How the Universe was born: scientists calculate the first moment after the Big Bang

A group of scientists from Italy was able to accurately describe the behavior of quark-gluon plasma in the first moments after the Big Bang and the formation of the Universe.

Scientists note, that the state of the quark-gluon plasma in the the very first moments of the Universe lasted only a few microseconds. After that, the Universe began to cool. At this stage, quarks and gluons combined into baryons, such as protons and neutrons. At the same time, there was an asymmetric formation of both matter, which prevailed, and antimatter, which mutually annihilated, turning into electromagnetic radiation.

For many decades, physicists have been trying to accurately describe the state of quark-gluon plasma, but the problem is that the strong nuclear interaction that binds quarks to each other is too complex to be described by traditional mathematical tools.

A group of researchers from Italy nevertheless managed to calculate the equations of state of this quark-gluon plasma in detail. They calculated the relationship between temperature, pressure, and energy in this plasma. The key problem was the strong nuclear interaction, which behaves abnormally and unpredictably under conditions corresponding to the state of the first moments of the Universe.

The perturbation theory, which calculates interactions step by step using Feynman diagrams, does not work in this case because the coupling constant of the strong interaction between particles is not small. This means that higher-order corrections are not reduced and the mathematical apparatus becomes uncontrollable. 

To solve this problem, a group of researchers used the method of quantum chromodynamics on a latticethis is quantum chromodynamics formulated on a discrete Euclidean spacetime lattice.. It can be imagined as a four-dimensional chessboard representing spacetime. There are particles on each of its squares, and the interaction between them can be calculated step by step.

But even this method has limitations. Preliminary results of lattice quantum chromodynamics simulations have demonstrated the ability to reach plasma temperatures below one gigaelectron volts, which is much lower of an electrically weak phase transition (about 100 GeV) at the moment when the particles gained mass. 

Thus, the researchers decided to combine lattice quantum chromodynamics with Monte Carlo simulations — a method that uses random sampling to solve complex problems. They focused on a simplified version of the Universe filled with three types of nearly massless quarks. This means that even if the quarks have tiny rest masses (less than 500 MeV/c²), at extremely high temperatures (several GeV) these masses are negligible compared to their total energy.

This accurately simulates the conditions during the first few milliseconds after the Big Bang. They then performed calculations over a wide range of temperatures, from three GeV to 165 GeV, before the electroweak transition. This allowed them to create a mathematical formula describing the entropy density of the quark-gluon plasma.

The scientists managed to discover an interesting thing: even at very high temperatures, quarks and gluons in the plasma did not behave like free particles. The strong interaction still dominated and began to play a key role in the formation of the Universe much earlier than physicists had expected.

The Universe will disappear much earlier than thought — scientists have clarified when