天文学奖
2014

2014年度邵逸夫天文学奖颁予丹尼尔．爱森斯坦 (Daniel Eisenstein)、肖恩．科尔 (Shaun Cole) 及约翰．皮考克 (John A Peacock)，以表彰他们在测量星系大尺度结构特徵上的贡献，这些测量包括重子声振荡 (BAO) 和红移空间扭曲，其结果足以对宇宙学模型作出约束。爱森斯坦为美国哈佛大学天文学教授；科尔为英国杜倫大学物理学教授；皮考克为英国爱丁堡大学宇宙学教授。

早期宇宙的温度很高，密度也很大。重子物质高度电离，由裸原子核和自由电子组成，称为等离子体。无论当时还是现在，光子的数目较原子核或电子都多很多。由於光子和电子的散射，使等离子体和光子紧密耦合。这种情况在大爆炸后的初期维持了40万年，直至温度降至3000 开氏度，电子和原子核遂结合成中性原子，与光子解耦，中性原子与光子变成互相独立的系统。

The early universe was hot and dense. Baryonic matter was highly ionized and consisted of bare nuclei and free electrons, a state known as plasma.  Then as now, photons were far more numerous than either nuclei or electrons.  As a consequence of photon-electron scattering, the plasma and photons were tightly coupled into a single fluid whose pressure opposed gravity. This situation pertained during the first 400,000 years after the big bang. At that point the temperature had dropped to 3000 kelvin, the electrons and nuclei combined into neutral atoms which decoupled from the photons, and baryonic matter fell into gravitational potential wells of the dominant dark matter.

Primordial density perturbations on all scales arose shortly after the big bang and later seeded the formation of structure from galaxies to superclusters. The density perturbations excited baryon acoustic waves, essentially sound waves, that propagated through the primordial plasma at about half the speed of light prior to decoupling. After decoupling, these waves ceased propagating, thereby imprinting a well-defined length scale of about 500 million light years on matter density correlations at the current epoch.