Is the Impossible “Emdrive” Possible?

A controversial concept called the electromagnetic drive, or Emdrive for short has been called impossible. But one company believes the concept is viable and has worked for several years on building demonstration models. The Emdrive is a reactionless propulsion system that supposedly generates thrust by converting electrical energy via microwaves. If it works it could provide an almost endless supply of thrust for satellites and possibly other spacecraft. But no detectable energy emanates from the device, and most scientists say the Emdrive violates the well-established principle of the conservation of momentum. Satellite Propulsion Research, Ltd. (SPR), the company working on the drive now says researchers from China have confirmed the theory behind the Emdrive, and they should have a trial engine ready to test by the end of this year.

A reactionless drive was first proposed in the 1950’s, but came to attention in 2006 when New Scientist published an article about Dr. Roger Shawyer, who founded SPR, and claimed he had constructed a prototype that produced 88 millinewtons of forces while using only 700 watts of power. The idea was met with criticism from nearly all fronts.

The idea of the Emdrive involves forces created by reflecting microwaves between opposite walls of a cavity. If a cavity could be designed which would cause the forces on one side to be greater than the other, thrust could be achieved. The proposed cavity is cone shaped, which supposedly would provide the unequal force design.

In principle, no microwaves or anything else leaves the device, and so it is considered reactionless. But Shawyers website claims that the device is not reactionless, or a perpetual motion machine, because the force is created by a “reaction between the end plates of the waveguide and the Electromagnetic wave propagated within it.”

Originally, Shawyer, a British scientist, got funding from the UK, and then from am US company. Now the researchers at China’s Northwestern Polytechnical University (NPU) in Xi’an say they have confirmed the Emdrive theory, and have gotten funding to build the device.

Their device is based on Shawyer’s theories, and if it works, it would confirm what Shawyer has been claiming all along. The Chinese lead researcher, Professor Yang Juan, previously has worked with microwave plasma thrusters, which has similar engineering principles. A recent article in Wired said he Chinese should be capable of determining whether the thruster really works or whether the apparent forces are caused by experimental errors.

If the Emdrive works, what would it mean for spaceflight? Shawyer says a solar-powered Emdrive could take a manned mission to Mars in 41 days.

Paper by Shawyer on the Emdrive (not peer reviewed)
Opposing paper by Dr. John Costella

Sources: Wired,, Wiki

57 Replies to “Is the Impossible “Emdrive” Possible?”

  1. Is it real? I have my doubts. But if one can prove it works, and show a working model, then it would certainly be a breakthrough, to put it mildly.
    If they can get it working that is.

  2. A propellantless source of thrust would be very good indeed. My questions are…for longer space flights (where solar sails don’t apply), how will this technology fair with other sources of power. Given the success of the ion engine, where do costs and comparisons stack up?

    Can someone explain to me by what they mean of endless thrust…are we talking acceleration, or maintaining a constant speed?

  3. @Steve: They are meaning acceleration when talking about endless thrust, as in a vacuum no thrust is required to maintain a constant speed due to lack of friction.

  4. This sounds like an April’s fool joke.
    Why they do not open one end of the chamber and let the microwaves be radiated (this will then behave as a classical horn antenna)? This will certainly produce the thrust (VERY small, but it will be there for sure)

  5. Highly dubious. I cannot possibly see how this would work through the mechanism they are describing, unless I’m misunderstanding some part of the concept. For the moment, I’m sticking with the tried and true physics of conservation of momentum in a closed system, as opposed to the claims of some small, unknown company.

  6. Instead of microwaves, use flashlights! Tie a bunch of flashlights around your ship and wait a couple hundred years and away you go. DOH!

  7. I am frankly shocked and saddened that this crackpot’s idea got onto the Universe Today.

    Read the refutation. It explains exactly what’s wrong.

    The “emdrive” is logically equivalent to a closed box with balls bouncing around inside it. No matter how funny-shaped the box is, you can’t get net momentum out of such a thing.

  8. “# GekkoNZ Says:
    October 9th, 2008 at 7:56 pm
    @Steve: They are meaning acceleration when talking about endless thrust, as in a vacuum no thrust is required to maintain a constant speed due to lack of friction.”
    Yeah, Yeah, pure newton, BUT even in a vacumn area such as our solar system I would think that particle friction, solar wind, magnetic fields will affect the velocity of an object.

  9. I want to believe…….

    That flashlight idea could be fashioned here in the US. That’s one piece of hardware the US has down pat. We buy them from China.

  10. Of course this idea won’t work, there are many possible resonant modes in such a superconducting cavity. Quantum Uncertainty Principle would have it that the pressures will be equivalent throughout the cavity via modal diffraction effects, ergo no unbalanced forces.

  11. If I were a betting man, I would be putting money on the theories. I’m *very* skeptical about this, but the proof of the pudding, as always, is in the eating. If they demonstrate it working, then we’ll have to work to change the theories, and that will be exciting.

  12. I’m going out on a limb here, because I really don’t know all that much about theoretical physics, but…

    Would a device like this work on similar principles to the Casimir effect (ie, changing the vacuum expectation value on one side of the device and therefore causing thrust)?

    Or is it something totally different, and I’m just mixing up my physical effects again? 🙂

  13. I call it bunk. There’s no way of creating momentum from nothing. This goes into the same box as cold fusion and zero point energy machines.

    It’s almost as ridiculous as the water powered car.

  14. Completely agree with Costella’s assessment of Shawyers paper. At first I was intrigued by the idea that some relativistic effect takes place here, but something was bugging me from the very beggining of the paper. It soon dawned on me that the forces, that tapered walls experience, are going to cancel out any difference between the forces that opposing plates feel. Shawley’s paper somehow misses that fact. Costella’s rebuttal confirmed my suspicions.

    If this contraption actually works it is not the way Shawley describes it and I doubt it works at all.

  15. All you naysayers are going to have to eat humble pie. The underlying science, (not specifically for this device), is about to be published and it will change almost everything you know.

    This device works and the full understanding why is about to be revealed.

  16. I don’t know much about China’s Northwestern Polytechnical University, but are they a credible university that has done this kind of research in the past? Since they have claimed to have proven out the theory then the evidence should prove or disprove the claim.

    To borrow and twist a saying from ESPN, “That’s why they test the theories.”

    And why research is peer reviewed (eventually).

    And, Thank You, Universe Today. This is an interesting story I know something about even if the theory turns out to be wrong.

  17. In all honesty, the developers do claim that momentum laws are obeyed, as the EM wave is pushing on the machinery. A flashlight would do the same, except at very poor energy conversion rate.

    Now whether the machine can produce in full scale will be very interesting to see.

  18. This is about on par with something that crazy Tesla would come up with…no thanks. I’ll keep my direct current and my filament lightbulbs.

  19. Curtis wants to remind the naysayers that Supersonic speed was once considered impossible. Human going to the moon was once considered impossible.

    In fact, there is almost no limit to human imagination. Science is imperfect at best, and is still in its infancy. Hell , we can’t even define a theory for the fundemental principles of the Universe. Just because YOU specifically can’t see how a device like this could work, does not make it an absolute impossibility. I agree with one of the commenters above, that Humble Pi shall be served a la mode soon.

  20. It’s quite embarrasing to see Physicists slagging each other off in such a way, however it was the same in the time of Newton and Darwin.

    As a closed system the idea of propulsion from this engine is utterly impossible.

    However day physicists close their minds to ‘crackpot’ ideas is when all progress stops, the inventor should find out for himself if this system works.

    If or when it doesn’t, the inventor will have learned that the conservtation of momentum really has been tested an proven to be true.

    Without free thinkers otherwise known as ‘crackpots’ numerous laws of physics would have gone undiscovered, just don’t bother eminent or even partially famous physisists or expect them to pay any attention, as all of them have to be seen to be towing-the-line.

    The standard model is perfect – it just needs a few adjustments to explain why laws seem to break down all over the place, in black holes, at the beginning of the Universe, the inability to unify the very big and the very small, does the Higgs actually exist, what gravity actually is, why was the Universal constant regarded as a huge and embarrasing mistake and now thought to be quite likely? Why was ‘m’ theory laughed at and still is by so many? Why are scientists so split on so many points of view and so mean to each other when someone dares to propose a new idea that doesn’t fit with current and proven thinking? Apart from that and numerous other problems the standard model is not only good, it’s all we have, and anyone who says anything different even though we know the standard model is no way complete are ‘crackpots’.

    Wasn’t it said that man could not travel faster than 26mph before exficiating?

    In the words of Arthur C. Clarke “It’s normally about 10 years after everybody’s stops laughing that ideas get developed”.

    Though I’ve read a lot of physics books I’m not embarrased to ask questions.

    If anyone would like to answer some or all of these questions for me I would love to hear the answers.

    I would like to know at *exactly* what point do Relativity and QED break down with each other and why?

    Why is light dimmer from distant galaxies? Is it? Is it just the wavelength of light that gets stretched or does the photon loose actual energy. If light doesn’t loose actual energy ever how come? What happens when light becomes so stretched it’s waveform becomes a parallel line, how far into the gamma ray light band can we detect and why this limit? How far into the infrared can we detect and why this limit?

  21. Just went through the PDF on this (for about the third time; I already had a headache so why not?)
    It is not an easy thing to understand micro-wave propagation in wave guides; I haven’t messed with this type of stuff for 40 years.
    Efficiency wise this will make a fair pizza oven (think Jean’s cube) your order to the Moon in thirty minutes or less or half your appropriation back.
    I can actually see this working but about as well as Browne’s disks from back in the 50’s and we all know how that worked out.
    I also see that many physicists will die bringing us this technology (from old age) ; but that is how science works, eh?

  22. @Curtis
    I may not see how this device can work, but, after reading the provided PDFs, its obvious that the inventor himself has no clear idea either, as the paper is fundamentally flawed. That small detail should bother you more than someone’s critical mind.

  23. “Sounds like a perpetual motion machine”? Read carefully…this device requires solar power to operate. This power requirement means this device cannot run perpetually until the end of time, i.e. not a perptual motion machine.

    I understand the need for critical review of science but seriously, it’s not your money, it’s not your time, let them build it. If it works, it works. If not, case closed.

    I honestly think critics who “know” the science behind this project and projects like these, are more concerned with their egos and the possibility of having their foots put in their mouths than being open to new ideas. Well, best get a glass of water ready because sooner or later some “crackpot” idea is going to come along and you’re going to need something to wash down that foot.

    Thanks UT for giving this some exposure. Hope it works! If not, on to the next idea!

  24. I saw this a while ago, and emailed both parties, Dr Costella was very kind to reply personally to my email Roger Shawyer did not.
    Someone said why not let him research, but this guy has taken taxpayers money to develop this non-drive. My taxpayer money at that. So I’m a bit peeved at that.
    The EMdrive shouldn’t work, he has some videos on his website showing the drive prototype… Not working, vibrating a bit but not moving. I’m not sure if I should congratulate him for getting the grant or if I should be contacting the fraud office.

  25. “Why they do not open one end of the chamber and let the microwaves be radiated (this will then behave as a classical horn antenna)? This will certainly produce the thrust (VERY small, but it will be there for sure)”

    I have to assume (without knowing what physics they claim to be at work) that it would be less effective than using the microwaves their way. If you could get their claimed performance by normal ‘exhaust’ of the same intensity of microwave energy, wed’ve been using ‘microwave rockets’ long ago…

    Of course, the ultimate tests of any claimed reactionless drive is to suspend a test device from a pair of wires, and see if it produces a steady net-offset in one direction (as opposed to perhaps oscillating back and forth, or around its starting point).

    Better still, take one into orbit, put it in vacuum (which is where you most want to use the thing), motionless with respect to the ship that brought it there…and see what happens.

    And if it’s not bogus, net unidirectional motion, however slight, will occur.

  26. It’s not worse than the Mayan doomsday story. When will the test launch? 2012? (just kidding)

  27. I didn’t understand the cold fusion theory and I don’t understand this either. With my lab technique both would have seemed OK , but as said the proof is in the pudding. MOK

  28. Lots of new ideas come from folks who think outside the established norm.
    Ah, lets just wait and see if it works. If it don’t the naysayers can pat themselves on the back. If it works the naysayers will probably say they knew it would work all along!

  29. We all wish it would work. I wish it would work. Unfortunately the laws of physics don’t give one whit about what we wish. That’s why we call it wishful thinking.

    Side bet: the Chinese Polytechnical whatever will fake their results to avoid embarassment, but will make an error that reveals their subterfuge.

  30. it’s a difficult one… let me try and have a stab at understanding it by asking myself some questions:
    1) Is it a closed system?
    A: absolutely NOT – if it was, it would fuse after a while…
    2) Is it a “perpetual motion” or “over unity” device?
    A: no, it is not – it uses an external power source: the Sun.
    3) Is it really “reactionless”?
    A: hmmm… there seems to be some kind of interaction between the two ends of the inside of the engine, where “all the weird stuff is happening”
    4) What is being ejected in order to generate thrust?
    A: I have no idea, but something IS ejected, in some form or other, else the system would overload and fuse

    Finally: Is it possible to calculate (and work with) observing a system from two different frames of reference simultaneously?
    A: I can’t see how, I lack either the knowledge or the imagination
    IF it is possible, then the Thing CAN work.

    This is a genuine mind twister. I wish I could just write it off as a hoax and get some sleep… but somehow I can’t. It’s not as obvious a hoax as any of the web conspiracies…. IF it is a hoax at all. I cannot get rid of the feeling that this could be genuine – not exactly spectacular, producing many kilonewtons but it could possibly work….. IF I can postulate observing from two frames of reference all at once…

  31. I love how people are so quick to turn down ideas these days, quite pathetic really.
    What will you do if this actually did somehow work?
    These areas of research are actually still in the realms of the “unknown”, believe it or not.

    Face facts, we haven’t even nearly discovered everything about this universe, and i’d say we haven’t even learned 1% of what there is to know.

    If it weren’t for people stepping outside the box, we’d probably still be worshipping the sun.

  32. Well, this drive is almost certainly not going to work. But, there’s no way we’ll know until we try. Good luck.

  33. Microwave propulsion, the “theory” behind the Emdrive, is not a worthwhile idea. Here’s why? Roger Shawyer makes a basic mistake in vector addition and doesn’t explain it. It’s like having a bank statement that doesn’t add up.
    One assumes the error is in the calculation, and not an improper understanding of money. If the statement is correct then the bank had better have a very good explanation. But the Emdrive uses microwaves so special relativity changes things. Would changing the currency make the bank statement more acceptable? For anyone who believes a simple error in calculation represents a revolutionary new way of understanding the universe, I would like to be your accountant.

  34. For reasons I will not go into here, I had occasion to make a cone shaped cone of brass (not having gold) and lined it with woollen carpet, and inserted another brass cone, and lined that with more carpet, and inserted another brass cane. Yes: I built an orgone-engine! It quivered on the drive-way, and then took off, and it has not been seen since, anywhere by anyone who admits it. Next time I build the body and load, and work out its trajectory before I build the engine. Let that be a warning to you all. [ my joke ]

    Entropy: Nothing from nothing; and everything to nothing eventually.
    New ideas are good, and great if they are substantial.

  35. No detectable emission?

    … so the microwaves simply bounced back and forth forever inside, becoming more and more intense as the solar arrays power it up, never being absorbed and re-released as heat?

    So the inner surface is a perfect mirror including the microwave emitting device itself?

    If you say yes in support of the device, then you must concede there is no thrust because the vector sum of all the bouncing microwaves in the closed device will always be zero.

    If you say no to the infinite perpetual internal reflections of the microwaves, in defiance of the device, then at the very least the device emits heat … a detectable emission that contradicts the author.

    However If the heat is all coming out the back of the engine then maybe you’ll get some thrust in a manner similar to a solar sail … but NOT by the erroneous mechanism the scamming author is promoting.

    This scam idea has been around for decades, just waiting for ignorant people in positions of power to fund it. File this crap in the same category as the ‘water fueled’ car scams.

    You would think the guy who runs this blog would see through it. He is a scientist isn’t he?

    Perhaps I will visit this website less often now, the credibility of this website is damaged.

  36. The momentum exchange is between the electromagnetic wave and the engine, which is attached to the spacecraft. As the engine accelerates, momentum is lost by the electromagnetic wave and gained by the spacecraft, thus satisfying the conservation of momentum. In this process, energy is lost within the resonator, thus satisfying the conservation of energy.

  37. “As far as I know, Shawyer has never claimed his drive exists as a closed system (and how can it ?) therefore those who prattle on about conservation of momentum rather miss the point that all he states is an empirical effect and then provides a theory of explanation. If his theory is incorrect, but the effect is real, what then ?”

  38. I stick out my right hand and then step up onto it with my left foot. Then I stick out my left hand and step up onto it with my right foot…

  39. Meh, not too far fetched. Is this supposed to be anything like what Heim and Droscher had in mind? I’ll save my naysaying till I read more

  40. Ok, so ultimately speaking, the device must allow microwave frequency photons to exchange momentum with the waveguide in a preferential direction. So, unlike a poptart in a microwave, the exchange of momentum from photon to solid matter must be, on average, in one direction. I don’t follow the math in the author’s paper yet because I haven’t tried to, I’ve got my own research to attend to.

    As to the issue with the vector addition, any vector can, of course, be expressed as the summation of two or more other vectors. Has anyone bothered to see if the author just skipped the step of telling his readers that he broke down the components of the vector that hits the sloping wall into their x and y components? It seems to me that he’s claiming that over time the microwaves are converted from a random distribution of x and y components into being mostly x (the direction of travel) and very little y (which cancel each other out).

    In a sense, this concept is the reverse of the flashlight on a train thought experiment. Instead of increasing the frequency of the light shining from the front of the train, the microwaves moving around in the chamber must become red-shifted as the give up their momentum. If, that is, this device actually functions.

  41. Whoops, 2nd to last sentence should read:

    “In a sense, this concept is the reverse of the flashlight on a train thought experiment. Instead of increasing the frequency of the light shining from the front of the train, the microwaves moving around in the chamber must become red-shifted as they give up their momentum.

  42. Reminds me of the Dean Drive which was featured in Missiles & Rockets magazine back in the 60’s.

  43. i didint read all the posts so i dont know if anyone already posted this but in the FAQ os states:

    Q. Is the thrust produced by the EmDrive a reactionless force?
    A. No, the thrust is the result of the reaction between the end plates of the waveguide and the Electromagnetic wave propagated within it.

  44. This is a funny discussion! If you lean out of the window too much here … (well, one can sense a lot of group pressure here. So as usual, either be careful what you write or else you are already hardened against being f’ed up!)

    Conservation of Momentum and of energy both do not need an advocatus diaboli to speak for them against the mass who shouts “she shall burn” because they cannot be disregarded. They are not negotiable (only gods can break the laws of nature… anyone?)

    But on the other hand the scientific method is for sure not fulfilled by the methods which Mr. Costella has chosen to refute Mr. Shawyer.

    Look at what Mr. Costella did.

    The abstract of his article starts with a prejudice:

    It is well known that Roger Shawyer’s ‘electromagnetic relativity drive’ violates the law of con-servation of momentum.


    In the very beginning Mr. Costella claims that if you do not already share a pre!judice, then shame on you. No, you don’t learn anything here if you do not already know beforehand! That is not the way things start if you expect to LEARN something trustfully.

  45. @ RL
    Don’t let the name fool you
    Northwestern Polytechnical University is not a polytechnic institute. It is a key government funded research university under direct jurisdiction of ministry of industry and information technology. (restructured from Commission of Science, Technology, and Industry for National Defense)
    Professor Yang worked for china’s space program.

  46. In his article, Dr. Costella tries to explain “what’s wrong in Shawyer’s paper”. He refers to a scetch and concludes:

    “Now look back at Shawyer’s Figure 2.4. He has Fs1 and Fs2 pointing perpendicular to the axial direction, not perpendicular to the cone’s walls.
    His arrows are wrong.
    This is the fundamental blunder that renders Shawyer’s paper meaningless.”

    But the point is that whatever arrows he skipped in this figure Mr. Swayer claimed that instead “he had constructed a prototype that produced 88 millinewtons of forces while using only 700 watts of power.”

    So it is rediculous to refer to an imperfect scetch when there is an experimental evidence. But how does Dr. Costella demonstrate that the result of the experiment is wrong? The point is that he is too lazy to proof that Shawyers experiment is of no meaning. He just refers to a missing arrow in a scetch. This is what he writes:

    “I started having waking nightmares about what would be needed to disprove him: complicated mathematical solutions of horrendous equations; complex computer simulations of conical waveguides; … I shuddered at what I had, mentally, committed myself to. But just as the computer-ised woman in the train’s roof told me that we were approaching Seaford Station, the penny dropped. It was something that I could have explained to my Year 11 students when I was a still a teacher.”

    And thus he builds his critics on a figure which is of no meaning for Mr. Shawyers experimental results.

    I don’t know what is wrong with Mr. Swayer’s engine. But I know that Dr. Costella does miss the point.

  47. Scientific method (and for that matter, engineering) implies reproducible results.

    Mr. Shawyers who built the “Emdrive” releases the design and someone else builds an identical copy and tries to make it work. The new drive either works or it doesn’t.

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