We just got another EmDrive question, https://physics.stackexchange.com/questions/185380/emdrive-in-relation-to-newest-nasa-article-does-it-extract-energy-out-of-the-q, and much as you would expect it swiftly got closed and an OP probably went away feeling fairly upset. I feel we get enough EmDrive questions that this is something we ought to handle with more care and specificity.

Posts on the subject seem to be along several different lines:

  1. "could it possibly work?"
  2. "how do its proponents claim it works?"
  3. "do those claims have merit?"
  4. "if not, how do they fail?
  5. "assuming that it works, how does it do so?"

If you look at them like that, they are not really all that bad. The problem is that posters tend to pretty much always ask that final question, and that tips the question definitely into the territory discouraged by our non-mainstream physics guidelines. The third question is on the boundary (we are not here to evaluate pet theories) but if the question is appropriately phrased, for something this recurrent, I feel we're better off showing a bit more flexibility and allowing a few canonical questions about this.

So, what I propose is separating these different components, which will help us better address the ones that we can, and cleanly close the ones that we can't. I have therefore asked this question:

and provided a basic answer. (I do not think, though, that there are any more worthwhile references. The ones I did find are singularly thin on the theory even by my low prior expectations. However, if you can find more references, by all means add them in.) This addresses question (2) above. With this in place, questions asking what the claims are can be referred there. If they don't find the resources there sufficient - i.e. if they don't find this community's response to be thorough enough in helping them scour the web for references - well, tough luck. They can look for their own and add them there, or they can offer a bounty on it to try and draw attention to it.


does a very good job at addressing (1). In the absence of multiple peer-reviewed tests performed in vacuum and published in reputable journals, question (5) is very clearly off-topic. Questions (3) and (4) can be evaluated on a case-by-case basis but are almost certainly off-topic as well.

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    $\begingroup$ I think your question addressing (2) is a good idea, and I pretty much agree with everything else you have said. $\endgroup$
    – ACuriousMind Mod
    May 22, 2015 at 17:35
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    $\begingroup$ To me the real problem is not how to explain to people that the concept can't work/does not work/violates known theory (which is automatically a defensive position) but to teach them that outrageous claims require the same solid evidence as all of science. By asking the supporters of, let's just call it "extreme science", to adhere to the usual rules of evidence, we can easily point out why none of these claims come even close to living up to the requirements of a typical experimental undergrad student paper. $\endgroup$
    – CuriousOne
    May 27, 2015 at 5:16
  • $\begingroup$ One of the (many) problems with current scientific practice is that we consider independent replications as such that don't include skeptic scientists in their teams. Maybe this is difficult to do in all cases, but it seems to be the trend, and this makes skepticism worse, as everyone suspects biases, interests and agendas other than scientific truth. Notwithstanding the above, 6 approximately independent confirmations require further examination. While I agree that Noether theorems rule out the naive interpretations of the physics of this cavity, there is still might be nontrivial physics $\endgroup$ Apr 21, 2016 at 18:31
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    $\begingroup$ to be learned from this. Note as a side consideration, that the EMdrive cavity is quite similar to cavities used to detect axion dark matter. Maybe the asymmetric tapering results in some nontrivial effect with background dark matter. This is unlikely, but it is an example of a possible hypothesis for experimentalists and skeptic theorists need to work on together $\endgroup$ Apr 21, 2016 at 18:34


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