(Submitted by reader Jim Houston)

A few years after graduating from college in upstate New York, I returned to where I grew up in Pennsylvania and found a job about 20 miles away  from my hometown. The job wasn’t related to my major in Physics, but computer programming was something that was a bit more portable, and within a few months, I was asked to find other programmers for the project team.

Sifting through stacks of résumés is an exercise in looking for familiar experiences that would suggest someone can do the job you need done, so one morning I see a résumé that looks so familiar I could have written it myself. I realized as I read it that I must know this guy and so decided right away to call him in for an interview. He went to the same college as I, graduated the same year, and in the same major.  There were about 100 of us freshmen in the department and we all took the same intro courses for the first two years.  While 100 classmates is not a large group, I  may not have known many of their names, but usually recognized them if we passed each other in the halls.  So that I couldn’t place the  interviewee from the name on the resume didn’t strike me as unusual.

When my classmate walked in for the interview, I felt that I had never ever seen this guy before.  It was so unlikely that we could be in the same classes and not have recognized each other, that we actually spent a fair amount of time in the initial chat comparing notes on where we lived, who our professors were, who we knew etc…  Freshman year, he lived one dorm over in a complex of about 2000 students.  The next year, we both moved up to the newer North Campus dorms and again lived a couple of dorms apart, and for the remaining two years we both lived in apartments that were about three blocks from each other.

It turned out that we probably didn’t take classes together because we were six months out of sync on the prerequisites, but largely knew the same people and had the same professors.

What came next floored me. He not only grew up his entire life in my hometown, but I discovered he lived two streets away from where I had lived my entire life up to that point.  He had gone to a different school system and was on the other side of a major street that I had rarely crossed. He was as convinced as I was that even if we had somehow crossed paths, we had never seen each other before.

So when people bring up stories of chance encounters that demonstrate what a small world it is, I like to bring up my counter story of what a BIG world it is. For twenty years, I lived within two hundred yards of a person with very similar interests, went to many of the same playgrounds, stores, and parks and yet were still complete strangers.

(For the statistically inclined, college size was 16,000 students. Class sizes were about 40 people. The population density of my hometown is 15,000 people per square mile. The number of people who lived on the two streets in question is about 250. The rest is an exercise for the reader

Below are the extended notes provided by Barbara Drescher for use in Skepticality Episode 201. Take a look and leave your comments below.

I love this story. There is, of course, nothing shocking about the coincidences except that the men did not remember each other at all. This should not be the case given the size of the school and the proximity of their childhood homes. And yet it is not surprising at all to me as a psychologist who has studied attention and memory.

The fact of the matter is that the author almost certainly interacted with the interviewee many times and simply did not notice or remember him. It is even more interesting that neither noticed the other while they were in college. I would expect at least that “I know you, don’t I?” feeling.

We all probably encounter many of the same strangers often, but without an interaction that is out of the ordinary, we don’t even encode their faces. If human beings were not so selective, we would be unable to function as we would need to sort through enormous amounts of information on a constant basis. Instead, we encode what we think might be important later and store it as connections to other bits of information.

To see this for yourself, try to draw the heads side of a penny–right now, without looking at one.  You have seen hundreds in your lifetime and you can probably recreate the gist of the coin and some of the details, but do you know where to put everything? Did you draw something that is actually on the tails side? Is the date in the right place? Which direction is Lincoln looking?

For some fun and interesting demonstrations of selective attention and memory, I highly recommend “The Invisible Gorilla” by Daniel Simons, a psychologist who has studied this phenomena.