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.
I will present an efficient quantum algorithm for an additive
approximation of the famous Tutte polynomial of any planar graph at
any point. The Tutte polynomial captures an extremely wide range of
interesting combinatorial properties of graphs, including the
partition function of the q-state Potts model. This provides a new
class of quantum complete problems.
A relativistic modified gravity (MOG) leads to a self-consistent, stable gravity theory that can describe the solar system, galaxy and clusters of galaxies data and cosmology without dark matter. A review is given of fits to galaxy rotation curves, mass profiles of X-ray clusters and weak and strong lensing of galaxy clusters including the bullet cluster E10657-56. MOG can explain the CMB power spectrum and the observed acceleration of the expansion of the universe.
We show that the recently suggested Euclidean quantum gravity density matrix of the Universe which generates the set of inflationary universes is, in fact, the density matrix of the microcanonical ensemble in {\em Lorentzian} quantum cosmology.
I describe how vacuum energy can be controlled by a symmetry principle that necessitates a ghost sector. I argue that the implied instability of Minkowski spacetime is natural and consistent with experience if gravity is fundamentally Lorentz-violating, and describe attempts to construct such exotic dynamics. I briefly discuss the more robust experimental/observational signatures of such a scenario.