Natural units

Part of my units pages

There are alternatives to SI called “natural units”. Whilst the metric and SI systems take their derived units from physical equations like F = ma, natural units go one step further and take their base units from physical constants like the speed of light (in a vacuum). Using natural units can make physical calculations much easier, for example the equation E = mc² becomes E = m if the speed of light is a base unit.

There are three problems with switching to natural units:

There isn’t just one set of natural units, so we would need to pick one to standardise on. This isn’t insurmountable.
Natural units can choose different dimensions for familiar quantities. For example, some set the speed of light to be dimensionless (rather than “length over time”). This requires changing other dimensions to maintain consistency, which could make for a confusing system. This might not be too bad, but is important to keep in mind.
These units are very far removed from everyday scales, so would need some pretty powerful prefix factors (both big and small) to make them usable.