Scientists Slow Down the Speed of Light

For the first time ever, scientists have slowed down the speed of light as it travels through free space, helping them to better understand the properties of light, a new study says.

It has long been known that the speed of light can be delayed as it passes through materials such as water or glass, but going through free space is a different story. In fact, scientists thought it was impossible to reduce the speed of light, considering free space is by definition unimpeded by interactions with any materials.

But as described in the journal Science, a team from the University of Glasgow has managed to make the impossible, possible.

We've achieved this slowing effect with some subtle but widely-known optical principles. This finding shows unambiguously that the propagation of light can be slowed below the commonly accepted figure of 299,792,458 meters per second, even when travelling in air or vacuum," co-lead author Jacquiline Romero said in a statement.

A single pulse of light contains many photons, and each photon travels at its own velocity. During the study, the team released two photons simultaneously across identical distances towards a defined finish line. They found that one photon reached the finish line as predicted, but the other photon, to which they applied a mask to reduce its speed, arrived later.

Specifically, they successfully slowed the structured photon by up to 20 wavelengths, across a one-meter distance. This breakthrough shows that, after passing the light beam through a mask, photons can move more slowly through free space.

"The results give us a new way to think about the properties of light and we're keen to continue exploring the potential of this discovery in future applications," said lead author Miles Padgett. "We expect that the effect will be applicable to any wave theory, so a similar slowing could well be created in sound waves, for example."

For more great nature science stories and general news, please visit our sister site, Headlines and Global News (HNGN).