← Space Without Formulas: From the Moon to Black Holes
Lesson
Echo of the birth: the cosmic microwave background
Learn about the cosmic microwave background (CMB) — the oldest light in the universe — and understand why it is the best evidence for the Big Bang.
Light that is almost 14 billion years old
Cosmic microwave background
In its first moments, the universe was so hot that light couldn't travel freely — it kept colliding with particles, as if in a thick fog. About 380,000 years after the Big Bang, the universe cooled enough, the “fog” cleared — and light was finally able to set out.
This most ancient light is still traveling, from every direction. Over billions of years, the expansion of the universe has stretched it and “cooled” it — it is no longer visible light but faint, very cold microwaves. It is called the cosmic microwave background, or CMB. It is literally the afterglow of the Big Bang, its echo.
Scientists picked it up by accident in 1965 as a puzzling “noise” in an antenna that they just couldn't get rid of — and won a Nobel Prize for it. By the way, a small share of the “snow” (static) on an old analog TV with no signal comes from the cosmic microwave background, too.
Maps of the CMB show tiny temperature fluctuations. These minuscule irregularities are the seeds of future galaxies: where there was a little more matter, gravity over time gathered the first stars and galaxies.
Lesson notes
Cosmic microwave background
In its first moments, the universe was so hot that light couldn't travel freely — it kept colliding with particles, as if in a thick fog. About 380,000 years after the Big Bang, the universe cooled enough, the “fog” cleared — and light was finally able to set out.
This most ancient light is still traveling, from every direction. Over billions of years, the expansion of the universe has stretched it and “cooled” it — it is no longer visible light but faint, very cold microwaves. It is called the cosmic microwave background, or CMB. It is literally the afterglow of the Big Bang, its echo.
Scientists picked it up by accident in 1965 as a puzzling “noise” in an antenna that they just couldn't get rid of — and won a Nobel Prize for it. By the way, a small share of the “snow” (static) on an old analog TV with no signal comes from the cosmic microwave background, too.
Maps of the CMB show tiny temperature fluctuations. These minuscule irregularities are the seeds of future galaxies: where there was a little more matter, gravity over time gathered the first stars and galaxies.