[That, on the other hand, he expected.]

Shepard's a little more technically inclined than I am, so she'd be the better person to ask. The short version is that it's based on element zero, and if you run a current through it, you can increase or decrease the mass of things around it. It's the basis for most technology worth a damn where I come from. Weapons, shielding, advanced construction materials, FTL drives ...