It is assumed in this paper that the substances in the universe can be described by the state equation of pressured perfect gasses ρ=k/c~2p. In this assumption

the solution of Einsteins field equations with marginally open universe have been obtained: the scale factor of the universe is R(t)= Rm[|c/Rm 3(k+1)/2k t|]~(2k/3(k+1))the density of the substances in universe is ρ(t)=1/6πG((k+1)/k t)-2

and the deceleration parameter is q=(k+3)/2k. It can easily be seen

when k→∞

these quantities would spontaniously turn to correspond pressure--free cases which we are familiar early.Key words: marginally open universe

scales factor

the source or pressured perfect gasses.