Physicists have just published new calculations that suggest the controversial EM drive, or electromagnetic drive, could work, and doesn’t defy Newton’s third law after all.
In case you’ve missed the hype, here’s a quick catch-up; a lot of space lovers are freaking out about the EM drive because of claims it could get humans to Mars in just 10 weeks, but just as many are sick of hearing about it, because, on paper at least, it doesn’t work within the laws of physics.
Despite that not-insignificant setback, the EM drive shows no signs of quitting, and test after test, including trials by NASA scientists at the Eagleworks lab, and an independent researcher in Germany, has conceded that the propulsion system, somehow, does produce thrust.
Why is that so surprising? That’s because of how the EM drive is supposed to work, in theory at least.
First designed by British scientist Roger Shawyer back in 1999, the EM drive uses electromagnetic waves as fuel and creates thrust by bouncing those microwaves back and forth within a metal cavity to trigger motion.
According to Shawyer’s calculations, that could produce enough thrust to blast humans to Mars in just 70 days, and potentially even help us reach the next Solar System, Alpha Centauri, in just 92 years, all without the need for heavy, expensive rocket fuel.
That sounds pretty incredible, right? But there’s one big problem, according to Newton’s third law, everything must have an equal and opposite reaction, which means that something needs to be pushed out the back of propulsion system for it to move forwards.
You pretty quickly see the dilemma, the EM drive doesn’t use any fuel propellants, and so it doesn’t have an exhaust, and so… it can’t produce thrust.
According to their new peer-reviewed study published in AIP Advances, the EM drive doesn’t actually defy Newton’s third law, because it does produce exhaust.
According to the researchers, the exhaust being blasted out is actually light, or more specifically, photons that have become paired up with another out-of-phase photon to shoot out of the metal cavity and produce thrust.
The researchers predict that’s because photons need to become paired up to escape the fuel cavity, but the two photons in those pairs are out of phase, which means they completely cancel each other out and have no net electromagnetic field.
If you think of it as waves of water, if the crest of one wave occurs at the same time as the trough of another, they’ll cancel each other out and produce a flat patch of water, despite the fact that two waves are still passing through it.
“The EM drive operates by the same principle, for example, like a jet engine, where the high-speed exhaust gases backwards push the airplane forwards,” said, Arto Annila, one of the researchers.
“Light at microwave lengths is the fuel that’s being fed into the cavity … and the EM drive exhausts backwards paired photons,” he says.
Those escaping photons are the equal and opposite reaction that’s producing the EM drive’s thrust.
It’s not the first time photons have been used to propel spacecraft forward; it’s also the idea that Bill Nye’s solar sail is based on.
If scientists can verify that these paired photons are being pushed out the back, sh*t’s going to get real for EM drives, because it’ll help engineers design better cavities and produce even more thrust.
As exciting as that is, for Annila the space travel aspect is less interesting than the fundamental physics behind the controversial propulsion system.