Technically speaking, an engine is a device that converts some form of energy into mechanical energy. Taking that definition to heart, physicists harnessed the strange rules of microscopic physics and created the hottest engine ever—which also happens to be the smallest engine ever made.

In a forthcoming paper for Physical Review Letters, researchers describe a tiny engine crammed inside a microscopic particle trapped in electrical limbo. Using this setup, the engine reportedly achieved a temperature of 10 million Kelvins, or about 18 million degrees Fahrenheit—colder than the Sun’s core (27 million degrees F) but much hotter than the corona (up to 3.5 million degrees F).

“By getting to grips with thermodynamics at this unintuitive level, we can design better engines in the future and experiments which challenge our understanding of nature,” Molly Message, study lead author and a PhD student at King’s College London (KCL) in the United Kingdom, said in a statement.

Rules get funky in the microscopic world

In the engine, electrodes trap and levitate the microparticle in a near-vacuum setup called a Paul trap. When the researchers applied a noisy voltage to the electrodes, the particle started to aggressively jiggle, causing exponential increases in temperature for the overall system.

The results were intriguing. According to the researchers, the engine fluctuated between being highly efficient and outright defying the basic laws of thermodynamics. In some cycles, the engine’s power output exceeded the energy it consumed.

Other times, the engine randomly cooled down when subjected to conditions that should have made it hotter. This was likely on account of unseen forces at play, given the tiny size of the system, the researchers noted.

“We can see all these odd thermodynamic behaviors, which are totally intuitive if you’re a bacterium or a protein, but just unintuitive if you’re a big lump of meat like us,” explained James Millen, study senior author and a physicist at KCL, to New Scientist.

Future applications?

Due to the engine’s small size, it probably won’t end up in cars or household appliances, at least not any time soon. Instead, the researchers envision more theoretical applications for their small powerhouse. For instance, the trap is ideal for simulating other microscopic phenomena, such as how proteins fold inside our body, driving various metabolic processes.

“Proteins fold over milliseconds, but the atoms [that] make them move over nanoseconds,” explained Jonathan Pritchett, study co-author and a postdoctoral researcher at KCL, in the statement. “These divergent timescales make it very difficult for a computer to model them. By just observing how the microparticle moves and working out a series of equations based on that, we avoid this problem entirely.”

That’s just one example of many, the researchers added. As the engine demonstrates, the physics of the microscopic world work in mysterious ways—mysteries that perhaps require microscopic tools to solve.