I've read the references in Wikipedia and most of the Loll et al. papers. At wikipedia: http://en.wikipedia.org/wiki/Causal_dynamical_triangulation I read: This sounds logical, but the mechanism doesn't make sense to me. For example, in the July 2008 Scientific American article: http://www.scientificamerican.com/article.cfm?id=the-self-organizing-quantum-universe&page=3 Renate Loll says: What I don't understand is how one can have a single-direction spacetime. If the arrows point in the same direction or there is a one-way direction of causality, this implies to my naive brain that time would only flow in one direction in this spacetime. So I feel like I must be missing something important. What exactly is involved in the gluing of the 4-simplices together and how do these arrows work? Is it that the 4-simplices are supposed to represent all of space and all of time (i.e. past, present, and future)?