Thrust from Microwaves - The Relativity Drive

dfenstrate writes "The latest New Scientist has an article about an engine that exploits relativity and microwaves to generate thrust. There is a working prototype." From the article: "Roger Shawyer has developed an engine with no moving parts that he believes can replace rockets and make trains, planes and automobiles obsolete ... The device that has sparked their interest is an engine that generates thrust purely from electromagnetic radiation — microwaves to be precise — by exploiting the strange properties of relativity. It has no moving parts, and releases no exhaust or noxious emissions. Potentially, it could pack the punch of a rocket in a box the size of a suitcase. It could one day replace the engines on almost any spacecraft. More advanced versions might allow cars to lift from the ground and hover."

a bit more advanced

[User 956 (568564)]

"The latest New Scientist has an article about an engine that exploits relativity and microwaves to generate thrust.

That sounds a bit more advanced than these two guys [youtube.com], who exploit explosives and a microwave to generate thrust.

Forgetting some things?

[qbwiz (87077)]

A) Any pressure from the microwaves on the walls.
and
B) Conservation of Momentum

Re:Forgetting some things?

[jonnyelectronic (938904)]

I think you're forgetting that it involves relativity, therefore doesn't need to make sense. Plus I seem to remember that conservation of momentum was a by product of that 4-vector thing, so maybe something funny happens. Maybe.

Re:Forgetting some things?

[ZombieWomble (893157)]

Point A) does, indeed, seem to be exactly what he's forgetting. A quick glance at the outline of the theory in the paper seems to show that he only considers the forces at either end, states that they are not equal, and claims this difference as the thrust, and does up some calculations to evaluate this difference (claiming relativity as the explanation for why he chooses not to treat the microwave/cavity system as closed). He completely neglects to mention (as far as I can see) the fact that the forces acting on the sides of the chamber would differ along its length, and cause a net force on the cavity as well, which would probably act counter to the force induced on the end-plates (I haven't done the math, it's 2am and I'm about to go to bed)

But, he does claim to have a working prototype, and it will be interesting to see if anything does come of it. I've been known to be wrong in the past, after all.

Re:Forgetting some things?

[ZombieWomble (893157)]

It's really not addressed. The closest thing is a vague, hand-wavy argument stating that it has something to do with relativity requiring that the photons must be treated only in their own reference frame, which makes little sense - the defining feature of relativity is that the laws of physics behave identically in all reference frames, and stating that it requires you to only consider some given frame seems to indicate either a reporter who doesn't understand what he's being told or a mistake on the part of the person who put forward the idea.

It's possible that it's covered more accurately in his paper, I haven't got around to reading that yet, but TFA is certainly not the place to go for a serious treatment of this information.

Re:Forgetting some things?

[Wilson_6500 (896824)]

A photon's own reference frame? I didn't think you could consider things from the perspective of a photon and still achieve physical results. In a photon's frame of reference, it and all other photons would constantly be at rest, since they all move at the same speed. That doesn't make any sense, though, since photons always travel at the speed of light and can never rest.

Re:Forgetting some things?

[ZombieWomble (893157)]

Ok, so, instead of sleeping like a sensible person, I read the paper a bit. He seems to suggest (I think, I'm tired and it's quite possible that I've misunderstood) that you have to consider the motion (that is, the group velocity) of the microwaves relative some seemingly arbitrary "stationary" reference frame, in which he did his initial derivation, even when the entire system is moving at some constant speed. (I put stationary in quotes, because the concept of a truly stationary rest frame in relativity is nonsense, and in fact the exact antitheses of the core principle, which is that intertial reference frames are indistinguishable.)

He then proceeds to derive a maximum speed this engine can attain, relative to this arbitrary stationary frame, to illustrate the consequences of this idea. He has, as far as I can see, recreated the ether in his attempt to justify the machine using relativity.

Read this last week...

[meringuoid (568297)]

... and yeah, it seemed terribly vague. I went through counting the number of ways it ignored basic physics: conservation of momentum, check. Principle of relativity, check. Simple high-school resolution of forces along different axes, check. Microwave photons moving at near lightspeed, check.

But what really got me fuming wasn't the author's total failure to notice that any of these were an issue - which I'll grant got me quite livid, being as bad as a football report from someone who doesn't know the offside rule. That it violates basic physics is bad, and should certainly have been seriously raised as an issue in the article, but if it works then that's just too bad for basic physics.

What upset me most of all was the lack of imagination. What if this thing works as advertised? Oh, then we can have planes that work a bit differently. Hovercars, perhaps. For the love of God, man, it's a reactionless drive! Strap a few to a nuclear reactor and go to Saturn and back in a week! A rocket that doesn't have to carry vast tanks of reaction mass around with it? The whole galaxy would open up!

I'll buy this week's New Scientist in the hope of some sort of grovelling apology for this appalling mess of an article. Or at least of a proper flaming of the editors in the letters pages. And then I think I'll see if I can't get a reliable supply of Scientific American - it's quite scarce in UK newsagents but always has some really solid science in it.

Re:Is anyone else reminded...

[megaditto (982598)]

It is, in fact, possible to this Bugs Bunny trick, but by positioning the fan airflow perpendicular to the keel, then setting sail plane oblique to the airflow. It is somewhat similar to sailing against the wind [maztravel.com]

It is also possible to accelerate a rocket by shining a beam of light off it...

While in both cases there are much better ways to achieve same result, these will certainly work.

That actually works - kinda...

[Ungrounded Lightning (62228)]

Is anyone else reminded...of those cartoons where Bugs Bunny or someone is sitting in a sailboat, pulls out a fan, aims it at the sail... ...and the boat moves?

That actually works. A little bit.

But it works MUCH BETTER if you just point the fan to the rear.

The fan sucks air from a lot of directions and ejects it in one direction, creating a net thrust (and reaction - backward - on the boat via the person holding the fan) and a net wind.

Diverting that wind to the rear via the sail produces somewhat more reaction forward on the boat via the sail and the mast than the reaction backward from the fan - IF the trim is good enough that the diverted wind ends up going backward rather than just off to the sides. Result: Slight net forward thrust on the boat.

But pointing the fan to the rear - using it as a jet - eliminates the inefficiencies of using the sail in this way, putting the fan's whole reaction into moving the boat forward.

Re:Is anyone else reminded...

[wealthychef (584778)]

Um, I have to ask. What about the air being deflected off the fan? Doesn't it create thrust in the opposite direction from the sail? In fact, I'd expect the boat to move backward, because most of the air from the fan would disperse and not hit the sail.

Re:Forgetting some things?

[tftp (111690)]

The photon is massless, has no electric charge ... (quoted from here [wikipedia.org])

The radiation pressure [wikipedia.org] does exist, but it has nothing to do with Lorentz force [wikipedia.org]. And you can, actually, propel yourself by shining a flashlight away from you. The matter annihilation engines work on this principle, for some decades [wikipedia.org] by now.

The only problem with this propulsion method is that you need an awful number of photons, and you wouldn't like to be in a spot that they hit. Some writers theorized that the Solar system would need an energy shield before it can launch a photon-driven starship from anywhere close to it.

Re:Forgetting some things?

[Quadraginta (902985)]

The only problem with this propulsion method is that you need an awful number of photons...

Hmmm, I'd always thought the major problem with matter-annihilation drives was the lack of antimatter deposits in the Earth's crust from which the fuel could be mined...

Aditional Features

[celardore (844933)]

It also warms soup, and is great for reheating food.

Re:Aditional Features

[rthille (8526)]

God damn it! Every time the neighbors hover by in their new car my internet connection goes out!

Re:Aditional Features

[Predius (560344)]

Good news everybody, it's also a suppository!

attempt #2

[User 956 (568564)]

Roger Shawyer has developed an engine with no moving parts that he believes can replace rockets and make trains, planes and automobiles obsolete ... The device that has sparked their interest is an engine that generates thrust purely from electromagnetic radiation

Of course, his first effort was to create a drive that ran purely on improbability, but you could never be sure where you'd end up or even what species you'd be when you get there.

Re:attempt #2

[Jhon (241832)]

Heisenberg gets stopped by a cop for speeding.

"Do you have any idea how fast you were going?", asks the cop.

"No. But I know exactly where I am!"

'bout damn time I get my flying cars

[grasshoppa (657393)]

Seriously, we were supposed to have these things *years* ago. The scientific community should be ashamed of themselves.

( yes, this is a joke )

Re:'bout damn time I get my flying cars

[Azarael (896715)]

Joke well taken, but in all honesty the bigger joke is that we technically could have had flying cars already. You know what the problem is? the general public couldn't be trusted not to crash the things left and right. In no time there would be more flying lawsuits than cars.

Re:'bout damn time I get my flying cars

[Azarael (896715)]

It's a bit harder to drive your car into the side of a highrise buidling.

Save New Scientist!

[exp(pi*sqrt(163)) (613870)]

The complete and utter bogosity of this story has prompted Greg Egan to try to start a movement to save New Scientist. Anyway, check out this [utexas.edu] story.

Re:Save New Scientist!

[Morphine007 (207082)]

It does seem rather bogus

His references include an undergrad level textbook on physics, as opposed to the usual slew of papers outlining new developments in the field. Undergrad physics books are geared towards undergrad courses... which is why you see things like: "assume no friction due to air" in trajectory problems. His second reference is Maxwell's treaty on electricity and magnetism... hardly a new work.

In short, odds are he picked up a textbook and started playing with simplified equations and figures he's made a "discovery" that no one else has noticed until now.... HUGE HUGE Kudos if it's true.... but the magic 8-ball's sayin "outcome not likely"

Re:Save New Scientist!

[exp(pi*sqrt(163)) (613870)]

If one side of the cavity is bigger than the other then one side is receiving more momentum than the other.. so the cavity should move.

Between the ends of the cavity must be walls joining them. If the ends are circular we're talking about conical walls. The photons are slamming into these too. (If this is a proper waveguide then they're actually bouncing rather than being absorbed.) If you think about it, the conical walls aren't orthogonal to the ends, their inside surface points more towards the wide end. So photons bouncing off these walls will also provide thrust. This thrust is in the same direction as the thrust from the narrow end and exactly makes up for the shortfall from its being narrow.

The trick would be to join a narrow and wide end using walls that don't point more towards the wide end. But alas, that's an impossibility of geometry.

Re:Save New Scientist!

[CTachyon (412849)]

Newton was wrong with his description of gravity. It was the best he could do to describe it, however in the end, its wrong. Could this be the same?

Almost certainly not. Newton's Laws were incomplete, not wrong. Newton's Laws are today seen as a mere special case of General Relativity, and yet we still use Newton's Laws on a day to day basis, and when some new theory of quantum gravity replaces GR, Newton's Laws will still be used on a day to day basis, because they're not wrong.

The "EMDrive", on the other hand, would throw out one of the most established principles of physics, Conservation of Momentum, a principle found in every coherent system of physics a human being has ever written (at least, those systems of physics meant to describe the universe we live in). And while it's conceivable that we really do need to rewrite the physics textbooks from scratch and add an error bar to Conservation of Momentum (then figure out why it's possible to break it in the first place), the article hardly constitutes a good reason to do so. Science isn't done by asking "Wouldn't it be great if X were possible?"

Oblig comment

[QuantumFTL (197300)]

"In this house we obey the Laws of Conservation of Momentum!"

Erm... I don't get it.

[TheSHAD0W (258774)]

What's the difference between letting the microwaves bounce around in a cavity and just shooting them out the back? Or if you must bounce them, just bounce them off a 45 degree reflector. What's the benefit of the multiple bounces?

Re:Erm... I don't get it.

[RsG (809189)]

Because that would be a photon drive. And we already know how well those work - the amount of energy you need to input to get even a tiny amount of thrust out of them is astronomical (pun not intended). We've had the basic idea of light propulsion for at least fifty years, and it's been a major cornerstone of hard science fiction. But it just isn't workable with modern power generation.

You could describe either a photon drive, or it's passive counterpart, the light sail, as a "relativity drive", since they too operate on the oddities of conservation of momentum as it applies to light. Doesn't mean we're going to be using them in lieu of rockets anytime in the next few centuries.

Either this guy has found a revolutionary new way to build a photon drive (and I'm more than a little skeptical), or else the device doesn't actually work. I'm more optimistic about this than I am about the usual lot of crackpot science, since from TFA it sounds like this guy is applying good scientific procedures to his work (documenting, trying to get outside review), but I'm not exactly holding my breath.

Re:Erm... I don't get it.

[RsG (809189)]

I actually meant more that he was trying to get his idea reviewed from the outside, something the vast majority of crackpots fail to do.

One of the conditions of Shawyer's £250,000 funding from the UK's Department of Trade and Industry is that his research be independently reviewed, and he has been meticulous in cataloguing his work

Assuming that part of TFA is true, then he's already way ahead of the usual "free energy" crowds.

Typically when somebody's claims violate the laws of physics, the usual challenge is for them to provide a repeatable experiment for others to test the theory in question with. This challenge is most often met with weaseling or silence. When such theories are tested from outside, they most often do not pan out (see the cold fusion experiments as an example).

If he's willing to get outside review already, then I at least will acknowledge that he is an honest crackpot rather than a snake oil salesmen. And it's always better to actually test the blue sky ideas than it is to dismiss them out of hand.

Re:Erm... I don't get it.

[kfg (145172)]

If he's willing to get outside review already, then I at least will acknowledge that he is an honest crackpot rather than a snake oil salesmen. And it's always better to actually test the blue sky ideas than it is to dismiss them out of hand.

Oh, there have been any number of people who have put forward various intertialess drives for independant review. You are right, there is a difference between the honest crackpot and the snake oil salesman (thank god, or I might be in real trouble myself), but sometimes tests actually just waste time and resources when the theoretical failures can be defined without actual test.

And my point was that he hasn't actually built anything legitimately testable in a lab yet. The forces are so small that we'll need to fly the puppy to judge it at all. This is different from the solar sail which already know could work by theory and ground based test.

I can build you three or four mechanical variations on the theme that will even stand up to review in the sense that they seem to work perfectly well in the lab, much better than this one does because they'll actually scoot across the airtable, but the reason why they won't work in space are well enough understood that no one is going to waste a bird to send one up.

It's perfectly possible to become an honest crackpot by simply getting a bit of the equations wrong and have that failure perfectly obvious to other people.

KFG

Re:Erm... I don't get it.

[AK Marc (707885)]

The benefit of the multiple bounces is that they never leave the chamber. The chamber is shaped like a horn, and he's claiming that the force on the big part of the horn is greater than the forces towards the little side of the horn. An imbalanced force inside the chamber result in a net force from a closed system. Plus side, no moving parts and sealed. Minus side, current physics indicate this to be impossible. I know of no theory, even including the magical "relativistic" physics that allow for or predict unbalanced forces in a closed system. I'll believe it when I see it demonstrated to move a satellite in space. If he can do that, I'll drink the cool-aid.

If I managed to figure out something like this..

[QuantumG (50515)]

I wouldn't tell anyone. I'd maybe show a few keen investors what my prototype could do, but that's it. Then I'd develop a flying car, a launch vehicle, whatever, and insidiously take over existing markets. "So, SpaceX has made you the best offer for launch services eh? I'll beat it." "What kind of safety guarentees can you give us?" "Err, umm, what kind of safety guarentee is SpaceX giving you, I'll beat it!" "Right.. hmm, ok. You don't even have a rocket do you?" "Look, do you want your satelite in orbit or what?" and so on. That's me though, could be this guy just doesn't have balls that big.

Key points from TFA

[PatrickThomson (712694)]

Buried right at the end, it says that if the engine is allowed to actually accelerate, it consumes energy from the cavity, so this is NOT a perpetual motion device or some other bollocks. You can't get out more kinetic energy than the cost you put in - at best, this would be like using momentum from laser light.

However, it talks about hovering. There's nothing intrinsically unscientifically sound about two black boxes that exert a force on each other despite being physically disconnected (think maglev), effectively hovering one on the other - the transmission of force just doesn't happen via a physical carrier. I, for one, look forward to my hoverboard.

Re:Key points from TFA

[Goaway (82658)]

Yes, that's the part where you should finally realize the whole thing is nothing but bullshit.

He's claiming that the effect depends on the absolute velocity of the engine - a concept that has been meaningless ever since we did away with the coelestial aether and Maxwellian electrodynamics.

He's not using relativity, he's using the exact opposite.

Power?

[misleb (129952)]

Um, I didn't read TFA, but wouldln't this require a power source? Specifically, eletricity? How does one generate that much wattage? Flux capacitor?

-matthew

Slashdot - where science makes no sense (TM)

[davidoff404 (764733)]

Pity thee, dearest /. This New Scientist article has already received a lot of attention [columbia.edu] from the physics community, much of it bemoaning the abysmal standards to which New Scientist has slipped. Not only does the article suggest that this "drive" violates conservation of momentum, the author actually realises this but tries to sweep this (rather fundamental) point under the carpet with lots of handwaving and muttering about "frames of reference". Not only is this atrocious journalism, it's also a sad indication of the levels to which a once-great magazine has now sunk

In fact, the article in question is so bad, a petition has been started among scientists to save New Scientist from itself [utexas.edu]. On a somewhat related note, do /. editors even bother to read the submissions any more? Even a cursory glance at the article would have been enough to convince anyone that it's unintelligible garbage.

Slashdot - where science is just a word that goes before fiction.

Re:Slashdot - where science makes no sense (TM)

[MrSteveSD (801820)]

It was a really bad article. It was clearly a dodgy claim and you would think they would have an expert in the area totally vet the article, but alas no.

There are some other worrying things in the article. For example, the author says...

What of the impact of such a device? On my journey home I have plenty of time to speculate. No need for wheels, no friction.

Yet it is precisely the friction between the wheels and road which make a car go forward. Friction with the car wheels is not bad, you need it. Friction with the air is bad, but not the wheels.

If I had do the EM Drive story, a story which sounds highly suspect, I would have looked at some critiques of similar schemes. Within a few minutes of searching I found similar "Reaction-less Drive" schemes which all turned out to be Oscillation drives. It's the same phenomena as when you move across the room in a swivel chair (without touching the floor) by shifting your body-weight around. When you do that you are exploiting the non-linear nature of friction between surfaces. A similar thing can happen with these reaction-less drives interacting with air, water or other surfaces. So it's quite possible that a prototype drive would appear to work. So I would have asked for some kind of proof that this was not an oscillation drive.

Another issue is that it's not clear that this Em Drive prototype has been tested in a vacuum. In one of the other articles on it, it says that the thrust only reaches the maximum after a few seconds. Now that sounds much more like a mechanical oscillation effect (building up to maximum amplitude) than a photon/microwave effect.

Some of what I have said here is re-posted from a discussion I had on the Elmurst Solutions Science forums. (http://www.elmhurstsolutions.co.uk/cgi-bin/yabb2/ YaBB.pl?num=1157719780/0)

Re:Slashdot - where science makes no sense (TM)

[kestasjk (933987)]

Yet it is precisely the friction between the wheels and road which make a car go forward. Friction with the car wheels is not bad, you need it. Friction with the air is bad, but not the wheels.

I thought it was the exhaust coming out of the back that propelled the car forward.. I mean, if electromagnetic radiation can propel something forward surely gaseos exhaust can?

Re:Slashdot - where science makes no sense (TM)

[davidoff404 (764733)]

Surprisingly, New Scientist used to be a great magazine. When I first became interested in science as a kid it was the place I went to get my weekly fix of science news (I discovered Scientific American a couple of years later, I must have been ten or so at the time). The point is that the journalism was of a much higher standard back in the day; certainly, the "old" New Scientist would never have allowed an article to be published which suggested that conservation of momentum can be overcome by messing around with frames of reference.

Seriously, the claims in the article about relativity are shockingly, shockingly stupid. It's sad to see that something which was such an important part of my childhood (and which probably helped me to decide to become a physicist) allows its writers and editors to get away with this crap.

The Rocket Monopolist Conspiracy!

[smclean (521851)]

Shawyer argues that for companies investing billions in rockets and launch sites, a new technology that leads to fewer launches and longer-lasting satellites has little commercial appeal.

Yeah, those companies are just dying to spend as much money as possible trying to get their satellites in orbit. They are looking into purchasing rockets made from ground up hundred dollar bills.

I hope his invention is better than his explanations for why he has no investors (I know, I know, it's not).

Awesome!

[LewsKinslayer (87724)]

Now I can have what I've always dreamed of, a flying car with a Phantom game console running Duke Nuke'em Forever on HURD with Copland running in virtualization on a BitBoys Oy Glaze3D graphics system whose driver was programmed in Perl 6 running on top of Parrot!

I love it when dreams come true.

journalist, at least, is totally clueless

[coyote-san (38515)]

I'm rolling on the floor laughing at that article, but have to remind myself that it's probably an ignorant reporter and (not necessarily) Shawyer.

"Since the microwave photons in the waveguide are travelling close to the speed of light"... no, the microwave photons ARE light and are, by definition, moving at the speed of light at that point. I'm not really weaseling -- 'c' is the speed of light in open vacuum and is the same thing for all photons, but a waveguide is only a few multiples of the photon's wavelength and various weird things (to us) happen. See also the (Shamir?) pressure you can get when you hold two conductive plates close together. Longer wavelengths can't exist between the plates but can exist outside of them so you get a very slight net force pushing the plates together.

"any attempt to resolve the forces they generate must take account of Einstein's special theory of relativity."... no, standard EM theory will suffice. (Well, you might need some QM in there, but definitely not special relativity.)

and my favorite

"by mounting it on a sensitive balance, he has shown that it generates about 16 millinewtons of thrust, using 1 kilowatt of electrical power."

Let that sink in. This is as much power as a hair dryer or stove element, and it generates 16 mN of thrust. Could it be, oh, Satan?! I mean, thermal?!

This is particularly ironic since the article referred to the discovery of light pressure earlier. Everyone knows those little bulbs with white and black fans that "demonstrate" this effect. What most people don't know is that it isn't a perfect vacuum in there and, gosh, the dark side gets slightly hotter than the white side. That means the gas heats up on one side, expanding, you know the rest. IIRC they spin leading with the white side. It should be the other way since you have twice as much momentum transfer to reflect light (white) than to simply absorb it (black).

(BTW, I agree 100% with everyone who's pointing out that the walls of the cavity account for the rest of 'thrust' and that the device will just sit there driving up your power bill.)

Re:journalist, at least, is totally clueless

[davros-too (987732)]

It really is sad that NewScientist published this. When I was a grad student we used to get sent the crackpot letters addressed to the professors - its an education! In this case the 'crackpot' signs are all around.

Some /.ers commented that at least there were some experiments, presumably a reference to:
"by mounting it on a sensitive balance, he has shown that it generates about 16 millinewtons of thrust, using 1 kilowatt of electrical power."

One of the many problems here is how incredibly easy it is to stuff up sensitive measurements. For example, I have seen electronic balances and other equipment read a lot more than 16mN in error due to em interference (could be the microwaves, could be slop-over RF, could be induction into the mains. Remember Cold Fusion? Did you know the neutron detectors they were using were incredibly sensitive to temperature? No? Nor did Pons and Fleischmann, unfortunately...

This is complete bollocks

[LauraScudder (670475)]

By the way, this engine would violate conservation of momentum, and is thus incredibly dubious. On top of that, the "working" prototype was measured to generate an incredibly tiny force, a measurement which was given without error bars in the only numbers I've seen, so he's probably just measured his noise floor. It has never been published in a peer reviewed journal. Because of this article, John Baez has posted an open letter from Greg Egan [utexas.edu] to the editors of New Scientist, which includes gems like "I really was gobsmacked by the level of scientific illiteracy in the article".

In other words, reader beware. Crackpots abound.

complete and utter nonsense

[jonniesmokes (323978)]

I'm very surprised that this is being reported on. There's nothing to this.

What's probably happening is that the microwaves are leaking out heating up one side of the thruster more than the other causing the air on that side to warm up and become bouyant which is whats creating the apparent thrust. I could make a lot more thrust with a 700 Watt fan than 88 millinewtons.

I'm starting to dispair over the state of science in this so called modern world when I see articles like this. Maybe next we could have an argument over whether sidereal or tropical based astrology is more accurate at predicting the future.

Re:complete and utter nonsense

[exp(pi*sqrt(163)) (613870)]

I'm starting to dispair over the state of science in this so called modern world when I see articles like this

It could be a lot worse. People could start claiming completely insane things like that we should replace scientific research in fields like biology and cosmology with the contents of ancient Middle Eastern scrolls. Then we'd really be in trouble.

Easy to test, no satellite needed

[sehlat (180760)]

Easy to test: no satellite needeed. From Jerry Pournelle [jerrypournelle.com]'s web site:

TESTS If anyone does have a candidate device for producing reactionless acceleration -- that is, linear acceleration without throwing mass overboard and without reacting with a medium such as air or water -- the first test is to suspend it on two wires attached so that the plane of the two wires is normal to the direction of thrust-- that is, make a swing and put your gadget on it facing in the normal direction of travel of the swing. Now turn it on. If it will hang non-vertically, get interested. Now cover it with a plastic garbage bag and see if it will still hang non-vertically. If it will still do so, turn it off, and if it settles to a vertical angle, and you can do this repeatedly, and it hasn't lost any mass during the experiments, call your local physics professor. Or call me. I'll take care of notifying the Swedish Academy. But until it will do that, I don't need to look at it...

Experimental proof

[SysKoll (48967)]

The maths is wrong and the theory is fishy, but the inventor could skip all the hubub and get a Nobel just by doing this:

1. Get a vaccuum chamber
2. Hang the drive on a rope from the chamber's ceiling
3. Hang a plumb line next to the rope
4. Turn the thing on
5. Report any deviation from the vertical.
6. If so... Profit! Seriously.

If there is a sustained, measurable deviation not explained by known physics, the guy will get a Nobel. That's 1.1 million dollars. If I was sure I had a winner for getting a million, I'd certainly be ready to invest into a vaccum chamber and build a prototype.

If we don't see this happen, then the drive doesn't work. End of story.

here you go

[Tibor the Hun (143056)]

you can have it for free:
</i>

The aRocket post with paragraphs...

[by Anonymous Coward]

Peter Fairbrother zenadsl6186 at zen.co.uk
Tue Sep 19 17:56:42 PDT 2006

Russell McMahon wrote:

As already noted on ARocket - it "*can't* work - but wouldn't it be nice if he was right, even though he's not :-(.

I don't know that a reactionless drive can't work - although I don't know how to build one :( - but I do know that this particular one doesn't work.

For those who haven't met the emdrive before - it's not your usual snake oil and mirrors type device - the inventor is highly capable and has convinced a number of substantial organisations, including the US Air Force, British Govt research granters and NASA to be cautiously interested. All of which just means that it's not yet obvious to all where the hole in his theory is.

Without having gone into it in detail, his math seems okay up to eq 6 (when he is quoting well-known math), but thereafter he veers into the realms of error and fantasy.

Eqation 7 is incorrect in so far as it purports to describe the total forces on the waveguide - while it does correctly describe the sum of the forces on the ends of the waveguide, it does not take into account the forces produced on the sides of the tapered waveguide.*

All by itself that is enough to blow the conclusions of the paper completely out of the water. It is simply wrong. It doesn't work. You can stop reading here.

Now we get into the rather more dubious portion of the paper.

Eq. 8 is also in error - it is based on the incorrect statement "...as the two forces Fg1 and Fg2 are dependent upon the velocities vg1 and vg2, the thrust T should be calculated according to Einsteins law of addition of velocities." - but the conclusion does not follow, and use of Einstein's equation is inappropriate. There is no real-world summing of velocities, it is a mathematical trick (and there is an error int the math too). The ends of the waveguide are stationary relative to each other.

That is an elementary schoolboy (or snake-oil salesman's) mistake.

There are several other obvious mistakes in the paper, and he frequently states as fact things that are unjustified and on occasion untrue. There are also parts of it which seem to be meaningless.

For example, this is also incorrect: "The second effect is that as the beam velocities are not directly dependent on any velocity of the waveguide, the beam and waveguide form an open system."

The conclusion does not follow.

This is actually very confused - I don't think he even knows what he is saying. Relativity theory does not (directly) come into it at all.

I stopped looking for more errors about here.

Snake oil or error?

There was some mention of licencing the technology, but as it is in the UK patenting it here would be impossible - it is, after all, a perpetual motion machine (or it would be if Q approached infinity, which there seems no theoretical reason to suppose impossible), and you cannot patent a perpetual motion machine in the UK.

Even if it worked.

The question of how he got a grant is still ... puzzling, but not totally unexpected. Grants are often assigned by managers and politicians rather than scientists or engineers.

To the DTI, NASA etc: Please can I have half his grant for pointing out his mistakes? I promise I will use it do space r+d. :)

*Of course if you want to consider the waveguide as two pieces, forces on the tapered walls do not affect the result - but the math in eq7 would be wrong if you are looking at it that way, eg the lambda-g1 and lambda_g2 figures are for the ends of the waveguide, not the middle.

I think he first went wrong in his mind here - in fig 2.4 there is a vertical line in the middle of the diagram, implying that he was looking at the waveguide as two pieces, rather than as two ends and a tapered middle. You can of course look at it in either way, but in his analysis (even before we get into the error-full "relativity" stuff) he is trying to do both at once, and that will and has lead to error.

--
Peter Fairbrother

--a different AC