The global dynamics of a homogeneous universe in Loop Quantum Cosmology is viewed as a scattering process of its geometrodynamical equivalent. This picture is applied to build a flexible (easy to generalize) and not restricted just to exactly solvable models method of verifying the preservation of the semiclassicality through the bounce. The devised method is next applied to two simple examples: (i) the isotropic Friedman Robertson Walker universe, and (ii) the isotropic sector of the Bianchi I model. For both of them we show, that the dispersions in the logarithm of the volume ln(v) and scalar field momentum ln(p_phi) in the distant future and past are related via strong triangle inequalities. This implies in particular a strict preservation of the semiclassicality (in considered degrees of freedom) in both the cases (i) and (ii). Derived inequalities are general: valid for all the physical states within the considered models.
We provide a quantum picture for the emergence of a bouncing cosmology, according to the idea that a semiclassical behavior of the Universe towards the singularity is not available in many relevant Minisuperspace models. In particular, we study the Bianchi I model in vacuum adopting the isotropic Misner variable as an internal clock for the quantum evolution. The isomorphism between the Wheeler-DeWitt equation in this Minisuperspace representation and the Klein-Gordon one for a relativistic scalar field allows to identify the positive and negative frequency solutions as associated to the colla…
We argue that standard tools of holography can be used to describe fully non-perturbative microscopic models of cosmology in which a period of accelerated expansion may result from the positive potential energy of time-dependent scalar fields evolving towards a region with negative potential. In these models, the fundamental cosmological constant is negative, and the universe eventually recollapses in a time-reversal symmetric way. The microscopic description naturally selects a special state for the cosmology. In this framework, physics in the cosmological spacetime is dual to the vacuum phys…
Exactly one hundred years ago, in May 1922, Alexander Friedmann discovered that General Relativity (GR) predicts non-stationary Universe. His equation describing the evolution of the Universe is now named after him. In this paper we briefly recall the human and scientific aspects of this revolutionary change in our picture of the world. We also recall that immediately after finishing his seminal paper Friedmann wrote a book on GR for a wide audience. In that book he presented an impressive picture of the expanding Universe created from nothing.
Recently, Wang with Stankiewicz (Phys. Lett. B 800 (2020) 135106) opposed the widespread belief that due to quantization, the Big Bang singularity {\em must} necessarily get smeared and replaced by a non-singular "Big Bounce" process. Their claim is supported in a methodically independent manner in which just a highly schematic model (viz., the discrete and drastically simplified Wheeler-DeWitt equation) is considered. Our comparatively elementary argumentation is constructive, based on the assumption that the evolution of the Universe can fully consistently be described using an innovative, h…
Bootstrapped Newtonian gravity was developed with the purpose of estimating the impact of quantum physics in the nonlinear regime of the gravitational interaction, akin to corpuscular models of black holes and inflation. In this work, we set the ground for extending the bootstrapped Newtonian picture to cosmological spaces. We further discuss how such models of quantum cosmology can lead to a natural solution of the cosmological constant problem.
We analyze the size and evolution of quantum fluctuations of cosmologically relevant geometric observables, in the context of the effective relational cosmological dynamics of GFT models of quantum gravity. We consider the fluctuations of the matter clock observables, to test the validity of the relational evolution picture itself. Next, we compute quantum fluctuations of the universe volume and of other operators characterizing its evolution (number operator for the fundamental GFT quanta, effective Hamiltonian and scalar field momentum). In particular, we focus on the late (clock) time regim…
Holographic cosmology with logarithmic equation of state based on a new generalized entropy
Norwegian University of Science and Technology（挪威科技大学）；Tomsk State Pedagogical University (TSPU)（托木斯克国立师范大学）；International Centre of Gravity and Cosmos, Tomsk State University of Control Systems and Radio electronics (TUSUR)（托木斯克州立控制系统与电子大学国际引力与宇宙学中心）
Big-Bounce in Quantum f(R)-Cosmology: Polymer Dynamics with Internal Time
Sapienza University of Rome（罗马第一大学）；INFN Section of Rome, Sapienza University of Rome（罗马国立核物理研究所罗马分部，罗马第一大学）；ENEA, Fusion and Nuclear Safety Department, C.R. Frascati（意大利国家新可再生能源技术局聚变与核安全部弗拉斯卡蒂研究中心）
