Physicists Discover Surprising Properties of Light That Challenge Scientific Expectations

An international team led by researchers from the University of East Anglia (UEA) in the UK, in collaboration with South African scientists, made the discovery. Their experiments show that carefully prepared light can be controlled through its internal geometry, offering a new way to manipulate the rotation and twisting of light.

The discovery challenges long-held assumptions about how different properties of light interact. In the future, the findings could contribute to more sensitive medical tests, faster and more secure communications, and advanced quantum technologies that use light to transmit and protect information.

Why Is the Direction of Light Rotation Important?

One of the most important aspects of the discovery involves chirality, a scientific term used to describe the difference between left-handed and right-handed structures.

The human hand is a familiar example. The left and right hands are mirror images of one another, but they cannot completely overlap. Many molecules have similar properties, including compounds used in pharmaceuticals. Two versions of the same molecule can have almost identical chemical structures while producing very different effects in the body.

Scientists can distinguish between these molecular forms by studying how they interact with light that has a specific rotational behavior. Traditionally, producing and controlling this type of light has often required special materials, carefully designed surfaces, or powerful lenses that focus a beam very tightly.

This study demonstrates that properly prepared light can spontaneously develop this behavior as it travels, without the need for additional optical components.

“Our study shows that light can develop this type of behavior naturally and independently,” said Dr. Kane Forbes from UEA.

“You just have to prepare it the right way. Most people think of light as traveling in straight lines, but scientists can also create structured light—light whose brightness, shape, and direction are carefully adjusted.”

One extreme example is light that twists as it travels, forming a corkscrew shape known as a light vortex. Each twist can carry information, making this type of light valuable for high-speed internet, secure communications, and advanced sensors.

“Light can also rotate as it travels, depending on how it is polarized. This rotation can be left-handed or right-handed. It is another form of chirality.”

How Light Creates Hidden Rotations

Light can exhibit several types of rotational behavior. A light vortex has a wave pattern that twists around its direction of travel, like a corkscrew. Light also has a property called polarization, which describes how its electric field oscillates. Certain polarization patterns produce a form of rotation called spin.

Physicists have long studied the relationship between these properties. However, the interactions responsible for the newly observed effects were generally thought to be very weak and difficult to detect without specialized experimental conditions.

The researchers found that the situation changes when a light beam is prepared in a specific balanced configuration.

Under these conditions, the beam may initially have no rotation. As it passes through free space, however, distinct regions with rotational behavior appear. The effect does not require the light to pass through artificial materials or additional optical devices.

“It starts with no rotation at all,” explained Wright Mukumbuza, the master’s student who conducted the key experiment. “But as the beam moves forward, regions of rotation appear and separate, as if the rotation was hidden and then revealed.”

Rather than generating spin through external optics, the researchers demonstrated that the beam’s existing internal structure can determine where a rotating region develops during propagation.

How Topology Controls the Behavior of Light

To explain this unexpected behavior, the researchers turned to topology. This branch of mathematics examines properties that do not change when objects are continuously stretched, bent, or reshaped.

Dr. Isaac Nape of the University of the Witwatersrand in Johannesburg, South Africa, offered a simple illustration.

“Imagine a mug and a donut,” he said. “They both have a hole, so you can transform one into the other without breaking it. That hole is a topological feature.”

Researchers have discovered that structured light has unique topological properties encoded in the arrangement of its polarization.

This underlying pattern acts like a mathematical fingerprint. Although a light beam changes shape as it travels, its phase structure remains and influences how different regions of the beam evolve.

As a result, the structure of the light determines where counterclockwise and clockwise rotation patterns become visible.

The discovery gives scientists a way to guide this behavior by designing the initial structure of a beam, rather than relying on specialized materials to produce the desired effect.

“This gives us a whole new optical tuning knob. By adjusting its topology, we can determine where and how the chirality appears,” Dr. Nape said.

Potential Applications in Medicine and Communications

The ability to control light through its shape could eventually make some optical technologies simpler, more affordable, and more versatile.

One promising application involves medical diagnostics and pharmaceutical research. Many biologically important molecules have left-handed and right-handed forms, so carefully structured light could help scientists distinguish between them with greater sensitivity. Such tools could be useful when assessing drug safety and detecting biological markers associated with disease.

The same principle could support small optical sensors capable of identifying chemical and biological substances without the need for large, sophisticated laboratory equipment.

Communications technology could also benefit. By encoding information into different twist and rotation patterns, researchers could potentially increase the amount of data carried by individual rays of light. This could contribute to faster optical communications, improved information security, and future quantum networks.

Other potential applications include manipulating particles, cells, and molecules with light, as well as developing more resilient quantum systems. Topological properties may help protect sensitive quantum information from certain forms of noise and interference.

“The implications are far-reaching,” Dr. Forbes said. “This research could lead to simpler and more sensitive medical tests, especially in drug development.

“It can also be used to pack more information into laser beams, increasing data capacity for communications, including future quantum networks.

“And because this effect does not rely on fragile materials or precisely engineered surfaces, it could be easier and cheaper to use in real-world technology.

“This work could lay the foundation for a new generation of light-based technologies by showing that the behavior of light can be controlled using the light’s own internal shape,” he added.

These applications remain open to future development, but the underlying findings give researchers another way to engineer and control the behavior of light.

The Hidden Geometry of Light

For decades, scientists have relied on increasingly sophisticated optical instruments to generate and manipulate unusual forms of light. This finding suggests that some of these behaviors may arise from carefully designed structures already encoded within a light beam.

By showing how topology controls the appearance of rotating regions during propagation, the researchers uncovered an underappreciated relationship between the geometry of light and its physical behavior.

The discovery also demonstrates how much remains to be learned about something as familiar and extensively studied as light.

“Light, something so familiar, is proving to be much richer, stranger, and more powerful than anyone imagined,” Dr. Forbes said.

“And surprisingly, this new behavior has been around all along, just waiting to be discovered.”

The research, titled “Topological control of chirality and spin using structured light,” was published in Light: Science & Applications.