Spin controls the flow of heat

The quantum vacuum is not empty space. It’s full of electromagnetic fluctuations. And when two thin conducting plates are a few nanometers apart, attractive forces or torques between them can emerge from those fluctuations. In the phenomenon, known as the Casimir effect, the plates attract or twist because electric and magnetic fields vanish at their boundaries and change the free energy in the gap. (See the Quick Study by Jeremy Munday, Physics Today, October 2019, page 74.) But the Casimir effect isn’t the only manifestation of vacuum…