Reductionism, Emergence and Levels of Reality

The attempt to explain the sensible world in terms of a few unifying principles has been a constant of scientific thought. In the fifth century B.C. Democritus boldly hypothesized that reality, which appears so varied and changeable, is nothing but a collection of indivisible and eternal parts or atoms. Over the centuries, despite the ups and downs, the doctrine of Democritus, has been a landmark of science, and in physics there has been a great deal of progress thanks to the clear distinction that has been made between subjective perception and objective reality. The founder of atomism formulated in a very clear fashion the problem that will be discussed in this book: the issue of theory reduction in physics. The idea, in its simplest form, is that the whole is nothing more than the sum of the parts; that is, the behavior of things is directly determined by the properties of their elementary constituents. The properties observed at the level of the whole are related to the properties at a lower level of observation, which hence seem to be more fundamental. Reductionism is the activity concerned with the relation between different theories that attempt to describe different levels of reality or different levels of observation and through a qualitative leap consisting of simplifications and extrapolations, ultimately to relate the different sciences: psychology, physiology, biology, chemistry and physics. The reality certainly shows a complicated (or complex?) structure of relations, and the dream of a unified interpretation of all phenomena in terms of several simple laws, from which all can be deduced, has attracted and continues to attract almost anyone who has genuine philosophical and scientific interests. If the most radical reductionist point of view was correct, the relationship between the different scientific disciplines would be of strictly inclusive type: chemistry contained in physics, biology in chemistry and so on. Eventually, only one science, indeed just a single theory, would survive, since all the others would eventually be embedded in the Theory of Everything. Is the current coexistence of different sciences a mere historical parenthesis which will end when the Theory of Everything has been worked out? At the same time, it seems that at every moment in history, some have doubted the possibility of a unified description of nature, and not only among scientists of little formalized disciplines, i.e. with a mathematical apparatus less advanced than that of physics, such as biology.§The analysis of full reductionism is beyond the scope of any essay of limited size. Therefore the first purpose of this book is to analyze some aspects of theory reduction in physics and to stimulate some reflection on questions that spontaneously arise in this field: Is there any evidence of actual reduction of theories? Are the examples that are found in books on the philosophy of science too simplistic or not completely correct? If the microscopic level is essential to determine the macroscopic one, why have we understood hydrodynamics quite well for centuries? What has been endangered by the search for (the) ultimate truth? Has the dream of reductionist reason created any monsters? Is big science one such monster? What is the point of embedding science Y within science X, if predictions concerning science Y cannot be made starting from science X?§