Algebraic approach to quantum gravity II: noncommutative spacetime

We provide a self-contained introduction to the quantum group approach to noncommutative geometry as the next-to-classical effective geometry that might be expected from any successful quantum gravity theory. We focus particularly on a thorough account of the bicrossproduct model noncommutative spacetimes of the form [t,x_i]=i \lambda x_i and the correct formulation of predictions for it including a variable speed of light. We also study global issues in the Poincar\'e group in the model with the 2D case as illustration. We show that any off-shell momentum can be boosted to infinite negative energy by a finite Lorentz transformaton.