Space Invaders

Not hostile extraterrestrials bent on conquest, but people who have no respect for personal space...

I dislike it when people invade my personal space. Unless the person in question is someone I know well and like, I prefer that people stay a handshake distance away. It's been my understanding that in western American culture, approximately 1 cubit (I love the Biblical reference there. A cubit is about 18 inches, or the distance from elbow to hand, i.e. handshake distance.) is the socially acceptable bubble of personal space for strangers and casual or professional acquaintances, BART during rush hour notwithstanding. I've heard that in Japan, it's even farther, more like bowing distance, but I've never been there, so I don't know for sure.

It's especially uncomfortable when professors become space invaders. Yesterday evening, I was sitting in the lounge studying. I was on a large couch-like piece of furniture. There were a few other people in the lounge on the other side of the room. Suddenly, I noticed that someone practically appeared right next to me. I looked up, and it was one of my professors. (We'll call him Professor Space-Invader.) He sat down on the couch right next to me (like, probably an inch away) and struck up a conversation. I made small talk, but I was really uncomfortable. Finally, he wrapped up the conversation and headed off. Then I relaxed.

Professor Space-Invader is from Alabama. I have another professor who is a bit of a space invader, too (though he doesn't really make me uncomfortable), and he's from New England. Both of them have lived in California for many years, though. Is there an eastern/western divide in how much personal space is socially acceptable? (I lived in North Carolina and Virginia for a year and a half, and I never noticed personal space being smaller out there.)