International Business Times writes:
A new peer-reviewed paper (open, DOI: 10.1063/1.4953807) on the EmDrive from Finland states that the controversial electromagnetic space propulsion technology does work due to microwaves fed into the device converting into photons that leak out of the closed cavity, producing an exhaust.
So how could something come out that you can't detect? Well, the photons bounce back and forth inside the metal cavity, and some of them end up going together in the same direction with the same speed, but they are 180 degrees out of phase. Invariably, when travelling together in this out-of-phase configuration, they cancel each other's electromagnetic field out completely.
That's the same as water waves travelling together so that the crest of one wave is exactly at the trough of the other and cancelling each other out. The water does not go away, it's still there, in the same way the pairs of photons are still there and carrying momentum even though you can't see them as light.
If you don't have electromagnetic properties on the waves as they have cancelled each other out, then they don't reflect from the cavity walls anymore. Instead they leak out of the cavity. So we have an exhaust – the photons are leaking out pair-wise.
Related Stories
After months of speculation and leaked documents, NASA's long-awaited EM Drive paper has finally been peer-reviewed and published [open, DOI: 10.2514/1.B36120] [DX]. And it shows that the 'impossible' propulsion system really does appear to work. The NASA Eagleworks Laboratory team even put forward a hypothesis for how the EM Drive could produce thrust – something that seems impossible according to our current understanding of the laws of physics.
In case you've missed the hype, the EM Drive, or Electromagnetic Drive, is a propulsion system first proposed by British inventor Roger Shawyer back in 1999. Instead of using heavy, inefficient rocket fuel, it bounces microwaves back and forth inside a cone-shaped metal cavity to generate thrust. According to Shawyer's calculations, the EM Drive could be so efficient that it could power us to Mars in just 70 days.
takyon: Some have previously dismissed EmDrive as a photon rocket. This is addressed in the paper along with other possible sources of error:
The eighth [error:] photon rocket force, RF leakage from test article generating a net force due to photon emission. The performance of a photon rocket is several orders of magnitude lower than the observed thrust. Further, as noted in the above discussion on RF interaction, all leaking fields are managed closely to result in a high quality RF resonance system. This is not a viable source of the observed thrust.
[...] The 1.2 mN/kW performance parameter is over two orders of magnitude higher than other forms of "zero-propellant" propulsion, such as light sails, laser propulsion, and photon rockets having thrust-to-power levels in the 3.33–6.67 μN/kW (or 0.0033–0.0067 mN/kW) range.
Previously: NASA Validates "Impossible" Space Drive's Thrust
"Reactionless" Thruster Tested Again, This Time in a Vacuum
Explanation may be on the way for the "Impossible" EmDrive
Finnish Physicist Says EmDrive Device Does Have an Exhaust
EmDrive Peer-Reviewed Paper Coming in December; Theseus Planning a Cannae Thruster Cubesat
The man behind the disputed thruster technology EmDrive has published a presentation detailing the third generation of the device. Roger Shawyer envisions EmDrive 3.0 enabling personal flying vehicles and a "space elevator without cables":
[Although] the second generation of the EmDrive can theoretically produce 3 tonnes of thrust for 1 kilowatt of power, it isn't able to move very far, so it is only useful for marine applications or for diverting asteroids, like in the new CBS sci-fi TV drama Salvation.
Shawyer has long said that his aim for inventing the EmDrive was to help get satellites into space cheaply, to enable more applications and new ways for the human race to combat global warming and the energy crisis. Essentially, the EmDrive needs to be able to move and work as well as a conventional rocket, in order to be a viable solution.
To negate these shortfalls, Shawyer's firm Satellite Propulsion Research Ltd (SPR) has also been researching a third generation of the EmDrive, which solved the acceleration problem by reducing the specific thrust.
So instead of getting 3 tonnes of thrust for every kilowatt, substantially less thrust is produced – but it can be used to accelerate the device (more about this theory can be read in a paper Shawyer presented in Beijing in 2013).
Speaking of that TV show, Roger would like some credit please.
Related UK patent application. Also at Next Big Future.
Previously: Finnish Physicist Says EmDrive Device Does Have an Exhaust
It's Official: NASA's Peer-Reviewed EmDrive Paper Has Finally Been Published
Space Race 2.0: China May Already be Testing an EmDrive in Orbit
Physicist Uses "Quantised Inertia" to Explain Both EmDrive and Galaxy Rotation
(Score: 3, Funny) by Anonymous Coward on Friday June 17 2016, @12:49AM
Space drive relies on conservation of momentum. Your space thingamajiggi shoots things backward, it moves forward, that way conservation of momentum is maintained.
So, this "emDrive" thing, somehow push the craft forward without shooting stuff back, so people are saying that's bullshit. Now this Fin dude is saying it does shoot things back, hence its forward propulsion.
Ok, carry on.
(Score: 0) by Anonymous Coward on Friday June 17 2016, @01:13AM
EmDrive is legit.
(Score: 0) by Anonymous Coward on Friday June 17 2016, @01:23AM
That probably works better for liberal arts majors.
(Score: 3, Interesting) by Immerman on Friday June 17 2016, @01:50AM
Except his explanation doesn't hold water - if it were generating thrust on par with a photon rocket nobody would care about it. Photon rockets are well understood, and too weak to be useful for much. What makes the EmDrive interesting is that it seemingly has a thrust-to-power ratio orders of magnitude greater than is possible with a photon rocket.
(Score: 0) by Anonymous Coward on Friday June 17 2016, @02:15AM
It's a resonant photon rocket.
(Score: 3, Interesting) by Immerman on Friday June 17 2016, @04:15AM
That wouldn't change anything. Every erg of energy generates X photons with Y momentum. You can do all the fancy bouncing and resonating you want, but so long as conservation of momentum holds, when the photons finally exit the device they will depart with Y momentum, and the device will gain Y momentum in the opposite direction.
(Score: 0) by Anonymous Coward on Friday June 17 2016, @07:59AM
Immerman, you are blowing everyone's "liberal arts" paradigm with your physics and logic and sciency stuff. Please stop.
(Score: 2) by Immerman on Friday June 17 2016, @03:03PM
Hey, if you can't take the math, get out of the science discussion :-D
(Score: 1) by Prune on Saturday June 18 2016, @02:16AM
Wow! Brilliant! You sure showed all those physicist peer reviewers of this paper how stupid they are to not have found such a basic flaw and rejected the paper! Ah, it's good to know that Soylent's own Immerman is here to vet the work of these ignorant scientists — I can now sleep at night!
(Score: 2) by Immerman on Saturday June 18 2016, @05:36PM
Hey, when has intelligence ever been a defense against your own stupidity?
Fact: Shawyers initial claims were that he generated 0.016N with 850W, or about 20uN/W
Fact: Nasa's tests found about 1/1000th the thrust, about 20nN/W
Fact: the theoretical upper limit for a perfectly collimated photon drive is about 2nN/W
So, even if this thing is in fact emitting photons in some new and interesting, virtually undetectable manner, which just happen to be perfectly collimated... it's still 10 times too weak to explain the even the weakest thrust we've measured. Maybe it actually does produce an exhaust in this manner, and the idea is certainly interesting, worthy of discussion, and may have serious implications both in other fields and in the practical considerations for EmDrive (if the EmDrive is proven to work).
It's just not a candidate to explain the thrust that's been measured.
(Score: 3, Interesting) by jmorris on Friday June 17 2016, @12:53AM
How hard would it be to just install one on the ISS, turn it on and see if it produces thrust in space? ISS has the electrical capacity, we know the device doesn't explode or do anything dangerous. Run it a week and it should produce a tiny but measurable change in the station's orbit.
If it works we can worry about discovering the theory behind it and refining it to be more efficient and if it doesn't we can stop dreaming about an electric rocket engine.
(Score: 1, Interesting) by Anonymous Coward on Friday June 17 2016, @01:00AM
The ISS is still bound to it's orbital gravity, and slightly to the very thin atmosphere still present at that altitude. It would be better tested in deep space.
(Score: 3, Interesting) by jmorris on Friday June 17 2016, @01:15AM
Building a full space probe complete with solar array large enough to drive and launching it beyond LEO is a lot more expensive than just sticking the drive on the ISS. The orbit of the ISS is well understood so any force shifting it, even a fairly small one, would be easy to spot. Remember the whole point of this gadget is that it can deliver a small but continuous thrust without consuming fuel. A small thrust adds up if it can be sustained for days. All they would need is the weight allowance on a supply mission and a single EVA to bolt the thing to the station and connect it to power.
(Score: 2) by Immerman on Friday June 17 2016, @01:54AM
Why do an EVA? If it's real it should generate the same thrust if you just bolt it to an inside wall.
(Score: 3, Insightful) by deimtee on Friday June 17 2016, @02:00AM
Just in case it really is emitting kilowatts of microwaves maybe? If I was on the station, I think I would prefer it to be outside.
If you cough while drinking cheap red wine it really cleans out your sinuses.
(Score: 2) by tangomargarine on Friday June 17 2016, @02:42PM
Are the walls of the ISS thick enough to protect from that anyway?
"Is that really true?" "I just spent the last hour telling you to think for yourself! Didn't you hear anything I said?"
(Score: 2) by Immerman on Friday June 17 2016, @03:11PM
Should be - microwaves are normally reflected by even a thin sheet of metal (like the mesh on the front of your microwave oven). The only real question is how question would be just how perfectly canceled any emitted photon pairs are. If they're perfectly aligned, then for most practical purposes they cease to exist and it's not a problem. If however they're only *almost* perfect you'll get interference patterns around the device. Not really sure how shielding would effect that... I think all the normal formulas assume that you're dealing with each photon individually, when pairs start effectively popping in and out of existence.... I wouldn't know where to start.
(Score: 0) by Anonymous Coward on Friday June 17 2016, @02:22AM
But that would fail to prove that EmDrive is not somehow dependent on gravity of larger object or some other property, like radio waves etc that are present in and near Earth's Orbit.
(Score: 3, Interesting) by Dunbal on Friday June 17 2016, @02:02AM
Nah, you put it on the end of a boom. Angular momentum doesn't care all that much about the gravitational field and the boom will magnify the torque you get. If you start getting rotation you know it works.
(Score: -1, Troll) by Anonymous Coward on Friday June 17 2016, @02:07PM
They've done that, and it's spun the stuff.
...
...
NIGGER!
(Score: 2) by takyon on Friday June 17 2016, @01:22AM
If it has a strong enough thrust to be measured reliably, it doesn't need to be tested in space.
The creator of the Emdrive has hinted at domestic applications of emdrive and thrust good enough to counteract Earth gravity (yup, Back to the Future 2 style flying cars, and probably bullshit). But there is no need to send an emdrive in space in order to determine if it can compete with ion drives. If it works, it will be very obvious. The Chinese teams testing emdrive have reported higher thrusts than NASA, the creator of emdrive is hiding behind trade secrets, so perhaps the problem is not the concept but the specific design and small budget that NASA scientists have to work with.
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(Score: 2) by jmorris on Friday June 17 2016, @02:25AM
Those high thrust figures are for a proposed version built with superconductors. To date the trusts have been small enough for reasonable people to suspect it is measurement error or side effects like the heat generating drafts of air, magnetic fields attractingt the test stand, etc. If the thing were levitating in mid air I doubt there would be any debate about whether it worked.
(Score: 3, Funny) by RamiK on Friday June 17 2016, @02:31AM
Here's the thing: Since the Higgs, all the theoretical physicists broke down and started mumbling about simulations and the matrix and AIs taking over the world...
Now, you drop this EmDrive gizmo that shows tests with results they just can't explain... Are you trying to get them all committed? Have some heart man.
compiling...
(Score: 2) by fritsd on Friday June 17 2016, @02:31PM
They were going to do that with the experimental VASIMR [wikipedia.org] drive, but I think they forgot..
(Score: 0) by Anonymous Coward on Friday June 17 2016, @05:03PM
YES, install on ISS and push it to Mars!! Big mobile warehouse.
(Score: 0) by Anonymous Coward on Friday June 17 2016, @01:04AM
So it squirts out photon pairs in all directions, but a bit more in one.
Doesn't sound like a very efficient engine.
The article is an easy read. Wish the climate folks were so gifted.
(Score: 3, Informative) by takyon on Friday June 17 2016, @01:26AM
There's a figure for efficiency: Newtons per Watt. If the thing works, it will become clear if it can compete with state-of-the-art ion drives like VASIMR [wikipedia.org].
Newtons per Watt isn't necessarily the whole story since emdrive also has the advantage of being "propellantless" (assuming it works). But I have heard talk about emdrive reaching anywhere from 4 times to hundreds of times the Newtons per Watt of ion drives, which would make a clear difference.
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(Score: 1, Interesting) by Anonymous Coward on Friday June 17 2016, @01:56AM
Adding-
there all different types of efficiency from volumetric efficiency, fuel efficiency, etc. (at least as applied to IC engines).
Depending on what this drive brings to the table (weight, output, reliability, fuel use), it could be a huge win even if it has low output.
(Score: 0) by Anonymous Coward on Friday June 17 2016, @12:06PM
While ion drives are electric, they still use propellant, usually Xenon. The electricity is used to accelerate the propellant out the exhaust. When the tank is empty, the engine is useless.
The interesting thing about this, is that it's electric only. No propellant. And electricity can be "refueled" on the fly with solar panels. That means that - if it works - it can run forever.
While getting into orbit takes huge rockets, due to air resistance, once you are in orbit, the size of the rocket doesn't matter. What matters is thrust multiplied by time. Think about how an engine that can run forever affects the result of that calculation.
(Score: 0) by Anonymous Coward on Friday June 17 2016, @02:10PM
>That means that - if it works - it can run forever.
Like fucking hitler.
Fucking Nazi.
(Score: 2) by takyon on Friday June 17 2016, @04:23PM
Yes... I noted that it was propellantless in the comment.
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(Score: 0) by Anonymous Coward on Friday June 17 2016, @01:33AM
Everybody knows gravitic drive is the best, and you can recycle its exhaust to power your antigrav deck plating.
(Score: 1, Funny) by Anonymous Coward on Friday June 17 2016, @01:51AM
....undetectable paired photons ...have mass-energy ... can't see them ... ... Holy Shit Batman, I've discovered Dark Energy.
Massive amounts of aliens are zooming around the cosmos on EmDrives and have filled it up with paired photons.
Where do I go to get my Nobel?
(Score: 3, Funny) by takyon on Friday June 17 2016, @01:57AM
You have to stick your head inside the RF resonant cavity thruster.
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(Score: 0) by Anonymous Coward on Friday June 17 2016, @05:07PM
There's a really weird echo in here. But I still can't see my Nobel.
(Score: 2) by takyon on Friday June 17 2016, @05:28PM
I guess we forgot to turn on the device *flip* aaaaaaarrrgggggggg
[SIG] 10/28/2017: Soylent Upgrade v14 [soylentnews.org]
(Score: 2) by DECbot on Friday June 17 2016, @07:24PM
Because it's dark. A dark Nobel.
cats~$ sudo chown -R us /home/base
(Score: 3, Interesting) by deimtee on Friday June 17 2016, @01:57AM
Wouldn't mean that you could get just as much thrust by using the same electric power to run a MASER? If the EmDrive is getting more thrust than a MASER would, then there is still some unexplained physics going on.
If you cough while drinking cheap red wine it really cleans out your sinuses.
(Score: 0) by Anonymous Coward on Friday June 17 2016, @02:23AM
What seems to be going on is phased photons provide more thrust just like laser beams are more coherent than flashlight beams.
(Score: 0) by Anonymous Coward on Friday June 17 2016, @02:32AM
That would violate conservation of momentum, so no.
(Score: 0) by Anonymous Coward on Friday June 17 2016, @02:12PM
OH SNAP!
Soljua boy tell em!
(Score: 0) by Anonymous Coward on Friday June 17 2016, @05:35AM
> That's the same as water waves travelling together so that the crest of one wave is exactly at the trough of the other and cancelling each other out. The water does not go
> away, it's still there, in the same way the pairs of photons are still there and carrying momentum even though you can't see them as light.
This analogy says exactly the opposite of what is intended. Water waves transport energy (and probably momentum, I am not sure); flat water, which is equal to two waves superposed in opposite phase, does not. It unintentionally elucidates the paper because the author is explicitly saying that photons are *not* like water waves, in that they can carry momentum while being superposed in this way - from the paper: "Thus, our explanation complies with conservation of momentum but departs from the current consent about photons by regarding photons as indivisible and indestructible basic building blocks of nature."
(Score: 0) by Anonymous Coward on Friday June 17 2016, @07:50AM
(Score: 2) by HiThere on Friday June 17 2016, @07:04PM
Not clear. IIUC, some models say that photons are absorbed rather than destroyed by energy absorption, and thus when they are emitted, they are actually being re-emitted from a previously absorption.
So creation and destruction may not happen. This probably depends on exactly what photons are. If they are just packets of energy, then it works fine, but photons also have spin, so I'm not sure that it does (or doesn't) work.
*IF* photons are just packets of energy, or even essentially packets of energy, then they can neither be created nor destroyed, only absorbed or emitted. But polarization makes this messier, so perhaps you can disassemble a photon into energy (absorbed into one process) and spin (absorbed into another). If so, I've never heard of this being done, but I'm not a specialist in this area...or even in physics.
Still, my first guess is that photons are neither created nor destroyed.
Javascript is what you use to allow unknown third parties to run software you have no idea about on your computer.
(Score: 1, Informative) by Anonymous Coward on Friday June 17 2016, @06:41AM
I am a physicist.
I have no idea how this got past peer review; I guess I have to start doubting AIP journals in general.
The concept of photons that cancel each other's EM fields makes no sense. If something like this could happen, we would have seen it before.
First thing: as another poster noted, this would mean the EM drive is no better than just pointing a laser/maser whatever in some direction, and then happily accelerating the other way (which is perfectly possible and real, except that the acceleration is minuscule).
Second thing: two photons overlapping exactly would mean that their location is "known" with infinite precision (it's known by the other photon). That would mean that their momentum could have any value possible, just because of Schrodinger. Being photons, their energy is proportional to the momentum, therefore the probability of the two photons having the same energy (thus the EM fields cancelling each other out) is zero.
Luckily, this EM drive thing is testable. I say we should not spend any public funds on testing it, but if there are enough idiots out there to believe it's worth investing time and money, whatever. I will be the one only checking the news from time to time to laugh when they finally admit it's a scam.
(Score: 0) by Anonymous Coward on Friday June 17 2016, @07:03AM
Umm, no. It means that the wave functions of the two photons are exactly opposite in phase. It is the opposite of how a laser works. Photons produced by lasers are just about exactly in phase, which is why their light is so coherent and so bright because their wave functions experience constructive interference. According to the article the photons generated are just about exactly out of phase, and so their wave functions experience destructive interference and as such there is hardly any electromagnetic field at all. You fail elementary quantum mechanics.
(Score: 0) by Anonymous Coward on Friday June 17 2016, @03:34PM
fucking made me read the fucking article.
article is junk, like I said.
there are a total of 4 equations, with a bunch of handwaving for 8 pages, no actual proofs.
I really have no idea how this article passed peer review.
(Score: 0) by Anonymous Coward on Friday June 17 2016, @08:07AM
Here is a thought experiment; consider two EM waves with nearly equal phase; we get the classical interference pattern. Now consider the effect in the limit that the two phases approach each other; we get peaks and troughs in the interference pattern (beat pattern), with the beat wave length large (infinite in the limit of two phases equal). This is like neutrino oscillation.
(Score: 0) by Anonymous Coward on Friday June 17 2016, @08:46AM
If something like this could happen, we would have seen it before.
I have a feeling of scientific déjà vu.
(Score: 0) by Anonymous Coward on Friday June 17 2016, @10:16AM
It's called the Double Penetration Experiment.
(Score: 2) by GreatAuntAnesthesia on Friday June 17 2016, @09:34AM
> Second thing: two photons overlapping exactly would mean that their location is "known" with infinite precision (it's known by the other photon). That would mean that their momentum could have any value possible, just because of Schrodinger.
OK, so to vreate your magic spacedrive you get two photons overlapping exactly, and then you persuade them to choose the highest of the possible values for momentum using a photonic vector plotter suspended in strong brownian motion producer (say, a nice hot cup of tea)...
(Score: 0) by Anonymous Coward on Friday June 17 2016, @09:50AM
Presto changeo. Infinite improbability drive.
(Score: 0) by Anonymous Coward on Friday June 17 2016, @08:11AM
well heres some crackpot.
i think everyone ligo agrees that space can have a geometry. so it's bendable.
i think every one also agrees that light lives "inside" space, that is, if space is flat then light goes straight, but if space is bent then light trajectory will be bend also ( something called a geodesic? )
so for now we always have concentrated on space and embedded mass and shot light through it to measure and observe it (space).
but what if we turn it around? what if we ignore space and mass geometrics and instead try to devise a way to bend light instead ... will the space then bend tooo, in response?
if it walks like a duck, quaks like a duck it probably is a duck.
i would like to hope that this new device uses light to bend space (and probably time too)...
note: it is tough going for new physics so please forgive if this might not help much to further support of this new propulsion type ...
(Score: 2) by Immerman on Friday June 17 2016, @03:23PM
Yep, all you need to do is something impossible, and then you can do impossible things.
How exactly would you bend light? You have to apply a force, and then the light is just bending in response to the force.. which is something it does all the time. May as well make it more mundane - throw a baseball in a vacuum and it will likewise follow a geodesic. So, just bend its path without applying a force, and maybe you bend the geodesic as well?
(Score: 0) by Anonymous Coward on Friday June 17 2016, @08:26AM
so its basically the opposite of what a laser does?
(Score: 3, Interesting) by opinionated_science on Friday June 17 2016, @12:50PM
This guy has worked up a nice model of the phenomena...
http://physicsfromtheedge.blogspot.in/2016/06/a-smoking-gun-in-every-galaxy.html [blogspot.in]
(Score: 3, Interesting) by opinionated_science on Friday June 17 2016, @01:04PM
this one.
http://physicsfromtheedge.blogspot.in/2016/05/we-learn-by-doing-mihsc-emdrive.html [blogspot.in]
(Score: 0) by Anonymous Coward on Friday June 17 2016, @02:05PM
No new physics :(