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.
Feynman was probably correct to say that the only mystery of quantum mechanics is the principle of superposition. Although we may never know which slit a photon has been passing in a Youngs double-slit experiment, we do have a corresponding classical concept in classical electromagnetic theory: the superposition of electromagnetic fields at a local space-time point is a solution of the Maxwell equations.
According to a widely accepted view, the emergence of macroscopic behavior is related to the loss of quantum mechanical coherence. Opinions on the possible cause of this loss diverge. In the present talk it will be shown how a small, assessable amount of indeterminacy in the structure of space-time may lead to the emergence of macroscopic behavior, in agreement with empirical evidence.
After giving an introduction to the Continuous Spontaneous Localization
(CSL) theory of dynamical wave function collapse, I shall discuss 10 problems of dynamical collapse models, 5 of which were resolved by CSL's advent, and 5 of which have been subsequently attacked with varying success.
If one is worried by the quantum measurement problem,a natural question to ask is: Does the quantum-mechanical description of the world retain its validity when its application leads to superpositions of states which by some reasonable criterion are _macroscopically distinct_? Or rather, does any such superposition automatically get "collapsed", even in the absence of "measurement" by a human observer, into one or other of its branches? Scenarios which predict the latter (for example the GRWP theory) may be denoted generically by the term "macrorealistic".
The way we combine operators in quantum theory depends on the causal relationship involved. For spacelike separated spacetime regions we use the tensor product. For immediately sequential regions of spacetime we use the direct product. In the latter case we lose information that is we cannot go from the direct product of two operators to the two original operators. This is a kind of compression. We will see that such compression is associated with causal adjacency.
Once again the problem of indistinguishability has been recently tackled. The question is why indistinguishability, in quantum mechanics but not in classical one, forces a changes in statistics. Or, what is able to explain the difference between classical and quantum statistics? The answer given regards the structure of their state
Taking for granted that the mathematical apparatus for describing probabilities in quantum mechanics is well-understood via work of von Neumann, Lüders, Mackey, and Gleason, we present an overview of different interpretations of probability in quantum mechanics bearing on physics and experiment, with the aim of clarifying the meaning and place of so-called objective interpretations of quantum probability.
It is often suggested that the special theory of relativity is incompatible with any notion of the passage of time. I shall try to show, following in the footsteps of Abner Shimony, that there is transience to be found in Minkowski spacetime, but this transience is local rather than global.