In this thesis, we will investigate a new method for detecting dark matter by circular polarization of photon. Moreover we will study the philosophical aspects of cosmology. In the first chapter, the history of dark matter and the signatures of the existence dark matter in the galaxies and galaxy clusters will be reviewed. As well as, we will describe different candidates of dark matter particles. In the second chapter, we will present the standard model of cosmology, including the horizon and flatness problems. Then, we will discuss how inflation theory can solve the horizon and flatness problems. In the third chapter, we will study the physics of early universe by assuming the thermodynamic equilibrium. In the fourth chapter, we will investigate the decaying dark matter and photon production in this process. We will find out that if we have asymmetry in the number of dark matter particles and antiparticles, a non-vanishing photon circular polarization is produced. Finally, the fifth chapter is devoted to discuss about the philosophy of cosmology. Here, we explore the relation between cosmology and philosophy from a critical point of view.