Added: 5 times down vote for now! Down voter is this religion or physics, please try to explain your decision. I'm confused about this. In physics we know for a vacuum, but I think that there is a ...
What are the current (popular(ish)) approaches to modelling the quantum nature of spacetime at the Planck scale?
My guess at a list of them would be: spin foams, casual sets, non-commutative geometry, Machian theories, twistor theory or strings and membranes existing in some higher-dimensional geometry... ...