No one can say for sure what exactly happened before, during and after the Big Bang. However, measurements of cosmic background radiation show that in its first phase of life, the universe went through a short period of strong, exponential growth, or cosmic inflation. After inflation, the universe was cold and empty. But for the Big Bang to take place, the universe needed high temperatures and lots of energy.
It’s still a puzzle how this phase of reheating and mass increase of the universe could have taken place, but physicist Wilke van der Schee and his colleagues have now developed a new model that allows them to simulate this process. "We are one step closer to understanding the run-up to the Big Bang," says Van der Schee.
Black holes
The new model allows the researchers to calculate the temperature of the early universe (see image: the coloured area at the top) from the properties of a black hole’s horizon, or ’bulk horizon’ (see image: the grey shadow at the bottom). The colours in the model show that, after the period of inflation, the universe is cold and empty, and the temperature and amount of matter rise sharply in a short period of reheating. Then, thermalisation takes place where particles reach an equilibrium, and the universe cools down again.Collisions of lead ions
Van der Schee and his team based the model on a similar process of thermalisation, albeit on a much smaller scale. When lead ions collide with each other in Cern’s particle accelerator, for a brief period (10-23 seconds) quark-gluon plasma is formed. These collisions release an enormous amount of energy and generate big accelerations, mimicking the conditions present in the early universe. In their article, the researchers provide arguments, grounded in string theory, to support the notion that these collisions are like the formation of black holes. However, this comparison is contingent upon the assumption that such a black hole exists within an imaginary universe comprising five dimensions.The universe as a hologram
At the core of their model lies the principle of holography, a component of string theory. The holographic principle was initially conceived by the Utrecht theoretical physicist and Noble Prize laureate Gerard ’t Hooft in the 1990s. A distinctive characteristic of holograms is their ability to project all the information pertaining to a three-dimensional object onto a two-dimensional surface.Without the principle of holography, which facilitates a connection between two realities of differing dimensions, our calculations would be impossible
Wilke van der Schee
When applied to the scale of the universe, this principle implies that all information about the universe can be stored on its own edge (or shell), without requiring knowledge of the events happening on the inside. In other words, the edge of space provides a flat representation of the higher-dimensional interior. Consequently, when information about lead ion collisions is stored on a (imaginary) four-dimensional shell, assumptions about the five-dimensional realm within this phenomenon can also be made.
After performing computations utilising data from lead ion collisions, the research team discovered similarities to the processes occurring on the surface of a five-dimensional black hole. Through their calculations, the scientists effectively demonstrate how the tiniest elementary particles can serve as models for the largest and most massive entities in the universe, effectively bridging the realms of string theory and quantum physics.
