J. Montgomery

At the South Pole, where the air is dry and transparent to millimeter waves, stands a telescope that looks not at stars but at the oldest light in the universe. This light is the cosmic microwave background — the radiation left over from the Big Bang, filling the entire sky.

A thermometer cooled to near absolute zero picks up the heat from a single particle. That's how cryogenic calorimeters work — instruments that catch ultra-rare events like neutrinoless double beta decay. But old thermistor thermometers respond slowly: in about a millisecond.

In the frozen desert of Antarctica, the SPT-3G telescope peers deep into the universe. Its target is the ancient microwave radiation left over from the Big Bang. But on its way to us, this radiation passes through giant galaxy clusters filled with scorching gas.

A superconducting detector usually works like an honest ruler: absorb a photon, get a pulse whose amplitude is strictly proportional to the energy. This mode is convenient, but it has a ceiling: a weak signal easily gets lost in the amplifier noise. Now imagine a swing.