A friend of mine was reading Penrose's new book on CCC; I do not want to discuss this story here but a rather interesting detail which could be relevant w/o the whole CCC stuff. SR and GR rely on (global and local) Lorentz invariance. From these symmetries one can derive invariant mass M² and spin (W² with the Pauli-Lubanski vector Wμ) as 1st and 2nd Casimir operator. Now there are scenarious where it seems to be appropriate to use deSitter invariance instead (inflation, positive cc, q-deformed spin networks, ...). Then one has to use the deSitter group instead - and I expect that the Casimir operators are indeed different and that M² and W² need no longer play a fundamenbtal role. Does anybody know about ideas how to modify QFT on deSitter spacetime? How to replace M² and W²? What happens with Einstein-Cartan theory when enlarging the underlying symmetry to deSitter?