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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."
Slashdot never loses its appetite for junk science, it seems. Couldn't we at least file this crap under "humor"?
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?
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.
I am one of many. My idea is not unique, nor do I expect my voice alone to sway you. I speak in a chorus of opinion.
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.
Erotic is when you use a feather. Exotic is when you use the whole chicken.
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.)
For every complex problem there is an answer that is clear, simple, and wrong. -- H L Mencken
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.
"..much of it bemoaning the abysmal standards to which New Scientist has slipped. "
well.ets be honest here, scientist always have a habit of doing that when something they don't agree with is published.
". Not only does the article suggest that this "drive" violates conservation of momentum,"
There is nothing in Relativity that says this someone can't exploit the difference in frames.
Do I have my doubts? certianly, and strong ones at that. strangly, the article doesn't ring the BS meter.
Having a working prototype(alledgedly) is a good start. His credtionals seem good.
Agreeing to independent review is also good. Most people BSing about this stuff say things like 'the scientific community is keeping me down.' and won't allow third parties to review the work unless they are paid money in advance.
The Kruger Dunning explains most post on
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.
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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
Seems to me you only need to incorporate this idea to reduce the inertial mass of the craft and then your radiation pressure can really make things happen. You then have... a flying saucer.
Only his tendency toward a dazed stupor prevented him from screaming aloud.
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.
I won't contradict you on Faraday, but as of Marconi, it's very very different in nature ; scientists believed transatlantic radio to be impossible because of the straight travel of electromagnetic waves ; therefore, as earth is round, they thought falsely that radio waves would go out in space following a straight path, and would never reach the other side. That was an established *law*. What they didn't knew, and learnt on that occasion, is that earth's atmosphere is not uniform and some of its layers bounce electromagnetic waves down. It doesn't change physics but it adds to the knowledge of another field of science. And the device (if it works) may uncover some "structures" we don't know about - yet. That doesn't mean it would prove current theories to be false, but it may change our views on something remote.
It's only a closed system if you think in terms of eletro-magnetics. Assuming the prototype works to any degree, what if he's found an electro-gravitational effect? Yes, I'm reaching a bit here, but gravitational effects aren't limited to an enclosure... or maybe even our dimensions... so it wouldn't be a closed system.
Forget thrust, drag, lift and weight. Airplanes fly because of money.
Yeah I haven't read the paper either, and all I know about special relativity are the general principles but all frames of reference are equal is certainly one of the most important points.
But now I think about it, another principle of GR is a constant acceleration is indistinguishable from a gravity field - so if this thing can supply a constant force against gravity, shouldn't it feel the same force and so accelerate when not in a gravity field (or in orbit etc?)
Yes, according to the article, 700 W of input produces 88 mN of force. From a 9 Kg device. This compares to 700 W of input producing 70 mN of force for a 94 Kg device, the ion engine in NASA's Deep Space 1 craft. It also has the benefit of not using any fuel (unlike ion engines,) so as long as you can get electrical energy (solar panels, anyone?) you can keep going.
(For comparison, 88 mN (milli Newtons) of force is approximately enough to lift three U.S. quarters (approx 9 grams at standard force of gravity, a U.S. quarter havin a mass of 2.5 g.) This isn't counting the weight of the device itself. I wonder how much of the mass of the device is due to the microwave generator, and if you can scale up the force per power faster than the mass of the device goes up? (As in, would a 1400 W microwave generator double the force output, without doubling the mass of the device?)
I find the part of the article talking about wingless airplanes, using these devices as sort of 'antigravity' devices, but using conventional thrust engines for forward thrust...
Uh, what? Why not keep the wings, and use one of these as the primary rearward thrust device? You need less thrust to keep a winged aircraft in the air than you do for keeping a device up off the ground. As evidenced by the Harrier 'jump jet', and the fact that a Boeing 747 has a maximum takeoff weight of 412 tonnes, yet has less than 1000 kN of thrust (224k pounds of force vs. 910k pounds of weight.) For a ratio of less than 1:4. A 'direct lift' device would need a greater than 1:1 just to get off the ground, PLUS the forward momentum thrust. The only way this could make sense is if it were more economical to produce these 'relativity drive' devices with sufficient power to lift the fuselage cheaper than the cost of wings.
As for the actual math behind it? Well, I read the actual explanation document. My advanced math is a little rusty, but it looked fine to me. (Then again, so do lots of 'trick' math problems...)
Another non-functioning site was "uncertainty.microsoft.com."
The purpose of that site was not known.
This purported 'invention' will surely not work. Relativity or not, conversation of momentum still holds true. A closed system (which his cylinder appears to be, at least in terms of E/M radiation) will never generate any net thrust. Even when E/M radiation can escape, it will impart at most a momentum of E/c - a very tiny amount indeed.