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.
Anthropic arguments based on selection effects for observers have been claimed to succesfully explain the measured value of the cosmological constant.In this talk I review the fundations of such claims in the context of probability theory and show that different (and equally legitimate) ways of assigning probabilities to candidate universes lead to totally different anthropic predictions. As an explicit example, I discuss a weighting scheme based on the total number of possible observations that observers can carry out over the entire lifetime of the Universe.
The possibility that rotational invariance ins broken during the inflationary era is discussed. The implications of this for the microwave background asymmetry are derived using a model independent approach. A particular inflationary model that realizes these ideas is studied.
Hollywood movies about aliens abound, but do they really exist? The real scientific search for evidence of life, and particularly intelligent life, elsewhere in the cosmos is just as exciting as the reel version, and a lot more logical. So far, there is life-as-we-know-it to guide our speculations and observations. But a new appreciation for the tenacity of life, a growing respect for the world of microbes, and new search technologies involving observatories and spacecraft are rapidly expanding our viewpoint. Many expect surprises.
We show that singlets composed of multiple multi-level quantum systems can naturally arise as the ground state of a physically-motivated Hamiltonian. The Hamiltonian needs to be one which simply exchanges the states of nearest neighbours in any graph of interacting d-level quantum systems (qudits) as long as the graph also has d sites. We point out that local measurements on some of these qudits, with the freedom of choosing a distinct measurement basis at each qudit randomly from an infinite set of bases, project the remainder onto a singlet state.