Mike's Notes
Fascinating. 😎
What a cool experiment to do. From Quanta Magazine.
Resources
- https://www.quantamagazine.org/sea-monkeys-show-scientists-how-to-rewrite-a-rule-of-turbulence-20261002/
- https://www.engineering.pitt.edu/people/faculty/lei-fang/
- https://www.researchgate.net/profile/Francesca-De-Serio
- https://academic.oup.com/pnasnexus/article/3/2/pgae056/7603763
- https://doi.org/10.1093/pnasnexus/pgae056
- https://www.science.org/doi/10.1126/sciadv.adv0956
- https://journals.aps.org/prfluids/abstract/10.1103/mkwg-hmgn
References
- Biologically generated turbulent energy flux in shear flow depends on tensor geometry by Xinyu Si, Lei Fang. PNAS Nexus, Volume 3, Issue 2, February 2024.
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Last Updated
30/10/2026
Sea Monkeys Show Scientists How To Rewrite a Rule of Turbulence
Stephen Ornes: Contributing writer
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Scientists assumed that energy flows in only one direction in a turbulent system. What they didn’t know, until they looked closely at brine shrimp, was that a simple factor can reverse the flow.
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In Lei Fang’s lab at the University of Pittsburgh, a brine shrimp swims through a two-dimensional turbulent system.
Xinyu Si/University of Pittsburgh
Introduction
In the 1960s and ’70s, colorful comic book advertisements from the Transcience Corporation in New York City promised to mail anyone who sent cash, check, or money order a “bowlfull of happiness” — in reality, a small paper envelope of freeze-dried eggs. Dropped into salt water, the eggs would produce brine shrimp, also known as sea monkeys.
Brine shrimp are about a centimeter long and swim upside down, beating their legs madly and trailing their elongated abdomens behind them like tails. As scientists recently learned, these tiny swimmers can do more than just move themselves.
Researchers have long thought that in a turbulent system like a current of water, energy flows in only one direction, from larger scales to smaller ones, or vice versa, depending on the system’s dimensions. But in observing the humble brine shrimp, scientists at the University of Pittsburgh realized that — with just a tiny adjustment — the flow of energy could be reversed.
The scientists discovered that they could direct the cascade of energy in a two-dimensional system by disrupting the system’s flow with a small obstacle, as long as it was angled just right. “The geometry matters,” said Lei Fang, the Pittsburgh engineer who led the new study.
The discovery capitalized on a fundamental, if often unrecognized, mathematical description of how forces interact to push energy through a system, said Gregory Falkovich, a physicist at the Weizmann Institute of Science and a pioneer in the study of turbulent two-dimensional systems. “This is a beautiful and skillful experimental work.”
These findings could extend to larger, more chaotic systems, including those in three dimensions. The work has implications for our understanding of fluid dynamics and may have applications in areas such as pollution control and drug design.
A translucent white invertebrate with red eyes and a long tail.
Brine shrimp are tiny invertebrates that inhabit waters with high salt concentration. They grow to about 10 millimeters long, the width of a pencil eraser.
Nature Picture Library/Alamy
A Cascade of Chaos
Turbulence is hard to miss. It stirs the raucous foam at the base of a waterfall and shapes the crest of a breaking wave. It’s behind the bumpiness of a flight, the swirls of milk in a cup of coffee, and the roil of plasma on the surface of the sun. “We observe turbulence generally everywhere in our lives, when we go to the beach or wash our hands,” said Francesca De Serio, a civil engineer and expert on hydrodynamics at the Polytechnic University of Bari in Italy.
"We observe turbulence generally everywhere in our lives, when we go to the beach or wash our hands." - Francesca De Serio, Polytechnic University of Bari
A turbulent system is complicated, characterized by complex forces and inner turmoil. But it can start simply enough. For example, turbulence arises when a flowing fluid encounters an obstacle that changes the velocity of part of the flow. In a river, water slows down by the bank due to friction, and the velocity mismatches can produce vortices or eddies. When a river divides to move around a rock, speeds change and voids form; water falls over itself and may start to rotate. Air, too, is a fluid, its turbulence produced by competing currents and changing temperatures.
In such a system, energy moves between size scales. English mathematician and physicist Lewis Fry Richardson, the founder of modern weather forecasting, discovered this when he studied the fluid systems formed by gases in the atmosphere. He found that the kinetic energy of a large eddy feeds into smaller and smaller eddies, until it reaches the scale where viscosity, which resists motion, takes over. The energy is ultimately dissipated as heat. In 1922, Richardson captured the concept in verse:
Big whorls have little whorls
Which feed on their velocity,
And little whorls have lesser whorls
And so on to viscosity.
Starting in the early 1940s, the Soviet mathematician Andrey Kolmogorov provided a clear and rigorous mathematical foundation for the study of turbulence. But his work, like Richardson’s, mainly focused on three-dimensional systems in which energy flows from large features to small ones.
In the late 1960s, the physicists Robert Kraichnan and George Batchelor extended the investigation to two-dimensional systems. Two-dimensional turbulent systems include phenomena like Jupiter’s Great Red Spot, which swirls so violently that it overwhelms any motion farther down in the atmosphere. This type of two-dimensional turbulent system transfers energy from one scale to another, like a three-dimensional one, but with a twist: The energy of a two-dimensional turbulent system cascades in the opposite direction, moving from small eddies up to large ones. In Jupiter’s Great Red Spot, smaller eddies and vortices near the perimeter feed the giant maelstrom in the center.
In the decades after those pioneering studies reported an inverse flux in two-dimensional systems, physicists did not deeply interrogate whether those flows were fixed. The underlying energy mechanisms of two-dimensional turbulent systems certainly weren’t on the mind of Xinyu Si around 2021, when he started investigating brine shrimp as a student in Fang’s lab.
Swimming in the Energy Flow
Fang’s lab focuses on “active matter,” a physics term describing things that move by themselves and inject energy into their environments. It’s a label broad enough to include networks of living things, like bacteria, and nonliving things, like tiny robots.
In this project, Si and Fang were interested in investigating how biological swimmers mix materials in fluids where turbulence shows up. The researchers had hypothesized that, in the mixing of fluids in large natural systems, turbulence generated by tiny organisms plays an underappreciated role. Billions of minuscule creatures, after all, agitate the waterways of the world.
In a laboratory lit with red light, a man holds a tube over a tank filled with cloudy liquid.
Xinyu Si, now a postdoc at the University of Rochester, prepares a research tank.
J. Adam Fenster/University of Rochester
To closely study this in a simple model, Si poured a thin film of salt water over a glass surface in a tank and positioned magnets underneath. When he applied an electric current to the conductive fluid, it interacted with the magnets and created motion in the water, which flowed in one direction along one side of a channel and in the opposite direction along the other side. This created a gradient of velocities across the center, to which Si added brine shrimp.
When Si and Fang calculated how the shrimp’s flailing bodies disrupted the moving water, they saw “something very, very strange,” Fang said: The shrimp weren’t just contributing to the chaos of the system; they also seemed to be shifting the direction in which energy flowed.
A turbulent system can be described in terms of how much it stretches and compresses the fluids within, due to the interactions of fluids flowing at different velocities. These dynamics show up, for example, when you pour confetti into a river and watch it organize into sweeping lines as it races on competing currents downstream.
"Every experiment suggested the same conclusion: The orientation of a brine shrimp’s body seemed to change the turbulent system’s energy flux."
Si and Fang ran the brine shrimp experiment repeatedly. They found that when a solo shrimp swam at an angle of less than 45 degrees to the direction of maximum stretching, the energy flowed from smaller scales to larger ones, feeding the flow itself, as they’d predicted for a 2D system. But if the shrimp swam at an angle of more than 45 degrees to the direction of maximum stretching, the energy went in reverse, pulling from the larger scale of the flow to energize smaller perturbations.
It appeared to be a clean about-face. Every experiment suggested the same conclusion: The orientation of a brine shrimp’s body seemed to change the turbulent system’s energy flux.
The scientists found a way to interpret what they were seeing through a field of mathematics called tensor geometry, which has long been a workhorse for physicists studying turbulence. A tensor is a mathematical tool that can help you measure something that changes in multiple ways at once. For example, when you press down on a sponge, its sides bulge outward. A tensor can describe how stress — the weight of your hand — affects strain — the deformation of the sponge. Tensors give fluid dynamics researchers a powerful way to model physical phenomena that can transform in terms of direction or strength.
Fang and Si found that their brine-shrimp situation made sense if they looked at it as the interaction of two tensors in two dimensions. One tensor represented how shear — the large-scale movement of the water — affected energy flux. The other represented how the energy flux was shaped by small-scale movements from the swimmers.
The orientation of the swimmer determined the alignment of the two tensors, and the alignment of the tensors determined how the energy flowed. As Fang and Si reported in 2024, the angle between the brine shrimp’s body and the forces of the fluid could alter the direction of the energy flux.
Turning the Tide
Fang, an engineer at the University of Pittsburgh, is interested in the influence of biological swimmers in natural systems.
University of Pittsburgh
Si had been releasing brine shrimp into the tank, pointing a camera at them, and patiently waiting until one swam through the test area at just the right angle. In the next iteration of the experiment, Si and Fang replaced the brine shrimp with an array of centimeter-long rods, which proved easier to measure. They found that, by altering the orientation of the rods relative to the flow, they were able to control whether energy transferred to higher or lower scales.
The findings held even when Si and Fang invited the scrutiny of two other scientists: Filippo De Lillo and Guido Boffetta of the University of Turin in Italy, whom Fang met at a conference. In the outside experts’ numerical simulations, the same effect clearly showed up. “That made me much more comfortable,” Fang said, “because it’s a very weird thing to manipulate energy flux.”
With renewed confidence, the researchers reported their findings(opens a new tab) in 2025. “It was interesting because they were saying that with small, specific interventions in the flow we can … show a transfer of energy between scales,” De Serio said. They demonstrated that with minimal manipulation, the energy flux in a 2D system can be steered to act more like (but not exactly like) the flux in a 3D one, which suggests that physicists might be able to apply insights from one dimensional domain to the other.
There are confounding issues to overcome. In their experiments, Si and Fang used a shallow pool of fluid whose friction made turbulence hard to initiate. And there are big differences between a weakly turbulent two-dimensional system like the one in their lab and the strongly turbulent three-dimensional ones more commonly found in nature.
Mathematically, though, there’s no reason the scientists’ observations shouldn’t extend to such scenarios. Si and Fang are investigating the possibility, testing ideas on tabletop tornadoes.
They’re also exploring how to influence the “transport barrier,” the threshold between two fluids as they mix. According to Fang’s theory, disrupting this boundary — which could be useful in controlling pollution or mixing fluids for drug development — would use less than 1% of the energy required to keep the boundary intact.
Other scientists have also begun experimenting with manipulating energy flux. De Serio, at the Polytechnic University of Bari, has been firing strong jets into large tanks of turbulent, rotating fluids with high viscosity. “I was attracted by this idea that these [manipulations] could be applied in a real context,” she said. In March 2026, she reported results from experiments conducted on a large rotating vortex manipulated with small, horizontal jets firing into the middle. She observed patches of inverse energy flux that started out as intermittent bursts but grew steady with increasing rotation. Those findings, she says, may point to practical strategies for controlling energy pathways in real-world situations.
Si, now a postdoc at the University of Rochester, said that the current work introduces a new hypothesis that’s testable in any setting where turbulence plays a role, from a tiny “bowlfull of happiness” to the enormous scale of Earth’s atmosphere. Turbulent systems may be notoriously difficult to understand, but what dictates the flow of energy may be an issue of simple geometry.
