# Video Library

Since 2002 Perimeter Institute has been recording seminars, conference talks, and public outreach events using video cameras installed in our lecture theatres.  Perimeter now has 7 formal presentation spaces for its many scientific conferences, seminars, workshops and educational outreach activities, all with advanced audio-visual technical capabilities.  Recordings of events in these areas are all available On-Demand from this Video Library and on Perimeter Institute Recorded Seminar Archive (PIRSA)PIRSA is a permanent, free, searchable, and citable archive of recorded seminars from relevant bodies in physics. This resource has been partially modelled after Cornell University's arXiv.org.

## Modifying Gravity in the Infra-Red by imposing an Ultra-Strong equivalence principle.

Wednesday May 27, 2009
Speaker(s):

I will give account of a work in progress in which I attempt to modify the metric-manifold structure of GR in the infra-red. The proposed modification does not contain any massive parameter as it is effective at length scales comparable with the inverse (extrinsic) curvature. The guiding line for this modification is an "ultra-strong" equivalence principle, according to which even semi-classical gravitational effects (i.e. particle production) are definitely banned from a sufficiently small free-falling elevator. Some cosmological consequences of this modification will be discussed.

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## Using Large-Scale Structure and CMB Observations to Probe the Properties of Dark Energy

Wednesday May 27, 2009
Speaker(s):

Cosmologists are struggling to understand why the expansion rate of our universe is now accelerating. There are two sets of explanations for this remarkable observation: dark energy fills space or general relativity fails on cosmological scales. If dark energy is the solution to the cosmic acceleration problem, then the logarithmic growth rate of structure $dlnG/dlna = \Omega^\gamma$, where $\Omega$ is the matter density independent of scale in a dark matter plus dark energy model.

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## Gravitational aether as a solution to the CC problem and more!

Wednesday May 27, 2009
Speaker(s):

## Is the cosmological constant a nonlocal quantum residue of discreteness of the causal set type?

Wednesday May 27, 2009
Speaker(s):

The currently accelerating Hubble expansion is in accord with the old heuristic prediction, from causal set theory, of a fluctuating and ever-present cosmological "constant''. More recently, a phenomenological model based on certain of the ideas behind the prediction has been devised, but it remains incomplete. I will review these developments and also mention a possible consequence for the dimensionality of spacetime.

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## Dynamics and the Cosmological Constant Problem

Wednesday May 27, 2009
Speaker(s):

TBA

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## Is there Eternal Inflation in the Cosmic Landscape ?

Wednesday May 27, 2009
Speaker(s):

TBA

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## Zero cosmological Constant from Normalized General Relativity

Tuesday May 26, 2009
Speaker(s):

Normalizing the Einstein-Hilbert action by the volume&nbsp;functional&nbsp;makes the theory invariant under constant&nbsp;shifts in the Lagrangian.&nbsp;The field equations then resemble unimodular gravity whose&nbsp;otherwise&nbsp;arbitrary cosmological constant is now determined as a&nbsp;Machian&nbsp;universal&nbsp;average. We first prove that an empty space-time is necessarily flat,&nbsp;and then demonstrate, by invoking the scalar field paradigm,&nbsp;that the cosmological constant is actually zero.

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## Observational Evidence for Cosmological-Scale Extra Dimensions

Tuesday May 26, 2009
Speaker(s):

TBA

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## Massive gravity in 3-D and the Chern-Simons-Proca theory

Tuesday May 26, 2009
Speaker(s):

TBA

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## Modified gravity, degravitation and equivalence principle

Tuesday May 26, 2009

TBA

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## Next Public Lecture

### Dr. Vilhelm Bohr - Niels Bohr: Life Behind the Physics

Wednesday Jun 03, 2015

## RECENT PUBLIC LECTURE

### Amanda Peet, University of Toronto and Perimeter Institute

Speaker: Amanda Peet