Understanding some physical features of quantum gravity

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“After all, atoms do fall, so the relationship between gravity and quantum is not a problem for nature,” stated physicist Lee Smolin in his book Three Roads to Gravity. However, the concrete unification of General Relativity and Quantum Theory is still an open issue.***My research program, which aims to better understand the quantum gravity regime, is based on the so-called “Loop Quantum Gravity” (LQG) and “Spinfoam” (SF) frameworks, which are based on the use of two different quantization techniques applied to general relativity. The LQG framework arises from the canonical quantization scheme, whereas SF models are constructed using the path integral quantization.***My long-term objective is to define a consistent theory of quantum gravity, from which physical predictions can be extracted. Recent announcements on the neutron stars collision observation marked the beginning of multi-messenger astronomy (gravitational waves and electromagnetic phenomena such as gamma ray bursts can be observed on a same event), which could open new exciting experimental windows for quantum gravity phenomena. To make physical predictions, which could be checked by the Fermi Gamma-ray Space Telescope for instance, one needs to understand how to introduce matter and its interactions with the LQG/SF framework. Also empirically, the cosmological data of the past decades strongly suggests that our universe has a positive cosmological constant Λ≈10-52m-2. It is therefore crucial to build a theory of quantum gravity with a non-vanishing cosmological constant. Concretely, in the short term, I want to:***- Improve the definition of the LQG and SF frameworks by introducing a non-vanishing cosmological constant and matter.***- Define a four-dimensional SF model in a more mathematically consistent way.***These are very challenging aims, which require technical innovations and the use of many different mathematical approaches. My research will use 3d gravity as a framework where several approaches can be compared, will borrow tools from non-commutative geometry, exploit new discretization schemes for LQG and relate the SF framework to the more standard quantum field theory framework.***My research group will investigate issues associated with LQG and SF models but also in non-commutative geometry, quantum field theory as well as mathematical physics. The results found by my team and I will provide new opportunities to make physical predictions for the quantum gravity regime.***Quantum Gravity is a field that attracts excellent students and provides exciting outreach topics. This contributes greatly to the total number of students choosing STEM subjects, and consequently impacts the research and development sector in Canada. My program will provide training for three MMath students and three PhD students and will prepare them to work in academia or in the private sector in highly qualified positions.