A bright idea that’s been around for centuries
By Tim Obermiller
To understand micro-optical technology, there’s one very important fact you need to
know: light can carry momentum. “It can hit something and have a mechanical effect,”
says Associate Professor of Physics Gabriel Spalding. “It’s not the way we normally
think of light.”
The photon particles that make up light can slam into an object, creating a billiard
ball effect, Spalding explains. Light also carries an electromagnetic field that can
influence matter. Both effects are useful.
Johannes Kepler first discovered that light has force.
In the early 1600s, the German astronomer Johannes Kepler (left) first noticed the
mechanical force of light by watching comets. Whether they were moving toward or away
from the sun, the comets’ tails always pointed away. Kepler assumed, correctly, that
sunlight caused this effect. It inspired the astronomer to write the first science-fiction
story about space travel. In it, a traveler floats to the moon on a kind of solar
sail powered by a stream of light.
“And here, in 2004, we expect to see the first solar sails launched,” Spalding notes.
However, taming the energy of light on this scale represents a “tremendous engineering
challenge,” he adds. The reason that light doesn’t exert much force in the world around
us is because “light fields are shaking so fast that most things just can’t respond.
… And so most things are just going to sit there when light is hitting them.” The
electrons within materials are the only parts which can respond quickly enough, and
the resulting forces on objects are not typically enough to overcome their weight.
However, that isn’t true on the microscopic scale, where Spalding focuses his research,
and where even the little force created by light can mean a lot.
> To return to the story on Professor Gabriel Spalding's research, click here.