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Thrust from Microwaves - The Relativity Drive 567

Posted by Zonk
from the yay-for-science dept.
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."
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Thrust from Microwaves - The Relativity Drive

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  • by User 956 (568564) on Friday September 22, 2006 @07:43PM (#16164200) Homepage
    "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.
  • by qbwiz (87077) * <john&baumanfamily,com> on Friday September 22, 2006 @07:44PM (#16164202) Homepage
    A) Any pressure from the microwaves on the walls.
    and
    B) Conservation of Momentum
    • by jonnyelectronic (938904) on Friday September 22, 2006 @07:48PM (#16164222)
      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: (Score:3, Informative)

        by ultranova (717540)

        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.

        Nothing funny, just a little omitted detail: the force light exerts on the side walls.

        Sure, the guy is taking into account the force exerted on side walls perpendicular to the direction this thing is supposed to travel to. However, the side walls are at an angle to that directi

    • ...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?
      • by megaditto (982598) on Friday September 22, 2006 @08:56PM (#16164504)
        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.
      • by Ungrounded Lightning (62228) on Friday September 22, 2006 @09:51PM (#16164674) Journal
        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.
    • by bunions (970377)
      it's addressed in TFA, if you'd care to read it.
      • by ZombieWomble (893157) on Friday September 22, 2006 @08:50PM (#16164480)
        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.

        • by Wilson_6500 (896824) on Friday September 22, 2006 @09:31PM (#16164619)
          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.
          • by ZombieWomble (893157) on Friday September 22, 2006 @09:53PM (#16164685)
            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.

          • Re: (Score:3, Insightful)

            In fact, the question that got Einstein started was "What would it be like to ride along with a beam of light?". The answers that classical physics produced made so little sense that he derived relativity. The original paper about relativity was entitled "The Electrodynamics of Moving Bodies".

            Conservation of momentum still works in relativistic physics. If this invention is working at all then it's working for some reason the inventor doesn't know about.
        • by meringuoid (568297) on Saturday September 23, 2006 @06:53AM (#16166133)
          ... 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.

    • by ZombieWomble (893157) on Friday September 22, 2006 @09:06PM (#16164546)
      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: (Score:3, Insightful)

      by Bloater (12932)
      Here's how it's supposed to work:

      The photon is the particle that carries momentum from one dipole to another so when the photons strike the surfaces they pass the momentum from the electrons in the syncrotron to the waveguide.

      Due to the shape of the waveguide and the position of the entrypoint, the photons are more likely to hit the top.

      Due to relativity, as the waveguide moves it does not strike the photons near the bottom more rapidly as they all move up with it.

      Since the synchrotron will move with it, th
  • by celardore (844933) on Friday September 22, 2006 @07:46PM (#16164212)
    It also warms soup, and is great for reheating food.
  • attempt #2 (Score:5, Funny)

    by User 956 (568564) on Friday September 22, 2006 @07:47PM (#16164216) Homepage
    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.
  • by grasshoppa (657393) <skennedy&tpno-co,org> on Friday September 22, 2006 @07:47PM (#16164218) Homepage
    Seriously, we were supposed to have these things *years* ago. The scientific community should be ashamed of themselves.

    ( yes, this is a joke )
    • They've had flying cars [strangebirds.com] since the 50s.
    • by Azarael (896715) on Friday September 22, 2006 @08:05PM (#16164299) Homepage
      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: (Score:3, Insightful)

        by Total_Wimp (564548)
        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.
        And exactly how is this different from cars with wheels?

        TW
        • by Azarael (896715) on Friday September 22, 2006 @08:40PM (#16164443) Homepage
          It's a bit harder to drive your car into the side of a highrise buidling.
          • Re: (Score:3, Insightful)

            by Total_Wimp (564548)
            My post was meant to be funny, but you make a good point. Unfortunately, I'm compelled to mention that Timothy McVeigh used a regular ol' truck to blow up the federal building in Oklahoma City and the first attempt on the world trade center was with an explosive laden van. It's a mistake for people to only look to the skies for threats, and as the Oklahoma City should have taught us, it's also a mistake to only look toward Arabs or Muslims as the bad guys.

            TW
      • Re: (Score:3, Insightful)

        by Mr. Flibble (12943)
        I would say it is really more of a case of costs of energy. My car uses energy to move around, but it does not use energy to suspend itself in the air.

        A flying car would have to use more energy, hence fuel of course, and cost an insane amount of money to fly. Yes, there would be the inherent risks of flying cars etc, but VTOL eats up a good deal of fuel, unless you use standard fixed wing, which requires landing space. Rotary wing works, but is not as efficent as fixed wing at speed.

        I would say it comes dow
        • Re: (Score:3, Informative)

          by Brickwall (985910)
          A flying car would have to use more energy

          Yes, and what was the energy to force ratio quoted in TFA? 700 watts (just a little less than 1 hp) to get 83 millinewtons of force? That force accelerates 83 grams at 1 metre per second squared. That's about 3 ounces. So we'd need 5 hp per pound to get 1 m/s2 acceleration. Take a 1000 lb car, add 350 lbs for two passengers, and we need over 6,500 hp to get minimal acceleration. (1 m/s2 gets you from 0 to 60 mph in about 30 seconds.. most cars do much better tha

  • Save New Scientist! (Score:5, Informative)

    by exp(pi*sqrt(163)) (613870) on Friday September 22, 2006 @07:48PM (#16164221) Journal
    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.
    • by Morphine007 (207082) on Friday September 22, 2006 @07:57PM (#16164269)

      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: (Score:3, Insightful)

        odds are he picked up a textbook and...made a "discovery" that no one else has noticed until now.... HUGE HUGE Kudos if it's true.

        It's not just unlikely, it's impossible. It's impossible to derive something that doesn't conserve energy and momentum from things like Maxwell's equations because the theory is an energy-conserving one. It may be that one day someone makes a drive like this using electromagnetism - but if they do, its principles won't be derived from Maxwell's equations, it'll have to utilize

    • by SQL Error (16383)
      It's about time. New Scientist started to go of the rails ten years ago, and has just been accelerating since then.
  • by QuantumFTL (197300) * <justin,wick&gmail,com> on Friday September 22, 2006 @07:49PM (#16164226)
    "In this house we obey the Laws of Conservation of Momentum!"
  • by TheSHAD0W (258774) on Friday September 22, 2006 @07:49PM (#16164228) Homepage
    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?
    • by RsG (809189) on Friday September 22, 2006 @08:02PM (#16164284)
      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.
    • by AK Marc (707885) on Friday September 22, 2006 @08:04PM (#16164296)
      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.
  • 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 (Score:3, Interesting)

    by PatrickThomson (712694) on Friday September 22, 2006 @07:54PM (#16164257)
    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: (Score:3, Insightful)

      by RsG (809189)
      I don't think anyone who read TFA assumed this was perpetual motion. What this claims to be is more of a reactionless thruster - a different beast. It's quite possible to put forward a theory that violates conservation of momentum without violating conservation of energy.

      Now, admittedly, one is as much in violation of the laws of physics as the other. We have no theoretical basis for reactionless propulsion. In the case of two black boxes acting on each other without being physically connected, the laws
    • by Goaway (82658) on Friday September 22, 2006 @08:55PM (#16164500) Homepage
      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.
  • by Anonymous Coward
    Would somebody please just go right ahead and post a scanned copy of Roger Shawyer's maths paper online after tracking him down and ordering the paper version from him? He says he has a maths paper, so let's cut out these waffling, nonsensically hand-waving explanations much loved by New Scientist that "relativity somehow causes microwaves to create thrust but we don't really know how it works but it does because I say so" and see the maths paper. Show us the maths and it will quickly become apparent whethe
    • Re: (Score:3, Informative)

      by helioquake (841463)
      It's an interesting reading here:

      http://www.newscientist.com/data/images/ns/av/shaw yertheory.pdf [newscientist.com]

      the link is provided by the article linked. It sounds interesting to me, though referring to the special "relativity" is a bit too much; basically one end of the tubes experience more normal force than the other (narrow end) would result in a net forward force, which drives the system.

      Of course the key is the generation of the cavity and its material, and the magentron design.

      Nontheless, it sounds intere
  • Not possible (Score:2, Redundant)

    by Watson Ladd (955755)
    1. The law of conservation of momentum is never violated.
    2. The drive is a closed system.
    3. So it cannot accelerate.
    Also he made a mistake in his calculations. The forces at the end might be different, but forces aren't only being exterted on the ends.
    • Re: (Score:2, Funny)

      by Anne Honime (828246)
      Mandatory : "Everybody said it was impossible, then a fool came who didn't knew and made it." It wouldn't be the first time in science history that something happens to work in spite of mathematics, not because maths are wrong per se but because the thing reveals an entirely unknown field of physics.
    • 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.
  • Power? (Score:3, Funny)

    by misleb (129952) on Friday September 22, 2006 @08:02PM (#16164285)
    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
    • Re: (Score:3, Funny)

      by R3d M3rcury (871886)
      Actually, that was one of my favorite quotes from the article:

      It needs a power supply for the magnetron, but there are no moving parts and no fuel - just a cord to plug it into the mains.
      So your future hovercar can go anywhere an electric cord can go! :^)
  • by davidoff404 (764733) on Friday September 22, 2006 @08:04PM (#16164294)
    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.
    • by naoursla (99850)
      I've always thought "New Scientist" was mostly junk. If I see something on /. that is scientifically questionable it is usually from "New Scientist". I thought the name even sold itself as being on the fringe. "New Scientist" being a scientist working on new stuff on the fringe that may or may not be valid.
      • by davidoff404 (764733) on Friday September 22, 2006 @08:59PM (#16164515)
        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.
        • Re: (Score:3, Funny)

          by naoursla (99850)
          Maybe they are just borrowing the momentum from a future frame of reference.
    • Re: (Score:3, Interesting)

      by geekoid (135745)
      "..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 proto
      • Re: (Score:3, Insightful)

        by Evil Pete (73279)

        Yeah. Get the prototype tested. Evidence beats theory any day, well almost.

    • by MrSteveSD (801820) on Friday September 22, 2006 @08:28PM (#16164396)
      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)
  • by smclean (521851) on Friday September 22, 2006 @08:09PM (#16164309) Homepage
    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).

  • I'd call it the em-motive... or e-motive (if it weren't for IBM's probable copyright for e-anything) e
  • Awesome! (Score:5, Funny)

    by LewsKinslayer (87724) on Friday September 22, 2006 @08:10PM (#16164319)
    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.

  • by coyote-san (38515) on Friday September 22, 2006 @08:17PM (#16164345)
    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.)
    • by davros-too (987732) on Friday September 22, 2006 @09:32PM (#16164623) Homepage
      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...
    • Re: (Score:3, Informative)

      by chgros (690878)
      See also the (Shamir?) pressure you can get when you hold two conductive plates close together.
      Close. The name is Casimir [wikipedia.org]
    • To clarify (Score:3, Informative)

      by David Rolfe (38)

      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 tra

  • My understanding of the basic math suggests that a photon-creating drive will tend to be inefficient. The amount of light energy necessary to get a significant amount of momentum is simply enormous, which is why you don't feel flashlights, even very bright ones, pushing backwards perceptably when you turn them on.

    The article makes this guys thing sound like some kind of perpetual motion machine limited only by his ability to build a perfecct cavity. I haven't read his paper yet, but I'm skeptical of his a
  • Potentially, it could pack the punch of a rocket in a box the size of a suitcase.

    That seals it. The terrerists could use this, so we must ban all further research!
  • by LauraScudder (670475) on Friday September 22, 2006 @08:20PM (#16164356) Journal
    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.
  • by jonniesmokes (323978) on Friday September 22, 2006 @08:27PM (#16164388)
    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.

  • The latest New Scientist has an article about...

    The New Scientist is a weekly publication. This article is from the Sept. 9th edition. In what way does this make it 'the latest', given that two subsequent editions (16th, 23rd) have been published?

  • by sehlat (180760) on Friday September 22, 2006 @08:47PM (#16164465)
    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...
  • Wikipedia article (Score:3, Informative)

    by FleaPlus (6935) * on Friday September 22, 2006 @09:07PM (#16164552) Journal
    Hm.. it looks like there isn't a Wikipedia article on Roger Shawyer, but there is an article on his "EmDrive":

    http://en.wikipedia.org/wiki/EmDrive [wikipedia.org]

    It's a fairly interesting read, and even though it's still rough in spots it's certainly better-informed than the scientifically-confused New Scientist piece linked in the submission. I particularly suggest reading through the analysis of Shawyer's claims.
  • Total Bullshit (Score:3, Informative)

    by DrJimbo (594231) on Saturday September 23, 2006 @12:06AM (#16164831)
    TFA says:
    ... while the thrust of a motionless emdrive is high, the faster the engine moves, the more the thrust falls. Shawyer now reckons the emdrive will be better suited to powering vehicles that hover rather than accelerate rapidly.
    Clearly either the reporter or the inventor does not know about relativity otherwise they would not claim that the thrust depends on the velocity of the engine (which would violate relativity).

    But even if this is the reporter's goof, confusing acceleration and velocity, the inventor claims that the device would work better for hovering (presumably in Earth's gravity) instead of accelerating. This shows that the inventor does not understand relativity or basic physics. If his device could make a car hover then it could also accelerate the car at 1 G.

    According to the physics fact book [hypertextbook.com], a 2001 Jaguar KX8 and a 2000 Mitsubishi Eclipse can each accelerate at 3.8 m/s^2 which is less than 1/2 G.

    Since the inventor does not understand one of the simplest applications of relativity (gravity is the same as acceleration) I do not trust his calculations that claim some relativistic effect is giving him a force that will violate the conservation of momentum and energy.



  • Experimental proof (Score:4, Insightful)

    by SysKoll (48967) on Saturday September 23, 2006 @12:43AM (#16164967)
    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.

  • by Yvanhoe (564877) on Saturday September 23, 2006 @04:27AM (#16165759) Journal
    Weight : 9 kilograms Thrust : 88 milinewtons Quite better than the european ion engine but still awfully far away from being able to lift its own weight (in earth gravity field). And I don't even speak about the weight of a car or a plane. Still an interesting effect though, but the reporter obviously overhyped it. I'll reconsider when it can thrust its own weight, that would only be a x1000 factor...
  • by Yartrebo (690383) on Saturday September 23, 2006 @10:13AM (#16166839)
    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.

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