Look long enough at the skies, and the Universe begins to resemble a city at night. Galaxies take on the characteristics of streetlights crowding neighborhoods of dark matter, linked by highways of gas that run along the shores of intergalactic nothingness.
This map of the Universe was preordained, drawn in the smallest of quantum physics chills moments after the big Bang launched into an expanse of space and time about 13.8 billion years ago.
Exactly what those fluctuations were, though, and how they set in motion the physics that would cause atoms to stack up into the massive cosmic structures we see today, is still far from clear.
A recent mathematical analysis of the moments after a period called inflationary epoch it reveals that some kind of structure could have existed even within the seething quantum furnace that filled the infant Universe, and could help us better understand its current design.
Astrophysicists at the University of Göttingen in Germany and the University of Auckland in New Zealand used a mix of particle motion simulations and a kind of gravity/quantum modeling to predict how structures might form in the condensation of particles after inflation occurred.
The scale of this type of modeling is a bit mind-boggling. We are talking about masses of up to 20 kilograms compressed in a space of just 10-twenty meters wide, at a time when the Universe was only 10-24 seconds old.
“The physical space represented by our simulation would fit into a single proton a million times.” said astrophysicist Jens Niemeyer of the University of Göttingen.
“It is probably the largest simulation of the smallest area of ​​the Universe that has been carried out so far.”
Most of what we know about this early stage of the Universe’s existence is based on precisely this kind of mathematical research. The oldest light we can still see flickering through the Universe is the Cosmic Background Radiation (CMB), and by then the whole show had already been on for about 300,000 years.
But within that faint echo of ancient radiation are some clues as to what was going on.
Light from the CMB was emitted as basic particles combined into atoms from the hot, dense soup of energy, in what is known as the recombination epoch.
A map of this background radiation across the sky shows that our Universe already had some kind of structure by a few hundred thousand years of age. There were slightly cooler parts and slightly warmer parts that could push matter into areas that would eventually see stars ignite, spiral galaxies, and mass accrete into the cosmic city we see today.
This raises a question.
The space that makes up our Universe is expanding, which means that the Universe once must have been much smaller. So it stands to reason that everything we see around us now was once crammed into too confined a volume for those hot and cold patches to emerge.
Like a cup of coffee in an oven, there was no way for any part to cool down before heating up again.
The inflationary period was proposed as a way to solve this problem. Within trillionths of a second of the Big Bang, our Universe jumped in size by an incredible amount, essentially freezing any quantum scale variation in place.
To say that this happened in the blink of an eye still wouldn’t do it justice. would have started around 1036 seconds after the Big Bang, and ended at 1032 seconds. But it was enough for the space to acquire proportions that prevented the small variations in temperature from smoothing out again.
The researchers’ calculations focus on this brief instant after inflation, showing how elementary particles that froze from the foam of quantum waves at that time could have generated brief halos of matter dense enough to crinkle the sky. own space-time.
“The formation of such structures, as well as their motions and interactions, must have generated gravitational wave background noise.” said University of Göttingen astrophysicist Benedikt Eggemeier, first author of the study.
“With the help of our simulations, we can calculate the strength of this gravitational wave signal, which could be measurable in the future.
In some cases, the intense masses of such objects could have drawn matter into primordial black holes, objects that are hypothesized to contribute to the mysterious attraction of black holes. dark matter.
The fact that the behavior of these structures mimics the large-scale clustering of our Universe today does not necessarily mean that it is directly responsible for the current distribution of stars, gas, and galaxies.
But the complex physics going on between those freshly baked particles could still be visible in the sky, among that undulating landscape of flickering 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.