论文标题
阐明“宇宙巧合”
Elucidation of 'Cosmic Coincidence'
论文作者
论文摘要
在标准的宇宙学模型中，尽管它们的进化历史截然不同，但在目前，在目前确定了黑暗能量（DE）和非派别（NR）物质。这个“宇宙巧合”谜 - 也称为“为什么现在？问题' - 依赖于其定义，依赖于宇宙（扩展）时空卷中对我们的“典型性”的隐含期望。否则，这个难题首先不存在。这里表明，这种明显的巧合可以解释为一种非人类观察性选择效果：要使我们成为com com comving（静态）时空体积中的典型观察者，宇宙能量预算必须包含非变化的DE组件。此外，这表明，不论宇宙学初始条件和假设没有“新物理学”，最有可能观察到宇宙在保形哈勃半径（$ \ nathcal {h}^h}^{ - 1} $时，都可以达到最大值。后者分别在$ρ_{de} $和$ρ_{m} $时，分别是DE和NR MATTER的能量密度是可比的。具体而言，我们沿形状时间表的假定“典型性”与其他一些合理的假设相结合，这意味着$ r \equivρ_{de}/ρ_{m} $是从beta Prime Prime概率分布函数中``采样''。比率的先验68 \％（95 \％）的置信范围为$ 0.20 <r <3.46 $（$ 0.033 <r <17.20 $），期望值为$ \ bar {r} = 3.5 $。这些与观察性推断的值一致，$ r_ {obs} = 2.23 $。
In the standard cosmological model the dark energy (DE) and nonrelativistic (NR) matter densities are observationally determined to be comparable at the present time, in spite of their greatly different evolution histories. This `cosmic coincidence' enigma -- also referred to as the `why now? problem' -- relies, by its very definition, on the implicit prior expectation for our `typicality' in the cosmic (expanding) spacetime volume. Otherwise, this conundrum does not exist in the first place. It is shown here that this apparent coincidence could be explained as a non-anthropic observational selection effect: for us to be typical observers in the comoving (static) spacetime volume, the cosmic energy budget must contain a non-vanishing DE component. In addition, it is shown that irrespective of the cosmological initial conditions and assuming no `new physics', the Universe is most likely to be observed at a time when the conformal Hubble radius, $\mathcal{H}^{-1}$, attains a maximum. The latter takes place at the epoch when $ρ_{DE}$ and $ρ_{m}$, the energy densities of DE and NR matter, respectively, are comparable. Specifically, our presumed `typicality' along the conformal timeline, coupled to a few other plausible assumptions, implies that $R\equivρ_{DE}/ρ_{m}$ is `sampled' from a Beta Prime probability distribution function. A priori 68\% (95\%) confidence range for the ratio is $0.20<R<3.46$ ($0.033<R<17.20$), with an expectation value of $\bar{R}=3.5$. These are in agreement with the observationally inferred value, $R_{obs}=2.23$.
