PHYSICS & ASTRONOMY FRIDAY || 2026.04.24
Light, however massless and ephemeral, can push and pull matter and even make objects spin. Now, researchers in Japan have shown that light can also nudge objects sideways.
In a study published in Nature Physics, a team led by scientists at Hokkaido University demonstrated a phenomenon known as transverse optical torque, a rotational effect caused by a force acting perpendicular to the direction a beam of light travels, akin to flipping or twisting.
By now adding this sideways twist to light’s toolkit, researchers may gain finer control over how they trap, rotate, and probe tiny objects, an advance that could sharpen everything from single-molecule biology experiments to the design of nanoscale devices.
Long-Predicted, Finally Observed
The notion that light can push on matter traces back to the foundations of electromagnetism. In the 1860s, James Clerk Maxwell showed through his equations that light is an electromagnetic wave carrying energy and momentum. That insight implied that light should be able to exert a physical force, a prediction later confirmed experimentally, now known as radiation pressure.
Over the twentieth century, physicists expanded this picture to include angular momentum, meaning light can also make objects spin. That capability underlies optical tweezers, which are sort of like laser beam fingers, developed in the early 1970s by Arthur Ashkin, who would be awarded the 2018 Nobel Prize in Physics at age 96.
But Maxwell’s theory goes further. Because light is a structured electromagnetic field and not just a simple beam, it can, under the right conditions, exert forces and torques sideways, perpendicular to its direction of travel. These transverse effects arise from subtle features of the light field, including weaker magnetic-field contributions that are usually too small to detect.
That is, these sideways forces are easily overwhelmed by the much stronger forward push of light, as well as by thermal noise, vibrations, and tiny imperfections in experimental systems. Even in advanced optical trapping setups, separating a faint lateral twist from dominant forces acting along the beam has proved exceedingly difficult.
The team at Hokkaido University designed an experiment to tease out this faint effect. They fabricated nanoscale structures that respond differently to specific parts of the light field, effectively making them sensitive to the weak sideways twist while minimizing the stronger forward push. Paired with an ultrasensitive system capable of detecting minute rotations, the setup allowed the researchers to isolate the transverse optical torque from the many competing forces that would otherwise obscure it.
Now that a sideways optical torque can be measured reliably, it can, in principle, be engineered. The same properties of light that determine how strongly it pushes or spins an object—for example, its polarization, intensity, or spatial structure—also govern these transverse forces.
By shaping those properties, researchers could begin to control not just how much force is applied, but in which direction and with what rotational effect. That added degree of control could extend optical manipulation beyond its current limits. Instead of simply trapping a particle or spinning it in place, scientists could more precisely orient irregular objects or guide them along more complex paths.
In effect, light could become a more dexterous tool at the nanoscale.
This could be used to rotate a single protein or strand of DNA just enough to expose a binding site, improving the precision of measurements in single-molecule experiments. In manufacturing, the same sideways twist could help align tiny components, such as nanowires or irregular particles, before they are fixed into place, reducing defects in nanoscale devices.
“This work represents a new measurement paradigm for nanoscale optomechanics,” said Yoshito Tanaka of Hokkaido University, senior author on the study, in a prepared statement. “Just as optical tweezers opened a new field in single-molecule biophysics, we hope this platform will unlock access to nanoscale mechanical phenomena that have so far remained beyond reach.”
More Information:
Journal Article (paywall): Fukuhara, R., et al., “Transverse optical torque observed at the nanoscale.” Nat. Phys. (2026). https://doi.org/10.1038/s41567-026-03268-6
Funding Source: Japan Society for the Promotion of Science (JSPS) and the Japan Science and Technology Agency (JST) FOREST Program
Related Video: “Trapping Particles In a Beam of Light—The Optical Tweezers Experiment”