Name: Muhammad Bilal Azam
Supervisor: Dr. Maqbool Ahmed (Google Scholar Profile)
Institution: Department of Physics, Lahore University of Management Sciences
Dark energy, with negative pressure, is the dominant energy component of the universe as indicated by the observations. Cosmological constant is one of the expected candidates for dark energy. However, it also raises a fundamental question that why “only now” cosmological constant is of the order of ambient density? Answer comes from the conjugacy which results in an uncertainty relation of spacetime volume and cosmological constant. This conjugacy must be a part of any theory that aims to be an ultimate theory of quantum gravity, as clearly obvious in unimodular gravity, and which favors spacetime discreteness at the fundamental level. Conjugacy predicts that the lambda need not to be a constant parameter but a fluctuating one while the spacetime discreteness of causal set theory in turn predicts the magnitude of this fluctuating lambda. Ahmed et al. (2004) showed that, for a flat universe, this ansatz provides a cosmological constant, which fluctuates about zero, and is comparable to the ambient energy density at all times. Using the same arguments from the unimodular gravity and causet theory, we find the fluctuations in the cosmological constant for a closed universe which answers the fine-tuning and naturalness problem. It makes it well-consistent with the observations. This model also helps to study that how curvature affects the behavior of dark energy and how the density of lambda changes under the effect of an arbitrary parameter, which governs the dynamics of the universe in causal set theory, and by the radius of the observable universe.