Ball lightning has been consistently reported for centuries, and yet we still know very little about it. Now, scientists at Amherst College and Aalto University have created quantum ball lightning by knotting together the magnetic spins of atoms, creating a quasiparticle that could help unlock the secrets of the strange phenomenon, or even make for more stable fusion reactors.
Like its better understood, forking counterpart, ball lightning glows brightly and fleetingly. As its name suggests, the main difference is its spherical shape, but it also behaves very differently. It's been known to hover above the ground, move around and in some cases remain visible for more than a minute. It usually accompanies regular lightning but has also surprised people by floating through houses and even airplanes.
Unfortunately, physical evidence is rare. Perhaps the most enlightening case occurred in 2012, when Chinese scientists were able to capture the phenomenon on video during a storm and subsequently analyze the optical spectrum of the ball lightning. Based on this study, the hypothesis the team came to was that a regular lightning bolt vaporized silicon in the soil where it struck, and the bright ball is that silicon sizzling away for a few seconds.
But the team acknowledged that its explanation doesn't cover all cases – particularly the indoor balls that are often seen startling people in 19th-century sketches. The Chinese scientists, along with other researchers, have suggested that the phenomenon may have several different causes.
To investigate another idea, the Amherst and Aalto team set about recreating ball lightning in the lab. The researchers started with a quirky supercooled gas known as a Bose-Einstein condensate, which has in the past helped scientists create exotic new states of matter like supersolids, excitonium, Rydberg polarons and fluids exhibiting negative mass.
In a Bose-Einstein condensate, the atoms are so cold they lose almost all their energy, and in effect act like one giant atom. In this state, the scientists applied a magnetic field to change the spin of the atoms to point upwards, before manipulating it very precisely to create a point in the center of the condensate where the magnetic field vanishes. Since the atoms near the center can have spins pointing in any direction at all, the spins all wind together into a knot.
This knotted structure forms a quasiparticle known as a skyrmion. According to the researchers, this marks the first time a skyrmion has been experimentally created, since it was first theorized in 1962. Although the knot can be loosened or moved, it can never be entirely untied, which gives the skyrmion the kind of stability ball lightning is known for.
"It is remarkable that we could create the synthetic electromagnetic knot, that is, quantum ball lightning, essentially with just two counter-circulating electric currents," says Mikko Möttönen, a researcher on the study. "Thus, it may be possible that a natural ball lighting could arise in a normal lightning strike."
The researchers found that the knotted artificial magnetic field created by their skyrmion perfectly matches the magnetic field seen in a model of ball lightning. If the technique can be scaled up, it might eventually allow scientists to create and harness macro-scale ball lightning at will.
"More research is needed to know whether or not it is also possible to create a real ball lightning with a method of this kind," says Möttönen. "Further studies could lead to finding a solution to keep plasma together efficiently and enable more stable fusion reactors than we have now."
The research was published in the journal Science Advances. The glow of the skyrmion can be seen in the video below.
Source: Aalto University
