(back from Asia, so will return to posting the backlog of posts I have)
A friend of mine related to me a few stories of random encounters with people he had not heard from in years. My response is that this happens so often, I am no longer surprised.
A girl I was in marching band with in high school in new jersey, who I never kept in touch with, I later bumped into on a random vacaction in banff canada, and then years later, she turns up as a student at the orientation picnic in the MBA program I teach in.
A key paper I cite in my dissertation, turns out to be written by one of R-'s classmate in med school, who wrote the paper with a darthmouth econ professor, and two weeks ago, the econ prof shows up to give a talk at Cornell. That econ prof's normal collaborator is the economist I worked with at the White House, who went to the same summer school I did in high school, which we found out since we were both being interviewed by the summer school director in the same week.
Sitting in a random starbucks in the upper west side in new york city, there were limited seats, so I shared a table with a guy who asked to borrow the book review from the sunday nytimes I was reading. He was looking for the review of a book he publishes. turns out he's a book agent for social science books. 3 days later, I am having dinner with a visiting harvard prof back in Ithaca, who is talking about his book agent, who sure enough is the guy I chatted with back at Starbucks.
A friend of mine from college, whom I hadn't seen or talked to since college turned out to live on my street in baltimore.
So what are the odds? I guess physicists call this a Fermi problem.
So let's say you have 4,000 acquaintances that you'd recognize and remember. (My high school had 300 people per class, I'd probably recognize all of them, plus a few hundred from adjacent classes. say 1000 total. then 1000 from college. 1000 from grad school. 1000 from work and otherwise).
Assuming most are yuppies, there are maybe 100,000 students who went to a top college per year. so 1,000,000 people within 5 years of you. so you probably know 0.4% of them. and if you include friends of friends, that's probably lots more. so given that you see say 50 yuppies in any given day, you have a 20% (50 * 0.4%) chance of bumping into a random person on any given day in a new place. Which doesn't sound too far off.