Jul 29 2015

Despite Headlines, the EM Drive Is Still Bullshit

Headlines declare, “To the Moon in Four Hours,” and “Star Trek Impulse Drive,” even from mainstream outlets like the Telegraph.

This is an old story that will likely rear its head for years to come. It’s the free energy of space travel. The allure is simply too great for the cranks to ignore.

At issue is the EM Drive, which I wrote about here. The makers of the drive claim that it produces thrust without propellant. Physicists say that such a thing would violate the law of conservation of momemntum. Devices that claim to break a well-established law of physics have a terrible track record.

The device is alleged to work by bouncing microwaves back and forth within its chamber. There is a subtle asymmetry to this, bouncing harder in one direction than the other, which produces thrust. The problem with this, of course, is that the thrust is not balanced by anything, you get net momentum in one direction without an equal and opposite momentum in the other. Newton is displeased.

Prior tests have been unconvincing, producing tiny amount of anomalous thrust that can easily be explained by experimental error. The EM drive is back in the headlines with the typical hyperbole because of a new study looking at the drive. Although not yet published, peer-reviewed, or even presented, the details of the study are made available here: Direct Thrust Measurements of an EMDrive and Evaluation of Possible Side-Effects.

Perhaps one reason the study is getting so much media attention is because the authors, Martin Tajmar and G. Fiedler, are mainstream scientists with reasonable credentials. The only thing that matters, however is the details of the study itself.

The study is an attempt to replicate a previous study showing a small amount of anomalous thrust. The authors conclude:

“Our test campaign can not confirm or refute the claims of the EMDrive but intends to independently assess possible side-effects in the measurements methods used so far. Nevertheless, we do observe thrusts close to the actual predictions after eliminating many possible error sources that should warrant further investigation into the phenomena.”

That statement should give any skeptical reader pause. The study results cannot confirm that the device works. However they did record anomalous thrust. The question is, however, where is the thrust coming from, and the study cannot tell us.

One likely source is that it is coming from heat, which is a known source of fake thrust measured in such experiments. Eric W. Davis, a Senior Research Physicist at the Institute for Advanced Studies at Austin, notes:

“I noted in [the study’s] conclusion paragraphs that [Tajmar’s] apparatus was producing hundreds of micro-Newtons of thrust when it got very hot and that his measuring instrumentation is not very accurate when the apparatus becomes hot,” Davis told io9. “He also stated that he was still recording thrust signals even after the electrical power was turned off which is a huge key clue that his thrust measurements are all systematic artifact false positive thrust signals.”

In other words, the measured thrust came and went with the heat, not with the power to the device. This is a huge red flag that the measured thrust was a side effect of heat, and not being produced by the EM drive. In other words – it’s crap.

Scientists generally are not taking the claims seriously, and not because they are closed-minded, or because they are shills for Big Propellant. They are skeptical because we have very weak evidence attempting to overturn a rock solid law of physics. Again – history has not been kind to such claims.

I also note that the experiment measured very tiny thrust, in micro-Newtons. This is a common pattern we see with free energy devices or cold fusion. They create tiny amounts of anomalous energy, in amounts that can easily be due to very subtle systematic flaws in the experimental setup. The proponents then claim that the effect can be scaled up – but that is the rub. We then never hear about a scaled up success, because the subtle errors don’t scale up.

The same is likely true here. I will be impressed when they develop an EM drive that produces actual Newtons of thrust – and effect so large that a subtle error cannot be the explanation. Start flying ships around the solar system without propellant, and I will consider the possibility we need to rewrite the physics textbooks.


The new study does not confirm that the EM drive works. It simply replicates a previously flawed experiment and shows the same flaws. The results strongly suggest a heat effect, not true thrust. Scientists remain correctly skeptical toward the claims.

Unfortunately we are getting another round of credulous and sensational reporting from the mainstream media.

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