Does the universe get dustier at certain redshifts?

The universe's opacity to light—how much dust and gas blocks photons—may not be uniform across cosmic time. Using strong gravitational lensing to measure distances independently, then comparing with supernova brightness data, the authors found the universe appears mostly transparent overall, but shows suspicious dimming in specific redshift bands (z = 0.3–0.4). If real, this could mean supernova-based measurements of cosmic acceleration have been systematically skewed.