The remarkable connections between gravity and thermodynamics seem to imply that gravity is not fundamental but emergent, and in particular, as Verlinde suggested, gravity is probably an entropic force. In this paper, we will argue that the idea of gravity as an entropic force is debatable. It is shown that there is no convincing analogy between gravity and entropic force in Verlinde’s example. Neither holographic screen nor test particle satisfies all requirements for the existence of entropic force in a thermodynamics system. Furthermore, we show that the entropy increase of the screen is not caused by its statistical tendency to increase entropy as required by the existence of entropic force, but in fact caused by gravity. Therefore, Verlinde’s argument for the entropic origin of gravity is problematic. In addition, we argue that the existence of a minimum size of spacetime, together with the Heisenberg uncertainty principle in quantum theory, may imply the fundamental existence of gravity as a geometric property of spacetime. This may provide a further support for the conclusion that gravity is not an entropic force.
问题是，微正则系综的定义有两种．定义一：微正则系综定义在一个能量面上，H=E．采取这个观点的人很多，例如Landau，Greiner等．定义二：微正则系综定义在一个能量面上的薄壳层DE(¹0)内，E-DE/2 < H < E+DE/2．前一个定义比较符合物理学对孤立系统的逻辑判断，即：孤立系统是体积V、粒子数N和能量E分别为常数的系统．后一个定义也可以接收，但不易处理干净，见仁见智的看法很多．举例如下：