This paper investigates anthropic bounds on the vacuum energy $Λ$. We first consider the possibility of cosmic observers existing at any random time (including the future) for constant $Λ$, and take into account the suppression of new structure formation as the universe approaches its eternal DeSitter (DS) geometry. Structures that collapse prior to the era of $Λ$-domination will lose causal contact with our Hubble volume within a finite (short) conformal time $τ_{\ast}$. Any remnants within our Hubble volume then suffer a cosmological heat death after the universe becomes DS. The probability for finding observers by random measurements in the volume bound by the DeSitter horizon is $P \simeq 0$, and it is a simple consequence of the information loss problem for eternal DS spaces resulting from the finite and constant value of its temperature $T_{DS} \simeq Λ^{-1/2}$ and entropy $S = 3/(GΛ)$. By contrast, for geometries with $Λ= 0$, structures can condense and entropy production can continue without bounds at any epoch. The probability of finding observers in $Λ= 0$ geometries is thus overwhelming higher than in DS spaces. As a result, anthropic reasoning does not explain the small but nonzero vacuum energy observed in our universe. We also address the case where observers are considered only at a specially chosen time -- like the present epoch -- but relax the allowed values of starting density fluctuations and hence the redshift of galaxy formation. In this latter case, the bounds on a $Λ$ can be millions of times larger than previous estimates -- and the observed value. We thus conclude that anthropic reasoning has limited predictive power.
Black Holes, Gravitational Waves and Space-Time Singularities Lemaitre Conference 2024
Università di Roma ‘Tor Vergata’（罗马托尔维尔加塔大学）；INFN, Sezione di Roma Tor Vergata（罗马托尔维尔加塔意大利国家核物理研究所）；DiSAT, Università dell’Insubria（因苏布里亚大学 DiSAT 学院）；INFN, Sezione di Milano（米兰意大利国家核物理研究所）；Como Lake centre for AstroPhysics (CLAP)（科莫湖天体物理中心）；Vatican Observatory（梵蒂冈天文台）；INAF/OAS Bologna（博洛尼亚意大利国家天体物理研究所观测天文学与天体物理学部门）；INFN, Sezione di Bologna（博洛尼亚意大利国家核物理研究所）；Laboratori Nazionali di Frascati, INFN（弗拉斯卡蒂意大利国家核物理研究所）；Dipartimento di Matematica, Politecnico di Milano（米兰理工大学数学系）；Lorentz Institute for Theoretical Physics, Leiden University（莱顿大学洛伦兹理论物理研究所）
