On 24 August 2026 at 14.15 Lucy Zheng will defend her doctoral thesis “Cartan Khronon – R eal space-time structure”.
Supervisor:
Dr. Tomi S. Koivisto Laboratory of Theoretical Physics, Institute of Physics, University of Tartu Laboratory of High Energy and Computational Physics, National Institute of Chemical Physics and Biophysics
Opponent:
Dr. William E. V. Barker Central European Institute for Cosmology and Fundamental Physics, Institute of Physics of the Czech Academy of Science
Summary
What is the difference between time and space? This thesis explores the possibility that the direction of time is selected by a clock field, called the khronon, which distinguishes time from space. The resulting theory, Cartan Khronon theory, describes emergent spacetime geometry and gravitation in terms of a fundamental symmetry. A new Euclidean formulation of Cartan Khronon gravity based on Spin(4) symmetry is developed, together with a coherent translation to the conventional Lorentzian description of spacetime. This correspondence is tested with explicit cosmological and black hole solutions, which recover standard results of general relativity in the appropriate regime. In cosmology, the thesis finds generalised background solutions and considers small perturbations to understand the structural evolution. This makes it possible to analyse an effective component generated by gravitational dynamics, which behaves like dark matter in the formation of cosmic structure. In black hole physics, the theory yields spherically symmetric and Kerr geometry describing astrophysical rotating black holes. This thesis establishes the Cartan khronon theory with Spin(4) symmetry as a coherent framework that opens new routes to studying two of the most extreme frontiers of gravitational physics: the early Universe and the interior geometry of black holes.
