We know that light has mass and that beaming enough light at something can push it away - solar sails that will move a craft through the cosmos are based on this idea and NASA tested that concept earlier today when it launched NanoSail-D, a nanosatellite (cubesat) which will unfold to a 100 square foot polymer sail and travel in low earth orbit for a few months.


Sails?  We don't need no stinking sails.  Credit: NASA

But research in Nature Photonics takes sails a step farther and generates actual lift using light.   A group of scientists were able to 'lift' their refractive wing-shaped object (an aerofoil, except for light, and made of rods) much like air does with airplanes, using differently shaped top and bottom surfaces.   Lift, if you don't remember your physics classes, occurs when flow in a direction produces a force in a perpendicular direction.

That isn't solar power in the sense that we think of it today, it is actual light particles at work and getting things done directly.  

How so?   

is lift as the integral of pressure forces over the surface area of the wing (not to get into that whole Bernoulli versus Newton thing in flight but, if you must, see We Can Put A Man On The Moon, But We’re Still Figuring Out How Birds Fly) as stated by our friends Kutta and Joukowski a hundred years ago and redone here for optics.   The pressure here is refraction pressure due to the difference in the refracted and reflected rays of light. 

In this case lift is being generated because the light is shining through the 'lightfoil' which refracts it and causes a change in momentum.  And the lift isn't slight.   The lift angles were 60 degrees.   “Most aerodynamic things take off at very gradual angles, but this has a very striking, very powerful lift angle,” Grover Swartzlander of the Rochester Institute of Technology in New York told Science News.   “You can imagine what would happen if your airplane took off at 60 degrees — your stomach would be in your feet.”

Don't get excited about flying one of these babies just yet.  Their lightfoils were essentially tiny rods flat on the top and curved on the bottom - and in water.  When they beamed light from the bottom of the chamber, the rods moved up but also began moving sideways, perpendicular to the light.   Spheres did not cause that effect, they said.   But they attained uniform motion of a few micrometers per second so it may go from academic exercise to applied science and get us moving on that interstellar space cruise some day - I've always been more of a flying than sailing guy.


Riding a beam of light, a tiny particle thousandths of millimeters in size is pushed sideways by the same force that keeps airplanes aloft.  Credit: Swartzlander et al.

Citation: Grover A. Swartzlander, Jr., Timothy J. Peterson, Alexandra B. Artusio-Glimpse 
and Alan D. Raisanen, 'Stable optical lift', Nature Photonics Dec 5 2010 DOI: 10.1038/NPHOTON.2010.266