Nexus [Paperback]

The level of mathematical sophistication needed to comprehend the matterial is minimal. I do not believe there are any equations in the entire book. There are many easily understood graphs and a few percentages.

The basic concept of the networks is very easy to explain and to understand. The applications are the interesting part. Thoughout the pages are clear and interesting examples that make you want to turn the page to see what is coming next. In my case I often found myself thinking how I would have approached the problem and more importantly what problems could this have been applied to. Any book that can do that is a good one in my book!

Like many good books, this one leaves more questions unanswered than it answers. The subject area is a generic one that allows it's self to be applied in many many different fields. The question becomes not is this model of the world valid but rather how can it be applied.

This was a quick read, certain to change my views on how the world works.

The phrase "six degrees of separation" comes from the fact that two randomly chosen people, A and B, will on average be connected by six social links. A knows C who knows D who knows E who knows F who knows G who finally knows B. Considering the world has over 6 billion people, an average separation of 6 seems unbelievable small, but the explanation of this incredible phenomenon lies in the makeup of our social network. Our close friends know each other but our cluster of friends has weak ties to other clusters through acquaintances, people we really don't know that well - that's why when one is looking for a job, it's better to tell an acquaintance rather than a friend so that our inquiry can jump to other clusters. Our social network is essentially highly clustered but enough links exist between these clusters to allow us to jump from ourselves to any other person through just an average of six links. Buchanan shows us how this kind of network exists everywhere as mentioned above although he distinguishes between egalitarian networks where clusters are roughly the same size and aristocratic networks such as the WWW where gigantic hubs like Amazon.com exist that link to millions of websites.

One of the most interesting chapters in the book deals with sexual networks. It turns out that in the network of sex partners, certain people have a great many more links than the average person in the network. Buchanan explains how the structure of the sexual network actually accounts for the rapid spread of HIV. The virus spread quickly because the hubs in the network spread it to their numerous partners. In fact, it turns out that a significant percentage of the inital HIV cases had a sexual relationship with one particular flight attendant.

As I wrote in my review for Strogatz's Sync, we are entering an era of science where disparate fields of study are being linked because many phenomena that we used to regard as unrelated now appear to have very similar underlying bases. It is exciting to read books like Nexus because it illustrates this point. You should definitely read this book if your are interested in the science of networks and want to know how so many different phenomena are being explained by the same underlying principles.