General Relativity & Quantum Cosmology

Effective field theory is a computationally powerful and flexible theoretical framework, finding application in many areas of physics. In particle physics, Weinberg’s folk theorem also promises that any theory that reproduces the predictions of the Standard Model will, at low energies, look like an effective field theory. In one sense the power of this framework should be a cause for pride in the progress of physics and discovery of real structural features of the world. But given the inability to fully unite quantum theory and gravity into a consistent theoretical picture, there is also cause for pessimism: indirect tests of candidate theories of quantum gravity will ultimately reduce to something like an effective field theory, undermining efforts to find low-energy windows into new physics. One way around this pessimism is to look at where and why effective field theory breaks down in current physical theories. I will point to familiar breakdowns (the cosmological constant, inflation, the hierarchy problem), offering a take on what these breakdowns tell us about the shape of physics beyond the Standard Model. Cracks in the wall of effective field theory allow for a dim glimpse of what might lie beyond. Zoom Link: https://pitp.zoom.us/j/95721802052?pwd=TE1iTGxGLzNqeTFSZlNGRXRYMHBCZz09

Effective field theory is a computationally powerful and flexible theoretical framework, finding application in many areas of physics. In particle physics, Weinberg’s folk theorem also promises that any theory that reproduces the predictions of the Standard Model will, at low energies, look like an effective field theory. In one sense the power of this framework should be a cause for pride in the progress of physics and discovery of real structural features of the world. But given the inability to fully unite quantum theory and gravity into a consistent theoretical picture, there is also cause for pessimism: indirect tests of candidate theories of quantum gravity will ultimately reduce to something like an effective field theory, undermining efforts to find low-energy windows into new physics. One way around this pessimism is to look at where and why effective field theory breaks down in current physical theories. I will point to familiar breakdowns (the cosmological constant, inflation, the hierarchy problem), offering a take on what these breakdowns tell us about the shape of physics beyond the Standard Model. Cracks in the wall of effective field theory allow for a dim glimpse of what might lie beyond.

Effective field theory analysis are inadequate to describe the evolution of the very early universe. I will describe an approach to obtain emergent time, emergent space, an emergent metric and an emergent early universe cosmology starting from the BFSS matrix model, a proposed non-perturbative definition of superstring theory. In this approach there is no cosmological constant problem.

"After reviewing some key hints and puzzles from the early universe, I will introduce recent joint work with Neil Turok suggesting a rigid and predictive new approach to addressing them. Our universe seems to be dominated by radiation at early times, and positive vacuum energy at late times. Taking the symmetry and analyticity properties of such a spacetime seriously leads to a new formula for the gravitational entropy of our universe, and a picture in which the Big Bang may be regarded as a kind of mirror. I will explain how this line of thought suggests new explanations for a number of observed properties of the universe, including: its homogeneity, isotropy and flatness; the arrow of time (i.e. the fact that entropy increases *away* from the bang); several properties of the primordial perturbations; the nature of dark matter (which, in this picture, is a right-handed neutrino, radiated from the early universe like Hawking radiation from a black hole); the origin of the primordial perturbations; and even the existence of three generations of standard model fermions. I will discuss some observational predictions that will be tested in the coming decade, and some key open questions."

I will review recent work on accelerating spacetimes in 3D, explaining how acceleration manifests for point particles and BTZ black holes, as well as a novel BTZ-like solution in a disconnect region of parameter space. I will also discuss some holographic aspects of the solutions.

I will give an overview of how the Event Horizon Telescope achieves its horizon scale science and what's to come. I will also review selected recent results from the Event Horizon Telescope both on Sgr A* and refined analysis of M87*. A focus will be on analysis aspects that are relevant for any theory / model building along with a few examples. The presentation aims to provide key conceptual aspects relevant to gravity experts who are new to VLBI.

To make progress in developing a quantum theory of gravity, we need to connect candidate theories to observations. I will review ideas on connecting quantum gravity to observations in particle physics, to searches for dark matter and to observations of black holes, in particular with the (next-generation) Event Horizon Telescope.

We are in a new era of gravitational physics in which both gravitational-wave measurements and cosmological observations can be used to test fundamental physics. Moreover, recent computational developments allow us to investigate (at present largely unexplored) regimes where the gravitational force is strong – a very promising area to search for new physics. In this talk I will overview two cases in which we aim to use strong-gravity to learn about the dark components of the universe: the interaction of binary black hole mergers with their dark matter environments and the emission and propagation of scalar gravitational waves, a distinct signature of theories aiming to explain dark energy.

Zoom link:  https://pitp.zoom.us/j/92308918921?pwd=UEk1aEt3bmRxdklqUUpSNlRocldVdz09