The world’s most advanced engines are remarkably compact, achieving astonishing levels of efficiency, mirroring some of nature’s tiniest machines.

A thermodynamic engine represents the most straightforward mechanism to illustrate how the laws of physics govern the conversion of heat into useful work. These engines feature areas of heat and cold interconnected by a “working fluid” that goes through cycles of contraction and expansion. Molly’s Message and James Mirren from King’s College London and their team have constructed one of the most extreme engines yet, utilizing microscopic glass beads in place of traditional working fluids.

The researchers employed electric fields to trap and position the beads in diminutive chambers crafted from metal and glass with minimal air. To operate the engine, they varied the electric field parameters to tighten and loosen the beads’ “grip.” A handful of air particles within the chamber acted as the cold section of the engine, while manipulated spikes in the electric field represented the hot section. These spikes enabled the particles to move significantly faster than the sparse air particles in their vicinity. Notably, the glass particles experienced speeds greater than what they could achieve in gas while remaining cool to the touch, despite their temperature briefly spiking to 10 million Kelvin—approximately 2,000 times the sun’s surface temperature.

This glass bead engine functioned in an atypical manner. During certain cycles, it displayed striking efficiency, as the strength of the electric field propelled the glass beads at unexpected speeds, effectively generating more energy than was inputted. However, in other cycles, the efficiency dropped to negative levels, as if the beads were being cooled in scenarios where they should have heated further. “At times, you believe you’re inputting the correct energy. You’re attempting to run the fridge with the appropriate mechanisms designed to operate the heat engine,” explains Message. The temperature of the beads fluctuated based on their location within the chamber, an unexpected outcome given that the engine was designed to maintain specific hot or cold sections.

These peculiarities can be attributed to the engine’s minuscule size. Even a single air particle colliding randomly with the beads can drastically impact the engine’s performance. Although traditional physical laws generally prevail, sporadic extreme phenomena persist. Mirren notes that a similar situation exists for the microscopic components of cells. “You can observe all these strange thermodynamic behaviors, which make sense on a bacterial or protein level, but are counterintuitive for larger entities like ourselves,” he states.

Raul Rika from the University of Granada in Spain mentions that while this new engine lacks immediate practical applications, it may deepen researchers’ understanding of natural and biological systems. It also signifies a technical breakthrough. Loïc Rondin from Paris’ Clay University asserts that the team can further investigate numerous unusual characteristics of the microscopic realm with this relatively straightforward design.

“We are significantly simplifying what will become a biological system ideal for testing various theories,” states Rondin. The team aspires to apply the engine in the future for tasks such as modeling how protein energy varies during folding.