This coupling plays a role in producing a difference in the temperature of neutral hydrogen and the cosmic microwave background at the end of the Dark Ages and the beginning of the epoch of reionization.
The period after recombination occurred and before stars and galaxies formed is known as the "dark ages".
This process causes a redistribution of the electrons between the hyperfine states, decoupling the neutral hydrogen from the CMB photons.
That this mechanism might affect the population of the hyperfine states in neutral hydrogen was first suggested in 1952 by S. A. Wouthuysen, and then further developed by George B.
There are multiple experiments and radio observatories that aim to detect the neutral hydrogen line the Dark Ages and epoch of reionization, the time at which Wouthuysen–Field coupling is expected to be important.
[6] Proposed observatories that aim to detect evidence of Wouthuysen–Field coupling include the Square Kilometer Array and the Dark Ages Radio Explorer.