KnowraLookback timeLinked fromLinked fromThe 7 pages that link to Lookback time, each with the reason it gives.All 7Related 4Compared with 3Cosmological redshiftRelated: A measured redshift helps infer how long the universe expanded during the photon’s journey.Scale factorRelated: Its relation to redshift depends on the scale factor’s history.Light-yearRelated: A distance in light-years also indicates how long the observed light has been traveling.Hubble Ultra-Deep FieldRelated: Distant galaxies appear as they were when their recorded light set out.