The Cosmos Was Alive With the Sound of Matter
When the universe speaks, astronomers listen.
When it sings, they swoon.
That’s roughly what happened late last month when a group of astronomers led by Caltech’s Andrew Lange published the most detailed analysis yet of the cosmos’ primordial song: a low hum, deep in its throat, that preceded both atoms and stars.
It is a simple sound, like the mantra “Om.” But hidden within its harmonics are details of the universe’s shape, composition and birth. So rich are these details that within hours of the paper’s publication, new interpretations of the data had already appeared on the Los Alamos web for new astrophysical papers.
“It’s stirred up a hornet’s nest of interest,” said UCLA astronomer Ned Wright, who gave a talk to his colleagues on the paper the next week.
So what is all the fuss about? Why are astronomers churning out paper after paper on what looks to a lay person like a puzzling set of wiggly peaks--graphic depictions of the sound, based on hours of computer analysis?
Because there’s scientific gold in them there sinusoidal hills.
The peaks and valleys paint a visual picture of the sound the newborn universe made when it was still wet behind the ears, a mere 300,000 years after its birth in a big bang. Nothing existed but pure light, speckled with occasional subatomic particles.
Nothing happened, either, except that this light and matter fluid, as physicists call it, sloshed in and out of gravity wells, compressing the liquid in some places and spreading it out in others. Like banging on the head of a drum, the compression of the “liquid light” as it fell into gravity wells set up the “sound waves” that cosmologist Charles Lineweaver calls “the oldest music in the universe.”
Then, suddenly, the sound fell silent. The universe had gotten cold enough that the particles, in effect, congealed, like the salad dressing left in the fridge; the light separated and escaped, like the oil on top.
The rest is the history of the universe: The particles joined each other to form atoms, stars and everything else, including people.
“The universe was very simple back then,” said Lange. “After that, we have atoms, chemistry, economics. Things go downhill very quickly.”
As for the light, or radiation, it still pervades all space. In fact, it’s part of the familiar “snow” that sometimes shows up on broadcast TV. But it’s more than just noise: When the particles congealed, they left an imprint on the light.
Like children going after cookies, the patterns of sloshing particles left their sticky fingerprints all over the sky.
The pattern of the sloshes tells you all you need to know about the very early universe: It’s shape, how much was made of matter, how much of something else.
The principle is familiar: Your child’s voice sounds like no one else’s because the resonant cavities within her throat create a unique voiceprint. The large, heavy wood of the cello creates a mellower sound than the high-strung violin. Just so, the sounds coming from the early universe depend directly on the density of matter, and the shape of the cosmos itself.
Astronomers can’t hear the sounds, of course. But they can read them on the walls of the universe like notes on a page. Compressed sound gets hot, and produces hot splotches, like a pressure cooker. Expanded areas cool. Analyze the hot and cold patches and you get a picture of the sound: exactly how much falls on middle C, or B flat.
What they’ve seen so far is both exciting and troubling. The sound suggests that the universe is a tad too heavy with ordinary matter to agree with standard cosmological theories; it resonates more like an oboe than a flute. Something’s going on that can’t be explained. The answers may come when an even more ambitious probe launches into space later this year.
Lest you think these sounds are music only for astronomers’ ears, consider: The same wrinkles in space that created the gravity wells that gave rise to the sounds also blew up to form clusters, galaxies, stars, planets, us.
Even Hare Krishnas murmuring: Om.