The first claimed signal from cosmic dawn and its first replication attempt flatly contradict each other. EDGES, a radio antenna in Western Australia, reported in 2018 a sky-averaged 21 cm absorption profile centered at 78 MHz (redshift 17): the fingerprint of the first stars' light coupling neutral hydrogen to the cold gas. The detection was sensational twice over: an absorption nearly twice the maximum depth standard cosmology permits, and a flat-bottomed profile no conventional model produces. The depth ignited theory, since gas colder than adiabatic cooling allows seemed to require new physics, baryon-dark matter scattering chilling the hydrogen, or an excess radio background raising the contrast against which absorption is measured.
SARAS-3, a differently designed radiometer floated on Indian lakes specifically to evade ground systematics, looked for the EDGES profile and found nothing: the claimed signal is rejected at 95.3 percent confidence (Singh et al. 2022, Nature Astronomy), implying the EDGES feature is plausibly an artifact of its instrument, likely its ground plane's frequency-dependent response interacting with the foreground, which is four orders of magnitude brighter than the sought signal. The collaborations dispute each other's systematics; neither experiment's result fully explains the other's; and the field is left with the foundational measurement of cosmic dawn unmade, while the exotic theory built on the EDGES depth, including its dark matter interaction literature, hangs on an unconfirmed artifact.
The standing is a clean experimental contradiction awaiting arbitration: REACH (Karoo desert), the lunar-orbiting and far-side concepts, and SKA-low are designed with the calibration rigor the 21 cm monopole demands, and one of the two results must be wrong.