back to article 'Impossible' EmDrive flying saucer thruster may herald new theory of inertia

An explanation for Roger Shawyer's seemingly impossible EmDrive has been offered. The RF resonant cavity thruster was first proposed by British aerospace engineer Roger Shawyer in 1999. It bounces microwaves around within a cone-nosed container, with the container moving in the direction of the cone end. Despite skepticism …

  1. bombastic bob Silver badge

    I think _I_ can explain it (and it's not that hard)

    Well, _I_ think that _I_ can explain it. And it's not that hard.

    Momentum IS being conserved, because it is SPEWING PARTICLES. Either that, or it's creating a gravity effect.

    If you were to shine a light in a particular direction in outer space, you'd create thrust due to the photons going at 'C' and of course their effective mass in an 'mv' momentum equation. This is well known.

    The obvious answer HERE is that there are particles being emitted. Microwave energy is a form of 'gamma'. now, that cone shaped thing just might be acting like a WAVE GUIDE of sorts, and JUST MIGHT be impedence coupling the gammas to "the air".

    Alternatively...

    There's some thought about a spinning disk causing relativistic effects due to a couple of physics properties. First, the NET velocity of a spinning disk is zero (this is why there's 'rotational velocity' and 'rotational momentum' to explain THOSE things). HOWEVER... the individual points on the disk exhibit instantaneous velocities that *MIGHT* result in RELATIVISTIC effects - you know, like mass increasing, time dilating, that sort of thing. BUT - the NET effect is ZERO because it's a solid piece of 'stuff'.

    Some experiments have been reported (though I can't find the web sites any more) that SUGGEST that a fast spinning disk may cause 'graviton emission' or 'gravity wave emission' (your choice, wave/particle, tomayto/tomahto) due to this somewhat self-contradicting "relativistic effect" of a spinning disk. A disk spinning horizontally might cause 'gravity shielding' or some other effect on items suspended above it, which REPORTEDLY WEIGH LESS by a measurable, though small, amount (according to the reports I read maybe a decade or so ago). This is, of course, 'Coast to Coast AM' material so take it for what it's worth. But so is *THIS* device.

    And so I'm suggesting that *IF* in fact the magnetron is energizing air, and 'spinning' it in the resonant cavity, that the 'spin' _MIGHT_ be causing gravitons to be emitted. Or it could be bremstralung, which would ALSO create a possible gamma source for 'shining a light' momentum effect.

    To prove this, fill the resonant cavity with high pressure Xenon gas. THAT might actually create a REAL graviton field. Or not. Provocative, no?

    1. PNGuinn
      Coat

      Re: I think _I_ can explain it (and it's not that hard)

      Mmm ... A microwave oven in spaaace......

      So - is it cooked tomayto or tomahto?

      Enquiring minds etc...

      El reg - we need a tomayto/tomahto in a vacuum icon. Cooked, of course.

      Thanks - it's the one drifting slowly round the lab with the slightly fluffy toasted sandwich in the pocket

    2. John H Woods Silver badge

      Re: I think _I_ can explain it (and it's not that hard)

      "of course their effective mass in an 'mv' momentum equation. This is well known." --- bombastic bob

      Almost as well known as that m=0 for a photon: photon momentum is not mv. So you are not really chucking any "stuff" out of the back in the conventional sense.

      1. bombastic bob Silver badge

        Re: I think _I_ can explain it (and it's not that hard)

        actually, m!=0 for a photon. its effective mass is a function of frequency/energy of the particle.

        http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/photon_mass.html

        zero "rest mass" would be more accurate.

        the photon mass is involved in how gravity affects it, and was part of the proof of Einstein's theory of relativity back in the day, when stars were observed to have "moved" due to their relative position near the sun during an eclipse. Predicting that was part of Einstein's theory, and so when it was finally observed, it proved his relativity theory was correct. FYI.

        (and if photons were truly 'massless', gravity would not affect them)

        1. Paul Hovnanian Silver badge

          Re: I think _I_ can explain it (and it's not that hard)

          "actually, m!=0 for a photon"

          Right. For a photon, momentum is equal to Planck's constant divided by the photon's wavelength.

          Which gives rise to an interesting idea: If this microwave powered EM drive produces thrust based upon such a low momentum (long wavelength), what could be achieved with shorter wavelengths, i.e lasers? I'm sure the relative efficiencies between microwave production (magnetrons or traveling wave tubes) compared to light emitting devices is a factor. But we are getting much better at making efficient LEDs.

        2. frank ly Silver badge

          Re: I think _I_ can explain it (and it's not that hard)

          "(and if photons were truly 'massless', gravity would not affect them)"

          Gravity, caused by the presence of matter, makes space itself curved and so a photon follows the curvature of space as it travels. The question is, has anyone performed experiments on trapped photons to determine if they are affected by gravity (attracted to matter) when they are fairly stationary?

          If you're equating the energy of a photon to an 'effective mass' via an e=mc^2 equivalence, then you'd have a situation in which X-ray photons have a larger effective mass than light photons and hence should be deflected more by gravity.

          I'll wait for the next commentard to add to this thread by explaining why I'm wrong.

          1. Chemist

            Re: I think _I_ can explain it (and it's not that hard)

            "If you're equating the energy of a photon to an 'effective mass' via an e=mc^2 equivalence"

            Which you shouldn't really AFAIK. A particle of zero rest mass has no increase in mass with velocity - indeed it is constrained to travel at c at all times in a vacuum.

            1. Brewster's Angle Grinder Silver badge

              @Chemist

              "Which you shouldn't really AFAIK. A particle of zero rest mass has no increase in mass with velocity - indeed it is constrained to travel at c at all times in a vacuum."

              No, he's right. GR has no notion of mass; its defined in terms of energy and momentum (cf the Stress-Energy tensor) and it's the energy that shapes the metric ("distorts spacetime"). So every particle and non-gravitational field distorts spacetime. (And if the gravitational field itself could distort spacetime then that might explain dark matter.)

              The reason we talk about rest mass is precisely because a particle has an "effective mass" or "relativistic mass" that depends on the relative speed between it and you. It's that effective mass that means two observers travelling at different speeds end up agreeing that a particle has the same total energy, even though they disagree about its kinetic energy (speed).

              1. Chemist

                Re: @Chemist

                "The reason we talk about rest mass is precisely because a particle has an "effective mass" or "relativistic mass" "

                I know why we talk about rest mass - the point is that a photon has no mass otherwise it couldn't travel at c.

          2. Brewster's Angle Grinder Silver badge

            @frank ly

            "...if they are affected by gravity (attracted to matter) when they are fairly stationary?"

            Photons are never stationary; however much you confine them, they'll still bounce around at the speed of light. Being massless means travelling at the speed of light; no ifs or buts.

            "If you're equating the energy of a photon to an 'effective mass'...then you'd have a situation in which X-ray photons...should be deflected more by gravity."

            This argument turns out to be the same as arguing heavier masses experience greater acceleration than lighter ones, which Galileo disproved. Do the full calculations and you'll see the angle of deflection is independent of mass. (And we can check this by looking for chromatic aberration in gravitational lensing which, AFAIK, isn't seen.)

            However Bob is right inasmuch as photons do distort space time. If that wasn't the case, ~90% of the mass in a proton wouldn't count for gravity (since only ~10% of the rest mass of a proton is due to the rest mass of its constituent quarks). But the distortion caused by a photon is negligible: we can't even measure the gravitational interaction between protons, and they have a rest mass of ~1GeV.

          3. john R

            Re: I think _I_ can explain it (and it's not that hard)

            Photons are never "fairly stationary", they travel at the speed of light.

            In Newtonian terms, an object twice as heavy does experience twice the gravitational force but it also requires twice the force to accelerate it.

            In terms of GR space-time is curved so there is no such thing as a straight line. The closest thing is a "geodesic". (For example the shortest route between two points on Earth is an arc of a Great Circle). So in GR the paths of photons trace geodesics in curved space-time.

            Think of ships wanting to follow the shortest route between ports on different sides of an ocean with no currents. It's the same path irrespective of the size of the ship.

          4. Paul Hovnanian Silver badge
            Boffin

            Re: I think _I_ can explain it (and it's not that hard)

            "If you're equating the energy of a photon to an 'effective mass' via an e=mc^2 equivalence, then you'd have a situation in which X-ray photons have a larger effective mass than light photons and hence should be deflected more by gravity."

            But the higher (effective) mass particle requires more force to accelerate (deflect) the same amount as a lighter particle. So the higher m (for either a real particle or photon) cancels out of the equation.

            Same reason a feather and a hammer fall at the same rate (on the moon).

          5. Jaybus

            Re: I think _I_ can explain it (and it's not that hard)

            "has anyone performed experiments on trapped photons to determine if they are affected by gravity (attracted to matter) when they are fairly stationary?"

            Well, the the current theory of gravitation is based on Einstein's theory of general relativity. Due to the equivalence of energy and mass, anything that has energy is also affected by gravity. In this case, the photon has momentum, and so has kinetic energy, and so is affected by gravity.

        3. Chemist

          Re: I think _I_ can explain it (and it's not that hard)

          "the photon mass is involved in how gravity affects it, and was part of the proof of Einstein's theory of relativity back in the day, when stars were observed to have "moved" due to their relative position near the sun during an eclipse."

          No it wasn't ! Einstein's theory of gravity involves mass/energy curving spacetime and light then following the shortest path in that spacetime.

        4. Anonymous Coward
          Anonymous Coward

          Re: I think _I_ can explain it (and it's not that hard)

          "and if photons were truly 'massless', gravity would not affect them"

          Didn't we enter the post "gravity is two objects of a certain mass attracting each other" era a looong time ago or have we kicked off the Newtonian debate again?

      2. D 13

        Re: I think _I_ can explain it (and it's not that hard)

        "Almost as well known as that m=0 for a photon: photon momentum is not mv. So you are not really chucking any "stuff" out of the back in the conventional sense."

        The momentum of a photon is described by the De Broglie relation as being Planck's constant divided by it's wavelength.

      3. Vic

        Re: I think _I_ can explain it (and it's not that hard)

        Almost as well known as that m=0 for a photon

        There's a bit more detail about this "explanation" over here.

        This bit caught my eye towards the end:

        McCulloch’s theory could help to change that, although it is hardly a mainstream idea. It makes two challenging assumptions. The first is that photons have inertial mass. The second is that the speed of light must change within the cavity.

        So, for this theory to hold water, photons must have m0 != 0. According to special relativity, that makes achieving lightspeed somewhat problematic. And that's not a good situation for photons...

        I'll let someone else go into the "c is not constant" aspect.

        Vic.

    3. Captain DaFt

      Re: I think _I_ can explain it (and it's not that hard)

      "I think _I_ can explain it (and it's not that hard)"

      I go with a simpler theory.

      It's actually remaining stationary and moving the universe around it!

      (What? Nobody remembers Futurama?)

      1. IT Poser

        Re: What? Nobody remembers Futurama?

        I first remember seeing that idea in a Star Trek novel I read in the mid-80s. I'm sure another commentard knows of something much earlier*.

        *I swear that is the reason I didn't bother to look up the title, not that I'm lazy.

    4. werdsmith Silver badge

      Re: I think _I_ can explain it (and it's not that hard)

      Well, _I_ think that _I_ can explain it. And it's not that hard.

      The whole scientific world has been missing a trick all this time. All that scientific methodology BS can go in the bin. All they ever needed to do is ask any question on the The Register and the answer will be forthcoming in pretty short order.

      Next on the agenda will be: Simple nuclear fusion at room temperature in a starbucks cup and anti-gravity bricks. And while you are there, could you bottle up some dark matter. Thanks dear.

    5. Nightkiller

      Re: I think _I_ can explain it (and it's not that hard)

      The person that REALLY understands this is not writing about it. They are busy building the damn thing and getting the hell out of Dodge.

      1. 9Rune5

        Re: I think _I_ can explain it (and it's not that hard)

        Who, the dolphins?

    6. Penguin7

      Re: I think _I_ can explain it (and it's not that hard)

      Well, I actually CAN explain it, and its not that hard. But it MAY require that you part with some treasured, but unsubstantiated, notions about electromagnetic phenomena, or anyway at least ONE widely-held belief. But before I tell you what that belief is, let me mention that several of the most revered physicists of all time did not hold that belief. The list includes Michael Faraday and James Clerk Maxwell, in part because they did their famous work before quantum theory came into existence. There are also a few more recent physicists who also do not cling to the aforementiond belief, but I don't want to name names because I may misremember them.

      The belief I am talking about is that all EM energy is ambiguous about whether it is in the form of waves or particles, namely photons. Nope, sorry, not true. Radio waves, including microwaves, generally DO NOT involve photons at radio frequencies. WBZ, in Boston, or WBT, in Charlotte, NC, generate purely WAVE signals, at 1030 KHz and 1100 KHz, respectively. No photons need apply, though all are welcome if they find an opportunity to absorb the requisite amount of energy (E=hf is the familiar formula for the energy of a single photon at frequency f Hz, replacing the usual "nu" of physics notation, since "f" is more familiar to engineers, but more importantly available on my keyboard and useable in ASCII text-only mode). In which case the same amount of energy, as a minimum, would have to be lost by some means from the wave.

      So, the microwave generator used by those experimenting with these not-so-surprising EM propulsion systems merrily draws energy from some very conventional source, runs it through some ingenious device which produces a microwave signal - electric current oscillating back and forth along a wire - and couples this oscillating current to a conductive structure designed to launch analog waves, satisfying Maxwell''s equations, into space. These waves are WELL-KNOWN to carry momentum, and the exact amount of it can be calculated correctly (albeit a bit mystically) by assuming that the ENERGY in the EM waves REALLY IS EQUIVALENT to an amount of mass given by the most famous of Einstein's equations, at least to the general public, namely the familiar "E=mc^2", the ^2 being the standard ASCII alphabet representation of "squared", or raised to the second power.

      Now, one of the main hindrances to more rapid advance in physics, IMO, is the rather "comprehension-free" form that a lot of the modern theory takes, this EM propulsion technology being a rather good example. So, folks, including some real physicists with real PhDs in that subject, I'm sorry to have to say, get your mind around the fact that EM waves DO carry momentum. This fact is NOT exotic, and in fact is dutifully explained in even Undergraduate physics texts such as the extremely highly respected one by Griffiths, used in the Junior year (3rd-year Undergraduate) Physics curriculum at many American schools. So now Conservation of Momentum indeed says that a thrust will be developed, in accordance with Newton's laws, by launching the microwaves out the back, either directly from the antenna or by bouncing waves off the surrounding structure and out through the opening at the back. The thrust should be accurately predicted by Newton's famous formula, most usefully put in the relativistically-correct form F=dp/dt, where p is the momentum, and dp/dt refers to the rate at which it is being blasted out in the backward direction, but the reaction force -- the thrust -- is of course going to push in the opposite direction -- you know, "equal and opposite"? This is nothing new - same as throwing rocks, or chemical molecules, out the back of a rocket engine, except that the momentum does not involve actual mass, but EM wave energy per unit time, converted to mass by dividing energy by the speed of light squared. Ask any science-oriented high-school student if you have trouble with the algebra! :^). As for optimization, it will be mostly a matter of finding better and better ways to narrow the beam width, as only the energy component in the backward direction contributes to propulsion - the lateral components of the beam of course cancel out, at best, and any actual forward components would SUBTRACT from the propulsive effect.

      NOW do you understand what is going on? Anyway, all but the "mysterious" part about exactly how the wave energy is able to make the leap, physically, from obviously real energy that can burn things, light flashbulbs, and even kill people in the beam, if it's zillions of times more intense than the beams from these engines, to acting as if it had real mass instead of just "equivalent" mass in terms of an innocent little equation that came out of Einstein's work?

      As I said above, coming to actual COMPREHENSION, in a practical sense, of such matters is what the next generation of physicists need to master, to bring us the next wave of advances in physics!

  2. Mage Silver badge

    tests in Germany, China and at NASA have corroborated

    Really?

    I thought the results were statistically dubious and within margin of error?

    Still, Microwaves and light are both EM and you can shove stuff with light.

    1. bazza Silver badge

      Re: tests in Germany, China and at NASA have corroborated

      I gather that groups repeating the experiment are indeed being rather careful about claiming that the effect is true.

      The problem with something as 'unlikely' as this is that it's very hard to prove that all sources of experimental error have been identified and accounted for, especially when the claimed effect is small. For example, this thing involves electrical currents, which produce magnetic fields, which in turn will interact with the earth's own magnetic field, etc. etc. There's plenty of room for this being bogus.

      However, the groups that have repeated it aren't stupid, and they will have tried their damndest to account for all the stray effects taking place in their experimental set ups. Either we're left with stray effects influencing the experiment that haven't been thought of (a deeply unsatisfactory situation for any hardened experimentalist) or we're left with a real effect that the theoreticians are struggling to explain (an equally unsatisfactory situation).

      An in-deep-space experiment would be the only way to adequately prove the effect is real. Which would cost rather than anyone is prepared to spend until there is a convincing theoretical basis for its operation. If there is one.

      It would be very cool if it turns out to be true. And hope, as has often been stated, is what drives us onwards!

    2. TitterYeNot

      Re: tests in Germany, China and at NASA have corroborated

      "I thought the results were statistically dubious and within margin of error?"

      I saw a Horizon programme on the BBC recently which looked at attempts to manipulate gravity. They showed a team of researchers (in Germany I think) who built their own EmDrive and tested its thrust using extremely sensitive and accurate equipment. They demonstrated that it did indeed produce a very small amount of thrust when powered up.

      Unfortunately, when they turned the device through 90 or 180 degrees, it still showed the same amount of thrust in the same direction, so it wasn't due to any exotic EmDrive propulsion, as the direction of thrust should move with the orientation of the device.

      Doesn't disprove anything of course, just means we need a certain degree of healthy scepticism when looking at these sort of claims.

      1. Whiskers

        Re: tests in Germany, China and at NASA have corroborated

        I saw that programme too. What struck me about the experment was that they failed to even mention the obvious way of eliminating any effects due to the external power supply or the rather basic connecting lead; ie to put the power source and the 'engine' into a single structure. I don't know how many AA cells would be required.

    3. Ken Hagan Gold badge

      Re: tests in Germany, China and at NASA have corroborated

      Probably worth pointing out that an experiment that shows an effect that is on the edge of significance is also showing an effect that is almost indistinguishable from zero. It all depends on how you choose to present the results.

      If you've got experimental evidence that Noether's Theorem doesn't apply in the real world, you've got a Nobel in the bag for the experiment and someone (perhaps even you) has another one for the first theory that makes a decent stab at going beyond the Lagrangian formulation of mechanics.

      If, on the other hand, you've got something that is almost indistinguishable from experimental noise and a null result, there are no prizes on offer. Sorry.

  3. Mage Silver badge

    enables high speed interstellar travel – but with only minimal fuel

    No, it doesn't. Even with 100% efficiency and fusion you have to coast most of the way and have enough fuel to decelerate.

    1. Destroy All Monsters Silver badge

      Re: enables high speed interstellar travel – but with only minimal fuel

      Yeah. The kinetic energy is not appearing from nowhere. Not even in make-believe physics.

      1. Arthur the cat Silver badge
        Boffin

        Re: enables high speed interstellar travel – but with only minimal fuel

        The kinetic energy is not appearing from nowhere

        If the EmDrive works you can power it (and probably the entire planet) from the rotations of Emmy Noether in her grave.

    2. Wilco

      Re: enables high speed interstellar travel – but with only minimal fuel

      Yes it does. It's electric. You gather your electrons using Solar panels. You accelerate half way there, then turn around a decelerate the rest of the way. No fuel. If you are heading away from the sun then you might need to start decelerating a bit sooner, to account for the lower power as you get further away

      1. Anonymous Coward
        Anonymous Coward

        Re: enables high speed interstellar travel – but with only minimal fuel

        "You gather your electrons using Solar panels. You accelerate half way there, then turn around a decelerate the rest of the way."

        Good luck gathering enough power even a 10th of the way to Alpha Centauri

      2. Anonymous Coward
        Anonymous Coward

        Re: enables high speed interstellar travel – but with only minimal fuel

        it gets pretty dark out there, halfway between stars.

        And, on a different subject, perhaps peripherally related: light sails: how does alight sail accelerate when the energy source becomes progressively weaker the further you go? Would not acceleration from,say Point A, approach zero as distance increases, until the point where it reverses, decelerating until velocity equals zero, then reverses, increasingly, in the opposite direction, driven by photons of the destination point, Point B, eventually damning the light sail to some stagnant, energy neutral point (say, AB')?

        That is intentionally simplistic, ignoring the velocity, direction, curvature of space, and acceleration of the two "points", as well as external forces,etc.

        Will someone explain,very simplistically, my error(s) in my reasoning and physics?

        1. Esme

          Re: enables high speed interstellar travel – but with only minimal fuel

          @AC - no need, you've got it about right. The notion with sending light-sail craft to the stars with light saisl though, involves using very high-powered lasers to provide the propulsion, and if you want to stop at the destination system, a sail that splits into two parts (see Rocheworld by Robert Forward for an SF story that covers this nicely https://en.wikipedia.org/wiki/Rocheworld).

          The outer ring of the sail detaches and accelerates past the payload section, which rotates 180 degrees to make use of the light reflected from the outer ring to decelerate.Of course, you also make use of a gravitational slingshot around the target star to help slow you down, too.

    3. mr.K

      Re: enables high speed interstellar travel – but with only minimal fuel

      If I understand these things correctly fuel in space propulsion is just not a source of energy but also mass to push against to propel the craft forward. That is, you throw particles backwards to gain a momentum forward. This presents a problem of course, since you will start to run out of stuff, fuel, to throw backwards. It is also why harnessing nuclear power is not as straight forward as turning nuclear power into electricity. There is also a problem that if you can throw stuff backwards at greater speed to save on the fuel, but since momentum is only velocity to the power one and kinetic energy is to the power of two you get far less increase in velocity per amount of energy that way. However if you manage to change momentum without throwing stuff out, you can circumvent all of this, all you need to care about is the energy requirement.

      1. Pompous Git Silver badge

        Re: enables high speed interstellar travel – but with only minimal fuel

        However if you manage to change momentum without throwing stuff out, you can circumvent all of this, all you need to care about is the energy requirement.

        That's the idea behind the gravitational slingshot (aka gravity assist manoeuvre, or swing-by) as used by interplanetary probes from Mariner 10 onwards. Also the idea behind the "space warp" of Science Fiction.

        1. cray74

          Re: enables high speed interstellar travel – but with only minimal fuel

          However if you manage to change momentum without throwing stuff out, you can circumvent all of this, all you need to care about is the energy requirement.

          That's the idea behind the gravitational slingshot (aka gravity assist manoeuvre, or swing-by) as used by interplanetary probes from Mariner 10 onwards.

          Momentum exchanges like a gravity slingshot throw the planet in one direction and the probe in an equal and opposite direction. Given the difference in masses between a typical interplanetary probe and a typical planet, it is admittedly a bit difficult to notice the planet's opposite motion but it is every bit as present as the motion in chemical rocket exhaust.

          The planet might not have come out of the probe's gas tanks, but it's still the stuff being thrown out.

          1. Pompous Git Silver badge

            Re: enables high speed interstellar travel – but with only minimal fuel

            Thanks for the correction cray74. It's 48 years since I did basic physics.

  4. ZSn

    Cold fusion

    This reminds me of cold fusion - that was unsubstantiated twaddle as well. It burned a lot of otherwise reputable physicists and so will this rubbish.

    1. cd

      Re: Cold fusion

      So an EmDrive powered by a cold fusion generator, then?

      1. KR Caddis

        Re: Cold fusion

        very long cord on the microwave is a downside; almost infinite free popcorn is a plus, however.

    2. bombastic bob Silver badge

      Re: Cold fusion

      hmmm... my reply seems to have been lost. I'll check back and delete it. UI problems or ?

      cold fusion probably happens at rates that are immeasurable, just like the radioactive decay of "stable" isotopes. It's "there" but you can't measure it because it's below the noise threshold.

      So it's not entirely 'twaddle' for cold fusion, just highly impractical. The probability of hydrogen fusion is related to temperature and pressure, and PROBABLY resonant energies. Current research may or may not be focusing on the resonant energy angle, but maybe they like their 'secret sauce' and so nobody's really talking about it. In any case, I don't know if cold fusion with palladium and monotomic hydrogen (or heavy water for that matter) actually WORKS in ANY capacity, and indications are that it does NOT, but I wouldn't rule out immeasurable reactions taking place. But yeah, its impractical.

      The EmDrive may ALSO be impractical for similar reasons. If it's MOMENTUM of light-speed particles that cause the thrust [regardless of how/why and Unruh radiation, or not] the energy required for propulsion goes up by a factor of 4 when you double the energy. Thrust = delta-momentum which is delta-velocity times mass. the mass flow rate of rocket exhaust multiplied by its delta-velocity (which is proportional to the square of the energy) equals the thrust. So, double the mass, double the thrust. QUADRUPLE the energy, double the thrust. Rocket engines are a compromise of needed mass and available energy. And the EmDrive could not POSSIBLY be efficient, based on accelerating things to light speed. The Xe ion drive would be a better choice in deep space.

  5. Anonymous Coward
    Anonymous Coward

    No reaction

    This kind of gadget pops up every so often. Last time we got the Dean Drive.

    1. Anonymous Coward
      Anonymous Coward

      Re: No reaction

      Its just a shame it wan't invented by a guy called Gravel

  6. Chozo
    Alien

    Keep Calm

    And

    Engage The Hyperdrive

  7. Ugotta B. Kiddingme

    question

    given that this is using microwaves to produce propulsion, might we need to be careful where the thing is pointed? Could be problematic at the other end of a journey when you turn round to decelerate. I can't remember which scifi author used something like this - using a ship's exhaust as a weapon to the roast a planet on approach.

    1. TeeCee Gold badge
      Happy

      Re: question

      ...using a ship's exhaust as a weapon....

      Or "the Kzinti lesson" as that is usually known as.

    2. israel_hands

      Re: question

      It's been used by a lot of people, Heinlein and Niven spring to mind but there are loads of others. Dan Smith mentioned it a few times in the Hyperion Cantos I seem to recall.

      The idea behind that is that a torch drive is basically an extremely powerful weapon the happens to have a payload and crew section strapped to it. The business end is still very dangerous.

      As to the microwave energy coming out, the problem with any drive either powered or fuelled by nuclear energy (which is usually the only thing energy dense enough to give you thrust worth the name) is that the crew need to be shielded from the drive, not just anything in the path of the exhaust.

      A decent radiation shield is very much in order between the engine bay and crew section but even then, the effects of high-enery radiation naturally leaking into the engine bay will in turn irradiate the bay itself. Which can make maintenance a very dangerous prospect.

      Anyway, enough sci-fi rambling. Like the idea of this EmDrive but it's likely bullshit or so inefficient as to be pointless. Space-Admiral Hawking's plan for postage-stamp sized ships powered by lasers is probably more well-grounded in reality (as well as being fucking awesome).

      1. Vic

        Re: question

        Like the idea of this EmDrive but it's likely bullshit or so inefficient as to be pointless.

        Never mind inefficient - if it works at all, we need to do some fundamental re-thinking of physics.

        Note that this "drive" has never been tested in microgravity, and Shawyer's former boss (for whom he was working when the idea first surfaced) has stated:

        I reviewed Roger's work and concluded that both theory and experiment were fatally flawed. Roger was advised that the company had no interest in the device, did not wish to seek patent coverage, and in fact did not wish to be associated with it in any way

        Vic.

      2. Ken Hagan Gold badge

        Re: the crew need to be shielded

        If you've got a crew, you're doing it wrong.

    3. matt747

      Re: question

      Was it the late, great Iain M. Banks?

    4. Alan Brown Silver badge

      Re: question

      "I can't remember which scifi author used something like this - using a ship's exhaust as a weapon to the roast a planet on approach."

      Bussard ramjets would certainly achieve this.

      The fun part about the microwave drive is not that it emits microwaves, but that the container is _sealed_ - ie, NO EM energy is leaking out.

    5. hplasm Silver badge
      Boffin

      Re: question

      I don't believe this has an exhaust. That's what all the excitement is about.

      1. Sir Runcible Spoon Silver badge

        Re: question

        From what I read, the wavelength is so long that it is smaller than the smallest 'unit' of conservation of momentum.

        So if it takes 10 sillybits to move mass the smallest amount possible (let's call it a moviebit), and this drive generates only 5 sillybits - apparently the Universe is obliged to still move the object one moviebit (even though the EM drive has only paid for 1/2 a moviebit*)

        *It's nice to know the Universe doesn't deal in small change :)

        One of the questions being asked is if they will still get the same output from *even less* energy :)

        Apparently this theory is holding up due to its prediction that if the shape of the drive is different, the thrust would be generated in the opposite direction - I recall reading that this would explain some of the results being observed!

        FREE ENERGY! Woot.

        1. Vic
          Joke

          Re: question

          One of the questions being asked is if they will still get the same output from *even less* energy :)

          The Homeopathic Drive?

          Vic.

      2. Anonymous Coward
        Anonymous Coward

        Re: I don't believe this has an exhaust. That's what all the excitement is about.

        s/excitement/skepticism/

        1. Andrew Orlowski (Written by Reg staff)

          Re: Re: I don't believe this has an exhaust. That's what all the excitement is about.

          It's up to the room-temperature fusion people so demonstrate that it works.

          EmDrive produces a reproducible effect, now we need to know why.

          Do you see the difference?

          1. Vic

            Re: I don't believe this has an exhaust. That's what all the excitement is about.

            EmDrive produces a reproducible effect

            That is not yet clear.

            Several groups have claimed to reproduce the effect. Just as several groups claimed to reproduce cold fusion. They were wrong.

            Vic.

          2. Ian Johnston Silver badge

            Re: I don't believe this has an exhaust. That's what all the excitement is about.

            Cold fusion produced plenty of reproducible effects, all of which turned out to be bogus. The effects of the EmDrive are not reproducible: every group to try it gets different ones, mostly within experimental error, and effects within experimental error aren't affects at all.

            Have you done any experimental physics? If so, you'll know that measuring anything at the very limits of detection is problematic and prone to unexpected errors. In my case, by the way, it was trying to detect milliwatts by liquid helium calorimetry.

          3. Alan Brown Silver badge

            Re: I don't believe this has an exhaust. That's what all the excitement is about.

            "EmDrive produces a reproducible effect, now we need to know why."

            It's not known if it works in space.

            _NONE_ of the vacuum chambers on earth can pull a vacuum as good as the partial pressure seen at ISS levels, let alone further out.

            Why does this matter? Look up radiometers - supposedly a vacuum effect but it turned out to be due to expansion of the tiny amount of residual gas inside the envelope.

    6. g e

      Re: question

      Wasn't that the high energy emission/flinging-off of particles 'stuck' to the front of an Alcubierre warp bubble upon deceleration/deactivation of the bubble.

      Seem to remember El Reg had an article some time ago about it.

  8. John Smith 19 Gold badge
    WTF?

    "f the axial length is equal to the diameter of the small end.." "..thrust should be reversed. "

    So it's only a lucky guess that the original design produced any thrust at all in a measurable direction?

    This is pretty exciting news as a viable explanation is the first step to moving beyond cut-and-try designs.

    However with something this big we need to be very cautious as extraordinary (and they are) claims need extraordinary evidence.

    The payoff for a system that turns electricity directly into thrust with no mass loss for everything in LEO and beyond is of course huge.

  9. channel extended
    Holmes

    The real universe doesnt care

    The law of gravity works, the Earth is still round, Congress still can't find it's a** with either hand and a guide dog. So a belief is not needed!!

    " But it can't work if we can't explain how it works, can it?"

    1. Sir Runcible Spoon Silver badge
      Headmaster

      Re: The real universe doesnt care

      The Earth isn't round, it's an oblate spheroid :)

      1. Mark #255

        Re: The real universe doesnt care

        Actually, it's a shape defined by the EGM96 coefficients.

        1. Ian Johnston Silver badge

          Re: The real universe doesnt care

          Actually, it's the shape it is. The EGM96 coefficients are only an approximation which, for example, miss out both Snowdon and the Thames Estuary.

  10. Martin Gregorie Silver badge

    Here's a link...

    ...to a much fuller analysis that I read last night:

    https://www.technologyreview.com/s/601299/the-curious-link-between-the-fly-by-anomaly-and-the-impossible-emdrive-thruster/#/set/id/601302/

    The link was on Jerry Pournelle's 'Chaos Manor' blog and is well worth a read.

  11. Killing Time

    So what is it???

    'An explanation for Roger Shawyer's seemingly impossible EmDrive has been offered.'

    As much as I would like to say otherwise the theorists blog lost me in the first paragraph, and there is the rub. If the blog is unintelligible to the layman then I have little hope for the paper.

    Successful theories invariably offer analogy and some elegance. Perhaps its me but currently I see neither.

    1. Uncle Slacky Silver badge
      Boffin

      Re: So what is it???

      Maybe it would be a good idea to look at the inventor's proposal for the theory behind it?

      From http://emdrive.com/principle.html :

      "At first sight the idea of propulsion without propellant seems impossible. However the technology is firmly anchored in the basic laws of physics and following an extensive review process, no transgressions of these laws have been identified.

      The principle of operation is based on the well-known phenomenon of radiation pressure. This relies on Newton’s Second Law where force is defined as the rate of change of momentum. Thus an electromagnetic (EM) wave, travelling at the speed of light has a certain momentum which it will transfer to a reflector, resulting in a tiny force.

      If the same EM wave is travelling at a fraction of the speed of light, the rate of change of momentum, and hence force, is reduced by that fraction. The propagation velocity of an EM wave, and the resulting force it exerts, can be varied depending on the geometry of a waveguide within which it travels. This was demonstrated by work carried out in the 1950’s. (CULLEN, A.L. ‘Absolute Power Measurements at Microwave Frequencies’ IEE Proceedings Vol 99 Part 1V 1952 P.100)

      Thus if the EM wave travelling in a tapered waveguide is bounced between two reflectors, with a large velocity difference at the reflector surfaces, the force difference will give a resultant thrust to the waveguide linking the two reflectors. If the reflectors are separated by a multiple of half the effective wavelength of the EM wave, this thrust will be multiplied by the Q of the resulting resonant cavity.

      The inevitable objection raised, is that the apparently closed system produced by this arrangement cannot result in an output force, but will merely produce strain within the waveguide walls. However, this ignores Einstein’s Special Law of Relativity in which separate frames of reference have to be applied at velocities approaching the speed of light. Thus the system of EM wave and waveguide can be regarded as an open system, with the EM wave and the waveguide having separate frames of reference.

      A similar approach is necessary to explain the principle of the laser gyroscope, where open system attitude information is obtained from an apparently closed system device."

      1. Paul Shirley

        Re: So what is it???

        It's not a closed system. If it was it would need to either convert 100% of input energy to momentum, have perfect lossless mirrors and tiny/zero input energy or melt. None of those is happening so waste energy must be leaving the drive. The em drive may just be an extremely inefficient photon rocket and simply aiming a laser into space would do a better job.

        Propellent free, maybe.. New physics, unlikely.

      2. Killing Time

        Re: So what is it???

        @Uncle Slacky

        I am aware of the inventors proposal for the theory, however this remains an unproven theory or else alternates would not be proposed and we wouldn't have this article.

        So again, said in the style of Red Dwarfs ships cat....So what is it???

  12. pmartin66

    garbage. this is BUNK. it's not going to happen for ages, if at all.

    1. Pascal Monett Silver badge

      Yeah, right. If we were supposed to fly, God would have given us wings.

      1. Vic

        If we were supposed to fly, God would have given us wings

        If we were supposed to fly, God would have given us a bigger wallet...

        Vic.

    2. hplasm Silver badge
      WTF?

      garbage. this is BUNK.

      There are kids on your lawn- did you know?

  13. Kaltern

    Wow.. it's nice to see so much openmindedness.

  14. Mark 85 Silver badge

    Until the reasons why the technology works are figured out, I'll go along with "magic" for now.

    1. VinceH Silver badge

      Magic is just technology we don't understand.

      (Yes, I know what the actual ACC quote is.)

    2. Captain DaFt

      "Until the reasons why the technology works are figured out, I'll go along with "magic" for now."

      Hm, your proposal has merit. On examination:

      a. This uses energy in a cone to produce a kinetic effect.

      b. Unicorns control magic with their conical horns to produce a kinetic effect.

      c. Therefore this is magic, QED!

  15. Ian Emery Silver badge

    Question

    When will it be ready to power my flying car??

  16. Anonymous Coward
    Anonymous Coward

    Zealots...also said

    1) Trains would never work as you'd die from asphyxia

    2) Cars would never replace the horse and cart

    3) Man would never fly

    1. bombastic bob Silver badge

      (zealouts also said)

      <quote>

      1) Trains would never work as you'd die from asphyxia

      2) Cars would never replace the horse and cart

      3) Man would never fly

      </quote>

      4) iron ships can't float

      5) heavy objects fall faster than light ones

      6) the earth is the center of the universe

      and so on, yeah.

      I still like the idea that spinning "stuff" might emit gravitons, or SOME kind of particle, and especially good if it can be used for propulsion. Lots of early work involving that concept... and even more recent contributions...

      https://en.wikipedia.org/wiki/Ehrenfest_paradox

      after all, relativistic effects gotta do SOMETHING... Bremsstrahlung at the very least

      https://en.wikipedia.org/wiki/Bremsstrahlung

      1. Inventor of the Marmite Laser Silver badge

        Re: (zealouts also said)

        7) 640k ought to be enough for anybody

        1. redpawn Silver badge

          Re: (zealouts also said)

          I remember pronouncing that no one could need more than 64k, 48k plus a 16k language card.

          Would this not be the converse of photon pressure. If you darkened the sun on one side solar sails would only work when the lit side faced them. Conservation of momentum would dictate that the sun would have to move in the opposite direction of the solar sails. This could be measured with sensitive instruments while standing on the dark side of the sun.

        2. Sir Runcible Spoon Silver badge
          Headmaster

          Re: (zealouts also said)

          "7) 640k ought to be enough for anybody"

          When I think about it, I think it should.

          Observe, now that we have loads more memory to play with there is a lot of inefficient programming.

          MS Word on Win3.1 for WG runs faster on a 486-DX than MS Word does on Win7 on a Core-i7-920 with 16GB RAM.

          Now, if he had said "640k *is* enough for anybody" - then that clearly isn't the case :)

      2. Anonymous Coward
        Anonymous Coward

        Re: (zealouts also said)

        Re : https://en.wikipedia.org/wiki/Ehrenfest_paradox

        You forgot : - This article needs attention from an expert in Physics. Please add a reason or a talk parameter to this template to explain the issue with the article. WikiProject Physics (or its Portal) may be able to help recruit an expert. (November 2008)

    2. Ian Johnston Silver badge

      1) Trains would never work as you'd die from asphyxia

      2) Cars would never replace the horse and cart

      3) Man would never fly

      4) That polywater was an illusion

      5) That N-rays didn't exist

      6) That cold fusion was somewhere between scam and delusion

      7) That homeopathic treatments don't work for AIDS

      8) That Tesla's wireless power distribution system was too lossy to be practical

      And so on. Remember, they also laughed at Bozo the clown.

  17. JC-Reg
    Joke

    Impossible EmDrive Thruster

    So... is the improbability drive far off then?

    1. matt747

      Re: Impossible EmDrive Thruster

      Infinitely so....

      1. moiety

        Re: Impossible EmDrive Thruster

        Should be ready by teatime then.

        1. Sir Runcible Spoon Silver badge

          Re: Impossible EmDrive Thruster

          Just enough time for another bath then...pass the rubber ducky first mate.

  18. Destroy All Monsters Silver badge

    Not this stuff again

    McCulloch suggests the same effect accounts for the anomalies observed when spacecraft accelerate around a planet: they jump.

    They what now?

    1. Old Handle

      Re: Not this stuff again

      Flyby Anomaly. First I'd heard of it, but apparently it's a real thing. Although "jump" sounds like a bit of an exaggeration.

  19. Destroy All Monsters Silver badge
    Holmes

    The first hint you are reading an Orlowski article

    Despite skepticism from the scientific priesthood

    People who know their shit are a "priesthood".

    1. Pompous Git Silver badge

      Re: The first hint you are reading an Orlowski article

      People who know their shit are a "priesthood".

      Perhaps it would be better to say scientists who teach scientific shit are a priesthood. Let's take the falling weights already mentioned above. According to ever so many scientists, Galileo disproved Aristotle's notion that heavier objects fall faster than light objects by dropping a musket ball and a cannon ball from the top of the tower at Pisa. The two balls hit the ground simultaneously thus disconcerting the Aristotelians (aka Scholastics).

      Galileo didn't record where he dropped identically sized wooden and iron balls, but if it was the tower at Pisa he was at least a hundred feet tall, or the towers was that much taller in his day. He also described the fall as the wooden ball initially being ahead of the iron ball, and the iron ball overtook the wooden ball to arrive at the ground first. To have both dropped the balls and observe this behaviour means he must have run very fast indeed to make the observation. Faster than the speed of sound even.

      Astrophysicist George Smoot in his book Wrinkles in Time wrote that he realised the historians' account was wrong when he saw the tower of Pisa in the moonlight.

      Other scientific horseshit includes:

      Columbus being the first person to realise the Earth is a sphere.

      Gravity in outer space is zero. At the top of a ladder that's about 500 km tall you would be in the vacuum of space, but you would not be weightless at all. You'd only weigh about fifteen percent less than you do on the ground.

      Medieval scholars debated how many angels could dance on the head of a pin.

      Benjamin Franklin's kite string was struck by lightning. And it didn't kill him and anyone else standing nearby?

      A prism can split a beam of sunlight into a rainbow. Science textbooks show how a second prism recombines the colours. Two prisms do not work as shown. Try to duplicate the effect illustrated with real prisms and you will discover it can't be done. You need either three prisms, or two different sized prisms.

      [Mutter, mutter...]

      1. Chemist

        Re: The first hint you are reading an Orlowski article

        "Other scientific horseshit includes:

        Columbus being the first person to realise the Earth is a sphere."

        What particular usage of scientific are you using here ? Someone or other may have said it, it may have been the common belief among even 'educated' people but scientific ?

        Ditto : "Gravity in outer space is zero", "Medieval scholars etc"

        1. Pompous Git Silver badge

          Re: The first hint you are reading an Orlowski article

          What particular usage of scientific are you using here ?

          Textbooks as used to teach science to students. Try reading some and you might be surprised. Much of the science I was taught at the secondary level was horseshit.

          You can see the result in the comments here. The phrase "scientific proof" has no meaning. Corroboration is not proof. Proof occurs in logic and mathematics, but scientific theories can never be proved.

          1. Chemist

            Re: The first hint you are reading an Orlowski article

            "Try reading some and you might be surprised."

            Oddly enough for a physical scientist I have read a few.

            You didn't answer any of my points BTW

            1. Pompous Git Silver badge

              Re: The first hint you are reading an Orlowski article

              You didn't answer any of my points BTW

              You asked "What particular usage of scientific are you using here ?" I gave the short answer as used in textbooks to teach science to students. Long answer:

              Scientific comes from medieval Latin: scientificus. This was a translation of the Greek epistemonikos ("making knowledge" in Aristotle's Ethics). Knowledge to Aristotle was justified true belief. One might then expect those who adopt the appellation "scientist" to promulgate knowledge in this Aristotelian sense rather than horseshit.

              I gave as an example astrophysicist George Smoot's disbelief of Galileo's own account of his falling weights experiment and his preference of the fictitious account by Vincenzo Vivianini written after Galileo's death. While Smoot's Wrinkles in Time is not a text book, it's a typical example of what scientists write for consumption by non-scientists. Another example is Reginald Lester (FR Met Soc) who wrote when I was a boy "It has been found that the cosmic rays about 14 miles up are 150 times stronger than at earth-level. When cosmic rays reach such a force they could crush to death both man and his machine." Stirring stuff that led me to ask why Gagarin wasn't crushed to death by cosmic rays.

              Needless to say I was told not to ask such questions by my teachers. Happy now?

              1. Chemist

                Re: The first hint you are reading an Orlowski article

                "Needless to say I was told not to ask such questions by my teachers. Happy now?"

                No ! You seem to be suggesting that scientific is something uttered by a scientist . The scientific method is not that. It's the scientific method that needs to be applied to problems. The practitioner might be right or wrong in their application, deduction or even mathematics and being human may well be influenced by fear, greed and prejudice but others will eventually test re-test, argue and adjust.

                1. Pompous Git Silver badge

                  Re: The first hint you are reading an Orlowski article

                  You seem to be suggesting that scientific is something uttered by a scientist . The scientific method is not that. It's the scientific method that needs to be applied to problems.

                  The Scientific method (as contained in ever so many science text books presumably):

                  * Ask a Question

                  * Do Background Research

                  * Construct a Hypothesis

                  * Test Your Hypothesis by Doing an Experiment

                  * Analyze Your Data and Draw a Conclusion

                  * Communicate Your Results

                  I take it then that when Michael Faraday made and distributed copies of his homopolar motor he wasn't doing science. Nor was Charles Darwin when he was establishing his scientific reputation by dissecting barnacles. Poor old Fred Hoyle misses out for his work on nucelosynthesis in stars. That great palaeontologist Stephen J Gould also appears to miss getting a gong.

                  Let me state the Method Position as follows:

                  There is something called the scientific method, and someone who understands this method will be able to understand all of science, regardless of the specific subject matter that person has been taught. Thus the goal of science education should be to teach that method.
                  It's hard for me to understand how anyone could hold a position that is so clearly untenable.

                  Dr. James Trefil, in Two Modest Proposals Concerning Scientific Literacy.

                  1. Chemist

                    Re: The first hint you are reading an Orlowski article

                    "Let me state the Method Position as follows:

                    There is something called the scientific method, and someone who understands this method will be able to understand all of science, regardless of the specific subject matter that person has been taught. Thus the goal of science education should be to teach that method.

                    It's hard for me to understand how anyone could hold a position that is so clearly untenable."

                    This all nonsense. I note that you've already admitted being rather rusty about Physics. I suggest your sense of logic and indeed commonsense is also lacking.

      2. israel_hands

        Re: The first hint you are reading an Orlowski article

        I was taught that Galileo did a thought experiment, not a physical one. He wondered what would happen if you tied the two balls together and dropped them. If they were to fall at different speeds then the wooden ball would make the iron fall slower, which made no sense.

        Astrophysicist George Smoot in his book Wrinkles in Time wrote that he realised the historians' account was wrong when he saw the tower of Pisa in the moonlight.

        A historical account of a scientific discover is in some way inaccurate? No shit? Next thing you'll be telling me Newton didn't get hit by a falling apple.

        Final point: If you're standing on a 500km tall ladder, you're not in "outer space", you're still firmly in Earth's gravity well.

        1. Pompous Git Silver badge

          Re: The first hint you are reading an Orlowski article

          I was taught that Galileo did a thought experiment, not a physical one. ...

          Final point: If you're standing on a 500km tall ladder, you're not in "outer space", you're still firmly in Earth's gravity well.

          Galileo performed the Gedanken experiment, but he also performed the real one as described. It's an interesting account. The Gedanken experiment was also performed by Jean Buridan in the 14thC long before Galileo in the 16thC.

          The interface between the Earth's surface and outer space is called The Kármán line at a height of 100 km. I guess by your account Gagarin's Vostok I never made it into outer space as it only achieved a height of 169 km. Alan Shepherd's flight reached 187 km, so he was well short of 500 km too. I guess very few early spacemen and women were true travellers in space by your account.

        2. Pompous Git Silver badge

          Re: The first hint you are reading an Orlowski article

          A historical account of a scientific discover is in some way inaccurate? No shit? Next thing you'll be telling me Newton didn't get hit by a falling apple.

          Can you explain precisely why historians are wrong for taking Galileo at his word, rather than the word of some scientist/priest who made stuff up at a much later date?

  20. kneedragon

    I am puzzled...

    Either this is an April fool's day joke, or the biggest story going... and if it is a very big story, then why have we heard nothing about it in the mainstream media? Seriously, I'm not clear on this - is it a joke?

    1. ZSn

      No, just a delusion

    2. Steve Davies 3 Silver badge
      Coat

      As seen on TV

      (in memory of Victoria Wood)

      There was a TV prog in this very thing. I caught a repeat of it a few months ago.

      The inventor was (IMHO) a very reluctant 'boffin'. Not someone after their 15 nano particles of fame.

      There is probably something real in this but bigger boffinbrains than mine will decidely pour scorn on it until it dies a death only to be reborn years later by some Stealth Startup, fleece the investors for bazillions and still get nowhere.

      Cynic? Moi? yep.

      time to go for a walk.

      "I may be sometime."

    3. Roger Greenwood

      It was on a recent UK TV program (Horizon?). I seem to recall the tests in Germany did measure some thrust. Unfortunately when they rotated the thing 90 degrees, the thrust stayed in the same direction! So obviously it's an anti-gravity machine :-)

      1. akeane
        Alien

        Maybe...

        ... it's interacting with the Earth's magnetic field?

        Or is that too obvious...

  21. thomas k

    it can't work if we can't explain it

    So, Fleischmann-Pons cold fusion IS real! I knew it!

  22. tempemeaty
    Devil

    IMHO

    The western world will likely tie itself up with its' own self imposed limits and mental masturbation about this discovery, doing nothing with it, long past the point Germany, China and possibly others are using it in space craft.

    1. Anonymous Coward
      Anonymous Coward

      Re: IMHO

      When did Germany stop being part of the Western World?!

      I mean I know they've a great record with space- neither the US or USSR would have got nearly as far as they did without their hijacked Nazis- so I can see where you're coming from on that front, but Germany is part of Europe, an important part. It's about as Western as you can get!

    2. Doctor Syntax Silver badge

      Re: IMHO

      "The western world will likely tie itself up ..., doing nothing with it, long past the point Germany, China and possibly others are using it in space craft."

      So you don't include Germany as part of the western world?

  23. Anonymous Coward
    Anonymous Coward

    Swingers

    Probably not related, but have you ever wondered how a swing works?

    You don't push against anything, where does the energy come from?

    1. Shades

      Re: Swingers

      Gravity and unbalanced weight transfer. And you push against the ropes/chains to remain stable while shifting your weight. Gravity tries to correct your centre of weight, you shift your weight again to counter and build up momentum.

      Now I've answered I'm not entirely sure if you were serious or not? lol

    2. Frumious Bandersnatch Silver badge

      Re: Swingers

      A quick guess would be that the entire system is effectively two coupled pendulums. When you hold onto the rope and swing your body around the point you're holding, you're doing work (expending energy to move against whatever inertia you already have). That's where the energy comes from, and because it's a coupled system, that energy gets transferred into making the swing as a whole go higher or damping its movement.

      You should be able to get a similar effect by suspending a piston (say a solenoid) vertically from a spring and setting the piston to oscillate at different frequencies. My intuition tells me that you should be able to get behaviours ranging from having a point that's fixed at a given height despite the paired oscillation to tracing out a smooth sine wave, with various chaotic patterns in between.

      1. Neil Barnes Silver badge

        Re: Swingers

        Two coupled pendulums (penduli?) might have a chaotically moving centre of mass, but there's still a constant momentum; they'll stop eventually from friction.

        A swing moves because the rider puts energy into it by flexing and extending their body to move their centre of mass and thereby provide an impulse: they supply it on one side and collect it on the other.

        Or in my granddaughter's case, it moves because she yells 'higher' at me.

  24. Duncan Macdonald Silver badge
    Thumb Up

    Useful for satellites

    If the results quoted by M E McCulloch in (http://arxiv.org/pdf/1604.03449v1.pdf) hold up to further testing, then getting over 0.75 milliNewton per watt with a very high Q cavity (row C1 in table 1) will have major implications for satellite design. Many satellites have lifespans that are determined by the exhaustion of fuel for positioning. If a few watts can be obtained from the satellites solar panels then this lifespan limit is removed. (One day at 10 watts with the above efficiency would change the velocity of a 1 ton satellite by over 60cm/sec - a fairly large delta-V in orbital terms.) The EmDrive could also provide a replacement for the reaction wheels used for fine positioning in space borne telescopes.

  25. Anonymous Coward
    Anonymous Coward

    More of a guideline, actually...

    So in laymans terms, when the law of conservation of momentum and quantum theory fight, quantum theory wins?

    Sounds a bit odd to me that we can observe macroscopic violation of CoM by running one of these engines for a while. Usually the universe applies some kind of accountant's rounding to stuff like this, so over time the effect of quantisation leads to as many round-ups and downs, and no net change is observed.

    Can we get quantum theory and the second law of thermodynamics to fight next? That'd be one worth watching.

  26. ocratato
    FAIL

    Conservation of Energy?

    This thing is supposed to produce some thrust from an input of energy. In other words it would have a constant acceleration as long as the power was provided. Since the kinetic energy of an object is proportional to the square of the velocity, it would eventually reach a point where the increasing kinetic energy was larger than the input energy.

  27. JeffyPoooh Silver badge
    Pint

    'Cannot be explained by known Physics' they say...

    ...But we're happy to propose 'light sails' and speak about using "laser beams" (sans sharks) to propel little spacecraft towards nearby star systems.

    'Yeah, but that's Light and this is Microwaves which are completely different things. Light is photons and microwaves aren't...'

    Sigh...

    1. Flocke Kroes Silver badge

      Re: 'Cannot be explained by known Physics' they say...

      Laser beams and light sails are easy: You put a big fan (laser) in you (space) port, and a big (light) sail on your ship. The fan pushes air in one direction and the Earth in the other, but as the Earth is so big, no-one notices. The air hits the ship. The air slows down (light bounces back) and the ship speeds up.

      The first good thing about the EmDrive is that the fan and the sails are both on the ship. The other clever bit is a trick to reduce the size of the fan: You put sails at both ends of the ship, and the fan in the middle. You change the direction the fan spins back and forth really quickly, in time with the frequency that air bounces back and forth between the sails so the air speed builds up like small pushes on swing.

      Because it is symmetrical, there is no net force. The trick to getting money out of investors is to make the sails at each end of the ship different sizes, and put a truncated cone around the ship to match the wind to each sail.

      1. JeffyPoooh Silver badge
        Pint

        Re: 'Cannot be explained by known Physics' they say...

        @Flocke Kroes

        Your post reads quite similar to the 'logic' of why "rockets cannot possibly work in a vacuum", circa Robert Goddard's time.

        https://en.wikipedia.org/wiki/Robert_H._Goddard#New_York_Times_editorial

        @Y'all

        Nobody seems to have an issue with 'pressure' from light. But we're all stumped why there could be some infinitesimal force from a microwave horn? None of you ever got the memo about the EM spectrum? If solar flux or "laser" beams can push a light sail (widely accepted, I believe it's been proven), then there should be an infinitesimally small force by the EM emission from a microwave horn. Obviously (Light and microwaves are the same thing. Just different wavelengths.).

        I'm not saying anything about the numbers. Just the concept.

        1. Pompous Git Silver badge

          Re: 'Cannot be explained by known Physics' they say...

          If solar flux or "laser" beams can push a light sail (widely accepted, I believe it's been proven), then there should be an infinitesimally small force by the EM emission from a microwave horn.

          School I went to in UKLand had a vacuum tube with a little "windmill" inside it with the vanes blackened on one side and reflective on the other. Didn't need a laser to drive it (they hadn't been invented yet).

          Yes, photons are photons.

          1. allthecoolshortnamesweretaken Silver badge

            Re: photons are photons / Pompous Git

            Yes, photons are photons, but if you are referring to a radiometer (or Crookes* radiometer ) you chose a bad example - the "windmill" isn't really moved by the photons hitting it, but by heat (thermal energy). Which is why it only works in a near-vacuum (and I don't mean a Dyson).

            And while the first working Laser was built in 1960, the theoretical foundations for the laser (and the maser) were established in 1917 by Albert Einstein in the paper Zur Quantentheorie der Strahlung. So if the Laser had not been invented yet while you were at school it really makes me wonder how old you were when you used to work as an artist's model. (^_~)

            *Interesting guy, by the way: Sir William Crookes and somehow IT-related, he was a pioneer in vacuum tubes.

    2. David Pollard

      Re: 'Cannot be explained by known Physics' they say...

      If the lasers were tapered rather than plain cylinders then the sharks would be able to swim faster.

  28. Anonymous Coward
    Anonymous Coward

    Let me guess

    They just need your money to get it working properly...

    I'll call it the: Space Conquering Astronomical Mover.

  29. eric.verhulst(Altreonic)

    The explanation could be very simple; The microwaves bounce of the inner wall and this releases atoms of which some escape through the back-end opening. I have seen this in microwave klystrons 30 years ago. No magic needed.

  30. JimmyPage Silver badge
    Boffin

    Einstein ...

    suggests that moving particles distort spacetime. Could it be that this distortion is shifting the centre of mass, and the thrust observed is the drive repositioning ?

  31. SeanEllis
    Flame

    Premature

    Any explanation of an effect should not precede reliable replication of the experiment that shows that there is an effect in the first place.

    Initial estimates of the thrust of this device have been reduced and reduced in line with the error bars on the increasingly accurate methods used to measure it. This is a classic sign of something with no real effect.

    Of course, as always, I am very willing to be proven wrong. But at the moment it's just red flags all the way.

  32. Loyal Commenter Silver badge

    Has it been tested in a vacuum?

    Because the first observation I'll make is that it will heat up if microwaves are being bounced around inside it, and if operated in an atmosphere, the larger end will heat more air than the smaller end. Boyle's law can take over from there, producing a small thrust.

    In other words, the reaction mass would be the air it heats up; this effect wouldn't work in a vacuum any more than a rowboat would.

    1. Mystic Megabyte Silver badge

      Re: Has it been tested in a vacuum?

      Although I would love it if you are wrong, yours is the first sensible assessment of the observed thrust.

    2. JimmyPage Silver badge

      Re: Has it been tested in a vacuum?

      Yes. If you watch the (not as dreadful as it might have been) recent "Horizon" on anti-gravity ...

      http://www.bbc.co.uk/iplayer/episode/b0752f85/horizon-20152016-2-project-greenglow-the-quest-for-gravity-control

  33. rdhood

    "But it can't work if we can't explain how it works, can it?"

    Uh, yes it can. We can't explain gravity, but we still use it to guide small vessels all over the solar system. Understanding something works is not a prerequisite to something using it. It is true, though, that optimizing that energy output will be difficult to do when they can't even explain it in the first place.

    1. Chemist

      Re: "But it can't work if we can't explain how it works, can it?"

      "We can't explain gravity,"

      What ! We can explain it as well as many other forces. GR makes many startling predictions from its rather ( for non-physicists) exotic mathematics. and when tested is shown to provide correct predictions. Sure it probably isn't complete or maybe will be refined or displaced one day.

      1. allthecoolshortnamesweretaken Silver badge

        Re: "But it can't work if we can't explain how it works, can it?" / gravity

        Gravity: still tricky.

  34. Palf

    It's a perpetual motion machine of the 1st kind

    And as such is capable of producing free energy forever. When allowed to freely accelerate on a wheel, there comes a point where the kinetic energy (quadratic with time) exceeds the total input energy (linear with time). Knock yourselves out. Throw away your coal and nuclear reactors and stop fracking.

    Or it doesn't work and what's seen is experimental artifact.

  35. Matthew Taylor

    MiHsC - an interesting new theory

    Mike Mcculloch's MiHsC theory, which he uses as a basis for his explanation of the EMDrive, also predicts galactic rotation far more accurately the General Relativity. Using MiHsC, the need for dark matter to be added in different places to make the equations work is removed, as the theory fits the observed galactic rotations without any tweaking. Mike has a list of over a dozen anomalies that his theory correctly predicts.

    My point being, even if you consider the EMDrive to be a bit sketchy, MiHsC is still well worth a look.

  36. Anonymous Coward
    Anonymous Coward

    Plymouth University, eh? I think that tells us all we need to know, thanks.

  37. Anonymous Coward
    Anonymous Coward

    Re. modified inertia

    This is actually consistent with a lot of other anomalies including the apparent mass reduction above a spinning superconducting disk: the reason why it wasn't replicated is that the one team that tried never got the exact formula right because bonding of two different formula superconductors together at the atomic level renders the composite very delicate and prone to fracture at high rotational speeds.

    As a result they only ever tried it at 50 rpm instead of the required 3500.

    I had some thoughts about this, one idea might be to use an iridium layer between the two different formula YBCO disks as an interface as it is nonreactive otherwise and mechanically very strong.

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