In a breakthrough combining physics and robotics, researchers have developed a new way to guide microscopic swimming robots using light patterns based on Einstein’s theory of relativity. The method could eventually help deploy microrobots in fields such as medicine and manufacturing.
One of the biggest challenges in building useful microrobots is navigation. Traditional sensors and electronics are too large to fit inside machines designed to operate at microscopic scales, especially for applications like working inside the human body.
To address this problem, physicists at the University of Pennsylvania created what they call “artificial space-time”. This system allows microscopic robots to move in patterns similar to how spacecraft or light travels through the curved space of the universe.
How the tiny robots move
In the study, researchers placed 100-micron electrokinetic (EK) swimming robots—about the width of a human hair—into an ionized liquid solution. The robots were then tasked with navigating a simple maze.
Each robot was equipped with tiny solar cells and electrodes on both ends. When light hit the solar cells, they powered the electrodes, generating an electric field that pushed the robots forward through the liquid.
The key challenge was guiding the robots precisely so they could reach a specific destination without crashing into the maze walls.
Using relativity as a navigation system
The solution came from Einstein’s general relativity, which explains how gravity bends space-time around massive objects. In the universe, light and matter follow geodesics, or the shortest possible paths, which appear curved around massive bodies.
A well-known example is gravitational lensing, where light traveling across space appears bent and magnified when it passes near a massive galaxy cluster.
Lead study author Marc Miskin, an assistant professor of electrical and systems engineering at the University of Pennsylvania, explained the connection in an email to a science publication.
“We showed that the way EK robots behave in patterned light fields is identical to the paths light follows in general relativity,” he said. “Amazingly, you can use the robots as a gravity analog since the correspondence is exact. Alternatively, you can turn general relativity ideas around to use them to guide robots: in the same way gravity pulls objects together, you can guide robots to a specific spot.”
Creating artificial space-time
To recreate the effect, the researchers modelled the maze as curved virtual space using equations from relativity. In this model, the routes to the maze’s target appeared as straight paths.
The model was then converted into a 2D light map. In this system, dark areas attracted the robots, while brighter areas repelled them. The maze’s final destination acted like a faux black hole, represented by the darkest region, while obstacles appeared brighter.
No matter where they started, the EK robots naturally followed these geodesic paths, avoiding walls automatically as if they were sliding through warped space.
The research findings were published in November 2025 in the journal npj Robotics.
Future possibilities
For Miskin, the project shows how physics and robotics can work together rather than compete.
“On the one hand, relativity and light are very well understood; connecting reactive control to them invites new ways of thinking and established tools for robotics. On the other hand, general relativity and optics are also very abstract (think bending spacetime), while robotics is mechanistic and concrete (it’s very easy to understand why the robot does what it does).”
Beyond robotics, the experiments could also offer new insights into physics, especially in studying “flat space-times” in 2D environments.
Although the maze experiment is an early step, researchers believe real-world applications could appear within 10 years.
“Some use cases we’re interested in exploring include checking up on teeth following a root canal, a kind of dental biopsy to make sure everything was cleared, eliminating tumors after making local measurements to confirm cells are cancerous, or even, outside of bio, assembly of microchips with tiny robotic helpers,” Miskin said. “The microworld is a fascinating place; I wouldn’t be surprised if these ideas are just the tip of the iceberg.”
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