A Unified Cosmological Model for Solution of Problems of Cosmological Constant, Cosmic Coincidence, Energy Conservation, Flatness and Homogeneity of Horizon

Cosmological constant problem is the difference by a factor of ~10¹²³ between quantum mechanically calculated vacuum energy density and astronomically observed value. Cosmic coincidence problem questions why matter energy density is of the same order as the present vacuum energy density (former is ~32% and latter is ~68%). Recently, by quantizing zero-point field of space, we have developed a cosmological model that predicts correct value of vacuum and non-vacuum energy density. In this paper, we remove some earlier assumptions and develop a generalized version of our cosmological model to solve three more problems viz. energy conservation, flatness and horizon problem along with the above two. For creation of universe without violating law of energy conservation, net energy of the universe including (negative) gravitational potential energy must be zero. However, in conventional method, its quantitative proof needs the space to be exactly flat i.e. zero-energy universe is a consequence of flatness. But, in this paper, we will prove a zero-energy universe without using flatness of space and then show that flatness is actually a consequence of zero energy density. Finally, using our model we solve the horizon problem of universe. Although cosmic inflation can explain the flatness of space and uniformity of horizon by invoking inflaton field, it cannot predict the present value of vacuum energy density or matter density. But, our cosmological model solves in an unified manner all the above mentioned five problems viz. cosmological constant problem, cosmic coincidence problem, energy conservation, flatness and horizon problem.