Planck time

[Simon Cox]

5.39116 x 10-44 s ​http://physics.nist.gov/cgi-bin/cuu/Value?plkt

[Christof Gessner]

Planck units (with base units length, mass, time, charge, temperature) can be regarded as derived units in the SI system. More specific, they can be derived solely using the universal physical constants, albeit this involves a fractional exponent (which is not currently supported in UCUM expressions).

I would like to learn more about the use case to add this as a unit here. Potentially, it could serve as a consistency cross check for the values of the universal constants (because the five physical constants take on the numerical value of 1 when expressed in terms of these units)?

I suggest to first shed some more light on the use of different systems of quantities (ISQ and others) in the context of informatics and UCUM.

[Gunther Schadow]

Could you elaborate on the fractional exponent issue please? We recently resolved the only previously known fractional exponent issue (see: #147).

[Christof Gessner]

The planck units are derived from the SI base units by multiplications with specific numerical values, that are functions of "fundamental physical constants", in UCUM those numerical values can be calculated from: [G] - Gravitational constant [c] - Speed of light in vacuum [h] - Planck constant [k] - Boltzmann constant [eps_0] - permittivity of vacuum and [pi] - the number pi

Each of those numerical calculations, however, includes a square root (a fractional exponent).

The addition of unit codes for the "Planck units" would not add new information to UCUM. However, it would add a nice facility to cross-check the correctness and consistency of the values of the fundamental constants: By comparing calculated values with the factors listed in UCUM, simple typos could be easily captured.

Proposal: to add five UCUM codes, corresponding to the scaled values of the SI base units.