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 classic debate between Einstein and Bohr over a realistic
interpretation of quantum mechanics can be cast in terms of the
measurement problem: Is there an underlying ontic state prior to
measurement which maps deterministically to the measured outcome?
According to the Kochen-Specker theorem, such a view is patently
inconsistent with quantum theory, leading to the paradox of quantum
contextuality. This result, however, relies upon the (arguably
unwarranted) assumption that the ontic state remains unchanged through
After reframing the question of the status of the quantum state in terms of J.S. Bell's "beables", I will sketch out a new theory which -- though nonlocal in the sense required by Bell's theorem -- posits exclusively local beables. This is a theory, in particular, in which the quantum mechanical wave function plays no role whatsoever -- i.e., a theory according to which nothing corresponding to the wave function actually exists. It provides, therefore, a concrete example of how the wave function might be regarded as (at best) "epistemic".
The screening of electric charge in plasma with Bose condensate of a charged scalar field is calculated. In all previous calculations before 2009 the effects of Bose condensation have not been considered. Due to the condensate the time-time component of the photon polarization tensor in addition to the usual terms k-squared and Debye mass squared, contains infrared singular terms inversely proportional to k and k-squared. Such terms lead to power law oscillation behaviour of the screened potential, which is different form Friedel oscillations known for fermions.
Bell and experimental tests of his inequality showed that it is impossible to explain all of the predictions of quantum mechanics using a theory which satisfies the basic concepts of locality and realism, but which (if not both) is violated is still an open question. As it seems impossible to resolve this question experimentally, one can ask how plausible realism -- the idea that external properties of systems exist prior to and independent of observations -- is, by considering the amount of resources consumed by itself and its non-local features.
All known hidden variable theories that completely reproduce all quantum predictions share the feature that they add some information to the quantum state "psi". That is, if one knew the "state of reality" given by the hidden variable(s) "lambda", then one could infer the quantum state - the hidden variables are additional to the quantum state.