标题： 暗能量与引力 显示英文标题

标题： Dark Energy and Gravity

摘要： 我回顾了暗能量问题，并重点关注宇宙学常数作为候选者，讨论了其对引力本质的影响。 第一部分简要概述了目前流行的“一致宇宙学”，并总结了暗能量的证据。它还提供了支持宇宙学常数作为候选者的观测和理论论据，并强调了没有其他方法真正解决了通常归因于宇宙学常数的概念性问题。 第二部分描述了一些理解宇宙学常数性质的方法，并试图提取任何可行解决方案中必须存在的关键要素。我论证了（i）除非引力作用在物质拉格朗日量由常数平移时保持不变，否则宇宙学常数问题无法令人满意地解决；（ii）如果度规是动力学变量，则这种情况不会发生。因此，宇宙学常数问题本质上与我们对引力本质的理解（或误解）有关。 第三部分讨论了一种关于引力的替代观点，其中作用量明确对此变换具有不变性。使此作用量极值化导致确定背景几何的方程，在最低阶次上给出爱因斯坦理论，并带有 Lanczos-Lovelock 类型修正。（浓缩摘要）。 显示英文摘要

摘要： I review the problem of dark energy focusing on the cosmological constant as the candidate and discuss its implications for the nature of gravity. Part 1 briefly overviews the currently popular `concordance cosmology' and summarises the evidence for dark energy. It also provides the observational and theoretical arguments in favour of the cosmological constant as the candidate and emphasises why no other approach really solves the conceptual problems usually attributed to the cosmological constant. Part 2 describes some of the approaches to understand the nature of the cosmological constant and attempts to extract the key ingredients which must be present in any viable solution. I argue that (i)the cosmological constant problem cannot be satisfactorily solved until gravitational action is made invariant under the shift of the matter lagrangian by a constant and (ii) this cannot happen if the metric is the dynamical variable. Hence the cosmological constant problem essentially has to do with our (mis)understanding of the nature of gravity. Part 3 discusses an alternative perspective on gravity in which the action is explicitly invariant under the above transformation. Extremizing this action leads to an equation determining the background geometry which gives Einstein's theory at the lowest order with Lanczos-Lovelock type corrections. (Condensed abstract).