Talks

The last years have seen a renewed interest in theories of massive gravity. They represent an infra-red modification of gravity where the gravitational force weakens at very large scales. Heuristically, they provide the playground to understand a possible modification of GR which could potentially provide a dynamical solution to the cosmological constant problem. In this talk I will discuss a number of theoretical aspects of massive gravity theories, focusing on the relevance of the so-called Vainstein mechanism, both at the classical and the quantum level. I will also discuss how we can use cosmology from the early and late universe to constrain these theories. For example, what does the Cosmic Microwave Background Radiation know about the graviton mass?

Cosmology in the 21st Century

Revolutionary progress has been achieved in the science of cosmology over the past 30 years. Powerful experiments, made possible by new technologies, have transformed our understanding of the universe. We have unveiled the laws of physics that govern time and space on the grandest scales, from the big bang to present day.

The universe, we’ve learned, is full surprises. For instance, dark matter – the invisible gravitational glue that permeates the vast majority of the universe – remains one of the greatest unsolved puzzles of astrophysics. Nor do we yet fully understand the quantum mechanical nature of the big bang, or the universe’s current transition into a new stage of rapid expansion.

Perhaps most surprising is how remarkably simple these phenomena are to describe, yet so vexing to comprehensively explain.  But as the pace of discovery continues to accelerate, so too will our ability to decode these grandest of puzzles.

During his public lecture, Perimeter Institute cosmologist Kendrick Smith will take the audience on a journey of discovery through the expanding universe, from the big bang to our present-day understanding of dark matter and other cosmic phenomena. He will explore the yet-unsolved mysteries of the universe, and explain how new research aims to shed light on these deep questions.

The Elitzur-Vaidman bomb tester allows the detection of a photon-triggered bomb with a photon, without setting the bomb off. This seemingly impossible task can be tackled using the quantum Zeno effect. Inspired by the EV bomb tester, we define the notion of "bomb query complexity". This model modifies the standard quantum query model by measuring each query immediately after its application, and ends the algorithm if a 1 is measured.

We show that the bomb query complexity is asymptotically the square of the quantum query complexity. Moreover, we will show how this characterization inspires a general theorem relating classical and quantum query complexity, and derive new algorithms from this theorem.