Scientists have built the world’s smallest engine. It’s also the world’s hottest. It consists of a single microscopic particle, smaller than a human cell, levitating in a vacuum. By exposing this little particle to noisy electrical fields, a team from King’s College London (KCL) has heated it to an astonishing 10 million degrees Celsius - way hotter than the sun’s surface. The engine won’t power a tiny vehicle, but the team believes their platform could provide an unparalleled understanding of the laws of thermodynamics on a small scale, and provide the foundation for a new, efficient way to compute how proteins fold, the focus of last year’s Nobel Prize in Chemistry.
A noisy voltage
To build this engine, the researchers used a device called a quadrupole ion trap, or Paul Trap. This machine uses oscillating electrical fields to trap a single, charged microparticle, levitating it in a near vacuum. The setup isolates the particle from its surroundings. The team then exponentially increased its heat by applying a noisy random voltage to the electrodes holding the particle in place. This noise violently jiggles the particle, causing it to move and generate a huge amount of heat. A noisy voltage is a random, unwanted fluctuation in voltage within an electronic circuit that deviates from the desired, steady voltage.
Hot and random
The experiment is the first of its kind to raise temperatures to such a high level on such a small scale. Engines are normally associated with motors, but in science their definition is simpler, they convert one form of energy to mechanical energy. The team’s Paul Trap is an engine under its most basic definition, converting heat to movement.
However, the team also found that their engine often contradicted the basic laws of thermodynamics and its behaviour wasn’t predictable. For any given engine run, the particle’s behaviour was sometimes random. When exposed to warmer temperatures, the system would sometimes cool down as opposed to heating up, in a direct contradiction of what they expected. In a paper published in the journal, Physical Review Letters, the team explains that this is due to the normally undetectable random influence of thermal fluctuations in the surrounding environment affecting dynamics in a way that is unique to the microscale and below. Studying these microscale variations could help the team better understand thermodynamics as a whole.
A microcosm of the wider universe
Molly Message, a PhD student at the Department of Physics at KCL and first author of the paper, explains: “Engines and the types of energy transfer that occur within them are a microcosm of the wider universe. Studying the steam engine brought about the field thermodynamics, which in turn revealed some of the fundamental laws of physics. The study of engines in new regimes could expand our understanding of the universe and the processes that drive its development. By getting to grips with thermodynamics at this unintuitive level, we can design better engines in the future, and experiments that challenge our understanding of nature.”
An engine to understand proteins
Proteins are the engines that power important processes in our body, so understanding their mechanics and what can go wrong, is vital to understanding disease and how it can be treated. The team hopes their platform can also be used to predict how proteins fold and assemble themselves.
Life operates at the microscopic scale. The molecular machines inside our cells are single-particle engines that exist with thermal noise. The team’s particle engine could act as an analogue computer to model protein folding. Proteins are long chains of amino acids that must fold into complex 3D shapes to function. Misfolding can cause clumping, leading to devastating disease. Predicting this process remains one of science’s toughest challenges. Google’s DeepMind achieved a breakthrough with AlphaFold, which predicts a protein’s final shape from its amino acid sequence. However, it can’t show the folding pathway, or the process itself, which is key to understanding misfolding.
Digital supercomputers struggle to simulate protein folding, because they must calculate billions of nanosecond-scale atomic movements. The KCL engine solves this by acting as an analogue computer, physically simulating the process. A levitating particle represents the protein, while tuned electrical fields mimic random thermal forces, allowing direct observation of folding. “By just observing how the microparticle moves and working out equations based on that, we avoid this problem entirely,” explains team member, Dr Jonathan Pritchett. The Paul Trap could thus offer a simpler, more physical route to decoding life’s molecular machinery. Like the steam engines that sparked the Industrial Revolution and modern physics, this microscopic engine might push us to the next frontier, where chaos isn’t a bug in the system, but the system itself.
For more information contact King’s College London,
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