Six Degrees by Duncan Watts, W. W. Norton, $29.95, ISBN 0393041425
HAD an email from Duncan Watts recently? It may seem a silly question unless you know him personally, but there鈥檚 a good reason you might have. A chain of acquaintances may have linked you into a repeat of a 36-year-old experiment with a modern twist. This experiment has invigorated a new field, the science of networks.
In 1967 the psychologist Stanley Milgram sent a letter to 96 people picked randomly from the Nebraska phone book, asking them to forward the letter to an acquaintance whom they thought could help get the letter to a target person: a Boston stockbroker.
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Milgram wanted to find out how many such hops (from one acquaintance to another) each letter would have to make before reaching its destination. He wanted to answer the question: do we live in a 鈥渟mall world鈥�? Famously, Milgram concluded we do, with an average distance of six hops, or degrees, between any two people chosen at random. The conclusion turned into folklore when John Guare鈥檚 play 鈥淪ix Degrees of Separation鈥� appeared on stage in 1990, and was subsequently given the Hollywood treatment in 1993.
Watts discovered that no one had independently verified Milgram鈥檚 experiment. And he found Milgram鈥檚 method seriously wanting. He is now coordinating an experiment to repeat Milgram鈥檚 trial to test the original claim 鈥� using the Web and email instead of a telephone directory and the post. So far, Watts reports, participation in the experiment has been disappointing. Perhaps his book will help to provoke responses to his emails.
Watts was a member of the first team to put forward a coherent theory of small worlds 鈥� an alternative way of mathematically describing networks that are not wired up absolutely at random, meaning some nodes in the network are more highly connected than others.
Many other researchers have joined the race since then, some producing even more startling results than Watts has so far (see 快猫短视频, 13 April 2002, p 24). But this is not their story. Six Degrees is a chronicle of Watts鈥檚 personal involvement in the birth of network science, mixing personal anecdote with technical sections to dilute the hard science.
Networks turn up everywhere, from the proteins in a cell to airline flight paths, the Internet, and even our pattern of sexual partners. All share features which are only beginning to be understood scientifically.
But dearest to Watts鈥檚 heart are social networks. He recounts his attempts to understand mathematically how people interact in networks, whether commercial, cultural or sexual, and then explains what we can conclude about these interactions.
In times of crisis, and given the right sort of 鈥渦nderlying鈥� net of relationships between people, networks can be remarkably resilient to disaster. Conversely, a precise strike at a key node in a network could incapacitate the network completely. Third, depending on the underlying network, fashions and diseases can burst without warning into epidemics simply by virtue of the way individuals are connected to each other.
Watts is undoubtedly a gifted researcher and evidently a competent writer. But Six Degrees feels rushed, maybe because it tries to keep up with the slew of similar titles that are appearing. Watts鈥檚 technical descriptions are solid and clear, but the personal narrative feels forced and is generally superfluous. The book reflects the fact that the field is in its infancy and gives a good description of how some researchers go about their work. But it lacks the flare and enthusiasms that popular science books need to bring their subject 鈥� which in this case often seems like common sense 鈥� to the attention of a wider audience.
Despite its shortcomings, readers who persevere with Six Degrees will be rewarded with a good view of an important new subject.