| © CAMBRIDGE UNIVERSITY PRESS 1998 |
1.10 Units
In particle physics it is usual to simplify the appearance of equations by using units in which = 1 and c = 1. In electromagnetism we set _{0} = 1 (so that the force between charges q_{1} and q_{2} is q_{1}q_{2} / 4r^{2}), and µ_{0} = 1, to give c^{2} = (µ_{0}_{0})^{-1} = 1. We shall occasionally reinsert factors of and c where it may be reassuring or illuminating, or for the purposes of calculation. It is useful to remember that
c 197 MeV fm, | e^{2} / 4 1.44 MeV fm, |
= e^{2} / 4 c (1/137), | c 3 x 10^{23} fm s^{-1}. |
Energies, masses, and momenta are usually quoted in MeV or GeV, and we shall follow this convention.