In free space , the permeability Î 1\/4 is the permeability of free space , Î 1\/4 0 , which is exactly 4 Ï Ã -- 10-7 W\/A Â m , by definition . Also , the permittivity is the permittivity of free space Î 0 . where Î 0 and Î 1\/4 0 are two universal constants , called the permittivity of free space and permeability of free space , respectively .