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.
f(R) theories are an alternative approach at the phenomenon of cosmic acceleration, in which the Einstein-Hilbert action for gravity is modified by adding a function of the Ricci scalar, f(R). While at the background level viable f(R) models must closely mimic LCDM, the difference in their prediction for the growth of large scale structures can be sufficiently large to leave detectable signatures in future surveys. In this talk, after reviewing the conditions for the background viability of f(R) theories, I will focus on scalar perturbations.
I'll discuss a reformulation of twistor-string theory as a heterotic string. This clarifies why conformal supergravity arises and provides a link between the Berkovits and Witten pictures. The talk is based on
arXiv:0708:2276 with Lionel Mason.
101 years ago William James wrote this about the Hegelian movement in philosophy: \'The absolute mind which they offer us, the mind that makes our universe by thinking it, might, for aught they show us to the contrary, have made any one of a million other universes just as well as this. You can deduce no single actual particular from the notion of it.
This talk follows on from Wayne Myrvold\'s (and is based on joint work with Myrvold). I aim (and claim) to provide a unified account of theory confirmation that can deal with the (actual) situation in which we are uncertain whether the true theory is a probabilistic one or a branching-universe one, that does not presuppose the correctness of any particular physical theory, and that illuminates the connection between the decision-theoretic and the confirmation-theoretic roles of probabilities and their Everettian analogs.
Much of the evidence for quantum mechanics is statistical in nature. Close agreement between Born-rule probabilities and observed relative frequencies of results in a series of repeated experiments is taken as evidence that quantum mechanics is getting something --- namely, the probabilities of outcomes of experiments --- at least approximately right. On the Everettian interpretation, however, each possible outcome occurs on some branch of the multiverse, and there is no obvious way to make sense of ascribing probabilities to outcomes of experiments.