Talk:EmDrive

From Wikipedia, the free encyclopedia

Physics Portal

This article is within the scope of WikiProject Physics, which collaborates on articles related to physics.

???

This article has not yet received a rating on the assessment scale. [FAQ]

???

This article has not yet received an importance rating within physics.

Help with this template

Please rate this article, and then leave comments here to explain the ratings and/or to identify the strengths and weaknesses of the article.

This is the talk page for discussing improvements to the EmDrive article. This is not a forum for general discussion about the article's subject.
Please sign and date your posts by typing four tildes (`~~~~`). Put new text under old text. Click here to start a new topic. New to Wikipedia? Welcome! Ask questions, get answers.	Be polite Assume good faith No personal attacks Be welcoming	Article policies No original research Neutral point of view Verifiability

This is a controversial topic, which may be under dispute.
Please read this talk page and discuss substantial changes here before making them.
Make sure you supply full citations when adding information to highly controversial articles.

This article was nominated for deletion on 13/9/2006. The result of the discussion was no consensus.

[edit] Cut the Gordian_Knot

Time to break several rules, WP:IAR like hijacking the start of the discussion, and putting our original research into the article. Is there a consensus to put in the main article that Sahwyer's theory has a clear and simple error where it claims the side wall forces add up to zero, thus violating the conservation of momentum? Our citation is physics reasoning, as embodied in the concensus of this discussion. Vote below for physics consensus or continuing cowardice

In my opinion, the clearest explanation for his theory being rubbish, relativity or not, is the presentation of John Costella, link at bottom, who consisders the total momentum of the box + single photon - they always add up to a constant, regardles of how many collisions on whatever walls. Unfortunately I have a problem with citing his paper in the main article, which is that he is stirring the pot on the JFK assisaination, which is a bit of a credibility liability whichever side he is on. This however does not diminish the accuracy of what he says.

Physics concensus NeilUK 11:22, 5 October 2006 (UTC)

[edit] Initial comments

(Note: refactored for readibility by CH 01:37, 22 September 2006 (UTC))

(The article states:)

"The New Scientist article also mentions that as the EMDrive begins to move, the microwave energy resonating in the chamber is drained very quickly - quicker than it can be replenished. This implies that the system is suitable for producing a static force, but not acceleration. This means the EMDrive, if developed further, could be suitable for hovering vehicles and objects, but not for flying around as people would like to imagine. Think of it as a frictionless replacement for wheels. With this consideration, the EMDrive no more violates conservation of momentum and energy than, say, a magnetically levitating train."

Where does the energy go to, then? As I saw the device it didn't violate conservation of energy - energy would drain from the cavity as the device accelerated, but that was just conversion of stored energy into kinetic energy. If the loss of energy is that rapid, then the device would be limited in the acceleration it could produce, sure, but it would still be a reactionless engine, not just a frictionless replacement for wheels; a hovering vehicle is still violating conservation of momentum if it's hovering without throwing out reaction mass, since it's managing to magic away the momentum it should be gaining due to gravity. The maglev train is pushing down on the rails, via the magnetic field; an EmDrive vehicle isn't pushing down on anything.

---212.18.243.162 (talk • contribs) 15:44, 10 September 2006 (the relief.warhead.org.uk anon geoloc near London)

(You stated:)

"it's managing to magic away the momentum it should be gaining due to gravity. The maglev train is pushing down on the rails, via the magnetic field; an EmDrive vehicle isn't pushing down on anything."

I'm not sure what you mean by the momentum it should be gaining due to gravity. Would that apply to me as I stand on the ground? If not, then I see no reason why it should apply any more to a stationary object hovering above the ground. Things don't gain imaginary momentum just because you think they ought to be falling. If the object is stationary - neither falling nor rising - then there is no momentum to account for. The stationary object has no momentum. The upwards force equals the downward force, hence no net force and no acceleration, and no gain or loss of momentum.

I appreciate the point about the system being a reactionless engine, and that is something I am not sure about. All that I have read about this thing, all the experiments that have been carried out, show a real, but static force. Whether it could ever form a real propulsion engine or not, is beyond me. We will have to wait and see what further independent reviews say.

---{user|82.39.204.250}} 17:20, 10 September 2006

Regarding you standing on the ground - if you were a metre above the ground to start with, you would gain downwards momentum, and the planet would gain upwards momentum (just that'd be a drop in the ocean of the planet's vast momentum). When you are standing on the ground, the repulsive force between the material of your feet and the material of the ground prevents this, so the net force on you and the planet is zero. Now, when the supposed EmDrive car is hovering, the EmDrive would be generating a force approximately equal to the force of gravity on the car, keeping it still - but the planet would still be attracted to the car, and as such would start moving upwards (infinitesimally). So the system as a whole violates conservation of momentum. Alaric 11:50, 12 September 2006 (UTC)

I agree. Although the theory looks bogus, there does seem to be some compelling emperical evidence that it might just work. Ever the open-minded optimist, despite the fact that I diss the theory, I hope it turns out that our understanding of mass and intertia is wrong, and this thing turns out to work :-) Alaric 11:50, 12 September 2006 (UTC)

No violation of conservation of energy. If in the hover, so no speed, then I guess there's no violation of memonetum conservation either. But Newton said all forces have equal and opposite reaction, and that 'conservation of opposite forces' is pretty deeply ingrained in our world view. But, Newton was wrong on relativistic dynamics, what exactly does relativity have to say about the distribution of the photon pressure in the cavity on any reactions there should be? Something has got to give the photons the momentum to hit the big end again and again, and that something is surely the reaction on the small wall *and the sloped sides of the cavity* so no net force, or does it? A moving cavity losing energy begs the question - moving relative to what? Do we have to recreate the Aether as a reference frame? NeilUK 22:31, 12 September 2006 (UTC)

The same point made slightly differently. Relativity requires the equivalence of all intertial frames of reference. If a force moves through a distance, it does work. The normal requirement that all forces have an equal and oppoiste reaction guarrantees that the work done in one frame of reference is the same as other frames, as both opposite forces move and do exactly cancelling amounts of work. However a reactionless force will do different amounts of work in different inertial frames, violating their equivalance. Or have I got this wrong? NeilUK 09:30, 13 September 2006 (UTC)

To put it yet a slightly different way. Relativity is self consistent, and is consistent with the conservation of Energy and Momentum. For a theory based on these to produce a prediction which violates them, means that the mathematical derivations *must* contain an error somewhere, the consistent theories are not capable of producing a violating result, if used consistently.NeilUK 20:45, 14 September 2006 (UTC)

[edit] Merge discussion

I think the merge with Emdrive should go ahead. The articles are on the same topic, beyond a shadow of a doubt, and differ only in case. I picked the case used on the official site [www.emdrive.com] to base my article title on, so I presume that is the 'correct' one. The Emdrive article has useful extra information that this one lacks, which would be well incorporated here. Alaric 11:54, 12 September 2006 (UTC)

Obviously merge, the only difference between the articles is the case of the 'd' NeilUK 22:31, 12 September 2006 (UTC)

Again, obviously merge. I suggest using EmDrive as that appears to be the most common formatting. –Gunslinger47 15:57, 13 September 2006 (UTC)

If this is to be kept, this one is obviously the better version. Suggest to do the redirect right now. --Pjacobi 16:35, 13 September 2006 (UTC)

For the record, this has been done. ---CH 02:20, 22 September 2006 (UTC)

[edit] Worst case

Ah well, assuming the worst case, that the AfD will fail, we should start cleaning up the articles. I've just removed the redundancies.

Giving that Roger Shawyer claims to have disproved momentum conservation, a pillar of physics, it's astonishing (or rather not) that no discussion of this extraordinary result can be found in physics journals, not even on the preprint servers. So, please don't report any of this as fact.

While checking the external links for redundancies, I've removed one completely (for total cluelessness):

Tom Shelley. "A force for space with no reaction", EUREKA, 2002-12-12.

BTW: If you still need a disproving argument for party talk: On a microscopical level, the drive consists photons and electrons (and the background electric field of the nuclei), and each interaction between microwave interaction and the wall can be seen as a sum of single eγ->eγ scattering events, just likes the ones occuring since 13 billions years everywhere. And all these scatterings obey the law momentum conversation, whether calucated by QED or classically, up to every velocity you would like.

Pjacobi 17:39, 15 September 2006 (UTC)

I could care less if its true science or not. But if a 250,000 pound grant was really given to the guy, that's the only reference to it. At a glance at the website, Eureka doesn't look to be a sensationalist tabloid... with that as a reference, the claim for notability is a bit higher. I don't see why you guys are so insistant on there not being an article for this. Worst case indeed. I honestly don't know if it's possible or not, not being a physisist... but I definitely want to be told the facts on the issue! If it is junk, then tell me that in an NPOV way. I want to know! Don't be silent... Fieari 05:33, 17 September 2006 (UTC)

Eureka may be used as source for the grant issue until proven to lie, but it was given as "further reading", which was a disservice to our readers. Everyone stating However while photons obey Newton's Laws in some respects, the idea of the solar sail being a typical example, in other respects, light and objects travelling at or near light speed do not obey them. should be excluded from a further reading list. --Pjacobi 18:04, 17 September 2006 (UTC)

[edit] Moved from Talk:emdrive

The following was moved by Uncle G (talk • contribs) 01:33, 14 September 2006. (Note added by CH 01:19, 22 September 2006 (UTC))

[edit] Information from Shawyer

I e-mailed Mr Shawyer for the mathematics behind it, and he obliged, and mailed the document to me. I suggest you do likewise, and request it for linking to this page.

--- 82.152.54.203 (talk • contribs) 08:34, 7 September 2006 (the Derby anon; unregistered IP address geolocated near Derby, England)

I imagine that, following the publication of the New Scientist article on the subject, Mr. Shawyer will be inundated with such requests. However, if it would be possible for someone (possibly you, since you already have the document) to post a link to such information, it would, of course, be very helpful. Robin S 19:52, 11 September 2006 (UTC)

[edit] disputed tag

This thing is ridiculous. Conservation of momentum requires that the momentum has to come from somewhere. Even if you can get a box of microwave photons to push asymmetrically on a container, that just imparts equal and opposite momentum to the microwaves - which, being contained, aren't going anywhere. You may as well blow on the inner hull of your ship. ---71.227.147.249 (talk • contribs) 22:25, 8 September 2006 (the or.comcast.net anon)

Whatever is done with articles about hoaxes should be done to this article.

On the other hand, New Scientist is not known for lying, and they say the prototypes are real and do work. ANTIcarrot 12:37, 9 September 2006 (UTC)

That's an argument from authority. They have been fooled, which is sad. I can think of all sorts of ways to make a box weigh slightly more in one orientation than another - the simplest would be to conceal a tube in the power cord that fills and drains a small container of water. And "stationary relative to their thrust" is an equivalence principle violation. I mean, come on.---71.227.147.249 (talk • contribs) 18:15, 9 September 2006

And saying they have been fooled and not signing your name is an agruement from anonimity, or possibly from the peanut gallery. It is possible of course that a mistake has been made, which would indeed be most sad, but that assumption does not automatically become true just because people say it is so, or because people do not understand how it works.ANTIcarrot 22:16, 10 September 2006 (UTC)

A lot of the criticisms which have been levelled at the veracity of this concept are by people who are speaking from intuition, or from the simplified physics they learned at school, making them appeals to ridicule and hence invalid. Similarly, a lot of the claims that the phenomenon is in fact genuine rest on arguments from authority. If you are going to make a claim about whether or not this thing is real, please give actual evidence. A link to a page supporting or denying the claims using rigorous physics and / or mathematics would be useful, if someone could find one. Robin S 18:26, 11 September 2006 (UTC)

Unfortunately I'm not sure scientific proof is relevent or helpful. If he has built a machine and the machine works, then the actual and truthful reason it works is largely irrelevent. We couldn't entirely explain why lightbulbs worked for a rather long time, but that doesn't mean they didn't. As a item of engineering, all you can supply is arguements from authority - that is independent evaluation and testimony that the machine apears to work as advertised and no experimental tampering has been found. ANTIcarrot 00:03, 12 September 2006 (UTC)

Actually, New Scientist is known for telling tale tales. At least in the physics community. Decades ago, it was a much better magazine. ---CH 01:16, 22 September 2006 (UTC)

"Whatever is done with articles about hoaxes should be done to this article."

I couldn't agree more. {{hoax}} added to article. The article needs to be edited to document a hoax, rather than perpetrate it. --Kjoonlee 07:42, 23 September 2006 (UTC)

"On the other hand, New Scientist is not known for lying, [...]"

I ~~couldn't disagree less.~~ very strongly disagree. Have a look at Subliminal message where they reported on a flawed experiment on subliminal messages, and yet titled the report "Subliminal messages may work after all". --Kjoonlee 07:45, 23 September 2006 (UTC)

[edit] criticism

Since there's doubts by scientists, perhaps it would be best to have a paragraph outlining the criticisms, and why they believe it won't work. --T@nn 06:13, 10 September 2006 (UTC)

[edit] The Obvious Criticism

It must have already occured to Shawyer and the few knowledgable people that have read the idea so far, that I hope it has already been refuted.

Radiation pressure is OK. Designing one end of the cavity to be greater area than the other to get more force on that end assumes constant pressure, and quietly ignoring the walls. However the sides of the cavity are sloping, and the effective area 'pointing rearwards' is exactly the same as the larger end. If the internal pressure is constant, and the pressure acts normally to all surfaces, then the net force in any direction is constant.

If the cavity is small with respect to the wavelength of the radiation, then the 'constant pressure on all walls' assumption breaks down, and the thing has to be solved like a waveguide. Equal pressure on the two ends, and lower pressure on the walls, would appear to give a net thrust.

As far as I can see, it does not break energy conservation laws, a thrust with no movement (a hover) does not require any energy input, so we are not in free energy territory. However it is not obvious whether momentum conservation is violated, and if not, where the balancing force operates.

---NeilUK (talk • contribs) 00:36, 12 September 2006

I mean clearly a reactionless drive violates conservation of momentum. Even if it simply hovers the Earth is being pulled towards the hovering vehicle by gravity, and there's absolutely no claim that any external force is involved to push the Earth away again, so momentum is being created from nothing. And violation of momentum implies lack of conservation of angular momentum.WolfKeeper 14:37, 13 September 2006 (UTC)

Slightly less clearly, the device must break conservation of energy. The engineer claims it works in zero gravity and can be used to raise the orbit. Suppose you start off with the device off, switch it on and accelerate, and then switch it off. From the inertial frame the device started in, for a given energy input it must have gained speed. Now do it again, and the device must have gained two delta's of speed (from galilean relativity), but the energy has increased by a factor of 4 relative to the original reference frame. That's impossible, energy conservation (including any heat energy waste) is inevitably violated since you've put in two units (in the general case N units) and ended up with four units (in the general case N^2 units). In fact it's possible to show that you can build a perpetual motion machine.WolfKeeper 14:37, 13 September 2006 (UTC)

These two things, the question of uniform internal pressure and the question of momentum conservation, are simple enough for most intelligent lay-persons to understand. It would be nice to see them directly addressed. Perhaps somebody on wiki with access to Shawyer's work could interpret what he says about these two specfic issues?NeilUK 07:36, 12 September 2006 (UTC)

I don't know that they are simple for the laymen to understand. The momentum of a photon is rather different from the momentum of a massy particle. Remember that photons never slow down. You can change the directional component of a photon's velocity but not the speed component. So when you reduce their momentum, you are actually reducing their mass (or frequency depending on how you look at it), not their speed. Thus if you think about it you are bouncing particles off one end of the tube and then those same particles (but lighter) off the other end. Suddenly it doesn't seem so surprising that there might be a net force in one direction. You are also converting the mass energy of the photons into kinetic energy of the device. There's no reason for conservation of energy to be violated since kinetic energy gained by the device should equal energy lost by the photons as their frequency decays within the tube. Using the device to hover will require a constant energy input since it is equivalent to accelerating the device in freefall at 1g. -- Derek Ross | Talk 07:15, 19 September 2006 (UTC)

It is easier to think of the system as a whole than to worry about the details of photons, some of which you have got wrong—for example, they have energy proportional to their momentum, but no mass. The bottom line is that the photons are created in the device, it somehow imparts their momentum; if all of them are reabsorbed somehow, then all net momentum returns to the device and it provides no acceleration. If they are emitted, then the device gains momentum equal and opposite to the emitted photons—you can shine a flashlight and try to feel the recoil if you want to know how well that works.

In principle, it is possible to suspend an object above the earth without expending energy. This can be done with magnetic fields for example. -- SCZenz 07:25, 19 September 2006 (UTC)

I'm well aware that photons have no rest mass. However the energy associated with their momentum does have mass (which can be calculated by m=E/c²). As for your point about re-absorbed photons: of course that's true if the photons have all their original energy. Likewise your point about (once) emitted photons. However the effect would appear to be caused by unabsorbed, unemitted photons. So talking about absorbed or emitted photons seems rather irrelevant in this case. One point made in the article was that the less absorption or emission of photons by the tube, the stronger the effect should be. I take your point on magnetic fields though. It did occur to me after I'd posted it but you'd already replied by the time I came back to remove my statement. -- Derek Ross | Talk 07:50, 19 September 2006 (UTC)

Your logic about photon mass doesn't work. Treating $m 0$ as rest mass and m as relativistic mass; one has $E = m c 2 = γ m 0 c 2$ , which is rather ill-defined for a photon, since $\gamma = \frac{1}{\sqrt{1-v^2/c^2}} = \infty$ . I can't think of any usage of "mass" under which the photon mass is anything but zero (except for the virtual ones in Quantum electrodynamics, which is certainly not what we're talking about here). Edit: I take it back: you can define relativistic mass as you suggest; it's not how physicists commonly do it, though. What one actually uses is $E^2 = p^2c^2+m_0^2c^4$ which works for photons and everything else, without confusion.

Um... what do you mean by "the effect would appear to be caused by unabsorbed, unemitted photons"...? Where do you claim the photons are coming from if they're not emitted by the device? -- SCZenz 08:02, 19 September 2006 (UTC)

I think we both mean the same thing by unabsorbed photons which I take to be photons which are being continually reflected by the ends of the tube. I think that we meant something slightly different by "emitted". You meant photons were emitted by the microwave generating part of the device into the tube. I meant photons which were emitted from the device into the outside environment and thus no longer contributed to the effect. So my claim of origin of the photons is the same as yours.

However I still think that you are missing the point here which, I think, is that momentum may well be conserved here in a rather unusual way. In that the part of the device made up particles with a rest mass changes its momentum by holding its mass steady and increasing its velocity while the part made up of particles with no rest mass changes its momentum by reducing its (relativistic) mass and keeping its velocity steady (or perhaps increasing it on average at the same rate as the device as a whole). This is very different from the way that momentum is normally conserved but it is "within the rules" and is why this device might just work. -- Derek Ross | Talk 08:33, 19 September 2006 (UTC)

You are mistaken. --Pjacobi 08:39, 19 September 2006 (UTC)

I may be. Time will tell. I await its verdict with interest. -- Derek Ross | Talk 08:42, 19 September 2006 (UTC)

No, you misunderstand how conservation of momentum and energy works; I'm not sure what you mean in your statements above, but it doesn't matter because details only confuse the issue. This device cannot work within the known laws of physics, because the net effect is that the spaceship goes one way and nothing (or very little) goes the other way. That is a net violation of conservation of energy and conservation of momentum. -- SCZenz 14:48, 19 September 2006 (UTC)

I understand that if you add up the the momentum/energy of all particles involved in the experiment at the end of the experiment you must have arrive at the same total as you started with. If that's a misunderstanding then there are a lot of confused people about. -- Derek Ross | Talk 15:25, 19 September 2006 (UTC)

Ok, we're on the same page on what the laws of physics are, so I don't quite understand what goes wrong in the next logical step... If momentum is conserved, how can this device work? What is balancing the momentum of the spaceship? -- SCZenz 15:33, 19 September 2006 (UTC)

Well assuming for the moment that the device does work as claimed (and I agree that the jury is definitely still out on that one), the change in momentum of the spaceship has to be balanced by the change in momentum of the photons inside the tube. We are agreed that these do have momentum even if we can quibble about whether they have mass or not. As their momentum drops their velocity remains constant but their frequency drops and their wavelength increases until it is large enough for the (by now) low energy photons to tunnel their way out of the tube quantum-mechanically. However by the time that the photons are low energy enough to escape they have transferred a portion (exact amount depends on how many times they are reflected within the tube) of their momentum to the spaceship. If we sum the change in momentum of the photons between their creation as high momentum particles in the magnetron and their escape as low momentum particles from the spaceship it should balance the change in momentum of the spaceship. Looked at from an energetic viewpoint, there should also be a balance between increase in kinetic energy of the ship and loss of energy of the photons. -- Derek Ross | Talk 16:23, 19 September 2006 (UTC)

The "jury's still out" stuff is a red herring; I'm stating it can't work as claimed, even in principle, without violating energy/momentum conservation. A photon's initial momentum must come from the spaceship (it gets pushed backward when it's produced). Then some of that momentum is transferred back, and finally the photon escapes (or not). By conservation of momentum, the final photon momentum must equal the change in momentum of the ship. So no matter what the drive does, it can't be any better than just shining a flashlight without violating momentum conservation. -- SCZenz 16:34, 19 September 2006 (UTC)

See the v9.3 pdf linked at literature, figure 2.4. He draws the sidewall force pure radially, neglecting its axial component. Duh! The elephant is in the room. Would pointing this out in the main article be rejected as being 'original research'? I don't think you need to do any research to read English and interpret the direction of the arrows he's drawn.NeilUK 21:42, 20 September 2006 (UTC)

[edit] Answering the momentum question

Most discussion here is asking the question as to what happens to momentum in this device.

Shawyer does not claim to have created a reactionless drive, nor broken the laws of momentum. The difference in momentum can be explained using quantum physics. It cannot be explained using Newtonian physics - such analogies as the 'two sailed boat' are flawed.

When a microwave photon strikes the surface at either end of the cavity, the interaction is similar to Compton scattering. The action is that energy from the photon is transfered to the surface upon which it struck. The reaction is that the reflected/scattered microwave photon has a reduced energy (and thus, reduced frequency) - the difference being the amount of energy transferred to the surface. This occurs at both ends of the cavity, but due to its shape the angle at which the photon strikes each end is different - this results in a larger transfer of energy to the wide end than the thin end.

Please consider that the New Scientist is a reputable magazine - any article that makes the front cover is sure to have been thought through very carefully indeed. This Wikipedia article does not deserve to be deleted, in fact it need to be developed so that the misconceptions that people have can be corrected.

--Lee.cook 00:04, 19 September 2006 (UTC)

It's unlikely to be deleted, and perhaps that's a reasonable decision (although I disagree). However, New Scientist did not say this isn't junk science, and it's not a peer-reviewed journal anyway. Our article reflects this. Now regarding momentum and energy, rather than getting bogged down in details, let's consider the entire system. The ship moves in one direction—what goes the other way? Where does the energy to change the kinetic energy of the ship come from? -- SCZenz 01:37, 19 September 2006 (UTC)

That's the claim, Lee.cook, but there's a whole lot of other claims that say that's just complete bunk. The only real way the thing can work, despite what is not being claimed by Shawyer (because if he claimed it, he'd be completely ignored instead of just largely ignored), is if it breaks some fundamental laws of physics. Since we all know that that is impossible, we all know the thing doesn't work. I would bet my house on it, and I rather like not being out in the cold and rain. _└ ^OzLawyer / _talk ^┐ 01:40, 19 September 2006 (UTC)

Lee.cook, unfortunately you are completely clueless. Momentum conversation also applies in quantum theory. Also, energy is not te same as momentum. --Pjacobi 06:34, 19 September 2006 (UTC)

Ditto PJacobi. One of the keepers made the same telling mistake in the AfD.---CH 01:41, 22 September 2006 (UTC)

[edit] Off topic cite removed

I've removed this cite from the article:

Satori, Shin; Okamoto, Hiroyuki; Sugiki, Ted Mitsuteru; Aoki, Yoshinori; Nagata, Atsushi; Kizaki, Takayoshi (2001). "Development of low power electric propulsion aiming for small satellite applications". AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, 37th, Salt Lake City, UT; UNITED STATES; 8-11 July 2001.

Another paper from this group is here.

It has nothing to do with a reactionless drive and is in full compliance with the law of physics.

Pjacobi 06:40, 19 September 2006 (UTC)

[edit] Factual Accuracy tag

Is there still a factual dispute (do you dispute that the people named have made the claims stated)... or is it just a dispute as to whether the device could work as advertised? Fieari 18:35, 20 September 2006 (UTC)

I'm not confident the article is 100% accurate. I've plugged holes in some spots, but the analysis section in particular doesn't seem to have been carefully edited and may contain inaccuracies. -- SCZenz 21:46, 20 September 2006 (UTC)

There was a good point about the lack of error bars on an incredibly small measurement. Couldn't find any mention in the article, but might've overlooked it. — Laura Scudder ☎ 22:17, 20 September 2006 (UTC)

It seems pretty clear that Shawyer didn't even realize that (as both he and the author of the article should have knonw) his claims appear to suffer from a fatal flaw: this device would appear to violate conservation of momentum. As someone pointed out above, since special relativity does not violate conservation of momentum, Shawyer's claim that his device is based upon some relativistic effect is absurd. It seems that the answer to Fieari's question is: either the device doesn't work the way Shawyer thinks it does (in which case something must be emitted to push in the satellite; if not matter, as in conventional rocket fuel thrusters or ion drives, then something else), or else it cannot work. Since he claims to measure a tiny net force well under likely sources of error, and since his grasp of physics is clearly shaky, the second explanation seems far more likely. (A third alternative, that the laws of physics as we know them are fundamentally incorrect, seems too unlikely to merit discussion at this time.) HTH---CH 01:47, 22 September 2006 (UTC)

Is the measurement really so tiny ? Two grams is about the weight of half a teaspoon of water. While that might be impossible to measure accurately with kitchen scales, I would have thought that it was well within the precision of a good analytical balance. In fact the experimental report in his paper states that he repeated the measurement with multiple balances one of which was a 16kg balance with a resolution of 100mg. That certainly sounds as if it should be both precise and accurate enough to do the job. Still as Laura says, he should have given some sort of error bars. -- Derek Ross | Talk 17:55, 24 September 2006 (UTC)

[edit] Theory

Wow! The theory paper is even weaker than imagined. Pearls of wisdom, so to say: Relativity theory implies that the electromagnetic wave and the waveguide assembly form an open system. Thus the force difference results in a thrust which acts on the waveguide assembly. --Pjacobi 07:08, 21 September 2006 (UTC)

I am not suprised that the very first thing I saw when I downloaded this paper was that, as I guesed, Shawyer is an engineer by training, not a physicist.

As we would expect from Kroger and Dunning, in my experience cranks tend to misunderstand what I just said, so let me try to fend off possible confusion. I have worked with engineers and I also have encountered many physics cranks over the past fifteen years or so. Consider these two statements, both of which hold true according to my experience:

Most engineers are perfectly sane and stick to their field of interest/competence, engineering, or if they should venture into physics, do so with all due caution and respect for the superior background knowledge of trained physicists.
By far the most likely occupation or formal training of a physics crank is engineer.

I have speculated that the reason for the second fact (I can't cite a statistical study without vio of WP:NOR, but I am confident that this is indeed a fact; even casual observation should support this) might be that engineers recieve some physics training in re electromagnetism, thermodynamics, mechanical stress and so forth, but they are trained in engineering applications of physics, not the scientific method! In particular, undergraduate engineering majors are not often trained in mathematical subjects which are needed for relativity (and useful in physics generally) such as perturbations, asymptotic expansions, topology, or manifolds, nor are they trained in experimental methadologies. As a result, I think a tiny minority of engineers who have certain personality traits associated with crankery tend to vastly overestimate their degree of physics expertise, and to vastly understimate the subtleties of subjects not covered in their training as an engineer.---CH 02:05, 22 September 2006 (UTC)

Wow is right, I cannot believe this is even discussed here! Come on people, just look at equation 1: this is applicable to particles, not to waves! Variable v cannot be replaced with the group velocity! Wikipedia will lose some of its credidibility if the article stays in this state too long... :-/

[edit] Rockets

This line from the article bothers me...

It is not possible for a spacecraft to be propelled in one direction without some matter being propelled in the other.

The reason being that it isn't actually true. If it were it would be impossible for a rocket to travel faster than the velocity of its exhaust gas. But rockets can and do. And when a rocket is travelling faster than its exhaust gas velocity, both it and its exhaust gases are travelling in the same direction, albeit the exhaust gases are travelling towards the destination more slowly than the rocket is. The rocket example shows that it is "possible for a spacecraft to be propelled in one direction without some matter being propelled in the other". Hence my concern. I think we should remove this misleading claim and I wanted to explain why first. -- Derek Ross | Talk 06:58, 23 September 2006 (UTC)

Your explanation for why it is wrong suffers a fatal flaw due to relativity. Consider a rocket accelerating. In the frame of reference of the rocket, some form of momentum-carrying stuff, be it chemical propellant exhaust, electrically accelerated ions, or even photons, is thrown out of the back. In the rocket reference frame, the gain of rocket momentum is equal to this reaction momentum. Now make the move to some other frame, like the planet that launched the rocket, and the rocket and its present exahust are all moving forwards (in order to launch from the planet, the exhaust emitted when on the planet's surface is actually travelling backwards).

In the rocket reference frame, the rocket will have no velocity and hence zero momentum. I think the momentum of the gasses must go to moving the rest of the universe, generating the acceleration felt by the rocket.

However, the line above should be re-written to say It is not possible ... in the other, without violating the law of conservation of momentum. Because who knows, although momentum convservation has never been observed to have been violated in every quality experiement done since the dawn of time, replicated across the globe by diligent scientists looking hard for some tiny error, maybe this guy's done it with a big dumb microwave ;-) It depends what is being claimed, is he claiming momentum conservation is invalid, or that he can get reactionless thrust without violating conservation? NeilUK 07:43, 23 September 2006 (UTC)

I'm fully aware that you can pick the frame of reference to look at it the way you say. But that's hardly a flaw. In fact it's rather the point. Depending on which frame of reference you pick the statement may be considered true or false. That's why I said that the statement was misleading rather than saying that it was out-and-out false. I don't see any disagreement between us on the way rockets or frames of reference work here. And that still leaves the objectionable statement as a half truth at best.

Moving on to your second point, it looks like he's claiming that he can get reactionless thrust without violating conservation (according to what I understood from reading his paper anyway). He attempts to show that the force produced falls off with increasing velocity (and in fact reverses in direction above 0.7c) and concludes that conservation of energy holds for the device. I can't comment on whether he's used the correct formula or got his sums right and I haven't seen anything on conservation of momentum but, going by his paper, he certainly wants to demonstrate that it isn't breaking any conservation laws (even if that can't actually be done).

I must admit that my own problem with the device comes down to two things: what PJacobi said about it all being electrons interacting with photons when you come down to it and a failure to understand why the forces on the internal surfaces of the device might not add up to zero as we would expect them to. -- Derek Ross | Talk 08:34, 23 September 2006 (UTC)

[edit] Perpetual Motion

The article states:

Furthermore, it is not clear how a superconducting chamber would improve matters because a lossless cavity would not only violate conservation of momentum, but also conservation of energy. Thus, this design constitutes a perpetual motion machine as well.

This is under the heading of the New Scientist article, near the "Engineers in Germany" bullet. However, I don't see any mention of perpetual motion in the New Scientist article. Does this come from another source? If so it should be attributed. (I also don't think that this machine -- even if it worked as advertised -- would be a perpetual motion machine, since the magnatron would still need to be powered by an external source.)

Davburns 20:54, 23 September 2006 (UTC)

That is because neither Shawyer nor New Scientist claim that it is a perpetual machine. This is purely the opinion of one of our editors and should be removed as unverified material. -- Derek Ross | Talk 22:12, 23 September 2006 (UTC)

This will not be a perpetual motion machine, because heat dissipated will be proportional to energy consumed in performing work. Also, for there to be thrust, I would expect heat dissipation to be directional. How does this differ from photon pressure? -- 74.98.142.235 00:56, 24 September 2006 (UTC)

[edit] Realistic Comments

New Scientist Issue Vol191, No 2568, Page 30, Fly by light (Reality Drive)

This article really caught my attention. I hope the emdrive works. We would live through a time similar to the pioneering time of the turbojet. But I can see some problems.

Roger Shawyer suggests that "there is the issue of acceleration" and believes that the emdrive will be most suited to the hover.

There is a problem with this that can be seen by applying Einstein's principle of equivalence. An emdrive stationary in a gravitational field is equivalent to an emdrive accelerating in empty space. It is in a non inertial frame of reference.

So the emdrive in hover will be as much of a problem as an emdrive accelerating at one G in empty space. (Also a good approximation to an emdrive accelerating in the horizontal plane on Earth at one G.) If the emdrive does work as hoped and there is an acceleration problem then perhaps the drive could be used to provide horizontal thrust that matches the vehicle drag and results in a cruise at constant velocity (keeping the wings I'm afraid.)

A quick calculation of the extra power consumed by the cavity doing work would be the vehicle velocity multiplied by the vehicle drag.

Another problem that is perhaps more fundamental is the idea that a shaped cavity could produce an asymmetric force. After initially accepting this at face value I started to think of a simple conical shaped cavity with different angles to the axis of the cavity.

Draw a conical cavity on paper with angles of 45 degrees, 30 degrees or any whole fraction of 90 degrees, then trace paths of photons initially parallel to the cavity axis and look at the forces at the cavity walls during the glancing reflections.

Resolving along the cavity axis reveals that the sum of the forces towards the thin end is the same as towards the fat end. Admittedly this is a gross oversimplification of the cavity behavior but I think it demonstrates that the reduction in the effective velocity of the radiation in the thin end is matched by an increase in radiation pressure as the effective velocity reduces.

I really hope that somehow an emdrive does work. We need propulsion devices that convert almost all of their energy into gravitational potential energy and if they don't have to carry their own fuel then even better.

One final question for Roger is how does the emdrive reconcile the conservation of momentum? This wasn't clear from the article.

I also wonder whether if you try to accelerate any high energy cavity it will produce a resistive force due to the Doppler shift in the radiation, giving the highly efficient cavity increased inertia and increasing it's effective mass, making it harder to accelerate.

Douglastribe 01:58, 24 September 2006 (UTC)

[edit] Excellent Article

I was very impressed w/ the article. This was my take on it before reading it just based on looking at a few diagrams. "You've all seen the cartoons of the electric fan blowing in the sail of the sailboat. It really doesn't work- the boat would stand still. To see that, imagine an airboat with the fan pointed backwards, the boat would travel forward. Point the fan forward, then the boat would travel in reverse. Put a sail in front of it, then the boat would stand still. It would be the same situation as if the fan was blowing in a sealed enclosure in the boat. In that case the boat would go nowhere.

Now the Shawyer drive is working courtesy of the principle of the the momentum of photons. I remember how surprised I was when I learned that light can impart momentum. Everybody has heard by now of light sails. the principle is of a light sail. Instead of a fan, you have a microwave generator. The odd-shaped cavity takes place of the sail. I'm having a hard time seeing how it would work. Doesn't it amount to a ship shining a flashlight on its own light sail? Why not just aim the flashlight straight out the back? very little momentum gained would be the answer.

But I"m sure he's tested a small prototype in the lab and meaured thrust, or has he? There's a pix of the experimental apparatus at [1]. Best Wishes Will314159 04:19, 24 September 2006 (UTC)

It turns out his prototype doesn't do much yet, which he blames on low-quality cavities but others think might be him misestimating uncertainties. Conservation of momentum applies with photons as much as with a fan in a sailboat, so your analysis in the second paragraph is entirely correct, and there's every reason to believe the device will never work as Shawyer hopes. -- SCZenz 06:56, 24 September 2006 (UTC)

[edit] New Scientist reaction

Article should mention what response New Scientist has had to the criticism, or should mention it hasn't responded in any way if that's the case. Tempshill 14:53, 24 September 2006 (UTC)

[edit] Neutral Point of View

Woah. What's up with this article? This reads like a blog entry rather than an article in an encylopedia. What happened to Neutral Point of View and No Original Research? Quoting from the later, "Moreover, articles may not contain any new analysis or synthesis of published arguments, concepts, data, ideas, or statements that serves to advance a position."

I'm not a regular here but I think this page should probably talk about what an 'emdrive' is. What is it? A theoretical propulsion device suggested by Roger Shawyer in the New Scientist. Shawyer claims it will work by x, y and z. He proposed it in w.

Then there can be a critism section describing who says it doesn't work and why they say that, the key being that it's not Wikipedia that claims it's not working, but other people. I don't think Wikipedia should be arguing anything - just documenting what other people have argued.

Siker 05:32, 25 September 2006 (UTC)

If we are required to make a specific citation that an object accelerating to a large velocity without using up stored energy somehow violates conservation of momentum, or that an object going in one direction without anything going the other way violates conservation of energy, then Wikipedia is fucked. Saying that something obviously violates the laws of physics (which it claims to obey) is not original research. -- SCZenz 23:02, 25 September 2006 (UTC)

I think it is OR; marginally so. So marginally that few other editors would call you on it. On the other hand, if you quote somebody else that says that, then you're in much better shape on policy. The policy is 'verifiability, not truth' after all; in general, it's much easier to verify that somebody said something than follow a (possibly long) argument that something is so.WolfKeeper 23:25, 25 September 2006 (UTC)

And if there is no source, because that analysis is so obvious that same physicists and engineers are ignoring EmDrive entirely? -- SCZenz 15:04, 30 September 2006 (UTC)

Verfiability, not truth. The wikipedia isn't supposed to have an agenda, like disprove the emdrive. It's supposed to report notable people's agendas [:-)], OK, opinions.WolfKeeper 22:54, 30 September 2006 (UTC)

When only one agenda has been published, a strict interpretation of the rules forces us to present obvious nonsense with the appearence of plausible truth. That is unacceptable, because it misinforms the public severely and contradicts the very purpose of the encyclopedia; if it requires an application of WP:IAR to avoid this, so be it. -- SCZenz 16:11, 4 October 2006 (UTC)

Don't get me wrong. I'm not a physicist but I do agree with the analysis that Newton's idea about forces and equal and opposite reactions has been tried and tested, and seems applicable in this case. However, it is none the less analysis, which NOR explicitly forbids. If the case is so obvious, then someone else must have said it, and it shouldn't be hard to find a good quote instead. Siker 17:56, 26 September 2006 (UTC)

I am a microwave engineer and this concept is bunk. Shawyer made a mistake in his calculations. He did not account for the force on the sloping walls which has a component towards the smaller end of the cavity. Sorry to see such a successful man eventually embarrassed but I am also sorry to see my government spend money on this. by H Perini

Unfortunately, I'm coming around to the opinion that it's fraud. It's difficult to see how anyone in Shawyer's position could fail to see the gaping holes in it.WolfKeeper 15:21, 29 September 2006 (UTC)

I know wiki requires no OR, but does that stand for Original Research, or Obvious Reasoning? The resultant force on the side walls from Shawyer's own diagram is so bloody obvious as to be beyond dispute, well, any unbiased dispute. Surely a council of the good and the great, or perhaps just a democratic vote, could include such reasoning in the main artcile. Perhaps we could break no OR for perhaps a 95% majority yes? Though I will admit that such a concession could be the thin end of a wedge for other articles. BTW, I'm glad to see the back of that "frames of reference two sails on a boat" paragraph, I wish I'd had the courage to kill it myselfNeilUK 19:29, 4 October 2006 (UTC)

[edit] A possible explanation

I heard about this from a student but couldn't find the New Scientist article. Having said that, though, it sounds like a reasonable explanation of the apparent experimental result (measured thrust) is that the tapered microwave cavity heats up more at one end than at the other. The fact that the microwave generator has to be kept running means that some of the microwave power is being absorbed by the cavity walls, and therefore heating them up. I would expect the narrow end to heat up more because more of the reflections of the microwaves happen down there; this would lead to a thrust in the direction of the wide end, as is apparently observed. In vacuum the thrust would come from the differential radiation pressure of the infrared radiation coming off the two ends. I assume that the experiments were done in normal atmosphere, though; in that case the differential pressure would come from heating the air on the warm end of the apparatus. Warmer air exerts more pressure when its molecules bounce off the microwave cavity; it's just like the radiometer toy. Once the thing starts moving through the air, you get the wind counteracting the warm/cool air pressure differential and killing the acceleration. You're never going to get the same thrust in vacuum because the thrust from the radiation pressure is going to be minuscule compared to the differential pressure from the thermal difference in air. HEL 02:20, 1 October 2006 (UTC)

I guess another explanation of Shawyer's "measured thrust" is that it isn't significant (he didn't give error bars, or at least New Scientist didn't report them) or that it's some unaccounted-for systematic effect. J. Costella's refutation should be the final word on the theory side. HEL 03:52, 7 October 2006 (UTC)

Shawyer's concept is the basis of the motion of the Mexican Jumping Bean. Energy encapsulated within the closed bean shell causes the bean to be propelled.

Um, no. The jumping bean is like Newton's cradle: the impact from the worm inside is transmitted as a shock through the shell of the bean to the floor. HEL 03:52, 7 October 2006 (UTC)

Radiant and convective heat leaves the cavity. Is it possible that air currents or radiant heat can push the cavity? In space there would be no convective heat transmission.

[edit] Just Suppose

How to reconcile the theory paper of Shaywer, which clearly ignores the radiation pressure on the sloping walls, and his positive results so far, which appears consistent with this same theory? Maybe there's a connection? Suppose Shawyer is so convinced about his 'only end plate force' theory, he so genuinely believes all the force acts on the end plates, that he has only measured the force on the end plates? We don't have any published details of the cavity, no technical drawings. The immediate supposition we make is that he used a solidly connected cavity, but that's not the only arrangement that would serve to contain microwaves. There is a very well known technique employed in microwave flanges called a choke flange, where instead of an electrical short circuit between the contacting faces to carry the current from side to side, there is a quarter-wave gap ending in an open circuit. This choke flange is tuned to the operating frequency of the radiation. To see one, look at the door of your domestic microwave oven; they tend to use a choke flange for sealing as they are more tolerant of food contamination than a regular electrical contact type. What if his cavity is in three non-contacting parts, with the sloping sides rigidly connected to the frame, and the end plates connected to the balance, perhaps each end plate connected to its own balance for convenience? The length defining part of the choke flange would be on the central section, to allow for misalignment of the end plates. It's a more difficult mechanical arrangement than a rigid cavity, but it would allow full confirmation of his theory by measuring the force seperately on each end plate. Why should he measure the force on the sloping sides, he *knows* it's zero from his theory. Just a thought NeilUK 07:41, 2 October 2006 (UTC)

[edit] My two cents

Sorry folks I don't know how wiki changes work, I just use it. My two cents on the drive are at http://www.assassinationscience.com/johncostella/shawyerfraud.pdf Use or ignore it as you wish. Thanks. John Costella

John-Are you telling me that Shawyer is no Einstein? Say it isn't so!

Einstein? I had students that failed Year 11 Physics that could have pointed out his mistake. He's a fraud.

Apologies again for not knowing how to drive this wiki change thing. Thanks for your tolerance.

John Costella

John- Shawyer is not so dumb. He got 250,000 pounds for his paper, mistake and all. I hope you get at least as much for yours!

Ha ha. Yes, Shawyer is sly. I don't want anything for mine -- I'd like to see Shawyer return the money to British taxpayers.

60.230.116.186 11:37, 6 October 2006 (UTC) John Costella

But remember They all laughed at Christopher Columbus when he said the world was round They all laughed when Edison recorded sound They all laughed at Wilbur and his brother when they said that man could fly They told Marconi wireless was a phony, it's the same old cry

Shawyer may have the last laugh!

Yes, but they also laughed at Koko the Clown.WolfKeeper 16:45, 7 October 2006 (UTC)

And they laughed at Kramer when he claimed he'd build "levels" in his apartment! --Cheese Sandwich 20:50, 7 October 2006 (UTC)

The problem is that Shawyer doesn't claim to be overturning every known law of physics. His 'Theory paper' assumes that relativistic electrodynamics, as we know it, is absolutely true. He then tries to use it to 'prove' his effect.

If he had actually come out and said that his machine was a perpetual motion machine, and violated every law of physics, then it could be judged on that basis.

Shawyer is no Einstein, Columbus, Edison, Wright, or even Kramer. :) An analogy with Ronnie Biggs might be more appropriate.

John Costella

John-there have been many superseded scientific theories proposed by past geniuses. See http://en.wikipedia.org/wiki/Obsolete_scientific_theory. Einstein superseded Newton. Now Shawyer's theories may supersede both Newton and Einstein. Who says conservation of momentum is forever true!

Nobody.WolfKeeper 20:52, 9 October 2006 (UTC)

This is how man progresses in knowledge.

Doubt it in this case. There's obvious mistakes in the paper, and the experimental evidence is so far unreproduced.WolfKeeper 20:52, 9 October 2006 (UTC)

Dr. John Costella, as someone who's been waffling as to believe this stuff or not, let me thank you enthusiastically. On behalf of all wikipedia, I'd like to thank you for publishing this report. Because due to the NewScientist article, I firmly believe that the EmDrive needed an article here, but because it was such a crackpot, no reliable review had actually been performed on the scam. What is the world to do when the "reliable source" (NewScientist, in this case, and yes, I'm using "scare quotes") isn't reliable anymore? For wikipedia, it means that we have to treat it as legitimate, which is not a good thing.

Thankfully, you came along, and provided us with a REAL reliable source that disputes the claims, and that's what we really needed. Wikipedia can now treat the EmDrive as it deserves to be treated... as a scam that was printed in a popular publication and also bilked a government out of a couple hundred thousand bucks.

A round of applause for this man. Hip hip, hooray! Fieari 21:48, 9 October 2006 (UTC)

[edit] EM Drive

The idea was to then allow this idea to test the enter western science.

Let the so called best refutation be allowed and let the drive fly. And test all your science.

A failure this size in public villification means the size of failure of the culture.

It was not to be classified as so called reactionless, that is a public lie.

Shawyer claims that this drive can be used to accelerate a spacecraft, and yet it emits no radiation, no exhaust nor otherwise exerts any external force on any other object to (allegedly) achieve this. That's the exact description of a reactionless drive. If you seriously doubt this, please explain what external force has been provided.WolfKeeper 22:33, 31 October 2006 (UTC

Reactionless appears the system without cause, and I was editied out. And the earth/device system was supposed to be the conserved frame. It will not function in interstellar space, but near earth, it literaly alters the mass of the earth. JUst like all such examples of double frames of reference under acceleration. A single design allows this peculiar conservation of energy and the designer uses it. where to go for the physics, ask the gravity probe-b people.

Unfortunately, we cannot do that under wikipedia's rules. However if you can find a reference from them to that exact effect, please post it here on the talk page, and we can then transfer it to the main article if it is appropriate.WolfKeeper 03:08, 1 November 2006 (UTC)

It clearly has a cause to the necessary force. Reaction appears the desire to publicly claim the failure without the proof.

Extraordinary claims demand extraordinary proof. It is incumbent on Shawyer to show without a shadow of a doubt that his device works. His theory paper has been widely criticised due to numerous fundamental theoretical errors. Still, if his device could actually levitate that wouldn't matter. But right now, nobody has reproduced his results; given the quality of his theoretical consideration I would rather doubt that people would be exactly falling overthemselves to try it for themselves.WolfKeeper 22:33, 31 October 2006 (UTC)

SO as written wiki fails objective science.

A battery usage for the clock operation duration is different for different altitudes near the large mass. Please explain this. If you have no explaination other then relativity, then your objective stance is proven fallacy.

So you go define the cause of the clock power change. And then write the article.

--207.69.139.10 02:39, 31 October 2006 (UTC)

I'm not 100% certain what you're trying to say, but wikipedia doesn't prove or disprove anything, and our purpose is not to write from a scientific point of view. Our purpose is to report what other people have proven, and to write from a neutral point of view. This isn't the same thing.

If other people write these things about the drive, and publish them in reliable sources, we can report on that here. If others remain silent or don't add anything more, we can't add anything more. All we can write about is what has already been written. Fieari 21:38, 31 October 2006 (UTC)

I agree write about the references of the civilization. A true discovery was made. And the cause is a mystery to only some. The gravity probe-b just flew after fifty years in the making to explain this device.

So on these terms remove the incorrect negative and positive conjectures concerning the device. I proved it general relativity. And it was edited out.

DOuglas Eagleson.

[edit] I've added a hoax tag.

As it stood, there was no flag warning the reader that this a suspect topic. Kghose 21:43, 4 December 2006 (UTC)

The end of the article is appropriately critical though the watered down nature is ... well ... watered down. This coming at the end, to me, seems not appropriate. I think the article should start off by saying that this is a disputed claim, with no independent verification, and may indeed turn out to be a hoax. I'm rewriting bits to that effect. I will take out hoax Kghose 21:51, 4 December 2006 (UTC)

http://www.blogger.com/comment.g?blogID=27128970&postID=115987727397773151

[edit] This article is a train wreck

And it contains evidence of significant copyright violations -- text like "a copy of which is attached," meaningless in this context but copied from some other document. Perhaps as a result of this copy & paste construction, the article is extremely repetitive too. Uucp 14:09, 15 March 2007 (UTC)

Retrieved from "http://en.wikipedia.org../../../e/m/d/Talk%7EEmDrive_571b.html"

Categories: Unassessed physics articles | Wikipedia controversial topics