Edward Witten on LQG "for lambda > 0, QG does not exist in any dimension" arxiv.org/abs/0706.3359 - page 6 "for lambda > 0, QG does not exist in any dimension" ...the reason... "cannot provide precise observables" As I understand Edward Witten, deSitter space is not stable but metastable, and can be explained as a part of a larger system, AdS. If Edward Witten is right, "it is not possible to define mathematically precise observables" then all solutions of LQG/Spinform/CDT's and BI's that describe deSitter spacetime are hopeless in any dimension (which is what astronomers believe our spacetime is). Witten proceeds to work with AdS spacetime in 2+1 dimensions. I have no doubt pro-stringers would agree with this, but any LQG'ers can comment? Specifically, Edward Witten believes that LQG is hopeless in describing quantum gravity with a positive cosmological constant (see Smolin and recent work on Kodama wavefunction) since it is not possible to define mathematically precise observables, in any dimension, but including 3+1.