Two metal plates in a perfect vacuum attract each other. Even Richard Feynman compared emptiness to a boiling foam: particle pairs are born and immediately vanish, creating the Casimir effect. If the plates are asymmetric, they also start to twist — that's a vacuum motor.
But rotation doesn't require oddly shaped parts. Following the equations of James Clerk Maxwell, physicists discovered that in altermagnets — special magnets with a wave-like magnetization — a perpendicular magnetic field breaks time symmetry. The void responds with a torque that grows as the square of the field.
As temperature rises, thermal noise ( entropy ) weakens the rotation. The most surprising part: the same quantum fluctuations that spin nanoparticles are suspected to drive the expanding Universe — that's dark energy. Engineers hope to create contactless nanomotors, since in micromachines the usual Casimir effect, on the contrary, glues parts together.
The Casimir effect was calculated by Dutch physicist Hendrik Casimir back in 1948, but it wasn't experimentally confirmed until 1996–1997 with the help of ultra-precise measurements.
In Arthur C. Clarke's science fiction novel 'The Fountains of Paradise', engineers build a space elevator. Perhaps one day Casimir-effect nanomotors will become part of such structures.