  Scale invariant fluctuations of metric are universal feature of quantum
gravity in de Sitter spacetime. We construct an effective Lagrangian which
summarizes their implications on local physics by integrating super-horizon
metric fluctuations. It shows infrared quantum effects are local and render
fundamental couplings time dependent. We impose Lorenz invariance on the
effective Lagrangian as it is required by the principle of general covariance.
We show that such a requirement leads to unique physical predictions by fixing
the quantization ambiguities. We explain how the gauge parameter dependence of
observables is canceled. In particular the relative evolution speed of the
couplings are shown to be gauge invariant.
