14 billion years ago, according to the Big Bang model, our Universe began to expand at very high speeds. A new study at the University of Copenhagen explains what happened during the Universe’s first microsecond by studying a specific type of plasma.
The Quark Soup
You Zhou, associate professor at the Niels Bohr Institute at the University of Copenhagen, and his team have studied a particular substance called Plasma Quark-Gluon (or QGP), the only ‘matter’ that existed during the first microsecond of the Big Bang.
The quarks are elementary particles that are fundamental constituents of matter; there are six types and they are subdivided according to different flavours (i.e. a set of quantum numbers or symmetry): up, down, strange, charm, bottom and top. The gluon, on the other hand, is an elementary particle that acts as an exchange particle in the strong interaction between quarks; in this respect there is a strong analogy with the exchange of photons in the electromagnetic interaction between two charged particles. Simply put, gluons ‘glue’ quarks together, forming hadrons, like protons and neutrons.
Firstly, it has been discovered that Plasma Quark-Gluon was present in the first 0.000001 seconds of the Big Bang and was separated by the hot and very fast expansion of the Universe, so the quark chunks were ‘transformed’ into hadrons. A hadron with three quarks forms a proton, a fundamental building block in the structure of atomic nuclei and everything around us.
Thanks to the use of CERN’s Large Hadron Collider, researchers have been able to recreate the story of what happened. But how exactly does a collider tell us so much? The job of the collider is to destroy plasma ions at ultrarelativistic speeds, i.e. close to the speed of light. By doing this, scientists are able to understand how QGP evolved into the building blocks of life.
An incredible breakthrough, besides the use of the collider, is the development of an algorithm that can analyse the expansion in a set of particles. This showed us that the Plasma Quark-Gluon was in a liquid form that changed its shape over time, and not in the form of a gas, as had long been thought.
“It took 20 years to discover that Plasma Quark-Gluon flowed before it turned into hadrons. Therefore, our new knowledge about the evolving behaviour of plasma is an important step forward for us,’ concludes You Zhou.