The collider’s magnets are colder than the afterglow of the Big Bang

The Large Hadron Collider’s superconducting magnets run at 1.9 kelvin. The cosmic microwave background is 2.7 kelvin. The magnets are the colder of the two.

Superfluid helium cools the magnet string to 1.9 K, below the 2.17 K where helium-4 becomes a superfluid and can carry heat with almost no resistance of its own. The magnets are superconducting so that a huge current can circulate and bend 6.5-teraelectron-volt protons into a ring 27 kilometres around. The microwave sky, the cooled remnant of the early universe, sits at 2.725 K. The helium is colder than that sky. The phrase ‘colder than space’ is this comparison, and only this comparison.

The protons are not a hot gas filling the tunnel. They are a thin thread, a few bunches, and each proton carries an enormous energy while the tunnel itself stays ordinary. The cold is in the magnets. The energy is in the beam. Reporting either number as if it described the building is how this fact gets ruined in the retelling.