Physicists have simulated the primitive quantum structure of our universe

Long enough peer in the sky, and the universe begins to resemble a city at night. Galaxies take on the characteristics of streetlights crammed into neighborhoods of dark matter, linked to highways of gas that run along the shores of intergalactic nothingness.

This map of the universe was predetermined, drawn up in the tiniest moments of shivers in quantum physics after the Big Bang set off an expansion in space and time about 13.8 billion years ago.

However, what exactly those fluctuations were, and how they set in motion the physics that would see atoms assemble into the massive cosmic structures we see today are still far from clear.

A recent mathematical analysis of moments after a period called the inflationary age reveals that some kind of structure may have even existed within the raging quantum furnace that filled the infant universe, and could help us better understand its layout today.

Astrophysicists from the University of Göttingen in Germany and the University of Auckland in New Zealand used a combination of particle motion simulations and some sort of gravity/quantum modeling to predict how structures would form in particle condensation after inflation occurred.

The scale of this type of modeling is a little astounding. We’re talking about 20-kilogram masses crammed into a space of barely 10 .-20 meters, at a time when the universe was only 10 meters wide-24 seconds.

“The physical space represented by our simulation would fit a single proton over a million times,” said astrophysicist Jens Niemeyer of the University of Göttingen.

“This is probably the largest simulation that has been made to date of the smallest region of the universe.”

Most of what we know about this early stage of the universe’s existence is based solely on this kind of mathematical espionage. The oldest light we can still see swaying through the universe is the cosmic background radiation (CMB), and the entire show had already started about 300,000 years ago by then.

But within this faint echo of ancient radiation, there are some clues as to what was going on.

CMB light was emitted as fundamental particles embedded in atoms of a hot, dense energy soup, in what is known as the Recombination Era.

A map of the background radiation across the sky shows that our universe already had some kind of structure a few hundred thousand years old. There were slightly cooler bits and slightly warmer bits that might push matter into regions that would eventually see stars flaring up, galaxies rising up, and clumps gathering in the cosmic city we see today.

This begs a question.

The space that our universe is made of is expanding, which means that the universe was once a lot smaller. So it stands to reason that everything we see around us now was once packed into a volume too confined to have such warm and cold spots appearing.

Like a cup of coffee in the oven, there was no way for any part to cool down before it got hot again.

The inflationary period has been suggested as a way to fix this problem. Within a trillionth of a second after the Big Bang, our universe had jumped in size by an insane amount, essentially freezing any quantum-scale changes in place.

To say that this happened in the blink of an eye is still unfair. It was going to start around ten o’clock36 Seconds after the Big Bang, and it ended with 10 seconds32 Seconds. But it was long enough for the space to gravitate into proportions that prevented slight differences in temperature from fading out again.

The researchers’ calculations focus on this brief moment after inflation, illustrating how elementary particles that freeze from the foam of quantum ripples at that time can generate short halos of matter dense enough to wrinkle spacetime itself.

“The formation of such structures, as well as their motions and interactions, must have created background noise for gravitational waves,” said Benedikt Egmaier, an astrophysicist at the University of Göttingen, first author of the study.

“With the help of our simulations, we can calculate the strength of this gravitational wave signal, which may be measurable in the future.”

In some cases, the intense masses of such objects can pull matter into primordial black holes, objects presumed to contribute to the mysterious clouds of dark matter.

The fact that the behavior of these structures mimics the large-scale agglomeration of our universe today does not necessarily mean that it is directly responsible for the distribution of stars, gas, and galaxies today.

But the complex physics unfolding among those freshly baked particles may still be visible in the sky, among those rolling landscapes of twinkling lights and dark voids we call the universe.

This research was published in physical review d.

A version of this article was first published in March 2021.

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