When I See An Elephant Fly

In Physics by Brian Koberlein14 Comments

I’ve been getting a number of questions about NASA’s supposed discovery of a warp drive engine, and I’ve been resisting writing about it. Partly because I’ve written about it before, and partly because of the difficulty in separating the facts from wild speculation. Unfortunately none of the results have been submitted to peer review, so there’s no clear summary of the work that one can point to. That also means it hasn’t been publicly vetted, which is absolutely vital for this kind of claim. It should also be stressed that NASA hasn’t said they’ve discovered warp drive. They haven’t said anything on the matter. The buzz is coming from discussions on a site called NASA Spaceflight, which is not affiliated with NASA. With that in mind, what seems to be the evidence one way or the other?

The discussion centers on a so-called “reactionless drive.” That is, a device that can produce a thrust without a corresponding propellant. The idea is extremely controversial, because such a device would violate Newton’s third law (of action-reaction) which is one of the foundational laws of physics. There are actually two devices that claim this effect. One is known as the EmDrive, developed by Roger J. Shawyer, and the other is the Cannae Drive, developed Guido Fetta. Both of these devices bounce radio waves inside a resonant chamber to create a reactionless drive. The buzz this time around seems to be about the EM drive.

About a year ago, an EM drive experiment found a thrust of about 50 micronewtons. This is an extraordinarily small force, less than the weight of a small snowflake, but it’s not zero. This experiment was performed at atmospheric pressure, so the effect could have easily been due to experimental error. For example, uneven heating across the device could cause the air around it to recoil with different energies, causing a net thrust. We see a similar effect with a Crookes radiometer. This year a similar experiment has been done in a vacuum (about 5 microtorr) and again measured a thrust of about 50 micronewtons. That basically eliminates the atmospheric effects, but there are other more technical effects that could still be producing a false positive. The experiment has also been done in different orientations, and there seems to be directionality to the thrust. That would seem to work against the idea that the device is somehow coupling to the Earth’s magnetic field.

There has also been a basic experiment where a Michelson interferometer was placed next to the device. In principle, such a device could measure any variation of spacetime near the device. The results are supposedly consistent with the theoretical warping of an Alcubierre drive effect (which is a theoretical warp drive). What “consistent with” actually means is unclear, but that’s why so many popular articles are claiming “NASA accidentally discovers warp drive!” No scientist is actually claiming that.

On the face of it, this might seem pretty promising. A thrust has been observed, it seems to work in a vacuum, and there are hints of a warp effect. Here’s why we shouldn’t plan a party just yet. To begin with, one does not simply violate a fundamental law of physics. There are several ideas proposed to explain the thrust as a real effect, but they all involve a violation of basic physics. If this device is real, then Newton’s third law will have to be either thrown out or seriously revised. That by itself doesn’t mean the effect is false, since in the end the evidence wins. But history shows that long established scientific principles are very robust. I don’t doubt that the teams working on these devices are in earnest, but it is frustratingly difficult to account for all extraneous effects, particularly with such a small result. More than one scientist has thought they were on to something that didn’t pan out.

Which brings me back to my original statement that the work hasn’t been submitted to peer review. Much of it is hearsay based on discussion groups. While I’ve tried to present an even-handed summary, all of this should be read with an extremely skeptical eye. Both the EM drive and Cannae drive fans are claiming a violation of basic physics. Extraordinary claims require extraordinary evidence, and the threshold of evidence hasn’t remotely been reached yet. Is it interesting? Sure. Is it valid? We have no idea (but lots of reasons to doubt), and until formal evidence is submitted to peer review there is no reason to assume it’s real.


  1. Thanks Brian! Reports about the EM drive are appearing in increasingly mainstream media outlets and the journalists don’t seem to be able (or interested) to distinguish official NASA annoucements from forum posts on the Space Flight board, nor fussed about assessing the quality and grounds for the evidence so far. I was really hoping that somebody would come along and make the analysis you’ve just made – great work and thanks

  2. I agree with the conclusion. But I dislike the logic you use to reach that conclusion. The logic is wrong.

    1./ There is a big Appeal to Authority Logical Fallacy in this article. Newton says this, Newton is an authority, so the proposed idée can’t be right.

    2./ You are dishonest with yourself. Now Newton is right, in other cases you give Einstein all the credits.

    3./ Warping space(and time) can be done, in fact it happens all around us, every second. It is a fact because the idea agrees with so many experiments. The time to denied is over. Mass warps space (and time), period. By stating that (and you do that too) we accept that Einstein is right, and that Newton needs to be adjusted.

    At the same time you never stated (and you should never state that) warping space (and time) breaks Newton’s 3th law. And then again, that’s is the turnkey in the logic that leads to a conclusion in this article.

    Yes, my English sucks. But it is better than your Dutch.

    1. Author

      There is no appeal to authority here. While we call it Newton’s third law, the conservation of momentum has been rigorously supported by experimental evidence. This is an appeal to evidence if anything. No one denies that warping of space occurs, but it doesn’t violate conservation of momentum. The question is whether this device warps space in a way consistent to “warp drive,” which would violate conservation of momentum.

      Je hebt gelijk, ik heb geen Nederlands spreken.

  3. Brian, as far as I remember, this notorious EmDrive works at 935 MHz. This frequency is used in GSM. The GSM emisions often produce noise in measuring devices. So that I am very sceptical. The experiment must be made in EM shield room. Only in this case we can be sure.

  4. Thank you for accepting that language should not be a wall.

    I still do not agree with the logic. I still strongly agree with the conclusion. Let my try to explain.

    I do not beleive that any device smaller then the planet Earth can develop a force that warps space more than the planet does in the act of frame dragging. Common sense. That would be like beleiving that someone can barehanded pull the Moon. The thing is, you have the whole universe against you, as stated in Mach’s Principle. Its is not about conservation of energy and/or momentum. It is about trying to develop a force that moves the whole (counter acting) univers.

    Yes, that is not a very scientific way of handling this whole warp engine idea. But, looking deeper into warp engines wil break my own conservation of energy laws.

    But then again. Who am i. I also know (you will state that i beleive) that a perfect understanding of frame dragging is needed to really explain the falling apple. I know that a perfect understanding of how the apple falls also will map the tidal forces of frame dragging. I know that perfectly mapped tidal forces due frame dragging wil eliminate the need for mathematical dark matter. And now you and i live in differend universes, because you beleive in dark matter. So again, who am i.

    I sincerly hope that (minor) critisisme from a minor person (like me) does not make you dislike blogging (against the mass of disbeleivers). Keep up the good work. You are a hero by writing this blog.

  5. So what about the possibility that there is an interaction with dark matter/dark energy? That interaction might be what preserves Newton’s third law.

    1. Author

      Most of the models are proposing a reaction with the quantum vacuum or some such. Light doesn’t interact strongly with dark matter, so that isn’t likely to save Newton’s third law in this case.

  6. Dr. Koberlein

    Thanks for this well reasoned and appropriately skeptical write-up. I appreciate that you didn’t resort to personal attacks against the NASA group behind this work, as some physicists have. Apparently the NASA group is planning on testing the device at higher powers later this year, and if the measured thrust is found to be a function of the power, to have the results replicated by Johns Hopkins Applied Physics and JPL. I think you’d agree that these are the appropriate next steps.

    I assume that if all that pans out (unlikely) we’ll see a peer reviewed paper. In the meantime, I haven’t seen any evidence that these guys are bad scientists, although leaking primary data to a public discussion board on a website is a little sketchy…but I’ll give them the benefit of the doubt and assume they needed fresh eyes to help sort things out.

    By the way, I always enjoy your appearances on Weekly Space Hangout. Keep up the good work!


  7. This kind of experiments should actually be done in highly shielded laboratory: magnetism, high vacuum, heat shielding and em radiation shielding.

  8. Just a thought experiment. Einstein says that there is a direct connection between mass and energy. In fact, if you take two particles that are “anti” of each other, you get the energy back and destroy the mass. It’s what virtual particles are supposed to do, but I won’t get into that. Now, I don’t know of any system that takes energy and creates mass, but assuming that it is not aberrant (one could take the Big Bang as a real life example, I suppose), one can imagine a “drive” that would use insane amounts of energy to create mass, then push it away from the vehicle, thus creating thrust.
    I have just described a system that uses energy to generate trust, without using any spooky quantum theory. Does it violate Newton’s third and, if so, how?

    1. Author

      Something doesn’t need mass to have momentum. Photons, for example, have no mass but do have momentum. So any thrust produced by created mass would create a counter thrust of energy. So it wouldn’t violate Newton’s third law. That’s not what this device is claiming to do.

      1. I just wanted to get out of the way the idea that any energy based engine would automatically be wrong because of the third law of thermodynamics.

        Not being a physicist, it is difficult to carry an argument in this. There are a lot of things that I don’t get, for example why a laser would push a craft if hit by the beam, but it wouldn’t push it if fired from the craft itself. Or how the Yarkovsky effect is producing thrust when heated by the sun, but there is no thrust if you heat the body with an internal source. Or how something that is defined as the product of mass and velocity – momentum – can exist for a particle with no mass. Or how if two metal plates can be pulled together by the Casimir force due to a difference of density in virtual particles a drive cannot harness the same idea to move around. You see, it’s idiots like me you have to convince, you have to use primary school physics 🙂 Anything could happen if you combine a microwave oven and non-dairy creamer. Maybe they used some in the EmDrive.

  9. I’m no physicist, and thus obviously have no practical understanding of the math involved here. But one solution that seems blindingly obvious here, even as an observer, to the question of whether or not it works is to simply build the thing and test it in space.

    Scientists have built and tested numerous seemingly pointless experiments with less potential for possibly profound results and with far less motivation, so why the hesitation to do so now? What are they afraid of?

    Build and test it under the practical conditions it’s intended to operate under, and it’ll either prove or disprove this debate once and for all. No more need for wordy scientific smack-downs or pseudo-scientific debates.

    If scientists can waste money and time building an experiment that studies the mating practices of earthworms in a zero-G environment then they can certainly build a practical experiment that studies and tests whether or not this EMDrive works in space or doesn’t…

    1. Author

      Feel free to donate about $50 million to do the experiment then. It’s easy to criticize scientists for “wasting money” when you don’t understand the implications of the research. But it’s ironic when in the same statement you argue in favor of spending money on a project that would violate basic known physics.

      The proponents of the EMDrive are looking into sending an experiment into space, but it won’t happen overnight, and they’ll have to spend millions to do it.

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