Physicists constantly struggle to explain the void that exists between the phenomena that we see. First, there was gravity, and the impact of gravity’s discovery on philosophy was huge. (It is no coincidence that Newton’s discoveries are parallel with Kant’s.)
Most recently, we saw the discovery of the Higgs boson, helping to explain why particles have mass. I won’t pretend to be familiar with the particulars, but it was clear even to the layman that the Standard Model of physics did not account for everything. Until that moment, we seemed to exist within a void, but that void could not be absolute, otherwise it would surely collapse in on itself. And so we developed theories like dark matter and the like, to potentially explain why nothingness nonetheless has a mass.
Perhaps it is useful to think of Deleuze and Guattari’s plane of immanence in a similar way. It is not enough to say “I think therefore I am”, because we are yet to fully understand how thought is manifest and how our vast array of (often conflicting) conceptions of the world around us are able to coexist without reality collapsing in on itself. The plane of immanence becomes a kind of apperceptive field; perhaps similar to what Kant called “transcendental apperception”: our present understanding of “the pure, original, unchangeable consciousness that is the necessary condition of experience and the ultimate foundation of the unity of experience.”
However, even this scientific analogy is a limit on thought. In many ways, it is putting the cart before the horse, as we are all too prone to do. How can we think of thought in a way that isn’t limited by what we presently know?