I haven't fully worked through it yet, but I've been really enjoying reading John Baez's Gauge Fields, Knots, and Gravity [1]. [1]: http://www.worldscientific.

I haven't fully worked through it yet, but I've been really enjoying reading John Baez's Gauge Fields, Knots, and Gravity [1]. [1]: http://www.worldscientific.com/worldscibooks/10.1142/2324 http://www.worldscientific.com/worldscibooks/10.1142/2324