Wired Magazine
Issue 11.06 - June 2003
Six Degrees of Interconnection
RELATIONSHIP SPACE: Meet Your Network Neighbors
By Duncan Watts
When we talk about distance, we almost always mean the space between
objects or locations in the physical world. And for good reason: Most
of the time, that's the sort of distance that makes sense. But after a
century-long revolution in communications and transportation, physical
space can be limiting or even misleading. Sociologists have long
thought in terms of social space, the gap between individuals' wealth,
education, ethnicity, or religion. More recently, however, social
scientists and mathematicians have begun to examine another kind of
distance, one increasingly important to our understanding of the world:
network space.
A fascinating (and deceptively simple) example of network space is the
small-world phenomenon, the idea that anyone on the planet can be
connected to anyone else through just six degrees of separation.
Although the notion had been floating around in popular culture for
much of the 20th century, it was only tested in the late-'60s in an
experiment conducted by social psychologist Stanley Milgram. Milgram
gave letters to about 300 people in Boston and Omaha with instructions
that the envelopes ultimately reach a single "target," a Boston
stockbroker. The letters could be sent only to a personal friend of the
current holder, who then received the same instructions. To the
surprise of many, more than 60 of the letters reached their goal,
changing hands, on average, only six times. Milgram's conclusion was
that people who seem very distant in physical or social space may
actually be closer than we imagine.
To account for this, we need to start thinking of individuals as nodes
embedded in a complex web of social, economic, and institutional ties.
In network space, two nodes can be closely connected regardless of
their physical or social proximity. Physical and social influences
don't go away, of course - often we know people because they live near
us or share important characteristics such as education or profession -
but the relationship of these factors with network space has remained a
mystery for decades. Milgram, for example, was never able to explain
why his experiment worked. Network data is difficult to collect, and
analysis of complex networks is nearly impossible without powerful
computers.
In the past five years, we've begun to understand how network space
plays out both within and beyond the social world. The small-world
phenomenon, it turns out, also shows up among power grids, neural
networks, biochemical reactions, interlocking corporate boards of
directors, collaborative networks of scientists, and even movie stars.
Which is why Kevin Bacon appears to be the center of the cinematic
universe. (It's just happenstance - any Hollywood actor would work just
as well.)
In terms of our perception of the world, though, six degrees from
someone is still a long way. We care a great deal about our friends
(one degree), a bit about friends of friends we haven't met (two
degrees). But a friend of a friend of a friend? Someone three degrees
away is, for all practical purposes, a stranger, no more relevant to us
than someone off the street.
But what happens to them can matter a lot. The explosion of HIV into a
global pandemic, for example, was driven in part by the widely held
perception that it was confined to gay men and intravenous drug users.
If you didn't know anyone "like that," you didn't have anything to
worry about. But it turns out that what happens beyond our limited
network horizon can still hurt us. Or help us: We can't just call up a
friend of a friend of a friend and request a job, but we can ask that
person for help by making the right connections. In fact, we do this
all the time, tracking down people by email, over the phone, or at
cocktail parties by "networking."
Now that we're starting to understand network space, the implications
of it are vast. Whether we're considering contagious diseases, cultural
fads, or trends in the stock market, we need to start thinking in terms
of networks. Sometimes they help us, and sometimes they hurt us - being
connected can be good or bad. But either way, networks are always
there. And when not just you but anyone can be connected to anyone else
on earth in just six steps, what goes around comes around - faster than
you think.
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Duncan Watts, the author of Six Degrees: The Science of a Connected
Age, is associate professor of sociology at Columbia University and an
external faculty member of the Santa Fe Institute.
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