00:00There is light reaching Earth right now that has been travelling for 13.8 billion years.
00:06It left its source before the Earth existed, before the Sun existed, before any star existed.
00:12And what produced it will change how you understand the beginning of everything.
00:17This ancient light is called the Cosmic Microwave Background, the CMB.
00:22It was discovered accidentally in 1965 by two American radio astronomers, Arno Penzias and
00:29Robert Wilson, who noticed a persistent hiss in their radio antenna that would not go away
00:35no matter which direction they pointed it.
00:38That hiss was the oldest light in the observable universe, and the discovery earned them the
00:44Nobel Prize.
00:46Here is what produced it.
00:48In the first 380,000 years after the Big Bang, the universe was so hot and dense that atoms
00:56could not form, electrons were stripped from nuclei, and the universe was a plasma, an opaque
01:02fog of charged particles through which light could not travel.
01:06The universe was completely dark, despite being unimaginably hot.
01:11Then, 380,000 years after the Big Bang, the universe cooled just enough, to about 3,000
01:17degrees Celsius, for electrons to combine with nuclei and form neutral atoms for the first
01:23time.
01:23This moment is called recombination.
01:26The moment it happened, the universe became transparent.
01:30Light was released in every direction simultaneously, a flash that filled the entire universe.
01:37That light has been traveling ever since.
01:40In 13.8 billion years, it has been stretched by the expansion of the universe from visible
01:46light down to microwave radiation, which is why we call it the cosmic microwave background.
01:53It now bathes the entire universe uniformly from every direction.
01:58It is the afterglow of creation itself.
02:02When you look at the static on an old television, a small percentage of that noise is CMB radiation.
02:09Ancient light from the edge of the observable universe entering your living room.
02:13And what came before those 380,000 years?
02:18Darkness.
02:19The universe existed, expanding, evolving, filled with matter and energy, in complete darkness.
02:26No light could move, no star existed, nothing could be seen.
02:31The Quran says in Surah Al-Ambiyyar, Chapter 21, Verse 30, and I translate, Do they not see
02:38that the heavens and the earth were joined together and we split them apart?
02:42The moment of separation.
02:45The moment light was first released into a universe that had been sealed in darkness.
02:50The oldest light in existence is...
