46 | New Scientist | 24 October 2020O
N 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.
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
PA charges to separate or, indeed, how an electric
TR
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R
Features
Great balls
of fire
The source of ball lightning has been a
mystery for centuries. Are we any closer
to an explanation, asks Eric Canan