Book review of
An Introduction to Econophysics: Correlations and Complexity in Finance by Rosario N.
Mantegna & H. Eugene Stanley, Cambridge University Press, $34.95, ISBN 0521620082
SINCE the last decade, physicists have been trying to cope with the issues traditionally approached by economics using their own tools and methodologies. This research has been dubbed 'econophysics'. One reason why this incursion should be welcomed is the failure of mainstream economics to recognise financial systems as complex systems. Take mainstream international finance, for instance. In the most respectable workhorse model--so-called 'new open economy macroeconomics model'--foreign exchange rates always reach some sort of stable equilibrium. To put it bluntly, this means that currencies do not exhibit complex behaviour.
However, financial markets do demonstrate several of the properties that characterise complex systems. What is more, they are highly complex, open systems in which many subunits interact nonlinearly in the presence of feedback and stable governing rules. Earlier attempts to find chaos in financial data, for instance, have been disappointing exactly because the phenomenon is likely to emerge in systems which are only moderately complex. Although it cannot be ruled out that financial markets follow chaotic dynamics, econophysics assumes that asset price dynamics are stochastic processes.
A fundamental commitment of the mainline model of international finance is to theory itself, and not to data. Modelling is devoted to equipping the discipline with an underlying rational behaviour at the individual level. Yet this is at odds with the fact that financial markets are prone to collective 'irrational exuberance'. Instead, econophysics attempts to build up stochastic models that encompass essential features observed in the financial data. Now that the time evolution of many financial markets is continually monitored, it is possible to test the accuracy and predictive power of the developed models using available data. One common objection to such a practice is that it is impossible to perform large-scale experiments in economics that could falsify any given theory. The authors note that this limitation is not specific to economics, but also affects such well developed areas of physics as astrophysics, atmospheric physics, and geophysics. By analogy with the activity in these more established areas, we are able to test and falsify any theories associated with the current available sets of financial data.
Complex systems can sometimes behave in remarkably simple ways. These are reflected in power law distributions and scaling. The authors illustrate these concepts and others, and apply them to the financial time series. The book is thus useful not only for physicists but also for economists and people in the financial world. Some familiarity with probability theory or statistical physics is required, though. Economists dissatisfied with the mainline approach of their discipline will find the book opportune. The others might end up welcoming econophysics as well. After all, economists implicitly see physics as nature's economics. What is then wrong with physicists thinking of economics as social physics?
