The Challenge in Merging Quantum Mechanics and Gravity: Taming the Infinities

Barry McFarland will continue with quantum gravity topics.

One reason that Quantum Mechanics and Gravity do not fit together is the fact that the usual way physics handles infinity in Quantum theories does not work for Gravity. Quantum theories are re-normalizable, meaning that there is a way to make sense of the infinities that show up when calculating the probabilities that certain events occur or do not occur. For Gravity, those infinity-taming methods are not available. The goal is to get an appreciation for why Gravity is different in this regard.

The discussion will begin by reviewing a simple ways to understand that Gravity is not-renormalizable. It is because interactions between Gravitational degrees of freedom entail dimensionful couplings which pose a hurdle for standard perturbative techniques. Then a more subtle and complex way to understand the non-renormalizability of Gravity will be presented. This deeper way to understand why any sensible quantum theory gets renormalized will require understanding what the "Partition Function" of Quantum Field Theory is and will highlight the privileged role played by so-called "Conformal Field Theories" in renormalization. It will be shown that, using standard techniques, it is not possible to formulate Gravity as a deformation (i.e. as a slight perturbation away from) a UV fixed point Conformal Theory. It should be noted that this hurdle has not stopped the progress of physics in pursuit of Quantum Gravity: we will talk about Asymptotic Safety and other non-pertubative methods which are currently being pursued.

Some good background materials will be emailed to you upon request, along with some notes that Barry has pieced together in his own personal research on the topic.

If you do not get the zoom link through Meetup pls let me know.

Cheers,
Moshe Rozenblit PhD
moshe_rozenblit@yahoo.com