The carbon mano tubes at the heart of this mystery have what's known as atomic smoothness. They have no defects, so there's nothing really for the water to rub against to generate friction. It turns out that there can still be friction, and this is what we call quantum friction. At such tiny scales, quantum interactions between atoms are relevant. In fact, using quantum theory, the team were able to mathematically explain the fast flow in narrow tubes that has been seen in previous experiments.