Hi all, Sorry, I'm not quite sure that I've posted this question in the proper place, but I figured field theory matches best with lie groups in this context. Anyway, my question has to do with the relationship between the fundamental forces (electromagnetism, weak, and strong) and their lie groups -- U(1), SU(2), and SU(3), respectively. For example, what exactly does it mean to say that electromagnetism has U(1) gauge symmetry? I understand that it might have something to do with invariance with respect to rotations -- but then, how does something's electric charge correspond to U(1), which is simply the circle group of complex numbers [itex]\left|z\right|=1[/itex]? Thanks.