


(Seminar) Finetuning of the cosmological constant is not needed 
CAS Key Laboratory of Theoretical Physics

Institute of Theoretical Physics

Chinese Academy of Sciences

Seminar

Title
题目

Finetuning of the cosmological constant is not needed 
Speaker
报告人


Affiliation
所在单位

不列颠哥伦比亚大学 
Date
日期

20190829 10:00 
Venue
地点

Room 6420,ITP new Building/理论物理所新楼6420报告厅

Abstract
摘要

We point out that the standard formulation of the cosmological constant problem itself is problematic since it is trying to apply the very large scale homogeneous cosmological model to very small (Planck)scale phenomenon. At small scales, both the spacetime and the vacuum stress energy are highly inhomogeneous and wildly fluctuating. This is a version of Wheeler's ``spacetime foam". We show that this ``foamy" structure would produce a large positive contribution to the averaged macroscopic spatial curvature of the Universe. In order to cancel this contribution to match the observation, the usually defined effective cosmological constant $\lambda_{\mathrm{eff}}=\lambda_B+\langle\rho^{\mathrm{vac}}\rangle$ has to take a large negative value. The spacetime dynamics sourced by this large negative $\lambda_{\mathrm{eff}}$ would be similar to the cyclic model of the universe in the sense that at small scales every point in space is a ``microcyclic universe" which is following an eternal series of oscillations between expansions and contractions. Moreover, if the bare cosmological constant $\lambda_B$ is dominant over the quantum vacuum fluctuation, the size of each ``microuniverse" would increase a tiny bit at a slowly accelerating rate during each microcycle of the oscillation due to the weak parametric resonance effect produced by the fluctuations of the quantum vacuum stress energy tensor. In this way, the large cosmological constant generated at small scales is hided at observable scale and no finetuning of $\lambda_B$ to the accuracy of $10^{122}$ is needed. This at least resolves the old cosmological constant problem and suggests that it is the quantum vacuum fluctuations serve as the dark energy which is accelerating the expansion of our Universe.

Contact Person
所内联系人

郭宗宽 



