Turbulence remains one of the central open problems of classical physics, largely due to the absence of a clear ontology for a fluid in motion. Traditional formulations of fluid dynamics, based on local velocity fields defined point by point, are effective in describing established flow regimes, but do not causally explain the origin of motion, its spatial propagation, nor the physical mechanism responsible for the turbulent transition. In this work, a reformulation of liquid fluid dynamics is proposed in which the fundamental physical object is not the pointwise field, but a finite set of laminar, material flow lines of finite length. The fluid at rest is described as a set of particles without a privileged direction, whereas the fluid in motion is described as a bundle of flow lines that emerge in active regions of the flow, grow through the progressive capture of fluid initially at rest, and transport mass and momentum along their tangents. A dimensionless geometric-viscous parameter is introduced, dependent on the characteristic angular velocity of the flow, the effective length of the lines, and the intrinsic viscosity of the fluid, which acts as a physical criterion for the loss of laminar stability. It is shown that turbulence emerges when the geometric demand imposed on the bundle of lines exceeds the capacity of the fluid to accommodate them, providing a causal and non-statistical interpretation of the turbulent transition. The formulation presented does not replace the classical equations of hydrodynamics, but recovers them as emergent averaged descriptions, offering a new physical framework for the dynamics of liquid fluids in motion.
Kauê Basso (Thu,) studied this question.