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Finnish Scientist Provides Another Explanation For The 'Impossible' EM Drive (examiner.com) 299

MarkWhittington quotes a report from Examiner: Ever since the EmDrive entered the news about a year or so ago, it has sparked considerable controversy. The device is alleged to work by using microwaves that produce, in some fashion as yet unknown to science, thrust. Many scientists suggest that the EM drive is impossible as it violates known physics. However, a number of tests conducted in Great Britain, Germany, China, and at NASA's Eagleworks at the Johnson Spaceflight Center have resulted in thrust that cannot, as yet, be explained by experimental error. The International Business Times reported that a Finnish scientist has published an article in a peer-reviewed science journal with a possible explanation as to how the drive works. International Business Times writes, "A new peer-reviewed paper on the EmDrive from Finaland states that the controversial electromagnetic space propulsion technology does work due to microwaves fed into the device converting photons that leak out of the closed cavity, producing an exhaust. The research, entitled "On the exhaust of electromagnetic drive," is published in the journal AIP Advances 6 and is the brainchild of Dr Arto Annila, a physics professor at the University of Helsinki; Dr Erkki Kolehmainen, an organic chemistry professor at the University of Jyvaskyla; and Patrick Grahn, a multiphysicist at engineering software firm Comsol."
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Finnish Scientist Provides Another Explanation For The 'Impossible' EM Drive

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  • by Crashmarik ( 635988 ) on Thursday June 16, 2016 @10:35PM (#52333591)

    Unless the photons are perfectly out of phase and co linear you will get interference patterns on all three axes. Seeing as they are microwave photons that should make them nice large and obvious.

    • by flyingfsck ( 986395 ) on Friday June 17, 2016 @12:19AM (#52333819)
      Well, maybe you should read the article. They postulate that the exhaust is indeed paired photons, which are impossible to observe. I'm just not convinced that such an EM drive will be more efficient than simply placing a lump of decaying matter at the focus of a reflector and using ordinary infrared photons as the drive.
      • by jeepies ( 3654153 ) on Friday June 17, 2016 @01:17AM (#52333925)
        That's not how destructive interference works in the EM field. The photons at a point of destructive interference are diverted to area of constructive interference. They don't continue on as an unobservable photon pair. A point of destructive interference in a wave means the photons aren't there. In terms of the wave equation it means the probability of finding a photon at that location is 0. That's not because photons masking each other, it's because physically they are never present at that point.
      • by silentcoder ( 1241496 ) on Friday June 17, 2016 @03:43AM (#52334377)

        Assuming the theory is correct, you may be right. But this is a new theory - and key to it is that it means the EM-drive does, in fact, have an exhaust - it's just that the exhaust is mass-less photons rather than matter. But the whole reason we have the name 'photon' is because light behaves so much like a particle to begin with - and photons are known to have momentum after all.

        That said, since it's apparently able to convert something like sunlight into useful thrust without fuel - it could, in theory, keep providing thrust for many centuries (well until something hits or damages it). Your decaying matter will be useful only as long as the fuel remains(but may provide more thrust since the particles it exudes have mass which hugely increases their momentum). Then again - depending what you use, quite a lot of decaying matter have half-lives in the thousands-of-years category.

        All that said - assuming both technologies prove viable, you can expect more prosaic and immediate concerns to dominate the decision - like what happens if something goes wrong and the damn thing crashes to earth. Space agencies tend to be rather reticent about putting things in orbit which, if they crash, could spread highly reactive material around the area they land in. This is why RTG's tend to only be used on long-range space-probes, the only risk of spreading that plutonium on the planet is if it crashes during launch.

        Having said all that - if we imagine an EM-drive which uses solar-power to produce microwaves to produce photons to produce miniscule levels of thrust - well magnetrons are fairly heavy, and the parts in there are quite pricey... would you not be able to do it more cheaply for about the same weight (if not volume) by skipping all the intermediary steps and just fitting the satelites with solar sails ?

      • The bigger problem is the question of trust-to-power ratio. Specifically, the fact that the EMDrive exhibits way too much thrust-to-power to be a photon drive unless the photons are *way* more energetic than microwave photons. The momentum of a photon is a function of the photon's frequency (or, inversely, wavelength), and the momentum is also proportional to the energy. This means it's pretty easy to compute the maximum possible force from a given frequency of EM radiation at a given power level (assuming

    • by goombah99 ( 560566 ) on Friday June 17, 2016 @12:59AM (#52333893)

      Their claim, to my ears, is even more ludicrous than the EM drive itself. What they say is that if two photons co-propogate with opposite phase they exist in the sense of carrying momentum and energy but they can't intereact with anything like say the wall. Isn't his bananas? the dark nodes of an interference pattern don't contain any ray-like photons. they seem to be saying it does. Now one can argue what's a photon? ie. can we really talk about ray-like photons (photons going along an axis), or do we need to talk about full 3D modes which are the eigen modes of the cavity. However in either case this seems bananas to me. if two photons are canceling it's the same as no photons. the energy didn't disappear, it just was reflected at the time you injected the second photon. you do not get two photons co-propagating out of phase like they claim.

      Some one please explain this seeming madness.

      • Your understanding is correct. There are no photons at a point of destructive interference. Co-propagating out of phase photons makes no sense what so ever.
        • If two out of phase photons, carrying momentum, cancel each other out and 'cease to exist', what happened to the momentum?

          If that, too, ceased to exist, and all the cancelled photons were going in the same direction, it would have a net effect on the momentum of the drive.

          • Elementary E&M. The EM field, quantum or not, "particle like" or not, is a FIELD. If you set up the two slit experiment there are places on the screen where the fields from two coherent sources (slits) are out of phase and no energy or momentum is transferred. Even if you turn the intensity down to where one "photon" at a time goes through the pair of slits (yes, it goes through BOTH slits, or at least the FIELD does) the photons appear only in the BRIGHT bands where the fields are IN phase. No ene

          • Photons don't cancel each other out. A point of destructive interference in the EM field is a place where photons are not physically present, not a place where they met and ceased to exist. Where do the photons go? They go to points of constructive interference.

            Interference just causes the photons to be somewhere else: points of constructive interference, not oblivion. I was going to type up the double slit experiment but someone beat me to it. Their explanation is correct.

            Simply put the article
      • by Z00L00K ( 682162 )

        Go to ludicrous speed [youtube.com].

    • Large and obvious elementary particle, what sort of Universe do you live in?

  • by Crashmarik ( 635988 ) on Thursday June 16, 2016 @10:42PM (#52333605)

    Recent reports about propulsion without reaction mass have been met on one hand with enthusiasm and on the other hand with some doubts. Namely, closed metal cavities, when fueled with microwaves, have delivered thrust that could eventually maintain satellites on orbits using solar power. However, the measured thrust appears to be without any apparent exhaust. Thus the Law of Action-Reaction seems to have been violated. We consider the possibility that the exhaust is in a form that has so far escaped both experimental detection and theoretical attention. In the thruster’s cavity microwaves interfere with each other and invariably some photons will also end up co-propagating with opposite phases. At the destructive interference electromagnetic fields cancel. However, the photons themselves do not vanish for nothing but continue in propagation. These photon pairs without net electromagnetic field do not reflect back from the metal walls but escape from the resonator. By this action momentum is lost from the cavity which, according to the conservation of momentum, gives rise to an equal and opposite reaction. We examine theoretical corollaries and practical concerns that follow from the paired-photon conclusion.

    Relevant portion of abstract bolded

    • The electromagnetic field strength is linked to the energy density of the field. If the electric fields from the photons cancel in some location, then there is no energy density in that location and no probability of finding a photon there. If the photon fields cancel at the metal, then there is nothing to escape. eg. the article doesn't make any sense at all.

      Conservation of (relativistic) momentum is conserved in all particle interactions - even in quantum mechanics. The only way the EM drive can work is

      • The only way the EM drive can work is if there is entirely new physics.
        All articles I have read explain it with standard physics. Perhaps I missed something, care to point it out?

        It is as certain as anything is in science that the EM drive cannot work.
        So far you failed to explain, why it can't work.

        Why don't you simply read the theories about it and debunk it for us, so we can share your wisdom?

        • In the article they say "These photon pairs without net electromagnetic field do not reflect back from the metal walls but escape from the resonator" This doesn't make sense. If the electromagnetic fields from the photons cancel, then the energy density and probability of finding a photon vanishes. There is nothing in that location to escape.

          The more general argument is that all known physics (including quantum, gravity and relativity) conserves momentum (4-momentum if you are using relativistic terms). S

          • Your argumentation makes no sense.

            If the photons vanish as you claim in your first part, then obviously the momentum is conserved, contrary to your claim in the second part.

            You can not start arguments with claims and then turning them around to explain why something is not working.

            I suggest to start with the conversation of momentum, and then work backward. Explain us why momentum is not conserved when every physicist involved in this drive is explaining us: it is. If it was not conserved: the drive would n

            • To be clear I was quoting the article's INCORRECT description.

              In locations where the photons fields vanish, the energy density vanishes. The probability of finding photons IN THOSE LOCATIONS goes to zero. Think of it as waves - if I drop two rocks in the water, there will be places where the waves interfere and there is not wave amplitude. That means that there are no waves in that location, but it doesn't mean that all the waves have vanished everywhere.

              I believe that the drive is not in fact working. T

    • by jeepies ( 3654153 ) on Friday June 17, 2016 @01:08AM (#52333909)
      The author of that paper clearly does not understand how constructive and destructive interference work in the EM field. He's correct that the photons do not simply disappear when there is destructive interference, however they are diverted to areas of constructive interference and this would not allow them to leave the cavity of the device if they otherwise couldn't.

      What they wrote in the paper may sound good to someone who has a passing knowledge of EM fields and constructive/destructive interference in waves, but to someone who understands this more clearly it makes about as much sense as asking a mechanic to change your blinker fluid.
    • by gweihir ( 88907 )

      Well, if they are right then something good came from this thing after all. This is also the first explanation that at least sounds as it could hold water.

  • If the theory is correct, then researchers will actually know how the damned thing works. That should allow allow them to make the drive much more efficient.

    • by wierd_w ( 1375923 ) on Thursday June 16, 2016 @10:57PM (#52333637)

      There's one problem though...

      I seem to recall that the net thrust exhibited by the em-drive is greater than the photon pressure of the microwaves. if the thrust was being produced by cancelling photon pairs escaping the system, then it would be some fraction of that potential, not greater than.

      I can see this explaining SOME of the thrust, but the deal breaker is the thrust being higher than the photon pressure of the microwaves it runs on. (Else, it would be easier and more efficient to just aim the magnetron's waveguide out the back of the ship.)

      Shawyer's non-peer reviewed "quantized inertia" explanation that abuses unruh radiation is more likely to explain the greater thrust values (and also makes some testable predictions.)

  • No No No (Score:5, Funny)

    by Greyfox ( 87712 ) on Thursday June 16, 2016 @11:07PM (#52333675) Homepage Journal
    Clearly running the microwave creates a virtual quantum burrito. As long as there's a burrito in the microwave, thrust is guaranteed to be generated,shortly!
    • I dont see "quantum burrito" on the standard menu-- Is this something you have to ask the universe for directly?

    • Yes, but until you eat the burrito you are not sure exactly how much thrust there is going to be.

  • I love when we find stuff that defies what we know about the known universe. It could open up all sorts of new discoveries if found to be legit. I wonder if Elon will plop one of these things in space with an on switch hit.
  • Next we need research on how the flux capacitor works.

  • by fzammett ( 255288 ) on Friday June 17, 2016 @12:37AM (#52333853) Homepage

    You've got a cavity. Inside you pump some energy. The energy is nominally trapped and bounces around. Eventually, some of it finds its way out in a coherent way. Seems like the paper is describing a similar explanation as to how LASERs work, roughly-speaking. Sounds plausible for sure.

    • Comment removed based on user account deletion
    • Re: (Score:2, Informative)

      by thegarbz ( 1787294 )

      It's like a LASER with microwaves. Dare I say a MASER? :-)

    • I have a cavity. I pump energy into it, in the form of some small bits of food (chewing would be a better term than pumping). This energy is trapped, but it sticks rather than bouncing around.

      Eventually it finds its way out, via a dentist, in some coherent way. The cavity is also filled.

      Please, dear god, please don't let there be lasers involved!

      Anyway, I apologize, I just had to...

  • The explanation is that it works by Swimming through Spacetime [brophy.net].

  • How did he conceive it in the first place? I mean, surely he didn't invent it by accident, provided that its effects are so little that they must be measured by NASA in their labs, so I presume he knew what he was doing and what physical laws he was looking for. Unless he is an alien or a man from the future and he can not tell us the truth, of course.
  • pfff.. (Score:4, Insightful)

    by SuperDre ( 982372 ) on Friday June 17, 2016 @03:55AM (#52334413) Homepage

    All it shows is that our knowledge of physics is just very limited.. Laws of physics are only a template to try to explain stuff, it isn't set in stone, it's just our (lack of) understanding of physics..

  • Dirk Gently (Score:4, Insightful)

    by mlwmohawk ( 801821 ) on Friday June 17, 2016 @05:46AM (#52334663)

    Sherlock Holmes: "Once you have discounted the impossible, then whatever remains, however improbable, must be the truth"
    Dirk Gently: "The impossible often has a kind of integrity to it which the merely improbable lacks."

    I'm not ready to give up on a plausible answer based on physics we understand, it may be that it is doing something we understand and we are simply not realizing it.

  • So, all we need to do is shine a flashlight out the back of the spaceship and we are good to go?
  • The explanation for the photons escaping the cavity sound similar to the comments by Tesla about longitudinal waves versus regular transverse waves being attenuated.

  • Comment removed based on user account deletion

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