Secrets of the Cosmic Microwave Background

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College football is back, so Hilton called on me, the superstition concierge, to make your fan rituals a reality.

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Need a room to match your lucky number?

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We got you.

SPEAKER_2 (0:09)

Wanna make sure our team doesn't wash your lucky jersey?

SPEAKER_1 (0:12)

Ooh, that smells lucky.

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Hilton's unmatched hospitality can keep up with any superstition. Even a marching band wake up call at 555 in 55 seconds. Hit it! When you need a team that will do whatever it takes on game day, it matters where you stay.

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Hilton, for the stay.

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Matt O'Dowd (1:00)

Thanks to CuriosityStream for supporting PBS Digital Studios. Hook up an old analog antenna to your TV and scan between the channels. That static buzz you hear is mostly due to the ambient radio produced by our noisy pre-galactic civilization.

But around 1% of that buzz is something very different. It's the cosmic microwave background radiation, the remnants of the heat glow released when the hot dense early universe became transparent for the first time.

It sounds like random static, but that buzz contains an incredible wealth of hidden information. It holds the secrets to the composition of the universe and allows us to peer into its fiery beginning.

It's not surprising that scientists have spent half a century and built multiple satellites to unlock the mysteries of the cosmic microwave background. We've delved into its nature before, from its formation 380,000 years after the Big Bang, to its 1964 discovery by Penzias and Wilson with the Holmdel Horn Antenna, to its incredibly accurate mapping across the sky with ever better satellites. It all culminated in this, the Planck satellites map of the CMB. Those blotches are tiny differences in temperature, deviations of one part in 10,000 from the average temperature of only 2.7 Kelvin. Those differences result from tiny variations in the density of matter right after the Big Bang, which evolved as colossal sound waves reverberated through the first few hundred thousand years of the universe's life. We explored these baryon acoustic oscillations in last week's episode, and that's really worth watching first if you haven't yet. That episode painted a simplistic picture, a quick review. In the very beginning, dark matter flowed towards tiny regions of increased density drawn by gravity. Regular matter, what we call baryons, was in plasma form, with the simple atomic nuclei stripped of their electrons in that extreme heat.

In this plasma state, light and matter were locked together. As the baryons compressed into overdense regions, this led to a massive buildup of pressure. Collapsing baryons rebounded, producing an expanding sound wave. That expanding shell was eventually frozen in place 380,000 years later, when light decoupled from matter at the formation of the first atoms, the moment of recombination. As the universe evolved, those frozen shells collapsed into galaxies. We still see them today, interwoven patterns of rings drawn in galaxies on the sky. But those rings are not the whole story. Today we are going to explore the intricate patterning, not of the galaxies, but of the cosmic microwave background map, the image of the hot universe at the moment of recombination. We will see that the complex dynamics of the early universe are frozen into its spots.

That patterning will tell us exactly what the universe is made of. As I said, this picture of a single expanding shell of plasma is simplistic. In reality, these acoustic waves pulsed in and out of their overdense regions. They oscillated, and the number of oscillations depended on how large that overdensity was. In some places, the overdensities were so large that matter only just had time to float at the center before being frozen in place by recombination. No rebounding happened. And in other places, the overdensities were smaller. The density wave had time to flow in, reverberate out, and then get captured by the gravitational field once more, falling back to the center. College football is back.

SPEAKER_2 (5:02)

So Hilton called on me, the superstition concierge, to make your fan rituals a reality. Need a room to match your lucky number?

SPEAKER_1 (5:08)

We got you.

SPEAKER_2 (5:09)

Wanna make sure our team doesn't wash your lucky jersey?