# BP2 achievements 2013-16: the Universe could survive the Big Bang

A team of physicists from NCBJ and France has proposed a method to take quantum effects into consideration when analysing evolution of the early Universe. The performed calculations [3] have suggested a possibility that the Bib Bang cosmological hypothesis might be replaced by a “Big Reflection” scenario. Observations of relic gravitational waves help to verify the proposed model.

Numerous alternative cosmological models (both classical physics-based and quantum physics-based ones) assume that the Universe existed before Big Bang. According to the theories, Big Bang just marked the transition from an earlier phase during which the Universe was contracting to the current phase during which it is expanding. Such scenario emerged also in the model currently investigated by a team of scientists from NCBJ Theoretic Physics Division in Warsaw working in cooperation with some colleagues in Paris. The scientists have assumed that the Space is a 3-D sphere. According to classical Einstein equations, such an Universe had to be born in a point-like singularity of infinite matter/energy density. On the other hand, should the Universe exist in some earlier (Space contracting) phase, then some geometry disturbances called gravitational waves were inevitable. Energy of the disturbances (“weight” of the waves) were so large that the Universe had to eventually collapse into a singularity.

The team has shown that quantum effects make viable the hypothesis that the now expanding Universe previously existed during some contracting phase [3]. Due to some formal similarity of the investigated cosmological model and the model of a molecule composed of restless electrons orbiting heavy nuclei, the scientists could use mathematical methods worked out earlier for atomic physics needs. It turned out that quantum effects decrease weight of gravitational waves so that the Space contracting phase could proceed less violently. Additionally, with decreasing volume of the Space, quantum repelling forces increased and eventually prevailed pressure exerted by gravitational waves. At that “reflection” moment cosmological contraction was suddenly replaced by the now observed cosmological expansion of the Universe. Authors believe that some unique traces of the proposed Big Reflection dynamics could be found in relic gravitational waves also these days.

Recently, quantisation of the space-time with the help of the so-called affine coherent states was applied for the first time in the world [3,4]. The obtained results have suggested that quantum gravitation is a theory without any singularity, therefore it can be useful in describing quantum phenomena specific for astrophysics and cosmology [1-4].

[1] J-P. Gazeau, J. Mielczarek and W. Piechocki, Phys. Rev. D 87, 123508 (2013).

[2] H. Bergeron, O. Hrycyna, P. Małkiewicz and W. Piechocki, Phys. Rev. D 90, 044041 (2014).

[3] H. Bergeron, E. Czuchry, J-P. Gazeau, P. Małkiewicz and W. Piechocki, Phys. Rev. D 92, 061302 (2015).

[4] H. Bergeron, E. Czuchry, J-P. Gazeau, P. Małkiewicz and W. Piechocki, Phys. Rev.D 92, 124018 (2015).