Recent Efforts Towards Understanding the Early Universe from a Fundamental Quantum Perspective

Abstract

The observable universe is fundamentally inhomogeneous and anisotropic. Quantum description of the generation of these inhomogeneities and anisotropies is ill-understood and unsatisfactory. After providing a brief account of the standard approach of the generation of the classical density perturbations starting from the quantum fluctuations of inflaton field, I critically review various assumptions which are crucial for the success of this description, and point out various shortcomings around it. I also discuss the basic ideas and recent works by using an alternative path to overcome those shortcomings which is motivated by the so-called Collapse Model interpretation of quantum mechanics. Inspired by these works, I argue the necessity of constructing a class of manifestly inhomogeneous and anisotropic quantum states after inflation and discuss my recent works which provide one such prescription of building such a state, called the $T-$vacuum, defined in the radiation dominated stage of the early universe.