Talks

Part I: OGRePy: Object-Oriented General Relativity in Python   I will present a detailed introduction to my new Python package, OGRePy: (O)bject-Oriented (G)eneral (Re)lativity for (Py)thon, a port of my popular Mathematica package OGRe, which is used by many researchers in general relativity and related areas. I will demonstrate the package's usage and features, including its ability to manipulate tensors of arbitrary rank using an intuitive interface, and calculate arbitrary tensor formulas involving any combination of addition, multiplication, trace, contraction, and partial and covariant derivatives - while automatically figuring out the proper index configuration and coordinate system to use for each tensor, eliminating user error.   Part II: Time Travel Paradoxes and Entangled Timelines   If time travel is possible, it seems that it would inevitably lead to paradoxes, indicating an internal inconsistency in our current theories of nature. Can these paradoxes be resolved by new laws of physics, or perhaps even existing ones? I will first review the different types of time travel paradoxes and their proposed resolutions. Then I will present the results of my 3 recent papers (1911.11590, 2110.02448, 2303.07635) discussing different aspects of time travel paradoxes from the perspectives of both general relativity and quantum mechanics. I will argue that generic time travel paradoxes can only be resolved using the concept of parallel timelines, and suggest possibilities for how such timelines may manifest themselves.

Lorentzian path integrals exhibit profoundly different properties from Euclidean ones due to the oscillatory integrand which weighs different configurations through interference. Key troubles encountered in Euclidean quantum gravity are the conformal factor problem of Euclidean quantum GR and divergences due to spike configurations in Euclidean quantum Regge calculus. The first part of this talk will focus on how these troubles are resolved in Lorentzian quantum Regge calculus. I will emphasize the unambiguous choice of contour for the integral over the conformal mode in a saddle-point expansion and furthermore show that bulk-length expectation values are finite for spike and spine configurations away from the classical regime. The second part of this talk will focus on properties of Lorentzian path integrals beyond GR. I will illustrate that higher-derivative and non-local actions can be expected to suppress spacetime configurations with curvature singularities. Finally, I will revisit the long-standing question of global symmetries in quantum gravity by providing examples for non-local actions designed to suppress global-symmetry-violating black-hole configurations in the Lorentzian path integral.

Horizons can occur in a wide range of physical situations, many of which we can construct in the lab. Most gravity simulators observe features, like super-radiance, that are analysed as a continuum effect in gravity, whereas many interesting "beyond GR" features theorise about the impact of quantised aspects of the black hole.   In this talk, I will describe recent experimental work on a liquid helium giant vortex that naturally has quantisation, and how we hope to explore "black hole" phenomena in a broader context.   Based on [arXiv:2308.10773 [gr-qc]] with: Patrik Svancara, Pietro Smaniotto, Leonardo Solidoro, James MacDonald, Sam Patrick, Carlo Barenghi and Silke Weinfurtner