What units in the physical universe are not arbitrary? E.g. time (as measured in seconds and years) is arbitrary since it's based on the changing orbit of this little planet in some odd solar system on the edge of an insignificant galaxy. Atomic mass is arbitrary since it relies on which molecule you pick (why C12 instead of H1 I don't know). Absolute zero is not arbitrary, but the temperature scales are. Pi and e are not arbitrary, but they are unitless. In contrast the speed of light (c) is constant in the elegant presence of a vacuum. One could define a unit of speed based on this scale, but not for time or distance independently. Similarly the gravitational constant (G) ties together distance, mass, and time. I'm interested in an exhaustive list of all such constants, those that are fundamental rather than, say, used in approximations or a result of poorly understood behavior. Even G is kind of iffy because we don't have a theorem unifying all the forces. By combining G and c one can produce non-arbitrary values for units of mass/time and mass/distance, whatever that's supposed to mean, and force: c^4/G = 1.2E44 Newtons. Is it possible to arrive at non-arbitrary units for mass, energy, temperature, etc?