British Columbia

Researchers tuned in to the sound of light during 3-year momentum study

A team of researchers has come a little closer to solving the mystery of how light exerts force on matter, which has been puzzling scientists for hundreds of years.

Experiments into how light exerts force on matter could benefit technology such as solar sails

Kenneth Chau of UBC Kelowna was part of the team that studied how light's momentum affects matter. (UBC Okanagan)

A team of researchers has come a little closer to solving the mystery of how light exerts force on matter, which has been puzzling scientists for hundreds of years. 

A team including Kenneth Chau, an associate professor of engineering at the University of British Columbia's Kelowna campus, recently published a three-year study on the topic, which involved tuning in to the sound of light.

"In addition to being an exciting basic discovery about something that surrounds all of us on a day-to-day basis … there are some neat applications this could lead to," Chau told Daybreak South host Chris Walker.

The new research has implications for solar sail-powered spacecrafts, which are propelled by radiation pressure, and other technology, according to the study. 

It's all in the momentum

Chau's research team studied the momentum carried by light.

They attached an acoustic sensor to a special mirror, then shot laser beams into the mirror. The researchers used the sensors to listen to the waves created as light hit the surface of the mirror, according to the study. 

"From recording these sound waves, we were able to trace the features back to the momentum of light itself," Chau said.

Before this experiment, scientists were only able to measure how light transfers momentum to an object as a whole, Chau told the CBC. These new experiments, however, allowed the researchers to see exactly how force is distributed throughout the matter. 

People can feel the warmth of the sun, which proves light carries energy, Chau explained — but now, for the first time, researchers actually heard the light bumping into the matter. 

"We definitely cannot feel the force light exerts, but it's there," said Chau. He said that light's sound waves are minute — comparable to just a few atoms — and therefore hard to measure.

Kenneth Chau in his lab, holding a lightweight sheet of reflective gold — much like a solar sail that could be used to power spacecraft. The technology could benefit from Chau's team's experiments on light momentum. (UBC Okanagan)

Reinforcing Einstein's work 

These new experiments reinforce the work of physicists such as Albert Einstein, Chau said. 

"Because light has energy it also must have some mass. And that's why the effects of momentum are really hard to observe and require really careful experimentation," he said.

There is still much more to discover about light, Chau said.

"If we improve the quality of our signal even further, there's potential to gain even greater insights about how momentum exists inside matter, and uncover more secrets about light and how we can use it."

Listen to the full interview:

With files from Daybreak South

Read more from CBC British Columbia

About the Author

Laura Sciarpelletti

Associate Producer

Laura is a journalist for CBC Vancouver. Some of her previous work has appeared in The Globe and Mail, VICE Canada, The Georgia Straight and The Tyee. Follow Laura on Twitter: @MeLaura. Send her news tips at