Since 2002 Perimeter Institute has been recording seminars, conference talks, and public outreach events using video cameras installed in our lecture theatres. Perimeter now has 7 formal presentation spaces for its many scientific conferences, seminars, workshops and educational outreach activities, all with advanced audio-visual technical capabilities. Recordings of events in these areas are all available On-Demand from this Video Library and on Perimeter Institute Recorded Seminar Archive (PIRSA). PIRSA is a permanent, free, searchable, and citable archive of recorded seminars from relevant bodies in physics. This resource has been partially modelled after Cornell University's arXiv.org.
We understand the history of our universe very well but remain ignorant on one key question: what is most of the universe actually made of? Beautiful measurements, by satellites, balloon-basted observatories, the Hubble telescope and ground-based telescopes have allowed us to accurately trace this history of the history of the ordinary matter we are made of. Yet these measurements also show us that most of the universe is dark - that is to say it cannot be seen visibly no matter how bright a light is shone on it.
Physics emerged from the twentieth century with two remarkably successful descriptions of nature which stand in striking contrast. Quantum mechanics describes the subatomic realm with intrinsic uncertainties and probabilities. On the other hand, Einstein's general relativity describe gravitational phenomena in an exacting geometric arena. Theoretical physicists have struggled for over fifty years trying to combine these views in a single unified framework. More recently, superstring theory has drawn a huge amount of interest as a leading contender to provide such a unification.
The Baryon Acoustic Oscillations (BAO) are the latest weapon in the quest for precision cosmology and dark energy. Many presentations on BAO are complicated and unclear and I will therefore present BAO with particular emphasis on trying to give the simplest theoretical description, both at the linear and nonlinear level, and will describe some of the observational challenges to measuring BAO.
Non-equilibrium processes such as inflationary preheating or the ekpyrotic bounce can turn fluctuations of light scalar fields into potentially highly non-Gaussian curvature perturbations. I show how these perturbations can be calculated at fully non-linear level using lattice field theory simulations. As concrete examples, I present results for preheating in chaotic inflation and resonant curvaton decay.
Recently there has been renewed interest in cosmological gravity, namely 3d gravity coupled to a Chern-Simons term with parameter $\mu$, following claims that at $\mu =1$ the theory becomes chiral and stable. In this talk we will investigate cosmological gravity by setting up a concrete holographic dictionary with a dual 2d field theory and we will demonstrate that the theory is in fact not chiral in the limit $\mu = 1$. Instead our holographic dictionary implies that at $\mu =1$ the dual field theory becomes a logarithmic CFT (LCFT).
Cosmological bubble collisions arising from first order phase transitions are a generic consequence of the Eternal Inflation scenario. I will present our computational strategy for generating and evolving these bubbles in 3+1 dimensions and in a self-consistently expanding background. I will show the existence of classical field transitions--the classical nucleation of bubbles during collisions--which can dramatically alter the canonical description of eternal inflation.
I review three challenges faced by attempts to develop a quantum theory of the universe and examine possible relationships between them. 1) The clock ambiguity: The choice of time parameter leads to profound ambiguities. 2) The choice of state: I contrast the de Sitter equilibrium picture with eternal inflation. 3) The Born rule crisis: The born rule is insufficient to construct probabilities in a large multiverse without additional rules or assumptions (as discussed by Don Page).
We propose a holographic description of four dimensional single scalar inflationary universes, in particular asymptotically de Sitter cosmologies and power-law inflation. We show how cosmological observables such as the primordial power spectrum and non-gaussianities are encoded in correlation functions of a three dimensional QFT.