polymer molecule 聚合物分子 When the polymer molecule is immersed into a heat bath, it tends to put itself into a randomlycoiled configuration since this configuration has higher entropy

http://blog.sciencenet.cn/blog-376604-451990.html

牛顿，爱因斯坦，Erik Verlinde？

已有 2748 次阅读 2011-6-5 19:06 |个人分类:引力起源|系统分类:论文交流|关键词:爱因斯坦 荷兰人 引力 熵力 牛顿 黑洞

引力的起源至今仍是一个谜。继牛顿和爱因斯坦之后，谁会是下一个引力理论的提出者呢？去年年初荷兰人Erik Verlinde提出了引力的熵力假说，引起了不小的轰动¹。他的文章最近已被JHEP接受发表。但是，他的想法是对的吗？为了回答这个问题，必须首先理解熵力的物理机制，而大多数研究者似乎忽视了这一点。我在最近的一篇文章中详细分析了Verlinde的论证，结论是他的熵力假说很可能是错的。

 

 

Understanding Entropy Force

In order to see whether gravity is an entropic force or not, we need to first understand the concept of

an entropic force. An entropic force can be defined as an effective macroscopic force that originates in

a thermodynamics system by its statistical tendency to increase entropy. As a typical example, let us

see the elasticity of a polymer molecule, which was also discussed by Verlinde [9].

A polymer molecule is a large molecule composed of repeating structural units, typically connected

by covalent chemical bonds. The simplest polymer architecture is a linear chain, and it can be modeled

by joining together many monomers of fixed length, where each monomer can freely rotate around the

points of attachment and direct itself in any spatial direction. Each of these configurations has the same

energy. When the polymer molecule is immersed into a heat bath, it tends to put itself into a randomly

coiled configuration since this configuration has higher entropy. There are many more such

configurations when the molecule is short compared to when it is stretched into an extended

configuration. The statistical tendency to reach a maximal entropy state then generates the elastic force

of a polymer, which is a typical entropic force.

 

Is Gravity an Entropic Force? Published in the Special Issue Black Hole Thermodynamics of Entropy.

 

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.

 

[1] 荷兰的确人才辈出。惠更斯曾与牛顿齐名，而洛仑兹则被爱因斯坦称为“我们时代最伟大的人”。