QUESTION #129

# Why is there no degree in Kelvin?

Asked by: Sirisak

### Answer

In general, 'degrees' are found in units which are mainly arbitrary. Like, degrees Fahrenheit and Celsius, which are both arbitrary in the sense that their origin is chosen in an arbitrary way, and they are meant to be convenient instead of absolute. The same goes for angle degrees, since that also divides the circle into 360 degrees arbitrarily.

When the units are absolute, or measured directly with respect to something else, one drops 'degrees' from the units. Like, there is no 'degrees' in radians, which is the 'natural' way of measuring angles. (One can appreciate the 'natural'ness of radians after one sees how sines and cosines work, and some series expansion of those, and their relations with the exponential function, and complex numbers...).

It is the same way for Kelvin. Temperature is defined in terms of the average energy of particles in a system, and Kelvin is directly proportional to that -- the zero in the Kelvin scale corresponds to absolute zero, and not any arbitrary temperature, and Kelvin is the 'natural' unit to measure temperature.

However, let me also note that degrees are still used with Kelvin in some sources, even textbooks, although it is generally agreed that they should not.
Answered by: Yasar Safkan, Ph.D. M.I.T., Software Engineer, Istanbul, Turkey