🌈 THE COSMIC MICROWAVE BACKGROUND
PAGE 1 OF 5 — THE OLDEST LIGHT
380,000 YEARS AFTER THE BIG BANG
THE UNIVERSE SENDS ITS FIRST LIGHT
For 380,000 years after the Big Bang, the universe was a hot, opaque fog of plasma. Light could not travel freely. Then, as the universe cooled to around 3,000 degrees, electrons combined with protons to form neutral hydrogen atoms. In an instant, the fog cleared. Light streamed freely across the cosmos for the very first time. That light is still travelling today, filling every corner of the universe.
🌡️ HOW COLD IS IT NOW?
The CMB has cooled from 3,000 degrees to just 2.725 degrees above absolute zero as the universe expanded over 13.8 billion years. It is the coldest and most uniform light source ever measured.
FREEDOM!
THE PLASMA FOG
🌉 Hot plasma was opaque: light bounced off free electrons
⌛ This opaque era lasted 380,000 years
⛔ No light could escape or travel in any direction
⌛ This opaque era lasted 380,000 years
⛔ No light could escape or travel in any direction
RECOMBINATION
☀️ Electrons and protons unite: neutral atoms form
🌅 The fog clears in an instant across the entire universe
📡 Light flies freely for the first time in cosmic history
🌅 The fog clears in an instant across the entire universe
📡 Light flies freely for the first time in cosmic history