Riemann Center for Geometry and Physics, Leibniz Universität Hannover, Appelstrasse 2, 30167 Hannover, Germany.
Phys Rev Lett. 2013 Jul 19;111(3):031301. doi: 10.1103/PhysRevLett.111.031301. Epub 2013 Jul 16.
We identify a class of condensate states in the group field theory (GFT) formulation of quantum gravity that can be interpreted as macroscopic homogeneous spatial geometries. We then extract the dynamics of such condensate states directly from the fundamental quantum GFT dynamics, following the procedure used in ordinary quantum fluids. The effective dynamics is a nonlinear and nonlocal extension of quantum cosmology. We also show that any GFT model with a kinetic term of Laplacian type gives rise, in a semiclassical (WKB) approximation and in the isotropic case, to a modified Friedmann equation. This is the first concrete, general procedure for extracting an effective cosmological dynamics directly from a fundamental theory of quantum geometry.
我们在量子引力的群场论（GFT）表述中识别出一类凝聚态，它可以被解释为宏观的均匀空间几何。然后，我们直接从基本的量子 GFT 动力学中提取这种凝聚态的动力学，遵循在普通量子流体中使用的方法。有效动力学是非线性和非局部的量子宇宙学的扩展。我们还表明，任何具有拉普拉斯类型的动能项的 GFT 模型，在半经典（WKB）近似和各向同性的情况下，都会导致一个修正的弗里德曼方程。这是第一个从量子几何的基本理论中直接提取有效宇宙学动力学的具体的、通用的程序。
