The Gaussian unit system is a centimetre-gram-second (CGS) system for electromagnetism in which the Coulomb constant equals one, so electric charge carries mechanical dimensions and factors of 4*pi*epsilon_0 disappear from formulas while factors of the speed of light appear explicitly in field equations.The Gaussian unit system is a variant of the centimetre-gram-second (CGS) system tailored for electromagnetism. Its defining feature is that the Coulomb constant is set to one, making electric charge have mechanical dimensions (such as cm^(3/2)·g^(1/2)/s). This choice simplifies many equations: the force between two charges is simply q1*q2/r^2, without the 4*pi*epsilon_0 factor that appears in SI units. However, it introduces explicit factors of the speed of light in magnetic field equations, reflecting the deep connection between electricity and magnetism.
The system was developed in the 19th century by Carl Friedrich Gauss and Wilhelm Weber, who were among the first to study electromagnetism quantitatively. It became a standard in physics literature, especially in the early 20th century.
In Gaussian units, electric and magnetic fields have the same dimensions, which makes the symmetry between them more apparent. Maxwell's equations take a cleaner, more symmetric form, but the price is that factors of c appear where SI units hide them inside constants. This system is particularly favored in theoretical physics because it makes the relativistic nature of electromagnetism more transparent.
Gaussian units are still widely used in theoretical physics, particularly in particle physics and cosmology, where the cleaner equations simplify derivations. Many classic textbooks and research papers use this system.
In Gaussian units, the fine-structure constant — a dimensionless number characterizing the strength of electromagnetic interaction — is simply e^2/(ħc), a form that reveals its fundamental nature more directly than in SI units.