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posted by martyb on Friday June 17 2016, @12:39AM   Printer-friendly
from the invisible-light dept.

International Business Times writes:

A new peer-reviewed paper (open, DOI: 10.1063/1.4953807) on the EmDrive from Finland states that the controversial electromagnetic space propulsion technology does work due to microwaves fed into the device converting into photons that leak out of the closed cavity, producing an exhaust.

So how could something come out that you can't detect? Well, the photons bounce back and forth inside the metal cavity, and some of them end up going together in the same direction with the same speed, but they are 180 degrees out of phase. Invariably, when travelling together in this out-of-phase configuration, they cancel each other's electromagnetic field out completely.

That's the same as water waves travelling together so that the crest of one wave is exactly at the trough of the other and cancelling each other out. The water does not go away, it's still there, in the same way the pairs of photons are still there and carrying momentum even though you can't see them as light.

If you don't have electromagnetic properties on the waves as they have cancelled each other out, then they don't reflect from the cavity walls anymore. Instead they leak out of the cavity. So we have an exhaust – the photons are leaking out pair-wise.


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  • (Score: 3, Funny) by Anonymous Coward on Friday June 17 2016, @12:49AM

    by Anonymous Coward on Friday June 17 2016, @12:49AM (#361342)

    Space drive relies on conservation of momentum. Your space thingamajiggi shoots things backward, it moves forward, that way conservation of momentum is maintained.

    So, this "emDrive" thing, somehow push the craft forward without shooting stuff back, so people are saying that's bullshit. Now this Fin dude is saying it does shoot things back, hence its forward propulsion.

    Ok, carry on.

    • (Score: 0) by Anonymous Coward on Friday June 17 2016, @01:13AM

      by Anonymous Coward on Friday June 17 2016, @01:13AM (#361348)

      EmDrive is legit.

      • (Score: 0) by Anonymous Coward on Friday June 17 2016, @01:23AM

        by Anonymous Coward on Friday June 17 2016, @01:23AM (#361353)

        That probably works better for liberal arts majors.

    • (Score: 3, Interesting) by Immerman on Friday June 17 2016, @01:50AM

      by Immerman (3985) on Friday June 17 2016, @01:50AM (#361359)

      Except his explanation doesn't hold water - if it were generating thrust on par with a photon rocket nobody would care about it. Photon rockets are well understood, and too weak to be useful for much. What makes the EmDrive interesting is that it seemingly has a thrust-to-power ratio orders of magnitude greater than is possible with a photon rocket.

      • (Score: 0) by Anonymous Coward on Friday June 17 2016, @02:15AM

        by Anonymous Coward on Friday June 17 2016, @02:15AM (#361367)

        It's a resonant photon rocket.

        • (Score: 3, Interesting) by Immerman on Friday June 17 2016, @04:15AM

          by Immerman (3985) on Friday June 17 2016, @04:15AM (#361403)

          That wouldn't change anything. Every erg of energy generates X photons with Y momentum. You can do all the fancy bouncing and resonating you want, but so long as conservation of momentum holds, when the photons finally exit the device they will depart with Y momentum, and the device will gain Y momentum in the opposite direction.

          • (Score: 0) by Anonymous Coward on Friday June 17 2016, @07:59AM

            by Anonymous Coward on Friday June 17 2016, @07:59AM (#361452)

            Immerman, you are blowing everyone's "liberal arts" paradigm with your physics and logic and sciency stuff. Please stop.

            • (Score: 2) by Immerman on Friday June 17 2016, @03:03PM

              by Immerman (3985) on Friday June 17 2016, @03:03PM (#361585)

              Hey, if you can't take the math, get out of the science discussion :-D

      • (Score: 1) by Prune on Saturday June 18 2016, @02:16AM

        by Prune (4334) on Saturday June 18 2016, @02:16AM (#361963)

        Wow! Brilliant! You sure showed all those physicist peer reviewers of this paper how stupid they are to not have found such a basic flaw and rejected the paper! Ah, it's good to know that Soylent's own Immerman is here to vet the work of these ignorant scientists — I can now sleep at night!

        • (Score: 2) by Immerman on Saturday June 18 2016, @05:36PM

          by Immerman (3985) on Saturday June 18 2016, @05:36PM (#362131)

          Hey, when has intelligence ever been a defense against your own stupidity?

          Fact: Shawyers initial claims were that he generated 0.016N with 850W, or about 20uN/W
          Fact: Nasa's tests found about 1/1000th the thrust, about 20nN/W
          Fact: the theoretical upper limit for a perfectly collimated photon drive is about 2nN/W

          So, even if this thing is in fact emitting photons in some new and interesting, virtually undetectable manner, which just happen to be perfectly collimated... it's still 10 times too weak to explain the even the weakest thrust we've measured. Maybe it actually does produce an exhaust in this manner, and the idea is certainly interesting, worthy of discussion, and may have serious implications both in other fields and in the practical considerations for EmDrive (if the EmDrive is proven to work).

          It's just not a candidate to explain the thrust that's been measured.

  • (Score: 3, Interesting) by jmorris on Friday June 17 2016, @12:53AM

    by jmorris (4844) on Friday June 17 2016, @12:53AM (#361343)

    How hard would it be to just install one on the ISS, turn it on and see if it produces thrust in space? ISS has the electrical capacity, we know the device doesn't explode or do anything dangerous. Run it a week and it should produce a tiny but measurable change in the station's orbit.

    If it works we can worry about discovering the theory behind it and refining it to be more efficient and if it doesn't we can stop dreaming about an electric rocket engine.

    • (Score: 1, Interesting) by Anonymous Coward on Friday June 17 2016, @01:00AM

      by Anonymous Coward on Friday June 17 2016, @01:00AM (#361344)

      The ISS is still bound to it's orbital gravity, and slightly to the very thin atmosphere still present at that altitude. It would be better tested in deep space.

      • (Score: 3, Interesting) by jmorris on Friday June 17 2016, @01:15AM

        by jmorris (4844) on Friday June 17 2016, @01:15AM (#361350)

        Building a full space probe complete with solar array large enough to drive and launching it beyond LEO is a lot more expensive than just sticking the drive on the ISS. The orbit of the ISS is well understood so any force shifting it, even a fairly small one, would be easy to spot. Remember the whole point of this gadget is that it can deliver a small but continuous thrust without consuming fuel. A small thrust adds up if it can be sustained for days. All they would need is the weight allowance on a supply mission and a single EVA to bolt the thing to the station and connect it to power.

        • (Score: 2) by Immerman on Friday June 17 2016, @01:54AM

          by Immerman (3985) on Friday June 17 2016, @01:54AM (#361361)

          Why do an EVA? If it's real it should generate the same thrust if you just bolt it to an inside wall.

          • (Score: 3, Insightful) by deimtee on Friday June 17 2016, @02:00AM

            by deimtee (3272) on Friday June 17 2016, @02:00AM (#361365) Journal

            Just in case it really is emitting kilowatts of microwaves maybe? If I was on the station, I think I would prefer it to be outside.

            --
            If you cough while drinking cheap red wine it really cleans out your sinuses.
            • (Score: 2) by tangomargarine on Friday June 17 2016, @02:42PM

              by tangomargarine (667) on Friday June 17 2016, @02:42PM (#361571)

              Are the walls of the ISS thick enough to protect from that anyway?

              --
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              • (Score: 2) by Immerman on Friday June 17 2016, @03:11PM

                by Immerman (3985) on Friday June 17 2016, @03:11PM (#361589)

                Should be - microwaves are normally reflected by even a thin sheet of metal (like the mesh on the front of your microwave oven). The only real question is how question would be just how perfectly canceled any emitted photon pairs are. If they're perfectly aligned, then for most practical purposes they cease to exist and it's not a problem. If however they're only *almost* perfect you'll get interference patterns around the device. Not really sure how shielding would effect that... I think all the normal formulas assume that you're dealing with each photon individually, when pairs start effectively popping in and out of existence.... I wouldn't know where to start.

        • (Score: 0) by Anonymous Coward on Friday June 17 2016, @02:22AM

          by Anonymous Coward on Friday June 17 2016, @02:22AM (#361369)

          But that would fail to prove that EmDrive is not somehow dependent on gravity of larger object or some other property, like radio waves etc that are present in and near Earth's Orbit.

      • (Score: 3, Interesting) by Dunbal on Friday June 17 2016, @02:02AM

        by Dunbal (3515) on Friday June 17 2016, @02:02AM (#361366)

        Nah, you put it on the end of a boom. Angular momentum doesn't care all that much about the gravitational field and the boom will magnify the torque you get. If you start getting rotation you know it works.

        • (Score: -1, Troll) by Anonymous Coward on Friday June 17 2016, @02:07PM

          by Anonymous Coward on Friday June 17 2016, @02:07PM (#361540)

          They've done that, and it's spun the stuff.

          ...

          ...

          NIGGER!

    • (Score: 2) by takyon on Friday June 17 2016, @01:22AM

      by takyon (881) <reversethis-{gro ... s} {ta} {noykat}> on Friday June 17 2016, @01:22AM (#361351) Journal

      If it has a strong enough thrust to be measured reliably, it doesn't need to be tested in space.

      The creator of the Emdrive has hinted at domestic applications of emdrive and thrust good enough to counteract Earth gravity (yup, Back to the Future 2 style flying cars, and probably bullshit). But there is no need to send an emdrive in space in order to determine if it can compete with ion drives. If it works, it will be very obvious. The Chinese teams testing emdrive have reported higher thrusts than NASA, the creator of emdrive is hiding behind trade secrets, so perhaps the problem is not the concept but the specific design and small budget that NASA scientists have to work with.

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      • (Score: 2) by jmorris on Friday June 17 2016, @02:25AM

        by jmorris (4844) on Friday June 17 2016, @02:25AM (#361371)

        Those high thrust figures are for a proposed version built with superconductors. To date the trusts have been small enough for reasonable people to suspect it is measurement error or side effects like the heat generating drafts of air, magnetic fields attractingt the test stand, etc. If the thing were levitating in mid air I doubt there would be any debate about whether it worked.

    • (Score: 3, Funny) by RamiK on Friday June 17 2016, @02:31AM

      by RamiK (1813) on Friday June 17 2016, @02:31AM (#361372)

      Here's the thing: Since the Higgs, all the theoretical physicists broke down and started mumbling about simulations and the matrix and AIs taking over the world...

      Now, you drop this EmDrive gizmo that shows tests with results they just can't explain... Are you trying to get them all committed? Have some heart man.

      --
      compiling...
    • (Score: 2) by fritsd on Friday June 17 2016, @02:31PM

      by fritsd (4586) on Friday June 17 2016, @02:31PM (#361565) Journal

      How hard would it be to just install one on the ISS, turn it on and see if it produces thrust in space?

      They were going to do that with the experimental VASIMR [wikipedia.org] drive, but I think they forgot..

    • (Score: 0) by Anonymous Coward on Friday June 17 2016, @05:03PM

      by Anonymous Coward on Friday June 17 2016, @05:03PM (#361654)

      YES, install on ISS and push it to Mars!! Big mobile warehouse.

  • (Score: 0) by Anonymous Coward on Friday June 17 2016, @01:04AM

    by Anonymous Coward on Friday June 17 2016, @01:04AM (#361345)

    So it squirts out photon pairs in all directions, but a bit more in one.

    Doesn't sound like a very efficient engine.

    The article is an easy read. Wish the climate folks were so gifted.

    • (Score: 3, Informative) by takyon on Friday June 17 2016, @01:26AM

      by takyon (881) <reversethis-{gro ... s} {ta} {noykat}> on Friday June 17 2016, @01:26AM (#361354) Journal

      There's a figure for efficiency: Newtons per Watt. If the thing works, it will become clear if it can compete with state-of-the-art ion drives like VASIMR [wikipedia.org].

      Newtons per Watt isn't necessarily the whole story since emdrive also has the advantage of being "propellantless" (assuming it works). But I have heard talk about emdrive reaching anywhere from 4 times to hundreds of times the Newtons per Watt of ion drives, which would make a clear difference.

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      • (Score: 1, Interesting) by Anonymous Coward on Friday June 17 2016, @01:56AM

        by Anonymous Coward on Friday June 17 2016, @01:56AM (#361362)

        Adding-

        there all different types of efficiency from volumetric efficiency, fuel efficiency, etc. (at least as applied to IC engines).

        Depending on what this drive brings to the table (weight, output, reliability, fuel use), it could be a huge win even if it has low output.

      • (Score: 0) by Anonymous Coward on Friday June 17 2016, @12:06PM

        by Anonymous Coward on Friday June 17 2016, @12:06PM (#361498)

        While ion drives are electric, they still use propellant, usually Xenon. The electricity is used to accelerate the propellant out the exhaust. When the tank is empty, the engine is useless.

        The interesting thing about this, is that it's electric only. No propellant. And electricity can be "refueled" on the fly with solar panels. That means that - if it works - it can run forever.

        While getting into orbit takes huge rockets, due to air resistance, once you are in orbit, the size of the rocket doesn't matter. What matters is thrust multiplied by time. Think about how an engine that can run forever affects the result of that calculation.

        • (Score: 0) by Anonymous Coward on Friday June 17 2016, @02:10PM

          by Anonymous Coward on Friday June 17 2016, @02:10PM (#361543)

          >That means that - if it works - it can run forever.

          Like fucking hitler.

          Fucking Nazi.

        • (Score: 2) by takyon on Friday June 17 2016, @04:23PM

          by takyon (881) <reversethis-{gro ... s} {ta} {noykat}> on Friday June 17 2016, @04:23PM (#361616) Journal

          Yes... I noted that it was propellantless in the comment.

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  • (Score: 0) by Anonymous Coward on Friday June 17 2016, @01:33AM

    by Anonymous Coward on Friday June 17 2016, @01:33AM (#361356)

    Everybody knows gravitic drive is the best, and you can recycle its exhaust to power your antigrav deck plating.

  • (Score: 1, Funny) by Anonymous Coward on Friday June 17 2016, @01:51AM

    by Anonymous Coward on Friday June 17 2016, @01:51AM (#361360)

    So how could something come out that you can't detect? Well, the photons bounce back and forth inside the metal cavity, and some of them end up going together in the same direction with the same speed, but they are 180 degrees out of phase. Invariably, when travelling together in this out-of-phase configuration, they cancel each other's electromagnetic field out completely.

    ....undetectable paired photons ...have mass-energy ... can't see them ... ... Holy Shit Batman, I've discovered Dark Energy.
    Massive amounts of aliens are zooming around the cosmos on EmDrives and have filled it up with paired photons.

    Where do I go to get my Nobel?

  • (Score: 3, Interesting) by deimtee on Friday June 17 2016, @01:57AM

    by deimtee (3272) on Friday June 17 2016, @01:57AM (#361364) Journal

    Wouldn't mean that you could get just as much thrust by using the same electric power to run a MASER? If the EmDrive is getting more thrust than a MASER would, then there is still some unexplained physics going on.

    --
    If you cough while drinking cheap red wine it really cleans out your sinuses.
    • (Score: 0) by Anonymous Coward on Friday June 17 2016, @02:23AM

      by Anonymous Coward on Friday June 17 2016, @02:23AM (#361370)

      What seems to be going on is phased photons provide more thrust just like laser beams are more coherent than flashlight beams.

      • (Score: 0) by Anonymous Coward on Friday June 17 2016, @02:32AM

        by Anonymous Coward on Friday June 17 2016, @02:32AM (#361373)

        That would violate conservation of momentum, so no.

        • (Score: 0) by Anonymous Coward on Friday June 17 2016, @02:12PM

          by Anonymous Coward on Friday June 17 2016, @02:12PM (#361545)

          OH SNAP!

          Soljua boy tell em!

  • (Score: 0) by Anonymous Coward on Friday June 17 2016, @05:35AM

    by Anonymous Coward on Friday June 17 2016, @05:35AM (#361421)

    > That's the same as water waves travelling together so that the crest of one wave is exactly at the trough of the other and cancelling each other out. The water does not go
    > away, it's still there, in the same way the pairs of photons are still there and carrying momentum even though you can't see them as light.

    This analogy says exactly the opposite of what is intended. Water waves transport energy (and probably momentum, I am not sure); flat water, which is equal to two waves superposed in opposite phase, does not. It unintentionally elucidates the paper because the author is explicitly saying that photons are *not* like water waves, in that they can carry momentum while being superposed in this way - from the paper: "Thus, our explanation complies with conservation of momentum but departs from the current consent about photons by regarding photons as indivisible and indestructible basic building blocks of nature."

    • (Score: 0) by Anonymous Coward on Friday June 17 2016, @07:50AM

      by Anonymous Coward on Friday June 17 2016, @07:50AM (#361449)
      Photons are not "indestructible". Far from it. Photons are created and destroyed all the time in interactions with matter. An excited electron in an atom creates a photon when it falls from a higher energy level to a lower one. There is also the photoelectric effect, where a photon hits an electron, destroying it in the process, but passing on its momentum. A high-energy photon can interact with a heavy atomic nucleus and materialise into an electron-positron pair. Similarly, a positron and an electron can collide and produce two high-energy photons.
      • (Score: 2) by HiThere on Friday June 17 2016, @07:04PM

        by HiThere (866) Subscriber Badge on Friday June 17 2016, @07:04PM (#361737) Journal

        Not clear. IIUC, some models say that photons are absorbed rather than destroyed by energy absorption, and thus when they are emitted, they are actually being re-emitted from a previously absorption.

        So creation and destruction may not happen. This probably depends on exactly what photons are. If they are just packets of energy, then it works fine, but photons also have spin, so I'm not sure that it does (or doesn't) work.

        *IF* photons are just packets of energy, or even essentially packets of energy, then they can neither be created nor destroyed, only absorbed or emitted. But polarization makes this messier, so perhaps you can disassemble a photon into energy (absorbed into one process) and spin (absorbed into another). If so, I've never heard of this being done, but I'm not a specialist in this area...or even in physics.

        Still, my first guess is that photons are neither created nor destroyed.

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  • (Score: 1, Informative) by Anonymous Coward on Friday June 17 2016, @06:41AM

    by Anonymous Coward on Friday June 17 2016, @06:41AM (#361433)

    I am a physicist.
    I have no idea how this got past peer review; I guess I have to start doubting AIP journals in general.

    The concept of photons that cancel each other's EM fields makes no sense. If something like this could happen, we would have seen it before.

    First thing: as another poster noted, this would mean the EM drive is no better than just pointing a laser/maser whatever in some direction, and then happily accelerating the other way (which is perfectly possible and real, except that the acceleration is minuscule).

    Second thing: two photons overlapping exactly would mean that their location is "known" with infinite precision (it's known by the other photon). That would mean that their momentum could have any value possible, just because of Schrodinger. Being photons, their energy is proportional to the momentum, therefore the probability of the two photons having the same energy (thus the EM fields cancelling each other out) is zero.

    Luckily, this EM drive thing is testable. I say we should not spend any public funds on testing it, but if there are enough idiots out there to believe it's worth investing time and money, whatever. I will be the one only checking the news from time to time to laugh when they finally admit it's a scam.

    • (Score: 0) by Anonymous Coward on Friday June 17 2016, @07:03AM

      by Anonymous Coward on Friday June 17 2016, @07:03AM (#361441)

      Second thing: two photons overlapping exactly would mean that their location is "known" with infinite precision (it's known by the other photon).

      Umm, no. It means that the wave functions of the two photons are exactly opposite in phase. It is the opposite of how a laser works. Photons produced by lasers are just about exactly in phase, which is why their light is so coherent and so bright because their wave functions experience constructive interference. According to the article the photons generated are just about exactly out of phase, and so their wave functions experience destructive interference and as such there is hardly any electromagnetic field at all. You fail elementary quantum mechanics.

      • (Score: 0) by Anonymous Coward on Friday June 17 2016, @03:34PM

        by Anonymous Coward on Friday June 17 2016, @03:34PM (#361602)

        fucking made me read the fucking article.
        article is junk, like I said.

        there are a total of 4 equations, with a bunch of handwaving for 8 pages, no actual proofs.

        I really have no idea how this article passed peer review.

    • (Score: 0) by Anonymous Coward on Friday June 17 2016, @08:07AM

      by Anonymous Coward on Friday June 17 2016, @08:07AM (#361455)

      Here is a thought experiment; consider two EM waves with nearly equal phase; we get the classical interference pattern. Now consider the effect in the limit that the two phases approach each other; we get peaks and troughs in the interference pattern (beat pattern), with the beat wave length large (infinite in the limit of two phases equal). This is like neutrino oscillation.

    • (Score: 0) by Anonymous Coward on Friday June 17 2016, @08:46AM

      by Anonymous Coward on Friday June 17 2016, @08:46AM (#361463)

      If something like this could happen, we would have seen it before.

      I have a feeling of scientific déjà vu.

      • (Score: 0) by Anonymous Coward on Friday June 17 2016, @10:16AM

        by Anonymous Coward on Friday June 17 2016, @10:16AM (#361479)

        It's called the Double Penetration Experiment.

    • (Score: 2) by GreatAuntAnesthesia on Friday June 17 2016, @09:34AM

      by GreatAuntAnesthesia (3275) on Friday June 17 2016, @09:34AM (#361469) Journal

      > Second thing: two photons overlapping exactly would mean that their location is "known" with infinite precision (it's known by the other photon). That would mean that their momentum could have any value possible, just because of Schrodinger.

      OK, so to vreate your magic spacedrive you get two photons overlapping exactly, and then you persuade them to choose the highest of the possible values for momentum using a photonic vector plotter suspended in strong brownian motion producer (say, a nice hot cup of tea)...

      • (Score: 0) by Anonymous Coward on Friday June 17 2016, @09:50AM

        by Anonymous Coward on Friday June 17 2016, @09:50AM (#361474)

        Presto changeo. Infinite improbability drive.

  • (Score: 0) by Anonymous Coward on Friday June 17 2016, @08:11AM

    by Anonymous Coward on Friday June 17 2016, @08:11AM (#361456)

    well heres some crackpot.
    i think everyone ligo agrees that space can have a geometry. so it's bendable.
    i think every one also agrees that light lives "inside" space, that is, if space is flat then light goes straight, but if space is bent then light trajectory will be bend also ( something called a geodesic? )

    so for now we always have concentrated on space and embedded mass and shot light through it to measure and observe it (space).

    but what if we turn it around? what if we ignore space and mass geometrics and instead try to devise a way to bend light instead ... will the space then bend tooo, in response?

    if it walks like a duck, quaks like a duck it probably is a duck.

    i would like to hope that this new device uses light to bend space (and probably time too)...

    note: it is tough going for new physics so please forgive if this might not help much to further support of this new propulsion type ...

    • (Score: 2) by Immerman on Friday June 17 2016, @03:23PM

      by Immerman (3985) on Friday June 17 2016, @03:23PM (#361594)

      Yep, all you need to do is something impossible, and then you can do impossible things.

      How exactly would you bend light? You have to apply a force, and then the light is just bending in response to the force.. which is something it does all the time. May as well make it more mundane - throw a baseball in a vacuum and it will likewise follow a geodesic. So, just bend its path without applying a force, and maybe you bend the geodesic as well?

  • (Score: 0) by Anonymous Coward on Friday June 17 2016, @08:26AM

    by Anonymous Coward on Friday June 17 2016, @08:26AM (#361461)

    so its basically the opposite of what a laser does?

  • (Score: 3, Interesting) by opinionated_science on Friday June 17 2016, @12:50PM

    by opinionated_science (4031) on Friday June 17 2016, @12:50PM (#361509)

    This guy has worked up a nice model of the phenomena...

    http://physicsfromtheedge.blogspot.in/2016/06/a-smoking-gun-in-every-galaxy.html [blogspot.in]

  • (Score: 3, Interesting) by opinionated_science on Friday June 17 2016, @01:04PM

    by opinionated_science (4031) on Friday June 17 2016, @01:04PM (#361515)
  • (Score: 0) by Anonymous Coward on Friday June 17 2016, @02:05PM

    by Anonymous Coward on Friday June 17 2016, @02:05PM (#361536)

    No new physics :(