From Wikipedia:

EmDrive (also Relativity Drive) is a spacecraft propulsion system proposed by British aerospace engineer Roger J. Shawyer, who develops prototypes at Satellite Propulsion Research Ltd (SPR),[1] the company he created for that purpose in 2000.[2] New Scientist ran a cover story on EmDrive in its 8 September 2006 issue.[3] The device uses a magnetron producing microwaves directed inside a specially shaped, fully enclosed tapering high Q resonant cavity whose area is greater at one end, upon which radiation pressure would act differently due to a relativistic effect caused by the action of group velocity in different frames of reference. The inventor claims that the device generates a thrust even though no detectable energy leaves the device. If proven to work as claimed, the EmDrive could allow the design of spacecraft engines that would be electrically powered and would require no reaction mass. Such an engine would be a breakthrough in airflight and spaceflight.[4][5][6][7][8][9]

The device and its mode of operation are highly controversial. As of 2014, there are still arguments about whether the EmDrive is a genuinely new propulsion method, a misinterpretation of spurious effects mixed with mathematical errors, or a scam. The proposed theory immediately received virulent criticism because it seems to violate basic Newtonian laws of physics, notably conservation of momentum,[10][11] though the inventor insists on the contrary.[12] Chinese researchers from the Northwestern Polytechnic University (NWPU) in Xi'an first repeated the experiment in 2010,[7][13][14][15] then NASA in the Eagleworks Laboratories at the Johnson Space Center in 2014.[9][16]

Should the EmDrive produce a real thrust, various conjectures have been made to explain the underlying physics. Shawyer claims the thrust would be caused by radiation pressure imbalance due to group velocities of electromagnetic waves within the framework of special relativity. Dr. Yang from NWPU predicts a resulting net force using classical electromagnetism.[15] An alternative theory has been proposed in 2013 by Argentine physicist Fernando Minotti from CONICET, who explains the alleged forces on asymmetric electromagnetic resonant cavities by a particular class of scalar-tensor theory of the Brans–Dicke type.[17] Dr. Harold G. "Sonny" White, who investigates field propulsion at Eagleworks, NASA's Advanced Propulsion Physics Laboratory, notes that such resonant cavities may operate by creating a virtual plasma toroid that would realize net thrust using magnetohydrodynamics upon quantum vacuum fluctuations.[18] The named quantum vacuum based theories, however, can predict maximal efficiency of 3.33 nN/W, on the order of a millionth as much as EmDrive proponents claim.[citation needed]

Even with a known mechanism, it is still cool! This is the sort of stuff (and the Alcubierre drive) that NASA should be dinking with (if we are paying them to dink out of our taxes - I'd prefer that space effort be totally privatized), not placating the Muslim nations because they have fallen behind the tech curve.

"Impulse power only! Aye, capt'n!"

Jan

If the device emits microwaves then it produces thrust for the same reason that solar sails derive thrust from photon pressure. While photons do not exhibit rest mass they do convey energy and considering E=MC^2 they have virtual mass. As a result they follow Newtons third law. This should surprise no one.

I thought NASA was supposed to be working on global warming.

smells like Cold Fusion

Careful how much we talk about this. If we discuss it too much the government will think there is something to it and want a piece of the action. And I'm sure they will throw a few trillion $ at it to make sure it works as it should. :)

Zen, on your suggestion, I went to their site and read their papers. Read my original comment. From their site: "no transgressions of these laws have been identified. The principle of operation is based on the well-known phenomenon of radiation pressure. ... This was demonstrated by work carried out in the 1950’s. (CULLEN, A.L. ‘Absolute Power Measurements at Microwave Frequencies’ IEE Proceedings Vol 99 Part 1V 1952 P.100) ... http://emdrive.com/principle.html

It is the same principle as the laser, which itself began as an o-maser (optical maser) from the microwave amplification by stimulated emission of radiation. (Their theory paper here: http://www.emdrive.com/theorypaper9-4.pd... )

As I said, this is interesting and has potential. What I found "baloney" was the hype from Mashable. "EmDrive Is an Engine That Breaks the Laws of Physics .... since it violates the law of the conservation of momentum. ..."

The NASA paper was also interesting in that it only underscored the initial claim that the engine works with the wavefronts at relativistic velocities.
"Test results indicate that the RF resonant cavity thruster design, which is unique as an electric propulsion
device, is producing a force that is not attributable to any classical electromagnetic phenomenon and
therefore is potentially demonstrating an interaction with the quantum vacuum virtual plasma. Future test
plans include independent verification and validation at other test facilities. -- http://ntrs.nasa.gov/archive/nasa/casi.n...

"... not attributable to classical ... and therefore ... potentially ... quantum ...." I do note that the NASA test also produced an effect on the null test bed. Thus, they called it an "anomaly."

I got to look at a textbook from the dreaded "Waves and Fields" course over the weekend. That course is where engineers learn to apply classical electromagnetic theory. From what I hear, it can be a real "ball buster" if you don't have vector analysis down cold.

Anyhow, in a regular wave cavity the photons just travel in zig-zag paths. Remember the angle of incidence thing? I don't think the design has or requires the photons to bounce back and forth between the "reflectors" parallel to the line of thrust, like what happens in a laser or maser.

Also in a regular wave cavity, the photons just bounce around until they absorbed. They never escape. Even if they did, they wouldn't be going in any particular direction.

B.T.W, engineers use resonant cavities in things like tv transmitters, cell towers and radar where the power output would fry any semiconductor. But the ones they design all have uniform cross sections. Designing something that shape to resonate is really out in the weeds.

So, classical electromagnetic theory just predicts the thing will sit there and get warm.

Lastly, back to Rand and who does what in our society. It is up to the boys at S.P.R. ltd. to prove it works. It's their baby.

The Chinese say they tested the Idea and said they got it to work. That got the attention of the guys at NASA. They probably assigned their least favorite "Quentin Daniels" to go look at it and he found something he couldn't explain. Hopefully he volunteered, because I don't think that that would be a plum assignment (you could come out looking really foolish if you screw up). At least the guy says he needs to run more tests.

Wasn't Albert Einstein's Nobel Prize not for the Theory of General Relativity, but for his work on the photoelectric effect, which is in essence the fundamental concept behind this engine?

Junk science. If it had any potential at all I can tell you one thing for certain, they would NOT be releasing any images of it.
If they claim it "works" but they don't know how, then it simply doesn't work.

Dean drive: https://en.wikipedia.org/wiki/Dean_drive...

May be applicable here, maybe not, but the asinine theories about quantum mechanics are completely freaking wrong. The idea that any object can have a non-deterministic location is utterly absurd.

The scientists who founded modern science did so because they were, *gasp* Christians, and in their knowledge of the Creator, they knew that He was unchanging and utterly reliable. Therefore, they postulated that his creation may also be reliable and not based on the "whims of the gods" as was widely believed at the time.

Now, we have a whole new voodoo science called quantum physics, going back to the days where things are non-deterministic... it's stupid. I'll tell you something... God does not play dice. Einstein had it right to begin with on a lot of these things, and then just went off the deep end.

Where is John Gault?

Now this is cool with a capital C!!!

This is baloney. As described, it glides over the fact that it needs energy input. After that, yes, the microwaves (ahem) "bouncing around inside" will leave to produce some small thrust as stated. It is interesting. It could be worthwhile. Nothing is mysterious here, except as the hype attempts to make it so.