This series covers all areas of research at Perimeter Institute, as well as those outside of PI's scope. http://pirsa.org/podcast/S001 Science 2009 http://blogs.law.harvard.edu/tech/rss en-ca Thu, 08 Jan 2009 11:44:20 -0500 sbradwell@perimeterinstitute.ca Thu, 08 Jan 2009 11:44:20 -0500 G 180 sbradwell@perimeterinstitute.ca Steve Bradwell's - Podcast Generator Jan Gutowski http://streamer.perimeterinstitute.ca/mp3/c48bf037-9d8d-4464-87a3-5468b84ee1b5.mp3 Science http://streamer.perimeterinstitute.ca/mp3/c48bf037-9d8d-4464-87a3-5468b84ee1b5.mp3 Thu, 16 Sep 2004 13:30:00 -0400 Maxim Pospelov http://streamer.perimeterinstitute.ca/mp3/16fa358e-9ae1-40cb-a6a8-53c3b4c90570.mp3 Science http://streamer.perimeterinstitute.ca/mp3/16fa358e-9ae1-40cb-a6a8-53c3b4c90570.mp3 Wed, 06 Oct 2004 14:00:00 -0400 Grigori Volovik http://streamer.perimeterinstitute.ca/mp3/3b2b321b-6223-45fd-bcb2-7f7a97ab6362.mp3 Science http://streamer.perimeterinstitute.ca/mp3/3b2b321b-6223-45fd-bcb2-7f7a97ab6362.mp3 Wed, 13 Oct 2004 12:45:00 -0400 Stefan Hofmann http://streamer.perimeterinstitute.ca/mp3/30a5c039-7735-4dba-ab88-e7b6affc13ca.mp3 Science http://streamer.perimeterinstitute.ca/mp3/30a5c039-7735-4dba-ab88-e7b6affc13ca.mp3 Wed, 27 Oct 2004 12:55:00 -0400 Jim Brown http://streamer.perimeterinstitute.ca/mp3/a8d40a1c-79c3-4487-915a-319484ed5c9a.mp3 Science http://streamer.perimeterinstitute.ca/mp3/a8d40a1c-79c3-4487-915a-319484ed5c9a.mp3 Wed, 03 Nov 2004 14:05:00 -0500 Chetan Nayak http://streamer.perimeterinstitute.ca/mp3/b5bfe36f-963b-4149-9d1b-bff445433192.mp3 Science http://streamer.perimeterinstitute.ca/mp3/b5bfe36f-963b-4149-9d1b-bff445433192.mp3 Wed, 10 Nov 2004 14:00:00 -0500 Nigel Hitchen http://streamer.perimeterinstitute.ca/mp3/fa93ef4f-2c18-4f77-9d89-07f385d4fa73.mp3 Science http://streamer.perimeterinstitute.ca/mp3/fa93ef4f-2c18-4f77-9d89-07f385d4fa73.mp3 Wed, 17 Nov 2004 14:00:00 -0500 Curt Callan http://streamer.perimeterinstitute.ca/mp3/a879317d-0111-4fda-bb71-9789b497bbf3.mp3 Science http://streamer.perimeterinstitute.ca/mp3/a879317d-0111-4fda-bb71-9789b497bbf3.mp3 Wed, 01 Dec 2004 14:05:00 -0500 Leonard Susskind http://streamer.perimeterinstitute.ca/mp3/553b0946-5b33-4369-8b7b-5a1a776b858e.mp3 Science http://streamer.perimeterinstitute.ca/mp3/553b0946-5b33-4369-8b7b-5a1a776b858e.mp3 Tue, 01 Feb 2005 14:00:00 -0500 James Bjorken http://streamer.perimeterinstitute.ca/mp3/a9522b35-895d-49fb-a826-82c71dab0541.mp3 Science http://streamer.perimeterinstitute.ca/mp3/a9522b35-895d-49fb-a826-82c71dab0541.mp3 Wed, 09 Feb 2005 02:00:00 -0500 William Trischuk http://streamer.perimeterinstitute.ca/mp3/61c9418d-d361-4e5f-a85e-35815e7625ac.mp3 Science http://streamer.perimeterinstitute.ca/mp3/61c9418d-d361-4e5f-a85e-35815e7625ac.mp3 Wed, 23 Feb 2005 14:05:00 -0500 The existence, and enigmatic nature, of 'Dark Energy' is one of the biggest theoretical upsets of recent times. In this seminar we present ideas on alternative theoretical and phenomenological approaches to the Dark Energy problem, in particular the issue of whether dark energy is a matter or gravity-based phenomenon, and the ways in which such approaches can been constrained and guided by observation. We also focus on some of the exciting future approaches that could provide unprecedented insights into the fundamentals of Dark Energy Rachel Bean http://streamer.perimeterinstitute.ca/mp3/65e123e5-f0b6-4027-ab98-19257867543b.mp3 Science http://streamer.perimeterinstitute.ca/mp3/65e123e5-f0b6-4027-ab98-19257867543b.mp3 Wed, 09 Mar 2005 14:00:00 -0500 In this talk we assume that Quantum Einstein Gravity (QEG) is the correct theory of gravity on all length scales. We use both analytical results from nonperturbative renormalization group (RG) equations and experimental input in order to describe the special RG trajectory of QEG which is realized in Nature. We identify a regime of scales where gravitational physics is well described by classical General Relativity. Strong renormalization effects occur at both larger and smaller momentum scales. The former are related to the (conjectured) nonperturbative renormalizability of QEG. The latter lead to a growth of Newton's constant at large distances. We argue that this effect becomes visible at the scale of galaxies and could provide a solution to the astrophysical missing mass problem which does not require dark matter. A possible resolution of the cosmological constant problem is proposed by noting that all RG trajectories admitting a long classical regime automatically imply a small cosmological constant. Martin Reuter http://streamer.perimeterinstitute.ca/mp3/8f60f41a-3c7f-4bc2-9cf6-ede89587f70c.mp3 Science http://streamer.perimeterinstitute.ca/mp3/8f60f41a-3c7f-4bc2-9cf6-ede89587f70c.mp3 Wed, 16 Mar 2005 14:00:00 -0500 Since the seminal discovery of the neutrino by Cowan and Reines in the late 1950's, intense experimental and theoretical effort has focused on the elucidation of neutrino properties and the role they play in elementary particle physics, astrophysics, and cosmology. Neutrinos are born in the fusion reactions powering our Sun and are thought to be the driving mechanism for supernova explosions. Neutrinos exist in copious amounts as the primordial afterglow of the Big Bang and, if massive, would play a role in the evolution and ultimate fate of the Universe. Central to many of the key issues in neutrino physics is the question of whether neutrinos possess non-zero rest mass. If neutrinos are massive, then one expects flavor mixing to occur in the neutrino sector which could lead to the phenomena of neutrino oscillations and the possibility of CP violation in the neutrino sector. A detailed understanding of the microscopic properties of neutrinos can serve to pave the way to a unified description of the fundamental forces of Nature. Andrew Hime http://streamer.perimeterinstitute.ca/mp3/0f2b1392-e8ab-4f7c-a264-0c93da527c76.mp3 Science http://streamer.perimeterinstitute.ca/mp3/0f2b1392-e8ab-4f7c-a264-0c93da527c76.mp3 Wed, 23 Mar 2005 14:00:00 -0500 A key issue in the context of (compact) extra dimensions is the one of their stability. Any stabilization mechanism is effective only up to some given energy scale; if they can approach this energy, 4$d observers can excite the fluctuations of the internal space, and probe its existence. Stabilization mechanisms introduce fields in the internal space; perturbations of these fields are mixed with perturbations of the metric, so that their study requires a complete GR treatment. After presenting the general framework, I will then discuss some relevant applications. I will present the exact coupling of the radion to codimension one branes, extending the regime of validity of the results in the literature. I will then focus on de Sitter compactifications, showing that the cosmological expansion has typically the effect of destabilizing the internal space. The final part of the talk will be devoted to related work in progress in less conventional areas of brane models: the localization of gravity towards the IR brane (corresponding to a dual description of emerging gravity from the CFT), and the inclusion of ghost fields in the bulk. Marco Peloso http://streamer.perimeterinstitute.ca/mp3/cb8002ac-d550-4745-8731-35979e5bca65.mp3 Science http://streamer.perimeterinstitute.ca/mp3/cb8002ac-d550-4745-8731-35979e5bca65.mp3 Wed, 06 Apr 2005 14:00:00 -0400 Seth Lloyd http://streamer.perimeterinstitute.ca/mp3/e8ecffa6-4ea7-420d-9d7a-d78bf6ada013.mp3 Science http://streamer.perimeterinstitute.ca/mp3/e8ecffa6-4ea7-420d-9d7a-d78bf6ada013.mp3 Wed, 13 Apr 2005 02:00:00 -0400 Superconducting circuits based on Josephson junctions are promising candidates for the implementation of solid-state qubits. In most of the recent experiments on these circuits, the qubits are controlled by a classical field containing a large number of photons. The possibility of coherently coupling these systems to a single photon has been recently suggested, opening the possibility to study analogs of quantum optics in condensed matter systems. I will review one of these proposals based on a superconducting charge qubit fabricated inside a high quality transmission line resonator and will describe its recent experimental realization. When the qubit is brought into resonance with the resonator, vacuum Rabi splitting is observed indicating that the regime of strong coupling has been reached. When the qubit is detuned from the cavity, I will explain how quantum non-demolition measurement can be realized. I will discuss how the measurement process can be quantitatively understood in this regime allowing us to explore the effect of measurement back-action on the qubit and to extract, for the first time in superconducting qubits, large visibility in Rabi oscillations. Alexandre Blais http://streamer.perimeterinstitute.ca/mp3/e9e35f74-b16e-47a3-ae45-d81c356914ba.mp3 Science http://streamer.perimeterinstitute.ca/mp3/e9e35f74-b16e-47a3-ae45-d81c356914ba.mp3 Wed, 20 Apr 2005 14:00:00 -0400 Michael Peskin http://streamer.perimeterinstitute.ca/mp3/9e4bbaf2-9aca-4445-a0ae-0384432ecb3f.mp3 Science http://streamer.perimeterinstitute.ca/mp3/9e4bbaf2-9aca-4445-a0ae-0384432ecb3f.mp3 Wed, 27 Apr 2005 13:55:00 -0400 John Stachel http://streamer.perimeterinstitute.ca/mp3/f5472d48-8c87-4003-abe0-02ba86392327.mp3 Science http://streamer.perimeterinstitute.ca/mp3/f5472d48-8c87-4003-abe0-02ba86392327.mp3 Wed, 04 May 2005 14:00:00 -0400 Hideo Mabuchi http://streamer.perimeterinstitute.ca/mp3/c8532884-4401-4931-9eaf-f480e45a17a0.mp3 Science http://streamer.perimeterinstitute.ca/mp3/c8532884-4401-4931-9eaf-f480e45a17a0.mp3 Wed, 11 May 2005 13:40:00 -0400 John Preskill http://streamer.perimeterinstitute.ca/mp3/612d177b-8a25-49a5-8641-78b1f7825433.mp3 Science http://streamer.perimeterinstitute.ca/mp3/612d177b-8a25-49a5-8641-78b1f7825433.mp3 Wed, 29 Jun 2005 14:00:00 -0400 The causal set -- mathematically a finitary partial order -- is a candidate discrete substratum for spacetime. I will introduce this idea and describe some aspects of causal set kinematics, dynamics, and phenomenology, including, as time permits, a notion of fractal dimension, a (classical) dynamics of stochastic growth, and an idea for explaining some of the puzzling large numbers of cosmology. I will also mention some general insights that have emerged from the study of causal sets, the most recent one concerning the role of intermediate length-scales in discrete spacetime theories. Rafael Sorkin http://streamer.perimeterinstitute.ca/mp3/dd4544c7-f06e-4a32-893b-1fcc2c3c9aa8.mp3 Science http://streamer.perimeterinstitute.ca/mp3/dd4544c7-f06e-4a32-893b-1fcc2c3c9aa8.mp3 Wed, 07 Sep 2005 14:00:00 -0400 Noncommutative geometry is a more general formulation of geometry that does not require coordinates to commute. As such it unifies quantum theory and geometry and should appear in any effective theory of quantum gravity. In this general talk we present quantum groups as a microcosm of this unification in the same way that Lie groups are a microcosm of usual geometry, and give a flavour of some of the deeper insights they provide. One of them is the ability to interchange the roles of quantum theory and gravity by `arrow reversal'. Another is that noncommutative spaces typically carry a canonical 1-parameter evolution or intrinsic time created from the fundamental conflict between noncommuting coordinates and differential calculus. In physical terms one could say that quantising space typically has an anomaly for the spatial translation group and this forces the system to evolve. We give an example where we derive Schroedinger's equation in this way. Shahn Majid http://streamer.perimeterinstitute.ca/mp3/5f587763-1bf3-441e-9721-e1d3bc6dbb33.mp3 Science http://streamer.perimeterinstitute.ca/mp3/5f587763-1bf3-441e-9721-e1d3bc6dbb33.mp3 Wed, 14 Sep 2005 14:00:00 -0400 Many systems take the form of networks: the Internet, the World Wide Web, social networks, distribution networks, citation networks, food webs, and neural networks are just a few examples. I will show some recent empirical results on the structure of these and other networks, particularly emphasizing degree sequences, clustering, and vertex-vertex correlations. I will also discuss some graph theoretical models of networks that incorporate these features, and give examples of how both empirical measurements and models can lead to interesting and useful predictions about the real world. Mark Newman http://streamer.perimeterinstitute.ca/mp3/e4c48209-19c0-4e4b-91ae-19c9ae3e6150.mp3 Science http://streamer.perimeterinstitute.ca/mp3/e4c48209-19c0-4e4b-91ae-19c9ae3e6150.mp3 Wed, 21 Sep 2005 14:00:00 -0400 Synchronization phenomena are abundant in nature, science, engineering and social life. Synchronization was first recognized by Christiaan Huygens in 1665 for coupled pendulum clocks; this was the beginning of nonlinear sciences. First, several examples of synchronization in complex systems are presented, such as in organ pipes, fireflies, epilepsy and even in the (in)stability of large mechanical systems as bridges. These examples illustrate that, literally speaking, subsystems are able to synchronize due to interaction if they are able to communicate. Second, general physical mechanisms for synchronization and de-synchronization phenomena in coupled complex systems are presented and conditions for synchronizability are discussed. It is explained that diffusion properties give a crucial insight into this problem. I will show that the general concepts of curvature and recurrence are helpful to uncover complex synchronization. Third, applications of these new techniques are given. They range from El Nino – Monsoon interactions via electrochemical oscillators and lasers to cognitive processes during reading and to neuroscience. Jürgen Kurths http://streamer.perimeterinstitute.ca/mp3/de7a3558-452c-412c-a5ec-5b134867574b.mp3 Science http://streamer.perimeterinstitute.ca/mp3/de7a3558-452c-412c-a5ec-5b134867574b.mp3 Wed, 28 Sep 2005 14:00:00 -0400 The problem of vacuum energy is reviewed. The observational evidence in favor of a non-zero cosmological constant is described. I then discuss several possible explanations for how a theoretically natural huge value of vacuum energy could be adjusted down to the unnaturally tiny but observed value. Alexander Dolgov http://streamer.perimeterinstitute.ca/mp3/2b695468-bfae-4c03-b34e-8edcaff3e4dd.mp3 Science http://streamer.perimeterinstitute.ca/mp3/2b695468-bfae-4c03-b34e-8edcaff3e4dd.mp3 Wed, 05 Oct 2005 14:00:00 -0400 Paul Busch http://streamer.perimeterinstitute.ca/mp3/ff57d52b-0087-48e1-b0c0-8caa9ed32896.mp3 Science http://streamer.perimeterinstitute.ca/mp3/ff57d52b-0087-48e1-b0c0-8caa9ed32896.mp3 Wed, 12 Oct 2005 14:00:00 -0400 Preon models enjoyed considerable popularity during the early 1980s, but have seen little progress since then. I will describe a correspondence between one of the more successful preon models and a simple game involving the twisting and braiding of ribbons, subject to straightforward topological conditions. This reproduces the fermions and gauge bosons of the standard model, as well as the electromagnetic, weak and colour interactions. The prospect that such structures may occur naturally within Loop Quantum Gravity will be discussed Sundance Bilson-Thompson http://streamer.perimeterinstitute.ca/mp3/e949d11b-a1a5-4365-a152-7e2014cb3867.mp3 Science http://streamer.perimeterinstitute.ca/mp3/e949d11b-a1a5-4365-a152-7e2014cb3867.mp3 Wed, 16 Nov 2005 14:00:08 -0500 Richard Feynman is said to have said that philosophy of science is of no more use to scientists than ornithology is to birds. I will describe how a sociologist looks at the search for gravitational waves. Is it ornithology to birds? Harry Collins http://streamer.perimeterinstitute.ca/mp3/75ef088e-af64-4f95-865a-ceb124567266.mp3 Science http://streamer.perimeterinstitute.ca/mp3/75ef088e-af64-4f95-865a-ceb124567266.mp3 Tue, 22 Nov 2005 16:00:33 -0500 We show that the origin of the dark matter and dark energy problems originates in the assumption of standard Einstein gravity that Newton's constant is fundamental. We discuss an alternate, conformal invariant, metric theory of gravity in which Newton's constant is induced dynamically, with the global induced one which is effective for cosmology being altogether weaker than the local induced one needed for the solar system. We find that in the theory dark matter is no longer needed, and that the accelerating universe data can be fitted without fine-tuning using a cosmological constant as large as particle physics suggests. In the conformal theory then it is not the cosmological constant which is quenched but rather the amount of gravity that it produces. Philip Mannheim http://streamer.perimeterinstitute.ca/mp3/1f9afb4d-5c39-46d8-980d-a4cedceac650.mp3 Science http://streamer.perimeterinstitute.ca/mp3/1f9afb4d-5c39-46d8-980d-a4cedceac650.mp3 Wed, 23 Nov 2005 14:01:50 -0500 In the standard cosmological model, galaxies and large-scale structure grew by a process of gravitational instability from initial perturbations which were of the simplest statistical form imaginable: a statistically homogeneous and isotropic Gaussian random field. One of the properties of such a field is that its Fourier transform has real and imaginary parts which are independently Gaussian and consequently the phases are uniformly random. The same thing applies to the phases of the spherical harmonic coefficients involved when observed fluctuations over the celestial sphere, such as in the cosmic microwave background. Defining anything other than random phases as "weird", I discuss various aspects of cosmic weirdness and the non-randomness they produce in harmonic space. I introduce some novel methods for visualizing weirdness in CMB data and elsewhere, and discuss their relationship to more conventional statistical analyses. If I have time I will also discuss a few other interest things to do with CMB fluctuations. Peter Coles http://streamer.perimeterinstitute.ca/mp3/9f8eeacd-c2b4-442d-ba0b-e864ffb40f46.mp3 Science http://streamer.perimeterinstitute.ca/mp3/9f8eeacd-c2b4-442d-ba0b-e864ffb40f46.mp3 Wed, 30 Nov 2005 14:00:08 -0500 The origin of the chemical elements that make up our world is one of the oldest most fundamental scientific questions. The universe after the Big Bang consisted only of hydrogen and helium with traces of lithium. All the other elements, including the carbon in our bodies, the iron, silicon, and oxygen that makes up most of our earth, have been created later by nuclear reactions in stars. However, the origin of many elements beyond iron, including gold and uranium, is still a mystery. These elements are attributed to a process called the r-process (rapid neutron capture process) which is of fundamental importance in explaining the origin of stable nuclei and isotopes beyond the iron group (A>90-100). The site of the r process is not known but supernova explosions and/or colliding neutron stars are prime suspects. The problem is that none of the models (related to these sites) can produce r-process elements in the correct proportions as we find them, for example, in the solar system or in certain very old stars. I will discuss an exciting alternative related to quark stars, a new class of compact stars that contain matter at the highest densities. Proposed observational features of quark stars, the probability of their detection, as well as some interesting connections to r-process nucleosynthesis will be presented. I will focus on an alternative based on a dynamical picture of decompressing neutron matter from the surface of quark stars in the scenario termed the Quark-Nova, which is particularly effective for producing the r-process pattern of heavy elements. Rachid Ouyed http://streamer.perimeterinstitute.ca/mp3/76860bd7-d713-480a-a895-e3f3f4074be5.mp3 Science http://streamer.perimeterinstitute.ca/mp3/76860bd7-d713-480a-a895-e3f3f4074be5.mp3 Wed, 07 Dec 2005 14:00:50 -0500 Up to 90% of matter in the Universe could be composed of heavy particles, which were non-relativistic, or 'cold', when they froze-out from the primordial soup. I will review current searches for these hypothetical particles, both via elastic scattering from nuclei in deep underground detectors, and via the observation of their annihilation products in the Sun, galactic halo and galactic center. The emphasis will be on most recent results, and on comparison with reaches of future particle colliders, such as the LHC and ILC. Laura Baudis http://streamer.perimeterinstitute.ca/mp3/72c8ee99-fc8e-4ebc-afa3-d2d2cdc53873.mp3 Science http://streamer.perimeterinstitute.ca/mp3/72c8ee99-fc8e-4ebc-afa3-d2d2cdc53873.mp3 Wed, 25 Jan 2006 14:00:27 -0500 It is shown that inflationary cosmology may be used to test the statistical predictions of quantum theory at very short distances. Hidden-variables theories, such as the pilot-wave theory of de Broglie and Bohm, allow the existence of vacuum states with non-standard field fluctuations (“quantum non-equilibrium”). It is shown that such non-equilibrium vacua lead to statistical anomalies, such as a breaking of scale invariance for the primordial power spectrum. The results depend only weakly on the details of the de Broglie-Bohm dynamics. Recent observations of the cosmic microwave background are used to set limits on violations of quantum theory in the early universe. Antony Valentini http://streamer.perimeterinstitute.ca/mp3/348a3b51-9627-436b-8ec6-fcef3a66bb3c.mp3 Science http://streamer.perimeterinstitute.ca/mp3/348a3b51-9627-436b-8ec6-fcef3a66bb3c.mp3 Wed, 01 Feb 2006 14:00:54 -0500 I look at the information-processing involved in a quantum computation, in terms of the difference between the Boolean logic underlying a classical computation and the non-Boolean logic represented by the projective geometry of Hilbert space, in which the subspace structure of Hilbert space replaces the set-theoretic structure of classical logic. I show that the original Deutsch XOR algorithm, Simon's algorithm, and Shor's algorithm all involve a similar geometric formulation. In terms of this picture, I consider the question of where the speedup relative to classical algorithms comes from. Jeffrey Bub http://streamer.perimeterinstitute.ca/mp3/7576ec28-7dc1-496b-a008-9809ec06af0b.mp3 Science http://streamer.perimeterinstitute.ca/mp3/7576ec28-7dc1-496b-a008-9809ec06af0b.mp3 Wed, 08 Feb 2006 14:00:23 -0500 The TeV energy range is a privileged part of the EM spectrum for astrophysical observations, allowing a view of some of the most energetic processes in the Universe, in objects as diverse as supernova remnants and black-hole driven Active Galactic Nuclei. Driven by new instruments, TeV gamma-rays astrophysics has made enormous strides in recent years with the discovery of many new sources, including new classes of sources such as galactic micro-quasars. This talk will give an overview of the state of TeV gamma-ray astrophysics, including the air Cherenkov technique used by ground-based TeV gamma ray detectors, the new instruments in operation or coming on line soon, and some of the results already obtained. Ken Ragan http://streamer.perimeterinstitute.ca/mp3/df890638-b8aa-49b4-ae8f-8662d4d8eec6.mp3 Science http://streamer.perimeterinstitute.ca/mp3/df890638-b8aa-49b4-ae8f-8662d4d8eec6.mp3 Wed, 15 Feb 2006 14:00:44 -0500 V Parameswarn Nair http://streamer.perimeterinstitute.ca/mp3/95a6e8c2-4261-4b04-a4ce-9fc870d9f805.mp3 Science http://streamer.perimeterinstitute.ca/mp3/95a6e8c2-4261-4b04-a4ce-9fc870d9f805.mp3 Wed, 22 Feb 2006 14:00:02 -0500 Kilometer-scale neutrino detectors such as IceCube are discovery instruments covering nuclear and particle physics, cosmology and astronomy. Examples of their multidisciplinary missions include the search for the particle nature of dark matter and for additional small dimensions of space. In the end, their conceptual design is very much anchored to the observational fact that Nature produces protons and photons with energies in excess of 1020 and1013 electronvolts, respectively. The cosmic ray connection sets the scale of cosmic neutrino fluxes. The problem has been to develop a robust and affordable technology to build the kilometer-scale neutrino detectors required to do the science. The AMANDA telescope using clear deep Antarctic ice as a Cherenkov detector of muons and showers initiated by neutrinos of all 3 flavors, has met this challenge. We review the results obtained with more than 10,000 well-reconstructed neutrinos in the 50 GeV~500 TeV energy range collected during its first 5 years of operation. More importantly, we will show that AMANDA represents a proof of concept for the ultimate kilometer-scale neutrino observatory, IceCube, now under construction. Francis Halzen http://streamer.perimeterinstitute.ca/mp3/e7f649fc-c483-4e4c-bcc1-e5346ea78a80.mp3 Science http://streamer.perimeterinstitute.ca/mp3/e7f649fc-c483-4e4c-bcc1-e5346ea78a80.mp3 Wed, 01 Mar 2006 14:00:47 -0500 Strongly correlated many-body systems are often formulated as gauge theories where gauge field plays a role of Lagrangian multiplier and fundamental matter field represents a fractional degree of freedom which carries only a fractional quantum number of microscopic particle. Although the fractional particles are prone to be confined at high energy owing to an infinite bare gauge coupling, they can emerge as deconfined degrees of freedom at low/intermediate energy scales as the gauge coupling is renormalized to a finite value by fluctuating matter fields. The resulting dynamics of the gauge field crucially depends on the number and the dynamics of the matter fields. In this talk, I will discuss how a change in the dynamics of matter fields affects the dynamics of gauge field. I will consider a field theory where a 2+1D compact U(1) gauge field is coupled to a large number of fundamental matter fields with an infinite bare gauge coupling and the matter fields are, in turn, subject to an additional strong interaction. This field theory can be realized as a low energy theory of a D-brane configuration and nonperturbative effects of the strong interaction can be studied from the AdS/CFT correspondence. Using the dual gravity theory, I will discuss how the strong interaction between matter fields can drastically modify the dynamics of the U(1) gauge field. Our result suggests that even an unstable brane configuration can define a consistent field theory once tachyonic modes are frozen. Sung-Sik Lee http://streamer.perimeterinstitute.ca/mp3/09aea37a-6337-43e8-be43-6bbdcbb07c90.mp3 Science http://streamer.perimeterinstitute.ca/mp3/09aea37a-6337-43e8-be43-6bbdcbb07c90.mp3 Mon, 06 Mar 2006 14:00:50 -0500 In this expository talk, I describe how "chaotic behavior" not only was discovered in the study of the Newtonian N-body problem, but also is responsible for several strange appearing motions. Then, a mathematical outline of the general evolution of the universe, under Newton's laws, is provided. No prior background in dynamics or the mathematics of the N-body problem is needed to follow this lecture Don Saari http://streamer.perimeterinstitute.ca/mp3/00a2df07-7b0a-40cc-aa1b-bc35197313a7.mp3 Science http://streamer.perimeterinstitute.ca/mp3/00a2df07-7b0a-40cc-aa1b-bc35197313a7.mp3 Thu, 09 Mar 2006 16:00:29 -0500 Janna Levin http://streamer.perimeterinstitute.ca/mp3/c99dd198-0ed1-4561-a565-4628fe3bd4be.mp3 Science http://streamer.perimeterinstitute.ca/mp3/c99dd198-0ed1-4561-a565-4628fe3bd4be.mp3 Wed, 15 Mar 2006 14:00:46 -0500 The Laser Astrometric Test of Relativity (LATOR) is a Michelson-Morley-type experiment designed to improve current tests of the Einstein’s theory of general relativity by more than four orders of magnitude. The LATOR mission uses laser interferometry between two laser sources placed on separate small spacecraft, whose lines of sight pass close by the Sun, to measure accurately the deflection of light in the solar gravity field. The key element of the experimental design is a redundant geometry optical truss provided by a long-baseline (~100m) Michelson stellar optical interferometer assembled on the International Space Station (ISS). The interferometer is used to measure the angles between the two spacecraft (with accuracy of 0.1 picoradian) and for orbit determination purposes (via laser-ranging-enabled orbit determination). The three arms of the spacecraft-ISS-spacecraft triangle are monitored with laser ranging (accurate to less than 1 cm). From these three length measurements one can calculate the Euclidean value for any of the angles in this triangle. The direct interferometric angular measurement and resulting geometric redundancy enables LATOR to measure the departure from Euclidean geometry caused by the solar gravity field to a very high accuracy. LATOR is a new fundamental physics experiment designed to test relativistic gravity at an accuracy never achieved before – probing for the first time the second-order effects in the gravitational field strength. By using independent time-series of highly accurate measurements of the Shapiro time-delay and gravitational deflection of light, LATOR will test Einstein's general theory of relativity in the most intense gravitational environment available in the solar system -- the close proximity to the Sun -- measuring gravitational deflection of light in the solar gravity with accuracy of 1 part per billion, a factor ~30,000 better than currently available (i.e. Cassini 2003 experiment). LATOR will perform series of highly-accurate tests of gravitation and cosmology in its search for cosmological remnants of scalar field in the solar system, ultimately providing addition information on the nature of dark matter and dark energy. In this talk we will discus the science, technology and mission design for the LATOR mission. The work described here was carried out at the Jet Propulsion Laboratory, California Institute of Technology under a contract with the National Aeronautics and Space Administration. Slava Turyshev http://streamer.perimeterinstitute.ca/mp3/ef88a7e4-4ef1-4db8-bfe9-ca6c113e27fa.mp3 Science http://streamer.perimeterinstitute.ca/mp3/ef88a7e4-4ef1-4db8-bfe9-ca6c113e27fa.mp3 Wed, 22 Mar 2006 14:00:02 -0500 Michael Douglas http://streamer.perimeterinstitute.ca/mp3/0323c91d-6a10-4c1c-b395-145d9290d62b.mp3 Science http://streamer.perimeterinstitute.ca/mp3/0323c91d-6a10-4c1c-b395-145d9290d62b.mp3 Wed, 29 Mar 2006 14:00:45 -0500 Neutrinos are the big unknown in Particle Physics. Since their very beginning they behaved strangely. However, in the last decade experiments were able to solve some of their secrets. The talk will review the current experimental status of neutrino experiments and give an outlook on future activities. Kai Zuber http://streamer.perimeterinstitute.ca/mp3/507ebe29-7900-4e24-8ba6-f7d691337140.mp3 Science http://streamer.perimeterinstitute.ca/mp3/507ebe29-7900-4e24-8ba6-f7d691337140.mp3 Wed, 05 Apr 2006 14:00:05 -0400 Familiar textbook quantum mechanics assumes a fixed background spacetime to define states on spacelike surfaces and their unitary evolution between them. Quantum theory has been generalized as our conceptions of space and time have evolved. But quantum mechanics needs to be generalized further for quantum gravity where spacetime geometry is fluctuating and without definite value. This talk will review a fully four-dimensional, sum-over-histories, generalized quantum mechanics of cosmological spacetime geometry. In this generalization, states of fields on spacelike surfaces and their unitary evolution are emergent properties appropriate when spacetime geometry behaves approximately classically. The principles of generalized quantum theory would allow for further generalization that would be necessary were spacetime not fundamental. Emergent spacetime phenomena are discussed in general and illustrated with the examples of the classical spacetime geometries with large spacelike surfaces that emerge from the `no-boundary' wave function of the universe. These must be Lorentzian with one, and only one, time direction. The question will be raised as to whether quantum mechanics itself is emergent. Jim Hartle http://streamer.perimeterinstitute.ca/mp3/c800b8d7-aeb4-4f29-85a7-a12b2baa4dc2.mp3 Science http://streamer.perimeterinstitute.ca/mp3/c800b8d7-aeb4-4f29-85a7-a12b2baa4dc2.mp3 Wed, 19 Apr 2006 14:00:42 -0400 I will describe some recent advances in the simulation of binary black hole spacetimes using a numerical scheme based on generalized harmonic coordinates. After a brief overview of the formalism and method, I will present results from the evolution of a couple of classes of initial data, including Cook-Pfieffer quasi-circular inspiral data sets, and binaries constructed via scalar field collapse. In the latter case, preliminary studies suggest that in certain regions of parameter space there is extreme sensitivity of the resulting orbit to the initial conditions. In this regime the equal mass black holes exhibit behavior reminiscent of "zoom-whirl" particle trajectories in the test-mass limit. Frans Pretorius http://streamer.perimeterinstitute.ca/mp3/cfda0239-1872-44c9-855c-2077b1733612.mp3 Science http://streamer.perimeterinstitute.ca/mp3/cfda0239-1872-44c9-855c-2077b1733612.mp3 Wed, 26 Apr 2006 14:00:39 -0400 A variety of physical phenomena involve multiple length and time scales. Some interesting examples of multiple-scale phenomena are: (a) the mechanical behavior of crystals and in particular the interplay of chemistry and mechanical stress in determining the macroscopic brittle or ductile response of solids; (b) the molecular-scale forces at interfaces and their effect in macroscopic phenomena like wetting and friction; (c) the alteration of the structure and electronic properties of macromolecular systems due to external forces, as in stretched DNA nanowires or carbon nanotubes. In these complex physical systems, the changes in bonding and atomic configurations at the microscopic, atomic level have profound effects on the macroscopic properties, be they of mechanical or electrical nature. Linking the processes at the two extremes of the length scale spectrum is the only means of achieving a deeper understanding of these phenomena and, ultimately, of being able to control them. While methodologies for describing the physics at a single scale are well developed in many fields of physics, chemistry or engineering, methodologies that couple scales remain a challenge, both from the conceptual point as well as from the computational point. In this presentation I will discuss the development of methodologies for simulations across disparate length scales with the aim of obtaining a detailed description of complex phenomena of the type described above. I will also present illustrative examples, including hydrogen embrittlement of metals, DNA conductivity and translocation through nanopores, and affecting the wettability of surfaces by surface chemical modification. Tim Kaxiras http://streamer.perimeterinstitute.ca/mp3/07dd1870-4c06-4f28-845d-958cc71904e1.mp3 Science http://streamer.perimeterinstitute.ca/mp3/07dd1870-4c06-4f28-845d-958cc71904e1.mp3 Wed, 10 May 2006 14:00:58 -0400 Nanostructured materials continue to be the focus of intense research due to their promise of innumerable practical applications as well as advancing the fundamental understanding of these intriguing materials. From physics, to chemistry, to biology, to computer science, across the engineering disciplines and into the imagination of the general event, nanotechnology has become an extremely popular buzzword that represents both hope and hype to many people. This talk will outline and describe the exploding field of nanotechnology, including its potential for promising new applications, and for negative societal implications that cause many to fear it. Recent work in our group in the area of integration of nanoscale structures with silicon will be outlined to show the scope and approaches to building nanoscale architectures; the applications of these frameworks include molecular computing, nanoscale sensing platforms, integration of silicon with biology, and intricate structures with unforeseen properties. Jillian Buriak http://streamer.perimeterinstitute.ca/mp3/5c3b9038-c72c-474c-a423-8554c677ee53.mp3 Science http://streamer.perimeterinstitute.ca/mp3/5c3b9038-c72c-474c-a423-8554c677ee53.mp3 Wed, 17 May 2006 14:00:23 -0400 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. John Baez http://streamer.perimeterinstitute.ca/mp3/a4065be2-4828-4015-b3d2-3b311edcaffe.mp3 Science http://streamer.perimeterinstitute.ca/mp3/a4065be2-4828-4015-b3d2-3b311edcaffe.mp3 Wed, 31 May 2006 14:00:59 -0400 At low energy and small curvature, general relativity has the form of an effective field theory. I will describe the structure of the effective field theory, and show how it can be used to calculate low energy quantum effects. John Donoghue http://streamer.perimeterinstitute.ca/mp3/ffca9eba-18bc-44e6-acef-472a14978871.mp3 Science http://streamer.perimeterinstitute.ca/mp3/ffca9eba-18bc-44e6-acef-472a14978871.mp3 Wed, 14 Jun 2006 14:00:16 -0400 Not only general relativity but also quantum theory plays important roles in current cosmology. Quantum fluctuations of matter fields are supposed to have provided the initial seeds of all the structure of the current universe, and quantum gravity is assumed to have been essential in the earliest stages. Both issues are not fully understood, although several heuristic effects have been discussed. In this talk, implications of an effective framework taking into account the coupling of matter and gravity are discussed. This touches on interpretational issues of quantum mechanics, cosmological observations and properties of quantum gravity. Martin Bojowald http://streamer.perimeterinstitute.ca/mp3/fdc17b7c-eb85-47fd-be5d-25368d8ab3d7.mp3 Science http://streamer.perimeterinstitute.ca/mp3/fdc17b7c-eb85-47fd-be5d-25368d8ab3d7.mp3 Wed, 28 Jun 2006 14:00:21 -0400 How should we think about quantum computing? The usual answer to this question is based on ideas inspired by computer science, such as qubits, quantum gates, and quantum circuits. In this talk I will explain an alternate geometric approach to quantum computation. In the geometric approach, an optimal quantum computation corresponds to "free falling" along the minimal geodesics of a certain Riemannian manifold. This reformulation opens up the possibility of using tools from geometry to understand the strengths and weaknesses of quantum computation, and perhaps to understand what makes certain physical operations difficult (or easy) to synthesize. Michael Nielsen http://streamer.perimeterinstitute.ca/mp3/eb29a499-df68-44e0-8409-e4c21a99c6d6.mp3 Science http://streamer.perimeterinstitute.ca/mp3/eb29a499-df68-44e0-8409-e4c21a99c6d6.mp3 Wed, 02 Aug 2006 14:00:00 -0400 I will first argue that the notion of black hole entropy extends universally to causal horizons. Then I will deduce the causal dynamics of spacetime from the equilibrium thermodynamics of causal horizons. Specifically, it will be shown how the Clausius relation dS = dQ/T between entropy change, energy flux, and acceleration temperature for all local causal horizons implies the Einstein equation, with Newton's constant determined by the universal horizon entropy density. Implications, non-equilibrium processes, and relations to AdS/CFT duality will also be discussed. Ted Jacobson http://streamer.perimeterinstitute.ca/mp3/d0516b49-f37a-43d5-b753-fe662453c97a.mp3 Science http://streamer.perimeterinstitute.ca/mp3/d0516b49-f37a-43d5-b753-fe662453c97a.mp3 Wed, 06 Sep 2006 14:00:00 -0400 Roger Penrose http://streamer.perimeterinstitute.ca/mp3/f41bae02-4a81-448f-8eb5-c0939859f6bf.mp3 Science http://streamer.perimeterinstitute.ca/mp3/f41bae02-4a81-448f-8eb5-c0939859f6bf.mp3 Tue, 12 Sep 2006 14:00:00 -0400 Traditional quantum state tomography requires a number of measurements that grows exponentially with the number of qubits n. But using ideas from computational learning theory, I'll show that "for most practical purposes" one can learn a quantum state using a number of measurements that grows only linearly with n. I'll discuss applications of this result in experimental physics and quantum computing theory, as well as possible implications for the foundations of quantum mechanics. quant-ph/0608142 Scott Aaronson http://streamer.perimeterinstitute.ca/mp3/bb627e24-36c4-4dca-a945-7d52492c0f65.mp3 Science http://streamer.perimeterinstitute.ca/mp3/bb627e24-36c4-4dca-a945-7d52492c0f65.mp3 Wed, 20 Sep 2006 14:00:00 -0400 Conventional wisdom holds that the majority of high energy atomic nuclei ("cosmic rays") that continually rain upon the Earth originate in galactic supernova shock waves, although some different (likely extragalactic) origin must be invoked to explain the highest energy particles. Despite many decades of intensive research on the subject, only indirect clues to these ideas exist at present. Direct measurements of the spectrum and mass composition of high energy cosmic rays are needed to validate these notions, but are hampered by rapidly dwindling fluxes with energy. Indeed, there is an expectation that the cosmic nuclei should have progressively more charge (and therefore mass), on average, with increasing energy, up to the astrophysical "knee" (spectral break) in the spectrum at around 3x10^15 eV. At energies beyond the knee, only indirect measurements are possible. The CREAM (Cosmic Ray Energetics And Mass) experiment is a complex particle detector flown by high altitude balloon to directly measure the charge and energy of the cosmic rays at energies near the spectral knee. It flew successfully in Antarctica in Dec 04 / Jan 05 for a record-breaking 42 days, and again in Dec 05 / Jan 06. We will review the science and performance of the instrument in flight, and present preliminary results and discuss prospects for additional CREAM missions. The Auger experiment is the largest cosmic ray detector ever built, currently nearing completion in Argentina, covering an area of 3000 km^2. Its aim is to resolve a number of mysteries surrounding the highest energy cosmic rays, beyond 10^18 eV, whose very existence and ability to reach the Earth are difficult to understand. The rarity of the highest energy particles has precluded definitive answers to the question of their nature and origin, and indeed some controversy surrounds the existing experimental evidence. The Auger experiment will afford an order of magnitude improvement in statistics over previous efforts, as well as much improved control of systematics. We will briefly review the science of the highest energy cosmic rays and present first results obtained with the growing Auger array, and discuss plans for the future of these efforts. Stephane Coutu http://streamer.perimeterinstitute.ca/mp3/debde252-d769-4dd5-8d37-2ceb3a5dca41.mp3 Science http://streamer.perimeterinstitute.ca/mp3/debde252-d769-4dd5-8d37-2ceb3a5dca41.mp3 Wed, 04 Oct 2006 02:00:00 -0400 We consider the hypothesis that quantum mechanics is an approximation to another, cosmological theory, accurate only for the description of subsystems of the universe. Quantum theory is then to be derived from the cosmological theory by averaging over variables which are not internal to the subsystem, which may be considered non-local hidden variables. I will explain the motivation for this view, give some examples of theories of this kind and investigate general conditions for such an approach to succeed. Lee Smolin http://streamer.perimeterinstitute.ca/mp3/19f4c951-3249-4259-80a8-e4047add9a2b.mp3 Science http://streamer.perimeterinstitute.ca/mp3/19f4c951-3249-4259-80a8-e4047add9a2b.mp3 Wed, 11 Oct 2006 02:00:00 -0400 Weakly interacting massive particles (WIMPs) are excellent candidates for cold dark matter. After the first millisecond, WIMPs have decoupled from standard model matter, both chemically and kinetically, they enter the free streaming regime and the formation of cosmic structure begins. Another 40 million years pass before the typical first structures enter the nonlinear regime and collapse to the first WIMPy halos. Therefore, it has been assumed that structure formation is insensitive to the WIMP field theory and can be neglected. However, this leads to a monotonically increasing power of structure formation on small scales and some kind of regularization procedure would be required to make the hierarchical picture of structure formation well defined. It will be shown that nonequilibrium processes give rise to a physical regularization of hierarchical structure formation. This has important consequences for indirect and direct dark matter searches which are sensitive to sub-galactic and sub-milli-parsec scales. Furthermore, due the existence of a physical regulator, the problem of structure formation can consistently be solved using N-body simulations. Stefan Hofmann http://streamer.perimeterinstitute.ca/mp3/c68df443-ee62-4ece-8264-173f5219b70c.mp3 Science http://streamer.perimeterinstitute.ca/mp3/c68df443-ee62-4ece-8264-173f5219b70c.mp3 Wed, 18 Oct 2006 14:00:00 -0400 We discuss motivations, observational constraints and consequences of modifying the fundamental laws of gravity at large distances. Such modifications of gravity can be the reason for the observed late-time acceleration of the Universe, and can be differentiated from conventional dark energy via precision cosmology. The inevitable additional polarizations of graviton lead to observably large perihelion precession of the Lunar and Martian orbits. These theories also have potentially observable consequences at LHC . Georgi Dvali http://streamer.perimeterinstitute.ca/mp3/d517e944-c8c1-44ce-90c1-b7c06d60498f.mp3 Science http://streamer.perimeterinstitute.ca/mp3/d517e944-c8c1-44ce-90c1-b7c06d60498f.mp3 Wed, 25 Oct 2006 14:00:00 -0400 Boundary conformal field theory finds applications not only to high energy physics but also to condensed matter systems containing quantum impurities, whose world lines can sometimes be modelled as boundaries of 2-dimensional space-time. This technique leads to exact predictions for the low temperature behaviour of gated semi-conductor quantum dot devices which have been recently confirmed experimentally. I will give a non-technical overview of both the theory and the experiments. Ian Affleck http://streamer.perimeterinstitute.ca/mp3/49e28d95-d02b-4995-b82d-6de789a16990.mp3 Science http://streamer.perimeterinstitute.ca/mp3/49e28d95-d02b-4995-b82d-6de789a16990.mp3 Wed, 01 Nov 2006 14:00:00 -0500 The nature of an unusual class of cosmic X-ray source, dubbed "Anomalous X-ray Pulsars," was a mystery since 1982 when the first example was discovered. In this talk, I will show the recent observational evidence that unambiguously links them with another equally exotic class of object, the explosive "Soft Gamma Repeaters." The evidence todate strongly supports the picture that both are "magnetars:" isolated young neutron stars having surface magnetic fields ~1000 times greater than those in conventional neutron stars. Victoria Kaspi http://streamer.perimeterinstitute.ca/mp3/329a3ced-fd6d-4098-b50e-6f85abab80c1.mp3 Science http://streamer.perimeterinstitute.ca/mp3/329a3ced-fd6d-4098-b50e-6f85abab80c1.mp3 Wed, 08 Nov 2006 14:00:00 -0500 I will explain how a quantum circuit together with measurement apparatuses and EPR sources can be fully verified without any reference to some other trusted set of quantum devices. Our main assumption is that the physical system we are working with consists of several identifiable sub-systems, on which we can apply some given gates locally. To achieve our goal we define the notions of simulation and equivalence. The concept of simulation refers to producing the correct probabilities when measuring physical systems. The notion of equivalence is used to enable the efficient testing of the composition of quantum operations. Unlike simulation, which refers to measured quantities (i.e., probabilities of outcomes), equivalence relates mathematical objects like states, subspaces or gates. Using these two concepts, we prove that if a system satisfies some simulation conditions, then it is equivalent to the one it is supposed to implement. In addition, with our formalism, we can show that these statements are robust, and the degree of robustness can be made explicit. Finally, we design a test for any quantum circuit whose complexity is linear in the number of gates and qubits, and polynomial in the required precision. Joint work with Frederic Magniez, Dominic Mayers and Harold Ollivier. Michele Mosca http://streamer.perimeterinstitute.ca/mp3/2ebadc29-05e8-46da-b041-9d424004e911.mp3 Science http://streamer.perimeterinstitute.ca/mp3/2ebadc29-05e8-46da-b041-9d424004e911.mp3 Wed, 15 Nov 2006 14:00:00 -0500 We have previously isolated and characterized a multipotent precursor cell (termed SKPs for SKin-derived Precursors) from both rodent and human skin, and have shown that these stem cells share many characteristics with a multipotent stem cell that is found in the embryo termed a neural crest stem cell. Here I will discuss our current work with regard to the basic biology of these stem cells, with a focus on the “what, where and why”, and on their therapeutic potential with specific regard to the nervous system. Freda Miller http://streamer.perimeterinstitute.ca/mp3/9d7c8b75-6976-427b-8845-1492578e0d7c.mp3 Science http://streamer.perimeterinstitute.ca/mp3/9d7c8b75-6976-427b-8845-1492578e0d7c.mp3 Wed, 22 Nov 2006 14:00:00 -0500 Viatcheslav Mukhanov http://streamer.perimeterinstitute.ca/mp3/bf2647ec-fd55-43f6-9387-1e0f9380fc06.mp3 Science http://streamer.perimeterinstitute.ca/mp3/bf2647ec-fd55-43f6-9387-1e0f9380fc06.mp3 Thu, 23 Nov 2006 11:00:00 -0500 David Archer http://streamer.perimeterinstitute.ca/mp3/97d6805d-776c-432d-bcf7-b32f60dc5d14.mp3 Science http://streamer.perimeterinstitute.ca/mp3/97d6805d-776c-432d-bcf7-b32f60dc5d14.mp3 Wed, 06 Dec 2006 14:00:00 -0500 In this talk I describe a possible connection between quantum computing and Zeta functions of finite field equations that is inspired by the 'spectral approach' to the Riemann conjecture. This time the assumption is that the zeros of such Zeta functions correspond to the eigenvalues of finite dimensional unitary operators of quantum mechanical systems. To model the desired quantum systems I use the notion of universal, efficient quantum computation. Using eigenvalue estimation, such quantum systems should be able to approximately count the number of solutions of the specific finite field equations with an accuracy that does not appear to be feasible classically. For certain equations (Fermat hypersurfaces) one can indeed model their Zeta functions with efficient quantum algorithms, which gives some evidence in favor of the proposal. In the case of equations that define elliptic curves, the corresponding unitary transformation is an SU(2) matrix. Hence for random elliptic curves one expects to see the kind of statistics predicted by random matrix theory. In the last part of the talk I discuss to which degree this expectation does indeed hold. Reference: arXiv:quant-ph/0405081 Wim van Dam http://streamer.perimeterinstitute.ca/mp3/92e878d4-06db-43d8-a8cf-07bda27f79ac.mp3 Science http://streamer.perimeterinstitute.ca/mp3/92e878d4-06db-43d8-a8cf-07bda27f79ac.mp3 Wed, 13 Dec 2006 14:00:00 -0500 A full analysis of QCD, the fundamental theory of subnuclear structure and interactions, relies upon numerical simulations and the lattice approximation. After being stalled for almost 30 years, recent breakthroughs in lattice QCD allow us for the first time to analyze the low-energy structure of QCD nonperturbatively with few-percent precision. This talk will present a non-technical overview of the history leading up to these breakthroughs, and survey the wide array of applications that have been enabled by them. It will focus in particular on the impact of these new techniques on experiments that explore such areas as heavy-quark and Standard Model physics. Peter Lepage http://streamer.perimeterinstitute.ca/mp3/54ad8d35-0908-46c5-8139-3296d06aa34c.mp3 Science http://streamer.perimeterinstitute.ca/mp3/54ad8d35-0908-46c5-8139-3296d06aa34c.mp3 Wed, 10 Jan 2007 14:00:00 -0500 If spacetime is "quantized" (discrete), then any equation of motion compatible with the Lorentz transformations is necessarily non-local. I will present evidence that this sort of nonlocality survives on length scales much greater than Planckian, yielding for example a nonlocal effective wave-equation for a scalar field propagating on an underlying causal set. Nonlocality of our effective field theories may thus provide a characteristic signature of quantum gravity. Rafael Sorkin http://streamer.perimeterinstitute.ca/mp3/f9b56930-6d88-4ccf-8218-c8f42a6cb37e.mp3 Science http://streamer.perimeterinstitute.ca/mp3/f9b56930-6d88-4ccf-8218-c8f42a6cb37e.mp3 Wed, 17 Jan 2007 14:00:00 -0500 Understanding magnetic reconnection is one of the major challenges of plasma physics. It plays an essential role in a wide range of physical systems such as stellar flares, accretion disks, active galactic nuclei, astrophysical dynamos and closer to home, intense magnetic energy releases in the Earth's magnetosphere. It is a phenomena which can be created in the laboratory. Magnetic reconnection occurs when oppositely directed components of field lines are broken and re-connected resulting in destruction of magnetic flux and topological rearrangement of magnetic field lines on very small scales. This can induce the release of magnetic energy on large scales resulting in high speed flows, heating and energetic particle production. There is a strong connection between formation of singular structures in flows and magnetic reconnection which I will discuss and tie this into some of the laboratory and natural physical systems under recent study. In addition to giving a contemporary overview on this subject I will discuss some open questions. Richard Sydora http://streamer.perimeterinstitute.ca/mp3/2ef92089-e8da-4956-868e-e5db641fdba9.mp3 Science http://streamer.perimeterinstitute.ca/mp3/2ef92089-e8da-4956-868e-e5db641fdba9.mp3 Wed, 24 Jan 2007 14:00:00 -0500 With a cosmic flight simulator, we'll take a scenic journey through space and time. After exploring our local Galactic neighborhood, we'll travel back 13.7 billion years to explore the Big Bang itself and how state-of-the-art measurements are transforming our understanding of our cosmic origin and ultimate fate. We then turn to the question of whether this can all be described purely mathematically, and discuss implications ranging from standard physics topics like symmetries, irreducible representations, units, free parameters and initial conditions to broader issues like parallel universes, simulations and and Goedel incompleteness. Max Tegmark http://streamer.perimeterinstitute.ca/mp3/db3d7b18-128d-43ab-bd20-19b0f0efbff2.mp3 Science http://streamer.perimeterinstitute.ca/mp3/db3d7b18-128d-43ab-bd20-19b0f0efbff2.mp3 Wed, 31 Jan 2007 14:00:00 -0500 Soon after Quantum Chromodynamics (QCD) was shown to exhibit asymptotic freedom at short distances, it was realized that it might be possible to create a new form of matter at high temperatures (T „d 150 MeV) in which hadrons dissolve and quarks and gluons become locally deconfined. Experiments have been carried out for the last two decades attempting to create this new form of matter, called ¡§quark-gluon plasma¡¨ (QGP), via high-energy collisions of large nuclei. In 2000, the Relativistic Heavy Ion Collider (RHIC) started operation at Brookhaven National Laboratory in the US and results obtained from the first five years of RHIC operation provide the first convincing evidence for creation of the quark-gluon plasma in the laboratory. Measurements at RHIC show that the QGP is opaque to the passage of high-energy quarks and gluons and that interactions between the quarks and gluons in the QGP appears to be much stronger than initially expected. The estimated viscosity to entropy ratio of the QGP has been interpreted as showing that the QGP produced at RHIC is the most perfect fluid ever observed in the laboratory. Measurements from RHIC also suggest that the strong, coherent gluon fields in the incident nuclei play a significant role in the initial particle production and early evolution of the quark gluon plasma. Within the next few years, the large hadron collider will provide Pb+Pb collisions at a nucleon-nucleon center of mass energy of 5.5 TeV, thus opening a new frontier in the study of the QGP. I will provide a summary of the key experimental observables at RHIC, a discussion of their canonical interpretation and then discuss how measurements at the LHC can be used to test these interpretations. Brian Cole http://streamer.perimeterinstitute.ca/mp3/6b2eaf1d-29d0-4ec9-9603-e3f84675b419.mp3 Science http://streamer.perimeterinstitute.ca/mp3/6b2eaf1d-29d0-4ec9-9603-e3f84675b419.mp3 Wed, 07 Feb 2007 14:00:00 -0500 Experimentalists at the Relativistic Heavy Ion Collider create exploding droplets of quark-gluon plasma, the stuff which filled the universe for the first microseconds after the big bang. I'll give one theorist's perspective on what we are learning about the properties of quark-gluon plasma from these experiments, including the conclusion that it is closer to an ideal liquid than to an ideal gas and the observation that it "quenches" high energy quarks ("jets") trying to plow through it. The static properties of quark-gluon plasma can be calculated from first principles, but we have no rigorous calculations of what QCD predicts for the viscosity and jet quenching ability of the evidently very strongly interacting quark-gluon plasma that RHIC has discovered. In desperation, theorists are resorting to calculating the properties of quark-gluon plasma in theories other than QCD, wherein difficult dynamical questions like how does a strongly interacting plasma quench jets can be answered by doing easy string theory calculations. I will discuss two examples where such calculations have been compared quantitatively to inferences drawn from existing RHIC data, and close with one prediction for data to come. Krishna Rajagopal http://streamer.perimeterinstitute.ca/mp3/edfb9c69-408d-4b0d-92f7-1071f9da0953.mp3 Science http://streamer.perimeterinstitute.ca/mp3/edfb9c69-408d-4b0d-92f7-1071f9da0953.mp3 Wed, 14 Feb 2007 14:00:00 -0500 tba Sean Carroll http://streamer.perimeterinstitute.ca/mp3/dd50a341-af34-4cea-b8c6-41c74f2a076f.mp3 Science http://streamer.perimeterinstitute.ca/mp3/dd50a341-af34-4cea-b8c6-41c74f2a076f.mp3 Wed, 28 Feb 2007 14:00:00 -0500 Some of the speculations on new physics, beyond what is in the standard model are reviewed. Particular attention is paid to ideas that try to address the hierarchy puzzle, i.e., why is the weak scale so much smaller than the Planck scale. These new theories will be tested at the large hadron collider in the near future. Mark Wise http://streamer.perimeterinstitute.ca/mp3/93bec70b-b760-4569-9069-1d828ade10ae.mp3 Science http://streamer.perimeterinstitute.ca/mp3/93bec70b-b760-4569-9069-1d828ade10ae.mp3 Wed, 07 Mar 2007 14:00:00 -0500 Theories of physics beyond the Standard Model predict the existence of relativistic strings, either as composite objects, or as fundamental constituents of matter. If they were created in the Big Bang, they would very likely still be present in the universe today. This talk reviews the thirty year history of cosmic strings, and describes the latest work which finds intriguing hints in the Cosmic Microwave Background data that the universe is filled with string. Mark Hindmarsh http://streamer.perimeterinstitute.ca/mp3/ebf2c192-dc2a-4d32-9d93-ba89e58eb352.mp3 Science http://streamer.perimeterinstitute.ca/mp3/ebf2c192-dc2a-4d32-9d93-ba89e58eb352.mp3 Wed, 21 Mar 2007 14:00:00 -0400 Shear viscosity is a transport coefficient in the hydrodynamic description of liquids, gases and plasmas. The ratio of the shear viscosity and the volume density of the entropy has the dimension of the ratio of two fundamental constants - the Planck constant and the Boltzmann constant - and characterizes how close a given fluid is to a perfect fluid. Transport coefficients are notoriously difficult to compute from first principles. Recent progress in string theory, in particular the development of the gauge-gravity duality, has enabled one to approach this problem from a totally unexpected perspective. In my talk, I will describe the connection between the dynamics of black hole horizons (encoded in their quasinormal spectra) and the hydrodynamics of certain strongly coupled plasmas. I will comment on the relevance of this approach for the interpretation of data obtained in experiments on heavy ion collisions. Andrei Starinets http://streamer.perimeterinstitute.ca/mp3/f37db538-5bdb-4a01-8c52-c8af6d4395c1.mp3 Science http://streamer.perimeterinstitute.ca/mp3/f37db538-5bdb-4a01-8c52-c8af6d4395c1.mp3 Wed, 28 Mar 2007 14:00:00 -0400 The theory of strong interactions is an elegant quantum field theory known as Quantum Chromodynamics (QCD). QCD is deceptively simple to formulate, but notoriously difficult to solve. This simplicity belies the diverse set of physical phenomena that fall under its domain, from nuclear forces and bound hadrons, to high energy jets and gluon radiation. In this talk I show how systematic limits of QCD, known as effective field theories, provide a means of isolating the essential degrees of freedom for a particular problem while at the same time supplying a powerful tool for quantitative computations. The adventure will take us from the fine structure of hydrogen, to weak decays of B-mesons, to the behavior of energetic hadrons and jets in QCD. Iain Stewart http://streamer.perimeterinstitute.ca/mp3/f880f63f-f692-43cc-8cc4-b7e39492eeef.mp3 Science http://streamer.perimeterinstitute.ca/mp3/f880f63f-f692-43cc-8cc4-b7e39492eeef.mp3 Wed, 11 Apr 2007 14:00:00 -0400 tba Paul Wiseman http://streamer.perimeterinstitute.ca/mp3/bb32203a-5650-49bb-96ef-eb6ee238c7e4.mp3 Science http://streamer.perimeterinstitute.ca/mp3/bb32203a-5650-49bb-96ef-eb6ee238c7e4.mp3 Wed, 18 Apr 2007 14:00:00 -0400 Among the possible explanations for the observed acceleration of the universe, perhaps the boldest is the idea that new gravitational physics might be the culprit. In this colloquium I will discuss some of the challenges of constructing a sensible phenomenological extension of General Relativity, give examples of some candidate models of modified gravity and survey existing observational constraints on this approach. I will conclude by discussing how we might hope to distinguish between modifications of General Relativity and dark energy as competing hypotheses to explain cosmic acceleration. Mark Trodden http://streamer.perimeterinstitute.ca/mp3/81eecf94-e17c-49ba-9a68-f090e5e852e2.mp3 Science http://streamer.perimeterinstitute.ca/mp3/81eecf94-e17c-49ba-9a68-f090e5e852e2.mp3 Wed, 25 Apr 2007 14:00:00 -0400 The progress in neutrino physics over the past ten years has been tremendous: we have learned that neutrinos have mass and change flavor. I will pick out one of the threads of the story-- the measurement of flavor oscillation in neutrinos produced by cosmic ray showers in the atmosphere, and its confirmation in long distance beam experiments. I will present the history, the current state of knowledge, and how the next generation of high intensity beam experiments will address some of the remaining puzzles. Kate Scholberg http://streamer.perimeterinstitute.ca/mp3/a3fbde4b-424f-4730-b138-3a281bc43655.mp3 Science http://streamer.perimeterinstitute.ca/mp3/a3fbde4b-424f-4730-b138-3a281bc43655.mp3 Wed, 02 May 2007 14:00:00 -0400 Modern motivations for extra spacetime dimensions will be presented, in particular the surprising AdS/CFT connection to particle compositeness. It will be shown how highly curved, "warped", extra-dimensional geometries can naturally address several puzzles of fundamental physics, including the weakness of gravity, particle mass hierarchies, dark matter, and supersymmetry breaking. The possibility of direct discovery of warped dimensions at particle colliders such as the CERN Large Hadron Collider will be discussed. Some current questions in warped cosmology will also be introduced. Raman Sundrum http://streamer.perimeterinstitute.ca/mp3/ef1d5591-8481-43a5-b16c-0889092924ae.mp3 Science http://streamer.perimeterinstitute.ca/mp3/ef1d5591-8481-43a5-b16c-0889092924ae.mp3 Wed, 09 May 2007 14:00:00 -0400 I will discuss an alternative approach to simulating Hamiltonian flows with a quantum computer. A Hamiltonian system is a continuous time dynamical system represented as a flow of points in phase space. An alternative dynamical system, first introduced by Poincare, is defined in terms of an area preserving map. The dynamics is not continuous but discrete and successive dynamical states are labeled by integers rather than a continuous time variable. Discrete unitary maps are naturally adapted to the quantum computing paradigm. Grover's algorithm, for example, is an iterated unitary map. In this talk I will discuss examples of nonlinear dynamical maps which are well adapted to simple ion trap quantum computers, including a transverse field Ising map, a non linear rotor map and a Jahn-Teller map. I will show how a good understanding of the quantum phase transitions and entanglement exhibited in these models can be gained by first describing the classical bifurcation structure of fixed points. Gerard Milburn http://streamer.perimeterinstitute.ca/mp3/bdab86ea-f1e0-4dec-afec-94905b756e2b.mp3 Science http://streamer.perimeterinstitute.ca/mp3/bdab86ea-f1e0-4dec-afec-94905b756e2b.mp3 Wed, 12 Sep 2007 14:00:00 -0400 Quantum field theory in curved spacetime (QFTCS) is the theory of quantum fields propagating in a classical curved spacetime, as described by general relativity. QFTCS has been applied to describe such important and interesting phenomena as particle creation by black holes and perturbations in the early universe associated with inflation. However, by the mid-1970's, it became clear from phenomena such as the Unruh effect that 'particles' cannot be a fundamental notion in QFTCS. By the mid-1980's it was understood how to give a mathematically rigorous formulation of the theory of a free quantum field in curved spacetime. During the past decade, major progress has been made in providing a completely mathematically satisfactory formulation of renormalization in interacting QFTCS, thereby overcoming the difficulties caused by the absence of Poincare symmetry as well as the lack of a preferred vacuum state and a fundamental notion of 'particles'. This talk will describe these developments and some of the insights that have thereby been attained. Robert Wald http://streamer.perimeterinstitute.ca/mp3/301aa4e5-8e76-4b42-817d-024051ab17eb.mp3 Science http://streamer.perimeterinstitute.ca/mp3/301aa4e5-8e76-4b42-817d-024051ab17eb.mp3 Wed, 19 Sep 2007 14:00:00 -0400 One of the cool, frustrating things about quantum theory is how the once-innocuous concept of "measurement" gets really complicated. I'd like to understand how we find out about the universe around us, and how to reconcile (a) everyday experience, (b) experiments on quantum systems, and (c) our theory of quantum measurements. In this talk, I'll try to braid three [apparently] separate research projects into the beginnings of an answer. I'll begin from the premise that you make a measurement to find something out, then attack some specific questions: "How do we find out about quantum systems?", "What can we find out about quantum systems?", and finally "What do we actually know, afterward?" I'll give precise statements of these questions, then present [partial] answers. Robin Blume-Kohout http://streamer.perimeterinstitute.ca/mp3/917f9d0d-e7ec-4d4f-a700-1aaf44f0400c.mp3 Science http://streamer.perimeterinstitute.ca/mp3/917f9d0d-e7ec-4d4f-a700-1aaf44f0400c.mp3 Wed, 03 Oct 2007 14:00:00 -0400 The role of outflows in global star formation processes has become hotly debated even as fundamental questions about the nature of these outflows continues to receive attention. In this talk I discuss both problems and new approaches to their resolution. Astrophysical outflows have always been a subject at the forefront of the numerical technologies and in the first act of the talk I introduce AstroBEAR, a new Adaptive Mesh Refinement MHD tool developed at Rochester for the study of star formation outflow issues. The question of 'feedback', the mechanisms by which protostellar outflows can drive turbulence in either clouds or clusters, is then addressed via AstroBEAR simulations. In these studies we seek to understand the detailed mechanisms by which outflows can return energy to their environment and, perhaps, drive turbulent motions. Finally we turn to the MHD processes involved with the outflows themselves and focus on a new tool, High Energy Density Laboratory experiments. I will present results from a campaign of experiments carried out at Imperial Collage in London which directly address issues of magnetically dominated radiative outflows and jets. Adam Frank http://streamer.perimeterinstitute.ca/mp3/e1d5c8de-17e5-4bb4-8c17-614f26223916.mp3 Science http://streamer.perimeterinstitute.ca/mp3/e1d5c8de-17e5-4bb4-8c17-614f26223916.mp3 Wed, 10 Oct 2007 14:00:00 -0400 The manifold of pure quantum states can be regarded as a complex projective space endowed with the unitary-invariant Fubini-Study metric. The physical characteristics of a given quantum system can then be represented by a variety of geometrical structures that can be identified in this manifold. This talk will review a number of examples of such structures as they arise in the state spaces of spin-1/2, spin-1, spin-3/2, and spin-2 systems, and various types of entangled systems, all of which have fascinating and beautiful geometries associated with them. The geometric approach offers interesting insights into the nature of quantum systems, and is also useful in the consideration of foundational issues such as those related to the measurement problem. Lane Hughston http://streamer.perimeterinstitute.ca/mp3/6954021b-9402-4d44-88a9-ea0276406c7a.mp3 Science http://streamer.perimeterinstitute.ca/mp3/6954021b-9402-4d44-88a9-ea0276406c7a.mp3 Wed, 17 Oct 2007 14:00:00 -0400 Laser cooling and precision spectroscopy provide powerful tools for exploring quantum measurement and metrology using atoms as sensors. In this talk I will discuss our ongoing work to bring together abstract ideas of quantum parameter estimation and concrete physical details of atom-photon interactions in the specific context of magnetometry. I will also present some new ideas on how laser probing of cold atoms could provide a basis for developing entanglement-enhanced spin gyroscopes. Hideo Mabuchi http://streamer.perimeterinstitute.ca/mp3/a300d444-9291-41fb-af41-cc3f7a224dfa.mp3 Science http://streamer.perimeterinstitute.ca/mp3/a300d444-9291-41fb-af41-cc3f7a224dfa.mp3 Wed, 24 Oct 2007 14:00:00 -0400 This will be an introductory talk about Topological Quantum Computation. TQC is attractive because it is intrinsicaly decoherence free. We introduce the basic notions, such as non abelian anyons, quantum symmetries and topological order. A topologically ordered phase is a gapped phase in which the basic degrees of freedom are of a topological nature (denoted as anyons), charactetized by their fusion and braiding properties. If time permits possible implementations based on Quantum Hall systems will be discussed as well. Sander Bais http://streamer.perimeterinstitute.ca/mp3/d627a488-d11d-4b2c-97ea-af8706a24ec4.mp3 Science http://streamer.perimeterinstitute.ca/mp3/d627a488-d11d-4b2c-97ea-af8706a24ec4.mp3 Wed, 07 Nov 2007 14:00:00 -0500 The Universe offers environments with extreme physical conditions that cannot be realized in laboratories on Earth. These environments provide unprecedented tests for extensions of the Standard Model. I will describe three such "astrophysical laboratories", which are likely to represent new frontiers in cosmology and astrophysics over the next decade. One provides a novel probe of the initial conditions from inflation and the nature of the dark matter, based on 3D mapping of the distribution of cosmic hydrogen through its resonant 21cm line. The second allows to constrain the metric around supermassive black holes based on direct imaging or the detection of gravitational waves. The third involves the acceleration of high-energy particles in cosmological shock waves. I will describe past and future observations of these environments and some related theoretical work. Abraham Loeb http://streamer.perimeterinstitute.ca/mp3/0aa7e29d-fb5e-4422-b826-3892571c1050.mp3 Science http://streamer.perimeterinstitute.ca/mp3/0aa7e29d-fb5e-4422-b826-3892571c1050.mp3 Wed, 14 Nov 2007 14:00:00 -0500 The Cosmic Microwave Background (CMB) consists of a bath of photons emitted when the universe was 380,000 years old. Carrying the imprint of primordial fluctuations that seeded the formation of structure in the universe, the CMB is one of the most valuable known tools for studying the early universe. In our modern, post WMAP era, the utility of studying temperature anisotropies in the CMB is clear and much of the work has been done. I will describe two exciting new directions in which the field is currently heading: small-scale secondary CMB anisotropy and CMB polarization anisotropy. In this context, I will briefly discuss preliminary results from our small-scale secondary anisotropy experiment, the Sunyaev-Zel'dovich Array (SZA), and will describe our two upcoming CMB polarization experiments, the Q U Imaging ExperimenT (QUIET) and the E B EXperiment (EBEX). Amber Miller http://streamer.perimeterinstitute.ca/mp3/5546069d-2d12-4c8d-ba85-5464b1a8e0e2.mp3 Science http://streamer.perimeterinstitute.ca/mp3/5546069d-2d12-4c8d-ba85-5464b1a8e0e2.mp3 Wed, 28 Nov 2007 14:00:00 -0500 After almost a century of observations, the ultra-high energy sky has finally displayed an anisotropic distribution. A significant correlation between the arrival directions of ultra-high cosmic rays measured by the Pierre Auger Observatory and the distribution of nearby active galactic nuclei signals the dawn of particle astronomy. These historic results have important implications to both astrophysics and particle physics. Angela Olinto http://streamer.perimeterinstitute.ca/mp3/0ecd870d-8d3f-48f7-910d-f761dabe5f05.mp3 Science http://streamer.perimeterinstitute.ca/mp3/0ecd870d-8d3f-48f7-910d-f761dabe5f05.mp3 Wed, 09 Jan 2008 14:00:00 -0500 As physicists, we have become accustomed to the idea that a theory\'s content is always most transparent when written in coordinate-free language. But sometimes the choice of a good coordinate system is very useful for settling deep conceptual issues. Think of how Eddington-Finkelstein coordinates settled the longstanding question of whether the event horizon of a Schwarzschild black hole corresponds to a real spacetime singularity or not. Similarly we believe for an information-oriented or Bayesian approach to quantum foundations: That one good coordinate system may (eventually!) be worth more than a hundred blue-in-the-face arguments. This talk will motivate and chronicle the search for one such candidate coordinate system---the so-called Symmetric Informationally Complete Measurement---which has caught the attention of a handful of us here at PI and a handful of our visitors. Christopher Fuchs http://streamer.perimeterinstitute.ca/mp3/a896a90b-b72d-475b-b4e0-529e38087240.mp3 Science http://streamer.perimeterinstitute.ca/mp3/a896a90b-b72d-475b-b4e0-529e38087240.mp3 Wed, 16 Jan 2008 14:00:00 -0500 The basic problem of much of condensed matter and high energy physics, as well as quantum chemistry, is to find the ground state properties of some Hamiltonian. Many algorithms have been invented to deal with this problem, each with different strengths and limitations. Ideas such as entanglement entropy from quantum information theory and quantum computing enable us to understand the difficulty of various problems. I will discuss recent results on area laws and use these to prove that we can use matrix product states to efficiently represent ground states for one-dimensional systems with a spectral gap, while certain other one-dimensional problems, without the gap assumption, almost certainly have no efficient way for us to even represent the ground state on a classical computer. I will also discuss recent results on higher-dimensional matrix product states, in an attempt to extend the remarkable success of matrix product algorithms beyond one dimension. Matt Hastings http://streamer.perimeterinstitute.ca/mp3/d4e2fd3e-246f-41e1-a0e5-e6b585991bb4.mp3 Science http://streamer.perimeterinstitute.ca/mp3/d4e2fd3e-246f-41e1-a0e5-e6b585991bb4.mp3 Wed, 23 Jan 2008 14:00:00 -0500 The Achilles\' heel of quantum information processors is the fragility of quantum states and processes. Without a method to control imperfection and imprecision of quantum devices, the probability that a quantum computation succeed will decrease exponentially in the number of gates it requires. In the last ten years, building on the discovery of quantum error correction, accuracy threshold theorems were proved showing that error can be controlled using a reasonable amount of resources as long as the error rate is smaller than a certain threshold. We thus have a scalable theory describing how to control quantum systems. I will briefly review some of the assumptions of the accuracy threshold theorems and comment on experiments that have been done and should be done to turn quantum error correction into an experimental reality. Raymond Laflamme http://streamer.perimeterinstitute.ca/mp3/85da5b5a-9f0e-4685-aed9-5fec2aa53811.mp3 Science http://streamer.perimeterinstitute.ca/mp3/85da5b5a-9f0e-4685-aed9-5fec2aa53811.mp3 Wed, 06 Feb 2008 14:00:00 -0500 A convergence of climate, resource, technological, and economic stresses gravely threaten the future of humankind. Scientists have a special role in humankind\'s response, because only rigorous science can help us understand the complexities and potential consequences of these stresses. Diminishing the threat they pose will require profound social, institutional, and technological changes -- changes that will be opposed by powerful status-quo special interests. Do scientists have a responsibility to articulate the dangers of inaction to a broader event beyond simply publishing their findings in scholarly journals? Should they become more actively involved in the politics of global change? Thomas Homer-Dixon http://streamer.perimeterinstitute.ca/mp3/b4bf8dfa-4c8e-43e6-8541-96a046d8f11c.mp3 Science http://streamer.perimeterinstitute.ca/mp3/b4bf8dfa-4c8e-43e6-8541-96a046d8f11c.mp3 Wed, 13 Feb 2008 14:00:00 -0500 The history of human knowledge is often highlighted by our efforts to explore beyond our apparent horizon. In this talk, I will describe how this challenge has now evolved into our quest to understand the physics at/beyond the cosmological horizon, some twenty orders of magnitude above Columbus' original goal. I then recount how the study of physics on the horizon scale has led to the successful development of inflationary cosmology, and how we can use the Integrated Sachs-Wolfe effect in the Cosmic Microwave Background to probe cosmological physics, such as late-time inflation, the nature of gravity, and primordial non-gaussianity on the horizon scale. Niayesh Afshordi http://streamer.perimeterinstitute.ca/mp3/3631317d-5fce-47c4-846c-110b2cce537e.mp3 Science http://streamer.perimeterinstitute.ca/mp3/3631317d-5fce-47c4-846c-110b2cce537e.mp3 Wed, 20 Feb 2008 14:00:00 -0500 It is common to assert that the discovery of quantum theory overthrew our classical conception of nature. But what, precisely, was overthrown? Providing a rigorous answer to this question is of practical concern, as it helps to identify quantum technologies that outperform their classical counterparts, and of significance for modern physics, where progress may be slowed by poor physical intuitions and where the ability to apply quantum theory in a new realm or to move beyond quantum theory necessitates a deep understanding of the principles upon which it is based. In this talk, I demonstrate that a large part of quantum theory can be obtained from a single innovation relative to classical theories, namely, that there is a fundamental restriction on the sorts of statistical distributions over classical states that can be prepared. This restriction implies a fundamental limit on the amount of knowledge that any observer can have about the classical state. I will also discuss the quantum phenomena that are not captured by this principle, and I will end with a few speculations on what conceptual innovations might underlie the latter set and what might be the origin of the statistical restriction. Robert Spekkens http://streamer.perimeterinstitute.ca/mp3/2cb017af-6ab3-4f61-93cf-a3c8a950e454.mp3 Science http://streamer.perimeterinstitute.ca/mp3/2cb017af-6ab3-4f61-93cf-a3c8a950e454.mp3 Wed, 27 Feb 2008 14:00:00 -0500 At a very basic level, physics is about what we can say about propositions like 'A has a value in S' (or 'A is in S' for short), where A is some physical quantity like energy, position, momentum etc. of a physical system, and S is some subset of the real line. In classical physics, given a state of the system, every proposition of the form 'A is in S' is either true or false, and thus classical physics is realist in the sense that there is a 'way things are'. In contrast to that, quantum theory only delivers a probability of 'A is in S' being true. The usual instrumentalist interpretation of the formalism leading to these probabilities involves an external observer, measurements etc.In a future theory of quantum gravity/cosmology, we will have to treat the whole universe as a quantum system, which renders instrumentalism meaningless, since there is no external observer. Moreover, space-time presumably does not have a smooth continuum structure at small scales, and possibly physical quantities will take their values in some other mathematical structure than the real numbers, which are the 'mathematical continuum'. In my talk, I will show how the use of topos theory, which is a branch of category theory, may help to formulate physical theories in a way that (a) is neo-realist in the sense that all propositions 'A is in S' do have truth values and (b) does not depend fundamentally on the continuum in the form of the real numbers. After introducing topoi and their internal logic, I will identify suitable topoi for classical and quantum physics and show which structures within these topoi are of physical significance. This is still very far from a theory of quantum gravity, but it can already shed some light on ordinary quantum theory, since we avoid the usual instrumentalism. Moreover, the formalism is general enough to allow for major generalisations. I will conclude with some more general remarks on related developments. Andreas Doering http://streamer.perimeterinstitute.ca/mp3/658fb0d7-7f1a-4b35-b3b6-37b4d214face.mp3 Science http://streamer.perimeterinstitute.ca/mp3/658fb0d7-7f1a-4b35-b3b6-37b4d214face.mp3 Wed, 05 Mar 2008 14:00:00 -0500 There are two notions that play a central role in the mathematical theory of computation. One is that of a computable problem, i.e., of a problem that can, in principle, be solved by an (idealized) computer. It is known that there exist problems that 'have answers', but for which those answers are not computable. The other is that of the difficulty of a computation, i.e. of the number of (idealized) steps required actually to carry out that computation. It is known that, given any appropriate 'degree of difficulty', there exists a problem that, while computable, is at least that difficult. These two notions, while purely mathematical, are designed to reflect, in some broad sense, the physics of the computation process. But there are indications that physics may have something further to say about them. Indeed, it has been suggested that, by using general relativity, some problems that are (mathematically) non-computable may become computable; and that, by using quantum mechanics, some problems that are (mathematically) difficult may become less so. Are there, in principle, any limitations on what physics can do for us in this area? Robert Geroch http://streamer.perimeterinstitute.ca/mp3/a526a801-3fd0-45b1-bd54-6ba906480a15.mp3 Science http://streamer.perimeterinstitute.ca/mp3/a526a801-3fd0-45b1-bd54-6ba906480a15.mp3 Wed, 12 Mar 2008 14:00:00 -0400 TBA Leonard Susskind http://streamer.perimeterinstitute.ca/mp3/dad621ba-f499-4ecd-9717-86dbe14b8dc3.mp3 Science http://streamer.perimeterinstitute.ca/mp3/dad621ba-f499-4ecd-9717-86dbe14b8dc3.mp3 Wed, 19 Mar 2008 14:00:00 -0400 The Great Plague of London, which claimed the lives of one fifth of London's population in 1665, is one of the most famous epidemics of all time. We have recently digitized the mortality records for London during the Great Plague, yielding weekly data for each of the 130 parishes. I will describe the temporal and spatial dynamics of the plague, and discuss our efforts to estimate the transmissibility of the infectious agent. I will also briefly describe other projects in progress inspired by disease-specific mortality records for London over the past 650 years. David Earn http://streamer.perimeterinstitute.ca/mp3/1ac3cbff-334d-4a9a-8bf2-52c8051fa059.mp3 Science http://streamer.perimeterinstitute.ca/mp3/1ac3cbff-334d-4a9a-8bf2-52c8051fa059.mp3 Wed, 26 Mar 2008 14:00:00 -0400 I will summarize current observational constraints in cosmology with emphasis on what we have learned about the properties of the primordial density perturbations. I will describe future directions including observations of high redshift neutral hydrogen through is 21 cm line. Matias Zaldarriaga http://streamer.perimeterinstitute.ca/mp3/8887d460-1ece-49c7-88c9-e4880edc1e45.mp3 Science http://streamer.perimeterinstitute.ca/mp3/8887d460-1ece-49c7-88c9-e4880edc1e45.mp3 Wed, 02 Apr 2008 14:00:00 -0400 Hawking's black hole information paradox is one of the great thought experiments in physics. It points to a breakdown of some central principle of physics, though which one breaks down is still in dispute. It has led to the discovery of ideas that seem to be key to unifying quantum mechanics and gravity, namely the holographic principle and gauge/gravity duality. I review this subject, and discuss ongoing work and future directions. Joe Polchinski http://streamer.perimeterinstitute.ca/mp3/eed33a96-a41c-4a31-8a0e-54804be75bb2.mp3 Science http://streamer.perimeterinstitute.ca/mp3/eed33a96-a41c-4a31-8a0e-54804be75bb2.mp3 Wed, 09 Apr 2008 14:00:00 -0400 Graphene, a single atomic layer of graphite, was created only a few years ago. It is a remarkable system, whose law energy effective theory has a lot in common with relativistic 2 + 1 dimensional ones. Graphene allows tabletop experiments for observing nonperturbative relativistic phenomena, most notably spontaneous chiral symmetry breaking both in vacuum and in an external magnetic field. The latter is in turn crucial for the dynamics of Quantum Hall effect in this system. I will review the basic physics and the latest results obtained both in the experimental studies and the theory of graphene. Volodya Miransky http://streamer.perimeterinstitute.ca/mp3/c7847f43-d55a-48bf-ac24-c301350a8fa8.mp3 Science http://streamer.perimeterinstitute.ca/mp3/c7847f43-d55a-48bf-ac24-c301350a8fa8.mp3 Wed, 16 Apr 2008 14:00:00 -0400 I will describe antiferromagnets and superconductors near quantum phase transitions. There is a remarkable analogy between their dynamics and the holographic description of Hawking radiation from black holes. I will show how insights from this analogy have shed light on experiments on the cuprate high temperature superconductors. Subir Sachdev http://streamer.perimeterinstitute.ca/mp3/72d51713-84d3-4513-b635-70f3fac44acc.mp3 Science http://streamer.perimeterinstitute.ca/mp3/72d51713-84d3-4513-b635-70f3fac44acc.mp3 Wed, 23 Apr 2008 14:00:00 -0400 The theory of Quantum Mechanics requires 'completeness', that is, we need to know the complete set of physically allowed states before we can reliably compute quantum mechanical amplitudes. Among these possible states are microscopic black holes, since they are valid solutions to Einstein's equations for the gravitational force. However, a quantum description of black holes requires a drastic revision of our notions of space and time, in particular if we were to accept the interpretation of their microstates as given by superstring theories. The logical foundations of our physical world view are touched upon here. A natural sounding solution of our problems here could come from a re-interpretation of what quantum mechanics really is. The first thing to dispose of should be all references to 'magic' and 'mystery' when dealing with quantum mechanics or string theory. Gerard 't Hooft http://streamer.perimeterinstitute.ca/mp3/68975924-0c5a-4faf-862b-c44b34cb66e6.mp3 Science http://streamer.perimeterinstitute.ca/mp3/68975924-0c5a-4faf-862b-c44b34cb66e6.mp3 Wed, 07 May 2008 14:00:00 -0400 The last years have seen tremendous progress in simulations of inspiral and coalescence of binary black holes. I will present recent results of the Caltech/Cornell collaboration simulating inspiral and collision of two black holes. Furthermore, while currently no talk on numerical relativity seems to be complete without a discussion of binary black hole coalescence, there are many more aspects of Einstein's equations that can be probed numerically. I will discuss some of these unexpected and intriguing features, among them black holes with five horizons and super-extremal black holes. Harald Pfeiffer http://streamer.perimeterinstitute.ca/mp3/ba989ee8-feb5-424e-a1a2-b86f8de8002a.mp3 Science http://streamer.perimeterinstitute.ca/mp3/ba989ee8-feb5-424e-a1a2-b86f8de8002a.mp3 Wed, 28 May 2008 14:00:00 -0400