Abstract: Recent work has shown that by taking into account non-perturbative contributions to the gravitational path integral, the actual number of degrees of freedom becomes much smaller than the number of degrees of freedom predicted by semiclassical EFT. In particular, in the context of black hole evaporation, this guarantees that entropy of the radiation is bounded by the Bekenstein-Hawking entropy, thus produces the Page curve. This establishes a map between a larger “naive" Hilbert space and a smaller “physical" Hilbert space, where a large number of null states are quotiented out. In this talk, I will discuss two questions about the dynamics of quantum gravity in the presence of null states: 1) Can we transfer null states into a gravitational system by coupling it to a non-gravitational quantum system? 2) How do we compare time evolutions in the naive and physical Hilbert spaces? I will show explicit results that address these two questions using the Marolf-Maxfield topological gravity model as a toy model. 

Bio ：Zhencheng Wang is a PhD student at UC Santa Barbara, working with Professor Donald Marolf. Before this, he finished his undergraduate study at Nankai University. He is interested in research on the holographic duality, especially on the interplay between gravitational path integral and gravitational entropy.

Contact: Wu Jieqiang