In 1971, the British physicist Roger Penrose proposed that energy could be extracted from a spinning black hole. A particle entering the ergosphere, the region where spacetime is dragged along by the black hole’s rotation, could split in two, with one fragment falling in with negative energy and the other escaping with more energy than it arrived with. The Soviet physicist Yakov Zel’dovich extended the idea to waves: a wave scattering off a rapidly rotating object could emerge amplified, carrying away some of the object’s rotational energy.
For more than half a century, this remained a theoretical prediction, impossible to test directly because no one can manipulate a black hole in a laboratory. Now, researchers at the City University of New York (CUNY) Advanced Science Research Center have built a tabletop device that reproduces the essential physics of the Penrose-Zel’dovich process, using no gravity, no event horizon, and no moving parts.
The work, published July 8 in Nature and led by Hadiseh Nasari and Andrea Alù, demonstrates “Floquet rotational super-radiance”: the amplification of electromagnetic waves through interaction with a synthetically rotating medium.
How to fake superluminal rotation
The key challenge was creating an object that rotates faster than the speed of light at its surface — the condition required for the Zel’dovich effect — without physically spinning anything at impossible speeds. The CUNY team solved this with a ring of coupled electronic resonators, each roughly the size of a coin, whose electrical properties are modulated sequentially around the ring. A traveling wave of capacitance changes sweeps around the circuit like a rotating strobe light, creating what the researchers call a “space-time crystal” — a medium whose properties vary in both space (around the ring) and time (the sequential modulation).
The effective rotation speed of this synthetic medium can exceed the speed of light — not because any physical object exceeds that limit, but because the modulation pattern sweeps around the ring faster than a wave could propagate through the unmodulated circuit. This “superluminal effective rotation” opens angular-momentum bandgaps in the system’s band structure, creating parametric gain channels that transfer energy from the modulation itself into specific electromagnetic wave modes.
Only waves with the correct orbital angular momentum properties couple to these channels. The result is angular-momentum-selective amplification: a steady transfer of energy from the synthetic rotation to selected wave modes, exactly the wave analogue of the Penrose-Zel’dovich process.
“We have created a versatile experimental platform for studying extreme rotational dynamics in a controlled laboratory setting,” said Alù, a distinguished professor at the CUNY Graduate Center and founding director of the ASRC Photonics Initiative. “This bridges Floquet engineering, time-varying media, and black-hole analogue physics.”
What was actually measured
The team measured rotational Doppler shifts in the modulated ring, confirmed the existence of angular-momentum bandgaps at superluminal effective speeds, and observed parametric amplification of selected modes within a dissipation-shaped spectral bandwidth. The amplification is broadband — it works across a range of frequencies, not just at a single resonance — and is angular-momentum-selective, meaning that different rotational modes of the electromagnetic field are amplified differently depending on their coupling to the synthetic rotation.
The experiment does not involve actual gravity, spacetime curvature, or a black hole. It reproduces the mathematical and wave-physics essence of the Penrose-Zel’dovich process in an electromagnetic circuit. This is the same distinction that applies to other gravity analogues — sonic black holes in flowing fluids, optical black holes in nonlinear media — where a mathematical analogy allows the study of phenomena that would otherwise be inaccessible.
“Additional work will be needed before these ideas can be translated into practical devices,” Nasari noted. The researchers identified potential applications in wireless communications, photonics, quantum technologies, and broadband signal processing, but these remain speculative.
Nevertheless, the experiment validates a five-decade-old theoretical prediction in a controlled laboratory setting and provides a new platform for studying wave interactions with rotating media — a regime that has been extraordinarily difficult to access experimentally. The device is compact, all-electronic, and uses no exotic materials, making it readily reproducible by other laboratories.
Source: Nasari, H., Moussa, H., Kasahara, Y. et al. “Observation of Floquet rotational super-radiance.” Nature (2026). DOI: 10.1038/s41586-026-10725-y