Seyed Ali Sebt - Science and Research Branch, Islamic Azad University, Tehran, Iran
Mohamad Reza Abolhassani - Science and Research Branch, Islamic Azad University, Tehran, Iran
Ana Khajehnezhad - Science and Research Branch, Islamic Azad University, Tehran, Iran

Einstein equations give minimum and maximum limits of cosmic scale factor by considering pressure. The contraction before expansion is like the birth of a star. As in nuclear fusion stage, the temperature and pressure of the star depends on its mass, in the order of magnitude of universe mass fusion after gravitational contraction brings about explosion. This does not require to accept the big bang singularity. Explosions have thrown external layers and formed parts of the expanding cosmos in several stages. In observable part of the universe high percentage of dark energy and dark matter confirms that these are the remains of other parts of the cosmos. Neutrinos being highly energetic and without any interaction are the most suitable candidates for dark energy and massive black holes being found at the central part of galaxies and in stellar clusters are the most suitable candidates for dark matter. We dealt with the problem of horizon by considering the idea of step- by step explosions.

Big bang, Scale factor, Dark energy, Dark matter, Horizon problem