Emergent lengthscales in confined 3D Active Incipient Nematics*

An incipient nematic is a system whose density is smaller than the critical density for isotropic-nematic transition. The stationary isotropic state, which is the stable equilibrium of a passive incipient nematic, can be destabilized by the effects of extensile activity combined with flow alignment. We study the properties of flows that arise from this instability in confined 3D systems. Calculations from hydrodynamic theory, and experimental measurements on a microtubule-based system show long-range velocity correlations, in the absence of such correlations in nematic order. Further, we show that there exists a confinement-independent lengthscale intrinsic to flows in an active incipient nematic that determines its bulk behavior.