Shining an appropriate light on such a wire from the outside would alter its refractive index (a measure of how fast light travelling inside the wire can move).

ECONOMIST: New-age crystals

Astrophysicists can determine how the blazar grew brighter in different parts of the spectrum at different times and refine their models of how fast-moving particles within the jets give rise to the high-energy light.

BBC: Blazar Markarian 421's flare-up is cosmic coincidence