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(Seminar) Fine-tuning of the cosmological constant is not needed
2019-08-29  【 】【打印】【關閉

CAS Key Laboratory of Theoretical Physics

Institute of Theoretical Physics

Chinese Academy of Sciences

Seminar

Title

題目

Fine-tuning of the cosmological constant is not needed

Speaker

報告人

王清滌

Affiliation

所在單位

不列顛哥倫比亞大學

Date

日期

2019-08-29 10:00

Venue

地點

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 ``micro-cyclic 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 ``micro-universe" would increase a tiny bit at a slowly accelerating rate during each micro-cycle 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 fine-tuning 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

所內聯系人

郭宗寬
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