Response from John Daly

It occurs to me that there may be a deep parallel in your book's exposition that might be worth exploring.One might consider two spaces. One is our ordinary geographic space. The other is more complex. You have defined a network in which scientists are nodes and coauthored papers are links. One can define metrics on this network, describing the distance between scientists in terms of the numbers and strengths of the linkages between them in the network.There are centripetal forces in both spaces resulting in clustering of scientists. In geographic space scientists cluster in cities which are poles of scientific ferment. in the network space I think scientists cluster around hubs, which may perhaps be especially collaborative scientists or subnetworks of scientists collaborating on a specific subfield of science. I would think that as some geographic areas have many cities as clusters of scientific activities, so to there are larger areas in your network with many clusters of activity that are close to each other.In both cases there are complementary forces: scientists make independent choices as to where to work, based on their interests and on an assessment that the benefits of working in a cluster are worth the costs of doing so; people at the center of the cluster seek to attract others to work with them, again based on an assessment that the costs of attracting others are more than justified by the benefits the others will bring to the cluster.Maps, as we usually draw them, may not be very good at reflecting the difficulty of traveling from one place to another. We could alternatively seek a map based on travel times or on travel costs. So too, the European Union has decreased the difficulty of moving from one scientific center in Europe to another. So conceptualizing a space with both intellectual and geographic dimension to fully describe distance does not seem too odd.In both geography and "coauthorship" space, I think there are centrifugal as well as centripetal forces. In both cases there are scientific needs and opportunities to be explored outside of the major clusters.-- John Daly
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