  Cosmic structure on the largest scales preserves the pattern laid down by
quantum fluctuations of gravity in the early universe on scales comparable to
inflationary horizons. It is proposed here that fluctuations create physical
correlations only within finite regions enclosed by causal diamonds, like
entanglement in other quantum systems. Conformal geometry is used to calculate
a range of angular separation with no causal correlation. Correlations of the
cosmic microwave background in this ``causal shadow'' are measured to be three
to four orders of magnitude smaller than expected in standard inflation models.
It is suggested that this measured symmetry of the primordial pattern signifies
a new symmetry of quantum gravity associated with causal horizons.
