The Global 21-cm Absorption Trough in a Bounced Cosmology: Depth and Timing

Observations of the sky-averaged radio spectrum target a single number that summarises cosmic dawn: the depth and central redshift of the absorption feature produced when the first stars couple the hydrogen spin temperature to the cold gas. Using the stated cosmology and the brightness-temperature relations described in the Methods, the calculation gives the following headline values: z centre = 17.8; depth mK = -184; Tg K = 6.4; Tcmb K = 51.2. The comparison values taken from the published record — including the EDGES and SARAS reports, HERA limits and the Planck optical depth where relevant — are used exactly as published, and the bounce contribution enters only through the named timing, heating or shear inputs. The result is a computed prediction for the delayed-onset history, with its sensitivity to each input stated in the Discussion. This study is simulated and computed from stated assumptions; it is not a measurement.