Natural units Totally Explained

Everything about Natural Units totally explained

In physics, natural units are physical units of measurement defined in terms of universal physical constants, such that some chosen physical constants each have a numerical value of exactly 1, when expressed in terms of a particular set of natural units. Natural units are intended to elegantly simplify particular algebraic expressions appearing in physical law or to normalize some chosen physical quantities that are properties of universal elementary particles and that may be reasonably believed to be constant. However, what may be believed and forced to be constant in one system of natural units can very well be allowed or even assumed to vary in another natural unit system. Natural units are natural because the origin of their definition comes only from properties of nature and not from any human construct. Planck units are often, without qualification, called "natural units" but are only one system of natural units among other systems. Planck units might be considered unique in that the set of units are not based on properties of any prototype, object, or particle but are based only on properties of free space.
As with any set of base units or fundamental units the base units of a set of natural units will include definitions and values for length, mass, time, temperature, and electric charge. Some physicists have not recognized temperature as a fundamental dimension of physical quantity since it simply expresses the energy per degree of freedom of a particle which can be expressed in terms of energy (or mass, length, and time). Virtually every system of natural units normalizes the Boltzmann constant to k=1, which can be thought of as simply another expression of the definition of the unit temperature. In addition, some physicists recognize electric charge as a separate fundamental dimension of physical quantity, even if it has been expressed in terms of mass, length, and time in unit systems such as the electrostatic cgs system. Virtually every system of natural units normalizes the permittivity of free space to ε₀=(4π)^-1, which can be thought of as an expression of the definition of the unit charge.

Candidate physical constants used in natural unit systems

The candidate physical constants to be normalized are chosen from those in the following table. Note that only a smaller subset of the following can be normalized in any one system of units without contradiction in definition (for example, m_e and m_p can't both be defined as the unit mass in a single system).

Constant	Symbol	Dimension
speed of light in vacuum
Newtonian constant of gravitation $G ,$	$1 ,$	$1 ,$	$1 ,$	$- ,$	$- ,$	$- ,$
electron mass $m_e ,$	$- ,$	$- ,$	$- ,$	$1 ,$	$1 ,$	$- ,$
caesium ground state hyperfine transition frequency	$- ,$	$- ,$	$- ,$	$- ,$	$- ,$	$9 192 631 770 ,$

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