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Of course, this question runs perilously close to this site's prohibition against discussing non-mainstream physics. However, the accepted answer in meta about what is acceptable and what is not acceptable regarding non-mainstream physics, says that it's okay to ask for an evaluation within mainstream physics of a new concept or paradigm. I believe my question falls under this heading. The new concept is that it might be possible (counter-intuitively) to accelerate a body in a vaccuum without a traditional propellant. My understanding from this article (paragraph starting "Dr. White proposed") is that the engineers at NASA have some kind of theory which is supposed to fit into mainstream physics about how this would work. But I'll understand if people vote to close.

The article I've linked to is not technical, and provides no technical references. My Google-fu has not managed to uncover a more technical description anywhere (I can't even find a homepage for the group doing this research). So

Question: What exactly is the theoretical mechanism that NASA (in particular, Sonny White, in particular, not Roger Shawyer) is proposing? And where can I read about it?

The proposal is apparently precise enough to build a computer simulation off of it (see near the end of the article, the section labeled "Progress Update"), so I'm assuming that it must be intelligible.

For example, here's something that might be the sort of thing they're talking about. Imagine that on your spacecraft you have a gamma-gamma collider (powered by a nuclear reactor or solar panels or whatever). When the photons collide, they create lots of high-energy electron-positron pairs spraying out in all directions. By clever design of the hull of your spacecraft, let's say that you preferentially readsorb electrons / positrons moving toward the bow of the ship (e.g. put a big lead block to the bow of the collider). Then you will generate momentum going forward. Your propellant particles have been bought from the vaccuum.

Now, the EM fields involved in the NASA setup are nowhere near this strong, so the mechanism can't be quite this. The article I linked to says something about virtual particle-antiparticle pairs, so maybe the proposal is that the "propellant" is made up of waves in the electron field which are not localized as particles?

EDIT Earlier questions have focused on whether the proposed effect would violate conservation of momentum. My assumption is that if we actually look at NASA's proposed mechanism, we will see that it's not violating conservation of momentum, just sending that momentum off into "new" particles, as in the example version I sketched. I'm really mostly interested in seeing the actual proposal, so maybe this question is best viewed as a reference request.

EDIT I'm disappointed to see this question marked as a duplicate. I'm asking for a specific link, and I haven't seen that link, nor have I seen a definitive claim that the link I'm looking for doesn't exist.

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  • See also http://physics.stackexchange.com/q/135115/ and links therein. – Kyle Kanos May 01 '15 at 17:20
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    @KyleKanos Thanks, those are good links, since they're about the same project. But those questions were asking whether the experimentally observed effects were correctly interpreted as violating conservation of momentum. I'm asking what the proposed mechanism behind the effect is, which I think is a different question. – tcamps May 01 '15 at 17:22
  • Then I suggest reading the second set of links more fully (particularly the comments), as links are provided elsewhere for the papers from last year. It is likely far too early to see any publications for the current test. – Kyle Kanos May 01 '15 at 17:30
  • Can you shorten your question? It's a lot of text for what is basically, "Can someone explain, in technical terms, NASA's EM drive?" – innisfree May 01 '15 at 17:32
  • @KyleKanos I see a link discussing the theory proposed by Shawyer, the originator of the idea. But supposedly NASA has their own theory which is more recent. I agree that it's a highly suspect chain of events, but I'd still like to see this new explanation. – tcamps May 01 '15 at 17:33
  • @innisfree well, I'm not particularly interested in just anyone's explanation, but particularly in NASA's explanation. I can try to edit to highlight my question, but I think in a case like this it's important to head off responses to slightly different questions. – tcamps May 01 '15 at 17:36
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    Mach Effect Thruster, aka the Woodward effect. See http://en.wikipedia.org/wiki/Woodward_effect . I'm voting to close as off-topic. – David Hammen May 01 '15 at 17:37
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    @DavidHammen Do you have a reference saying that this is NASA's proposed explanation? – tcamps May 01 '15 at 17:38
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    From a quick look, I tentatively think this is on topic for the reasons outlined in previous comments. That being said, we do need to be careful in general about what EMdrive questions we allow, since the topic straddles the boundary of non-mainstream physics. – David Z May 01 '15 at 18:14
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    I can't see anything new here. The only recent development seems to be a NASA engineer reporting independent experiments at the NASASpaceflight forum (apparently, post 1632 here, which I don't find intelligible or novel). Note that NASASpaceflight is not officially related to NASA. IF NASA releases an official technical report on tests in vacuum, that's something we can talk about. As it is, the only thing to talk about so far is whether this can work, which has been well covered already. Voting to close as a duplicate. – Emilio Pisanty May 01 '15 at 18:55
  • @EmilioPisanty But I'm not asking about the experimental results. I'm asking about the theoretical proposal, which is referenced in the article I linked to. This may be old news; if it's been discussed and the technical details linked to, please point me to where that is! – tcamps May 01 '15 at 18:55
  • Do you mean this one? Note that NASASpaceflight is not officially related to NASA. I cannot find any official NASA documents on it - tracing through it only leads to the forum post I linked to. There are two questions to be asked: (i) has NASA made any official claims to the effect that EmDrive works, and (ii) what do EmDrive claimants (including NASA if (i) is affirmative, not including it if not) claim the mechanism is. – Emilio Pisanty May 01 '15 at 19:04
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    We can help with (ii), and it would not be a duplicate, but you need to make that very clear, and you need to present very specific references to the claims you're asking us to dissect. We cannot help with finding those documents, or with question (i) (which is a much better fit for Skeptics). We are here to do physics, not to dissect conspiracy theories. – Emilio Pisanty May 01 '15 at 19:04
  • If you want to read up on the theory discussions, a good place to start might be rationalwiki. If you want to see what Shawyer claims makes the device work, go to the emdrive website itself. These are really not that hard to find, I think. – Emilio Pisanty May 01 '15 at 19:10
  • @EmilioPisanty I agree that my references are very sketchy (I referenced two points in the linked article in my question, but that's the best I have) and that that's kind of the point. As I said, I'm not interested in Shawyer's proposed mechanism, but in NASA's (specifically Sonny White's) proposed mechanism. I don't see that on either the EM drive website or the rationalwiki. If this isn't an appropriate place to ask for such a link, then please reject my question on those grounds, but not for being a duplicate. Thanks for your help, though. – tcamps May 01 '15 at 19:14
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    If you are asking for a THEORETICAL explanation, then you are out of luck, because there is none. If you are asking for a HYPOTHETICAL one, then you can come up with as many as you like, since you are not constrained by standard physics any longer. The problem with hypothetical explanations is that you would have to re-check the entire knowledge of physics against their predictions and come up with consistency except for the emDrive. How likely is that? – CuriousOne May 01 '15 at 19:21
  • Well, I think the hypothetical explanation I outlined in my question statement shows that it's not impossible to use purely gamma-gamma interactions to generate thrust without a propellant in the traditional sense. Maybe I do have an axe to grind; it does seem to me like some low-energy version of what I outlined (if the details were to work out) could be a plausible theoretical explanation. Maybe I'm wondering if that's in fact what they're proposing. Oh well. – tcamps May 01 '15 at 19:23
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    @tcamps: Once you enter the words "gamma-gamma" interactions into this, you have already expended an unnecessary amount of thought on this non-problem. In a homogeneous space-time it is not possible for Baron Munchausen to pull himself out of a swamp by his pigtail. Anything beyond that is just an obfuscation of trivial physics. – CuriousOne May 01 '15 at 20:38
  • I guess it's not really important how these particle pairs are generated for my point to stand: there are ways to create thrust without violating momentum conservation and without carrying along a propellant. I'd like to give these researchers the benefit of the doubt, assume that what they're proposing is not crazy, and actually look at what they're proposing. – tcamps May 01 '15 at 20:41
  • @tcamps: Extraordinary claims require extraordinary evidence. So far not even trivial evidence has been presented. It is, by the way, telling, that most of these extremely extraordinary things (like perpetual motion) are always happening to people you wouldn't even trust with the break assembly of your car. :-) – CuriousOne May 02 '15 at 02:04
  • I'm not asking about the evidence. I'm not asking whether it's true. I'm not even asking whether it makes sense. I'm simply asking where I can read a statement of a particular theory. – tcamps May 02 '15 at 02:54
  • I'm simply asking where I can read a statement of a particular theory. It's never been published because no reputable source would publish such bunk theory (which is what everyone's been saying). There was an easily found conference paper (linked in the other questions I told you to go through, which you seem to have apparently ignored), but that only covers the 2014 'results' of the test, not the theory itself. – Kyle Kanos May 02 '15 at 17:57
  • I've seen this paper (which I would agree presents some very unconvincing experiments). As you say, it's not what I'm asking for. The theory in question might not be published in a journal (I apologize if that puts it outside the scope of the site - if so, then please close the question on those grounds). It would be enough to point to a preprint or something. – tcamps May 03 '15 at 03:55
  • @tcamps you've hit on an issue that we have some internal debate about. I think it's reasonable to ask whether there is a journal paper, conference presentation, or arXiv preprint that explains a particular effect (of course it seems the answer you'll get is no, there is not). But others think differently. It might be worth bringing this up on [meta], if nothing else so that we make the discussion explicit. (Perhaps I'll do it later, but you're welcome to do so first.) – David Z May 03 '15 at 06:26
  • @DavidZ I'm a little reluctant to start a meta conversation myself as a newbie user. But please feel free to start such a discussion. I worry that this example might not be the strongest one to make your case with, since there are other issues present that might distract from the main issue, as they did here. – tcamps May 04 '15 at 12:15
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    I just happened back here a year later and was gratified to discover that only a few weeks after I initially posted this question, @EmilioPisanty not only asked essentially what I was trying to ask in a more general setting (here), but also put in some great work into recording the best available answers. I just wanted to register my appreciation to Emilio and to record (without making an edit that might bump this question onto the front page) that I consider Emilio's question the definitive version of what I was trying to get at here. – tcamps Jul 06 '16 at 15:08

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