Designing a tube that completely resists fluid flow is challenging, with current technologies like the ferrofluidic seal and Tesla valve offering partial solutions. The Tesla valve, while having no moving parts, allows for some backflow despite its high resistance to forward flow. The discussion raises questions about the definition of a tube and the necessary inlet pressure to achieve resistance. Surface tension and viscosity are suggested as potential approaches to enhance fluid resistance. Ultimately, achieving complete fluid flow resistance remains an open question in fluid dynamics.
