GENESIS OF THE PROJECT

Determining the interaction strength between molecules, atoms or nucleons was a major task for physicists during the 20th century. They used various experimental techniques and introduced different concepts to define such interactions, such as the binding or dissociation energies, bond length and so on. The section entitled ``Measurement of interactions in physics'' (in the menu entitled ``Interaction measurements: known methods'') provides a summary of experimental techniques used in physics.

In the early 2000s econophysicists began to study many different systems from the perspective of network science. It soon became apparent that in order to provide a realistic description these networks had to be WEIGHTED networks. Indeed, except for systems in which the interaction is of a binary type (0: no link; 1: existence of a link) as for instance between an author and the references that he gives in a paper, the vast majority of interactions differ in strength. In an unweighted network representation, the earth would experience the same attraction from the stars of the Andromeda galaxy as from the Sun and similarly a vegetable retailer in Beijing would be as connected as closely to farmers in California as to those in the vicinity of Beijing.

In other words, realistic network representations of natural as well as social systems require a knowledge of the STRENGTH of INTERACTIONS. There are many different sorts of physical interactions depending on the size of the elements (galaxies, stars, planets, molecules, atoms, nucleons, quarks,...) or on their nature (charged or neutral particles, particles with or without electric or magnetic moment and so on). For social systems there are also many sorts of interactions: economic interactions between countries, relations between employers and employees, between producers and consumers, social interactions within families, political parties or churches, and so on and so forth. For us, because we belong ourselves to many social organizations, it is of course much easier to enumerate and describe social interactions than it is to say something about physical systems.

But this familiarity with social systems is also a big obstacle to a scientific understanding for (at least) two reasons. (i) The awareness of so many forms of social interactions may suggest that the situation is hopelessly complicated and that the kind of approach used in physics can be of no value here. (ii) Because we have a detailed knowledge of social interactions we may be reluctant to attribute them simple attributes such as a numbers representing their strength. Such reasons should not discourage us however. As an answer to the first objection, observe that for any social behavior there will be usually a small number of interactions which are really relevant. For instance the attraction between men and women (including certain institutional obstacles to this attraction) will certainly play a leading role in many phenomena which are studied in the field of demography. As to the second objection, we should keep in mind that the interaction strengths measured in physics are always averages over time and over a large number of particles. At the level of individual particles and for times of the order of picoseconds (10^(-12) second) there would also be much variability.

The study of interactions is more advanced in some fields than in others. We already mentioned physics and chemistry, but one should also mention ecology, a discipline which has developed reliable methods for measuring interactions. It is of course natural to take inspiration from these methods and to try to adapt some of them for analyzing social interactions. The ambition of the present webpage is to be a meeting center where researchers can find information about attempts which are done in fields adjacent to their own, where they can report their own measurements and compare them to other measurements of the same effect performed by others.

Trying to draw parallels between different fields is the hallmark of systems science. For some reason research in systems science seems to be more active in China than in Western countries. The status enjoyed by systems science in China is attested by the existence of an Institute of Systems Science at the National Academy of Science. In Western countries (and also to some extent in China) a major obstacle to the development of systems science is of course the current trend toward ever greater specialization. That interest in systems science lead in 1994 [?] to the creation of the Department of Systems Science at Beijing Normal University. During the past 15 years this department has conducted a wide range of inter-disciplinary investigations ranging from linguistics, to finance, macroeconomics neuroscience or ecology.

The present website devoted to social interactions was created at Beijing Normal University in October 2008 after it was realized that the issue of measuring interaction strength turns up in many of these fields and in fairly similar terms. A related webpage (it is not exactly a mirror site because the contents of the two sites are not identical) was constructed on this server of the Institute for Theoretical and High Energy Physics (LPTHE).