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Gravitational wave, from the origin of the universe. Fractions of a second after the big bang has generated a gravitational wave, the shape of which was predicted by a new theoretical study. In the future, its existence could be detected by instruments. A split second after the big bang, the universe has issued gravitational wave that could reach up to us. This is asserted in an article on “Physical Review Letters” a group of theoretical physicists at the University of Basel, in Switzerland.

Gravitational waves jumped to the headlines in 2015, when they were detected for the first time by the joint research group of the two LIGO interferometers twins, which are located in the United States, and the European Group Virgo interferometer, located near Pisa (Italy). But for theoretical physicists are an old acquaintance. It is in fact ripples that cross the fabric of space-time already provided by the theory of Einstein’s general relativity, formulated in 1915. According to experts, these perturbations are produced by catastrophic events that occur in the cosmos, such as the merger of two blacks holes and supernova explosions.

An often overlooked fact is though that gravitational waves also provide valuable information on the formation of the universe. According to the model currently shared, shortly after the big bang, the universe was very small, dense and very high temperature. Suddenly, it underwent a rapid expansion called inflation, passing by dimensions billion times smaller than a proton to those of a soccer ball. In more precise terms, in the 10 -35 seconds of the universe he swelled by a factor of 10 to 30. To explain this process we resort to the hypothesis of inflaton, an elementary particle and a scalar field, ie a function that associates to each point of a numerical value space, as happens for example in the case of the temperature.

Beyond the technicalities, it is important to remember that the field of inflaton, like all quantum phenomena, was subject to fluctuations: the energy it stored underwent slight changes, and space appeared as well denser in some places than in others. The tiny ripples however were greatly expanded by inflation, producing gigantic structures, and finally galaxies.

Immediately after the end of the inflation process, the field of inflaton suffered considerable fluctuations, the width of which, however, was gradually decreasing, in part because the universe was expanding, in part because the energy, before totally associated with the field, was gradually transferred to the particles that were forming. These oscillations, also called oscillons, can be thought of as standing waves, such as those that run a rope fixed to the extremes. Although oscillons have ceased to exist since then, the waves emitted are ubiquitous, and we can use them to look back into the past as it had never been done so far. Using numerical simulations, cosmologists have been able to calculate the shape of the oscillon signal, emitted only a fraction after the big bang: it appears as a pronounced peak with respect to a wide spectrum of gravitational waves.

Before our calculations, we never thought that oscillons could produce such a strong signal at a specific frequency. Through this work, the experimental physicists in the future will try the tools the existence of this signal.



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Gravitational wave, from the origin of the universe.