Quasar polarization vectors know about each other across billions of light-years. Hutsemekers (1998) and successive extensions found that the optical polarization position angles of quasars are not randomly oriented but coherently aligned within huge regions of the sky, with characteristic scales near 1 Gpc and chance probabilities below 0.1 percent; the alignments are organized along the line of sight and appear to rotate systematically with redshift. Radio follow-up sharpened the case: Mandarakas et al. (2021) found parsec-scale VLBI jets, whose orientations are set by the spin axes of the central black holes, aligned across 400 to 900 Mpc regions at greater than 99.5 percent significance. Black hole spin axes, the most local property imaginable, are correlated over distances exceeding any causal astrophysical mechanism in the standard model.
ΛCDM's largest coherence machinery, tidal torque theory, organizes angular momentum over at most 30 to 50 Mpc; the observed coherence exceeds it by a factor of 20 to 30. Proposed conventional outs, propagation effects (dichroism, birefringence) for the optical sample, selection artifacts, or chance, fail individually: the VLBI jets are immune to propagation effects, the samples are independent, and the joint significance compounds. Exotic proposals (axion-photon mixing for the optical rotation) cannot touch the radio jets either. The alignments stand as a direct measurement of structure in the universe's angular momentum field at gigaparsec scales, where the model has none.
The standing is two decades old, repeatedly confirmed, and quietly devastating: spin axes should be the noisiest, most history-dependent vectors in astronomy, and they are organized across scales only initial conditions can reach. SKA polarization surveys will map the alignment field with order-of-magnitude better statistics.