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.
The relic neutrino background contains a gapless, spin-2 sound mode, as well as a spin-1 mode if there is a neutrino-antineutrino asymmetry. The self-coupling of the spin-2 mode is given by Z boson exchange in the Standard Model and is parametrically similar to Newton's constant given the expected density of relic neutrinos. I will describe this emergent gravity theory and also describe how emergent theories avoid the Weinberg-Witten theorem, when the constituent degrees of freedom live in a flat Lorentz invariant space.
How do we weigh the Universe? Where is the Dark Matter? I will discuss these questions and show that several independent methods, including the observed present-day abundance of rich clusters , the evolution of cluster abundance with redshift, the baryon-fraction in clusters, the observed Mass-to-Light function from galaxies to superclusters, and other large-scale structure observations, all reveal a universe with a low mass density parameter of ~20% of the critical density.