Since 2002 Perimeter Institute has been recording seminars, conference talks, public outreach events such as talks from top scientists using video cameras installed in our lecture theatres. Perimeter now has 7 formal presentation spaces for its many scientific conferences, seminars, workshops and educational outreach activities, all with advanced audio-visual technical capabilities.
Recordings of events in these areas are all available and On-Demand from this Video Library and on Perimeter Institute Recorded Seminar Archive (PIRSA). PIRSA is a permanent, free, searchable, and citable archive of recorded seminars from relevant bodies in physics. This resource has been partially modelled after Cornell University's arXiv.org.
Accessibly by anyone with internet, Perimeter aims to share the power and wonder of science with this free library.
Within a histories-framework for quantum field theory, the condition of \bold{persistence of zero} (PoZ for short) tries to capture (a part of) the elusive idea that no cause can act outside its future lightcone. The PoZ condition, however, does not easily carry over to theories like gravity where the causal structure is not only dynamical but indefinite (subject to quantum fluctuations).
VisIt (https://wci.llnl.gov/simulation/computer-codes/visit/) is an interactive, powerful visualization, animation, and analysis tool.
VisIt is an open source and available for Unix, Windows or Mac users.
In this tutorial, after a brief introduction of VisIt, we will walk through several basic plotting/animation functions by using some toy data.
There are three natural currents for Maxwell theory on a non-dynamical background: the stress, Noether and canonical current. Their associated fluxes across null infinity differ by boundary terms for asymptotically flat spacetimes. These boundary terms do not only quantitatively change the behavior of the flux associated with an asymptotic Lorentz symmetry, but also qualitatively: the stress flux contains both radiative and Coulombic information, whereas Noether and canonical ones are purely radiative.
Neutrinos are established to be massive and the mass differences have been measured, but the absolute neutrino mass values remain unknown. Cosmic neutrinos with finite mass slightly suppress the matter power spectrum below their free-streaming scale and this effect can be applied to constrain neutrino masses. However, the challenge of this method is to disentangle the complex and poorly understood baryonic effects and to obtain better optical depth measurements from the cosmic microwave background experiments.
Linking quantum gravity approaches could be important to make progress in quantum gravity. In my talk, I will try to make this case using asymptotically safe gravity as an example. I will briefly review the status of the approach and highlight the open questions, and discuss proposed ideas how the link to other approaches could be useful to tackle these. Finally, I will emphasize the need for universality in quantum gravity, and argue that there might be universal features from quantum gravity in black-hole shadows.
According to general relativity, the coalescence of a compact binary system creates a gravitational wave signal generically described by an inspiral-merger-ringdown waveform. The recent observations of gravitational waves by LIGO allow us to test our theory of gravity in the strong field regime. In binary black hole detections, the ringdown portion of the wave can provide tests of the no-hair theorem, the most stringent proof of the existence of astrophysical black holes and even possible hints of quantum gravity.
In physics, every observation is made with respect to a frame of reference. Although reference frames are usually not considered as degrees of freedom, in all practical situations it is a physical system which constitutes a reference frame. Can a quantum system be considered as a reference frame and, if so, which description would it give of the world?