Niayesh Afshordi: Reflections on Spacetime

The speaker begins by expressing his enjoyment of the conference and his thoughts on the distinction between science and religion. He proposes that there is a spectrum between the two, with most disciplines lying somewhere in between. He introduces his topic of discussion: the fundamental nature of space-time and the potential evidence of quantum gravity. The speaker also hints at a prelude about the interplay between elegance, faith, and the driving forces of scientific and religious disciplines.

The speaker delves into the concept of quantum ether, which he believes is a promising approach to making quantum gravity normalizable or finite. He discusses the properties of an incompressible fluid in space-time and its implications for the understanding of black holes and dark energy. The speaker also touches on the potential for this model to solve the black hole information paradox and explain black hole entropy.

The speaker explores the connection between dark energy and black holes, suggesting that the properties of an incompressible ether could predict the pressure of dark energy observed in the universe. He discusses the potential for this theory to be tested through the study of stellar-mass black holes and the implications for cosmic acceleration. The speaker also addresses the challenges in fitting this model with astrophysical data and the potential for empirical evidence to support or refute the theory.

The speaker discusses the recent discovery of gravitational waves from merging black holes and the potential for these events to provide evidence of quantum gravity effects. He describes the expected 'echoes' from the event horizon and how they could be indicative of quantum mechanical properties at the horizon. The speaker also talks about the statistical analysis of the signals and the high probability that the observed signals are not due to random noise.

The speaker presents a case for the existence of quantum gravity based on observational evidence from gravitational wave events. He discusses the potential for these events to provide insights into the nature of the horizon of black holes and the possibility of reflecting signals off of quantum gravity objects. The speaker also addresses the challenges in interpreting the data and the implications for our understanding of quantum gravity.

The speaker connects the concept of quantum ether to the Big Bang, suggesting that the early universe's thermal properties could provide evidence for quantum gravity. He discusses the implications of a universe that was hot all along, leading to a nearly scale-invariant power spectrum. The speaker also presents a unique action principle that arises from these conditions, which could explain the observed spectral index of the cosmic microwave background.

The speaker addresses the hierarchy problem in particle physics, which is the large discrepancy between the scales of dark energy and the electroweak scale. He proposes that quantum gravity could provide a solution to this problem by introducing a new scale that is consistent with current observations. The speaker discusses the implications of this for high-energy physics and the potential for new particles to be discovered.

The speaker discusses the infrared catastrophe, a phenomenon where the fluctuations of vacuum energy in quantum field theory lead to large-scale gravitational effects. He argues that this could impose constraints on the ultraviolet physics, potentially limiting the mass of particles that can be observed in colliders. The speaker also presents a formula that relates the stability of cosmic structures to the mass of particles, providing an upper limit on the mass of scalar particles.

The speaker summarizes the various lines of evidence and theoretical considerations that point towards the existence of a quantum ether fundamental to space-time. He discusses the convergence of ideas from the Big Bang, black holes, and the hierarchy problem, suggesting that these phenomena are all manifestations of quantum gravity. The speaker acknowledges the lack of a fully consistent framework to explain all the evidence but expresses optimism about the potential for future discoveries.

The speaker reflects on the phenomenological approach to understanding quantum gravity, emphasizing the importance of interplay between theoretical principles and observational data. He discusses the challenges of building theories based solely on data and the need for a coherent framework that can explain the various phenomena related to quantum gravity. The speaker also addresses questions about the implications of quantum gravity for the nature of space-time and the potential for observing effects in our universe.