Three days of separation

The idea that we are only six introductions away from any other person on this planet is both beautiful and compelling. It has inspired research, provided inspiration to a film starring Will Smith and even launched a charity. According to Microsoft researchers it might also be true. They found that the  that the average path length connecting 180 million Messenger users in 2008 was 6.6. That was before Facebook and Twitter took off. By now the path length has probably shrunk further.

Distance of Zurich residents to their friends.
from: Axhausen, K.W. and A. Frei (2008)

And it isn't just the internet that is shrinking the world. On Friday at the Future Institute, Kay Axhausen, showed that road travel times have halved over the last 50 years, that we dedicate up to 40% of our leisure time to visiting friends and meeting new people, and that these friends are spread over the entire world. In one study, Kay and his colleagues looked at the distance from Zurich residents and their friends. It isn't unusual anymore to have friends spread over 5 orders of magnitude.  Kay argues that this effect isn't limited to Europeans and North Americans, citing recent data from Concepcion, Chile where people have similar friend-distance distributions as Europe. There are apparently a few die-hards who refuse to join the global-village, but they are becoming increasingly rare (as well as isolated).

But the thing that struck me most was the time scale of the links. A recent paper in PNAS looked at bus trips in Singapore. Kay and colleagues drew a line between people if they travelled on the same bus on the same day. In the figure above the red lines show a shared bus trip on Monday, the greens are trips together on Tuesday and a cyan are trips on Wednesday. The last picture are all the weekday trips put together. By Friday, all the people are now connected through shared trips.

It turned out that even by Wednesday all Singapore bus travelers were connected. There are just three days of separation between bus travelers.

A bus trip isn't enough time to make friends. But it is enough time to check out what other people are wearing, what mobile they are using, what newspaper they are reading and even to overhear a few opions about the world. It is enough time for all sorts of interesting social information to spread. This result would have appealed to Stanley Milgram, whose small-world study first led to the 6-degrees idea. Cities fundamentally change the individual's social world in many different ways, not least in the time it takes for us to connect to each other.