Can one observe quantum-gravitational effects in the cosmic microwave
  background?
  In order to find the correct theory of quantum gravity, one has to look for
observational effects in any candidate theory. Here, we focus on canonical
quantum gravity and calculate the quantum-gravitational contributions to the
anisotropy spectrum of the cosmic microwave background that arise from a
semiclassical approximation to the Wheeler-DeWitt equation. While the resulting
modification of the power spectrum at large scales is too weak to be
observable, we find an upper bound on the energy scale of inflation.
