In chapter V of Difference and Repetition, “The Asymmetrical Synthesis of the Sensible,” Deleuze engages with the various scientific theories of 19th and 20th century thermodynamics, not by identifying his fictions with scientific facts, but by detonating the philosophical idea of “intensive depth” in range of the qualitative extensity studied in terms of the scientific concept of entropy. The scientific concept of entropy, when subject to the dogmatic image of thought, comes to be described as the universe’s smooth and continuous causal transition from an improbably heterogeneous past state into more probable homogeneous future state. Deleuze, it seems to me, wants to save the metaphysical implications of the concept of entropy from the physical reductionism of a still all too Cartesian science.

Some commentators, like Badiou and Joe Hughes (A Reader’s Guide, 2009), insist that Deleuze’s engagement with natural scientific concepts is purely metaphorical and not at all physical. Hughes writes (153):

“We therefore have to be careful about concentrating too much on the scientific notion of intensity. Deleuze is concerned with founding representation, not thermodynamics. He says of Nietzsche at one point in the chapter that ‘[i]t is true that Nietzsche was interested in the energetics of his time, but this was not the scientific nostalgia of the philosopher’ (D&R, 243). The same can be said of Deleuze. In the same way that Deleuze’s theory of Ideas was not fundamentally related to mathematics, his theory of intensity is not tied to thermodynamics (and his theory of individuation is not tied to biology). Deleuze is neither a scientist nor a philosopher of science. Science never leaves the realm of fact, but Deleuze is interested in the constitution of facticity itself. What is at issue in these discussions then is not the nature of intensity as it appears in science, or even of founding the scientific notion, but of drawing inspiration from science in order to develop a philosophical concept. ‘Intensive quantity is a transcendental principle, not a scientific concept’” (D&R, 240-241).

I must disagree with Hughes’ reading here. It is at best a partial reading. Partial because, when Hughes quotes Deleuze as saying that intensive quantity is transcendental and not physical, he shortens Deleuze’s sentence, which actually begins: “Energy or intensive quantity is a transcendental principle…” Deleuze is not just drawing inspiration from science, he is ungrounding representational interpretations of natural science to show that general concepts like “energy” in thermodynamics, “differential” in calculus, “gene” in biology, or “phoneme” in linguistics (D&R, 278) are really virtual intensive quantities which only become recognizable to scientific consciousness after they’ve been covered over by qualities and explicated in extensity. Far from turning to the natural sciences merely to extract their metaphorics, Deleuze critiques the naïve physicalism of these sciences in order to install the genetic power of the transcendental at the heart of nature itself.

Deleuze is trying to provide the natural science of his day with a metaphysics; but like Schelling (see Preface to Ideas for a Philosophy of Nature), he meant his metaphysics to come after physics, and not before it. By engaging with the natural sciences, Deleuze doesn’t mean to undermine them by applying transcendental limits to subjective knowledge; his transcendental empiricism aims to unsettle the clear and distinct categories of scientific representation by pointing to the ceaseless rumbling of a volcanic nature whose groundless ground (Abgrund) constantly disturbs the smooth surface features that allow for lawful generalization. The inner nature of the scientist, with all the truth and good sense of his inductive method, projects an external nature that circles and so repeats lawfully without undue difference. Deleuze’s philosophy of difference is a direct assault upon such a Cartesian science, on the way it covers over the implication of ideal intensities without affirming the virtual processes that remain behind or beneath these coverings, processes which Deleuze argues provide the conditions for the actuality of the qualitative extensities measured by the scientist. Deleuze’s differential concept of nature is spiralic: nature is groundlessly creative; it is eternally recurring but only by repeatedly disguising its own intensive depth; it is always spinning out of the general categories or circles of control posited by the spectating scientific Cogito. There is a ceaseless rumbling in nature that forms cracks in every smooth ground or sufficient reason that might pretend to hold back the transcendental volcano of virtual intensities, a rumbling forever forcing thought to think.