In this paper, by taking the structure of universe to be a 3-sphere and assuming that the zero-point oscillator for all particles is same, we derive an analytical expression for vacuum (or dark) energy density and eliminate the discrepancy of ~10¹²³ between quantum mechanical prediction and astronomical observation. Thus, we solve the cosmological constant problem. Then, using the analytical expression of the dark energy, we derive the expression for non-vacuum contribution to energy density (ordinary/dark matter, radiation) and show that ratio between non-vacuum to vacuum energy is ~1/2, thus solving the cosmic coincidence problem which questions why the matter energy density is of the same order as the vacuum energy density. Finally, using the above expressions for energy density, observed flatness of space is explained, Hubble’s constant is proved to be exactly equal to the reciprocal of the age of universe and size of universe is estimated. The calculated age and radius of universe comes out to be ~14.4 billion years and ~50 billion light years respectively which match well with the astronomically observed data.