Nov 21 2016

The EM Drive – Again

The Eagleworks team at NASA have just published a peer-reviewed paper that claims to show net thrust from the EM drive, which is an alleged reactionless thruster – Measurement of Impulsive Thrust from a Closed Radio-Frequency Cavity in Vacuum. They conclude:

Thrust data from forward, reverse, and null suggested that the system was consistently performing with a thrust-to-power ratio of 1.2±0.1  mN/kW1.2±0.1 mN/kW.

The paper concludes that they measured a consistent, although very small, amount of thrust in one direction. This claim remains highly controversial, for good reason. The claim is that they can convert electricity into thrust by creating a tapered resonant chamber. The radio waves produced bounce around the chamber, but because of its tapered shape they push off one side more than the other.

The problem with this claim, and the reason it remains controversial, is because it would break the laws of physics as we currently understand them. Specifically it would break the conservation of momentum – for every action there is an opposite and equal reaction (hence “reactionless” drive).

Further, such a drive could potentially result in a free energy machine. At high enough speed the energy of the momentum generated by the thrust would be greater than the electrical energy used, therefore creating net energy. You could argue that at higher speeds the drive is less and less effective, but there is no reason to suspect that would be the case.

Some proponents argue that the radio waves are essentially pushing against quantum virtual particles. Invoking quantum mechanics is often a red flag. Such arguments sometimes amount to little more than, “Well, this effect is weird, and QM is weird, so that probably explains it.” In this case there is a more detailed theory, dealing with Unruh radiation, but so far quantum physicists aren’t buying it.

The inventor of the drive, Shawyer, claims that it creates warp bubbles which create the thrust. This idea remains in the realm of pure speculation.

Supporters of the drive point to the fact that several teams have apparently replicated the effects. The Chinese team, however, have since retracted their results once discovering the source of their experimental error. However, proponents argue that their equipment was not capable of detecting thrust as tiny as what was seen by the NASA team.

Where do things stand?

What is a reasonable skeptical and scientific position to take regarding the EM drive given what we currently know? On the one hand, serious teams of researchers have attempted to find an effect and have sometimes found a small thrust. This is enough of a result to spark interest, but it is not accurate to say that the current research has “confirmed” an effect. The current research should be considered preliminary.

What we have at this time is an apparent anomaly in preliminary testing.

From a theoretical point of view, there is no good explanation for how the EM drive might work. The result appears to break the laws of physics and proposed explanations are highly speculative and have serious problems. Therefore, it is fair to consider the reactionless drive an extraordinary claim.

Further, the alleged effect size is very tiny. This is important because the smaller the effect size the greater the number of possible conf0unding factors or sources of error. Large experimental errors are easier to rule out, because there are only so many things that can produce erroneous but large effects. Tiny experimental errors, however, become increasingly difficult to eliminate.

So, we have preliminary evidence showing a tiny effect size and requiring new physics. This is an overall pattern that we have seen many times before. If history is any guide, such results tend not to pan out.

The situation is very similar to alleged free energy machines, cold fusion, and anything faster-than-light. All such claims, even when they emerge from serious research labs, have eventually evaporated. It does not seem rational to be confident that this time the Great Pumpkin is really going to make an appearance.

The most likely possibility here is that there is simply a subtle source of thrust that the researchers have not yet identified. The EM drive is emitting something, for example, that is generating the thrust, or there is something in the equipment that is generating the error. As we saw with the recent example of the alleged faster-than-light neutrinos, a team of physicists and engineers were fooled for years by an error in the experimental setup that was not detected until after they went public and essentially asked for help in finding the source of error.

Another possibility is that this experimental setup is producing some previously unknown phenomenon. There might be some wrinkle in the laws of physics that can produce the effect seen without breaking those laws, just adding a new effect. While I think even this outcome is highly unlikely, it’s not impossible. If it were true, however, the amount of thrust seen so far is probably too small to be useful. Current ion drives produce much more thrust, for example.

The researchers claim, however, that the devices built so far are crude and not optimized for performance. Fair enough, but that does not necessarily mean an optimal device will produce significantly more thrust. It’s just another unknown.

The most unlikely outcome is that the device essentially demonstrates that our current understanding of physics is not just incomplete but fundamentally flawed. When optimized, such a device would revolutionize propulsion, resulting in flying cars and ships that can get to Mars in a week. Of course, we all hope that this is the outcome. I will gladly be monumentally wrong on this issue if it means I can have a flying car. Such a drive would be an incredible boon for humanity.

In fact I also hope that such a device can be rigged to generate endless free and clean energy. Why not?

I also have no problem with research teams investing in highly speculative and unlikely science and technology. This should not be the main focus of our expenditure on science, but little side bets with high payoffs is a good idea. I like the idea of mad geniuses following crazy ideas. Even if they are ultimately wrong, something interesting can come out of it.

The problem, really, is with science news reporting. The fringe research that is almost certainly not true is reported alongside solid science. The public often cannot discern one “gee whiz” claim from another. Even worse, sometimes the fringe science becomes the source of fraud and cons. Think of the investors who sunk 20 million Euros into the Stoern free energy boondoggle. This is most concerning in the realm of health care where people’s lives are literally on the line.

On the bright side, these cases are excellent opportunities to teach the public about science and skepticism.


10 responses so far

10 Responses to “The EM Drive – Again”

  1. Karl Withakayon 21 Nov 2016 at 11:03 am

    Typically science (theory) proceeds engineering (practical implementation), and thus you don’t need to figure out how it works because you already know how it’s supposed to work, and you’re trying to find a practical way to implement the theory.

    Where is the prior body of scientific work in this field suggesting such an effect that lead to an attempt at real world implementation?

  2. Willyon 21 Nov 2016 at 11:08 am

    The entire story in a nutshell: “So, we have preliminary evidence showing a tiny effect size and requiring new physics.” THAT is worth remembering!!!

  3. Aceofspades25on 21 Nov 2016 at 11:10 am

    This is a great video which I recommend:

  4. garyacrowellsron 21 Nov 2016 at 1:56 pm

    Funny thing is, this EM drive was described almost exactly in the 1980 juvenile SF novel ‘Star Driver’ by Lee Correy (G. Harry Stine).

  5. daniel1948on 22 Nov 2016 at 7:11 pm

    Thanks for this article. I am continually amazed by the credulity that always greets the announcement of “discoveries” or inventions that, if real, would require us to abandon everything we know about the laws of nature.

  6. Sarahon 24 Nov 2016 at 3:05 pm

    Not to mention, bombs capable of destroying earth trivially that we’d have no hope of stopping.

  7. sfurboon 25 Nov 2016 at 3:46 am

    “Further, such a drive could potentially result in a free energy machine. At high enough speed the energy of the momentum generated by the thrust would be greater than the electrical energy used, therefore creating net energy. You could argue that at higher speeds the drive is less and less effective, but there is no reason to suspect that would be the case.”

    Wouldn’t the speed-dependent efficiency also fly in the face of relativity? There are always inertial frames of reference in which the drive is moving fast enough for it to violate the conservation of energy, so if the energy won depends on the speed, all inertial frames of reference are not equivalent.

  8. randallkrippneron 25 Nov 2016 at 8:43 am

    The way the media reports stories like this is indeed an issue here. From ‘alien structures’ discovered around other stars, to stories claiming ‘immortality’ treatments have been found because some researcher somehow reset an organism’s biological clock, I see so many stories that take research results out of context, extrapolate from limited data to just plain making stuff up, that I long ago reached the point where I never believe any claims from science related stories until I dig up the original research.

    the results of the EM drive experiments are interesting, certainly, and there should definitely be additional research into what is going on here. But as has been pointed out, the measured effects are so small that it remains to be seen if the amount of thrust generated is even going to be useful for anything. Right now it is a curiosity, an unexplained anomaly.

  9. datiheinon 26 Nov 2016 at 10:39 pm

    That is actually _not_ an insignificant amount of thrust. Quoting from the paper (in the paragraph just before the ‘acknowledgements’ section):

    The 1.2 mN∕kW performance parameter is over two orders of magnitude higher than other forms of “zero-propellant” propulsion, such as light sails, laser propulsion, and photon rockets having thrust-to-power levels in the 3.33–6.67 μN∕kW (or 0.0033–0.0067 mN∕kW) range.
    [end quote]

    So a couple orders of magnitude more powerful than a light sail. Seems like it could be useful (if it is real).

    That also means the effect is not that tiny, not insignificant. The researchers believe their measurement error to be about +/- 0.1 mN/kW. Not great, but not awful either; an order of magnitude less than the measured effect.

    I’m not disputing the main point that this could turn out to be a problem with the equipment or the experimental setup or design. Maybe it’s pushing against the earths magnetic field (even though they think they’ve accounted for that) or something similar. But I do think you should reconsider the size of the effect as a reason to dismiss the claims.

  10. Charonon 29 Nov 2016 at 10:38 am

    OK, datihein, the reason to dismiss the claims is that they violate conservation of momentum (which is far more fundamental than the Newton’s Third Law formulation Steve gave above). Spatial symmetry leads to conservation of momentum, period. This principle is so fundamental that Pauli postulated a new (and he thought unobservable) particle on its basis, the neutrino.

    Fortunately the neutrino was observed a couple decades later. Highlighting that physicists have been doing far more sensitive and precise experiments than this NASA team for a long time – we can detect freaking neutrinos, and regularly. LHC scientists would love to detect something that didn’t appear to conserve momentum (because it would mean a new particle we’d been missing, perhaps dark matter, or yeah, I guess it could mean this fundamental idea is wrong). Hasn’t happened yet.

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