The universe we live in is “3+1 dimensional”, meaning 3 spacial dimensions and one temporal dimension. We can expect those patterns to continue into higher dimensions (example here!). Almost every law in physics is written in terms of cause and effect, initial conditions to later conditions. The result of the initial conditions from one time direction will usually disagree with the initial conditions on the other times. “Characteristic lines” are the paths that solutions to an equation “propagate along”, and having initial conditions on them basically means putting more information onto what should already be a solved problem.