The switchable vacuum rotor
University. · 1 min read
What it proposes
Build a nanoscale motor whose only power supply is the vacuum, with an ordinary electrical switch on the front. Two recent results give the two halves: a voltage that flips the Casimir force from attraction to repulsion, and a magnetic field that switches on a Casimir torque between surfaces that carry no built-in direction at all. Put them together and you have a rotating element driven by vacuum fluctuations, turned on and off, and reversed, by a knob.
Who it is forCondensed-matter fabricatorsMagnetics engineersPrecision-mechanics engineers
Why the library suggests it
Benjamin Spreng, Calum Shelden, Tao Gong and Jeremy Munday show that a modest forward bias across a semiconductor gives its emitted photons a chemical potential, and that adding this push to the ordinary Casimir pull flips the sign — gallium arsenide facing gold turns repulsive beyond a few hundred nanometres, with the crossover moving closer as the voltage rises, and tens to hundreds of piconewtons of repulsion predicted in the sphere-and-plate geometry every Casimir laboratory already owns (Casimir repulsion with biased semiconductors, 2024). Zixuan Dai and Qing-Dong Jiang show that altermagnets — magnets with no net magnetisation whose spin pattern is tied to the crystal's own rotation symmetry — develop a Casimir torque under a field pointing straight through the plates, which picks out no direction in the plane at all; the torque grows as the square of the field and a magnetic underlay chooses which way it turns (Vacuum Torque Without Anisotropy: Switchable Casimir Torque Between Altermagnets, 2026). The torque itself is an established branch of the subject (Recent developments on the Casimir torque, 2022).
The experiment or build
Fabricate a disc of altermagnetic material suspended tens of nanometres above a second one, with a coil supplying the out-of-plane field and a bias line on a semiconductor spacer. Read the rotation optically. Sweep the field and confirm the torque follows the square of it; reverse the underlay and confirm the direction reverses; apply the bias and confirm the levitating branch appears. The settling measurement is the torque in newton-metres as a function of applied field, with the sign reversing on command and the whole curve returning to zero when both the field and the bias are removed. A vacuum device that switches off is a vacuum device you can believe.
Where it stands
Designed, not yet built — both halves are full theoretical proposals with named materials, geometries and predicted magnitudes; neither has been assembled into one machine.
Take it up
- The measurement that settles it
- The settling measurement is the torque in newton-metres as a function of applied field, with the sign reversing on command and the whole curve returning to zero when both the field and the bias are removed.
- What it costs to start
- University.
- The engineer it grows
- This is the card where engineering an asymmetry in the vacuum stops being a slogan and becomes a part with a datasheet.
What it rests on
Where it sits in the curriculum