The stepping stones of life – Degrees of separation

Materials World magazine
1 Apr 2007

During the past decade and a half I have written about 160 columns for Materials World and its predecessors, and I am beginning to wonder how much longer I can continue making these contributions, and indeed be asked to do so. It all started in December 1991 with an article, in what was then Metals and Materials, entitled ‘Materialism and material science', a thinly disguised appeal for support of the Institute's Benevolent Trust, in which I explored the role of friendship within a learned society such as ours. More than 15 years on, I would like to comment further on the significance of one's circle of friends and acquaintances.

Each of us has experienced meeting a complete stranger only to discover that we have a mutual acquaintance, and this should not be too surprising considering that each member of our own circle of associates has his or her own circle and so on ad infinitum. Such occurrences can, however, be startling. In 1959 when my family moved north to Sheffield, we discovered that our next-door neighbour was the son of the midwife who delivered me in Wales 26 years earlier (when his mother visited and I was introduced, she rather embarrassingly exclaimed, ‘I saw you before your mother!').

I have greatly increased my number of friends within the Institute as a result of receiving letters commenting on views expressed in my columns, and occasionally these new companions have known or have met by chance my old comrades, representing more coincidences.

Stanley Milgram's experiment into degrees of separation

Intersecting circles of friends can become short circuits for the spread of information and opinion, which can feed back to the original individual. The contacts a powerful individual makes can have a global impact - were it not for President W Bush's ‘neocon' allies it is unlikely that the US would have invaded Iraq, for example. All of this prompts the question - What is the average number of interconnected friendship circles which separates each of us from, say, President Bush or Prime Minister Blair, or indeed between us and any other specified individual?

To try to answer this, a Harvard psychologist, Stanley Milgram, devised the following experiment - he sent packages to 196 randomly selected individuals in Omaha, Nebraska, with a request that they forward them to a stockbroker who lived near Boston. They were given no address, but were asked to send the parcel to friends who they thought would be better placed than they were to channel it towards the final destination, their contact/friend being asked to repeat the sequence.

A colleague of Milgram's thought it would take at least 100 steps for a package to reach its target - in fact, the average was between five and seven steps. In 2003, Duncan Watts of Columbia University in the USA repeated Milgram's experiment on a global scale using e-mail instead of the postal system. He recruited 61,168 participants in 166 countries and each was assigned one of 18 destinations in 13 different countries. Again it was discovered that a typical chain length was between five and seven steps.

What all this implies is that through the good offices of our friends, and their acquaintances and so on, only about six individuals provide a link with anyone else on earth - an astonishing fact. Scaling down to our institution, surely even fewer links would be required. It would be interesting, and possibly useful, to discover this number. To find out more, read Philip Ball's Critical Mass, Arrow Books, 2004.


Further information:

Stanley Milgram's experiment