Dimensionless Quantity - Dimensionless Physical Constants

Dimensionless Physical Constants

Certain fundamental physical constants, such as the speed of light in a vacuum, the universal gravitational constant, and the constants of Planck and Boltzmann, are normalized to 1 if the units for time, length, mass, charge, and temperature are chosen appropriately. The resulting system of units is known as natural. However, not all physical constants can be eliminated in any system of units; the values of the remaining ones must be determined experimentally. Resulting constants include:

• α, the fine structure constant, the coupling constant for the electromagnetic interaction: α ≈ 1/137;
• μ or β, the proton-to-electron mass ratio, the rest mass of the proton divided by that of the electron. More generally, the rest masses of all elementary particles relative to that of the electron: μ ≈ 1836;
• α_s, the coupling constant for the strong force;
• α_G, the gravitational coupling constant: α_G ≈ 1.75×10−45.