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EmDrive Back in the News

Martin Tajmar’s presentation at the American Institute of Aeronautics and Astronautics’ Propulsion and Energy Forum and Exposition in Orlando yesterday has been getting plenty of press. Tajmar is looking at the device now commonly called an EmDrive, studied by Sonny White’s team at Eagleworks (Johnson Space Center) and advocated by Roger Shawyer, Guido Fetta and Chinese experimenters as a way of producing thrust in a way that seemingly violates conservation of momentum.


Tajmar (Dresden University of Technology) offers a paper entitled “Direct Thrust Measurements of an EmDrive and Evaluation of Possible Side-Effects” in his presentation on apparent thrust produced by the test device. As he told WIRED (which announced that The ‘impossible’ EmDrive could reach Pluto in 18 months), the current work will not close the story. From the paper itself:

The nature of the thrusts observed is still unclear… Our test campaign can not confirm or refute the claims of the EmDrive but intends to independently assess possible side-effects in the measurements methods used so far. Nevertheless, we do observe thrusts close to the magnitude of the actual predictions after eliminating many possible error sources that should warrant further investigation into the phenomena. Next steps include better magnetic shielding, further vacuum tests and improved EmDrive models with higher Q factors and electronics that allow tuning for optimal operation. As a worst case we may find how to effectively shield thrust balances from magnetic fields.

Image: Physicist Martin Tajmar. Credit: Dresden University of Technology.

An example of something needing attention is that the thrust measurements linger even after the power is turned off. Such behavior is indicative of thermal effects, but it is premature to reach that conclusion.

A thruster that operates through methods we do not understand naturally seizes the attention, because we seem to do away with the need for a propellant, which would make all manner of missions possible that would otherwise be achieved only through more costly chemical rocket methods. And if we are uncovering something that gets at ‘new physics,’ so much the better, as productive things happen when we find anomalies that lead to deeper investigation and, if we are lucky, a formulation of new principles.

Will that happen here? What needs to be emphasized is that this is work in progress, as Tajmar himself points out, so we cannot draw premature conclusions. We’re at the beginning of a process that includes peer review analysis and publication of papers widely disseminated in the physics community, as well as replication of experimental results examined in those papers. Finding out that momentum is not necessarily conserved would be a result so startling that it would demand the highest level of scrutiny, especially in terms of possible systematic errors — i.e., are there effects being registered which we can account for through the experimental apparatus itself? Tajmar knows this and says as much in his paper.

A bit of background: If you’ll check our book Frontiers of Propulsion Science, you’ll see that Martin Tajmar did an independent series of replication experiments on work performed by James Woodward (the ‘Woodward effect’), while working at the Austrian Research Center’s department of electric propulsion physics. While that work produced a null result, Tajmar went on to pursue experiments with rotating superconductors and, for a time, believed his apparatus was producing anomalous gravitomagnetic forces. Replication experiments that researchers at EarthTech in Austin planned to perform were abandoned because of what they believed to be flaws in the experimental apparatus Tajmar was using, including issues with the laser ring gyro Tajmar used that produced systematic noise that was being misinterpreted as a positive anomalous force signal. Tajmar continued the work for a time but eventually ended the experiment.

Does a similar fate await the EmDrive? We learn as we go, and if we can find ways to reduce or eliminate the problem of onboard propellant, we will utterly change the game of deep space. So, as experiments continue, let’s look for analysis in the journals as the work is subjected to peer review, and let’s insist on the same degree of caution we would use with any result that seems to contradict known physical law. If the effect Tajmar is studying is genuine, science will ferret it out, a process that is usually time-consuming and often subject to misinterpretation.

Addendum: George Dvorsky’s piece No, German Scientists Have Not Confirmed the Impossible EMDrive cites Eric Davis, Tau Zero founder Marc Millis and physicist Sean Carroll (Caltech), and is well worth your time.

An article that brings a determinedly neutral perspective to the matter is Suggestion: The EM Drive Is Getting the Appropriate Level of Attention from the Science Community. Thanks to Sonny White (NASA JSC) for the link to this one.


Comments on this entry are closed.

  • Al Jackson July 28, 2015, 9:42
  • James Stilwell July 28, 2015, 10:44

    Concerning matter, we have been all wrong. What we have called matter is energy, whose vibration has been so lowered as to be perceptible to the senses. There is no matter.”
    Albert Einstein

  • RobFlores July 28, 2015, 11:17

    If there were a chance of a real effect from either White’s and Woodward’s
    propulsion rigs, then someone would have ponied up 5-10 million to send
    up a test device, cube sat sized. It is the only way to eliminate most interferences at such exceeding small effects . Reading through the back round information available I thought Woodward’s theory and device was a more plausible breakthrough. Quite disappointing that Tajmar’s team has gotten a null result.

    Even with a LEO success, there would still be influential skeptics and any test device would need to be on a solar orbit away from any effects of Earth’s magnetic, gravity, & other possible forces acting upon it. (at these incredibly low energy thrusts even solar thermal/pressure effects are probably not insignificant)

  • Alex Tolley July 28, 2015, 12:16

    One has to wonder whether shining a light out of the back would produce more thrust than the EmDrive for the same power input. To be excited, I would need to see a clear and unambiguous thrust that responds to power levels. at this point we are measuring thrust close to noise levels.

  • Craig Watkins July 28, 2015, 12:38

    Thanks for addressing this. It’s hard to believe its a propellentless drive, but I have a feeling that whatever the anomaly/error is, the explanation will be interesting in its own right. Very curious about this and how it will play out.

  • Eric July 28, 2015, 13:19

    Chances are, this will all blow over as experimental error of some sort. But I don’t think this is a waste of time and money (really, very little money has gone into this), since even a small chance of some interesting effects would be very significant.

    This Wiki has some interesting ideas about how this may work (if it does):

    My main worry is the DIY community will get some interesting but problematic results, never to see wider confirmation by better equipped professional labs. It takes time, effort, expertise and money to do good experimental work, and given the implausibility of the EmDrive, I don’t expect much in the way of experimental follow up.

  • ljk July 28, 2015, 14:53

    I am being reminded more and more of when cold fusion first appeared:


  • Andrew Palfreyman July 28, 2015, 15:48

    The intriguing thing about this EmDrive is that the apparent thrust-to-power ratio (Newtons per Watt) exceeds that of a photon rocket (=1/c) by about 3 orders of magnitude. That shouldn’t be possible, of course.

  • Larry Kennedy July 28, 2015, 17:03

    @ ljk
    Sad but true.

  • Charlie July 28, 2015, 18:09

    Can anyone here explain to me in simple language, how this EM drive is supposed to work ? From all this technical gobbledygook that I keep reading about on this subject, I have absolutely no idea whatsoever how this thing is supposed to operate. To me it looks like an overgrown microwave oven

  • Charlie July 28, 2015, 18:11

    I forgot to add, is this type of drive really nothing more than radiation pressure driven ? If it’s radiation pressure driven it’s old hat – why so exciting, at this time?

  • Charlie July 28, 2015, 18:16

    An example of something needing attention is that the thrust measurements linger even after the power is turned off. Such behavior is indicative of thermal effects, but it is premature to reach that conclusion.

    It works when you turn it off !? I’m sorry, but the whole thing is than just a hoax. Things don’t operate when they don’t have a source of power – it’s just common sense here folks. As an aside, Paul can you tell me what the book is that you have it advertised on the right-hand side of the column, please.

  • Charlie July 28, 2015, 18:21


    I DID read through Woodward’s theory on his particular drive in fact, there was a book that came out in Springer’s press on all the work that he did on this particular type of drive. I was NOT impressed by what he had to say, at all. Why am I so adamant ? Well I can tell you this, for one thing, this particular drive has to do with the ENTIRE UNIVERSE undergoing a spatial shift of some type to permit this operation of the drive. What a bunch of balderdash ! And I was just being pleasant in my use of words here. If there really was any effect like this then you’d see a whole bunch of people pouring money into it !

  • Paul Gilster July 28, 2015, 19:01

    Charlie writes:

    Paul can you tell me what the book is that you have it advertised on the right-hand side of the column, please.

    I always show the space-related book that I’m reading at the moment. Right now it’s Leaving Orbit, by Margaret Dean. You can read about it on Amazon:


    If you’re talking about Frontiers of Propulsion Science, it was edited by Marc Millis and Eric Davis and I wrote Chapter 1. Also can be found on Amazon if you want to learn more about it, or search the archives on Centauri Dreams.

  • Rob Flores July 28, 2015, 21:51

    One of the reasons I was following Woodward’s work is that
    it is based on the same inspiration that led to the Wheeler-Feyman Absorber

    That inspiration was from Ernst Mach and his hypothesis of inertia. Which basically states that past and future distribution of matter does influence the present in a non-local way. Since energy is related to matter, it was a natural leap to electromagnetic waves

    Some feel that using mach’s intertia hypothesis
    leads to seemingly outlandish effects, that any device using Woodward’s device changes the rest of the universe in instantly to erase the conservation
    inequities. I don’t understand the objection. Even if large devices worked
    and were used, the effect on the rest of the universe would be insignificant.

    On the opposite side of the coin , If Woodward’s device worked and had a huge impact on the universe it might be taken for proof of
    no other intelligent life in our universe, because anyone else in the past using Woodward’s derived machines in vast quantities, would have had physical
    effects in our part of space. So either the Woodward’s theory is wrong OR we are alone in universe. If only life were that simple.

  • J. Jason Wentworth July 29, 2015, 1:07

    In response to Charlie’s postings:

    While I am interested (although not holding my breath) in the possibility of a breakthrough here, even a liquid propellant rocket engine continues to produce thrust for a brief (sometimes measured in seconds) period after shutdown. (The S-IC first stage of Apollo 15’s Saturn V hung dangerously close behind the rest of the “stack” after staging due to residual thrust; half of that S-IC’s solid propellant retrorockets had been left off to save weight, and the remaining ones weren’t able to push the S-IC back away from the rest of the vehicle.) Also:

    While the EmDrive’s post-turnoff lingering thrust might be due to thermal effects, it’s worth investigating what’s going on there to make sure. As Isaac Asimov said, world-changing scientific discoveries are less frequently discovered in a dramatic “Eureka!” moment; they usually take the form of a small, unexciting anomaly that makes the experimenter say, “That’s funny.”

  • kzb July 29, 2015, 7:50

    I’m 90% sure this will turn out to be bunkem -the fact that thrust apparently continues after the supposed source of that thrust is turned off is a bit of a giveaway.

    On the other hand, the nitty gritty of special relativity has its controversies even between experts in the field. It’s not as well settled as we assume. For example, the other week there was some discussion about what a Lorentz-contracted object would actually look like.

    Personally, my limit is the Bell’s spaceship paradox (see link below). It seems to me energy is coming out of nowhere to break the string. I’m sure this has been explained but it just shows how counter-intuitive SP can be.


  • Eric July 29, 2015, 10:55

    Related to Woodward, it seems that Machian perspectives on inertia, the equivalence principle (that gravitational and inertial mass are the same), etc. are still very much issues in physics. For example, see this paper that combines the holographic principle with Mach’s ideas for the origins of inertia:

    I’m not saying Woodward is on to something, I’m just noting that the physics of inertia still needs continued work. I have no idea if any of this can apply to exotic space drives though I strongly suspect no easy loop-holes that would let us flit around the solar system, much less the stars.

  • Bob Shaw July 29, 2015, 14:38

    The Dean Drive, Prof Eric Braithwaite’s fall from grace over his reactionless drive, Cold Fusion, Linus Pauling’s ‘enthusiasm’ for Vitamin C… …all follow the same trajectory (especially when established scientists make statements on matters outwith their subject, and less-established scientists smell grants).

    The universe gives nothing for nothing, and wishes don’t build warp (or other) drives.

    And the online discussion and hand-waving about this is certainly a prime example of the WWW in full flight – the World Wide Waste of time!

  • Robert July 29, 2015, 16:09

    I have followed Shawyer’s work for some time and am very interested in this topic. As I read the accounts of Tajmar’s work, I thought to myself, how long will it take for the skeptics to pile on? Apparently, no time at all which is indicative of the amount of thought they tend to put into it. I read the article you mentioned Paul at the end and was really disappointed by both the hostile, not just skeptical, tone as well as how closed minded Dr. Davis is on this issue.
    Sean Carroll’s comment ““My insight is that the EMDrive is complete crap and a waste of time” can be discounted as well as he then mumbles something about momentum “I’m going to spend my time thinking about ideas that don’t violate conservation of momentum”. Indeed, so does Shawyer, Fetta and everyone else doing this work. The Millis heat comment has no real data to back it up.

    If one thinks about all the experiments done to date by several groups, each with their own setup and procedures, the likelihood that all experience the same systematic error is astoundingly small. The likelihood that each experiment has a uniqly different but fatal error is vanishingly small. The likelihood that each team is uniqly incompetent is vanishingly small.

    Davis comments “What’s more, my professional colleagues who all work in the space propulsion engineering business at the major aerospace corporations are not at all interested in any new electric space propulsion inventions or claims that can only produce thrust on the order of micro-Newtons (via devices that require high voltages and high electric currents and high E & M field strengths) because that magnitude of propulsive thrust is not applicable to any meaningful space mission propulsion needs.” Very short sighted and frankly self serving comment. Isn’t this the same Dr. Davis who affiliates himself with Hal Puthoff at the so-called Institute for Advanced Physics at Austin? Puthoff helped originate psychic “Remote Viewing”. Davis writes about “extracting energy from the quantum vacuum”. According to Shawyer, the effect can be huge for a high Q superconducting cavity.

    Ironically, Shawyer’s paper just passed peer review.

  • Robert July 29, 2015, 16:27

    On the other hand, I looked at Shawyer’s work and while I am open to the basic effect, I do have a problem with the interstellar probe design he discusses. How can a 200 KW reactor possibly provide the energy to bring a 9 ton probe to 0.67c in ten years? I think it would have to be closer to 200 GW. Where does the energy come from? 200 KW for ten years does not supply enough energy to give the probe the final kinetic energy. BTW, I tried two times to point this out privately to Mr. Shawyer but he never responded. If I am missing something please tell me!

    From the abstract:

    “The full potential of EmDrive propulsion for deep space missions is illustrated by the performance of the interstellar probe. A multi-cavity, fixed 500 MHz engine is cooled by a closed cycle liquid nitrogen system. The refrigeration is carried out in a two stage reverse Brayton Cycle. Electrical power is provided by a 200 kWe nuclear generator. The 9 ton spacecraft, which includes a 1 ton science payload, will achieve a terminal velocity of 0.67c, (where c is the speed of light), and cover a distance of 4 light years, over the 10 year propulsion period.”

  • ljk July 29, 2015, 17:25

    From N-rays to EM-drives: when does science become pseudoscience?

    July 29, 2015

    A fair amount of pseudo-science begins as blue-sky, basic scientific hypotheses and experiments. Hypotheses can challenge basic accepted notions, or begin with them, and may yet somehow go off the rails. How does this happen, and at what point do scientific inquiries become obsessive or pathological? Consider N-rays.

    Full article here:


    To quote:

    Recently, there have been some rather breathless accounts of the discovery of a new form of propulsion that appears to violate the Newtonian law of conservation of momentum. It uses no propellant, and yet has been reported to produce thrust via creation of microwaves in a certain-shaped cavity. The EM-drive was first developed by British scientist Roger Shawyer, versions of which have been tested by labs in China, the US (at the Johnson Space Center, NASA) and now Germany.

    So far, in each of the labs conducting tests, force has been observed at varying levels, and in each of the slightly varying experimental setups. So far, no one can account for the force measured, and even while all labs are measuring force while trying to eliminate experimental artifacts that might create false positives, no negative or falsifying experiments have yet shown EM-drives to be totally fruitless.

    Something interesting may be happening, and no doubt still more labs will attempt to replicate force, measure possible thrust, and may even try to create working prototypes, unless someone falsifies the hypothesis. This can be done by a) locating the experimental artifact that is causing measurements of force where there is no real thrust, or b) replicating the experiment and measuring no force (perhaps having eliminated somehow whatever effects may be causing false positive results).

    Has the EM-drive slipped over the line yet toward pseudo-science? Not yet. However, with each new experiment, the apparent thrust measured appears to be dwindling, which may be because indeed there is something going on that causes false positive measurements. There is certainly reason to remain skeptical, especially since the proposed propulsion system appears to violate a basic, well-accepted physical law.

    Of course, many of us hope for cheaper, better, more efficient means to achieve long distance space travel, and the EM-drive may lead to such technology, but it may well not and we should pursue any and all theoretically feasible means besides the EM-drive, considering it could well turn out to be just like N-rays or cold fusion.

  • Eniac July 30, 2015, 0:45


    How can a 200 KW reactor possibly provide the energy to bring a 9 ton probe to 0.67c in ten years? I think it would have to be closer to 200 GW. Where does the energy come from? 200 KW for ten years does not supply enough energy to give the probe the final kinetic energy

    Robert, you have put your finger on it. Think it through, though: It can easily be shown that ANY reactionless drive more efficient than a photon rocket will be able to violate energy conservation in the way you describe: Kinetic energy goes up with the square of time, energy consumed goes up linearly. Run it long enough, and the former will exceed the latter. QED.

    If you allow for relativity, a reactionless drive IS possible, but its thrust/power ratio can not exceed 1/c. A common LED flashlight is an implementation of it that is fairly close to optimal.

  • Eray Ozkural July 30, 2015, 5:10

    The article is fair, but can we please clarify that by conservation of momentum we are referring to Newtonian physics, which clearly cannot explain how such a device operates, if it were true. I was very frustrated to see many bloggers “refuting” the drive based on their knowledge of high-school physics. The fact here is that we are expending energy, and in principle this might be converted to other interactions….

    About the thermal effect, sure, so my question is why don’t we just use a 10 times higher Q value, what’s holding Sonny or anyone else back, why do they want to keep hypothesizing on micro-newtons? :) Not enough budget?

  • Ron S July 30, 2015, 10:21

    Eray: “…why do they want to keep hypothesizing on micro-newtons? :) Not enough budget?”

    They need to generate more noise, within which they can speculate about a larger signal.

  • Alex Tolley July 30, 2015, 12:44

    @Eray The article is fair, but can we please clarify that by conservation of momentum we are referring to Newtonian physics, which clearly cannot explain how such a device operates, if it were true. I was very frustrated to see many bloggers “refuting” the drive based on their knowledge of high-school physics. The fact here is that we are expending energy, and in principle this might be converted to other interactions….

    If high school physics was obsolete, you would then allow perpetual motion machines. As Eniac point out so eloquently, that is exactly the consequences of a reactionless drive as posited. That should rule it out. If any “drive” can result in more energy being accumulated than used, that would be a game changer for humanity, and presumably any aliens out there.

  • Robert July 30, 2015, 13:22


    The current results are already much greater than a photon rocket and this is not a reactionless drive, but a propellantless drive. That distinction seems to be lost by critics who seem uninterested in exploring why Shawyer claims momentum is conserved so they set up a strawman argument and knock that over.

    My objection is simply Shawyer’s calculation. And my simplistic calculation may be naive. I just think that the interstellar probe calculation would, get to
    a terminal velocity of more like 200,000 m/s rather than 200,000 km/s. Is it possible that aeronautical engineers are programmed to think in km not meters and lose track of units? Even NASA had unit conversion issues before. No doubt many critics would use that point to claim the entire concept is fatally flawed but they would be misguided and unfair if they do. But that usually does not stop critics.

    Funny thing is, if the Emdrive pans out in the end, the same critics will be congratulating themselves and lauding the process of science as they usually do.

  • Robert July 30, 2015, 13:45


    The problem with the article you quote is that it claims if a single experiment claims the effect is zero and claims to account for some artifact, then the issue is dead. Unfortunately, that is true. But what it really means if someone with a reputation says it ain’t so, everyone else will agree it ain’t so even if their attempt at replication is fraught with error and a predetermined outcome.

    Also, the comment about the results getting smaller with each paper is bogus.
    The power used and the Q of the latest paper were set far smaller than some other attempts. The Chinese replication got almost 1 N.

  • RobFlores July 30, 2015, 14:45

    I’d like to remind everyone that theoretical physics does miss things
    sometimes, Nobody expected neutrinos to have mass, and no mainstream model predicted it, but there you are. Which means that while the primary established theories on physical universe out there do explains its workings to a high accuracy, it is an incomplete understating.

  • Charlie July 30, 2015, 17:42


    just some further amplification on my previous statement concerning the Woodward Drive. As stated earlier, I did read the entire book concerning Woodward’s work and I entered into the book and a skeptical view point and I left with even a more skeptical viewpoint. My particular beef with his particular theory is that to receive a reaction (and acceleration) in the mechanism it necessitates that the entire universe undergo a responsive shift as a reaction to the mechanisms operation and that it must do so in lockstep.
    I have no objection to interactions between physical objects throughout the universe as that is the way in which gravitation operates, but I do have they STRONG OBJECTION to the universe operating in lockstep in response to the operation of the mechanism. I confess that I had a much better and deeper understanding of what Woodward was trying to do while I was actually reading the book, but time has since been my memory as to the details. So I did want to be upfront about that. That is why I’m not a candidate to believe in Woodward’s ideas are experimental results.

  • Larry Kennedy July 30, 2015, 18:21

    I’m always the first person to point out that our physics are incomplete. The problem with this story is that so many people have taken a tiny unexplained effect and declared it to be a space propulsion system even assigning specific characteristics to it.

  • Project Studio July 30, 2015, 23:58

    What’s intriguing about the theory behind the presumed effect is the consideration of the microwave beam and resonant waveguide chamber as an ‘open system.’ This shows an insight into the meaning of relativity theory, as the microwave velocity (c), and the group velocity resulting, define a separate reference frame from the chamber itself traveling at velocity less than c. This is where our non relativistic common sense notions could lead us to a short-sighted dismissal of a new approach to a propellant-less drive.
    This insight along seems to merit further investigation and may provide the framework for the difficult ‘action at a distance’ conceptual hurdle to any device designed to harness Mach’s principle.
    What is frustrating is the wide divergence of informed opinion of whether the frustrum is a resonance chamber, a waveguide, or both and whether the group velocity at the narrow end is actually different at the narrow end from the wide end. Various means of analysing the geometry, standing wave patterns, optical path lengths, and electromagnetic energy densities seem to lead to contradictory results.
    I’d be interested a limited ‘optical’ analysis (empirical study) of what is happening inside the chamber, leaving out any net thrust measurements, that could determine if a net force imbalance is possible at all. Even a computer simulation of how the waves would propagate could be enlightening. (The COMSOL simulation seems to have been used to design the resonant chamber but not to analyse the waves forming in the chamber).

  • Dave July 31, 2015, 5:01

    This may be long, but I’ll dive in.

    Tajmar was quoted: “Nevertheless, we do observe thrusts close to the magnitude of the actual predictions after eliminating many possible error sources …” In a good experiment one accounts for all the error sources that can impact the result, not just “many”.

    100 microNewtons is a tiny force, easily generated by a multitude of effects in cables, supports, mechanisms, microwave guides, air, etc. All knowable effects ought to be accounted for in a quantitiative physics-based error budget before constructing an experimental apparatus – otherwise how does one know what to build? An error budget and corresponding design sized to expose the target effect with sufficient significance is the mark of a good start on a technology experiment. Even so, such experiments are weak at hypothesis testing since they are not designed to falsify.

    The conference paper does not give enough information to allow a careful reader to have confidence in the measurement. Necessary masses, dimensions, materials, mechanical/thermal/EM boundary conditions, and experimental procedures including calibrations are missing. Information that is given provides cause for skepticism. Analyzing the setup shown in the photos reveals potential effects with magnitudes experience shows could influence the results. I’ll just mention a few basic mechanical ones. (1) when one end of the metallic bar of the offload system grows sideways as the EMDrive heats it up a small amount, the relative balance between the two sides of the balance beam will be affected and a corresponding force recorded. (2) a shear component to the loads at the weighing pan contact point will affect the measurement; these sideloads are not present during the normal operations of the balance for which it is designed; however these sideloads are virtually impossible to avoid in the experimental configuration because of the difficulty in precisely aligning these three locations along the vertical: the counterweight assembly contact point with the balance beam, the counterweight assembly center of mass, and the counterweight contact point with the weighing pan; consequently results from differing configurations will not be repeatable; further, no apparent care was taken in this regard. (3) a precision balance is not designed to be a precision load cell, it is designed to measure the weight of an object constrained only by virtue of sitting in the weighing pan; since the counterweight assembly is stiffer than a free sample sitting in the pan – it is constrained above by the rest of the test article – the operational conditions during test differ from the conditions during calibration so there will be a (possibly large) calibration error. (4) the 3 power & ground cables leading in to the EMDrive will impart time-dependent forces and torques on the test article due to changes in their elastic properties as they undergo resistive, conductive, radiative and convective heating during operations; but not repeatably between configurations because the cable runs & contact points are not the same for different configurations (5) rotational pivots, including even the knife edge, will store and release torsional strain energy in a nonlinear time dependent manner giving rise to force transients at the precision balance’s transducer.

    Without accounting for these, and undoubtedly a host of other effects, the experiment looks to me like a random number generator. It probably doesn’t have much to say one way or the other about the presence of weak anomalous forces.

  • Ron S July 31, 2015, 13:16

    Project Studio: “This shows an insight into the meaning of relativity theory, as the microwave velocity (c), and the group velocity resulting, define a separate reference frame from the chamber itself traveling at velocity less than c.”

    You can stop right there because you’re already into a fundamental error. Photons have *no* frame; they follow a null path.

  • Robert July 31, 2015, 14:03


    You are implying the experimenters were incompetent which is unwarranted. You also are setting an impossibly high bar for any experiment. Tajmar himself put caveats on the data yet after all their work they still felt it was worthy of further study. That is all they said. I fail to see what so many critics essentially want to declare the results worthless and imply the work should stop. Even if the Tajmar experiment were eventually retracted, critics would likely assume that is the end, completely ignoring the NASA and other data. I do not understand the outright hostility for a concept people, especially in this group, should be hoping pans out? I guess it offends peoples neat little paradigms.


    “If you allow for relativity, a reactionless drive IS possible, but its thrust/power ratio can not exceed 1/c. A common LED flashlight is an implementation of it that is fairly close to optimal.”

    Again, propellantless, not reactionless. Does anyone argue with Young Bae’s photon recycling? Yes, it is easier to understand but the thrust is thousands of times 1/c for the same power. In both cases, the device would accelerate forever but as the velocity increases, the acceleration the power could support diminishes to but never quite gets to zero and in the limit approaching a terminal velocity.

    Project Studio,

    You have excellent insight into this!

  • Marc Millis July 31, 2015, 14:56

    When running NASA’s BPP, I learned to focus on HOW an investigation was being done, instead of its hypotheses (or ‘claims’). Regardless of the potential benefit, if the work was biased (pro or con) or had vague techniques, then I would drop it. There would not be enough reliability to learn anything. Conversely, if the work was impartially aimed at determining how mother nature truly works, and with enough rigor to ensure that the findings are reliable, then it got my attention. In that case, even if the results indicated a dead end, we would have based that conclusion on reliable data instead of pedantic rejections.

    The ideal case is to have honest, impartial, and competent researchers investigating the edges of physics that are relevant to propulsion (and power). We attempted to define those physics edges in our Frontiers of Propulsion Science book, albeit to a limited degree. For those who want to produce serious progress toward ‘space-drive’ goals, please pick one of those unknowns and work it with the normal scientific method and standards.

    On the subject of ‘space drives’ the common issue is indeed conservation of momentum. The undiscovered physics, in this case, is the nature of inertial frames – the reference frames upon which these conservation rules are defined. It is still not understood why space has the properties of being an inertial frame or how those properties might have some dependence on surrounding matter and energy. I would LOVE to see serious research on that edge of knowledge, and yes, with an impartial bent toward pondering propulsive possibilities.

  • Charlie July 31, 2015, 18:22

    So I ask the question again. In simple terms what is this particular type of drive supposed to do in the physical sense? I still don’t have any clue as to what is the basic physics, the fundamental physics behind this. Can anyone explain please?

  • Project Studio July 31, 2015, 22:17

    “You can stop right there because you’re already into a fundamental error. Photons have *no* frame; they follow a null path.”

    I’m not sure if a light path is called an inertial frame or not. The photon has inertia, and is moving relative to the reference frame of the frustrum. Apologies if I’ve made a semantic error.

    I don’t feel I can paraphrase the ‘theory of operation’ if there is one. But what I take away from the SPR theory paper is that the shape of the frustrum guides the standing microwave inside the chamber in such a way that the light pressure on one end is greater than on the other end, creating a resultant unbalanced force. If this were a classical closed system (think about the pressure of a pressurised ‘gas’ with standing acoustic waves propagating against the walls of the chamber) it would be obvious that no unbalanced force would result. However, in a sense, light (or the microwave) is not ‘contained’ in the chamber the same way a gas is. Light propagates in a separate (or null?) inertial frame. The light ‘inside’ the frustrum is not accelerated by any possible acceleration of its housing (lightspeed being a constant). Only the path of the light is internally reflected and shaped by the shape of the chamber. The SPR theory suggests that this optical shaping causes the effective ‘group velocity’ of the internally reflecting wave fronts, which we can consider as the ‘photons’ in the beam, to be greater in one axial direction than the other. If that is true, it would result in a measurable net force on the frustrum.

  • Dave August 1, 2015, 1:50

    Robert you are reading too much into my comments, which I wrote with care, were directed at experiment design and execution, and where I avoided making claims regarding the team or the phenomenon being explored. The example confounding effects I noted are not mere opinions. They arise from the objective conditions of the experiment and can be quantitatively estimated using the standard engineering physics methods successfully applied throughout our technological base.

    There is a long history of precision force measurements going back at least to Cavendish’s 1798 measurement of G using a torsion balance. Cavendish measured a force of several hundred nanoNewtons, roughly a thousand times smaller than the forces reported in the Tajmar experiment. Also using a far more massive apparatus. Cavendish notes prominently (the paper is freely available online) that errors induced by thermal effects limit his precision. In the > 2 centuries since, the state of the art for precision force measurements has advanced many orders of magnitude further to the point where precision is limited by Brownian motion for objects of the size and mass being discussed. This incredible capability is richly documented in the scientific literature.

    It is a mistake to confuse skepticism with outright hostility. Skeptics are willing to be convinced but have a rational, evidence based reason for their skepticism. Do you prefer lowering that bar? To where? What then should our basis be for deciding what is real?

    I’m with Marc Mills: experimental rigor is key to adopting new truth statements about nature. If an experiment is unreliable then it can’t tell us much. In particular, an unreliable experiment can’t rule out an effect, as this one hasn’t. But a reliable experiment can set upper limits, or in the case of effects within reach of the state of the art, quantitatively establish their magnitudes and uncertainties.

    There is much we don’t know about physics – that’s why there are research physicists. History amply demonstrates that when we discover new phenomena new technologies emerge. But following this path is not easy. And when discovery is elusive due to lack of rigor, it is not even possible.

  • Charlie August 1, 2015, 5:17

    Well, Paul, I turn to you, since no one else seems to be able to answer my question – do YOU understand and able to explain to me how does this particular type of drive works?

  • J. Jason Wentworth August 1, 2015, 6:00

    A thought: Newton’s equations *describe* what gravity does and in what “amounts,” without -explaining- exactly what causes gravity; Einstein’s equations of gravity posit curved space instead of an attractive force between bodies as the cause of gravity’s observed effects, but this still doesn’t get to the root of what causes gravity (saying that gravity is a property of mass doesn’t do it, either; it just says where it is found to originate from). But despite not knowing what causes gravity, we still have no difficulty in using it for everything from pendulum clocks to gravity assist maneuvers. Now:

    Likewise, the EmDrive propulsive effect–assuming that it is real; I’m not saying that it is–could also be used without understanding what exactly causes it. If a suborbital test aboard a sounding rocket–which would be cheap–indicated that an EmDrive test article produced measurable (trajectory-altering) thrust, that would strongly suggest that the propulsive effect is real. (Skeptics could claim that the device was really reacting against the Earth’s magnetic field, but rotating the payload using attitude thrusters and having the EmDrive thrust in different directions could disprove that, if the device altered the payload’s trajectory even while thrusting in the wrong directions for the geomagnetic field to be a factor.) Then:

    If the results were positive, the next step would be testing an EmDrive aboard a satellite, or perhaps even aboard the International Space Station (it would be useful for maintaining the station’s orbit). Even if the exact physics of *why* the EmDrive worked were still unclear at this point, optimized designs could still be developed empirically. (Liquid propellant rocket engine start sequences are developed empirically; other than a few experience-based “rules of thumb,” there are no theoretical ways to calculate exactly how quickly to open the various valves, or how far apart in time to space these and other start-up functions–they are determined experimentally, not infrequently after explosions or more benign failures such as stripped turbopump gearboxes, cracked combustion chambers, etc.)

  • Paul Gilster August 1, 2015, 8:12

    Charlie writes:

    Well, Paul, I turn to you, since no one else seems to be able to answer my question – do YOU understand and able to explain to me how does this particular type of drive works?

    The problem here, Charlie, is that no one knows whether or not this ‘drive’ actually works, and there is no theory that satisfactorily explains how it works if it does. That’s why there’s so much contention about it.

  • Project Studio August 1, 2015, 9:41

    This summary of the theory is far better than mine:

    The referenced paper (CULLEN A.L. ‘Absolute Power Measurements at Microwave Frequencies’ IEE Proceedings Vol 99 Part IV 1952 P.100) can be purchased at:


    I don’t know if the above paper shows supporting solutions for a tapered waveguide or not.

  • Project Studio August 1, 2015, 12:09

    The referenced Cullen paper available here without fee:


    It describes apparatus to measure microwave radiation pressure but doesn’t appear to analyse group velocity withing a tapered waveguide.

    Tapered waveguide design principle and presumed standing wave pattern (showing a standing wave pattern with variable wavelength) are here:



    A related text description of what is meant to be happening is here (but this description doesn’t convey much to me I’m afraid):

  • Project Studio August 1, 2015, 13:35

    I found the type of analysis I was looking for describing the wave propagation within the frustrum. It will take some time to read through, and I expect this to be my last post on this topic.


  • Robert August 1, 2015, 13:48

    In answer to Paul, some have an idea of how it works but others are skeptical but I still think the critics are too dismissive of the work to date. It may not be final proof but it is definitely not just a series of incompetent experimentalist doing incompetent experiments. It’s funny that physicists demand a full theoretical explanation before they believe something new, putting theory above data. That makes it hard to discover new physics.


    You are making a judgement about the value of this experiment are you not? You seem to have decided it is worthless. That’s your right of course but do you or do you not think people should, continue working on this?

    Also, I got a copy of the new Shawyer paper and think I see where he makes some mistakes with total energy. He assumes a constant thrust means a constant acceleration for the whole mission. He attributes the thrust times distance covered as the work input which supplies the kinetic energy. That works for say an object falling through a constant gravitational field which is a conservative force. But the power required here is proportional to the velocity because in Shawyer’s case, the energy supplied is constant per unit time not per unit distance which is required for a constant acceleration. Mr. Shawyer is or probably was a decent microwave engineer but I think even good engineers can sometimes be fooled by their formulas.

    I hope beamed propulsion proponents have not made the same error.

  • Ron S August 1, 2015, 14:03

    Project Studio: “@Dave”

    That was me, not Dave.

    “I’m not sure if a light path is called an inertial frame or not.”

    You don’t know? Sorry, this is basic physics. Besides which I told you it is not. I recommend you brush up on the fundamentals before going further.

    “The photon has inertia…”

    A photon has momentum. Inertia has nothing to do with it.

    “Apologies if I’ve made a semantic error.”

    You’ve made physics errors.

    “Light propagates in a separate (or null?) inertial frame.”

    And you repeat the error.

    In any case, I thought Dave gave a nice summary of Woodward’s problems, which seems to coincide with my own understanding from reading one of his technical papers years ago. Pretty math, lousy physics.

    I also liked Marc’s comment about what we don’t know about inertia. We should avoid planting our desires in our present knowledge gaps. They will wither and die there since that is not fertile ground. Experimental data of course takes precedence over theory, but the data, so far, stinks.

  • Robert August 1, 2015, 15:49

    Thanks for the more neutral reference article Paul!

    Can anyone assure me that beamed propulsion proponents do not also assume a constant acceleration from a fixed power beam source? It’s really confusing because a constant beam should lead to a constant force which rationally leads to a constant acceleration for a fixed mass but as we have discussed, the energy is not available after a certain velocity to sustain it.

  • Dave August 1, 2015, 22:16

    Robert, yes I am making a judgement regarding the value of the experiment. Our knowledge of physics is no different after we learned its results than before. So I judge no value. But to continue this particular thread of the conversation: is it a bad thing to make scientific value judgements? That doesn’t sound like it leads to the goal of understanding physical reality or even to a more limited goal of improving experimental practice. Can we agree that those are appropriate goals for experimenters to have?

    The answer is not to do more of the same via repeated experiments using the same general, or even evolved, approach. If there is an effect, this class of experiments can’t demonstrate it. There are a number of reasons, many stated above and elsewhere by experienced commenters, but in the end the usual refrain sums it up: unreliable experiments can’t demonstrate anything reliably. So, if one wanted to continue this exploration the obvious answer is to design and carry out a reliable experiment. Can we agree it’s better in principle for experiments to be reliable because then they advance our scientific goals?

    You asked if I think people should continue working on this topic. Should is a loaded word. If it were me holding the pursestrings then no. There are too many competing needs, too many researchers on the cutting edge making progress in their own high-potential but under-funded research areas, too little underlying basis for thinking this will pan out, and teams here whose practices are too far behind the state of the art. By my experience this same view would prevail if these experiments were the basis of peer-reviewed funding proposals – they would not be competitive in a pool of typical proposals. However as a private research effort, why not? People are pretty much free to do whatever self-funded research they want, and properly so.