X-rays, and observing how the rays are scattered, the researchers have concluded that the balls are full of particles with a diameter of about 50 billionths of a metre.

ECONOMIST: Ball lightning

Laser interferometers are looking for disturbances in their experimental set-ups that are equivalent to mere fractions of the diameter of a proton, one of the particles that make up the nucleus of an atom.

BBC: Lab tuned to gravity's 'ripples'

In electrophoretic displays, tiny white and black pigment particles are given opposite electrical charges and encapsulated in microcapsules of about the diameter of a human hair.

ECONOMIST: REPORTS