1、Entropic cosmology: a unified model of inflation and late-time acceleration

在评价这篇文章之前，我拷贝一下它的摘要

Holography is expected as one of the promising descriptions of quantum general relativity. We present a model for a cosmological system involving two holographic screens and find that their equilibrium exactly yields a standard Friedmann-Robertson-Walker universe. We discuss its cosmological implications by taking into account higher order quantum corrections and quantum nature of horizon evaporation. We will show that this model could give rise to a holographic inflation at high energy scales and realize a late-time acceleration in a unified approach. We test our model from the SN Ia observations and find it can give a nice fit to the data.

第一，作者们说他们follow Easson等人。那篇文章我过去评价过了，有两个问题：1、边界项一般不影响运动方程，即使影响，也不是CLL等人文章中的方程(2)（通常是边界条件）。2、Danielsson已经指出，Easson等人的加速项，即CLL等人的方程(8)，要求加速能量与物质有交换，否则不是局域理论（关于这一点，我透露一下，我和一些学生在做一点工作，当然我们要求无能量交换，既然我透露了，反对恶性竞争 ）。再说一句关于边界项问题，即使边界项修改了运动方程，由于是delta函数形式的，怎么会使得整体宇宙加速？（也许我过虑了，期待有人能回答）

第二，作者用了黑洞，我不清楚是真的有黑洞，还是一种类比。

第三，我看不到inflation是怎么进来的，事实上，我和庞毅同学正在证明inflation的 no-go 定理。当然，如果你像Easson等人随便写一个加速项，也许no-go定理不存在。但随便一个加速项会出现Danielsson指出的类似问题。

2、On the Origin of Entropic Gravity and Inertia

这篇文章在提到存在一些批评Verlinde的熵力假设时，提到我和王一的工作，我很奇怪，因为我们并没有批评Verlinde的假设。

文章的主要内容是用局域的Rindler horizon推导Verlinde的熵变假设以及惯性，我觉得是可信的，很有意思。

但在讨论惯性时，用了等效原理。原则上，假设了伪黎曼几何，就有等效原理（也就是局域惯性系），可是，假定粒子在局域惯性系中满足惯性定律，却是动力学假设，Verlinde本人是要推导的。我没有仔细看Lee的这篇文章，不知道他的推导对假设依赖多大。

最后，附上摘要

It is suggested that, using the equivalence principle, the quantum informational interpretation of gravity can explain Verlinde’s formalism of entropic gravity. The holographic screen in the formalism can be identified to be a Rindler horizon for accelerating observers in the opposite direction. It is also suggested that inertia is related to dragging the Rindler horizon.

3、Black Hole Motion in Entropic Reformulation of General Relativity

We consider a system of black holes — a simplest substitute of a system of point particles in the mechanics of general relativity — and try to describe their motion with the help of entropic action: a sum of the areas of black hole horizons. We demonstrate that such description is indeed consistent with the Newton’s laws of motion and gravity, modulo numerical coefficients, which coincide but seem different from unity. Since a large part of the modern discussion of entropic reformulation of general relativity is actually based on dimensional considerations, for making a next step it is crucially important to modify the argument, so that these dimensionless parameters acquire correct values.

We study a process of equilibration of holographic dark energy (HDE) with the cosmic horizon around the dark-energy dominated epoch. This process is characterized by a huge amount of information conveyed across the horizon, filling thereby a large gap in entropy between the system on the brink of experiencing a sudden collapse to a black hole and the black hole itself. At the same time, even in the absence of interaction between dark matter and dark energy, such a process marks a strong jump in the entanglement entropy, measuring the quantum-mechanical correlations between the horizon and its interior. Although the effective quantum field theory (QFT) with a peculiar relationship between the UV and IR cutoffs, a framework underlying all HDE models, may formally account for such a huge shift in the number of distinct quantum states, we show that the scope of such a framework becomes tremendously restricted, devoiding it virtually any application in other cosmological epochs or particle-physics phenomena. The problem of negative entropies for the non-phantom stuff is also discussed.