  It is known that, theoretically, the Rees-Sciama effect may cause arbitrarily
large additional redshifts in the cosmic microwave background radiation due to
transparent expanding voids having sizes comparable with the size of horizon.
Therefore, again theoretically, eventual huge voids existing immediately after
the recombination may essentially change the predictions of the theory of big
bang nucleosynthesis. If this eventuality holds, then the dark matter can be
dominantly baryonic and, simultaneously, one can be in accordance with the
predictions of primordial nucleosynthesis theory. Studying this eventuality one
arrives at the result that the observed extreme isotropy of the cosmic
microwave background radiation rejects the existence of any such huge voids,
and hence this eventuality does not hold.
