光具有让你想不到的特质

Think about flying and you no doubt think about air. The wind in your face, the wind at your back, the wind beneath your wings. Now physicists note that light can also give you a lift. Their work appears in the journal Nature Photonics. [Grover Swartzlander et al., "Stable Optical Lift"]

Staying aloft is a matter of dealing with pressure. In the case of a plane, it’s the difference in pressure on the top and bottom of its wings that keeps the craft afloat. But air isn’t the only way to generate pressure. Light can do the same. When photons pass through or reflect off of something, they give that object momentum. That’s why comet tails always point away from the sun. Solar radiation and wind push them that way.

So physicists got to wondering whether radiation pressure could be harnessed to help an item soar. The craft they deployed was a wing-shaped rod the size of a bacterium. They plopped this rod into a beaker of water and hit it with a laser beam from below. And found that the rod moved upward and to the side—a sign of optical lift. The finding could aid the design of solar sails for interstellar sojourns. And perhaps give new meaning to the phrase “traveling light”.

—Karen Hopkin