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Scientists often describe electricity as a current flowing through a wire. This metaphor is useful, but it does not fully describe what happens inside a typical conductor. In a standard wire, electrons do not move together as a unified group. Instead, they bounce chaotically off one another and off the atoms in the metal. However, physicists have recently begun to make electrons behave like fluids. They force the electrons to act in a coordinated manner. This breakthrough effort could illuminate new ways of thinking about quantum systems. It might also lead to the development of novel electronic devices.
If you were asked to picture how electrons move, you might imagine a stream of particles moving down a wire like water rushing through a pipe. We frequently use the language of flow to describe electric current. In reality, however, water and electricity flow in completely different ways. Water molecules move together to form a swirly, coherent substance. Electrons tend to fly past one another independently. "Water is seeing nothing but other water," said Cory Dean, a physicist at Columbia University. "But in an electronic system, in a wire, that's manifestly not the case." While water molecules unite to flow, each electron in a typical circuit typically acts on its own.
This every-particle-for-itself movement serves as the foundation for all of electronic theory. It explains why a warm wire resists electricity more than a cold wire. It also explains why the shape of a wire, whether round or square, does not significantly alter its conductance. Since the 1960s, theorists have suspected that electrons could be coaxed to act more like their watery counterparts. They could form an electron fluid. In recent years, a string of experiments has confirmed this prediction. Last fall, in the most dramatic demonstration yet, Dean and his collaborators arranged for electrons to form a type of shock wave. This wave occurs when a quickly flowing fluid crashes into a slowly flowing fluid. It was a surefire sign that electrons were flowing at extremely high speeds. "That's really the frontier right now," said Thomas Scaffidi, a physicist at the University of California, Irvine, who was not involved in the experiment.
Making electrons behave like water might someday lead to new kinds of electronic devices. Furthermore, extending the familiar theory of water to electrons could spawn an entirely new way of thinking about quantum materials.
Andrew Lucas, a theoretical physicist at the University of Colorado, Boulder, compares electrons traveling down a wire to pinballs traveling around a pinball machine. Once they enter the playing field, pinballs bounce around in every direction. They travel up the machine, down the machine, and all around it. Similarly, when electrons in a copper wire collide with vibrating copper atoms or with impurities in the metal, they ricochet in all directions.
On average, pinballs do tend to travel farther down than up. In this sense, they flow downward. Analogously, the flow of electrons emerges only in an average sense. An electric field establishes an ever-so-slightly preferred direction in the wire. But this is a peculiar type of flow. An electron collides with an impurity much in the same way a hacky sack collides with the floor. It thuds more than it bounces. The impurity saps the electron's energy, preventing it from building up much momentum. Consequently, electrons move through a wire a bit like water seeping through packed sand. Physicists describe this motion as a dispersive flow.
In contrast, water molecules flowing down a pipe collide almost exclusively with each other. When they collide, they bounce like billiard balls. They share their momentum and keep on moving. This ability of water molecules to conserve their momentum defines the nature of liquidity. Since collisions with obstacles don't drain their momentum, water molecules can engage in complicated collective motions. They flow in faster- and slower-moving zones and in swirling eddies.
In 1963, a Soviet physicist named Radii Gurzhi was the first to calculate exactly what would happen if electrons found themselves in a situation where they could only knock into each other. They would conserve momentum like water molecules. Gurzhi found that the difference would lie in how the electric current reacted to heat. Warming a copper wire typically impedes electric current. Vibrations in the copper atoms intensify and more greatly impede electrons. But Gurzhi calculated that if momentum were conserved, heat would make electrons move more readily. Warm honey is runnier than cool honey, and electrons would move similarly. His observation became known as the Gurzhi effect. But it didn't attract much attention at the time. It seemed like a theoretical curiosity. It had little relevance to real electrons trapped in real-world wires full of dirt and impurities, Lucas said.
Fifty years later, that would change.
In 2004, Andre Geim and Konstantin Novoselov announced the discovery of graphene. It is a honeycomb sheet of carbon atoms they could peel off a block of pencil lead using only Scotch tape. The effort earned them a Nobel Prize.
A layer of graphene was like a pinball machine with no bumpers. Almost every atom was in its place. "It's just a thermodynamically beautiful crystal. It comes out of the earth well formed, with very few impurities," said Dean, who specializes in graphene experiments. It took physicists about a decade to figure out how to study graphene without interference from other materials. But when they did, they detected electrons truly flowing.
In one early experiment in 2017, Geim and his collaborators carved a choke point into a strip of graphene. They poured electrons through and measured the resistance. They found that as they turned up the temperature, the resistance fell. This was the Gurzhi effect in action. And in 2022, physicists at the Weizmann Institute of Science in Israel managed to directly watch electrons flowing. They shaped a material with some similarities to graphene, called tungsten diselenide, into a vertical wire. It was flanked halfway down by two circles resembling Mickey Mouse ears. As electrons flowed into the ears on their way down the wire, the group monitored their motion. They measured the magnetic field the electrons generated when moving around the wire. In doing so, they saw fluidic electric currents swirling backward into the ears. These were electron whirlpools. The whirlpools resembled the eddies that form when part of a river's current runs into a bend and turns upstream.
"They can really see these vortices," said Scaffidi, who collaborated with Geim's group on another electron fluid experiment, also in 2022.
In 2025, Johannes Geurs, a postdoc in Dean's lab, decided to push the idea of electron fluids to the extreme, Dean said. Slowly moving fluids act differently from quickly moving fluids. We can see this in the air, which is as much a fluid as water. Air molecules conserve momentum when they collide. When a plane accelerates past the sound barrier in the air, it generates a shock wave known as a sonic boom. Geurs wondered if it was possible to break an analogous sound barrier with electrons themselves. This would lead to another sort of supersonic shock wave.
To produce the speediest electron fluid possible, he carved a strip made from two sheets of graphene into a sleek shape known as a de Laval nozzle. Rocket engines use this shape to accelerate their exhaust. Then he sent electrons through the constriction formed by the nozzle. This boosted their speed beyond the rate at which ripples travel through the electron fluid. That's the speed of sound for an electron fluid, a few hundred kilometers per second. When the accelerated electrons crashed into other electrons lingering in an open region downstream of the nozzle, the slower, subsonic electrons couldn't get out of the way fast enough. The liquid compressed.
The researchers swept a metallic tip back and forth over the sample. They measured minute changes in the electric field and detected the pileup. The shock wave indicated that they had in fact broken the electron fluid's sound barrier.
Experiments like these allow researchers to flex and extend their control over electrons. This new level of mastery could lead to novel electronics components. For example, when electrons move like fluids, they start to respond to the shape of the channel through which they're moving. It could be Mickey Mouse ears or a nozzle. "By using different shapes for your device, you can realize very different physics," Scaffidi said.
These experiments could also help theorists develop an entirely new way of talking and thinking about electrons and subatomic systems. It is a baby step toward using what we know about the movement of liquids to understand quantum systems, Scaffidi said. When electrons flow like fluids, they form coherent patterns. Once you know some high-level properties of the fluid, such as density and viscosity, you can use standard equations to find out what the fluid will do. You do not need to keep track of the motion of every last electron.
The hope is that in other complicated quantum or semi-quantum systems, theorists might, for instance, be able to identify conservation laws. These laws will help them recognize similar large-scale flow behavior. One group was able to do this for certain chaotic quantum circuits in 2024.
Perhaps by continuing to cook up electron fluids in the lab, theorists will find a way to describe other, more enigmatic situations where electrons seem to melt away. They will use hydrodynamics to describe the way they swirl, said Lucas, who helped with some of the theory calculations for the Columbia experiment. "It's a very appealing showcase of something that can't be explained in any textbook paradigm," he said.