The Afterglow

The cosmic microwave background

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• The CMB is light released about 380,000 years after the Big Bang.
• It has cooled from about 3000 K to 2.725 K as the universe expanded 1100-fold.
• Its tiny ripples were the seeds of galaxies.

Steps

1. A glow from everywhere
2. Cooling with expansion
3. Where the glow peaks
4. Tiny ripples
5. Running the glow backwards
6. Photons everywhere