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EmDrive study officially published

595 points by babak_ap 10y ago

ctoth 10y ago
Thanks for submitting this, love to see feedback from the physicists who hang out around here!
- debunkit 10y ago
  There was a very elaborate experiment in Germany regarding this. They concluded that the force is excerted by coupling the RF-energy from the outside. If the system is fully self-contained (driven by a battery physically connected to the cavity) there is no thrust to be measured. It's very sad to see NASA being involved in such shitty research.
  - danbruc 10y ago
    Direct Thrust Measurements of an EM Drive and Evaluation of Possible Side-Effects [1] [1] https://tu-dresden.de/ing/maschinenwesen/ilr/rfs/ressourcen/dateien/forschung/folder-2007-08-21-5231434330/ag_raumfahrtantriebe/JPC---Direct-Thrust-Measurements-of-an-EM-Drive-and-Evaluation-of-Possible-Side-Effects.pdf?lang=en https://tu-dresden.de/ing/maschinenwesen/ilr/rfs/ressourcen/...
    - debunkit 10y ago
      Thanks for posting a link to the paper!
  - rocqua 10y ago
    You can't blame NASA for trying shit. They aren't claiming this stuff will work, just that they measured thrust. The fact that one study showed differently isn't binding. Many, many papers disagree. I believe they are going to put one of these in space, that'll give a definitive answer.
    - debunkit 10y ago
      I am blaming them for not being up to date on the state of the art and not following up on earlier research, especially on what has been hinted at in: https://tu-dresden.de/ing/maschinenwesen/ilr/rfs/ressourcen/dateien/forschung/folder-2007-08-21-5231434330/ag_raumfahrtantriebe/JPC---Direct-Thrust-Measurements-of-an-EM-Drive-and-Evaluation-of-Possible-Side-Effects.pdf https://tu-dresden.de/ing/maschinenwesen/ilr/rfs/ressourcen/... First you have to completely decouple the cavity from it's surrounding environment - especially the RF-field has to be generated by an apparatus fixed to the cavities frame of reference. Also the power has to come from a source connected to this frame of reference. For me this is Physics 101. As otherwise your system is not even closed. You are just neglecting that you are pumping LOTS of energy into an open system that you are measuring while assuming it to be closed -> thus leading to wrong conclusions (measuring a change in impulse in one part of the system) For me this in line with uBeam and the like. Whacko-science wherever one looks.
      - badlogic 10y ago
        Ah, so you created a new account because you are from TU Dresden. When I was in academia it was OK to call out other institutes without doing so anonymously. Has this changed?
        binarycoffee 10y ago
        I doubt Mr debunkit is from TU Dresden or he would probably have posted the link to the article first (though it could have been a ruse of course). In any case, I am not from TU Dresden and have only a passing acquaintance with Tajmar, but I do agree that credit and recognition is not going where it should in this case.
  - _benedict 10y ago
    The linked paper draws no such conclusion: "The nature of the signals observed is still unclear." They are, clearly, taking the tack of eliminating all sources of measurement error. But they haven't yet achieved that, and as yet a force remains. It seems perfectly reasonable to assume it will be attributed to measurement error, but that is not yet the case: " Next steps include better magnetic shielding.... We believe that this is a good education project to track down measurement errors..."
    - debunkit 10y ago
      Yes, and the is the point. NASA would have had the means to eliminate most of those sources of errors. I wouldn't call these measurement errors though -> the measurement is fine - your setup is the source of error. But they decided not to follow such a line of research. And yes, they are right "We believe that this is a good education project to track down measurement errors". The measurement error being the "thrust" that is due to your experimental setup. But let them waste some more money, time and reputation and build this in space so they can find out it does not actually work.
      - raverbashing 10y ago
        Did you create this account only to comment on this story? (just curious) > NASA would have had the means to eliminate most of those sources of errors. Yes. NASA as a whole yes. One group researching something that may or may not bear fruit no. So it's natural they try to eliminate easier errors first. But (as an example) it's one thing to have a good vacuum, another one to have an excellent vacuum for testing. So first you test on the good vacuum.
        debunkit 10y ago
        > Did you create this account only to comment on this story? (just curious) Yes i did, usually i just let certain topics pass by me and never comment here. RF-cavities though are the very core to my line of research, so my acceptance for bs is very low in this regard. If one wants to convince me of a thrust effect: build a prototype where the power source (a battery for example) and the RF-source are strapped onto the cavity, put the whole setup in a vacuum of your choice (i heard NASA has very nice and !large! facilities) and show me a sustained increase in impulse (just let it rotate for a while)
  - heisenbit 10y ago
    Can you point to any publication of this elaborate experiment?
  - Nokinside 10y ago
    NASA seems to be minimally involved. The group has been working five years in their own time in this small laboratory with shoestring budget. White has a day job in NASA and he and others are working with this project in their free time. NASA don't seem to be involved in any other way but "NASA Eagleworks Laboratories" makes it sound like official NASA organization.
  - davesque 10y ago
    I remember seeing this. I didn't see anywhere in the NASA paper that they tried to replicate the German results. Did anyone else see this?
    - binarycoffee 10y ago
      Yes, sadly grand-parent appears to have been downvoted for posting one of the most insightful comment so far. To be fair, the authors did enlist Tajmar's paper in the state-of-the-art but they do not discuss despite it being the most relevant prior art. For anyone who knows a little bit Tajmar, if there was a tiny hint of a possibility that this effect could be real, he would definitely have pursued it; after all, his self-admitted goal is nothing else but to discover the warp-drive... That being said, he is no crackpot and the thoroughness of his article confirms it. Incidentally, in a similar HN story a couple of days ago I shared my suspicion about spurious contributions from thermal drift, and unsurprisingly I see this was also the number 1 suspect for Tajmar. Beside using thermal barrier to mitigate the problem, he also went from electro-magnetic damping to oil damping and found completely different results. Meanwhile, the Eagleworks guys are still using an EM damper, working right next to a strong EM field source.
      - azernik 10y ago
        Probably for tone. "Sad to see NASA involved in such shitty research" is needlessly judgmental of authors who, though they had read (and referenced) a paper, did not do quite as well at eliminating potential error sources as that paper.
        binarycoffee 10y ago
        True, that could have been brought up with greater diplomacy. That being said, I can understand the over-reaction, it is indeed frustrating to see relatively weak articles making front page because they originate from NASA when earlier, more thorough research did not get any attention because their authors were more careful with their claims. Mind you, I am not saying the Eagleworks paper should not have been published; any data point is good as long as the experiment is sufficiently described for it to be reproduced or disproved, and in that respect I think it is OK. But very good it is not.
- bvv 10y ago
  The main problem is that the supposed violation of momentum conservation. This law is very deeply ingrained in all the current fundamental theories of physics, from the standard model to general relativity. These theories are extremely successful in describing phenomena all the way from subnuclear scales to cosmological scales, as well as nearly everything in between. This leads to two issues: (a) If these models break down somewhere I would expect it to happen under much more extreme conditions and not with a 'table-top' experiment like this one. (b) As far as I can see, giving up momentum conservation is not a feature that we can simply 'bolt onto' the existing models. It would require a radical rethinking of the very foundations of our current physical models. So my personal attitude is that extraordinary claims require extraordinary evidence and this paper is not remotely convincing. This experiment reminds me very much of the faster-than-light neutrinos. The authors of that experiment also seemed careful enough to not overstate their claims but this did not prevent a massive public interest in an ultimately debunked result. I expect the results in this paper to go the same way.
  - avian 10y ago
    > If these models break down somewhere I would expect it to happen under much more extreme conditions and not with a 'table-top' experiment like this one. I agree and I'm skeptical myself. But note that models just barely break in this experiment. The deviation from theory (if real) is so small that it's almost unmeasurable. The models might break in a more severe way if extreme conditions are applied in a correct way.
  - sfifs 10y ago
    > (a) If these models break down somewhere I would expect it to happen under much more extreme conditions and not with a 'table-top' experiment like this one. To push back on this kind of thinking a bit, Einstein's breakthrough papers on Brownian motion (which served as evidence of existence of Atoms and Molecules) and the photo electric effect (which demonstrated validity of the Quantum theory of light) were very much "tabletop" effects. While there's no denying this requires extraordinary proof, I think it's equally important for physicists to prevent themselves being biased by pre-conceived notions.
chopin 10y ago
There is an elaborate analysis of potential error sources, which I appreciate highly. However, I would have preferred a more rigorous quantitative analysis. The offered explanation model is highly fascinating. I'd appreciate if somebody would chime in with a more understandable version or resources thereto.
sabujp 10y ago
I don't understand how the 1.2mN/kW is better than the hall thruster that achieves 60mN/kW ? Isn't it better to achieve higher mN per kW than lower?
- mirimir 10y ago
  > Although this test campaign was not focused on optimizing performance and was more an exercise in existence proof, it is still useful to put the observed thrust-to-power figure of 1.2 mN/kW in context. The current state-of–the-art thrust to power for a Hall thruster is on the order of 60 mN/kW. This is an order of magnitude [more like two] higher than the test article evaluated during the course of this vacuum campaign; however, for missions with very large delta-v requirements, having a propellant consumption rate of zero could offset the higher power requirements. 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 [0.0033-0.0067 mN/kW] range.
- Shanea93 10y ago
  This is the first iteration of this device, I imagine that when the very first computing systems were being built, some humans were still on parity / better than the new systems. The interesting part will be to see how this performs when we scale it up in size and stick it in a true space vacuum - it seems based on the experiments done that the amount of thrust scales linearly based on kW/h input, I imagine there are some significant gains to be made in terms of efficiency and cavity design which could well see significant increases in performance. Then take in to account that the Hall Thruster requires a propellant - this only requires electricity, theoretically with a nuclear reactor on board, you could achieve constant acceleration, instead of our current methods of putting things in to deep space which consist mostly of "Blow up a ton of stuff behind it and then coast along for tens of millions of miles" I'm not a trained physicist, by the way, so there could be fallacies or inaccuracies here, this is based on my understanding.
  - stevetrewick 10y ago
    >I imagine that when the very first computing systems were being built, some humans were still on parity / better than the new systems. I mean I guess it depends on how far back you want to go. The early electronic systems (Collosus, ENIAC, the crazy relay boards and bedsteads in the Newmanry at Bletchley) were all pretty much built expressly to solve practical and immediate problems (breaking ciphers, calculating parameters for nuclear weapons) that would take too long or contain too many errors if done by hand. Babbage got his freak on because of error rates in (IIRC) log tables. My Mesopotamian history is a little rusty, but it's easy to imagine a similar development story for the abacus. (In the sense of 'tool to surpass unaugmented human in speed and accuracy of computation' rather than 'hacking crypto and nuke yields'). But I dunno. Maybe.
mrob 10y ago
Any chance this thing is using dark matter as reaction mass? We're confident that dark matter exists because it's the only thing that perfectly explains the evidence from gravitational lensing of colliding galaxies (eg. https://en.wikipedia.org/wiki/Bullet_Cluster https://en.wikipedia.org/wiki/Bullet_Cluster ). Finding a way to interact with dark matter sounds much more plausible than breaking thermodynamics.
- dozzie 10y ago
  Please read where the "dark matter" term came from. It's not a faerie dust that facilitates magic use. It's just a hypothetical matter in the universe that we can't observe, because for some yet-unknown reason it doesn't emit light. There's no reason it can't be just regular matter.
  - mtpro 10y ago
    Not only does it not emit light, it does not interact with electromagnetic waves in any way.
    - JoeAltmaier 10y ago
      And it doesn't obscure light - doesn't leave a shadow. No, its not regular matter at all. Its definitely something strange.
      - rebolek 10y ago
        If it is something at all and not only a flaw in our theories.
        Zigurd 10y ago
        Calling it "inexplicable gravity thing that makes galaxies work" does not exude confidence.
      - gizmo686 10y ago
snarfy 10y ago
If you pressurize a sealed cavity with a gas, it's not going to move due to the internal pressure regardless of what shape you make it. If you sum all of the collisions of the gas atoms along with the container, the sum momentum will be zero. Momentum is mass x velocity. Contrast this with pressure created via light. Velocities with light don't add that way. Instead there is a red/blue shift in the frequency. I can't put my finger on how this could work, but it seems there is a discontinuity here between the speed of light being constant in all reference frames and summing velocities to calculate momentum. Maybe with light, only energy conservation matters and momentum can be changed via redshift/blueshift relative to the container.
- ingenter 10y ago
  No, light is not different. If you want to adjust for "red/blue shift", you may use special relativity, and in special relativity you have the conservation of 4-momentum, which will give you the same result.
  - snarfy 10y ago
    Ah, if my understanding is correct then this makes sense. In my initial argument I bring in relativity and the invariant speed of light. What I neglected is everything else in relativity, like lorentz transformations. I mentioned a discontinuity between invariant speed of light and summing velocities to calculate momentum. The discontinuity is distance. Velocity is distance x time, but under lorentz transformations distance is relative. The discontinuity is resolved if you include length contraction (and time dilation).
- lisivka 10y ago
  You know that everything around us is both matter and wave at same time (wave-particle duality). Right? I.e. small bit of matter surrounded with wave. (See any of walking droplets videos to develop intuition). Unlike regular matter, waves are propagating through space, by contraction and expanding of a field. Because of particle-wave duality, when matter is moving, EM field around matter expands and contracts at high frequency. Right? EM radiation in form of radio-waves can interact with these surrounding waves because of interference. Right? IMHO, interference between radio-waves and surrounding waves may cause effect similar to used in acoustic levitation.
fitzwatermellow 10y ago
SPR's Roger Shawyer Explaining The Basic Science behind #EmDrive: https://www.youtube.com/watch?v=wBtk6xWDrwY https://www.youtube.com/watch?v=wBtk6xWDrwY
- jasonwatkinspdx 10y ago
  Since many people may be jumping into this topic without context/awareness: Shawyer's explanations simply do not hold up. Even the minority of folks that know physics and think the emdrive is real agree that Shawyer's proposals are invalid. Further, he's been at this for years, repeatedly making grandiose claims and failing to deliver on them. Take anything he says with a huge grain of salt.
jayajay 10y ago
If anyone's lazy, I highly suggest at least reading parts 9 and 10. One of the interesting takeaways here is that Q * -thrust is 2 orders of magnitude stronger than Photon-thrusters, and about 1-2 orders of magnitude lower than Ion-thrusters. * A Q-thruster is a thruster which pushes off of the zero point fluctuations in vacuum, which is still not understood.
- lisivka 10y ago
  But if you will try to discuss pilot-wave and walking droplets here (they are mentioned in part 10), you will receive lot of downvotes here. Quote: Although the idea of a pilot wave or realist interpretation of quantum mechanics is not the dominant view of physics today (which favors the Copenhagen interpretation), it has seen a strong resurgence of interest over the last decade based on some experimental work pioneered by Couder and Fort [13]. Couder and Fort discovered that bouncing a millimeter-sized droplet on a vibrating shallow fluid bath at just the right resonance frequency created a scenario where the bouncing droplet created a wave pattern on the shallow bath that also seemed to guide the droplet along its way. To Couder and Fort, this seemed very similar to the pilot-wave concept just discussed and, in subsequent testing by Couder and others, this macroscopic classical system was able to exhibit characteristics thought to be restricted to the quantum realm. To date, this hydrodynamic pilot-wave analog system has been able to duplicate the double slit experiment findings, tunneling, quantized orbits, and numerous other quantum phenomena. Bush put together two thorough review papers chronicling the experimental work being done in this domain by numerous universities [14,15].
  - highd 10y ago
    i.e. at best, it provides no new information at the expense of learning an entirely new framework.
    - lisivka 10y ago
      IMHO, if we will know better the physics of quantum and relativistic effects, we will be able to model them at macro level, so it will be much easier to understand and study these effects. Mathematics will not change, calculation results will not change, but understanding of processes will rise significantly, which may lead to new advances in physics.
Animats 10y ago
It's so frustrating. One micronewton per kilowatt. All that power going in, and so little force coming out. All it takes is some tiny noise effect to get that much force. The effect is so weak and they're so near the noise threshold. Quotes: "Components get warmer and the geometry changes slightly due to thermal expansion". "The thermal signal in the vacuum runs was slightly larger than the magnitude of the impulsive signal." "As the aluminum heat sink got warmer, its thermal expansion dominated the shifting center of gravity (CG) of the test article mounted on the torsion pendulum. This CG shift caused the balanced neutral point baseline of the torsion pendulum to shift with the same polarity as the impulsive signal when the test article was mounted in the forward or reverse thrust direction." "The seventh error is outgassing, which has the potential for a false positive from vaporization of surface molecules of the dielectric insert or other nonmetallic surfaces."
- davesque 10y ago
  True but, according to some expert opinions I've read, if this thing pans out (and it's looking more and more like it will), that thrust is actually pretty damn good compared to other propellantless engines and not too damn bad compared to even conventional space probe engines.
  - danbruc 10y ago
    [...] if this thing pans out (and it's looking more and more like it will) [...] Totally not, this is still with 99+ % a measurement error. We really understand theoretical physics pretty well, physicist have repeatedly predict measurement outcomes to a part in a million and less, have predicted particles decades ahead of the experiments discovering them. People really underestimate the power of theoretical physics and if there is a conflict between theory and experiment, it will almost always be the experiment that is wrong.
    - james0001 10y ago
      Tbh sounds like you're just a prude that doesn't like things you don't understand
chriskanan 10y ago
How much evidence is needed to motivate testing it in space? It seems that would settle the dispute regarding whether it works or not. Considering how inexpensive cubesats are to launch, it seems like it could be launched for about $100k, not including the additional R&D.
- bobwaycott 10y ago
  I could be mistaken, but I believe someone is lunching such a test next year. Edit: Cannae Inc. intends to launch a test with a small satellite. 2017 is so far a guess for launch based on a quick search.
s_kilk 10y ago
Can someone smarter than I explain the impact of this?
- allerhellsten 10y ago
  Further proof that there might actually be something to propellantless propulsion - which would be an incredible proposition for space travel.
  - zoren 10y ago
    Agreed. Yet even more incredible would be not even bringing energy for the propulsion. http://www.space.com/32546-interstellar-spaceflight-stephen-hawking-project-starshot.html http://www.space.com/32546-interstellar-spaceflight-stephen-...
- hannob 10y ago
  Most likely none at all. The tl;dr is that some scientists investigate some fringe technologies that violate the laws of physics and based on some preliminary studies it looks like there could be something. However it's still vastly more likely that the studies are flawed than that we'll have to rewrite the laws of physics.
  - matt_wulfeck 10y ago
    Haven't we been incrementally updating our understanding of physics since.. forever?
    - frozenport 10y ago
      Hard to say, certain conservation principles have been pretty constant.
      - thanatropism 10y ago
        Conservation principles come from fundamental symmetries. https://www.eng.fsu.edu/~dommelen/quantum/style_a/physsym.html https://www.eng.fsu.edu/~dommelen/quantum/style_a/physsym.ht...
tbrownaw 10y ago
If the vacuum is indeed mutable and degradable as was explored, then it might be possible to do/extract work on/from the vacuum, and thereby be possible to push off of the quantum vacuum and preserve the laws of conservation of energy and conservation of momentum. It is proposed that the tapered RF test article pushes off of quantum vacuum fluctuations, and the thruster generates a volumetric body force and moves in one direction while a wake is established in the quantum vacuum that moves in the other direction. ...well, at least it's better than calculating the theoretical produced thrust by ignoring the axial component of the radiation pressure against the side walls. Which is how tapered resonant cavities like this were supposed to produce thrust when I was in high school. But, leaving a wake in the vacuum should require that the vacuum exists in some particular reference frame. How's that supposed to work? Or since the paragraphs immediately before that one discussed the vacuum behaving differently when there's stuff in it, are they just saying that something is being exhausted out the back (which should be visible by some sort of effect on the vacuum?) even if they have no idea what that something might be?
cjensen 10y ago
For those new to this, the emdrive is very likely bogus. 1. It violates Conservation of Momentum. If the phenomena is real, a large number of basic Physics principles would need to be discarded. 2. It was designed based on certain principles. Those principles have been shown to be wrong. But it works anyway because reasons? 3. The results of each experiment are suspiciously close to the limits of measurement. There are two choices here: (a) experimental error or (b) profound alteration to fundamental physics. Occam's Razor applies. Also, "extraordinary claims require extraordinary evidence" and this evidence is far from extraordinary. That this is being published in a journal which does not cover basic physics is not helping.
- michwill 10y ago
  The trick is that this is not a closed discussion. The thrust was suspiciously repeated in many experiments, and question is whether it's some fundamental flaw with experiments, or it is real. I guess, the more info is available to the public, the better. Hopefully someone will test it properly. But no way it can be considered as "provably works"
  - lomnakkus 10y ago
    What do you mean by "closed discussion", specifically? We've been hearing about this for ~1 year at this point, so I'm not sure what you mean. > I guess, the more info is available to the public, the better. This is up for debate -- esp. given the whole "fake news" thing and the observation that people basically love echo chambers (as observed in the field of Behavioural Economics). If, by "info" you mean "actually provable[1] info", then I probably agree. [1] To some reasonable standard of "proof". Certainly we don't need "mathematical" proof, but we need something better than "a study says". (See: reproducibility crisis[2], the fact that a "study" doesn't require any particular standard of evidence, etc.) [2] Meta: I wonder if the BE field is itself suffering from a reproducibility crisis? Anyone know?
    - michwill 10y ago
      Oh yeah, I wasn't clear, yes. Not "everything is clear, the case is closed" - that's what I meant
thearn4 10y ago
Some criticism on reddit: https://www.reddit.com/r/science/comments/5dqy9b/em_drive_is_shown_to_work_measurement_of/da6n92f/ https://www.reddit.com/r/science/comments/5dqy9b/em_drive_is...
michwill 10y ago
Interesting what are the fundamental reasons for the thrust. It's certainly not throwing photons. Hypotheses: * Flawed study. It actually throws something (like, cavity material slowly ablating) or repels of Eddy currents in surroundings; * It repels of Earth (and the force has either gravitational or magnetic nature); then it's not suitable for deep space propulsion * A sort of ether actually exists, and it throws that. Though, then there would be some anisotropy showing ether wind; in this case it is suitable to be used in deep space
- politician 10y ago
  If you read through their conclusions, they suggest that there may be a quantum vacuum capable of transmitting oscillations and this vacuum is what this this device pushes off of leaving a wake behind.
  - ribble 10y ago
    pilot wave theory, the force is able to push upon itself despite lack of medium to otherwise push upon.
  - gus_massa 10y ago
    [Disclaimer: I think it's a measurement error.] Just ignore the theoretical explanations. Just imagine that it's something they wrote to avoid the crackpot tag. That explanation doesn't make any sense. Also avoid all the other theoretical explanations, they are also very sloppy. Just concentrate in the experiments, that is the less sloppy part of these reports. If they discovered something new, then they can make a working prototype and improve it until it's clear that they are measuring something really new and it's not an experimental error or a misattributed force. They can make foolproof instructions so anyone can make a version in a good enough lab and reproduce the experiment, or sell an experimental setup in Ebay. Then it will "confirmed". There has been a many famous experiments that were later debunked, like: * cold fussion https://en.wikipedia.org/wiki/Cold_fusion https://en.wikipedia.org/wiki/Cold_fusion , they had also some kind of theoretical excuse, but it was wrong and it was impossible to reproduce the experiment. * arsenic in DNA https://en.wikipedia.org/wiki/GFAJ-1 https://en.wikipedia.org/wiki/GFAJ-1 , they had also some kind of theoretical excuse, but it was wrong and it was impossible to reproduce the experiment. If you want success cases, my favorites are: * the asymmetric disintegration of cobalt in a magnetic field https://en.wikipedia.org/wiki/Wu_experiment https://en.wikipedia.org/wiki/Wu_experiment , I guess they had some wrong explanation, but the correct explanation was discovered like 20 years later * high temperature superconductivity https://en.wikipedia.org/wiki/High-temperature_superconductivity https://en.wikipedia.org/wiki/High-temperature_superconducti... IIRC they have some explanation or practical rules, but the correct explanation was discovered like 20 years later Just concentrate in the experiments, and wait 20 years for a good explanation.
jtchang 10y ago
This is pretty good news if only that we will get more research into this phenomenon. In 1933 von Neumann basically published a proof against the idea of any hidden-variable theory. It took 30 years but Bell then discredited it. My guess is that a lot of this will get revisited. The outcome of this in the next 10-20 years might be really cheap probes (via reusable launch vehicles like SpaceX is making) that need no propellent to continue onto their merry way for a long time. The current way of doing this would be using solar sails or something along those lines which is not exactly compact. Having a way to push your little probe along (even at a little bit of acceleration) without having to carry a lot of heavy propellant is a big deal. Maybe just some solar panels to generate the energy needed.
- perlgeek 10y ago
  > This is pretty good news if only that we will get more research into this phenomenon. Agreed. > Having a way to push your little probe along (even at a little bit of acceleration) without having to carry a lot of heavy propellant is a big deal. Maybe just some solar panels to generate the energy needed. I'm not sure that actually works. Most use cases are for exploring the outer solar system, or even outside of our solar system. As the probe gets away from the sun, the solar energy it gets decreases with the square of the distance, and so it probably will stop providing even the little bit of acceleration.
  - ajuc 10y ago
    > As the probe gets away from the sun, the solar energy it gets decreases with the square of the distance, and so it probably will stop providing even the little bit of acceleration. In space you move in elipses. It's possible to choose an elongated orbit that moves the probe closer and then further from the sun repeatedly and each time it is close to the sun it accelerates forward, moving the "far" side of orbit further away, until it gains enough speed to escape sun gravity. Or at least it's possible in Kerbal Space Program :)
    - cperciva 10y ago
      Yes, you move in ellipses; but you spend a lot of time far away and very little time close to the sun. I'm not sure that the average power is any higher than you would have for a circular orbit at the same energy... EDIT: Ok, let's think through the calculus here. Kepler's 2nd law says that the area swept by the line between a planet and the Sun is constant, i.e., r^2 dθ/dt = 2 π a b / P where a and b are the semi-major and semi-minor axes and P is the orbital period. Thus dt / r^2 = P dθ / (2 π a b); and the former is the instantaneous power absorbed. Integrating over an orbit, we get E = P / (a b); or the average power absorbed is proportional to 1 / (a b). Since the energy of an orbit is determined solely by the semi-major axis a, this means the power absorbed for any given orbital energy is maximized for b ≪ a; so you're right, that highly eccentric orbits are a better way to acquire energy for the purpose of orbital escape. (Subject of course to practical considerations of energy storage -- you'll absorb the most power at exactly the time you don't want to be changing your momentum.)
Odenwaelder 10y ago
The laws of physics prevailed, despite the LHC and other experiments. As awesome as it sounds, I find it hard to believe that this finding is something relevant.
daveguy 10y ago
One thing that bothers me about this paper: The measurement error is stated to be +/- 6 micro-Newtons. However, the difference between force measured at the same power is 30-40 micro-Newtons and the "measurement error" is listed as the +/- error. So if the measurement error is that low then the additional variation is unreliability of the effect itself or a miscalculation of the measurement error.
revelation 10y ago
Sounds like Polywater: https://en.wikipedia.org/wiki/Polywater https://en.wikipedia.org/wiki/Polywater
anotheryou 10y ago
Can't we put one in a cube sat and give it a go? (or: why can't we?)
- trothamel 10y ago
  I'd think power is a problem. This produces a very slight acceleration with a kilowatt of power, while it looks like a 3U (triple stack) cubesat might produce ~14 watts.
  - anotheryou 10y ago
    I feared so :) the unit looked so small and handy.... But does it have to take constant power?
  - int_19h 10y ago
    But even very small acceleration should add up to significant velocity over time, no? So if we launched something that's only 10 W, how long before we can easily observe the velocity difference?
  - lobster_johnson 10y ago
    Cannae is launching its thruster experiment in a 6U cubesat next year: http://www.popularmechanics.com/science/energy/a22678/em-drive-cannae-cubesat-reactionless/ http://www.popularmechanics.com/science/energy/a22678/em-dri....
    - anotheryou 10y ago
      Cool! Any chance a 6U could stay up for month with conventional thrusters? Or will it be proven to work or at least be better than other thrusters once and for all?
gigatexal 10y ago
For the uninitiated how good or bad is 1.2mN/kw?
- froogle 10y ago
  Garbage for anything Earth-travel related. Gravity is 9.8N/kg, so to generate enough force to counter gravity you'll need to feed this thing 9.8MW per kg. Your typical 100 HP car engine puts out 75.6kW, so you'd need 130 car engines' worth of power to lift a small 1 kg/~2 pound object. Not to mention that the machinery needed to channel/produce that kind of energy would be so heavy that it could not lift itself. But it's still possibly useful for space travel. Not needing propellant is huge for long-distance space travel. That said: they don't know why it works. (If it even works, which I strongly strongly strongly doubt.) If they figure out what produces the phenomenon, it's very possible they could get the drive to be way more efficient.
- Pxtl 10y ago
  A kilowatt is comparable to a space-heater or an insane gaming rig. A Tesla burns about 20kw for normal driving. Now, a Newton is the amount of force it takes to hold up an apple (or accelerate it at 1G). So a millinewton would be the amount of force it takes to hold up a blueberry.
  - MertsA 10y ago
    That is a great way to explain units to people.
- sonium 10y ago
  To put into proportions: The radio isotope thermoelectric generator (RTG) of the Voyager spacecraft wheighs 37kg. So let's say we can build a spacecraft using this and the EM drive weighing a total of 50kg. The RTG produces 157W of power. This translates to a change in speed 30cm per day. Bonus question: The power of the RTG halfes avery 87.7 years. What is the asymptotic speed the spacecraft will reach?
  - photogrammetry 10y ago
sergj 10y ago
I was pretty sure there was a seperate study where they debunct it? Gonna look for the link...
acqq 10y ago
http://blogs.discovermagazine.com/outthere/2014/08/06/nasa-validate-imposible-space-drive-word/ http://blogs.discovermagazine.com/outthere/2014/08/06/nasa-v... About the previous tests of the same team: "The testing was done by five NASA employees in a lab devoted to exploring unorthodox propulsion ideas. The team leader is a researcher named Harold “Sonny” White, himself a proponent of ideas about faster-than-light warp drives that most of his colleagues have classified as physically impossible. The lead author is one of White’s Eagleworks teammates, David A. Brady. Calling this group “NASA”—as almost every popular news story has done—is a gross oversimplification."
- SubiculumCode 10y ago
  They fund it, no?
  - acqq 10y ago
    Would it be better if NASA wouldn't have less then 10 people, out of their 18,000 employees (0.05%), working on testing nevertheless such claims which almost surely don't work? Maybe, if that 0.05% is used against NASA by claiming it doesn't do its job how it should.
    - binarycoffee 10y ago
      Interestingly, NASA used to have a group working on such projects. https://en.wikipedia.org/wiki/Breakthrough_Propulsion_Physics_Program https://en.wikipedia.org/wiki/Breakthrough_Propulsion_Physic... And I believe they actually did a serious job, which is probably why they never found any warp-drive ;-)
    - Nokinside 10y ago
      It's my understanding that they are working with this project on their free time. NASA pays small amount of money ($50,000 or so) and gives them a room to do experiments. Or at least did in 2011. Eagleworks and their team are not official NASA research. They just have facebook page. Contact attempts trough NASA don't work. Glenn Research Center offered to replicate the experiment in a hard vacuum if Eagleworks manages to reach 100 µN of thrust.
mrob 10y ago
Recent previous discussion: https://news.ycombinator.com/item?id=12992536 https://news.ycombinator.com/item?id=12992536
- dang 10y ago
  Since there's obvious appetite to discuss this, we've merged the comments here instead of burying the current (re)post as a dupe like we normally would. A couple more posts about this: https://news.ycombinator.com/item?id=12994541 https://news.ycombinator.com/item?id=12994541 https://news.ycombinator.com/item?id=12994400 https://news.ycombinator.com/item?id=12994400
- eln1 10y ago
  As the main hypothesis in this paper is that the momentum is transferred by pilot waves, it is worth to emphasize the (cited there) most known recent approaches - Couder's experiments which use classical object with wave-particle duality (droplet coupled with waves it creates), getting e.g. interference in double-slit, orbit quantization and many other quantum-like phenomena: https://en.wikipedia.org/wiki/Hydrodynamic_quantum_analogs https://en.wikipedia.org/wiki/Hydrodynamic_quantum_analogs https://www.youtube.com/watch?v=nmC0ygr08tE https://www.youtube.com/watch?v=nmC0ygr08tE
gfodor 10y ago
There seems to be a meme around the EmDrive where "it works" and "conservation of momentum is upheld" are mutually exclusive. Couldn't it be the case that there is some local phenomenon happening that we do not understand that still manages to maintain conservation of momentum? Isn't assuming that momentum conservation is violated a conjecture on the underlying physics of the device, which we don't know?
- colechristensen 10y ago
  It's only exciting if it violates the conservation of momentum. If it doesn't, it's not useful as a space thuster or a flying car, and whatever is causing the miniscule force is just some leaky edge case that's difficult to measure. It's boring if it doesn't violate momentum conservation.
  - nkoren 10y ago
    I dunno. Accidentally discovering a way to, say, shove dark matter around with microwaves and do useful work with it would not necessarily violate momentum conservation, and wouldn't really be that boring. (Not that I think this is what the EM drive is doing, or that I'd bet on it with anything other than very long odds, but I'm glad someone is looking into it).
  - int_19h 10y ago
    Is it really true said "leaky edge case" is applicable throughout our entire local space? e.g. the solar system? or even the vicinity of Earth?
- akiselev 10y ago
  It's a little more complicated than conservation of momentum, which is just a subset of conservation of energy useful for intuition about the non quantum world. If you're converting energy into massive particles or photons for propulsion you can still have a "massless" drive while maintaining conservation of momentum because what you're really conserving is the total energy of the system. Research has previously shown that it is possible to create particles but it requires ungodly amounts of energy and a specially designed apparatus that separates the resulting particle and antiparticle using quantum effects before they can annihilate each other. There is even some research into using a vibrating "quantum mirror" that forces virtual photons to become real using only energy from quantum fluctuations but that's even more complicated and difficult to engineer. Either the EM drive has a unique combination of features that allows efficient creation and separation of particles using electricity, some other unknown quantum effects are present that can convert energy to momentum without an opposite reaction on another particle/field, or there is still a hidden error. Given the scientific knowledge we have today, it's extremely likely to be the latter but that doesn't preclude the possibility that we have discovered something novel.
pmcollins 10y ago
Doesn't a standard microwave (or any other) transmitter produce a tiny force due to radiation pressure? I understand that this is different because the radiation bounces around an enclosed chamber and so momentum wouldn't be conserved, but if the issue is to create propellant-free propulsion, doesn't that already exist (even though it's not practical)?
- ribble 10y ago
  > Doesn't a standard microwave (or any other) transmitter produce a tiny force due to radiation pressure? pressure against what?
  - pmcollins 10y ago
    https://en.wikipedia.org/wiki/Radiation_pressure#Radiation_pressure_by_emission https://en.wikipedia.org/wiki/Radiation_pressure#Radiation_p...
    - ribble 10y ago
      this article includes a grey body that the force is acting upon. the difference with the EM drive's method of propulsion is, that while the article you posted describes a force reacting upon an external, "grey body," as is acceptable with the copenhagen interpretation of quantum mechanics, the EM drive force exhibits a characteristic betrayed by a theoretical pilot wave, which indicates a non-copenhagen interpretation of quantum mechanics, but rather a bohmann version of quantum mechanics, in which the force can act upon itself. run-on sentence alert.
- gus_massa 10y ago
  Yes, but they suppousedly got 4000 times the maximal theoretical value. I'll repost one of my old comments with more details: If you use a photon thruster (aka a laser or a flashlight in the right direction (or a microwave)), then the maximal thrust/energy ratio is at most 1/c = 3.33 nano-Newtons per Watt = 0.0033 uN/W = 0.0033 mN/KW. Someone compiled here two lists of experiments: http://forum.nasaspaceflight.com/index.php?topic=36313.msg1302455#msg1302455 http://forum.nasaspaceflight.com/index.php?topic=36313.msg13... http://emdrive.wiki/Experimental_Results http://emdrive.wiki/Experimental_Results Some of the experiments are few years old, but you can compare the current result with 0.0033 mN/KW. The results in the tables vary from 3x to 200000x the theoretical maximum of a photon thruster. I think that the typical current value is x4000. It's a theoretical upper bound that is very easy to calculate using special relativity, and it depends on very fundamental laws, not tricky details of the universe. The theoretical bound is so fundamental, that it's even true if you use a graviton thruster instead of a photon thruster. This example is not totally made up, someone have an alternative impossible massless drive that "push against the far away stars". They claimed also a thrust/energy ratio > 0.0033 mN/KW, so it was also impossible from a theoretical point of view. Also, for the EmDrive, someone proposed that it emits twin photons that somehow cancel each other, but the pair still carry momentum. That explanation extremely wrong.
smcameron 10y ago
If real, you could build a perpetual motion machine with it. Therefore it's not real.
- kobeya 10y ago
  This is violating conservation of momentum, not conservation of energy. You cannot build a perpetual motion machine using it. But even if you could, that is not a reasonable argument. Reality is what it is.
  - ncallaway 10y ago
    "But even if you could, that is not a reasonable argument" It may not be a reasonable argument to claim that it is impossible, but it is a totally fine argument to make that it is insanely unlikely and needs a mountain of evidence before we take the conclusions seriously.
    - kobeya 10y ago
      That's an argument about priors. In the face of actual evidence of its reality, priors establish significance not believability.
      - inimino 10y ago
        No... priors are precisely about believability. Any evidence can be explained either by the effect or by experimental error. Your prior is how relatively likely these two possibilities are. If something is "significant" then it is surprising and requires stronger evidence.
- eridius 10y ago
  Could you? How? Perpetual motion machines must put out at least as much energy as they take in. AIUI the EmDrive requires external power (such as solar panels) and produces a rather tiny amount of force. This does not sound to me like it's anywhere even remotely close to putting out as much energy as it takes in.
maverick_iceman 10y ago
As I said earlier this is bogus. We might as well try to prove virgin birth.
- photogrammetry 10y ago
  https://en.wikipedia.org/wiki/Parthenogenesis https://en.wikipedia.org/wiki/Parthenogenesis
caconym_ 10y ago
A while back I read an interesting but possibly also batshit crazy article that proposed an explanation possibly involving something like quantization of inertia, and/or generation of extremely long-wavelength photons, wavelengths on the order of the size of the universe. Does anyone know what I'm talking about? IIRC it was based on some theoretical work that was done before EmDrive was a thing, and it seemed less hand-wavey to me than simply "conservation of momentum is wrong" or "we're using the quantum vacuum as a tractive medium which is supposed to be impossible but whatever" explanations. I'm not saying this explanation is right (or wrong, or that the thrust observed in these experiments is or isn't caused by "new physics"); I'm just curious whether anyone knows what I'm talking about and can provide some more context. edit, found it: https://www.technologyreview.com/s/601299/the-curious-link-between-the-fly-by-anomaly-and-the-impossible-emdrive-thruster/ https://www.technologyreview.com/s/601299/the-curious-link-b... Any thoughts?
- kybernetikos 10y ago
  I think you're talking about McCulloch's quantisation of inertia theory. http://www.ptep-online.com/index_files/2015/PP-40-15.PDF http://www.ptep-online.com/index_files/2015/PP-40-15.PDF which I believe was originally inspired by the rotation of galaxies.
  - caconym_ 10y ago
    Yup, that's it. I found the article I read, edited my post to include it.
petters 10y ago
If this holds up I am prepared to believe in almost anything – like the universe being a simulation and this is a deterministic round-off error. Conservation of momentum is pretty fundamental.
walrus01 10y ago
1.2 millinewtons per kW is not a lot - the size of a 12kW solar array for a large satellite is quite considerable... Space based nuclear reactors anyone? No cosmos-954 incidents, hopefully.
recycle 10y ago
Open Source Projects / Experiments that might be relevant to the discussion: https://hackaday.io/project/5596-em-drive https://hackaday.io/project/5596-em-drive https://hackaday.io/project/10166-flying-an-emdrive https://hackaday.io/project/10166-flying-an-emdrive
philip142au 10y ago
When the super-conducting version work it will change the world.
kleigenfreude 10y ago
Fuck all the deniers. Fuck you. FUCK YOU!
- reitanqild 10y ago
  Why did you suddenly start posting like this?
- photogrammetry 10y ago
  Surely you realize that HN doesn't allow you to delete comments, ever.
microcolonel 10y ago
For those who wish to see the abstract page without enabling cookies. http://archive.is/zuVaz http://archive.is/zuVaz
binarycoffee 10y ago
Several comments have hinted at the possibility that this would be a over-unity device but as I couldn't find a specific demonstration, here is one that does not involve any fancy physics. Let's assume we have a spacecraft powered by an energy source with total energy `E` and mass `m`. The EM-drive produces a constant thrust `F` at a constant power `P`. Kinetic energy of the S/C after time `t`: Ek = 0.5 * F^2 * t^2 / m If `t` is the time at which the energy in the source is exhausted, then the ratio of kinetic energy developed to the expended energy (E = t * P) is: Ek/E = 0.5 * F^2 / P^2 * (E/m) So this basically says that we have a over-unity device whenever the energy source has a specific energy above: E/m > 2P/F ~ 1.6 10^6 J/kg which is certainly not achievable in practice, but in theory is totally fine being still well below c^2 (which by the way justifies a-posteriori the neglect of relativistic corrections in the above).
Symmetry 10y ago
So 1.2 mN/kW. By comparison the ion engine on the Dawn probe puts out 34 mN/kW (236mN / 6.9 kW). But of course that's for an effectively infinite exhaust velocity rather than just 42 km/s.
imdsm 10y ago
> Although this test campaign was not focused on optimizing performance and was more an exercise in existence proof, it is still useful to put the observed thrust-to-power figure of 1.2mN/kW1.2 mN/kW in context. The current state-of–the-art thrust to power for a Hall thruster is on the order of 60mN/kW60 mN/kW. This is an order of magnitude higher than the test article evaluated during the course of this vacuum campaign; however, for missions with very large delta-v requirements, having a propellant consumption rate of zero could offset the higher power requirements. The 1.2mN/kW1.2 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 3.33–6.67μN/kW3.33–6.67 μN/kW (or 0.0033–0.0067mN/kW0.0033–0.0067 mN/kW) range. Read More: http://arc.aiaa.org/doi/full/10.2514/1.B36120#_i36 http://arc.aiaa.org/doi/full/10.2514/1.B36120#_i36
tombone12 10y ago
Goddamit, I wanted to get to the comment about the superoptimizer, not this mass hallucination over crap sience :(
nepotism2016 10y ago
For those who dig this stuff...I strongly recommend you watch BBC Horizon episode Project greenglow http://www.dailymotion.com/video/x40a65t http://www.dailymotion.com/video/x40a65t

595 points by babak_ap 10y ago

ctoth 10y ago

Thanks for submitting this, love to see feedback from the physicists who hang out around here!

debunkit 10y ago
There was a very elaborate experiment in Germany regarding this. They concluded that the force is excerted by coupling the RF-energy from the outside. If the system is fully self-contained (driven by a battery physically connected to the cavity) there is no thrust to be measured. It's very sad to see NASA being involved in such shitty research.
- danbruc 10y ago
  Direct Thrust Measurements of an EM Drive and Evaluation of Possible Side-Effects [1] [1] https://tu-dresden.de/ing/maschinenwesen/ilr/rfs/ressourcen/dateien/forschung/folder-2007-08-21-5231434330/ag_raumfahrtantriebe/JPC---Direct-Thrust-Measurements-of-an-EM-Drive-and-Evaluation-of-Possible-Side-Effects.pdf?lang=en https://tu-dresden.de/ing/maschinenwesen/ilr/rfs/ressourcen/...
  - debunkit 10y ago
    Thanks for posting a link to the paper!
- rocqua 10y ago
  You can't blame NASA for trying shit. They aren't claiming this stuff will work, just that they measured thrust. The fact that one study showed differently isn't binding. Many, many papers disagree. I believe they are going to put one of these in space, that'll give a definitive answer.
  - debunkit 10y ago
    I am blaming them for not being up to date on the state of the art and not following up on earlier research, especially on what has been hinted at in: https://tu-dresden.de/ing/maschinenwesen/ilr/rfs/ressourcen/dateien/forschung/folder-2007-08-21-5231434330/ag_raumfahrtantriebe/JPC---Direct-Thrust-Measurements-of-an-EM-Drive-and-Evaluation-of-Possible-Side-Effects.pdf https://tu-dresden.de/ing/maschinenwesen/ilr/rfs/ressourcen/... First you have to completely decouple the cavity from it's surrounding environment - especially the RF-field has to be generated by an apparatus fixed to the cavities frame of reference. Also the power has to come from a source connected to this frame of reference. For me this is Physics 101. As otherwise your system is not even closed. You are just neglecting that you are pumping LOTS of energy into an open system that you are measuring while assuming it to be closed -> thus leading to wrong conclusions (measuring a change in impulse in one part of the system) For me this in line with uBeam and the like. Whacko-science wherever one looks.
    - badlogic 10y ago
      Ah, so you created a new account because you are from TU Dresden. When I was in academia it was OK to call out other institutes without doing so anonymously. Has this changed?
      - binarycoffee 10y ago
        I doubt Mr debunkit is from TU Dresden or he would probably have posted the link to the article first (though it could have been a ruse of course). In any case, I am not from TU Dresden and have only a passing acquaintance with Tajmar, but I do agree that credit and recognition is not going where it should in this case.
- _benedict 10y ago
  The linked paper draws no such conclusion: "The nature of the signals observed is still unclear." They are, clearly, taking the tack of eliminating all sources of measurement error. But they haven't yet achieved that, and as yet a force remains. It seems perfectly reasonable to assume it will be attributed to measurement error, but that is not yet the case: " Next steps include better magnetic shielding.... We believe that this is a good education project to track down measurement errors..."
  - debunkit 10y ago
    Yes, and the is the point. NASA would have had the means to eliminate most of those sources of errors. I wouldn't call these measurement errors though -> the measurement is fine - your setup is the source of error. But they decided not to follow such a line of research. And yes, they are right "We believe that this is a good education project to track down measurement errors". The measurement error being the "thrust" that is due to your experimental setup. But let them waste some more money, time and reputation and build this in space so they can find out it does not actually work.
    - raverbashing 10y ago
      Did you create this account only to comment on this story? (just curious) > NASA would have had the means to eliminate most of those sources of errors. Yes. NASA as a whole yes. One group researching something that may or may not bear fruit no. So it's natural they try to eliminate easier errors first. But (as an example) it's one thing to have a good vacuum, another one to have an excellent vacuum for testing. So first you test on the good vacuum.
      - debunkit 10y ago
        > Did you create this account only to comment on this story? (just curious) Yes i did, usually i just let certain topics pass by me and never comment here. RF-cavities though are the very core to my line of research, so my acceptance for bs is very low in this regard. If one wants to convince me of a thrust effect: build a prototype where the power source (a battery for example) and the RF-source are strapped onto the cavity, put the whole setup in a vacuum of your choice (i heard NASA has very nice and !large! facilities) and show me a sustained increase in impulse (just let it rotate for a while)
- heisenbit 10y ago
  Can you point to any publication of this elaborate experiment?
- Nokinside 10y ago
  NASA seems to be minimally involved. The group has been working five years in their own time in this small laboratory with shoestring budget. White has a day job in NASA and he and others are working with this project in their free time. NASA don't seem to be involved in any other way but "NASA Eagleworks Laboratories" makes it sound like official NASA organization.
- davesque 10y ago
  I remember seeing this. I didn't see anywhere in the NASA paper that they tried to replicate the German results. Did anyone else see this?
  - binarycoffee 10y ago
    Yes, sadly grand-parent appears to have been downvoted for posting one of the most insightful comment so far. To be fair, the authors did enlist Tajmar's paper in the state-of-the-art but they do not discuss despite it being the most relevant prior art. For anyone who knows a little bit Tajmar, if there was a tiny hint of a possibility that this effect could be real, he would definitely have pursued it; after all, his self-admitted goal is nothing else but to discover the warp-drive... That being said, he is no crackpot and the thoroughness of his article confirms it. Incidentally, in a similar HN story a couple of days ago I shared my suspicion about spurious contributions from thermal drift, and unsurprisingly I see this was also the number 1 suspect for Tajmar. Beside using thermal barrier to mitigate the problem, he also went from electro-magnetic damping to oil damping and found completely different results. Meanwhile, the Eagleworks guys are still using an EM damper, working right next to a strong EM field source.
    - azernik 10y ago
      Probably for tone. "Sad to see NASA involved in such shitty research" is needlessly judgmental of authors who, though they had read (and referenced) a paper, did not do quite as well at eliminating potential error sources as that paper.
      - binarycoffee 10y ago
        True, that could have been brought up with greater diplomacy. That being said, I can understand the over-reaction, it is indeed frustrating to see relatively weak articles making front page because they originate from NASA when earlier, more thorough research did not get any attention because their authors were more careful with their claims. Mind you, I am not saying the Eagleworks paper should not have been published; any data point is good as long as the experiment is sufficiently described for it to be reproduced or disproved, and in that respect I think it is OK. But very good it is not.
bvv 10y ago
The main problem is that the supposed violation of momentum conservation. This law is very deeply ingrained in all the current fundamental theories of physics, from the standard model to general relativity. These theories are extremely successful in describing phenomena all the way from subnuclear scales to cosmological scales, as well as nearly everything in between. This leads to two issues: (a) If these models break down somewhere I would expect it to happen under much more extreme conditions and not with a 'table-top' experiment like this one. (b) As far as I can see, giving up momentum conservation is not a feature that we can simply 'bolt onto' the existing models. It would require a radical rethinking of the very foundations of our current physical models. So my personal attitude is that extraordinary claims require extraordinary evidence and this paper is not remotely convincing. This experiment reminds me very much of the faster-than-light neutrinos. The authors of that experiment also seemed careful enough to not overstate their claims but this did not prevent a massive public interest in an ultimately debunked result. I expect the results in this paper to go the same way.
- avian 10y ago
  > If these models break down somewhere I would expect it to happen under much more extreme conditions and not with a 'table-top' experiment like this one. I agree and I'm skeptical myself. But note that models just barely break in this experiment. The deviation from theory (if real) is so small that it's almost unmeasurable. The models might break in a more severe way if extreme conditions are applied in a correct way.
- sfifs 10y ago
  > (a) If these models break down somewhere I would expect it to happen under much more extreme conditions and not with a 'table-top' experiment like this one. To push back on this kind of thinking a bit, Einstein's breakthrough papers on Brownian motion (which served as evidence of existence of Atoms and Molecules) and the photo electric effect (which demonstrated validity of the Quantum theory of light) were very much "tabletop" effects. While there's no denying this requires extraordinary proof, I think it's equally important for physicists to prevent themselves being biased by pre-conceived notions.

chopin 10y ago

There is an elaborate analysis of potential error sources, which I appreciate highly. However, I would have preferred a more rigorous quantitative analysis. The offered explanation model is highly fascinating. I'd appreciate if somebody would chime in with a more understandable version or resources thereto.

sabujp 10y ago

I don't understand how the 1.2mN/kW is better than the hall thruster that achieves 60mN/kW ? Isn't it better to achieve higher mN per kW than lower?

mirimir 10y ago
> Although this test campaign was not focused on optimizing performance and was more an exercise in existence proof, it is still useful to put the observed thrust-to-power figure of 1.2 mN/kW in context. The current state-of–the-art thrust to power for a Hall thruster is on the order of 60 mN/kW. This is an order of magnitude [more like two] higher than the test article evaluated during the course of this vacuum campaign; however, for missions with very large delta-v requirements, having a propellant consumption rate of zero could offset the higher power requirements. 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 [0.0033-0.0067 mN/kW] range.
Shanea93 10y ago
This is the first iteration of this device, I imagine that when the very first computing systems were being built, some humans were still on parity / better than the new systems. The interesting part will be to see how this performs when we scale it up in size and stick it in a true space vacuum - it seems based on the experiments done that the amount of thrust scales linearly based on kW/h input, I imagine there are some significant gains to be made in terms of efficiency and cavity design which could well see significant increases in performance. Then take in to account that the Hall Thruster requires a propellant - this only requires electricity, theoretically with a nuclear reactor on board, you could achieve constant acceleration, instead of our current methods of putting things in to deep space which consist mostly of "Blow up a ton of stuff behind it and then coast along for tens of millions of miles" I'm not a trained physicist, by the way, so there could be fallacies or inaccuracies here, this is based on my understanding.
- stevetrewick 10y ago
  >I imagine that when the very first computing systems were being built, some humans were still on parity / better than the new systems. I mean I guess it depends on how far back you want to go. The early electronic systems (Collosus, ENIAC, the crazy relay boards and bedsteads in the Newmanry at Bletchley) were all pretty much built expressly to solve practical and immediate problems (breaking ciphers, calculating parameters for nuclear weapons) that would take too long or contain too many errors if done by hand. Babbage got his freak on because of error rates in (IIRC) log tables. My Mesopotamian history is a little rusty, but it's easy to imagine a similar development story for the abacus. (In the sense of 'tool to surpass unaugmented human in speed and accuracy of computation' rather than 'hacking crypto and nuke yields'). But I dunno. Maybe.

mrob 10y ago

Any chance this thing is using dark matter as reaction mass? We're confident that dark matter exists because it's the only thing that perfectly explains the evidence from gravitational lensing of colliding galaxies (eg. https://en.wikipedia.org/wiki/Bullet_Cluster https://en.wikipedia.org/wiki/Bullet_Cluster ). Finding a way to interact with dark matter sounds much more plausible than breaking thermodynamics.

dozzie 10y ago
Please read where the "dark matter" term came from. It's not a faerie dust that facilitates magic use. It's just a hypothetical matter in the universe that we can't observe, because for some yet-unknown reason it doesn't emit light. There's no reason it can't be just regular matter.
- mtpro 10y ago
  Not only does it not emit light, it does not interact with electromagnetic waves in any way.
  - JoeAltmaier 10y ago
    And it doesn't obscure light - doesn't leave a shadow. No, its not regular matter at all. Its definitely something strange.
    - rebolek 10y ago
      If it is something at all and not only a flaw in our theories.
      - Zigurd 10y ago
        Calling it "inexplicable gravity thing that makes galaxies work" does not exude confidence.
    - gizmo686 10y ago

snarfy 10y ago

If you pressurize a sealed cavity with a gas, it's not going to move due to the internal pressure regardless of what shape you make it. If you sum all of the collisions of the gas atoms along with the container, the sum momentum will be zero. Momentum is mass x velocity. Contrast this with pressure created via light. Velocities with light don't add that way. Instead there is a red/blue shift in the frequency. I can't put my finger on how this could work, but it seems there is a discontinuity here between the speed of light being constant in all reference frames and summing velocities to calculate momentum. Maybe with light, only energy conservation matters and momentum can be changed via redshift/blueshift relative to the container.

ingenter 10y ago
No, light is not different. If you want to adjust for "red/blue shift", you may use special relativity, and in special relativity you have the conservation of 4-momentum, which will give you the same result.
- snarfy 10y ago
  Ah, if my understanding is correct then this makes sense. In my initial argument I bring in relativity and the invariant speed of light. What I neglected is everything else in relativity, like lorentz transformations. I mentioned a discontinuity between invariant speed of light and summing velocities to calculate momentum. The discontinuity is distance. Velocity is distance x time, but under lorentz transformations distance is relative. The discontinuity is resolved if you include length contraction (and time dilation).
lisivka 10y ago
You know that everything around us is both matter and wave at same time (wave-particle duality). Right? I.e. small bit of matter surrounded with wave. (See any of walking droplets videos to develop intuition). Unlike regular matter, waves are propagating through space, by contraction and expanding of a field. Because of particle-wave duality, when matter is moving, EM field around matter expands and contracts at high frequency. Right? EM radiation in form of radio-waves can interact with these surrounding waves because of interference. Right? IMHO, interference between radio-waves and surrounding waves may cause effect similar to used in acoustic levitation.

fitzwatermellow 10y ago

SPR's Roger Shawyer Explaining The Basic Science behind #EmDrive: https://www.youtube.com/watch?v=wBtk6xWDrwY https://www.youtube.com/watch?v=wBtk6xWDrwY

jasonwatkinspdx 10y ago
Since many people may be jumping into this topic without context/awareness: Shawyer's explanations simply do not hold up. Even the minority of folks that know physics and think the emdrive is real agree that Shawyer's proposals are invalid. Further, he's been at this for years, repeatedly making grandiose claims and failing to deliver on them. Take anything he says with a huge grain of salt.

jayajay 10y ago

If anyone's lazy, I highly suggest at least reading parts 9 and 10. One of the interesting takeaways here is that Q * -thrust is 2 orders of magnitude stronger than Photon-thrusters, and about 1-2 orders of magnitude lower than Ion-thrusters. * A Q-thruster is a thruster which pushes off of the zero point fluctuations in vacuum, which is still not understood.

lisivka 10y ago
But if you will try to discuss pilot-wave and walking droplets here (they are mentioned in part 10), you will receive lot of downvotes here. Quote: Although the idea of a pilot wave or realist interpretation of quantum mechanics is not the dominant view of physics today (which favors the Copenhagen interpretation), it has seen a strong resurgence of interest over the last decade based on some experimental work pioneered by Couder and Fort [13]. Couder and Fort discovered that bouncing a millimeter-sized droplet on a vibrating shallow fluid bath at just the right resonance frequency created a scenario where the bouncing droplet created a wave pattern on the shallow bath that also seemed to guide the droplet along its way. To Couder and Fort, this seemed very similar to the pilot-wave concept just discussed and, in subsequent testing by Couder and others, this macroscopic classical system was able to exhibit characteristics thought to be restricted to the quantum realm. To date, this hydrodynamic pilot-wave analog system has been able to duplicate the double slit experiment findings, tunneling, quantized orbits, and numerous other quantum phenomena. Bush put together two thorough review papers chronicling the experimental work being done in this domain by numerous universities [14,15].
- highd 10y ago
  i.e. at best, it provides no new information at the expense of learning an entirely new framework.
  - lisivka 10y ago
    IMHO, if we will know better the physics of quantum and relativistic effects, we will be able to model them at macro level, so it will be much easier to understand and study these effects. Mathematics will not change, calculation results will not change, but understanding of processes will rise significantly, which may lead to new advances in physics.

Animats 10y ago

It's so frustrating. One micronewton per kilowatt. All that power going in, and so little force coming out. All it takes is some tiny noise effect to get that much force. The effect is so weak and they're so near the noise threshold. Quotes: "Components get warmer and the geometry changes slightly due to thermal expansion". "The thermal signal in the vacuum runs was slightly larger than the magnitude of the impulsive signal." "As the aluminum heat sink got warmer, its thermal expansion dominated the shifting center of gravity (CG) of the test article mounted on the torsion pendulum. This CG shift caused the balanced neutral point baseline of the torsion pendulum to shift with the same polarity as the impulsive signal when the test article was mounted in the forward or reverse thrust direction." "The seventh error is outgassing, which has the potential for a false positive from vaporization of surface molecules of the dielectric insert or other nonmetallic surfaces."

davesque 10y ago
True but, according to some expert opinions I've read, if this thing pans out (and it's looking more and more like it will), that thrust is actually pretty damn good compared to other propellantless engines and not too damn bad compared to even conventional space probe engines.
- danbruc 10y ago
  [...] if this thing pans out (and it's looking more and more like it will) [...] Totally not, this is still with 99+ % a measurement error. We really understand theoretical physics pretty well, physicist have repeatedly predict measurement outcomes to a part in a million and less, have predicted particles decades ahead of the experiments discovering them. People really underestimate the power of theoretical physics and if there is a conflict between theory and experiment, it will almost always be the experiment that is wrong.
  - james0001 10y ago
    Tbh sounds like you're just a prude that doesn't like things you don't understand

chriskanan 10y ago

How much evidence is needed to motivate testing it in space? It seems that would settle the dispute regarding whether it works or not. Considering how inexpensive cubesats are to launch, it seems like it could be launched for about $100k, not including the additional R&D.

bobwaycott 10y ago
I could be mistaken, but I believe someone is lunching such a test next year. Edit: Cannae Inc. intends to launch a test with a small satellite. 2017 is so far a guess for launch based on a quick search.

s_kilk 10y ago

Can someone smarter than I explain the impact of this?

allerhellsten 10y ago
Further proof that there might actually be something to propellantless propulsion - which would be an incredible proposition for space travel.
- zoren 10y ago
  Agreed. Yet even more incredible would be not even bringing energy for the propulsion. http://www.space.com/32546-interstellar-spaceflight-stephen-hawking-project-starshot.html http://www.space.com/32546-interstellar-spaceflight-stephen-...
hannob 10y ago
Most likely none at all. The tl;dr is that some scientists investigate some fringe technologies that violate the laws of physics and based on some preliminary studies it looks like there could be something. However it's still vastly more likely that the studies are flawed than that we'll have to rewrite the laws of physics.
- matt_wulfeck 10y ago
  Haven't we been incrementally updating our understanding of physics since.. forever?
  - frozenport 10y ago
    Hard to say, certain conservation principles have been pretty constant.
    - thanatropism 10y ago
      Conservation principles come from fundamental symmetries. https://www.eng.fsu.edu/~dommelen/quantum/style_a/physsym.html https://www.eng.fsu.edu/~dommelen/quantum/style_a/physsym.ht...

tbrownaw 10y ago

If the vacuum is indeed mutable and degradable as was explored, then it might be possible to do/extract work on/from the vacuum, and thereby be possible to push off of the quantum vacuum and preserve the laws of conservation of energy and conservation of momentum. It is proposed that the tapered RF test article pushes off of quantum vacuum fluctuations, and the thruster generates a volumetric body force and moves in one direction while a wake is established in the quantum vacuum that moves in the other direction. ...well, at least it's better than calculating the theoretical produced thrust by ignoring the axial component of the radiation pressure against the side walls. Which is how tapered resonant cavities like this were supposed to produce thrust when I was in high school. But, leaving a wake in the vacuum should require that the vacuum exists in some particular reference frame. How's that supposed to work? Or since the paragraphs immediately before that one discussed the vacuum behaving differently when there's stuff in it, are they just saying that something is being exhausted out the back (which should be visible by some sort of effect on the vacuum?) even if they have no idea what that something might be?

cjensen 10y ago

For those new to this, the emdrive is very likely bogus. 1. It violates Conservation of Momentum. If the phenomena is real, a large number of basic Physics principles would need to be discarded. 2. It was designed based on certain principles. Those principles have been shown to be wrong. But it works anyway because reasons? 3. The results of each experiment are suspiciously close to the limits of measurement. There are two choices here: (a) experimental error or (b) profound alteration to fundamental physics. Occam's Razor applies. Also, "extraordinary claims require extraordinary evidence" and this evidence is far from extraordinary. That this is being published in a journal which does not cover basic physics is not helping.

michwill 10y ago
The trick is that this is not a closed discussion. The thrust was suspiciously repeated in many experiments, and question is whether it's some fundamental flaw with experiments, or it is real. I guess, the more info is available to the public, the better. Hopefully someone will test it properly. But no way it can be considered as "provably works"
- lomnakkus 10y ago
  What do you mean by "closed discussion", specifically? We've been hearing about this for ~1 year at this point, so I'm not sure what you mean. > I guess, the more info is available to the public, the better. This is up for debate -- esp. given the whole "fake news" thing and the observation that people basically love echo chambers (as observed in the field of Behavioural Economics). If, by "info" you mean "actually provable[1] info", then I probably agree. [1] To some reasonable standard of "proof". Certainly we don't need "mathematical" proof, but we need something better than "a study says". (See: reproducibility crisis[2], the fact that a "study" doesn't require any particular standard of evidence, etc.) [2] Meta: I wonder if the BE field is itself suffering from a reproducibility crisis? Anyone know?
  - michwill 10y ago
    Oh yeah, I wasn't clear, yes. Not "everything is clear, the case is closed" - that's what I meant

thearn4 10y ago

Some criticism on reddit: https://www.reddit.com/r/science/comments/5dqy9b/em_drive_is_shown_to_work_measurement_of/da6n92f/ https://www.reddit.com/r/science/comments/5dqy9b/em_drive_is...

michwill 10y ago

Interesting what are the fundamental reasons for the thrust. It's certainly not throwing photons. Hypotheses: * Flawed study. It actually throws something (like, cavity material slowly ablating) or repels of Eddy currents in surroundings; * It repels of Earth (and the force has either gravitational or magnetic nature); then it's not suitable for deep space propulsion * A sort of ether actually exists, and it throws that. Though, then there would be some anisotropy showing ether wind; in this case it is suitable to be used in deep space

politician 10y ago
If you read through their conclusions, they suggest that there may be a quantum vacuum capable of transmitting oscillations and this vacuum is what this this device pushes off of leaving a wake behind.
- ribble 10y ago
  pilot wave theory, the force is able to push upon itself despite lack of medium to otherwise push upon.
- gus_massa 10y ago
  [Disclaimer: I think it's a measurement error.] Just ignore the theoretical explanations. Just imagine that it's something they wrote to avoid the crackpot tag. That explanation doesn't make any sense. Also avoid all the other theoretical explanations, they are also very sloppy. Just concentrate in the experiments, that is the less sloppy part of these reports. If they discovered something new, then they can make a working prototype and improve it until it's clear that they are measuring something really new and it's not an experimental error or a misattributed force. They can make foolproof instructions so anyone can make a version in a good enough lab and reproduce the experiment, or sell an experimental setup in Ebay. Then it will "confirmed". There has been a many famous experiments that were later debunked, like: * cold fussion https://en.wikipedia.org/wiki/Cold_fusion https://en.wikipedia.org/wiki/Cold_fusion , they had also some kind of theoretical excuse, but it was wrong and it was impossible to reproduce the experiment. * arsenic in DNA https://en.wikipedia.org/wiki/GFAJ-1 https://en.wikipedia.org/wiki/GFAJ-1 , they had also some kind of theoretical excuse, but it was wrong and it was impossible to reproduce the experiment. If you want success cases, my favorites are: * the asymmetric disintegration of cobalt in a magnetic field https://en.wikipedia.org/wiki/Wu_experiment https://en.wikipedia.org/wiki/Wu_experiment , I guess they had some wrong explanation, but the correct explanation was discovered like 20 years later * high temperature superconductivity https://en.wikipedia.org/wiki/High-temperature_superconductivity https://en.wikipedia.org/wiki/High-temperature_superconducti... IIRC they have some explanation or practical rules, but the correct explanation was discovered like 20 years later Just concentrate in the experiments, and wait 20 years for a good explanation.

jtchang 10y ago

This is pretty good news if only that we will get more research into this phenomenon. In 1933 von Neumann basically published a proof against the idea of any hidden-variable theory. It took 30 years but Bell then discredited it. My guess is that a lot of this will get revisited. The outcome of this in the next 10-20 years might be really cheap probes (via reusable launch vehicles like SpaceX is making) that need no propellent to continue onto their merry way for a long time. The current way of doing this would be using solar sails or something along those lines which is not exactly compact. Having a way to push your little probe along (even at a little bit of acceleration) without having to carry a lot of heavy propellant is a big deal. Maybe just some solar panels to generate the energy needed.

perlgeek 10y ago
> This is pretty good news if only that we will get more research into this phenomenon. Agreed. > Having a way to push your little probe along (even at a little bit of acceleration) without having to carry a lot of heavy propellant is a big deal. Maybe just some solar panels to generate the energy needed. I'm not sure that actually works. Most use cases are for exploring the outer solar system, or even outside of our solar system. As the probe gets away from the sun, the solar energy it gets decreases with the square of the distance, and so it probably will stop providing even the little bit of acceleration.
- ajuc 10y ago
  > As the probe gets away from the sun, the solar energy it gets decreases with the square of the distance, and so it probably will stop providing even the little bit of acceleration. In space you move in elipses. It's possible to choose an elongated orbit that moves the probe closer and then further from the sun repeatedly and each time it is close to the sun it accelerates forward, moving the "far" side of orbit further away, until it gains enough speed to escape sun gravity. Or at least it's possible in Kerbal Space Program :)
  - cperciva 10y ago
    Yes, you move in ellipses; but you spend a lot of time far away and very little time close to the sun. I'm not sure that the average power is any higher than you would have for a circular orbit at the same energy... EDIT: Ok, let's think through the calculus here. Kepler's 2nd law says that the area swept by the line between a planet and the Sun is constant, i.e., r^2 dθ/dt = 2 π a b / P where a and b are the semi-major and semi-minor axes and P is the orbital period. Thus dt / r^2 = P dθ / (2 π a b); and the former is the instantaneous power absorbed. Integrating over an orbit, we get E = P / (a b); or the average power absorbed is proportional to 1 / (a b). Since the energy of an orbit is determined solely by the semi-major axis a, this means the power absorbed for any given orbital energy is maximized for b ≪ a; so you're right, that highly eccentric orbits are a better way to acquire energy for the purpose of orbital escape. (Subject of course to practical considerations of energy storage -- you'll absorb the most power at exactly the time you don't want to be changing your momentum.)

Odenwaelder 10y ago

The laws of physics prevailed, despite the LHC and other experiments. As awesome as it sounds, I find it hard to believe that this finding is something relevant.

daveguy 10y ago

One thing that bothers me about this paper: The measurement error is stated to be +/- 6 micro-Newtons. However, the difference between force measured at the same power is 30-40 micro-Newtons and the "measurement error" is listed as the +/- error. So if the measurement error is that low then the additional variation is unreliability of the effect itself or a miscalculation of the measurement error.

revelation 10y ago

Sounds like Polywater: https://en.wikipedia.org/wiki/Polywater https://en.wikipedia.org/wiki/Polywater

anotheryou 10y ago

Can't we put one in a cube sat and give it a go? (or: why can't we?)

trothamel 10y ago
I'd think power is a problem. This produces a very slight acceleration with a kilowatt of power, while it looks like a 3U (triple stack) cubesat might produce ~14 watts.
- anotheryou 10y ago
  I feared so :) the unit looked so small and handy.... But does it have to take constant power?
- int_19h 10y ago
  But even very small acceleration should add up to significant velocity over time, no? So if we launched something that's only 10 W, how long before we can easily observe the velocity difference?
- lobster_johnson 10y ago
  Cannae is launching its thruster experiment in a 6U cubesat next year: http://www.popularmechanics.com/science/energy/a22678/em-drive-cannae-cubesat-reactionless/ http://www.popularmechanics.com/science/energy/a22678/em-dri....
  - anotheryou 10y ago
    Cool! Any chance a 6U could stay up for month with conventional thrusters? Or will it be proven to work or at least be better than other thrusters once and for all?

gigatexal 10y ago

For the uninitiated how good or bad is 1.2mN/kw?

froogle 10y ago
Garbage for anything Earth-travel related. Gravity is 9.8N/kg, so to generate enough force to counter gravity you'll need to feed this thing 9.8MW per kg. Your typical 100 HP car engine puts out 75.6kW, so you'd need 130 car engines' worth of power to lift a small 1 kg/~2 pound object. Not to mention that the machinery needed to channel/produce that kind of energy would be so heavy that it could not lift itself. But it's still possibly useful for space travel. Not needing propellant is huge for long-distance space travel. That said: they don't know why it works. (If it even works, which I strongly strongly strongly doubt.) If they figure out what produces the phenomenon, it's very possible they could get the drive to be way more efficient.
Pxtl 10y ago
A kilowatt is comparable to a space-heater or an insane gaming rig. A Tesla burns about 20kw for normal driving. Now, a Newton is the amount of force it takes to hold up an apple (or accelerate it at 1G). So a millinewton would be the amount of force it takes to hold up a blueberry.
- MertsA 10y ago
  That is a great way to explain units to people.
sonium 10y ago
To put into proportions: The radio isotope thermoelectric generator (RTG) of the Voyager spacecraft wheighs 37kg. So let's say we can build a spacecraft using this and the EM drive weighing a total of 50kg. The RTG produces 157W of power. This translates to a change in speed 30cm per day. Bonus question: The power of the RTG halfes avery 87.7 years. What is the asymptotic speed the spacecraft will reach?
- photogrammetry 10y ago

sergj 10y ago

I was pretty sure there was a seperate study where they debunct it? Gonna look for the link...

acqq 10y ago

http://blogs.discovermagazine.com/outthere/2014/08/06/nasa-validate-imposible-space-drive-word/ http://blogs.discovermagazine.com/outthere/2014/08/06/nasa-v... About the previous tests of the same team: "The testing was done by five NASA employees in a lab devoted to exploring unorthodox propulsion ideas. The team leader is a researcher named Harold “Sonny” White, himself a proponent of ideas about faster-than-light warp drives that most of his colleagues have classified as physically impossible. The lead author is one of White’s Eagleworks teammates, David A. Brady. Calling this group “NASA”—as almost every popular news story has done—is a gross oversimplification."

SubiculumCode 10y ago
They fund it, no?
- acqq 10y ago
  Would it be better if NASA wouldn't have less then 10 people, out of their 18,000 employees (0.05%), working on testing nevertheless such claims which almost surely don't work? Maybe, if that 0.05% is used against NASA by claiming it doesn't do its job how it should.
  - binarycoffee 10y ago
    Interestingly, NASA used to have a group working on such projects. https://en.wikipedia.org/wiki/Breakthrough_Propulsion_Physics_Program https://en.wikipedia.org/wiki/Breakthrough_Propulsion_Physic... And I believe they actually did a serious job, which is probably why they never found any warp-drive ;-)
  - Nokinside 10y ago
    It's my understanding that they are working with this project on their free time. NASA pays small amount of money ($50,000 or so) and gives them a room to do experiments. Or at least did in 2011. Eagleworks and their team are not official NASA research. They just have facebook page. Contact attempts trough NASA don't work. Glenn Research Center offered to replicate the experiment in a hard vacuum if Eagleworks manages to reach 100 µN of thrust.

mrob 10y ago

Recent previous discussion: https://news.ycombinator.com/item?id=12992536 https://news.ycombinator.com/item?id=12992536

dang 10y ago
Since there's obvious appetite to discuss this, we've merged the comments here instead of burying the current (re)post as a dupe like we normally would. A couple more posts about this: https://news.ycombinator.com/item?id=12994541 https://news.ycombinator.com/item?id=12994541 https://news.ycombinator.com/item?id=12994400 https://news.ycombinator.com/item?id=12994400
eln1 10y ago
As the main hypothesis in this paper is that the momentum is transferred by pilot waves, it is worth to emphasize the (cited there) most known recent approaches - Couder's experiments which use classical object with wave-particle duality (droplet coupled with waves it creates), getting e.g. interference in double-slit, orbit quantization and many other quantum-like phenomena: https://en.wikipedia.org/wiki/Hydrodynamic_quantum_analogs https://en.wikipedia.org/wiki/Hydrodynamic_quantum_analogs https://www.youtube.com/watch?v=nmC0ygr08tE https://www.youtube.com/watch?v=nmC0ygr08tE

gfodor 10y ago

There seems to be a meme around the EmDrive where "it works" and "conservation of momentum is upheld" are mutually exclusive. Couldn't it be the case that there is some local phenomenon happening that we do not understand that still manages to maintain conservation of momentum? Isn't assuming that momentum conservation is violated a conjecture on the underlying physics of the device, which we don't know?

colechristensen 10y ago
It's only exciting if it violates the conservation of momentum. If it doesn't, it's not useful as a space thuster or a flying car, and whatever is causing the miniscule force is just some leaky edge case that's difficult to measure. It's boring if it doesn't violate momentum conservation.
- nkoren 10y ago
  I dunno. Accidentally discovering a way to, say, shove dark matter around with microwaves and do useful work with it would not necessarily violate momentum conservation, and wouldn't really be that boring. (Not that I think this is what the EM drive is doing, or that I'd bet on it with anything other than very long odds, but I'm glad someone is looking into it).
- int_19h 10y ago
  Is it really true said "leaky edge case" is applicable throughout our entire local space? e.g. the solar system? or even the vicinity of Earth?
akiselev 10y ago
It's a little more complicated than conservation of momentum, which is just a subset of conservation of energy useful for intuition about the non quantum world. If you're converting energy into massive particles or photons for propulsion you can still have a "massless" drive while maintaining conservation of momentum because what you're really conserving is the total energy of the system. Research has previously shown that it is possible to create particles but it requires ungodly amounts of energy and a specially designed apparatus that separates the resulting particle and antiparticle using quantum effects before they can annihilate each other. There is even some research into using a vibrating "quantum mirror" that forces virtual photons to become real using only energy from quantum fluctuations but that's even more complicated and difficult to engineer. Either the EM drive has a unique combination of features that allows efficient creation and separation of particles using electricity, some other unknown quantum effects are present that can convert energy to momentum without an opposite reaction on another particle/field, or there is still a hidden error. Given the scientific knowledge we have today, it's extremely likely to be the latter but that doesn't preclude the possibility that we have discovered something novel.

pmcollins 10y ago

Doesn't a standard microwave (or any other) transmitter produce a tiny force due to radiation pressure? I understand that this is different because the radiation bounces around an enclosed chamber and so momentum wouldn't be conserved, but if the issue is to create propellant-free propulsion, doesn't that already exist (even though it's not practical)?

ribble 10y ago
> Doesn't a standard microwave (or any other) transmitter produce a tiny force due to radiation pressure? pressure against what?
- pmcollins 10y ago
  https://en.wikipedia.org/wiki/Radiation_pressure#Radiation_pressure_by_emission https://en.wikipedia.org/wiki/Radiation_pressure#Radiation_p...
  - ribble 10y ago
    this article includes a grey body that the force is acting upon. the difference with the EM drive's method of propulsion is, that while the article you posted describes a force reacting upon an external, "grey body," as is acceptable with the copenhagen interpretation of quantum mechanics, the EM drive force exhibits a characteristic betrayed by a theoretical pilot wave, which indicates a non-copenhagen interpretation of quantum mechanics, but rather a bohmann version of quantum mechanics, in which the force can act upon itself. run-on sentence alert.
gus_massa 10y ago
Yes, but they suppousedly got 4000 times the maximal theoretical value. I'll repost one of my old comments with more details: If you use a photon thruster (aka a laser or a flashlight in the right direction (or a microwave)), then the maximal thrust/energy ratio is at most 1/c = 3.33 nano-Newtons per Watt = 0.0033 uN/W = 0.0033 mN/KW. Someone compiled here two lists of experiments: http://forum.nasaspaceflight.com/index.php?topic=36313.msg1302455#msg1302455 http://forum.nasaspaceflight.com/index.php?topic=36313.msg13... http://emdrive.wiki/Experimental_Results http://emdrive.wiki/Experimental_Results Some of the experiments are few years old, but you can compare the current result with 0.0033 mN/KW. The results in the tables vary from 3x to 200000x the theoretical maximum of a photon thruster. I think that the typical current value is x4000. It's a theoretical upper bound that is very easy to calculate using special relativity, and it depends on very fundamental laws, not tricky details of the universe. The theoretical bound is so fundamental, that it's even true if you use a graviton thruster instead of a photon thruster. This example is not totally made up, someone have an alternative impossible massless drive that "push against the far away stars". They claimed also a thrust/energy ratio > 0.0033 mN/KW, so it was also impossible from a theoretical point of view. Also, for the EmDrive, someone proposed that it emits twin photons that somehow cancel each other, but the pair still carry momentum. That explanation extremely wrong.

smcameron 10y ago

If real, you could build a perpetual motion machine with it. Therefore it's not real.

kobeya 10y ago
This is violating conservation of momentum, not conservation of energy. You cannot build a perpetual motion machine using it. But even if you could, that is not a reasonable argument. Reality is what it is.
- ncallaway 10y ago
  "But even if you could, that is not a reasonable argument" It may not be a reasonable argument to claim that it is impossible, but it is a totally fine argument to make that it is insanely unlikely and needs a mountain of evidence before we take the conclusions seriously.
  - kobeya 10y ago
    That's an argument about priors. In the face of actual evidence of its reality, priors establish significance not believability.
    - inimino 10y ago
      No... priors are precisely about believability. Any evidence can be explained either by the effect or by experimental error. Your prior is how relatively likely these two possibilities are. If something is "significant" then it is surprising and requires stronger evidence.
eridius 10y ago
Could you? How? Perpetual motion machines must put out at least as much energy as they take in. AIUI the EmDrive requires external power (such as solar panels) and produces a rather tiny amount of force. This does not sound to me like it's anywhere even remotely close to putting out as much energy as it takes in.

maverick_iceman 10y ago

As I said earlier this is bogus. We might as well try to prove virgin birth.

photogrammetry 10y ago
https://en.wikipedia.org/wiki/Parthenogenesis https://en.wikipedia.org/wiki/Parthenogenesis

caconym_ 10y ago

A while back I read an interesting but possibly also batshit crazy article that proposed an explanation possibly involving something like quantization of inertia, and/or generation of extremely long-wavelength photons, wavelengths on the order of the size of the universe. Does anyone know what I'm talking about? IIRC it was based on some theoretical work that was done before EmDrive was a thing, and it seemed less hand-wavey to me than simply "conservation of momentum is wrong" or "we're using the quantum vacuum as a tractive medium which is supposed to be impossible but whatever" explanations. I'm not saying this explanation is right (or wrong, or that the thrust observed in these experiments is or isn't caused by "new physics"); I'm just curious whether anyone knows what I'm talking about and can provide some more context. edit, found it: https://www.technologyreview.com/s/601299/the-curious-link-between-the-fly-by-anomaly-and-the-impossible-emdrive-thruster/ https://www.technologyreview.com/s/601299/the-curious-link-b... Any thoughts?

kybernetikos 10y ago
I think you're talking about McCulloch's quantisation of inertia theory. http://www.ptep-online.com/index_files/2015/PP-40-15.PDF http://www.ptep-online.com/index_files/2015/PP-40-15.PDF which I believe was originally inspired by the rotation of galaxies.
- caconym_ 10y ago
  Yup, that's it. I found the article I read, edited my post to include it.

petters 10y ago

If this holds up I am prepared to believe in almost anything – like the universe being a simulation and this is a deterministic round-off error. Conservation of momentum is pretty fundamental.

walrus01 10y ago

1.2 millinewtons per kW is not a lot - the size of a 12kW solar array for a large satellite is quite considerable... Space based nuclear reactors anyone? No cosmos-954 incidents, hopefully.

recycle 10y ago

Open Source Projects / Experiments that might be relevant to the discussion: https://hackaday.io/project/5596-em-drive https://hackaday.io/project/5596-em-drive https://hackaday.io/project/10166-flying-an-emdrive https://hackaday.io/project/10166-flying-an-emdrive

philip142au 10y ago

When the super-conducting version work it will change the world.

kleigenfreude 10y ago

Fuck all the deniers. Fuck you. FUCK YOU!

reitanqild 10y ago
Why did you suddenly start posting like this?
photogrammetry 10y ago
Surely you realize that HN doesn't allow you to delete comments, ever.

microcolonel 10y ago

For those who wish to see the abstract page without enabling cookies. http://archive.is/zuVaz http://archive.is/zuVaz

binarycoffee 10y ago

Several comments have hinted at the possibility that this would be a over-unity device but as I couldn't find a specific demonstration, here is one that does not involve any fancy physics. Let's assume we have a spacecraft powered by an energy source with total energy `E` and mass `m`. The EM-drive produces a constant thrust `F` at a constant power `P`. Kinetic energy of the S/C after time `t`: Ek = 0.5 * F^2 * t^2 / m If `t` is the time at which the energy in the source is exhausted, then the ratio of kinetic energy developed to the expended energy (E = t * P) is: Ek/E = 0.5 * F^2 / P^2 * (E/m) So this basically says that we have a over-unity device whenever the energy source has a specific energy above: E/m > 2P/F ~ 1.6 10^6 J/kg which is certainly not achievable in practice, but in theory is totally fine being still well below c^2 (which by the way justifies a-posteriori the neglect of relativistic corrections in the above).

Symmetry 10y ago

So 1.2 mN/kW. By comparison the ion engine on the Dawn probe puts out 34 mN/kW (236mN / 6.9 kW). But of course that's for an effectively infinite exhaust velocity rather than just 42 km/s.

imdsm 10y ago

> Although this test campaign was not focused on optimizing performance and was more an exercise in existence proof, it is still useful to put the observed thrust-to-power figure of 1.2mN/kW1.2 mN/kW in context. The current state-of–the-art thrust to power for a Hall thruster is on the order of 60mN/kW60 mN/kW. This is an order of magnitude higher than the test article evaluated during the course of this vacuum campaign; however, for missions with very large delta-v requirements, having a propellant consumption rate of zero could offset the higher power requirements. The 1.2mN/kW1.2 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 3.33–6.67μN/kW3.33–6.67 μN/kW (or 0.0033–0.0067mN/kW0.0033–0.0067 mN/kW) range. Read More: http://arc.aiaa.org/doi/full/10.2514/1.B36120#_i36 http://arc.aiaa.org/doi/full/10.2514/1.B36120#_i36

tombone12 10y ago

Goddamit, I wanted to get to the comment about the superoptimizer, not this mass hallucination over crap sience :(

nepotism2016 10y ago

For those who dig this stuff...I strongly recommend you watch BBC Horizon episode Project greenglow http://www.dailymotion.com/video/x40a65t http://www.dailymotion.com/video/x40a65t