Astrophysics

String theory should give a well-defined answer to the following question: What is the state of matter in the limit of infinite energy density? We use results obtained from the understanding of black hole entropy to conjecture this equation of state, noting that the maximum entropy state in string theory has vastly more entropy than the states used in traditional approaches to early Universe Cosmology. The evolution of the Universe with this equation of state can be obtained in closed form.

It is argued that the correct quantization of a scalar field theory in de Sitter spacetime involves a de Sitter invariant state which is not the Bunch-Davies vacuum. A novel but natural de Sitter invariant alternative exists and it is suggested that this and is the prefered state for scalar field theories. The argument is based on the exact solution of an interacting scalar field theory.

In the context of the AdS/CFT correspondence, I will discuss model-independent properties shared by bulk theories of gravity with consistent dual descriptions. I will then discuss the prospects of extending these ideas to non-conformal theories, in particular to attempts to realize cosmological theories holographically. I will address the status of in-principle falsifiability of various holographic proposals through internal consistency conditions of the boundary theory.

FRW/CFT duality is a proposal for a holographic dual description for universe created by bubble nucleation. For (3+1) dimensional universe, the dual theory is defined on 2-sphere at the boundary of open universe. I will study correlation functions and explain essential features of FRW/CFT duality: One bulk field corresponds to a tower of CFT operators The boundary theory contains 2D gravity, and the Liouville field plays the role of time. Energy-momentum tensor has dimension 2, as required from the 2D conformal symmetry.

In this talk, I attempt to gain insight into the description of quantum gravity on cosmological spacetimes by considering the physics of families of accelerating observers in spacetimes which admit non-perturbative descriptions vis AdS/CFT.