# Electrodynamics in particle physics

1. Jul 9, 2008

### ghery

Hi:

I've heard that in electromagnetism, there is a system of units called Lorentz - Heaviside system, and that in particle physics, tis system is used insted of the gaussian or the SI. Why do particle physicist use this system? and by the way, How do we go from the Gaussian system to the Lorentz-Heaviside system?

Thanks a lot for your support

2. Jul 9, 2008

### clem

Unfortunately particle physicists seem to use Gaussian and L-H in roughly equal numbers,
although I think (and hope) that Gaussian is winning more recent favor.
Fortunately, I know of no HEPist who uses SI, except to confuse undergraduates.
Heaviside "rationalized" that dividing e^2 by 4pi would make some equations simpler. The same confusion is introduced in SI. All you have to do to go from Gaussian to H-L is divide e^2 by 4 pi. The good news is that alpha is the same in all known systems. In Gaussian, alpha=e^2=1/137. In H-L, alpha=e^2/4pi=1/137.
Be careful in reading any paper or book because some authors don't state clearly which system they are using.