[en] Three difficulties are enumerated which arise when one tries to explain the nature of the 'hidden mass' due to the baryon matter. It is shown that if the 'hidden mass' is connected with the Hypothetical particles which interact with the baryon matter practically only via gravity, then their mass must be not less than mc²∼1 keV. Solution of the Friedmann equation shows that explanation of the hiden mass due to decaying hypothetical particles is inconsistent with the existence of the Sun. The annihilating particles must have a rather large mass, mc²≥10⁴ MeV