Units of measure defined exclusively in terms of 4 universal physical constants.
These were originally suggested in 1899 by Max Planck, hence the name.
They depend on:
- the speed of light
- the Gravitational Constant
- the Reduced Planck Constant
- the Boltzmann Constant
Some people add in the electromagnetic dimension by including the Electric Constant
These include:
| Name | Expression | Value in terms of SI |
|---|---|---|
| Planck length | l_p = root(h_bar*G/c^3) | 1.616e-35 m |
| Planck mass | m_p = root(h_bar*c/G) | 2.176e-8 kg |
| Planck time | t_p = root(h_bar*G/c^5) | 5.391e-44 s |
Using these, you can define derived units for many other types of units (area, volume, momentum, temperature, energy, force, density, acceleration, frequency, etc)
These are essentially useless in day-to-day life. They are useful when working at the “Planck Scale”, which only happens in university-or-greater-level physics classes.