pictures that we have of the universe?

Is this the same light that escaped? Does that mean the light was all in the microwave spectrum?

If so, how is it that we can still detect it today?

• baby pictures meaning CMB? That's the light that escaped – Jim Feb 25 '15 at 21:01
• so the light that escaped was microwave light? – Luke Feb 25 '15 at 21:03
• no. cosmic expansion has redshifted the light to the microwave range – Jim Feb 25 '15 at 21:03
• Does the universe expand faster than the speed of light? I am wondering how the light could not have hit and interacted with "the edge" of the universe – Luke Feb 25 '15 at 21:23
• two things are wrong with that question. First and foremost, there is no edge just as there is no center. Second, the expansion of the universe happens at all points in it, not just the edges. It expands at a rate of $67(km/s)/Mpc$, which you can interpret as for every Megaparsec something is away from us, the universe will expand so that there is an additional $67km$ in between us every second. So if you go far enough away, the universe is expanding faster than light speed, but close by it is slower – Jim Feb 25 '15 at 21:31