Because the universe is expanding, any wave of light emitted from a far-flung source is stretched out.

ECONOMIST: Fundamental physics

If an aggressor launches a nuclear device of whatever size and detonates it above the atmosphere and in the line of site of its target country, the x-rays and gamma rays emitted by the blast will cause an electromagnetic pulse, or wave a million times stronger than the strongest radio wave.

CENTERFORSECURITYPOLICY: An urgent memo to the next government

That surface wave, in turn, produces another electric signal, which is emitted via the transducer.

ECONOMIST: MONITOR