The open (hyperbolic) model of the Universe is characterized by the values of q < ½. The transition between open and closed models of the Universe is characterized by the flat (parabolic) model which corresponds to the critical value q = ½. In terms of the mass density it follows from that the critical mass density in the present day Universe is given by which marks the flat model of the Universe. The closed and open models are similarly characterized respectively by ru > 1.0 x 10-29 gm cm-3 and ru < 1.0 x 10-29 gm cm-3. The currently observed density of robs – 1.5 x 10-30 gm cm-3 then points in favor of the open model: but as we have already mentioned, the present day observational status is not sufficient to draw a definite conclusion in this regard. Extensive search, of course, is going on currently tundra we definite conclusion in this regard. Extensive search, of course, is going on currently in order to establish a more meaningful value of the mass density of the Universe. This is very important as it will determine whether our universe is open, closed or flat.
Keywords: Universe, Dynamical Nature, Galaxies, Interstellar.