Causal Dynamical Triangulations (CDT)

A background-independent, non-perturbative approach to quantum gravity that attempts to construct spacetime itself from the bottom up. The approach discretizes spacetime into tiny, fundamental geometric building blocks (simplices, or "triangulations") and sums over all possible configurations in a path integral. The crucial, defining feature is the enforcement of causality - each triangulation must have a well-defined global time foliation, preventing pathological, non-causal geometries from contributing. This restriction leads to the emergence of a macroscopic, four-dimensional de Sitter-like universe from the purely quantum ensemble, a remarkable success. CDT provides a computationally manageable way to explore the quantum microstructure of spacetime and suggests that the smooth geometry we experience is a large-scale, classical property emerging from a wildly fluctuating, discrete quantum substrate.