Linked: The News Science of Networks (Review)

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© 2002, Coert Visser

Networks
Nowadays, everybody talks about networks. Yet, what networks really are and how they function, often remains rather vague in conversations. Linked: The New Science of Networks, a new book by Albert-Laszlo Barabási, offers great insight into the evolution, the structure and the relevance of networks. The author, Albert Barabási, himself a creative and important contributor to network science, makes the rapid and fascinating advances made in this field comprehensible.

The structure of complex networks
Our world is filled with complex networks, webs of highly connected nodes. Not all nodes are equal, however. In fact, in many real-world complex networks, there is a typical hierarchy of nodes (called a POWERLAW DISTRIBUTION). This means there are a few extremely well connected nodes (these are called HUBS), there are quite a few moderately connected nodes and there are large numbers of tiny nodes (having very few connections to other nodes). The Internet, for instance, has only several hubs - like amazon.com and Yahoo - and countless tiny nodes -like my own website :-(.

Growth and preferential attachment
The structure of networks with a powerlaw distribution is called a SCALEFREE TOPOLOGY. Such a scale free topology is found in networks that 1) are GROWING (extra nodes and links emerge), and 2) are characterised by PREFERENTIAL ATTACHMENT (this means that some links are far more likely to get linked than others). Preferential attachment, is driven by two factors: 1) the number of links the node already has (this is in fact the first mover advantage: a node that has been there since the early development of the network gets the biggest chance to get connected), and 2) the node's fitness (for instance a new website offering a truely unique service has an excellent chance to get many links).

Robustness and vulnerability
A fascinating characteristic of scale scale free networks is the following. The density of the interconnectivity paradoxically creates two properties at the same time: 1) ROBUSTNESS (removing nodes will not easily lead to the breakdown of the network, precisely because of the fact that all nodes are connected. Only simultaneous removal of the largest hubs will break down the network), and 2) VULNERABILITY TO ATTACK (because of the fact that all nodes are indirectely connected to each other failures, like viruses, can very easily spread through the whole network. This fenomenon is called 'cascading failures'.

Implications for science and practice
Reading this book made me realise that the recently acquired knowledge about networks is revolutionizing many fields of science, like biology, medical science and economics. Also, the practical applications will be numerous, like protecting the internet, fighting terrorist networks, finding a cure for cancer (!), and developing new organizational forms.

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