Abstract: 

      In this talk, I will give a brief review of the cosmological constant problem --- the so-called "worst prediction in the history of physics" and then present my recent work on this problem. Basically, I noticed that the standard formulation of the cosmological constant problem is based on one critical assumption --- the spacetime is homogeneous and isotropic, which is true only on cosmological scales. However, this problem is caused by extremely small scale (Planck scale) quantum fluctuations and at that scale, the spacetime is highly inhomogeneous and anisotropic. The homogeneous Friedmann-Lemaitre-Robertson-Walker metric used in the standard formulation is inadequate to describe such small-scale dynamics of the spacetime. For this reason, I reformulate the cosmological constant problem by using a general inhomogeneousmetric. The fine-tuning problem does not arise in the reformulation since the large gravitational effect of the quantum vacuum is hidden by small scale spacetime fluctuations. The stress energy tensor fluctuations of the quantum field vacuum could serve as dark energy to drive the accelerating expansion of the Universe through a weak parametric resonance effect.

About the speaker: 

     Qingdi Wang obtained his PhD at the University of British Columbia in 2018. Since then, he continued to work at UBC as a postdoc. His research interests are in the areas of gravity, quantum gravity, cosmology and quantum field theory. In recent years, his work mainly focused on the cosmological constant problem.