What do you do when your kid become smarter than you?

I'm reaching the point where my son, Zach who is 10, is starting to challenge me intellectually.  He and I had a conversation on the Theory of Relativity this morning (prompted by Dr Who) and he kept up with no problem.  I still have a hard time wrapping my brain around the concept, but I do get the basic concept of the theory.  Zach then proceeded to give me an example of, in a sense, how it works.  Can we go back to yellow and blue make green and clap with glee?!  What's going to happen in a few years time?  Thank God for teacher's manuals!
I couldn't help, but look at my son and remember him as a toddler when he first entered childrens' church.  He grabbed a chair and sat in the corner so he could see the whole class.  He barely said a word, he just observed the class proceedings.  The teacher asked me if he was autistic.  I was a little freaked by this question! She told me Zach just sat there and didn't interact with the class at all.  I have an autistic cousin so I know the warning signs and I knew Zach wasn't.  I had to laugh because I could just imagine Zach watching the people and forming an opinion whether or not he wanted to be involved in this class.  Slowly, Zach decided to join in the activities and has now blossomed into a social chatter box that usually involve aliens or science, and occasionally politics. Yes, his political junky of a mother has rubbed off on him a little.
I know he will one day grow up in to an intelligent man, but I certainly didn't think it would start at the age of ten.