标题： 选择无的难题：什么决定了自然的低能真空态？ 显示英文标题

标题： The Issue of Choosing Nothing: What Determines the Low Energy Vacuum State of Nature?

摘要： 从一个（未知的）量子引力模型出发，可以通过一系列近似逐步得到弯曲时空中的量子场论（QFT）、平直时空中的量子场论、非相对论量子力学和牛顿力学。更精确的理论可以对近似理论允许的可能性范围施加限制，这些限制无法从后者推导出来——例如电子对波函数的对称性限制。我们认为，低能下的真空态选择可能是由量子理论和广义相对论原理结合而产生的“遗迹”，并在一个简单的玩具模型中证明了这一结果。我们的分析表明，当宇宙的波函数描述宇宙的大体积极限时，它会动态地为物质场选择一个真空态——这反过来定义了低能极限下的粒子概念。这一结果还有潜力提供一种具体的量子力学版本的马赫原理。 显示英文摘要

摘要： Starting from an (unknown) quantum gravitational model, one can invoke a sequence of approximations to progressively arrive at quantum field theory (QFT) in curved spacetime, QFT in flat spacetime, nonrelativistic quantum mechanics and newtonian mechanics. The more exact theory can put restrictions on the range of possibilities allowed for the approximate theory which are not derivable from the latter - an example being the symmetry restrictions on the wave function for a pair of electrons. We argue that the choice of vacuum state at low energies could be such a `relic' arising from combining the principles of quantum theory and general relativity, and demonstrate this result in a simple toy model. Our analysis suggests that the wave function of the universe, when it describes the large volume limit of the universe, dynamically selects a vacuum state for matter fields - which in turn defines the concept of particle in the low energy limit. The result also has the potential for providing a concrete quantum mechanical version of Mach's principle.