ON A summer’s day in the early 1980s, a teenager sat in his bedroom watching an afternoon thunderstorm roll over the seaside landscape near Rome. Without warning, a glowing sphere the size of a football suddenly appeared in the corner of the room. Emitting no heat or smell, it hovered about a metre in front of him and slightly over his head. The boy was dumbfounded. The ball was dark yellow, completely opaque, with a wispy surface made from layered sheets of slowly rippling light. It floated there for about 10 seconds before vanishing as silently as it had come. He didn’t even have time to be scared.
Andrea Aiello remains fascinated by what he saw as a boy – and now, as a theoretical physicist at the Max Planck Institute for the Science of Light in Germany, he is developing his own ideas about it. The most likely explanation is that he witnessed ball lightning, a rare form of atmospheric electricity that can hover gently above the ground inside or outside buildings and even pass through closed windows. Scientists around the world take the phenomenon seriously, while remaining unable to explain, reproduce or authoritatively document it.
Advertisement
There are plenty of hypotheses, but little certainty. Some believe the phenomenon’s origins lie in the electrical power play of vast thunderstorms. Others think it might be caused by lightning strikes themselves. A few believe it is a messy tangle of electromagnetic field lines wandering Earth alone. So far, at least, none of these ideas can explain everything ball lightning seems to do. Is it time to consider some more exotic alternatives?
The bare bones of how regular lightning forms is reasonably well established: dust and ice particles inside a storm cloud undergo so-called charge separation, with the positively charged particles rising and the negatively charged ones sinking. These, in turn, induce positive charges at raised points on Earth’s surface, generating powerful, widespread electric fields that steadily strengthen until the energy is released in a surge of electricity. Those surges are the lightning bolts we see from our windows.
But that explanation brushes an awful lot under the carpet. We still don’t know, for example, how collisions in the air cause the charges to separate or, indeed, how an electric field that is strong and compact enough to generate a lightning bolt is created inside a storm cloud. For an everyday phenomenon, lightning remains surprisingly mysterious. Few of its manifestations, however, are as poorly understood as ball lightning.
Aiello is far from the first to claim a sighting. Ball lightning has been repeatedly reported over the centuries. Tsar Nicholas II of Russia claimed to have seen a glowing ball glide through a cathedral during a late-night storm when he was a child. Laura Ingalls Wilder, who wrote Little House on the Prairie, described a winter storm during which balls of fire rolled down the outside of the stovepipe inside her home. They rolled onto the wooden floor, but left it unsinged. The physicist Nikola Tesla even claimed to have artificially produced ball lightning in his Colorado Springs lab.
Despite such apparent sightings, though, concrete evidence remains hard to come by. All records are anecdotal, and no image or video purporting to show the phenomenon has stood up to scrutiny.
There is no network to detect something like ball lightning, either. Rachel Albrecht at the University of São Paulo in Brazil has used lightning detection systems to map the world’s most active lightning hotspots. She says that something as dim as ball lightning, which is often reported to glow about as brightly as a 100 watt incandescent bulb, wouldn’t be picked up by satellites or the various land-based lightning detection systems. To record ball lightning, she says, “it would have to be happening right in front of your camera”.
Even without direct evidence to go on, Martin Uman at the University of Florida believes there is something to the phenomenon. Uman has spent nearly the entirety of his 50-year career studying lightning and has collected or reviewed hundreds of encounters with glowing spheres much like Aiello’s. A blue ball glancing off a student’s finger, a white ball rolling down the centre of a military tanker aircraft, a yellow ball hovering above an engineer’s desktop computer. “There are a number of published papers where ball lightning was inside of a commercial airplane and all the passengers saw it as it floated down the aisle,” says Uman.
“The ball floated there for 10 seconds before vanishing silently. He didn’t even have time to be scared”
Antimatter meteorites
While the details of any one account of ball lightning sound incredible, Uman thinks the accumulation of thousands of similar reports over the course of hundreds of years points to a genuine phenomenon with no sound scientific explanation.
Dozens of mind-bending suggestions have been published to explain ball lightning, ranging from mini black holes to meteorites made of antimatter, but it is more likely that something simpler is involved. Uman suspects that ball lightning is an after-effect of the electric discharge from standard lightning strikes, which could occasionally kick off strange chemical reactions capable of producing a glowing sphere.
If lightning hit a patch of ground rich in silica and carbon, for example, some researchers believe it could form a cloud of pure silicon nanoparticles, emitting light and heat as it oxidised. Any such explanation that depends on hot gases comes with problems of its own. Namely, ball lightning is consistently reported to hover in place, glide horizontally and move against the wind – none of which a hot gas should do.
“The field doesn’t need more theories,” says Karl Stephan, an electrical engineer at Texas State University. “The field needs experiments and observations that are instrumented well enough to get more observational data.” That’s why Stephan has been pursuing ball lightning experimentally for nearly two decades, testing plenty of hypotheses that rely on an electric discharge.
In one experiment, Stephan . Short-lived balls of hot, ionised gas, called Gatchina plasmoids, can be produced when high-voltage electricity is discharged near the surface of salty water. Stephan was able to steer these plasmas horizontally, but they disappeared in a fraction of a second while, like all hot gases, noticeably rising. “You take a still picture of it – it looks a whole lot like what people describe ball lightning to be,” says Stephan. “But I don’t think that’s the whole explanation or even most of the explanation.”
Uman has also conducted experiments aimed at producing ball lightning via electric discharge. By firing small rockets with trailing wires into active thunderstorms, he has . In a single summer, he guided lightning through dozens of different materials including pools of saltwater, various metals and even bat guano in the hope of creating ball lightning. Although he and his team were able to create a few spherical sparks – albeit ones that were far too short-lived to be ball lightning – and the same kind of rising plasmas Stephan and others have made, they resolutely failed to produce the phenomenon they were after.
Other ball lightning theorists rely less on lightning bolts themselves. Robert Cameron at the University of Strathclyde, UK, thinks ball lightning might be caused by electromagnetic knots: as-yet-unseen tangles of electromagnetic field lines that could be powerful enough to ionise the surrounding air. In 2018, Cameron and has since connected with Stephan and Wolfgang Löffler at Leiden University in the Netherlands to refine the idea and potentially create the knots in the lab.
“The experiments guided lightning through dozens of materials including saltwater, metals, and even bat guano”
Electric knots
Retired physicist and independent ball lightning researcher Herbert Boerner believes Cameron’s knots dovetail perfectly with his own idea that powerful, widespread electric fields produced in especially strong thunderstorms are the primary cause of ball lightning. Boerner has investigated several accounts of ball lightning where multiple spherical objects were produced simultaneously. As he correlated those sightings with European lightning detection archives, he found that ball lightning can appear several kilometres away from cloud-to-ground lightning strikes, leading him to believe that a storm’s electric field, rather than an individual lightning strike, causes ball lightning. However, he had no idea how a strong electric field itself could generate ball lightning until he came across Cameron’s paper. “Then suddenly things fit together,” he says.
In his 2019 book on ball lightning, Boerner explains that Cameron’s knot hypothesis could tally with his concept if a storm’s electric field is strong enough to pull a cloud of electrons out of the ground. That cloud may then be able to act as a kind of natural antenna, channelling a pulse of electromagnetic radiation from the lightning into a knot.
“I think the basic idea is certainly good, because it works. I calculated this myself,” Löffler says of Cameron’s idea. Yet he doesn’t think the knots will end up explaining ball lightning the way Boerner does. Stephan, too, is interested in Cameron’s work more as a purely electromagnetic puzzle and less as a cause of ball lightning. He says that the radiation coming from the lightning bolt would have to be in the form of microwaves for it to last long enough to explain ball lightning – and there is no reason to think a thunderstorm produces microwaves.
While ball lightning continues to defy easy explanation, it may be useful to turn to those who have witnessed it first-hand. As perhaps the only legitimate researcher to have actually seen ball lightning in person, Aiello has an idea of his own.
One of the most puzzling aspects of the glowing ball Aiello saw as a teenager was that it appeared to be made of light that was standing still. But because light has no mass, the laws of physics require that it must always move. “My explanation is that this light moves, but in an additional dimension,” he says. A quantum physicist used to thinking unconventionally, Aiello sees the problem geometrically. A cross section of an ordinary three-dimensional lightning bolt would be a two-dimensional circle. Logically, then, if you scale up by one dimension, the cross section of a four-dimensional lightning bolt would be a three-dimensional sphere. So, if an extra-dimensional lightning strike were able to break into our space-time through a wormhole, it would appear as a glowing, three-dimensional ball of light. Aiello hasn’t yet published his idea, but believes a mathematical explanation of the process is possible.
Uman, Stephan and Boerner all agree that ideas like Aiello’s are part of a long history of untestable hypotheses that invoke some form of new and exotic physics to solve the mystery of ball lightning without hard evidence. But with a smile and a shrug, Stephan admits: “I can’t rule it out.”
- Have you seen ball lightning? Some of the researchers in this story are collecting accounts of sightings. Report yours at
