Talk:EmDrive

Analysis

Can someone edit the analysis page, it was blatently written by someone who hasn't read either the New Scientist article or the more recent Eureka article. It doesn't violate either the conservation of momentum or energy, as it uses energy!

Every article on it specifically states that when the equipment accelerates it loses thrust. If anyone would like to check, this happens with every form of propultion and just because it doesn't spew matter out of it doesn't make it reactionless.

If it violated the conservation of energy, why would it take kilowatts of energy to run. If it actually violated the conservation of energy (like has never been claimed, and refuted in every article) it wouldn't take energy to run as you would be getting more energy out than in and at that point I doubt he'd need grants as he'd be able to make free energy and become the richest person on the planet after undercutting the prices of every power company.

The nice wholely verbose and highly infantile argument by 'Dr. John P. Costella' shows just how little attention he paid to the articles. He forgets fundamental facts of science, claiming he's disproved it by using particles to explain how a tapered WAVEguide won't work. Almost a century of physics was spent figuring out if light was a wave or a particle, and people won nobel prizes for proving both right.

He insults Shawyer, the absolute worst thing you can do when criticizing someone, all it screams is that Costella is incompitent and can't get enough evidence to prove his own point.

Costella is worse than a fraud, he's blatently ignorant.

Simply looking at the quantum theory of momentum disproves Costella, as it's based on waves not particles. He also completely ignores the conservation of four-momentum, which brings energy into the equation. As the equipment is storing aprox 17MW of energy, that should equate to the system gaining 0.002 grams in mass. However, there's no mention of basic theories that the EMdrive relies on.

Costella would have had a perfectly valid argument, without research, saying that Shawyers' apparatus could not gain more than 0.002 grams of thrust in any direction. Yet no, this Ph.D does zero research even though he claims to have gone on the 'net' to even look for something to disclaim Shawyer. This only serves to prove that Ph.D's are useless and can't even research after they've spent near a decade of their lives researching to get a Ph.D.

I don't have a Ph.D and it took me a few minutes to find a resonable basis for an argument AGAINST my point of view. So please, someone edit it before I delete the whole damn portion as being useless and bias as it's not an analysis at this point it's plain criticism. —Preceding unsigned comment added by 86.137.68.79 (talk) 20:48, 11 October 2007 (UTC)

Unfortunately, it violates conservation of momentum. It can be shown that if it violates that, then it inevitably violates conservation of energy as well, due to relativity considerations, in at least some inertial frames of reference. Shawyer tried to avoid that by asserting conservation of energy in his derivation, but because of lack of conservation of momentum, his derivation only holds in one reference frame, unlike Newtonian mechanics or Special Relativity, where it holds in all.WolfKeeper 02:11, 12 October 2007 (UTC)

The esoteric General Relativistic effect of asymmetric frame drag allows a very small force. It appears only in relation to the drag itself and not the energy expended. I have said before that Shaywer's theory is likely incorrect, but the effect he sees is a real esoteric frame drag. He postulates increasing efficiency to make cars float, for example. This is in error as it follows a failed theory. I predicted a five pound force as a sun probe. Near earth a small mass drag is far less. It does violate as with all drag. A photon has an odd property making only radiowave/light/etc. cause true asymmetry.

--74.9.129.85 (talk) 21:35, 10 March 2008 (UTC)

The creator asserts it does not violate the conservation of momentum or energy, the Wikipedia article asserts indirectly that it does by labeling it a reactionless drive (which the creator also disputes) and proceeding with criticism on that front without any citation of analysis of the actual drive or mathematics itself. That is why this section is original research, that is why this section is biased POV, that is why the Analysis section should be removed. If someone wants this information so badly, they should find some analyses of the drive and its theoretical underpinnings and write a wikipedia article on the controversy directly and actually cite it. Unless someone here can create a detailed analysis based on actual information and post it on their own site, they are playing armchair science critic and that's POV. This isn't even about whether or not the drive even works theoretically.

Whatever Costella's credentials and background, he is entirely correct and this Wiki entry should be deleted as being an 'accessory before the fact' in a blatant fraud. Moreover, it is a very sad modern trend that those with no knowledge of physics (but a great fondness for philosophical double-talk) defend crackpots in a knee-jerk manner and simultaneously accuse experts of - in effect - being brainwashed by their own expertise. Defenders of the concept should ask themselves how the situation differs from the old kindergarten puzzle about whether one can reduce the postage on a package of bees by stirring them into flight before putting it onto the scales. It doesn't: microwaves are not 'magic', and relativistic arguments change nothing. Also, those who cite quantum mechanics should check out what the 'correspondence principle' implies. Magazines such as New Scientist and Wired should be censured for even mentioning Shawyer; his only proper place is in the pages of Fortean Times or some ufology fanzine. Above all, (more) questions should be asked in Parliament about the quarter of a million pounds of public money which has already been squandered on this nonsense. — Preceding unsigned comment added by 81.147.128.77 (talk) 13:03, 18 September 2011 (UTC)

151.148.122.100 (talk) 15:44, 26 September 2008 (UTC)

Flight International

The EM drive is briefly mentioned in the news section of Flight International (26th May 2008). The news short said that the EM Drive woudl be presented as a thruster design for station keeping on satellites at an astronomy/space convention in (I think) London. News short makes no mention of technical feasibility or junk science. Haven't added it to the article yet because that's the extent of what I can remember from memmory. I'll add the details to the article after checking details today.ANTIcarrot (talk) 09:36, 27 May 2008 (UTC)

Presentation at Space '08

A presentation on the EmDrive were given at the Space '08 - slides available here: http://www.rocketeers.co.uk/?q=node/330

The wiki article here suggest that the EmDrive violates conservation of momentum or energy, which it's inventor says is not the case. If you want to keep the claims regarding violation of laws of physics in the article, you will have to show (with citations) that these violations actually exist in the theory of the EmDrive - anything else is intellectual dishonesty.

The claims made about the EmDrive's performance by its inventor sounds like science fiction - but so did rocket propulsion in space in its day. I'm no rocket scientist, but I see stuff going in (solar energy) and stuff going out (thrust) - I do not see how this system violates the laws of conservation. Present your proof that it does, or suffer my flaming sword of editorial justice. —Preceding unsigned comment added by AndersFeder (talk • contribs) 03:16, 13 September 2008 (UTC)

Energy and thrust are two very different things. If you saw someone put apples into an empty bag and then found that it was full of oranges, you wouldn't just say "well they're both stuff, so that explains it". Apples don't magically change into oranges. So you'd want a proper explanation. Likewise thrust is a very different thing from energy, so you don't expect to put energy into an item and magically get thrust. If it turns out that you do then you need a good explanation for that. As for conservation, there are two things that have to be conserved for devices operating according to our current understanding of physics. The first is energy and the second is momentum. While people can agree that a device like an ion drive conserves both, they find it difficult to see how a device like the Emdrive can conserve either. However proof is in the pudding. If the Emdrive works as advertised then it's up to the theoreticians to explain why, either by showing how it conserves the two quantities or by showing why there is an exception. Most theoreticians find it a lot easier to just claim that the device doesn't work. -- Derek Ross | Talk 06:10, 13 September 2008 (UTC)

I was not saying that Shawyer's claim are explained or even plausible, but merely that the article does not show the violations of physics that it claims the EmDrive exhibits. You will also note that putting apples into an empty bag and then subsequently finding oranges in it does not violate any laws of physics. The absence of evidence (that the bag's change of content is physically sound) is not evidence of absence (of physical soundness). I think the point where the article breaks down is when it, without citing any sources, asserts that the EmDrive is a reactionless drive. The only one who knows what the EmDrive is or isn't, namely Shawyer, specifically has said that the EmDrive is not reactionless. The unverifiable claim that the EmDrive is reactionless is idle speculation on the part of whoever authored that section and has no place in Wikipedia. I'm no physicist (though someone who were once told me that E=mc² and that p=mv, which naively(?) could be interpreted as p=(E/c²)v) - I'm just taking issue with the quality of this article. AndersFeder (talk) 22:52, 17 September 2008 (UTC)

The elements that go to make up an apple or an orange are not the same, so yeah, it would violate physics.- (User) Wolfkeeper (Talk) 23:18, 17 September 2008 (UTC)

It really wouldn't as I could have exchanged the apples with oranges without you noticing, which would be in perfect accordance with known laws of physics. --AndersFeder (talk) 03:40, 18 September 2008 (UTC)

Yes, fraud like that is in perfect agreement with the laws of physics ;-)- (User) Wolfkeeper (Talk) 22:30, 26 September 2008 (UTC)

The p=(E/c²)v) equation is great for showing how the momentum of a photon is related to its energy but unfortunately it doesn't tell us anything about thrust which is a force, ie a change in momentum per unit time. You need other equations for that which I will mention in a minute. In the meantime. I can agree with Shawyer's claim that the device doesn't violate conservation of energy. However his claim that it doesn't violate conservation of momentum is a bit more controversial. Shawyer's claim that that the device isn't reactionless is really another way of saying that it doesn't violate conservation of momentum. Now his claim is based on the fact that photons can change their mass but not their velocity. This is completely different from normal non-relativistic conservation of momentum where items can change their velocity but not their mass. Thrust is normally calculated as F = m * (v₁ - v₂) / t, whereas Shawyer is basically calculating it as F = (m₁ - m₂) * v / t. His opponents say that you can't do that. That's why they claim that his drive is reactionless and he doesn't. -- Derek Ross | Talk 00:23, 18 September 2008 (UTC)

That's interesting. But is his claim then not in fact contingent upon conservation of momentum? When the photons shed mass, something have to respond with an increase in velocity to conserve momentum? Or where does the mass in fact go when photons change mass?--AndersFeder (talk) 03:40, 18 September 2008 (UTC)

Well, I guess that he would say that the thing that responds with an increase in velocity is the drive and whatever it's attached to. In other words --

((m₁ - m₂) * v_photon) + (m_device * (v₁ - v₂)) = 0

-- and that's why the momentum of the overall system is conserved in his view. As far as I'm concerned the real difficulty is in the shedding of mass by photons. The only way that I know of doing that is to aim them straight up through a gravitational field. However he seems to think that he can do it via repeated reflection within the shaped cavity of his device. Maybe he can. We should know soon. If his superconducting version works as predicted it will demonstrate forces far too large to be ignored. As for where the photon mass goes, presumably it is converted into the kinetic energy of the device itself so that conservation of energy holds for the overall system too. -- Derek Ross | Talk 07:20, 18 September 2008 (UTC)

Look, when this first came out, it took me a few days to prove that, as described, this thing cannot possibly work. By work I mean, it cannot give you any *net* acceleration. So you can't switch it on, accelerate with it, then switch it off and maintain the velocity. For if it does that, it violates *both* momentum and energy conservation laws, and I was able to show you could build a perpetual motion machine. The reason is simple, if you can use it to change reference frames, in the initial reference frame it gains kinetic energy and (presumably) loses power from its power source. But in the final reference that it ends up in, since you switched it on, the kinetic energy has gone *down* as well as the loss of power in its power source. Where has this energy gone? Some has gone as heat, but only a proportion. Where's the rest of it? Because it has no external propellant emitted, there's nowhere for this missing energy to have gone (unlike rockets). It's just a mistake or a fraud, it can't work with any physics as we now know it. The same argument holds in relativity, and this thing is supposed to be relativistic.- (User) Wolfkeeper (Talk) 22:24, 26 September 2008 (UTC)

Biefield-Brown effect

Just read this guys blog, claims the device works on the principle of the Biefield brown effect. In short, the device does create some thrust, by the movement of charged ions throughout the device // ion wind //, but it would do precisely zero in a vacuum. Anyone familiar with the details of this concept?

http://www.rocketeers.co.uk/?q=node/349 —Preceding unsigned comment added by 217.34.37.92 (talk) 10:47, 26 September 2008 (UTC)

Could be. Vacuum testing on the EM drive would be essential to rule out causes of this type. Bit late to find out how much money you've been wasting if you have to wait until it's out in space. By the way, the blog link to the report on the NASA investigation of the Biefield-Brown effect was well worth reading. It gave a very solid (and not at all esoteric) explanation for that effect, whether or not it has anything to do with the EM drive. -- Derek Ross | Talk 14:57, 26 September 2008 (UTC)

Yeah I will be very interested to see what happens when you pop the EM drive in a near vacuum, im kind of surprised this hasnt been done already considering a) the drive is specified for space travel, and b) there is a well known effect which could potentially explain the function of the EM drive without destroying the laws of physics. Im actually considering emailing Shawyer, not that hed ever see it, just to get his opinion on the subject. —Preceding unsigned comment added by 217.34.37.92 (talk) 14:22, 3 October 2008 (UTC)

Unfortunately the Biefeld-Brown case was also fraud. Brown was the typical crackpot inventor and Biefeld was a highly respected academic and astronomer. However, by the time that Brown exploited him, Biefeld was clearly suffering from senile dementia (he was once found wandering around a strange city of no memory of how he got there). Nevertheless, 'electrogravitics' attracted a great deal of attention from 'high-tech' companies until a damning report from the Office of Naval Research outed Brown as a nutter. Among other things, he claimed that his instruments could detect changes in the Dow-Jones Index. It is very sad that Brown, Tesla, etc. are still referred to with awe, when they should be cited only as pseudoscientific fraudsters. — Preceding unsigned comment added by 81.147.128.77 (talk) 13:20, 18 September 2011 (UTC)

Northwestern Polytechnical University

Recently, Shawyer said researchers at Northwestern Polytechnical University (NPU) in Xi'an under the supervision of Professor Yang Juan independently created a mathematical simulation showing that a net force can be produced from a simple resonant tapered cavity. Shawyer said that NPU is currently manufacturing a drive based around this theoretical work. Yang Juan confirmed the results of the mathematical simulation, also saying that NPU is building a part of the drivee and that results had been submitted to a journal.

Moving this paragraph from the article, as I can find nothing more reliable than the cited Wired blogger's report on an interview with Shawyer. As Yang appears to be a legitimate published researcher, our biographies of living persons policy comes into play. The blogosphere certainly seems to have noticed this, though, so it would not surprise me to see better reporting in a few days if this is as it appears (and maybe even a mea culpa or two later on when conservation of momentum is upheld, demonstrating once again that the laws of physics apply everywhere). If there is nothing more than exaggeration, misunderstanding, and poor fact-checking to this story, though, it should remain excised. - Eldereft (cont.) 21:25, 26 September 2008 (UTC)

Yes, it is a blog, but seems fairly reliable. It includes quotes from Yang Juan (or it did, see below), so it can't just be an interview from Shawyer- else it would be much more suspect. I just now put back in the claim that it has be submitted to a journal, which is what the article says Juan said. However, I think the article has changed since I wrote the piece. It had that claim in it, and as I recall, it was sourced to Juan himself, not shawyer. It definitely said it was submitted to a journal and was under editorial review, as I remember (I'd never have manufactured that claim). So, this indicates the sources has something fishy about it. For some reason, it seems to have changed (and thus not everything I just said is true). Might be better just to wait for better sources. ——Martin^phi ☎ Ψ Φ—— 22:04, 26 September 2008 (UTC)

Anyone can submit anything to a journal. It's getting it published by a reputable, refereed, journal that is the trick ;-)- (User) Wolfkeeper (Talk) 22:13, 26 September 2008 (UTC)

The Reliable Sources Noticeboard] might disagree, but I would put this on the RS scale somewhat below a regular column in Wired, but well above a random WordPress account. By putting their imprimatur on the blog, the magazine is staking some reputation on the accuracy of the content and its relevant to their target audience. Two minutes of poking around did not yield a statement of editorial control or a vetting process, though. I only checked the English version of NPU's website, so we might be missing the obvious source. I am happy to wait for better coverage on this one, but if someone else actually is working on a prototype it is a pretty big deal and should be treated by this article. As a side point, to have manufactured that claim would have been drastically out of character for Martinphi. - Eldereft (cont.) 04:30, 27 September 2008 (UTC)

Yeah... but unless my mind is playing tricks it changed, so it isn't being very reliable at the moment. And thanks for the compliment (: I think there was more to this paragraph "The NPU have confirmed that they have reproduced the theoretical work, and are building a demosntration version of the Emdrive." I spent some time looking, and I doubt there are any better sources out there. ——Martin^phi ☎ Ψ Φ—— 07:15, 27 September 2008 (UTC)

Laymen should ignore such 'confirmations' and instead check out Langmuir's analysis of 'pathological science'. Initial confirmation from 'reputable people' is, in fact, the norm. It happened with cold fusion, for example. — Preceding unsigned comment added by 81.147.128.77 (talk) 13:29, 18 September 2011 (UTC)

Requested rename

The following discussion is an archived discussion of the proposal. Please do not modify it. Subsequent comments should be made in a new section on the talk page. No further edits should be made to this section.

No consensus to move. Vegaswikian (talk) 01:16, 29 April 2010 (UTC)

EmDrive → The 8 September 2006 Issue of New Scientist — This article focuses much more heavily on the date and title of this publication than the EmDrive itself. 76.27.230.215 (talk) 07:22, 22 April 2010 (UTC)

• Oppose Horrible name, and that issue does not solely cover the EmDrive either, so that name is wrong. 70.29.208.247 (talk) 05:25, 23 April 2010 (UTC)

• Oppose The name is the subject of the article Racklever (talk) 06:40, 23 April 2010 (UTC)
• Oppose Horrible name.--Oneiros (talk) 13:55, 24 April 2010 (UTC)

The above discussion is preserved as an archive of the proposal. Please do not modify it. Subsequent comments should be made in a new section on this talk page. No further edits should be made to this section.

Automate archiving?

Does anyone object to me setting up automatic archiving for this page using MiszaBot? Unless otherwise agreed, I would set it to archive threads that have been inactive for 30 days and keep ten threads.--Oneiros (talk) 14:03, 24 April 2010 (UTC)

Why? Typically you leave three discussion on the talk page, and there aren't that many discussions here at all, nor are they long. Setting up auto archiving when you don't need it just loads down various machines in processing things that don't need it, slowing Wikipedia, and the archival bots. 70.29.208.247 (talk) 02:27, 25 April 2010 (UTC)

Dr. John Costella

I read the citation that this article uses to assert that Dr. Costella is a credible critic and I do not believe he should be mentioned so much in this article. He is an irrelevant person, with no academic affiliation, and if not for his PhD he would have absolutely no basis to stand on. His attack on the EMDrive (which I also am skeptical of by the way) is ignorant and contains personal attacks. I am not a theoretical physicist, but I am a physics student at the University of Michigan and I believe that either a more qualified critic should be found or these challenges should be deleted. At the very least, the wording needs to be changed so the article doesn't sound like Dr. Costella is a resident expert on EmDrives.

You're probably right that he wouldn't be notable if it wasn't for his academic qualifications. On the other hand, he does actually have an academic qualification in the particular realm that the emdrive designers claim is the working principle behind it, and he does seem to be a notable critic of the drive.- Wolfkeeper 20:10, 26 April 2010 (UTC)

You can have a PhD and still make terrible and flawed arguments on a subject. Credentials should not excuse intellectual laziness. —Preceding unsigned comment added by 68.35.236.214 (talk) 17:09, 12 May 2011 (UTC)

Any 'intelligent schoolboy' could have made the Costella claim and have had a right to be believed without question. Scientific knowledge is not based upon the opinion of a few trendsetters (as pop culture is) but upon innumerable reproducible experiments which have led unavoidably to the consensus of opinion known as scientific laws. Any claim to have breached those laws, especially when it is put straight 'into production' without conducting any proof-of-principle experiments will always attract nothing but derision from professional physicists. — Preceding unsigned comment added by 81.147.128.77 (talk) 14:43, 18 September 2011 (UTC)

BUILD IT

Why, oh why is so little information given in the article about actual experiments both accomplished and underway with this technology? Over and over and over again we read excruciating detail about the theory behind the drive and analysis of the negative aspects of this.

Unfortunately, the article almost completely avoids any positive results or detailed analysis of actual experiments. Comments by skeptics are given more than adequate exposure. But there is virtually no countervailing commentary about the results of experiments or comments by those who witnessed them that call into question the skeptical arguments. Only ONE SENTENCE in the article deals with Chinese confirmation of the theory and NOTHING WHATSOEVER is said about THAT analysis.

Experiments make or break theories. This article and indeed this discussion page is NOT written from a Neutral Point of View (NPOV) but rather with a strong bias against the technology bordering on pseduoskepticism. There absolutely should be an examination of the weaknesses of skeptical comments given the stakes of the outcome in this matter. And experimental results ABSOLUTELY MUST be a cornerstone of challenges to any skeptical comments.

I can think of no better example of misplaced skepticism than that aimed against of another flight technology in the not-so-distant past. According to highly credible, learned people making the rounds on the rubber chicken circuit of the day, aerodynamic flight violated Newton's sine-squared law. We now know that this law only applies to hypersonic flight, not slow speed flight such as the one the Wright Brothers made. Their experiments proved beyond all doubt that heavier-than-air craft could fly. And not to put too fine a point on it, we also know today that hypersonic craft can fly. Theory and opinions by skeptical experts mean nothing when it comes to proving anything. It's the experiments that provide the proof of a new technology or disprove it.

Shawyer has outlined a theoretical construct that explains enough to construct his drive and it's not all that difficult to construct. The rest of the story is what happens when it's actually built. To the skeptics I say, BUILD IT! SHOW ME that it does or doesn't work but DON'T try to convince me with opinionated discussions that cherry-pick the facts. There are other experiments now underway and these should be reported in the article with some detail, complete with available information about the individuals involved.

The tags at the beginning of this article note that it was nominated for deletion. It's too bad it wasn't deleted because the article, as written, is clearly biased and not NPOV. Perhaps if it had been deleted, a better article would have been forthcoming.

USER I —Preceding unsigned comment added by 174.17.138.253 (talk) 19:29, 22 May 2011 (UTC)

No, it is absolutely not up to the skeptics (or sceptics on my side of the Atlantic) to build it and prove it doesn't work. It's up to the people who claim it does work to build it and prove that it does. Claims require proof, and extraordinary claims require extraordinary proof. This guy is claiming to be able to impart momentum to something without imparting an equal and opposite momentum to something else, which (if you know anything at all about physics) is a very extraordinary claim. The claim that you can do that without violating known physical theories is if anything even more extraordinary. So far the only evidence that the thing works seems to be a video on YouTube. That doesn't count as extraordinary proof. See Ockham's Razor.

HairyDan (talk) 18:12, 25 January 2014 (UTC)

Implications of EM-drive success or failure

It occurs to me that the EM-drive can be used to settle the Abraham–Minkowski controversy experimentally. Basically, if the EM-drive works, Minkowski is right; if it doesn't, Abraham is right. -- Derek Ross | Talk 19:11, 12 July 2011 (UTC)

Bloody biased article

This article is so biased that reaches the point of causing nausea... C'mon guys, is impossible to this point to look at the question without wanting to burn Shawyer alive because he committed the "heresy" of suggesting that what he is doing is not "magic"? What will you do after that, burn witches? I do not need to be a PhD to see what he suggests makes sense, deserves at least a "ok, let's try this and see what happens" rather than making ridiculous suggestions that he should be banished from the scientific community for trying. — Preceding unsigned comment added by 200.189.118.162 (talk) 15:56, 8 February 2013 (UTC)

I agree with you. However Wikipedia is just reflecting opinion in the mainstream physics community on this issue. And the mainstream opinion is that he is so wrong that burning is too good for him. -- Derek Ross | Talk 17:24, 8 February 2013 (UTC)

Sure, give the crazy guy a hearing (especially if his idea might be profitable). Jeez, that is how Hitler got started. Will you 'touchy-feely' people never learn. Extreme skepticism should always be the first reaction, not a last resort. — Preceding unsigned comment added by 86.136.217.164 (talk) 19:58, 25 April 2013 (UTC)

Then you'll understand why I treat your statement with extreme skepticism. -- Derek Ross | Talk 22:42, 25 April 2013 (UTC)

Stationary?

I realize there's bound to be a bit of sloppy terminology surrounding a subject such as this, but I must ask, What is meant by the phrase "stationary relative to their thrust"? Does the new scientist article illuminate? I couldn't access it. I assume it means "stationary in the direction of the thrust", but then the question becomes "relative to what object?" The Earth? Spiel496 (talk) 02:53, 19 February 2013 (UTC)

July 2014: Major expansion of the article

The article had became hardly readable, with many repetitions in various sections. Criticism of the theory was everywhere, letting almost no place for the theory basis itself to be explained, although a "Criticism" section existed, yet ridiculously empty. So I separated the article in 4 major parts: I first gathered all theoretical claims by Shawyer into a "Claims" section. I then created a section for devices that he built and tested. Criticism that were throughout the article has been put in "Criticism" section where it belonged (but warning about controversial aspect of the subject hence heavy criticism is done from the head summary), section which is now quite expanded, and the Chinese replication, which has a major impact on this work, has now its own section. I added some science with math equations because it was needed to explain Shawyer's point of view about conservation of momentum and energy, but I tried to keep the level of maths at a minimum; although it's a bit difficult when special relativity is involved to not transform a popularization article into a math essay… And I more than doubled the references. Tokamac (talk) 01:50, 9 July 2014 (UTC)

While I appreciate your hard work, the article has gotten too long. It now has more content than the articles on real propulsion systems like Jet engine and Ion thruster. Spiel496 (talk) 02:16, 9 July 2014 (UTC)

When defining the terms after the first set of equations, the phrase "the wavelength of the group velocity" appears several times. This must be a typo, or some obscure shorthand that I'm not comprehending. Perhaps it should be "wavelength of the microwaves"? Spiel496 (talk) 17:58, 9 July 2014 (UTC)

Yes, the article is a bit long. As you know it's because the subject is controversial and some additional explanation is needed for Shawyer's point of view about the system being "open" and subject to the laws of special relativity. This part balances the criticism part that participates to the length of the article too. Both parts are needed for NPOV (criterion the article didn't reach before) and would not be there is the subject was not controversial, as conventional articles about jet engine or ion thruster. I hope in the future the work done at SPR and NPU could be replicated and validated, or on the contrary clearly disproved. One would reduce the other part and shorten the article.

About ""the wavelength of the group velocity"": you're right about this one too, corrected. Tokamac (talk) 11:04, 10 July 2014 (UTC)

Group velocity

It doesn't seem appropriate to talk about group velocity in this context. According to the article on that concept, it has meaning only when the radiation is modulated (pulsed). The modulation envelope moves at the group velocity. The EmDrive is driven (I think) with a constant amplitude, constant frequency; there is no group. Elsewhere in this article, the term "phase velocity" is used. If "group velocity" was intended to be synonym, that was a mistake, and we should replace it with "phase velocity" throughout the article. Phase velocity does make sense in this context, and in waveguides it can take on values other than c. Spiel496 (talk) 19:06, 9 July 2014 (UTC)

Okay, now the article uses the bogus term "group velocity" throughout. The group velocity terminology originates from Shawyer's own paper. We can be NPOV without letting the fringe scientist dictate our terminology. I don't know what he means by "group velocity" but he doesn't mean dω/dk. We need to be clear about what v_g is, or just omit the math altogether. Spiel496 (talk) 01:10, 10 July 2014 (UTC)

No group velocity? Well, you seems mistaken by what you read in the article Group velocity.

Microwaves in a waveguide have a wavelength:

$\lambda _{g}={\frac {\lambda _{0}}{\left[1-(\lambda _{0}/2a)^{2}\right]^{1/2}}}$

where a is the width of the waveguide. This shows a wider waveguide makes the wavelength smaller.

The phase velocity u in a waveguide is given by:

$u=\lambda _{g}f={\frac {c}{\left[1-(\lambda _{0}/2a)^{2}\right]^{1/2}}}$

whereas the group velocity v in a waveguide is:

$v={\frac {df}{d(1/\lambda _{g})}}=c\left[1-{\frac {\lambda _{0}}{2a}}^{2}\right]^{1/2}$

Phase velocity can be higher than the speed of light but carry no information; whereas group velocity is always lower than the speed of light and conveys power. See this reference on Wikibooks for example. It is indeed group velocity which contributes to the radiation pressure. You can check this fact in any microwave engineering text book, in which you can read that the group velocity (sometimes referred to as the guide velocity) carries the energy and momentum of the electromagnetic waves along a waveguide. The equations for group velocity are well defined and show that the velocity decreases as the guide dimensions decrease until cut off where propagation stops. The equations are very non linear but a practical example of their effectiveness is the grid dimensions on the window screen of a microwave oven.

As for the Chinese papers they have been peer-reviewed (three times) and also use group velocity:

"For electromagnetic wave, energy of quantum is transferred at the group velocity v_g, its momentum is p = m v g = h f v_g / c². When the electromagnetic wave in the waveguide is transmitting in travelling-wave state, v_g= c λ_o / λ_g √µ_re_r, where µ_r and e_r are the transmission medium relative permeability and relative permittivity respectively, the wavelength of the electromagnetic wave within the waveguide is λ_g = λ_o / √µ_re_r - (λ_o / λ_c)², λ_c is the waveguide cut-off wavelength."

I don't think you can treat Dr. Yang and her team, as well as the referees of the Journal of Astronautics, the Journal of Northwestern Polytechnical University and Acta Physica Sinica of "fringe scientists".

Tokamac (talk) 12:20, 10 July 2014 (UTC)

Alright, you've convinced me; group velocity is the quantity related to energy transfer. I appreciate the time you put into your response. It still strikes me as counter-intuitive that group velocity matters in a situation where there are are not groups (pulses) in the waveform, but I can't argue with waveguide theory. Spiel496 (talk) 17:32, 10 July 2014 (UTC)

Velocity dependence

In EmDrive#Dynamic_equation_and_conservation_of_energy, the formula

$\left({\frac {Q_{l}}{Q_{u}}}\right)^{2}+{\frac {2Q_{l}\ {\bar {v}}\ D_{f}}{c}}=1$

implies that the Q-factor $Q_{l}$ depends on the velocity ${\bar {v}}$ of the resonator. What is this velocity relative to? The way the text is written, it sounds like the resonator can be used to determine absolute speed. Spiel496 (talk) 22:57, 18 July 2014 (UTC)

Shawyer's original paper, which the formula is taken from, states that ${\bar {v}}$ is the average velocity over time ∆t of an accelerating spacecraft. So that would be relative to its velocity at the start of the acceleration. Sounds like the text needs to be rewritten. -- Derek Ross | Talk 16:32, 19 July 2014 (UTC)

There's still something fishy here, though. If an observer sitting on the emdrive experiences a period of 1g acceleration, does that mean the Q of the cavity will change? Does it make a difference whether the drive is accelerating in free space vs hovering in a gravitational field? There's a lot of content in the article about acceleration and velocity, but after reading it I still can't answer simple questions like this. The source material often uses the exact same wording as the article, so that's no help. Spiel496 (talk) 21:12, 20 July 2014 (UTC)

Dunno if this will help. It's from Shawyer's 2013 paper at [1] and goes into a bit more detail about what Q is and how it is related to acceleration.

The Q factor of the cavity is defined as the stored energy divided by the energy lost per cycle. Thus as stored energy is transferred to kinetic energy, the decrease in stored energy results in a decrease in Q factor. Thus as acceleration increases, Q decreases and thus thrust decreases. The performance of superconducting thrusters was predicted using this simple energy theory, but without identifying the actual mechanism. This paper corrects this situation by describing the Doppler shifts which cause a decrease in stored energy, but which, more importantly, cause the frequency of the propagating wave to move outside the narrow resonant bandwidth of the cavity.

So it looks as if Shawyer expects Q to vary with acceleration. -- Derek Ross | Talk 05:02, 22 July 2014 (UTC)

Actually, to be very specific it's proper acceleration. Gravity does not cause proper acceleration, thus does not lower Q while the EmDrive is just being embedded in a gravitational field. I added the precision in the text. Tokamac (talk) 19:57, 23 July 2014 (UTC)

Regardless of terminology, can someone find an answer to this: Is the behavior of a resonator accelerating at 1g in free space different than that of a resonator hovering in a laboratory on Earth? If the answer is "yes", then the EmDrive violates the equivalence principle. Spiel496 (talk) 14:54, 24 July 2014 (UTC)

An "open system" from which no energy or matter leaves or enters

The article Lead says "no detectable energy leaves the device" but a later section explains that momentum is still conserved because relativity makes this an "open system". The wikilink to open system is about thermodynamics and makes no mention of relativity; also the defining characteristic of an open system is that energy and matter enter and exit the system. So, we have a terminology problem. Also, this isn't a credible answer to the momentum conservation objection. A rocket looks like an open system, but when one includes the propellent in the analysis, momentum is conserved. Spiel496 (talk) 15:18, 24 July 2014 (UTC)

True but if one includes the propellant, the system is no longer open. The rocket alone is an open system in which momentum is not conserved; the propellant is an open system in which momentum is not conserved. But the combination of the two is a closed system in which momentum is absolutely conserved. -- Derek Ross | Talk 19:16, 24 July 2014 (UTC)

Yes, I agree. In the case of a rocket, if one includes everything, then momentum is conserved. Understandably, the first criticism levied at the EmDrive idea is that it looks like momentum would not be conserved. So if Shawyer has a rebuttal to that, it makes sense to include it. But contradicting the first paragraph by saying "it's an open system" doesn't help anybody understand. Spiel496 (talk) 20:36, 24 July 2014 (UTC)

Under normal circumstances such as the rocket the momentum exchange is accomplished by changing the velocity of the propellant and of the rocket and it's not too difficult to visualise what's going on and to see how the momentum is conserved. In the case of the EmDrive it's more difficult to visualise because (as far as I can see and of course I may have misunderstood) the resonator changes its velocity but the photons in the resonator do not. Instead they change their mass (or to be more accurate their energy), so the system is rather different from that of a rocket but it is still possible to construct an equation in which momentum is conserved because the resonator's momentum (which is mv) is increased by as much as the photons' momentum (which is E/c since photons have no rest mass) is reduced even though no photons actually leave the resonator: their energy just drops to zero at which point they no longer exist. That's my understanding anyway but I'm no waveguide expert. -- Derek Ross | Talk 04:33, 25 July 2014 (UTC)

Speaking about the theoretical explanations. I am under the impression that Shawyer tries to explain the net thrust obtained in lab in term of classical electromagnetism, and then he adds bits of special relativity to fix the issues logically raised about conservation of momentum and energy, sometimes using weird wording for scientists, that does not help. The problem is, and I tend to agree with that, no net force should be possible if only Maxwell's equations and special relativity are the basis of the theoretical explanation. Chinese's maths also involve classical electromagnetism and thus have the same problem. When they show the energy and the momentum are separately conserved and correspond to Newton's second law, for example in the equation (8) of their fourth paper, a non-zero average thrust is not compatible with their explanation:

${\frac {\partial }{\partial t}}\int _{V}(\mathbf {g} _{f})\mathrm {d} V=\oint _{S}\mathbf {n} \cdot \mathbf {T} \mathrm {d} S$

In this equation they correctly identify the thrust with the right-hand side of the equation, but the time average of the left hand side is zero, since $\mathbf {g} _{f}$ is a periodic function of time. But should the actual theory be incomplete, does not mean the EmDrive must be thrown out with the bathwater. That's why physicists like Fernando Minotti addressed those issue with clean equations. He thinks for example that when the Chinese numerically evaluated the right-hand side of the equation above, the precise cancellations that should occur in an exact treatment did not happen, and a spurious residue of the order of magnitude of the measured forces may have appeared, giving a wrong idea of a classical explanation. He proposed a better way to handle the momentum and energy conservation, to be verified. That what is needed: more theoretical work providing verifiable predictions in lab, which will show falsifiability of the theories. A very interesting behavior predicted by Minotti is thrust reversal at some resonant frequencies (thrust vector in the direction from the big end toward the small end plate). Tokamac (talk) 09:49, 26 July 2014 (UTC)

I hesitate to be critical of Tokamac and Derek because you're doing your best to answer my concerns, and I realize it isn't your job to defend this technology. However, it seems to me that none of us is able to understand Shawyer's analysis fully enough to explain it to another person. The best one can do is to repeat his equations and terminology, so that other readers can also fail to follow the logic. I'm not convinced that is preferable to just providing a link to Shawyer's paper.

Regarding the conservation of momentum: the nice thing about this law is that it lets you skip all the intervening analysis and ask "did the momentum change?". I don't need to understand all the thrust formulas. If the entire system changes momentum, then momentum was not conserved. If there's some question about the momentum of the electromagnetic radiation inside the cavity, fine; wait until the EmDrive has been shut off and ask the equivalent question: If the center of mass has changed, i.e. the system moved to a new location, then momentum was not conserved. Spiel496 (talk) 18:16, 26 July 2014 (UTC)

We can say the same thing of Woodward's Mach Effect Thruster and Alcubierre's warp drive. They both violate conservation of momentum if you look at them without taking the physics involved into account. But if so they don't violate general relativity. Woodward effect relies on plain GR including Sciama's work over Mach's Principle, with momentum exchange between the local mass and the chiefly distant matter in the universe through a Wheeler–Feynman type field. Alcubierre drive relies on warp drive physics, which is standard GR with a negative energy source and thus is a reactionless drive as first noted by Lobo and Visser in 2004. The work of Lobo and Visser is the third most important work in warp drive physics after the works of Miguel Alcubierre in 1994 and José Natário in 2002. For resonant EM cavities, the scalar-tensor theory of Mbelek and Lachièze-Rey (of the Brans-Dicke type), cited by Minotti, behaves also as standard GR with a negative energy source. There is no violation of conservation of momentum in those works (theoretically speaking; if they are physically at work is another story).

But I agree with you that if Shawyer is wrong and say, Minotti is right, that Shawyer's theoretical explanations take currently too much place in the article. Tokamac (talk) 21:42, 26 July 2014 (UTC)

Spiel, I take no position on whether Shawyer's analysis is right or wrong. As you say, none of us is able to understand Shawyer's analysis fully because of our lack of expertise in the area. However, we all know that the system as a whole must obey conservation of energy and momentum at all times. The difficulty for me lies in identifying what the system actually comprises. If we could do that we could then sum up the component momenta to see what is really going on. Unfortunately I do not believe that even Shawyer himself understands what the full system is and what is going on with momentum at the most detailed level. So all we can do is describe his analysis fairly and to the best of our understanding and point out the problems with it. We have to leave it to our readers to realise just how speculative this is. I hope that our current article describes the controversy well enough to do that. -- Derek Ross | Talk 22:22, 26 July 2014 (UTC)

NASA testing

According to some recent news, it appears that a NASA test of a US-built prototype of this device seem to show that it actually does work. The original NASA publication is here, though I'm not sure how to integrate this into the article. Would someone be able to assist? Grandmartin11 (talk) 21:43, 31 July 2014 (UTC)

I was already working on it! Alanf777 (talk) 22:12, 31 July 2014 (UTC)

I can only get to the first page of the NASA paper. They say they tested the Cannae version (as reported by Wired) -- 40 micronewton at 28W , but ALSO a "tapered" version, which is an emDrive -- 91 micronewton at 17W. The latter wasn't reported by Wired. Maybe we should wait until the story's picked up elsewhere. Alanf777 (talk) 22:51, 31 July 2014 (UTC)

Interesting. If this is so then it appears that, like Wikipedia, the EmDrive may be one of these things which work in practice but not in theory! -- Derek Ross | Talk 04:58, 1 August 2014 (UTC)

Just because it's NASA doesn't mean it's true. The signal is small, much smaller than Shawyer's, and a signal that remains at the edge of practical measurement is usually not there in reality. We also don't know how many other groups have tried to replicate this and failed, and not published.

The NASA paper is a primary source. Wikipedia works on secondary sources wherever possible for this reason.GliderMaven (talk) 14:02, 1 August 2014 (UTC)

That's why I included ONLY what Wired UK said, pending further coverage. Alanf777 (talk) 15:15, 1 August 2014 (UTC)

Reading the NASA article I notice "Thrust was observed on both test articles, even though one of the test articles was designed with the expectation that it would not produce thrust. Specifically, one test article contained internal physical modifications that were designed to produce thrust, while the other did not". See http://ntrs.nasa.gov/search.jsp?R=20140006052

In other words it seems the EmDrive does not generate more thrust then a "fake drive". As far as I can tell news sources are just misquoting NASA.

Folket (talk) 14:03, 1 August 2014 (UTC)

Apparently this is for the Cannae drive test articles, not the EmDrive. According to the full paper (and here I quote the talk-polywell forum):

"This bothered me enough when I found it a few days ago that I bought their paper on AIAA; and it turns out that the abstract on ntrs.nasa.gov is misleading. The quote you are referencing from the ntrs.nasa.gov abstract is referring to two devices that cannae provided to EagleWorks for their test campaign. One had a set of slots in it and according to Cannae's proposed theory would produce thrust and according to the Eagleworks paper did. While the other device didnt, this is the "null" test article. this null test article was what Cannae though should be a null test article not what EagleWorks thought was a null test article. So in addition Eagleworks included a 50 ohm resistive load to verify no significant systemic effects. So basically the eagleworks testing invalidated what Cannae thought is the reason for the thrust."

Tokamac (talk) 14:50, 1 August 2014 (UTC)

3kN is not equivalent to 3 tonnes (assuming Earth)

"would allow static specific thrust of about 3 kN/kW, that is 3 tonnes of thrust per kilowatt of input power"