A geometrized unit system or geometric unit system is a system of natural units in which the base physical units are chosen so that the speed of light, c, and the gravitational constant, G, are set equal to unity.
The geometrized unit system is not a completely defined or unique system: latitude is left to also set other constants to unity. We may, for example, also set Boltzmann's constant, k, and the Coulomb force constant, kC, to unity.
Setting the reduced Planck constant, , to unity yields Planck units.
This system is useful in physics, especially in the special and general theories of relativity. All physical quantities are identified with geometric quantities such as areas, lengths, dimensionless numbers, path curvatures, or sectional curvatures.
Many equations in relativistic physics appear far simpler when expressed in geometric units, because all appearances of G or c drop out. For example, the Schwarzschild radius of a nonrotating uncharged black hole with mass m becomes simply r = 2m. Therefore, many books and papers on relativistic physics use geometric units exclusively. An alternative system of geometrized units is often used in particle physics and cosmology, in which 8πG = 1 instead. This introduces an additional factor of 8π into Newton's law of universal gravitation but simplifies Einstein's equations, the Einstein-Hilbert action, the Friedmann equations and the Newtonian Poisson equation by removing the corresponding factor.
Practical measurements and computations are usually done in SI units, however, conversions are generally quite straightforward.
Contents |
|
