Talks

Einstein\'s famous equation E=mc2 asserts that energy and mass are different aspects of the same reality. It is usually associated with the idea that small amounts of mass can be converted into large amounts of energy. For fundamental physics, however, the more important idea is just the opposite. Researchers want to explain how mass itself arises, by explaining it in terms of more basic concepts. In this lecture targeted for a general audience, Prof. Wilczek will explain how this goal can, to a remarkable extent, be achieved. He will also discuss some of the consequences - an explanation of why gravity is so feeble - and suggestions for new physical phenomena at the Large Hadron Collider (LHC) in Geneva. Prof. Wilczek is a distinguished scientist and lecturer. He is the author of Fantastic Realities: 49 Mind Journeys and a trip to Stockholm and co-author of Longing for the Harmonies. In addition to many distinguished memberships and affiliations, he is a member of Perimeter Institute’s Scientific Advisory Committee.

Category theory is a general language for describing things and processes - called "objects" and "morphisms". In this language, many counterintuitive features of quantum theory turn out to be properties shared by the category of Hilbert spaces and the category of cobordisms, in which objects are choices of "space" and emorphisms are choices of "spacetime". This striking fact suggests that "n-categories with duals" are a promising language for a quantum theory of spacetime. We sketch the historical development of these ideas from Feynman diagrams to string theory, topological quantum field theory, spin networks and spin foams, and especially recent work on open-closed string theory, 3d quantum gravity coupled to point particles, and 4d BF theory coupled to strings.

It has recently been proposed by Nayeri, Brandenberger and Vafa, that the thermodynamics of strings in the early universe can provide us with a causal mechanism to generate a scale invariant spectrum of primordial density fluctuations, without requiring an intervening epoch of inflation. We will review this mechanism, and report on more recent work which has uncovered several observational consequences of the NBV mechanism, some of which in principle, will be distinguishable from the generic predictions of inflation.

We propose a new brane world scenario. In our model, the Universe starts as a small bulk filled with a dense gas of branes. The bulk is bounded by two orbifold fixed planes. An initial stage of isotropic expansion ends once a weak potential between the orbifold fixed planes begins to dominate, leading to contraction of the extra spatial dimensions. Depending on the form of the potential, one may obtain either a non-inflationary scenario which solves the entropy and horizon problem, or an improved brane-antibrane inflation model.

Clifton, Bub, and Halvorson claim to be able to derive quantum mechanics from information-theoretic axioms. However, their derivation relies on the auxiliary assumption that the relevant probabilities for measurement outcomes can be represented by the observables (self-adjoint operators) and states of a C*-algebra. There are legitimate probability theories that are not so representable --- in particular, the nonlocal boxes of Popescu and Rohrlich. We explain the impact of nonlocal boxes on the interpretation of the CBH derivation, and we discuss possible generalizations of the CBH derivation in the framework of these more general probability theories.

Radiation Delivery, cancer, radiation therapy, electron, isocentre, planned target volume, adaptive radiotherapy, multi-leaf collimator, energy deposition, multi-beam delivery, intensity modulation, optimal radiation treatment, matrix inversion, inverse planning optimization, symmetries, fast inverse dose optimization

Quantum cryptography, quantum physics, cryptography, one-time pad, RSA, encryption, public key, decryption, private key, quantum computer, qubit, quantum key, distribution, QKD, Moore\'s Law, probability, quantum theory, complex number, beam splitter, superposition, electron orbital, Turing, quantum parallelism, EPR, Bell, information security