Which universe-scale observation is the oldest light we can still detect?
Quick Answer
The oldest light we can detect is the cosmic microwave background, released about 380,000 years after the Big Bang. It is the afterglow of the early universe, now cooled to just 2.7 K.
The Full Story
The cosmic microwave background, or CMB, is the oldest electromagnetic radiation we can observe. It was emitted when the universe cooled enough for protons and electrons to combine into neutral atoms, about 380,000 years after the Big Bang. Today that radiation fills all of space and has cooled to about 2.7 kelvin. Measurements of the CMB by missions such as COBE, WMAP, and Planck have transformed cosmology by revealing the age, composition, and geometry of the universe.
Key Facts
YouTube Angle
Suggested video title for this topic:
"We can still see the baby photo of the universe itself."