In particle physics and physical cosmology, Planck units are a system of units of measurement defined exclusively in terms of four universal physical constants: c, G, ħ, and kB (described further below). Expressing one of these physical constants in terms of Planck units yields a numerical value of 1. They are a system of natural units, defined using fundamental properties of nature (specifically, properties of free space) rather than properties of a chosen prototype object. Originally proposed in 1899 by German physicist Max Planck, they are relevant in research on unified theories such as quantum gravity.
The term Planck scale refers to quantities of space, time, energy and other units that are similar in magnitude to corresponding Planck units. This region may be characterized by particle energies of around 1019 GeV or 109 J, time intervals of around 5×10−44 s and lengths of around 10−35 m (approximately the energy-equivalent of the Planck mass, the Planck time and the Planck length, respectively). At the Planck scale, the predictions of the Standard Model, quantum field theory and general relativity are not expected to apply, and quantum effects of gravity are expected to dominate. One example is represented by the conditions in the first 10−43 seconds of our universe after the Big Bang, approximately 13.8 billion years ago.
The four universal constants that, by definition, have a numeric value 1 when expressed in these units are:
c, the speed of light in vacuum,
G, the gravitational constant,
ħ, the reduced Planck constant, and
kB, the Boltzmann constant.
Variants of the basic idea of Planck units exist, such as alternate choices of normalization that give other numeric values to one or more of the four constants above.
In particle physics and physical cosmology, Planckunits are a system of units of measurement defined exclusively in terms of four universal physical constants:...
the reduced Planck constant, G is the gravitational constant, and kB is the Boltzmann constant. Planckunits form a system of natural units that is not...
the Planck constant is expressed in SI units, it has the exact value h {\displaystyle h} = 6.62607015×10−34 J⋅Hz−1. It is often used with units of electronvolt...
for Planck's constant, which is of foundational importance for quantum physics, and which he used to derive a set of units, today called Planckunits, expressed...
constant Planck postulate Planck's law of black body radiation Planck-taper window Planck–Bessel window Planck–Einstein relation PlanckunitsPlanck energy...
Planckunits are more commonly used than Stoney units in modern physics, especially for quantum gravity (including string theory). Rarely, Planck units...
Max Planck Institutes and Research Units exist (in alphabetical order): Max Planck Institute for Biophysical Chemistry (merged with the Max Planck Institute...
A system of units of measurement, also known as a system of units or system of measurement, is a collection of units of measurement and rules relating...
frequency dependence of this approximation) or, by introducing natural Planckunits, I ( ν , x ) = 2 ν 3 e − x , {\displaystyle I(\nu ,x)=2\nu ^{3}e^{-x}...
example, Planckunits, constructed from c, G, ħ, and kB give conveniently sized measurement units for use in studies of quantum gravity, and atomic units, constructed...
defined by setting exact numerical values, when expressed in SI units, for the Planck constant (h), the elementary electric charge (e), the Boltzmann...
SI system of units, and it has been increasingly replaced by the nanometre or picometre. Up to 2019, it was listed as a compatible unit by both the International...
given special consideration, because they can be used to define all Planckunits and thus all physical quantities. The three constants are therefore used...
generally understood as length−2. Using the values known in 2018 and Planckunits for ΩΛ = 0.6889±0.0056 and the Hubble constant H0 = 67.66±0.42 (km/s)/Mpc...
where J{\displaystyle J} exceeds GM2/c{\displaystyle GM^{2}/c} (or in Planckunits, J>M2{\displaystyle J>M^{2}}); i.e. the spin exceeds what is normally...
A geometrized unit system : 36 or geometrodynamic unit system is a system of natural units in which the base physical units are chosen so that the speed...
nucleon) in a vacuum. The Planck time is the time light takes to travel one Planck length. The TU (for time unit) is a unit of time defined as 1024 µs...
black hole and one quarter of the area of the horizon as measured in Planckunits is in fact always increasing. This allows the formulation of the first...
chosen. The resulting system of units is known as the natural units, specifically regarding these five constants, Planckunits. However, not all physical constants...
The Max Planck Society for the Advancement of Science (German: Max-Planck-Gesellschaft zur Förderung der Wissenschaften e. V.; abbreviated MPG) is a formally...
constant in some systems of natural units, particularly geometrized unit systems such as Planckunits and Stoney units, the value of the gravitational constant...
electronics are driven. The units are sometimes also used as a representation of the energy of a photon, via the Planck relation E = hν, where E is the...
The SI base units are the standard units of measurement defined by the International System of Units (SI) for the seven base quantities of what is now...
physics, the Planck length, denoted ℓP, is a unit of length, equal to 1.616199(97)×10−35 metres. It is a unit in the system of Planckunits, developed by...
{\displaystyle J} exceeds G M 2 / c {\displaystyle GM^{2}/c} (or in Planckunits, J > M 2 {\displaystyle J>M^{2}} ), i.e. the spin exceeds what is normally...
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