Any two documents or sites on the Web are separated by only a small number of mouse clicks. The two teams also noted that the Web was structured according to a power law, with a handful of highly connected hubs and a steadily increasing number of less connected nodes a fact noticed by other groups as well. Reaching further, Dr. Barabasi and Ms. Albert found, in a paper last fall in Science, that a variety of networks may be organized this way. Included in their list were the small worlds of Dr. Watts and Dr. Strogatz as well as the connections on a computer chip and a network of citations in scientific publications. The question is how this kind of order arises.
New actors are more likely to be cast in films with well-known actors.
New scientific papers are more likely to cite well-established ones. The result, according to their model, is a power-law distribution. Their most recent sighting of the pattern was described in the Oct. 5 issue of Nature. Dr. Barabasi and his team worked with two members of the Northwestern University Medical School department of pathology to study the shape of metabolisms, the networks of chemical reactions inside living cells. Small molecules are linked to form large molecules, which are in turn broken back down into small molecules.