Thermodynamic aspects of quantum gravity

量子引力是为了完成爱因斯坦在1905年发起的科学革命，当时他同时提出了量子理论和相对论。在这个提议中，我提出了一个基于发现量子引力新原理来完成爱因斯坦革命的新策略。这项提议的目的是通过建立在过去45年的一个持续的研究主题上，即引力的热力学性质，在量子引力问题上取得重大进展。******有充分的证据表明，广义相对论的动力学，正如爱因斯坦方程所表达的那样，体现了与热力学有密切相似的现象。这些证据来自黑洞力学的经典定律，适用于静止的黑洞解。这表明可以用熵来识别地平面面积，用温度来识别地表重力。当我们把黑洞的质量与能量相对应时，这些量满足热力学定律形式的关系。******在过去的二十年里，一个非常令人兴奋的假设已经发展起来，根据这个假设，经典时空是一种新兴现象，由基本过程的离散理论给出的基本量子描述产生。因此，因果关系、能量和动量是根本。此外，广义相对论的爱因斯坦方程作为应用于基本量子过程的热力学定律的表达而出现。******近年来，PI和其他人提出了这一假设，将量子时空的基本过程模型称为自旋泡沫模型。将纠缠熵与全息术相结合也获得了鼓舞人心的见解。目前的建议从四个方面巩固了最近的进展。******首先，我们试图发现基本量子过程背后的原理。这些包括全息原理的一个版本，以及等效原理对量子过程历史的扩展。******第二，我们将直接推导出广义相对论，作为这些原理与热力学定律相结合的结果。******第三，我们寻求直接从这些原理发展新的实验预测，给我们新的量子引力现象，通过这些现象可以检验这些原理。******第四，我们将测试量子时空的特定模型是否满足这些原理。其中包括自旋泡沫模型、背景无关弦理论的建议、因果集模型和动态三角模型。******我们相信这是一种发现量子引力的策略，它充分利用了引力与热力学之间的深层联系，以及最近关于全息和纠缠的见解。它还建立在各种量子时空模型的进展之上。

Quantum gravity is the search for the completion of the revolution in science that Einstein launched in 1905 with his simultaneous proposal of quantum theory and relativity theory. In this proposal I put forward a new strategy for completing Einstein's revolution, based on discovering new principles for quantum gravity. The aim of this proposal is to make significant progress on the problem of quantum gravity by building on a persistent theme of research the last 45 years, which is the thermodynamic nature of gravitation. ******There is ample evidence that the dynamics of general relativity, as expressed by the Einstein equations, embody phenomena that have a close analogue to thermodynamics. Such evidence comes from the classical laws of black hole mechanics, which apply to stationary black hole solutions. These suggest an identification of horizon area with entropy and surface gravity with temperature. When we take the mass of the black hole to correspond to energy, these quantities satisfy relations that have the form of the laws of thermodynamics. ******Over the last two decades, a very exciting hypothesis has been developed, according to which classical spacetime is an emergent phenomenon, arising from a fundamental quantum description, given by a discrete theory of fundamental processes. Hence, causation, energy and momentum are fundamental. Moreover, the Einstein equations of general relativity arise as the expression of the laws of thermodynamics applied to the fundamental quantum processes. ******In recent years the PI and others have developed this hypothesis, taking for the fundamental processes a model of quantum spacetime called spin foam models. There have also been inspiring insights obtained by combining entanglement entropy with holography. The present proposal builds on this recent progress in four ways.******First, we seek to discover the principles which underlie the fundamental quantum processes. These include a version of the holographic principle as well as an extension of the equivalence principle to histories of quantum processes. ******Second, we will derive general relativity directly as a consequence of the principles, combined with the laws of thermodynamics.******Third, we seek to develop new experimental predictions directly from these principles, giving us new quantum gravity phenomena by which the principles may be tested.******Fourth, we will test whether specific models of quantum spacetime satisfy the principles. These include spin foam models, proposals for background independent string theories, causal set models and dynamical triangulation models.******We believe this is a strategy to discover quantum gravity which takes best advantage of the deep links connecting gravity to thermodynamics as well as recent insights regarding holography and entanglement. It also builds on progress in various models of quantum spacetime.