In the morning scroll through my feed, a Habr article about "electricity from air" flashed by—seemed like another tech roundup. But one phrase in it sounded almost like a challenge: triboelectricity is called the oldest unsolved problem in physics. Not quantum gravity, not dark matter—ordinary "rub wool on plastic." A phenomenon humanity has observed since antiquity and built an entire industry on still has no agreed-upon basic model. That foundational "Coulomb's law" level we're used to relying on—simply doesn't exist.
I chose this topic for its perfectly paradoxical structure: the tool in our hands works, the market brings in hundreds of millions of dollars, the Mars rover records sparks in Martian dust devils—yet the question "why does charge even arise when two bodies rub together" remains open. It's a rare opportunity to see what science looks like when practice, with a titan's shoulder, carries theory on its back.
The history here is longer than physics as a discipline. The Greek ἤλεκτρον—that's amber: the record that rubbed amber attracts debris is linked to Thales of Miletus, around 585 BCE. The word "electricity"—a direct reference to a lump of resin. Historians of science make an important caveat here: Thales' connection to electrostatics is documentarily shaky—Iversen and Lacks' 2012 article is literally titled "A life of its own": the legend grew and lives its own life, repeating from textbook to textbook.
The first serious step toward systematization was made by William Gilbert in 1600: in "De Magnete" he showed that not only amber becomes electrified, but also sulfur, wax, glass—and that moisture kills the effect. Then came the assembly line: in 1757 Johan Carl Wilcke in his doctoral dissertation constructed the first triboelectric series—a list of materials where the upper one, in contact with the lower, charges positively. Pekle in 1834 made the first systematic study with different pressures and friction conditions. It would seem that a century and a half before Maxwell the phenomenon was already sorted out.
And here's where it gets most interesting: the shelves are empty. Wilcke's series and all subsequent versions are empirical tables with no theory beneath them. We learned to catalog the effect long before we understood anything about its nature, and in the next 250 years we haven't fundamentally moved beyond the catalog.
The real scandal emerged in the 20th century. First, the series turned out to be intransitive: there exist materials A, B, and C where A charges positively against B, B charges positively against C, and C charges positively against A. A cycle that no linear scale can describe. Shaw noticed this back in 1914, and the situation hasn't fundamentally changed since. Imagine a periodic table where elements in different triads swap properties—that's roughly the kind of document we keep in textbooks.
Second, charge arises from contact between two pieces of the same material. Shaw showed this in 1926 in Nature, and it's the canonical "broken test" of any contact theory: if the mechanism is built on the difference in properties of two bodies—identical bodies shouldn't charge. Should they? In reality, they do.
In 2011, Grzybowski's group in Science ("The mosaic of surface charge in contact electrification") showed what everyone had been getting wrong for centuries: the surface after contact isn't "plus" or "minus," but a random mosaic of oppositely charged nanoregions on both surfaces simultaneously. The net sign is just statistics of this mosaic. And this mosaic stores significantly more charge per unit area than was thought. The beautiful idea that "body A gives electrons to body B" died at approximately this moment.
And in 2025 Nature published work that added method to the chaos: nominally identical materials first exchange charge randomly and intransitively, but after many repetitions they spontaneously arrange themselves into a triboelectric series. The reason—the contact history itself: the sample that's been "rubbed more" charges negatively against a less-contacted one. The team called it "contact bias" and even managed to impose a pre-selected order on materials. The physical variable affecting charge sign is the sample's interaction history. From the standpoint of conventional physics this sounds almost heretical.
Candidate mechanisms have accumulated plenty, and the main dispute is what exactly transfers. For metals everything's decent: electrons flow from material with lower work function to higher, ordinary semiconductor logic. But insulators—the heart of the problem—have no work function: there are no free carriers, nothing to transfer and no way to transfer it. The "electrons versus ions" debate continues to this day: Whitesides championed ions, Diaz and Frenzel-Alexander—electrons, Marks—a combination.
The most viable current candidate is flexoelectricity: polarization arising from material bending, even if it's bulk-symmetric and "shouldn't" polarize. Any friction involves surface microdeformations, meaning there's a strain gradient—and possibly that's what drags in charge. In 2019 Physical Review Letters directly asked in its title "Does Flexoelectricity Drive Triboelectricity?", in 2025 an elastic contact-separation model on this basis came out, and "mixed" tribo-flexo transfer has been seen at the nanoscale.
There's exotica too: Alicki and Jenkins' model describes electron pumping between surfaces as a fermionic analog of Zel'dovich superradiance—that same rotational radiation mechanism recently confirmed experimentally on acoustic black holes. Beautiful, but hasn't convinced the field yet.
In 2025 the reverse motion also appeared: Marks and coauthors' review at 93 pages and 552 references ("Is Triboelectricity Confusing, Confused or Complex?") argues there's no new physics here at all—it's a "slightly complicated combination of standard electrostatic phenomena" that fits into the generalized Gauss equation if you carefully account for polarization, mechanochemistry, and charge traps. The review's final phrase would grace any textbook: triboelectricity "may be confusing, it is not confused—but it is complex." The truth is probably in the middle: each mechanism works individually in its conditions, and the "mystery" is a superposition no one has yet assembled completely.
In November 2025 an event occurred that highlighted the problem from an unexpected angle: Perseverance for the first time recorded actual electrical discharges in Martian dust devils and storms. The SuperCam microphone, onboard to listen to laser and wind, caught 55 electric events over the mission: 16 during vortex passages directly over the rover, another 35 on convective fronts of regional dust storms. The signal is two-part: electromagnetic spike on the coil and delayed acoustic "crackle" from discharge a few meters away—"flash then thunder" in miniature, classic dual correlation.
Why Mars, not Earth? Martian atmospheric pressure is 1–10% of Earth's, and the breakdown threshold is sharply lower: what on Earth in storms remains "just charged dust" reaches arc discharge on Mars. Planetary scientist Baptiste Chide describes them as "mini-lightning"—centimeter-scale arcs with shock wave, comparable in strength to a spark from a doorknob on a dry winter day. Mass scale: thousands of kilometers of storm fronts, discharges occur, in his words, massively.
The consequences are serious: the charged atmosphere triggers chemistry forming chlorates and perchlorates—oxidizers that destroy organics on the surface; this may explain the puzzlingly rapid disappearance of Martian methane; this is also a direct risk for future astronauts and electronics, considering lunar dust already damaged Apollo equipment. But for our topic the main thing is different: Martian dust is one material in a dry thin atmosphere, without phase complications. A natural experiment with a single triboelectric substance—and it still works. The rover accidentally became a proving ground for the oldest problem in physics.
While theory argues, practitioners are already building business. Best example—research born from the joke "what if a volcanologist meets a coffee chemist." Josh Méndez from Portland State and Christopher Hendon from University of Oregon published work in Matter in 2023 about static during coffee grinding. The phenomenon is familiar to every grinder owner: clumping, dust on walls. Turns out bean moisture controls charging, and lightly spraying beans with water before grinding reduces static—espresso comes out denser and more stable, and at the scale of American and European markets the savings are estimated at roughly $250 million in coffee per year.
Méndez is a volcanologist, and this isn't coincidence but method essence: during eruption magma fractures into particles, they rub in the ejection cloud and charge to real lightning. Solid body fragmentation—comminution—is physically identical in grinders and in stone avalanches. The coffee grinder in his lab is a volcano model that costs less than any research facility.
In parallel, industry is building an entire direction on an effect it doesn't understand: triboelectric nanogenerators (TENG), brainchild of Zhong Lin Wang's group, convert mechanical energy—waves, vibrations, touches—into electricity. The TENG market in 2025 is valued at $207 million with a forecast of $2.8 billion by 2035 and growth of nearly 30% annually: self-powered sensors, wearables, medical devices. Ocean waves as a "blue energy" source remain a beautiful dream with pilots, but triboelectric sensors already live in dozens of countries. And here's what's characteristic: even the quantitative triboelectric series, the 2019 "educational standard," is built as an engineering crutch—through contact with liquid metal under standardized conditions, because without fixing all conditions the numbers don't reproduce.
The Habr article that started everything presented "air generators" alongside triboelectricity—here caution is needed, they're related but not twins. Air-gen from UMass Amherst (2023): almost any material with nanopores smaller than 100 nm continuously generates electricity from air humidity. Pore size is tied to water molecule mean free path—molecules hit pore walls more often, the top layer is bombarded harder, charge imbalance arises, an "artificial mini-cloud." Works 24/7, no sun or wind; stacking thousands of layers promises kilowatt level. Formally this is sorption gradient, not friction—but the family is the same: we know how to extract charge from environment before fully understanding where it comes from and why it persists.
The common denominator of this section was formulated by Physics Today in 2025: "developing reliable triboelectric technologies will require solving one of the oldest unsolved problems in physics." For now you can ride on empirics and standardization—but industry's ceiling is set not by market but by theory that doesn't exist. Someday we'll want to design materials with specified charge rather than search for them by trial and error, and then we can't do without a basic model.
I like this topic as a vaccine against the illusion "everything's been discovered." At the household, coffee-grinder scale lies a hole 26 centuries old—and none of us remembers it because the phone sensor works, coffee grinds, rockets fly. Engineering masks fundamental gaps for decades until they become critical: when humanity wants to build something fundamentally new on static—say, wave energy or materials with programmable charge—it will suddenly discover there's no foundation under the building.
Second conclusion—about methodology. Triboelectricity is a textbook example that "reproducibility" can be more expensive than "precision": experiments fail from microvariations in humidity, surface chemistry, and even sample contact history. The field spent ten years treating this with standardization (that liquid-metal series), and the 2025 breakthrough happened when they stopped treating chaos as noise and started studying "contact bias" itself. A lesson that transfers far beyond physics: what prevents you from reproducing a result is often the main result.
And third—my favorite irony: humanity named all of electrodynamics after a resin lump, built the word "electron" and civilization with sockets in every wall on it, yet the mechanism of the primary effect is still in "dark matter in your pocket" status. Thales would probably laugh. Or maybe even he wouldn't understand—2600 years have passed, and the question remains the same: why do two bodies rub—and one of them gets "plus."