Scientists Figured Out a Way to Cheat Newton's Third Law

Ever since the late 17th century, it's been understood that to every action there is an equal and opposite reaction. That's Newton's Third Law of Motion. But a group of German scientists recently came up with a trick that appears to break that law, one that lets light accelerate all by itself. And it could bring us faster electronics in the process.

This is not a simple trick. It involves fiddling with the mass of photons, particles that are believed not to have a mass at all, and requires a form of negative mass, a state that scientists believe does not exist. That's the trick part. And that's also why it merely appears to break Newton's third law. All that said, it's pretty impressive.

What these German scientists basically did is create an optical diametric drive. The basic principle behind a diametric drive calls for an object with positive mass to collide with an object with negative mass causing both to accelerate forever in the same direction. In the 1990s NASA tried and failed to build one, because it would make an awesome spaceship engine. However—and that's a big however—diametric drives are difficult to build because there's no such thing as an object with negative mass, at least not one that scientists have observed.

Bear with me here. To get around these basic rules of physics and quantum mechanics, our friends the German scientists used photons to create something called effective mass. This is what a particle seems to have when it's responding to forces, and there is such a thing as negative effective mass. So the scientists sent a series of laser pulses through a two loops of fiber-optic cable—one bigger than the other—that connect at a contact point. As the pulses are traveling through the different-sized loops at slightly different times, they share photons creating an interference that gives them effective mass, some positive and some negative. In this so-called optical diametric drive, the pulses accelerate in the same direction. Cool, huh? Complicated, but cool.

Needless to say, the idea of laser pulses that accelerate continuously bears big implications for anything that uses fiber optic cables. This method could make computers, communications networks, and so forth to get faster and more powerful. Just remember that it's a highly experimental new technology; it's going to take a while before this makes your iPhone better. [Nature Physics via New Scientist]