What does it mean when we notice a coincidence?

Most people brush off coincidences. Random strange things happen all the time, right? But they don’t mean anything. Like when you go to meet a friend run into a stranger that perfectly resembles your friend, waiting in precisely the same place (which once happened to me … creepy.) Or when farmers hundreds of years ago started noticing that milkmaids never got smallpox. Weird, huh?

The difference is, of course, is that the first example here is “mere” coincidence — something weird and fishy, but that’s about it. The second example, however, is a “suspicious” coincidence. It seems like it means something so juicy it’s got to be true. This is how science often works: Scientists get a hunch because they’re so stimulated by an inexplicable-but-suggestive connection. Guys like Louis Pasteur or Newton relied on hunches to get them going. And as for that smallpox thing? It turned out there was a connection: Milkmaids don’t get smallpox because they are constantly exposed to a mild form of it, and thus build up a resistance. Scientists in the 18th century didn’t know about microbes or viruses and could never have figured that out, but it didn’t stop them from having hunches — and quite useful ones — about the connection. In that latter case, noticing something that seems coincidental is part of how we discover knowledge.

I just got back from an MIT Knight seminar with the insanely brilliant MIT cognitive scientist Joshua Tenenbaum — who studies coincidence. As he argues, our penchant for seeing coincidence is part of very deep, intelligent processes in the brain. Our brains are making connections and theories about the world all the time, even when we’re not aware of it. We know more than we know we know, it seems — and sometimes this knowledge erupts as coincidence.

Mind you, scientists always warn us (and rightly so) that “correlation is not causation”. But as humans, we don’t believe it. When we see connections, we know damn well something is going on. We get hunches, and we’re so often right about them that — against reason — we learn to follow them:

For decades, all academic talk of coincidence has been in the context of the mathematical. New work by scientists like Joshua B. Tenenbaum, an assistant professor in the department of brain and cognitive sciences at M.I.T., is bringing coincidence into the realm of human cognition. Finding connections is not only the way we react to the extraordinary, Tenenbaum postulates, but also the way we make sense of our ordinary world. ”Coincidences are a window into how we learn about things,” he says. ”They show us how minds derive richly textured knowledge from limited situations.”

To put it another way, our reaction to coincidence shows how our brains fill in the factual blanks. In an optical illusion, he explains, our brain fills the gaps, and although people take it for granted that seeing is believing, optical illusions prove that’s not true. ”Illusions also prove that our brain is capable of imposing structure on the world,” he says. ”One of the things our brain is designed to do is infer the causal structure of the world from limited information.”

If not for this ability, he says, a child could not learn to speak. A child sees a conspiracy, he says, in that others around him are obviously communicating and it is up to the child to decode the method. But these same mechanisms can misfire, he warns. They were well suited to a time of cavemen and tigers and can be overloaded in our highly complex world. ”It’s why we have the urge to work everything into one big grand scheme,” he says. ”We do like to weave things together.

”But have we evolved into fundamentally rational or fundamentally irrational creatures? That is one of the central questions.”

Damn, this is cool, cutting-edge stuff! If you want to read more, check out the terrific New York Times Magazine story by Lisa Belkin, from which the quote above is taken.