Also note that this is an Inverse Square Law, and thereby similar to many other scientific laws ranging from gravitational pull to light attenuation. This law states that a specified physical quantity is inversely proportional to the square of the distance.formula_5In some modern systems of units, the Coulomb constant has an exact numeric value; in Gaussian units , in Lorentz–Heaviside units (also called "rationalized") . This was previously true in SI when the vacuum permeability was defined as . Together with the speed of light in vacuum , defined as , the vacuum permittivity can be written as , which gave an exact value of