52 thoughts on “The Reactionless Drive”

  1. You spend years on an unlikely but oh so desirable tech, finally get to the ultimate make or break test … and suppose the test proves beyond reasonable doubt that it doesn’t work at all. Do you admit the failure? Go silent? Or claim a success in a desperate effort so save face, hoping to get the rest of the world to believe you and expend even more trying to reproduce your “success”.

  2. What would be the point of announcing a successful test if the data was gathered didn’t give some basis for claiming success? Given secrecy around Chinese space efforts, it would be much easier to simply bury negative results and pretend the test never happened. Claiming success on negative results simply digs you in deeper and makes humiliation much more certain when others fail to reproduce the results.

    1. What would be the point of announcing a successful test under any circumstances, especially when it would be so easy to keep secret? The only case I can see for going public is to get your competition to chase a pitch in the dirt.

  3. I also remain skeptical, but of course communist science was always producing miraculous results because communism rewards what is politically correct, not what is factually correct.

    But if such drives do work, my inclination is to wonder whether I should think really hard about Erik Verlinde’s theory of physics, which has been getting some attention lately because it gets rid of the need for dark matter.

    From his 2010 paper (pdf)

    Abstract: Starting from first principles and general assumptions Newton’s law of gravitation is shown to arise naturally and unavoidably in a theory in which space is emergent through a holographic scenario. Gravity is explained as an entropic force caused by changes in the information associated with the positions of material bodies. A relativistic generalization of the presented arguments directly leads to the Einstein equations. When space is emergent even Newton’s law of inertia needs to be explained. The equivalence principle leads us to conclude that it is actually this law of inertia whose origin is entropic.

    What he’s basically done is take the point where physics ended up (black hole physics, information theory, statistical thermodynamics, etc) and show that if we worked backwards, just a few equations give you F=ma, F=Gm1m2/r^2, relativity, etc, just from extremely basic givens like “time exists, energy exists, there’s microscopic stuff that interacts with degrees of freedom according to some kind of microscopic laws.”

    So gravity and momentum are emergent behaviors due to things like entropy and conservation of energy, not immutable things in their own right. It’s simple and elegant (using almost no math), gets rid of the need to unite gravity and quantum mechanics, shows that macroscopic physics would be as we know it regardless of a bunch of universal constants or details of quantum mechanics, and gets rid of dark matter, It might even be right. But I’m still trying to wrap my head around it.

    So the question it raises for me regarding the EM drive is whether a microwave bundle of photons could change the underlying information (degrees of freedom, statistical thermodynamics of the underlying universe, energy density) that’s causes macroscopic particles to act like F=mA.

    1. “So the question it raises for me regarding the EM drive is whether a microwave bundle of photons could change the underlying information (degrees of freedom, statistical thermodynamics of the underlying universe, energy density) that’s causes macroscopic particles to act like F=mA.”

      I always assumed macroscopic particles to act like F=mA. The problem being the low mass and lack of energy to use it.
      Or a flashlight will give thrust, but it’s a very small amount of thrust- or essential nothing compared it the mass of flashlight.
      Do some macroscopic particles have more mass or made to have more mass- I have no clue.

      1. Verlinde’s work is one of the most interesting papers I’ve ever read. Even if it is wrong it is fascinating.

        In this paper we present a holographic scenario for the emergence of space and address the origins of gravity and inertia, which are connected by the equivalence principle. Starting from first principles, using only space independent concepts like energy, entropy and temperature, it is shown that Newton’s laws appear naturally and practically unavoidably. Gravity is explained as an entropic force caused by a change in the amount of information associated with the positions of bodies of matter.

        A crucial ingredient is that only a finite number of degrees of freedom are associated with a given spatial volume, as dictated by the holographic principle. The energy, that is equivalent to the matter, is distributed evenly over the degrees of freedom, and thus leads to a temperature. The product of the temperature and the change in entropy due to the displacement of matter is shown to be equal to the work done by the gravitational force. In this way Newton’s law of gravity emerges in a surprisingly simple fashion.

        Then he published another paper (PDF) extending his theory to regimes with low mass density and found that gravity would get supplanted by a cube law (instead of a square law) toward the edges of a galaxy.

        Some astronomers recently published a paper that found Verlindes predictions (which have no adjustable parameters) are as good a match to observations as the best dark matter predictions that have four adjustable parameters.

        But the theory is so new that there may be as yet unknown games we can play in the microscopic world that will have macroscopic effects that aren’t predicted by normal physics. Perhaps the EM drive is one of them. Or perhaps it’s experimental error and BS.

        1. Wouldn’t a 1/r^3 gravity fall off faster with distance, while dark matter is invoked to account for apparent gravity not falling off as fast as expected based on visible matter?

          1. That was very interesting, and pointed out the weaknesses that I think everyone sees, along with the thought that there might be something to most of it.

            Information theory and the thermodynamics of black holes shouldn’t be able to generate F=ma and all the rest, yet it does. Is local physics a result of bookkeeping instead of fundamental laws? As some of the fundamental laws are taken as givens instead of derived, perhaps so.

          1. Verlinde’s theory derives F=ma and all the rest (thus the conservation of momentum), but it does so as the result of laws governing entropy, energy, and temperature – basically bookkeeping. I would liken it to replacing the caloric theory of heat, which did work quite well in explaining how heat moved at a macro level but wasn’t an accurate description of what heat was.

          2. I suppose the other likelihood in something like Verlinde’s theory is that we started with F=ma and then extended that insight into thousands of other equations, which then of course can be combined in multiple ways so that everything else cancels out and you get back the F=ma you started with.

            Wouldn’t be the first time that’s happened.

          3. Darkstar, it’s hard to say with Wolfram. He spent a good part of his book congratulating himself on his own cleverness. I don’t think he’s quite right, but I think he’s pushing in the right general direction.

  4. A successful experimental test, means one did the test that you planned to do.
    Or for example there has been numerous successful tests related to orbital re-fueling- and that also includes doing them in orbit.

    And there has been many successful test related to Nuclear Orion. There has many test nuclear heated hydrogen, And etc. But we don’t have any nuclear Orion rockets nor do use nuclear powered rocket propulsion. Nor use nuclear powered airplanes.

    Or if this were a important successful test, we will see EM drive soon, and we probably aren’t going to- and there would be a few Chineses executed for giving up this important secret.
    All proves to me is Chinese are as gullible as everyone else- but I didn’t need that to be proven.

  6. Actually it demonstrates what’s wrong with our space program. Either the drive works or it doesn’t, but the implication if it does are so huge and the cost to test it in space so relatively minor that the fact that we didn’t (if we didn’t?) is a huge problem.

  7. They just launched their new station in September. Given lead times and all that, is it even likely that they had time to add such a drive system experiment?

    1. That is why a number of reports have put the test not on the space station, but on the tech demo satellite SJ-17. It launched in November.

    1. The major worry is that anything you do with significant power and current levels generates significant forces, to where you want to substitute 10-32 screws with 1/4-20’s so components don’t rip loose.

      In building countless panels that have nothing to do with thrust, where stray wire forces might be in Newtons, building a circuit that produces unexplained microNewtons is pretty trivial.

      The ways in which a power system can produce forces you didn’t anticipate is always educational.

      For a test nobody every did, hang everything within 30 feet of the EM drive by a string such that is oscillates like a pendulum with a particular period. Then cycle the EM drive with that period and see what starts swinging. That would be the conventional electric motor’s stator. Nobody has done that, even though it would occur to anyone in the 1800’s, or even the 1700’s. That’s because too many liberal NASA engineers are easier to fool than people in tube socks.

    2. Do you have a specific doubt of the Eagleworks test published last month

      One obvious specific doubt is a lack of a model to explain the alleged effect. That plus the small size of the effect is what’s driving resistance to the experiments.

      1. Yes, at milliNewtons per kW, it’s a pretty small effect.

        I have suspected that the high power may be producing high velocity ejections of ions from the surfaces that, due to the configuration, happen to be asymmetric, producing a pretty standard net reaction force. If surfaces near the device tend to acquire a metallic patina over time, that might be an indicator.

        1. But even one mN is pretty significant at orbital altitudes above a few hundred km. A solar-powered EM drive in a 500 km orbit should rapidly produce measurable perturbations on the orbit of a satellite weighing several hundred kg. Note that the thrusters on “zero-drag” satellites like GRACE compensate drag with mN or less thrust.

          So if this EM drive is for real (which I, personally, strongly doubt) it should be readily and unambiguously testable on a free-flying satellite.

          1. It’s very significant. But, it can be gotten with dramatically less power using existing means. The only advantage would be if it is truly reactionless. I still consider that very unlikely.

          2. > The only advantage would be if it is truly reactionless.

            Yes, though I prefer the term “propellantless” over “reactionless.” There are propellantless systems already in existence (solar sails, gravity assist, electrodynamic tethers) that nonetheless conserve momentum in one way or another. Some of the handwavy speculations about the EM drive fall into this category by, for example, transferring momentum to the quantum vacuum.

          3. I figured out how to make a “reactionless” drive system out of a ham sandwich. No matter how much power you apply, it produces no reaction.

      2. I have no shortage of models. They disagree with each other, but I have models (“if you don’t like those principles, I got others.”) But it seems to me that “does it work?” is a question that doesn’t need a model; “how does it work?” or “how do I control it?” is what needs a model.

        1. But it seems to me that “does it work?” is a question that doesn’t need a model

          It does need a clear demonstration that it works in that case. What has been done to date is not good enough.

          1. It has been done several times, including the NASA Eagleworks paper, and possibly again in situ on the Chinese station.

          3. One idea that just occurred to me is to have the drive riding on a tiny toy boat in a little kiddie pool filled with mercury, with the power fed down to a bearing in the middle of the pool and then over to the boat.

            boiling point of mercury.

            It looks like you could drop the pressure to 1 Pascal at room temperature (0.000145 psi).

            If the boat starts going in circles it means that there is some kind of real thrust, as no shift in center of mass due to any number of effects could maintain a continuous motion.

          5. what would be good enough?

            Use it in an unambiguous situation so that no reasonable refutation could exist. Using it in space would be completely unambiguous even if the force is small.

          6. Good catch Peter.

            There’s also the strong possibility that my test would just validate a microwave-frequency mercury thruster, perhaps thermally expanding the mercury behind the drive system.

  9. Mr. President, we must not allow an EmDrive gap!
    There I said it…

    I have a couple of comments to make:
    1) It’s the Daily Mail so don’t assume the Chinese actually confirmed anything. Until I see someone from CAST actually talking in an official press release by the main Chinese media (e.g. CCTV or Xinhua News) I wouldn’t put much faith into it. Not that the official Chinese media can’t be guilty of hyperbole either…
    2) It’s still 100-1000x too weak.
    3) I still don’t understand why people think it’s so impossible to make a reactionless drive, how do these people think propeller aircraft work? Just because we haven’t found anything to push against in space doesn’t mean there isn’t anything there to push against.
    4) I hope someone is really testing it in space. This seems to be important enough if it works and it’s easy and cheap enough to test.
    5) It wouldn’t be the first time the Chinese would be ahead of the US in technology in some way. I can list a couple of examples, even if nearly all if not all of it is imported from elsewhere, high-speed trains, hydrocarbon staged combustion engines, artillery (check the firing range of the PLZ-05 against the M109A6 Paladin).

    1. PS: Heck the Chinese are going to finish building a US designed Westinghouse AP1000 nuclear rector before the US will.

      1. In fairness it makes little sense to build one here when our natural gas is so cheap we’re exporting it to the Persian Gulf.

    2. Solar Sails are actually a good point in comparison. A couple of people at one time thought the basic technology was impossible. Try reading about the Crookes radiometer.

  12. Solar sails just aren’t practical due to the manpower requirements for changing course, which is why Lucas didn’t have Imperial star destroyers using them as they sailed in line of battle to exchange broadsides with other capital ships in orbit above Coruscant.

    By the time a crew of astronauts can climb all the way to a royal or topgallant, reef a sail, and make it back to the airlock, half their oxygen supply will be depleted.

    If Lucas rejects an idea as too dumb, it’s really dumb!

    1. At the very least, declarations of victory against the tyranny of local conservation laws are decidedly premature. Thanks for the link.

Comments are closed.