Background The cosmological constant problem As different fields of studies like Cosmology (involving gravitation and relativity theories), Quantum Electro dynamics (QED), Quantum Field Theory (QFT) emerged in their own ways, their contribution to each others also started emerging. A case in point was cosmological constant. Einstein devised the cosmological constant (whose units are cm -2 ) from a cosmology (Gravitation and Relativity) perspective to balance the curvature of space and define a static universe. Einstein abandoned the concept after Hubble 's 1929 discovery that all galaxies outside the Local Group (the group that contains the Milky Way Galaxy) are moving away from each other, implying an overall expanding universe. From 1929 until the early 1990s, most cosmology researchers assumed the cosmological constant to be zero. Since the 1990s, several developments in observational cosmology, especially the discovery of the accelerating universe from dis