Physicists Twist Light and Slow it Down

While attempts to travel at or faster than the speed of light are the glamorous experiments that get all of the attention as well as generate the most fears of breaking natural laws, slowing down the speed of light is just as exciting and almost as capable of breaking laws that could end life as we know it. Physicists have recently demonstrated how to slow light down by twisting it in a new way. They also speculate that light may be slower than we thought. Uh-oh.

As fans of Einstein know, the speed of light is 299,792,458 meters per second (186,000 miles per second) and is constant in a vacuum. Dr. Nathaniel Hermosa II and student Nestor D. Bareza, Jr. performed research at the University of Philippines' National Institute of Physics using beams of light called Laguerre-Gauss (LG) beams. LG beams are known to rotate or twist, a phenomena known as orbital angular momentum (OAM). Physicists say LG beams would look like a corkscrew if you could slow them down to see them. That’s what Hermosa and Bareza did, according to their paper published in Scientific Reports.

The researchers knew that LG beams have unique OAMs and travel in a helical (helix) path with transverse (crosswise) waves consisting of both radial and azimuthal (perpendicular) components. They found that they could adjust the angles of the twisting waves without interfering with them and that those new twists added a path in the propagation of the LG beam that slowed it down.

Did they change the speed of light? Technically, they changed its path so the beam took longer to get to its destination. This is still important because it shows that modes of light do not travel with the speed of light even in a vacuum. For computer communications and data transmission, this means information can be slowed by twisting its transportation medium (light), resulting in some information arriving at different times than others.

Did they break a natural law? Well, we’re still here. One theory is that we don’t know as much about light as we think we do. Just a few weeks ago, another group also experimenting with angular momentum discovered a new form of light.

What else is there to discover about light? Who knows? Let there be light experiments!