Dynamics in modified theories of gravity

虽然量子引力中的时间问题经常被现象学家视为“形而上学的”，但如果没有这个关键因素，很难看出量子引力如何与现实世界建立联系。在这个项目中，我们探索了一种可能性的观测含义，即自然常数的对偶正是量子引力中备受追捧的时间定义。初步的工作表明，不仅获得了一个可靠的半经典极限，而且量子宇宙学可以在“此时此地”（在宇宙尺度上）具有直接的观测意义。宇宙最近从减速膨胀到加速膨胀，这一事实可能预示着连接空间中的量子反射或反弹，以及一个时间向另一个时间的转换（例如，对偶时间向牛顿和宇宙学“常数”的转换）。合作工作导致许多论文详细探讨了这种可能性，这可能会使量子宇宙学走出猜测的领域和无法实现的普朗克时代，使整个领域最终可测试。具有讽刺意味的是，所有问题中最具哲学意义的问题——时间问题——可能就是缺失的线索。

Although the problem of time in quantum gravity is often dismissed as "metaphysical" by phenomenologists, it is hard to see how quantum gravity could ever make contact with the real world without this crucial ingredient. In this project we explore the observational implications of the possibility that the duals of the constants of nature are precisely the much sought-after definitions of time - or times - in quantum gravity. Preliminary work shows that not only a sound semi-classical limit is obtained, but also that quantum cosmology could then have direct observational implications "here and now" (on a cosmological scale). The fact that the universe has recently changed gears, from decelerated to accelerated expansion, could signal a quantum reflection or bounce in connection space, as well as the handover of one time to another (duals, for example, to Newton's and the cosmological ``constants''). Collaborative work leading to a number of papers exploring this possibility in detail could bring quantum cosmology out of the realm of speculation and the unattainable Planck epoch, rendering the whole field finally testable. Ironically the most philosophical of all the problems - that of time - might be the missing clue.