Physics is not events, but observations; relativity is the understanding of the world, not as events, but as relations.
Indeed, for me the most important idea behind the developments of twentieth-century physics and cosmology is that things don’t have intrinsic properties at the fundamental level; all properties are about relations between things. This is the basic idea behind Einstein’s general theory of relativity, but it has a longer history; it goes back to at least to the seventeenth-century philosopher Leibniz, who opposed Newton’s ideas of space and time because Newton took space and time to exist absolutely, while Leibniz wanted to understand them as arising only as aspects of the relations among things. For me, this fight between those who want the world to be made out of absolute entities and those who want it to be made only out of relations is a key theme in the story of the development of modern physics. Moreover, I’m partial. I think Leibniz and the relationalists were right, and that what’s happening now in science can be understood as their triumph.
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Relational Modelling and the Systematics of Categorisation
Bronowski noted that physics is not a study of events, but of observations; that relativity is not a theory of things, but of relations. Smolin (1996: 289–90) develops this insight further, arguing that at the most fundamental level, things do not have intrinsic properties — all properties are relational. This principle, central to general relativity, finds antecedents in Leibniz’s opposition to Newton’s absolutist conception of space and time. Where Newton imagined space and time as entities in themselves, Leibniz understood them as emerging from the relations among things. Smolin identifies this as a defining tension in the history of physics: the contest between absolutists and relationalists — a contest in which he judges the relationalists to be, ultimately, victorious.
To model is to systematise categorisations — and the value (valeur) of any categorisation is given by its relations to other categorisations. Categorisations are defined differentially: no category is meaningful in isolation. Each derives its function from a network of contrasts, just as the function of a neuronal group depends on its interaction with other neuronal groups, and the function of a gene depends on its participation in a larger system of genetic expression.
The act of categorising — of analysing — isolates units, but such units are only identified in relation to what they are not. Information is difference — and only becomes information in relation to other difference.