General Relativity & Quantum Cosmology

Our understanding of the physical world at the most fundamental level is based on two theories: quantum theory and general relativity. They are impressively successful when each is considered on its own, but in situations where both play a role, we are reduced to puzzles and absurdity. To the great frustration of researchers, candidate theories of quantum gravity produce more puzzles than answers. We shall tour of some of the problems, focusing on the role of spacetime and causality. We will consider the possibility that spacetime did not always exist but is instead emergent and explore how one can create a spacetime from a world with no notion of "here" and "there".

The idea behind an intersection between loop quantum gravity and noncommutative geometry is to combine elements of unification with a setup of canonical quantum gravity. In my talk I will first review the construction of a semi-finite spectral triple build over an algebra of holonomy loops. Here, the loop algebra is a noncommutative algebra of functions over a configurations space of connections, and the interaction between the Dirac type operator and the loop algebra captures information of the kinematical part of canonical quantum gravity. Next, I will show how certain normalizable, semi-classical states are build which connects the spectral triple construction to the Dirac Hamiltonian in 3+1 dimensions. Thus, these states can be interpreted as one-particle fermion states in an ambient gravitational field. This analysis indicates that the spectral triple construction involves matter degrees of freedom.

Mathematical aspects of modern theories of elementary particles and gravitation. Replacing the notion of particles with fundamental abstract fields (magnetic monopoles, vortices and Skyrmions) in an attempt to approach a formulation for quantum gravity.

Cosmology and cosmological implications of quantum gravity. Observable effects in cosmology help to identify the limits of general relativity, which could potentially be surpassed by modified theories of gravity and/or quantum gravity.

Collisions and subsequent decays of higher dimensional branes leave behind three-dimensional branes, one of which could play the role of our universe. This process also leads to the production of one-dimensional branes, D-strings, and fundamental ones (F-strings), known as cosmic superstrings. In the first part of this talk, I will discuss the mechanism we have proposed in order to explain the origin of the space-time dimensionality, while in the second part I will review formation and dynamics of cosmic superstrings.

Dr. Smolin is a faculty member at Perimeter Institute for Theoretical Physics and author of several books including most recently “The Trouble with Physics”. He is known for devising several different approaches to quantum gravity, in particular, loop quantum gravity. His research interests include cosmology, elementary particle theory, the foundations of quantum mechanics, and theoretical biology. This information Chalk and Talk will explore in special topics in Quantum Gravity.

Our universe has a split personality: quantum and relativity. Understanding how the two can coexist, i.e. how our universe can exist, is one of the greatest challenges facing theoretical physicists in the 21st century. The presentation focuses on a simple but mind-bending thought experiment that hints at some fascinating new ways of thinking that may be required to unravel this mystery. Could the world be like a hologram? The half hour multimedia presentation provides refreshing insight into how science works – how theoretical physicists search for the ultimate nature of reality, and is followed by a half hour question and answer session with PI researcher Sean Gryb.

I will discuss the contribution to black hole thermodynamics from a variation in the cosmological constant. The description of black hole with a cosmological constant is facilitated by introducing a two-form potential for the static Killing field. The resulting Smarr formula then includes a term proportional to the cosmological constant times an effective volume, which arises as the difference between the Killing potential on the horizon and the boundary at infinity. This volume is shown to be equal to the difference between the (infinite) volume of AdS and the (infinite) volume outside the black hole horizon of AdS containing a black hole--and so can be interpreted as the volume occupied by the black hole. I will outline the derivation for the first law for AdS black holes including a variation in the cosmological constant. This yields a new work term, the change in the cosmological constant times the effective volume. Hence this is analogous to a "volume times change in pressure" work term in classical thermodynamics. This suggests that the usual change in mass term is better interpreted as a change in the enthalpy, the mass plus the pressure times the volume. In the AdS/CFT correspondence a change in the cosmological constant corresponds to a change in the t'Hooft coupling, for example, a change in the number of degrees of freedom. The effective volume multiplier then looks like a chemical potential. Members of the audience will be asked to contribute their own interpretations at this point.