July 2015 – physics

The SI unit system and the natural unit system are equivalent ways of describing physical quantities. SI has the basis (meter, second, kilogram and Ampere). The natural system has the basis (speed of light, $\hbar$ , electron volt, and $4 \pi \varepsilon_0$ ).
This python script makes it easy and transparent to convert quantities between these systems. It is a simple command line tool, which is invoked with the value you want to convert, its unit system and the powers of its units. An easy example would be to check, if the speed of light, 2.998 10⁸ m/s, is ‘one’ in natural units. The power of meter is 1, the power of seconds is -1. The powers of the remaining kg and A are both 0. Running the code then looks like this

convert_SI_Natural.py --unit=si -- 2.998e8 1 -1 0 0
 converted 
   2.998000000e+08 m s^-1
 = 1.000025157e+00 c

Looks good! Now lets check the opposite direction. The power of c is 1. The powers of the remaining units ( $\hbar$ , eV and $4\pi \varepsilon_0$ ) are zero.

convert_SI_Natural.py --unit=nat -- 1.0 1 0 0 0
 converted 
   1.000000000e+00 c
 = 2.997924580e+08 m s^-1

This is the value by NIST definition. All the details for using the script can be found by invoking the script with

convert_SI_Natural.py --help

Download and have fun.
convert_SI_Natural.py

Month: July 2015

Script to convert between natural units and SI units