New paper claims that the EM Drive doesn't defy Newton's 3rd law after all

Physicists have just published a new paper that suggests the controversial EM drive - or electromagnetic drive - could actually 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 star 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. And, 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. Even though it does.

Now that we've taken that round-trip right back to the dilemma we started with, let's present you with a potential solution, from physicists at the COMSOL company, the University of Helsinki, and the University of Jyväskylä in Finland.

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 in order to shoot out of the metal cavity and produce thrust.

The researchers predict that's because photons need to become paired up in order to escape the fuel cavity, so that 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 like waves of water, if the crest of one wave occurs at the exact 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.

That's what's happening with the photons, so, in other words, the exhaust photons become invisible from an electromagnetic point of view because they're being masked by their out-of-sync partner.

"The EM drive operates by the same principle, for example, as a jet engine, where the high speed exhaust gases backwards (opposite reaction) push the airplane forwards," one of the researchers Arto Annila, told ScienceAlert over email.

"Light at microwave lengths is the fuel that's being fed into the cavity ... and the EM drive exhausts backwards paired photons," he says. "When two photons travel together, but having opposite phases, then the pair has no net electromagnetic field, and hence it will not reflect back from the metal walls, but goes through."

And those escaping photons are the equal and opposite reaction that's producing the EM drive's thrust.

To be clear, this is just a hypothesis based on theoretical calculations. But 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.

Annila is now hoping that engineers will take on the challenge of testing for these exhaust photon pairs in order to test whether their hypothesis holds up.

And that's going to be a challenge in itself, because without an electromagnetic signature, researchers are going to have to detect them by looking for "excess energy density above the surrounding background density of the gravitational field," Annila explained. That requires a device called an interferometer - not dissimilar to the ones that detect gravitational waves.

But if scientists can verify that these paired photons really 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.

"If our proposal is found worthy then EM drive research is no longer questioned but propelled," said Annila.

But as exciting as that is, for Annila the space travel aspect is less interesting than the fundamental physics behind the controversial propulsion system.

"In history often curious phenomena and perplexing observations have opened up a whole new paradigm," he says. Maybe this time, it'll open up a whole new pathway to the Universe. Watch this space.

Bill Nye's solar sail?

I read Arthur C. Clarke's story in Boys Life in 1964!

"Sunjammer" is a science fiction short story by Arthur C. Clarke, originally published in 1963, and included in the March 1964 issue of Boys' Life.

(from Wikipedia)

History of conceptP> Johannes Kepler observed that comet tails point away from the Sun and suggested that the Sun caused the effect. In a letter to Galileo in 1610, he wrote, "Provide ships or sails adapted to the heavenly breezes, and there will be some who will brave even that void." He might have had the comet tail phenomenon in mind when he wrote those words, although his publications on comet tails came several years later.[3]

James Clerk Maxwell, in 1861–64, published his theory of electromagnetic fields and radiation, which shows that light has momentum and thus can exert pressure on objects. Maxwell's equations provide the theoretical foundation for sailing with light pressure. So by 1864, the physics community and beyond knew sunlight carried momentum that would exert a pressure on objects.

Jules Verne, in From the Earth to the Moon,[4] published in 1865, wrote "there will some day appear velocities far greater than these [of the planets and the projectile], of which light or electricity will probably be the mechanical agent ... we shall one day travel to the moon, the planets, and the stars."[5] This is possibly the first published recognition that light could move ships through space.

Pyotr Lebedev was first to successfully demonstrate light pressure, which he did in 1899 with a torsional balance;[6] Ernest Nichols and Gordon Hull conducted a similar independent experiment in 1901 using a Nichols radiometer.[7]

Albert Einstein provided a different formalism by his recognizing the equivalence of mass and energy. He simply wrote p = E/c as the relationship between the momentum, the energy, and the speed of light.

Svante Arrhenius predicted in 1908 the possibility of solar radiation pressure distributing life spores across interstellar distances, providing one means to explain the concept of panspermia. He apparently was the first scientist to state that light could move objects between stars.[8]

Friedrich Zander (Tsander) published a technical paper in 1925 that included technical analysis of solar sailing. Zander wrote of "using tremendous mirrors of very thin sheets" and "using the pressure of sunlight to attain cosmic velocities".[9]

Konstantin Tsiolkovsky first proposed using the pressure of sunlight to propel spacecraft through space and suggested, "using tremendous mirrors of very thin sheets to utilize the pressure of sunlight to attain cosmic velocities".[10]

JBS Haldane speculated in 1927 about the invention of tubular spaceships that would take humanity to space and how "wings of metallic foil of a square kilometre or more in area are spread out to catch the Sun's radiation pressure".[11]

J.D. Bernal wrote in 1929, "A form of space sailing might be developed which used the repulsive effect of the Sun's rays instead of wind. A space vessel spreading its large, metallic wings, acres in extent, to the full, might be blown to the limit of Neptune's orbit. Then, to increase its speed, it would tack, close-hauled, down the gravitational field, spreading full sail again as it rushed past the Sun."[12]

The first formal technology and design effort for a solar sail began in 1976 at Jet Propulsion Laboratory for a proposed mission to rendezvous with Halley's Comet.[2]

Thanks 2ndDivisionVet.

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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 star system, Alpha Centauri, in just 92 years, all without the need for heavy, expensive rocket fuel. ... the EM drive doesn't use any fuel propellants, and so it doesn't have an exhaust, and so... it can't produce thrust. Even though it does... a potential solution, from physicists at the COMSOL company, the University of Helsinki, and the University of Jyväskylä in Finland... the EM drive doesn't actually defy Newton's third law, because it does produce exhaust... more specifically, photons that have become paired up with another out-of-phase photon in order to shoot out of the metal cavity and produce thrust... because photons need to become paired up in order to escape the fuel cavity, so that the two photons in those pairs are out of phase, which means they completely cancel each other out and have no net electromagnetic field.

So, while I was thinking all this over, a clown car pulled up, and a midget in a raggedy andy wig jumped out, set up stepladder, and another midget dressed just like him climbed up the ladder and smashed a pie in my face.

Then they got back in the clown car and made their getaway.

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