What happened after the Big Bang?
~700,000 years later: T ~ 104 K
- Neutral atoms can form by electrons binding to nuclei
- Photons “freed” because they do not interact strongly with neutral atoms
Universe continues to cool until now
- Galaxies, stars, planets, . . . . form
The radiation (photons) cool and is now observed as the “3 degree background”
- Observed at Bell Labs in 1964 as “extra noise” in antennas
- Interpreted as radiation pervading all space about the same in all directions
- Not due to galaxies or stars
- A remnant of BIG BANG! The radiation which has cooled to the present temperature of 3 K