The beginning of the universe--2/26/25

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Today's selection--from Things That Go Bump in the Universe by C. Renée James.  In a fraction of a second, the universe is born:

“‘Let's go right back to the beginning of the universe,’ [astronomer] Tamara Davis began, and then she took me back to a time when the entire universe­ the entire universe—was denser than the unfathomably dense interior of a neutron star and hotter than the hottest stellar interior.

“Somewhere between birth and a hundred millionth of a trillionth of a trillionth of a second later (0.00000000000000000000000000 000001, or 10–32, seconds), our universe ballooned to trillions upon trillions of times its original size, stretching the fabric of spacetime so tightly that random variations that existed before then were almost completely smoothed over. Almost.

“Some pockets of the universe ended up with densities that were ever so slightly greater than their surroundings, creating the shal­lowest of valleys in spacetime. If the universe were a trampoline one meter off the ground, these early depressions would have been less than a millimeter deep. There was no rhyme or reason to them, just as there is no rhyme or reason to the popularity of some internet memes over others, but their presence created the scaffolding of the material universe.

“Into those initial shallow depressions flowed gravitating matter. Mixed into this dense cauldron of electrons, protons, and neutrons—­the latter two collectively known as baryons—was light, bouncing from charged particle to charged particle and pushing at them as it tried to find some escape from this claustrophobic nightmare. As the matter jostled toward the centers of the gravitational valleys like eager concertgoers toward a stage, the photons pushed back and created compression waves that swept outward from the dips at the speed of sound. But these were not sound waves in air, a cold, empty medium that propels the waves along at a snail's pace of 343 meters per second. This was an unimaginably hot and dense fluid of photons and particles, a place where acoustic waves could travel at upward of 70 million meters per second, or nearly 60% of the speed of light, far faster than the supersonic shock wave racing out of the interior of an exploding star.

The Hubble Ultra-Deep Field image shows some of the most remote galaxies visible to present technology

“Which brings us back to the tiny variations in the inflating universal balloon. Complicating the early situation was the presence of dark matter, a substance that makes up over 80% of the gravitating matter in the universe, but that astronomers have yet to put their theoretical fingers on. What we do know is that dark matter doesn't interact with light, so while the baryons and photons were pushing each other around, dark matter continued sliding unobtrusively into the small pits in spacetime, making those pits bigger. Once ensconced, the dark matter tried to coax the massive baryons toward it, but the light continued to fight back. Wave after wave of baryons fell inward, only to be pushed outward by the multidimensional snowplow of photons.

“Meanwhile, the universe continued to expand. Baryons continued trying to fall into the dark matter clumps, and light snowplowed them away. Around the 380,000-year mark, something new happened. The conditions in the rapidly expanding and cooling universe allowed the first atoms to form as electrons and nuclei came together in an event known as ‘recombination,’ although most astronomers agree that it should simply be ‘combination.’ Because neutral atoms are largely immune to light's push, the photons were finally released from captivity and for the most part have never been bothered by matter since. In fact, this freed light has stretched with the expanding universe and now fills up the entire sky. It is known as the ‘cosmic microwave background,' one of the most compelling pieces of evidence for the big bang theory. Without the perpetual push of the snowplows, a pileup of snow (read: baryons) was left at a very specific distance away from that central dark matter concentration. It is called the ‘sound horizon.’

“Since the late 1960s, cosmologists have known there should be a greater concentration of matter at the last point of contact between photons and baryons, just as there should be a central peak where the dark matter set up shop in the shallow dents. In some respects, it would look very much like the snapshot of a pond just after a pebble was thrown in. There would be a central uplift and a ring whose radius was determined by the time the wave had traveled and the wave's speed, which was dependent on the conditions of the fluid.

“In a convenient universe, there would be only a single pebble dropped into the pond. In the real universe, though, things are much messier.

“‘It's like a whole bunch of pebbles were thrown at all different times into the pond,’ Davis explained, pulling up an animation to illustrate the point. ‘As a result, you get all these overlapping patterns out of it.' The outcome was a cacophony of interfering waves whose patterns became imprinted on both the material universe and the dis­tribution of light itself."

author:	C. Renée James
title:	Things That Go Bump in the Universe: How Astronomers Decode Cosmic Chaos
publisher:	Johns Hopkins University Press
pages:	237-239