Why physics still matters
Part 2 of 5: The science of phenomena
When we observe the world around us, we perceive a bewildering variety of particular things, enmeshed in a constantly changing web of relationships. Any science, as a systematic body of knowledge, has to focus on some part of this world, through the lens of an abstract organizing principle. Aristotle refers to the set of things considered by the science as the “material” object of the science, and the organizing principle as the “formal” object. For example, a human being can be studied as a type of mammal by biology, as a conscious being by psychology, or as a creator of culture by anthropology. All these sciences have overlapping material objects, but different formal objects, examining different aspects of the same concrete reality.
This kind of abstraction is necessary for scientific knowledge; otherwise we would be left with a collection of individual things and nothing to say about them. But the resulting proliferation of sciences seems to preclude the possibility of any one science making precise predictions about real-world situations. Consider an archer shooting an arrow, and trying to determine whether it will hit the target. His arrows can be studied from many angles: plant biology (to understand the wooden shaft), ornithology (to understand the feathers), geometry (to understand the shape of the arrow)… but none of these can tell him where the arrow will land. Since achieving any practical end demands this kind of concrete prediction, pre-modern societies tend to see the sciences as clearly distinct from the practical arts. The sciences are organized bodies of certain knowledge, based on knowing the real causes of things, where the arts are based on real-world experience of what usually happens in the messy scenarios of ordinary life.
The one exception to this rule was astronomy.1 This science studies the stars, but it abstracts entirely from the intrinsic nature of stars, and instead sees them only as things with a position in the sky, a position that can be represented with a geometrical figure or a set of numbers. By examining these quantities and how they change over time, the ancient astronomers formulated sets of geometric principles that made it possible to predict the precise time when any astronomical event would occur — from an eclipse of the sun to a conjunction of Saturn and Jupiter. The remarkable success of this science in representing real, concrete events, generated the hope that it could be extended to other phenomena as well. For the ancients and early medievals, this extension mainly took the form of correlating important earthly events such as plagues and famines with configurations of the heavenly bodies. If such correlations could be established, then the power of predicting the position of the planets would automatically provide forecasts for these phenomena as well.
Although we now know that this attempt was doomed to failure, it contains an important insight, which had to wait many centuries to be fully developed. These ancient thinkers saw clearly that the only possible science of phenomena, of the concrete things that actually happen in the world, is a science that is formally quantitative. Knowing the nature of a thing, such as a planet or a piece of wood, does give insight into the sorts of behaviors it can exhibit, and what it will do in different contexts. But the precision required for predicting astronomical events, or for carrying out any of the mechanical arts, can never be provided by this general understanding of a thing’s powers and tendencies. The only science adequate to this purpose is a science of physical things as objects of measurement.
Since every physical thing is potentially an object of measurement, this kind of science has a universal scope, uniting the entire material cosmos in a single field of study. But this universality is purchased at the price of specificity, with formally quantitative sciences being the least informative about the intrinsic nature of their object. Comets, moons, planets, stars and (now) artificial satellites can all be studied on an equal footing, as objects with a position in the sky, and even the most exhaustive study of their trajectories would never yield any knowledge about the fact that some of these are gas, some are rock and some are ice, or that some shine by their own light and others from reflected light. This limitation is not a defect in the science, but is rather a direct consequence of its aim, since the material composition of celestial bodies is irrelevant to determining their relative positions as a function of time.
An adequate evaluation of physics thus demands a balanced appreciation for both the power and the limitations inherent in any formally quantitative science. On the one hand, many of the critiques of physics by philosophers, sociologists and anthropologists are completely valid. Since the act of measurement is a characteristically human activity, and only exists in human societies, a science that studies things only as objects of measurement has an unavoidably anthropocentric character. On the other hand, physicists are right to insist that their discipline is fundamental, providing the only conceivable access to predictive knowledge of concrete phenomena.
Thomas Aquinas explains this exception in a passage from his commentary on the De Trinitate of Boethius (pars 3 q. 5 a. 3 ad 5-7), where he has just presented the traditional threefold classification of the sciences (physics, mathematics, metaphysics), and is responding to the objection that astronomy doesn’t seem to fit the scheme.