We finally know more about what would have preceded the Big Bang

In the framework of the "pre-Big Bang" model, implying that the Big Bang is preceded by a first inflation, scientists theorize that the universe was formed in two stages. It would first spread rapidly from a dense mass of matter, then entered a phase of expansion more progressive but very energetic, commonly called "Big Bang". However, the way in which these two stages are related has long been misunderstood by researchers. As part of a new study of this period of the Universe and involving this initial theory, physicists finally think they have solved this mystery remained unanswered for decades, and suggest a way to explain the connection between these two eras primitive.

During the first primitive period, the Universe would have gone from a small dense mass of matter to nearly a half-million times (x 10 48 ) its size in less than a trillionth of a second (10 -12 s) . In the context of the pre-Big Bang model, this period of rapid inflation was followed by a more gradual but violent expansion phase, the Big Bang.

During the Big Bang, a "ball" of extremely hot matter composed of fundamental particles (protons, neutrons and electrons ) then developed and cooled to form the first atoms, stars and galaxies .

The standard Big Bang theory , which also describes cosmic inflation, remains the most widely supported explanation for the beginnings of our universe. However, scientists are still puzzled as to how these completely different expansion periods are nested.

To solve this mystery, a team of researchers from Kenyon College, the Massachusetts Institute of Technology (MIT) and the University of Leiden in the Netherlands, simulated the critical transition between cosmic inflation and the Big Bang as part of a pre-Big Bang model; a period called "reheat".

" The post-inflation warm-up period defines the conditions of the Big Bang and, in a sense, places the 'Bang' in the Big Bang,  " David Kaiser, a professor of physics at MIT , said in a statement . " It's a time of transfer, when hell is unleashed and the matter behaves in a complex way  ."

The history of the universe (standard model of the Big Bang). Above, inflation, which generates two types of waves: gravitational waves and density waves. Below, the radius of the visible Universe, from the Big Bang (t0), then the inflation (white / yellow), the formation of the protons, the beginning of the nuclear fusion, the end of the nuclear fusion (3 minutes), up to the 13.8 billion years that the Universe has today. Credits: DrBogdan / Yinweichen / Wikimedia

When the Universe developed into a "fraction of a second" during cosmic inflation, all existing matter spread out in all directions, leaving in space an empty, cold place, devoid of "soup." primordial "(dense and hot cluster of particles) necessary to start the Big Bang. During the warm-up period, it is thought that the energy that propelled inflation broke down into particles, said Rachel Nguyen, PhD student in physics at the University of Illinois and lead author of the study.

Once these particles are produced, they bounce off and bump into each other, transferring inertia and energy,  " Nguyen said. " And this is what thermises and warms the universe to define the initial conditions of the Big Bang  ".

In their model, Nguyen and his colleagues simulated the behavior of an exotic form of matter called inflaton. Scientists believe that the scalar field of this material, which is similar in nature to that of the Higgs boson, is responsible for creating the energy field that has led to cosmic inflation.

Their model showed that, under proper conditions, the hypothetical scalar field energy could be efficiently redistributed to create the diversity of particles needed to warm the primitive Universe. The results of the study are available in Physical Review Letters.

Gravity: it would react differently to very high energies

" When we study the primitive universe, we perform an experiment with particles at very high temperatures,  " said Tom Giblin, an associate professor of physics at Kenyon College in Ohio and co-author of the study. " The transition from the cold inflationary period to the warm period should contain essential evidence about the particles that actually exist at these extremely high energies."

A fundamental question that still afflicts physicists is how gravity behaves to the extreme energies present during inflation. Albert Einstein's theory of general relativity defines that all matter is affected by gravity in the same way, where the force of gravity is constant, regardless of the energy of the particle. However, because of the strange properties of quantum mechanics, scientists now think that at very high energies matter reacts differently to gravity.

The team incorporated this hypothesis into their model by modifying the interaction force of particles with gravity. They then discovered that the more they increased the force of gravity, the more the inflaton effectively transferred energy to produce the Hot Bang's field of hot material particles.

Additional clues needed to support the model

" The universe contains so many secrets, encoded in a very complex way  ," said Giblin. " It's our job to study the nature of reality by offering a 'decoding device' - a way to extract information from the universe. For this, we use simulations to predict what the universe should look like, so that we can actually begin to decode it. This warm-up period should have left an imprint somewhere. We just have to find it  . "

But identifying this footprint could prove to be a very complex task. Our first glimpse of the Universe is a "bubble of radiation" left a few hundred thousand years after the Big Bang: the cosmic microwave background (CMB). However, the CMB only evokes the state of the universe during the first critical seconds of its birth. Physicists hope that future observations of gravitational waves will provide the additional clues needed to support their model.


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