"Quantum gravity in the accelerating Cosmos" Dr. Yaakov Neiman

Dr. Yaakov Neiman
Postdoctoral Fellow
Perimeter Institute for Theoretical Physics
 

Abstract

The task of reconciling gravity with quantum mechanics is historically peculiar. The world itself is evidence that an answer exists. Moreover, we expect it to transform our view of Nature, just as relativity and quantum physics have. At the same time, the project has long appeared intractable, and in any case immune from experimental test. In recent years, this situation has changed dramatically. On one hand, theoretically viable models of quantum gravity have been formulated, within the framework of holography. On the other hand, not only are they testable, but they are already falsified through astronomical observation! This contact between theory and experiment arises from a unique interchange between the roles of large and small scales.
The crucial property of our Universe that is in conflict with the holographic models is that the energy density of the vacuum, also known as the cosmological constant, is positive. This has the implication that the Universe can never be seen in its entirety. Instead, the curvature of spacetime and the speed-of-light barrier conspire to trap all observers inside a large but finite "cosmological horizon". This stands in sharp conflict with holographic theory, where processes begin and end at infinite distances.
Thus, our current task is to reconcile gravity not just with quantum mechanics, but also with the existence of a largest observable distance. The task is difficult, forcing us towards idealized models. I will describe my work on such a model, involving higher-spin gravity in de Sitter space. The approach is to adapt, rather than discard, holographic methods. Starting from a model that refers to the entire Universe, I am developing a procedure to deduce the physics inside an observable region.

Biography

I am a postdoctoral fellow at Perimeter Institute, working in fundamental theoretical physics. I am now in my second postdoctoral term, having finished my first at Penn State University. I obtained my Ph.D. in physics in 2013, from Tel Aviv University. I was born in Russia, but spent most of my life in Israel.
My scientific career so far has been characterized by multiple changes of subfields and research communities, occasionally across fierce sociological divides. At the same time, I've maintained a consistent overarching interest: the attempt to formulate and understand quantum gravity in finite observable regions. For me, this problem, situated at the interface between gravity, particle physics and cosmology, embodies most purely our search for the underlying language of the world.
In the last few years, I've pursued a "simplest case first" approach to this broad problem. This has led me to study higher-spin theory and its application to holography with positive cosmological constant.