Knots feel like a solid-world problem. You tie shoelaces, ropes, wires, and maybe headphones in your pocket. Liquids are supposed to flow, stretch, and smooth things out. For more than a century, that assumption kept scientists puzzled.
How could knots ever form inside fluids, let alone survive?
That mystery goes all the way back to the 1860s. Back then, physicists wondered if swirling fluids could naturally twist into stable knots. The idea sounded bold and strange. It also refused to go away. Now, thanks to two major breakthroughs, scientists finally have clear answers.
The Role of Gravity
FrontStory / One of the biggest surprises comes from studying a single falling filament in a thick liquid.
Researchers used high-powered simulations to watch what happens when a thin, flexible filament sinks through a viscous fluid under intense gravity. Think of conditions inside an ultracentrifuge. As the filament falls, it drags the surrounding liquid with it.
That moving fluid pushes back, bending the filament in uneven ways. Over time, the shape stops being simple.
The filament forms a dense front section and a stretched-out tail. This head and tail shape matters. The tail loops around the head. Those loops slide, cross, and tighten. Eventually, they lock into a real knot. No contact with other objects is needed. The fluid itself creates the forces that make knotting possible.
What decides whether a knot forms, and how long it lasts, comes down to flexibility and force. More flexible filaments knot more easily and produce more complex shapes. Stronger gravity increases both the odds and the lifetime of the knot.
Knots Made of Flow, Not Matter
While one group watched filaments knot themselves, another team took a completely different route. Instead of solid-like strands, they focused on knots made entirely of moving fluid.
They worked with liquid crystals, the same materials used in screens. These fluids are special because their molecules line up in organized patterns. That structure allows flow patterns to hold their shape much longer than ordinary water vortices.
Using carefully shaped laser light, the researchers created tiny three-dimensional knots inside the liquid crystal. These were not bits of matter tied together. They were patterns of motion, stable loops of swirling flow. The team gave them a name that fits their hybrid nature, heliknotons.
However, what makes this breakthrough stand out is control. By sending quick electrical pulses through the liquid crystal, the researchers could change the knots on demand. They could stretch them, shrink them, split one knot into two, or fuse separate knots together. All of it happened in fractions of a second, and all of it was reversible.
Why These Knots Matter Beyond Physics?
Amherst College / Even more impressive, the knots followed strict mathematical rules. When they merged or split, they behaved exactly as knot theory predicts.
At first glance, knotty fluids might sound like a niche curiosity. They are not. Both discoveries reach far beyond the lab.
The filament study sheds new light on biology. DNA and proteins often form knots, and those knots affect how they function. They influence how genetic material packs inside viruses and how proteins move through tiny channels in cells. Understanding how flow and force can create knots helps explain behaviors that once seemed random.
It also opens doors in materials science. Engineers could design soft materials whose strength and behavior depend on how they are knotted, not just what they are made of. That idea could lead to materials that respond differently under stress, heat, or motion.
