While the country song by this title refers to tractors in an agricultural context, the tractor beam is actually a theoretical physics concept. This beam is said to draw particles toward its source instead of pushing them away. Since the theoretical existence of such a sci-fi-style beam was first proposed a few years back, most physicists have come to accept the concept, and many have been trying to prove its existence ever since.
Now researchers in the Czech Republic have built the first working example of this technology. Not only did their real-life tractor beam attract polystyrene particles, but the researchers were surprised to find it could also sort them.
To deflect an asteroid, paint it white. That’s the idea that made MIT graduate student Sung Wook Paek the winner of the 2012 Move An Asteroid Competition, a contest set up by the United Nations’ Space Generation Advisory Council that sought innovative ways to deflect asteroids. Paek’s plan is to hurl pellets of white paint at an asteroid in order to make it more reflective, meaning that more photons, or particles of light, would bounce off it, rather than being absorbed. Over time, the force of those photonic collisions, combined with the initial force of the paintballs, would be enough, Paek thinks, to move the asteroid off its path toward Earth.
The Raman spectrometer emits a laser beam.
What’s the News: Using a laser, a super-strong telescope, and some physics know-how, researchers say they have impressive power to look through solid barriers. Scientists have developed a technique to do so using Raman scattering, which is the change in energy of photons bouncing off a material. The technique could be used to detect hidden explosives or do geological analysis.
Light is pushy. The physical pressure of photons is what allows for solar sail space missions that ride on sunlight, and what allows for dreams of lasers that will push those sails even faster. And light can trap objects, too: Optical tweezers can hold tiny objects in place. Pulling an object with light, however, is another matter. Though it’s counter-intuitive to think you could create backward-tugging force with a forward propagating laser and create a real-life tractor beam, the authors of a new physics paper write that they have shown a way it could be done.
Jun Chen’s research team says that the key is to use not a regular laser beam, but instead what’s called a Bessel beam. Viewed head-on, a Bessel beam looks like one intense point surrounded by concentric circles—what you might see when you toss a stone into a lake. The central point in a Bessel beam suffers much less diffraction than a standard laser, and so scientists can use them for precision operations like punching a hole in a cell.
If such a Bessel beam were to encounter an object not head-on but at a glancing angle, the backward force can be stimulated. As the atoms or molecules of the target absorb and re-radiate the incoming light, the fraction re-radiated forward along the beam direction can interfere and give the object a “push” back toward the source. [BBC News]
The anti-laser—a tech with such a cool name it doesn’t need an obvious application—first came to our attention last year when Yale’s A. Douglas Stone proposed the idea. Now Stone is back with the real thing. His new paper in Science documents the world’s first anti-laser.
Conventional lasers create intense beams of light by stimulating atoms to spit out a coherent beam of light in which all the light waves march in lockstep. The crests of one wave match the crests of all the others, and troughs match up with troughs. The anti-laser does the reverse: Two perfect beams of laser light go in, and are completely absorbed. [Wired]
Anti-lasers are a bit of a funny concept, because anybody who has worn black on an August afternoon knows that absorbing light and turning it into heat isn’t a problem. But creating a device that matches the concentrated beam of a laser and traps more than 99 percent of it—essentially reversing a laser—is an engineering feat.
Whereas a laser uses mirrors to bounce light back and forth through an amplifying material to concentrate it, the anti-laser, as the name would suggest, does basically the opposite.