Heaviside–Lorentz units

Heaviside–Lorentz units are a rationalized electromagnetic unit system in which vacuum permittivity and permeability are set to one, absorbing factors of 4π into charge and field definitions.

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Maxwell's equations: The equations describing how electric and magnetic fields are produced and how they evolve. In these units, the equations contain no explicit 4π factors in their source terms.
Rationalization (physics): A convention that places geometric factors such as 4π in definitions rather than repeatedly in physical laws. It explains why spherical symmetry does not leave 4π in the point-charge force law.
Oliver Heaviside: An English electrical engineer and mathematician who developed vector methods and reformulated electromagnetic theory. His work helped establish the rationalized conventions associated with this system.
Quantum electrodynamics: The quantum field theory of electromagnetic interactions between charged particles and photons. Its calculations commonly use rationalized Heaviside–Lorentz conventions.
Coulomb's law: The law stating that the electrostatic force between point charges varies with their product and inverse-square separation. Rationalization removes the 4π denominator from its vacuum form.
Vacuum permittivity: The constant relating electric displacement to electric field in vacuum in SI conventions. Heaviside–Lorentz conventions assign this constant the value one.
Hendrik Lorentz: A Dutch physicist whose work on electromagnetism and electron theory shaped modern physics. His name became attached to the unit convention alongside Heaviside's.
Quantum field theory: A framework describing particles and interactions through quantized fields. Its relativistic notation often sets electromagnetic constants to one and uses rationalized units.
Gaussian units: An unrationalized electromagnetic unit system that uses Gaussian conventions and places electric and magnetic fields on comparable footing. Its field equations place 4π in source terms, unlike the rationalized Heaviside–Lorentz form.
Vacuum permeability: The constant relating magnetic field strength to magnetic flux density in vacuum in SI conventions. Its value is also set to one in the stated convention.