Bewitching: the cursed enigma of ball lightning

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Science is the ultimate myth-buster. Notwithstanding, the mystery of ball lightning still remains unresolved.

This almost millennial-old enigma confounded Gervase of Canterbury in the 12th century. Recent interdisciplinary research by physicist Emeritus Professor Brian Tanner and historian Professor Giles Gasper at Durham University uncovered this earliest eyewitness account of ball lightning. Quoting from their translation of Gervase’s Chronicle: “a marvellous sign descended near London. For the densest and darkest cloud appeared in the air growing strongly […] into a spherical shape […] a sort-of fiery globe threw itself down into the river.”

It is hard not to romanticise as bewitching a phenomenon as Zeus’ Brimstone. Imagine: a white-hot, brighter-than-daylight, electrifying orb catapulting and whizzing through the air, at last exploding into a fiery, sulphurous mist. Ball lightning’s mythical charisma extends beyond the scientific community, even inspiring Nobel laureate in Literature Mo Yan to symbolise it, in one of his short stories, as an inauspicious phantasmagoria.

This time around, some scientists did conform to the antiromantic empiricists they are often misconstrued as. Through in-lab recreations and direct detections, several theories to unravel the physical nature of ball lightning have been proposed.

It is hard not to romanticise as bewitching a phenomenon as Zeus’ Brimstone

One of the simplest theories is the Vaporised Silicon Model. It is conjectured that a lightning bolt’s immense heat vaporises the silicon oxides in the soil it strikes. The oxide bonds with carbon in the soil and leaves pure silicon vapour hanging in the air. Chemical reactions between vapourised silica and atmospheric oxygen release energy through re-bonding, producing ball lightning’s quintessential shimmer. A direct measurement of ball lightning’s emission spectra by a group of Chinese scientists shows significant peaks at the characteristic wavelengths of silicon and oxygen, proving the theory successful in predicting the composition of ball lightning. Brazilian scientists have even succeeded at reproducing small semi-permanent orbs using electrical-shocked silicon wafers.

The Solid Electron Core Model rectifies the ‘fluid’ nature proposed by the Vaporised Silicon Model. It envisages ball lightning as a concentrically layered sphere with a solid core. A lightning strike induces an outward force which pushes electrons away from a positively charged solid core; balanced by Coulomb attraction, the electrons form a layer around the positive core, enclosing a vacuum permeated by electromagnetic radiations. The outermost core is what instils ball lightning its essence – a plasma envelope. This envelope is a pool of dissociated ions induced by the electron layer. This model prevails against the Vaporised Silicon Model as it also explains why ball lightning could spout sparks and float in rapid motion – the prior due to the fragmentation and dispersion of the positively charged core; the latter as a result of buoyancy, gravitational and electrostatic forces simultaneously acting on the semi-rigid conductive sphere.

However, the model neglects wave interferences and resonances due to higher electromagnetic modes. The inability to experimentally reproduce lightning balls of higher complexity has stalled the model’s potential to capture the intransigently complicated interior of ball lightning – despite some worth-mentioning recreations using low-complexity systems with high-current, low-voltage discharges.

The Resonant Microwave Cavity Model, however, fills the holes in the Solid Electron Core Model. It hypothesises ball lightning as a maser-soliton, which is simply a self-maintained wave-packet or -bubble in which microwaves are constantly emitted through stimulations. The physics behind the stimulations are similar to that of the Solid Electron Core Model, only with an extra boundary condition constraining the size of the lightning ball to which it facilitates resonances at microwaves’ wavelengths. These sort of plasma balls are reproducible even with home microwave ovens, although they are nowhere near the intensity and spatial extent with which Nature’s exultantly shine.

There are plenty more hypotheses, all no less entrancing; they are also no more experimentally or observational plausible, for now. In Gervase’s age of divine superstition, fear made his contemporaries think that ball lightning – as natural as lightnings in a tempest, albeit more exotic – is a manifestation of God’s wrath. In our age of reason, however, scientists are pushing the research frontier on ball lightning, utilising nanotechnology and advanced plasma physics, to reveal its physical nature – less than mythical, hence all the more beautiful. Just one day, our astute scientific enquiry will alchemise this age-old mystery into a blessing.

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