  We postulate that the fundamental principles of Quantum Gravity are
diffeomorphism symmetry, unitarity, and locality. Local observables are
compatible with diffeomorphism symmetry in the presence of diff anomalies,
which modify the symmetry algebra upon quantization. We describe the
generalization of the Virasoro extension to the diffeomorphism algebra in
several dimensions, and its off-shell representations. These anomalies can not
arise in QFT, because the Virasoro-like cocycles are functionals of the
observer's spacetime trajectory, which is not present in QFT. Possible
implications for physics are discussed.
