Planck unit
In physics, Planck units are physical units of measurement defined exclusively in terms of five universal physical constants listed below, in such a manner that these five physical constants take on the numerical value of 1 when expressed in terms of these units. Planck units have profound significance for theoretical physics since they elegantly simplify several recurring algebraic expressions of physical law by nondimensionalization. They are particularly relevant in research on unified theories such as quantum gravity.
Originally proposed in 1899 by German physicist Max Planck, these units are also known as natural units because the origin of their definition comes only from properties of the fundamental physical theories and not from interchangeable experimental parameters. Planck units are only one system of natural units among other systems, but are considered unique in that these units are not based on properties of any prototype object or particle (that would be arbitrarily chosen), but rather on properties of free space alone.
The universal constants that Planck units, by definition, normalize to 1 are
- the gravitational constant, G,
- the reduced Planck constant, ħ,
- the speed of light in a vacuum, c,
- the Coulomb constant, (4πε0)−1 (sometimes ke or k), and
- the Boltzmann constant, kB (sometimes k).
Each of these constants can be associated with at least one fundamental physical theory: c with electromagnetism and special relativity, G with general relativity and Newtonian gravity, ħ with quantum mechanics, ε0 with electrostatics, and kB with statistical mechanics and thermodynamics.
Planck units are sometimes called "God's units", since Planck units are free of anthropocentric arbitrariness. Some physicists argue that communication with extraterrestrial intelligence would have to employ such a system of units in order to be understood. Unlike the meter and second, which exist as fundamental units in the SI system for historical reasons, the Planck length and Planck time are conceptually linked at a fundamental physical level.
Natural units help physicists to reframe questions. Frank Wilczek puts it succinctly:
It is true that the electrostatic repulsive force between two protons (alone in free space) greatly exceeds the gravitational attractive force between the same two protons. From the point of view of Planck units, however, this is not a statement about the relative strengths of the two forces; rather, it is a manifestation of the fact that the charge on the protons is approximately the Planck charge but the mass of the protons is far less than the Planck mass.

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Planck units - Wikipedia, the free encyclopedia
In physics, Planck units are physical units of measurement defined exclusively in terms of five universal physical constants listed below, in such a manner that ...
en.wikipedia.org/wiki/Planck_units
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Planck time - Wikipedia, the free encyclopedia
In physics, the Planck time (tP) is the unit of time in the system of natural units known as Planck units. It is the time required for light to travel, in a vacuum, ...
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FUNDAMENTAL PLANCK UNITS
An essay on the extraction, uses and interpretation od the Planck fundamental units.
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Planck length - Wikipedia, the free encyclopedia
In physics, the Planck length, denoted ℓP, is a unit of length, equal to 1.616199( 97)×10−35 metres. It is a base unit in the system of Planck units, developed by ...
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Planck energy - Wikipedia, the free encyclopedia
In physics, Planck energy, denoted by EP, is the unit of energy in the system of natural units known as Planck units. E_\text{P} = \sqrt{\frac{\hbar c 1.956 × 109 J \  ...
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Q: What is the Planck length? What is its relevance? | Ask a ...
May 25, 2013 ... So, why not choose units so that G=1, and then ignore it? The Planck units are set up so that G (the gravitational constant), c (the speed of light), ...
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Planck Units | COSMOS
Note that we have expressed these constants in SI units: metres (m), kilograms ... These units are known as the Planck units (after Max Planck, the physicist who ...
astronomy.swin.edu.au/cosmos/P/Planck+Units
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The Planck scale: relativity meets quantum mechanics meets gravity ...
The Planck length LP is defined by taking the constants of nature and combining them in such a way that their units combine to give a length. Planck's constant ...
www.phys.unsw.edu.au/einsteinlight/jw/module6_Planck.htm
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Planck's constant - RationalWiki
The system of Planck units was designed to make the lives of quantum physicists easier still. In the Planck unit system, five basic ...
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The Planck Length
Planck noted that apart from numerical factors there is a unique way to use these constants to define units of length, time, and mass. For example, we can define ...
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Planck unit in science
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Max Planck Research Department for Structural Dynamics at the University of Hamburg. The Max Planck Research Department for Structural Dynamics at the ...
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Contact. Max Planck unit for Structural Dynamics at the University of Hamburg Dr . Monika Kaempfe, Research Coordinator c/o DESY, Bldg. 99, Room 01.077
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In physics, the Planck time (tP) is the unit of time in the system of natural units known as Planck units. It is the time ... Georgia State University. 19 June 2005.
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