The contrast between Einstein and Poincaré, and their different understandings of what they were doing represent two grand competing visions of modern science for the 20th century. Although the equations that Poincaré and Einstein come up with around relativity theory are very similar — essentially identical — Poincaré always thought of what he was doing as fixing, repairing, or continuing the past by applying reason to it by. As one of his relatives once put it, he was filling in the blank spots on the map of the world. Einstein was willing to do things rather differently, to say that the old way of proceeding is too complicated, too filled with piecemeal solutions, and that what we need is something that starts over again with the classical purity of a few stark principles. Poincaré saw himself in some ways as saving an empire—the empire of France, no doubt, but also the empire of nineteenth century physics. His was a grand ambition, but it’s a different kind of modernism from Einstein’s. It’s a reparative, ameliorative modernism, a modernism with all the rational hopefulness of a third Republic Frenchman. Einstein’s is a much more disruptive, classifying, purifying modernism. It is only by understanding this triple intersection of philosophy, physics, and technology that one can really grasp what each of these alternative visions of the new century is about.

You might ask, and I’ve often wondered, how to think about this kind of event in the present. That is to say, is there an analogy now to this kind of triple intersection? Here is how I think about it: When you consider Poincaré and Einstein you’re dealing with an attempt to understand time coordination and the synchronization of clocks at a huge variety of scales. In some ways they’re trying to figure out how to coordinate clocks inside a single room or observatory, or a block, or a whole city, at the same time that the people who are worried about these things are also sending cables across the Pacific and Atlantic Oceans. Einstein and Poincaré are not just worrying about such planetary scales, but also about how to coordinate clocks in different reference frames in the universe as a whole. They are asking, what does synchronization mean? What does simultaneity mean? These are questions that occur at every scale, from the smallest to the largest, from philosophy and physics all the way down to electrical wiring along train tracks. In that sense it is unlike most questions that we ask in science, since it doesn’t have the character of starting out as something purely abstract that then becomes applied physics and engineering, eventually ending up on the factory floor. It’s also not a platonic ascension, or a naive version of Marxism, in which machines and machine shop relations are slowly abstracted to ever wider spheres until they become a theory of the universe.

Questions of the conventionality of time, of how it becomes equated with physical processes and procedures are key to all of the domains considered. And the metaphor we need for this back-and-forth between the practical and the philosophical not just one of condensation from the abstract to the concrete. Nor is it one of evaporation, in which water grows less dense as it passes into a vapor. Instead, more helpful is that phenomenon physicists call critical opalescence. Ordinary opalescence is that oyster-shell color in which you see all colors reflected, that remarkable surface of a pearl or the inner surface of certain shells in which you can see red, green and white, all at once. Critical opalescence in matter occurs under very particular circumstances—for example in a system of water and vapor held under just the right combination of temperature. At this critical point something quite extraordinary happens. The liquid starts to evaporate and condense at every scale, from a couple of molecules to a whole system. Suddenly, because droplets form of every size—from couple of molecules coming together to the whole of the system—light of every wavelength reflects back. If you shine in blue you see blue, if you shine in red you see red, and if you shine in yellow you see yellow.

That’s the kind of metaphor that we need to look at a situation like this. Poincaré and Einstein are flipping back and forth between philosophical questions, physics questions, and practical questions. At the end of the 1890s Poincaré was publishing in journals for map makers and longitude finders at the same time he was publishing in physics journals and in the Journal of Metaphysics and Morals. In his thinking he was and flipping back and forth extraordinarily quickly between these three domains of philosophy, physics, and technology.

Now one can ask how this might compare to the present. What kind of critical opalescence marks the science of recent times? It seems to me fairly rare, but one place you might see it is in the collection of sciences that have grown up around computation. Here, ideas about the mind, about how computers function, and about science, codes, and mathematical physics all come together. Von Neumann thinks about the mind and its organs (memory, input-output, processing) as a way of designing a programmed computer. The programmed computer then becomes a model for the mind. The ideas of information, which are encoded into the development of computation, also become ways to understand language and communication more generally, and again feed back into devices. Information, entropy, and computation become metaphors for us at a much broader level. Such opalescent moments are not that common, surely rarer than whatever it is that we mean by scientific revolutions. They’re something else. No, points of critical opalescence in this sense point to science in times and places where we’re starting to think with and through machines at radically different scales—Where we are flipping back and forth between abstraction and concreteness so intensively that they illuminate each other in fundamentally novel ways, in ways not captured by models of simple evaporation or condensation. When we see such opalescence, we should dig into them, and deeply, for they are transformative moments of our cultures.

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