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 consider various attempts to derive the quantum probabilities from the HIlbert space formalism within the many-worlds interpretation, and argue that they either fail, or depend on tacit probabilistic assumptions. The main problem with the project is that it is difficult to understand what the state of system X is psi even *means* without already supposing some probabilistic link to definite observed or observable phenomena involving X.
I give a review and assessment of relational approaches to quantum theory – that is, approaches that view QM “as an account of the way distinct physical systems affect each other when they interact – and not the way physical systems ‘are’”. I argue that the “relational QM” is a misnomer: the correct way to understand these approaches is in terms of structuralism, whereby the correlations themselves are fundamental. I then argue that the connection to gravitational physics and gauge symmetries has a crucial impact on the attractiveness of such approaches.
It's been suggested that "decoherence explains the emergence of a classical world". That is, if we believe our world is quantum, then decoherence can explain why it LOOKS classical. Logically, this implies that without decoherence, the world would not look classical. But... what on earth WOULD it look like? Human beings seem incapable of directly observing anything "nonclassical". I'll show you how a hypothetical quantum critter could interact with, and learn about, its world. A quantum agent can use coherent measurements to gain quantum knowledge about its surroundings.
Perhaps the earliest explicit ansatz of a truly ontic status for the density operator has been proposed in [G.N. Hatsopoulos and E.P. Gyftopoulos, Found. Phys., Vol.6, 15, 127, 439, 561 (1976)].
TBA
Collisions and subsequent decays of higher dimensional branes leave
behind three-dimensional branes, one of which could play the role of
our universe. This process also leads to the production of
one-dimensional branes, D-strings, and fundamental ones (F-strings),
known as cosmic superstrings. In the first part of this talk, I will discuss the mechanism we have proposed in order to explain the origin of the space-time dimensionality, while in the second part I will review formation and dynamics of cosmic superstrings.
I will discuss properties of pre- and post-selected ensembles in quantum mechanics. I will also discuss the proper way to observe these properties through the use of a new type of non-disturbing measurement which I call 'weak measurement'. A number of these new experiments have already been successfully performed and others are in the planning stage. These experiments have confirmed the unique property of pre- and post-selected ensembles that I call 'weak values.' Theoretical analysis of the outcomes of these experiments have produced several very rich results.
We use black holes to understand some basic properties of theories of quantum gravity. First, we apply ideas from black hole physics to the physics of accelerated observers to show that the equations of motion of generalized theories of gravity are equivalent to the thermodynamic relation $\delta Q = T \delta S$. Our proof relies on extending previous arguments by using a more general definition of the Noether charge entropy. We have thus completed the implementation of Jacobson's proposal to express Einstein's equations as a thermodynamic equation of state.