A glow undetectable to the human eye permeates the universe. This light is the remnant signature of the cosmic beginning — a dense, hot fireball that burst forth and created all mass, energy, and time. The primordial cosmic microwave background (CMB) radiation has since traveled some 13.8 billion years through the expanding cosmos to our telescopes on Earth and above it.
But the CMB isn’t just light. It holds within it an incredible wealth of knowledge that astronomers have been teasing out for the past few decades. “It’s the earliest view we have of the universe,” Princeton University cosmologist Joanna Dunkley previously explained to Astronomy. “And it gives us so much information because all the things that we now see out in space — the galaxies, the clusters of galaxies — the very earliest seeds of those, we see in this CMB light.”
Extracting these clues from the CMB has taken multiple generations of telescopes on the ground, lofted into the atmosphere, and launched into space. In the mid-1960s, when Arno Penzias and Robert Wilson discovered the CMB’s pervasive microwave static across the sky, it appeared identical everywhere. It would take satellites launched above Earth’s obscuring atmosphere to map that microwave glow to precisions on the order of millionths of a degree. Specifically, three satellites — COBE, WMAP, and Planck — revealed that our current cosmos, which is complex and filled with clusters of galaxies, stars, planets, and black holes, evolved from a surprisingly simple early universe.
In this week’s episode of Infinity & Beyond, host Abigail Bollenbach will walk you through the basics of the cosmic microwave background, the universe’s oldest baby picture.
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