The Anomalous 21-cm Absorption at High Redshifts
  The EDGES collaboration has reported the detection of a global 21-cm signal
with a plateau centered at 76 MHz (i.e., redshift 17.2), with an amplitude of
500^(+200)_(-500) mK. This anomalous measurement does not comport with standard
cosmology, which can only accommodate an amplitude < 230 mK. Nevertheless, the
line profile's redshift range (15 < z < 20) suggests a possible link to Pop III
star formation and an implied evolution out of the `dark ages.' Given this
tension with the standard model, we here examine whether the observed 21-cm
signal is instead consistent with the results of recent modeling based on the
alternative Friedmann-Lemaitre-Robertson-Walker cosmology known as the R_h=ct
universe, showing that--in this model--the CMB radiation might have been
rethermalized by dust ejected into the IGM by the first-generation stars at
redshift z < 16. We find that the requirements for this process to have
occurred would have self-consistently established an equilibrium spin
temperature T_s~3.4 K in the neutral hydrogen, via the irradiation of the IGM
by deep penetrating X-rays emitted at the termination shocks of Pop III
supernova remnants. Such a dust scenario has been strongly ruled out for the
standard model, so the spin temperature (~3.3 K) inferred from the 21-cm
absorption feature appears to be much more consistent with the R_h=ct profile
than that implied by LCDM, for which adiabatic cooling would have established a
spin temperature T_s(z=17.2)~6 K.
