The EM Drive Might Not Work, but We Get Helicarriers If It Does

There is a device under test out there that promises to take humans to another star in a single lifetime. It means vacations on the moon, retiring at Saturn, and hovercars. If it turns out to be real, it’s the greatest invention of the 21st century. If not, it will be relegated to the history of terrible science right underneath the cold fusion fiasco. It is the EM drive, the electromagnetic drive, a reactionless thruster that operates only on RF energy. It supposedly violates the laws of conservation of momentum, but multiple independent lab tests have shown that it produces thrust. What’s the real story? That’s a little more complicated.

The EM Drive is a device that turns RF energy — radio waves — directly into thrust. This has obvious applications for spacecraft, enabling vacations on Mars, manned explorations of Saturn, and serious consideration of human colonization of other solar systems. The EM drive, if proven successful, would be one of the greatest inventions of all time. Despite the amazing amount of innovation the EM drive would enable, it’s actually a fairly simple device, and something that can be built out of a few copper sheets.

The basic design of the EM drive is a truncated cone, called a ‘frustum’ in the proper engineering parlance. This hollow frustum is sealed at both ends. An antenna, or a simple piece of wire, is placed into the device, about halfway between the small and large ends of the frustum. This antenna is connected to an RF generator, in most cases a magnetron or something else that can generate microwave frequency RF.

FrustrumThe EM drive produces thrust because of a differential force on each end of the frustum. Because one end of the frustum is larger than the other, the net force is the difference between the forces on the large and small end of the cone. As far as a theoretical explanation of why the EM drive works (if it actually does), that’s about as good as you’re going to get. Understanding some of the proposed theories of how the EM drive works requires at least a Master’s in physics and many years of experience with RF systems. It’s not light reading.

Although the EM Drive and similar RF reactionless drives have made the news recently, the first inklings in academic literature are actually relatively old. [Roger Shawyer], the person who will be called the grandfather of the EM drive, started down his current path of research in the early 2000s. The paper that can be considered the birth of the EM drive is The Performance Analysis of Microwave Thrust without Propellant Based on the Quantum Theory, published by [Yang] in 2008. This paper by [F.O. Minotti] from 2013 investigates the possible theoretical background of the EM drive. It was not until NASA’s advanced propulsion research group, also known as Eagleworks, found anomalies during their test of an EM drive that the media clued into the potential of a device that produces thrust using only electricity.

EM Drive Tests and Statistics

Right now there are a few lab results that are not conclusive. They do, however, point to some sort of effect, and recent tests have further refined how large the EM drive effect actually is. This is where scientists are separated from amateurs, and where the probability of the EM drive being real increases, even though that might not be the case. 

StatsTo visualize the strange statistical aberrations, imagine the statistician’s favorite example, the archer. An archer, by profession or proclivity, shoots arrows at a target. At the beginning of his career, he’s not a very good archer, but he does manage to hit the target a few times before he runs out of arrows.

After practicing a few months, the archer’s accuracy improves. His shots don’t go as wide as before, and he doesn’t have to walk as far to collect his arrows. In fact, he’s even hitting his target more often. Obviously, he’s improving.

A few more month’s worth of training later, and the archer can’t seem to land a single arrow on the target. Of course, he barely has to walk at all to collect his arrows, and all his shots land on the same square foot of ground. He’s amazingly accurate for a medieval archer, but he just can’t hit the target.

For anyone with any experience at all in statistics, this is how the difference between accuracy and precision is taught. Accuracy is hitting the target, precision is getting a tight grouping. This difference means strange things can happen when you slowly refine the accuracy of a measurement.

In the graphic to the left, the center of the ‘hit box’ in each of the three cases is in exactly the same place relative to the bull’s eye. The only difference is the reduction in accuracy makes the archer less precise.

This effect can be seen everywhere if you pay attention; in late 2004, the asteroid Apophis was discovered and predicted to have a 1 in 233 chance of colliding with Earth in the year 2029. Days later, the probability of colliding with Earth increased to 1 in 37. It was not until more data were collected that the threat to Earth from the asteroid Apophis was brought down to comfortable levels; in 2029, this asteroid will miss the Earth entirely.

This effect is also seen in the results from various EM drive tests. From the Chinese lab tests to the testing done at NASA’s Eagleworks, the observed effect has been further refined, and the signal to experimental noise figures increased. This is exactly what you would expect from anything that is being studied in increasing detail, and an increase in the probability that the effect is real is not proof of the effect being real.

However, this does not stop people from dreaming. The best research points to the EM drive generating 30kN of thrust for each kilowatt of power dumped into the frustum. Put more simply, one kilowatt (the power to light ten 100 W light bulbs, or run a microwave oven) could lift a 3000 kg object and hover a few feet off the ground.

Lifting Really Big Things

Helicarrier_aftTo put this in more practical terms, a Tesla Roadster has a 58kWh battery and weighs about 1500 kg. Strap an EM drive to a Tesla, and you have a hovercar. Hovercars are cool, but the aircraft carrier USS Nimitz displaces about 100,000 metric tons, and is powered by two nuclear reactors that produce a total of 208MW. That’s a S.H.I.E.L.D helicarrier. Visiting another star with an EM drive is just one goal; if the EM drive works, we’re also going to get vehicles we can’t even imagine right now.

There’s still a lot of work to be done to tease the EM drive signal out from underneath experimental noise. It might not even turn out to be a real effect. However, multiple labs have tested versions of the EM drive and have found strange effects in their data sets. As it stands right now, the EM drive is only a few notches above a crazy guy who says he has a perpetual motion machine in his workshop. But even Galileo was labeled a heretic; the key is in proving the theory. The EM drive has stood up to tests so far, and if it turns out to be real, it will be an invention more important than the internal combustion engine.

226 thoughts on “The EM Drive Might Not Work, but We Get Helicarriers If It Does

  1. Where did the estimated thrust data come from? From the garage guy to nasa the people creating and testing have always claimed its a micro thrust, only suitable for accelerating things in space over quite some time.
    If thats changed id love to read the papers.

        1. Why? It uses a large amount of power to generate a small force, I can give plenty of examples of devices that do the same, solenoids for example.

          To get a PM machne you need to turn that small force into power greater than the input, how do you propose to do that?

          1. It’s pretty simple, really. Let’s assume, for a moment, that we have a reactionless thruster that produce 1 N/W of thrust. The result is general, so I’m starting with some easy numbers.

            First, rig an EM Drive such that its upward thrust is equal to its weight. You can use a balance for this, of course. That means it’s hovering. Let’s assume for simple math’s sake that our device weighs 1 N, so its power consumption is 1 kW. Let’s also assume we’re in a vacuum to make things simpler.

            Second, give it an upward velocity of, say, 2 m/s. Now wait 1 seconds. Your device has consumed 1 J of energy. Its kinetic energy has not changed, but its potential energy has — it’s now 2m higher, so its potential energy has gone up by 2 J. QED.

            It should be obvious that you can fiddle the velocity as required to produce a net gain in energy for any thrust per kW claim higher than radiation pressure.

          2. @Pierce Nichols:

            “Second, give it an upward velocity of, say, 2 m/s”

            Where does your energy producing that upward velocity of 2 m/s come from, to accelerate a hovering device weighting 1 N and consuming 1 kW at a specific thrust of 1N/kW?

            “Its kinetic energy has not changed”

            Are you really explaining that after ACCELERATING an objet up to 2 meters per second from a stationary position in a 1g gravity field, the object has no kinetic energy?

          3. @Pierce, I’m not a physicist, but I’ll weigh in anyways.

            You claim that a device that uses 1kW of power to hold up (hover) a 1N device is not possible. So how are RC Helicopters physically possible? 1N is about a .1kg mass on earth. That is a good weight for most toy helicopters, and most helicopters would use far less than 1kW to hover. A toy helicopter could easily be accelerated to 2m/s.

          4. @Pierce-Wow that is just so flawed. First of all if the device weighs 1N and the thrust is 1N/W then the power it consumes is 1W, not 1kW.

            But more importantly the watt of power has to come from somewhere, likely a battery. Just making something go up isn’t enough to claim it’s perpetual motion. It’s consuming energy the whole way no matter what. Unless you are claiming that simply gaining height instantly adds electrical energy in the battery. The scenario you described is easily accomplished with helicopters and electromagnets, which obviously aren’t perpetual motion.

          5. Gaining height increases gravitational potential energy, which is proportional to your distance from the ground. If you could make an object ‘weightless’ in a gravity field with constant energy, then a single impulse upwards would translate into a theoretically infinite amount of kinetic potential energy as it ascends.

          6. If you read the papers on how the Emdrive works, you’ll find that its efficiency decreases with speed. It can provide a constant thrust at slow velocities, but as it speeds up, the effect (which is based on some interesting electromagnetics theory) decreases.

            The Emdrive may not get us to the stars – that will require something like the Abicurre drive – another invention at the fringes of possibility that we have yet to confirm works.

          7. @pierce

            This does not create a perpetual motion machine, because the energy has to come from somewhere. In your example there was no source, and potential energy is not actual energy. The moon has a lot of “potential energy” when considering how “high” up it is, but that does not give it “energy” magically. It has to actually fall to get real energy.

          8. @flux_capacitor: The kinetic energy at the beginning and the end of the period stated are the same and therefore irrelevant. The point it that it’s trivial to arrange a system that gains more energy than is put in over some time period.

            @kratz: An R/C helicopter accelerates air downward in order to support itself, and therefore does not violate conservation of momentum.

            @captainspirou: The device gains gravitational potential energy in excess of the energy expended. Therefore, it is a perpetual motion machine.

            @Vik: That’s pure handwaving.

            @David: Did you just claim that gravitational potential energy isn’t real?

          9. @Pierce, conservation of momentum is irrelevant, as your argument is about conservation of energy. Regardless, after reading through all of this and refreshing my basic physics, the RC helicopter would necessarily need to increase its energy consumption/output to meet the constant thrust/acceleration as in your example.

            This is the center of why few agreeing with you. As someone else wrote, and what I think most are missing, is that one of the authors of one of the papers made the claim of constant thrust/acceleration at a constant energy input. Yes, as your argument shows, this claim cannot possibly be true due to conservation of energy. This is the basis of your argument, but I think few others believe that to be true (or they do but do not understand it).

            However, that does not disprove that there may be some previously unobserved phenomena occurring. If it exists, it just has to obey conservation of energy (obviously).

            I think someone else made reference to the lack of a reference frame, due to no expelled thrust material. I feel that is irrelevant, as any object object must obey conservation of energy in any reference frame it is examined in. A rocket doesn’t only obey conservation of energy in a reference frame based on its expelled fuel, it also obeys it from any other reference frame the system is examined in.

            TL;DR, yes you are correct based on your assumption of constant acceleration from constant power. I respectfully disagree with that assumption because it must be false.

        2. Armchair Physicist here…… @Pierce I think your logic is flawed. If the EM drive works then you would be able to build a machine that *appears* to be a perpetual motion machine. Your statement implies that someone is claiming that the EM drive powers itself; which is neither a statement anyone has made or a true statement. There is absolutely a “fuel” powering the engine.

          1. Right now the big problem a lot of people have with the EM drive is that it is achieving thrust levels greater than a theoretically perfect photon drive could achieve for the same amount of power. This means it has a conversion of energy->motion efficiency of over 100%. With drives that eject some mass (rockets, etc) everything works out nicely as far as the math is concerned. The problem that arises from this is that if you have a system with this level of efficiency, there WILL exist a circumstance that you can arrange that can be used for free infinite energy. Now, this doesn’t exclude the possibility that the EM drive is doing something currently unknown that equalizes this, but in keeping with the usual methods of science, this explanation is to be a last resort only.

            The big thing the EM drive has going for it, above perpetual motion machines and cold fusion, is that anybody can build one and test it to get reproducible results. And they are!

            Amusingly enough, in a lot of ways we are now at the point where the possibly glory of being the one to find out the error that everyone else is missing exceeds the credibility hit you get as a scientist for working on the EM drive. So we are seeing (slowly) even more scientists that are starting to look into it, even if only because they are trying to find out why it DOESN’T work.

          2. Short answer: 2nd Law of thermodynamics (All systems <100% efficient)= No perpetual motion machines

            You could hypothetically violate the 2nd law of thermodynamics in all kinds of ways that had nothing to do with perpetual motion. However, the "impossible perpetual motion machine" is the common example of the 2nd law, so the example is being invoked.

          1. It’s maths that fits well enough to be used coupled with a theory that fits the maths.
            We still can’t categorically prove the underlying reason the maths gives the correct answer.

        3. The problem with people like you is that they can’t see beyond what has been teached to them. Your knowledge clouds your vision my friend. There will always be mistakes in current theories and if you fail to see that, then you are no scientist and your knowledge is worth nothing. Therefore … you will never make any groundbreaking discoveries … ever.

          1. “Iff x is true, we would be able to build a perpetual motion machine; therefore x is almost certainly not true” is a pretty reasonable conclusion, actually, because a universe that permitted the wholesale violation of the conservation of energy would look pretty radically different from the one we live in.

  2. Not a fan of the intro, yes the EM Drive and the Cold fusion thing are both very debatable, but shooting them down in the first paragraph is kinda silly, especially because we don’t even know anything for sure yet, but recent tests of both do appear to be successful (like the article even points out minutes later)

    Besides that, fuck yes, “i believe”, EMDrives will take me to mars ~20 years from now, cant wait.

    1. The EM-drive is bogus because of both theoretical and empirical reasons.

      1) If the drive was real, it would break the conservation of energy principle of physics: A force applied to a mass causes constant acceleration, and constant acceleration requires constant increase in power proportional to v^2 whereas the input power of the device remains constant. Energy must appear out of thin air – therefore it’s bogus.

      2) The actual measurements as pointed out in the NASA and other papers actually say that they’re unable to rule out the possibility that the effect is not from the device but from the measuring setup itself, because they get a signal while testing the no-thrust case – i.e. the device is “off” or in a no-thrust configuration – yet the experiment says it is producing thrust.

      The latter problem has nothing to do with measurement precision or accuracy, but the fact that the testing setup itself is generating thrust in some as of yet unknown way that has nothing to do with the EM-drive.

      1. > because they get a signal while testing the no-thrust case

        That’s not true. They were testing three conditions with a similar EM drive with ‘vanes’ inside the cavity. The ‘null’ test was without the vanes, and it still produced thrust. It’s not an invalidation of the EM drive, it’s an invalidation that the ‘vanes’ are required for an effect.

          1. They had 3 articles for test. They had the Cannae Drive (with vanes). The control (standard EM drive, no vanes). And then the actual null test (just an RF load, no engine), that is basically the control’s control. This test was done this way to test if the Cannae interpretation (Shawyer’s theoretical model) for what makes the EM drive tick was correct.

            The Cannae drive was tested, thrust resulted. The control was tested, thrust resulted. In fact, the control produced MORE thrust than the Cannae drive by a slight, yet detectable, margin. Thus proving the Cannae interpretation was flawed. The null test (the RF load) produced zero thrust.

          2. ….at this very moment, 300 people in Scotland are chuckling at this comment to the total confusion of the rest of the world:)

            “hae they no drivin license?”

      2. I don’t see how your point number 1 has any validity at all. Were your argument valid, a regular rocket engine, which trades constant energy output for constant acceleration, would also violate conservation of energy.

          1. …and that’s what leads to the Tsiolkovsky rocket equation, which means the same amount of thrust results in an _increasing_ acceleration as the mass decreases. The decrease in mass isn’t required to avoid violating the conservation of energy!

          2. I mean, in your opening statement you literally say “force applied to a mass causes constant acceleration”, then go on to claim that that very thing isn’t possible.

          3. …except that the rocket equation is basically also saying that a rocket with unchanging mass will not accelerate, or just maintains its velocity. If you’re not going to accelerate, what’s the point of having the EM drive on board? You might as well just coast on already built up kinetic energy, just like the Voyager probes are now doing.

          4. But that’s not what it says at all. In the absence of external forces (gravity, for instance), a force is always going to result in an acceleration – proportional to the force and the mass of the object, and unrelated to its present velocity.

          5. “The decrease in mass isn’t required to avoid violating the conservation of energy!”

            A rocket would not work without shedding mass, because it derives the thrust by throwing the reaction mass out.

            Work equals force over distance (W=Fs) and therefore power must equal work over distance per time (P = Fs/t) where s/t = v which becomes (P = Fv). Even at this basic point we can see that both force and power cannot be constants if speed increases, and this must apply to the rocket.

            The illusion that it breaks the conservation of energy comes from the fact that you consider only the speed of the rocket and not the exhaust gasses which go in the opposite direction. The v for velocity is really the sum of both the rocket and the exhaust gasses, not the velocity of the rocket alone.

            If we have a “rocket” that does not shed mass or leave anything behind, and we say that force remains a constant “1”, we can arrive at the conclusion that:

            P = v

            That is saying that the output power of the device must continue to increase linearily, but the claim is that P is constant, so we arrive at a contradiction. The device as described is impossible.

          6. You’re really seriously claiming that in a vaccum, the force required to accelerate an object by a constant amount depends on its current velocity? Not only is that directly contradictory with the second law of motion that you yourself cited, but velocity depends on your reference frame. I guess all I really have to do is keep redefining my reference frame to be stationary relative to my rocket, and I’m back to only needing a=F/m.

          7. Dax, while I tend to agree that this device is implausible, your first reason and follow-up about how a rocket works shows that you really don’t have a good understanding of the physics you are talking about. In the interest of not being jerky, I’ll do my best to explain why:

            “1) If the drive was real, it would break the conservation of energy principle of physics: A force applied to a mass causes constant acceleration, and constant acceleration requires constant increase in power proportional to v^2 whereas the input power of the device remains constant. Energy must appear out of thin air – therefore it’s bogus.”

            First: a force applied to a mass does not cause constant acceleration. This, in fact, is why calculus was developed, to account for such cases as changing forces and changing masses. The rocket equation has already been mentioned for the case of a massy fuel, where burning the fuel reduces mass, and, if thrust is constant, the acceleration will increase with time due to reduced mass. A constant force applied to a constant mass, on the other hand, does produce constant a. I’ll give you half marks on this part.

            Second: Once you bring power into it, you lose any further marks, as power and energy do not apply. The force in these discussions is purely internal to the system, and the due to conservation of momentum. We tend to think of F=ma as the definition of force, as it is what most students see first. No calculus needed, simple, clear, and, unfortunately, not the best choice here. The best choice here is F=dp/dt. Force is rate of change of momentum. For a fuel burning rocket, we can find the force on the rocket body two ways: figure the acceleration of the exhaust gasses (which isn’t constant over between the time between combustion and expulsion from the nozzle), time over which they accelerate, and a whole host of other things, then use F=ma with a bit more calculus, since what we actually have is a mass flow rate- mass per unit time- rather than a fixed mass. Or, we do it the easy way: Use the final velocity of the exhaust gas relative to the rocket and the mass flow rate to get change in momentum per unit time directly, otherwise known as force. The force on the exhaust is equal to the force on the rocket, so we can get acceleration.

            Nothing requires energy to “appear out of thin air”. Energy goes into the device via a waveguide from whatever microwave generator is used, and the microwave generator is powered from some electric power source, which converts energy from some other form (chemical, thermal, etc) to electric.

            I will not worry about your point 2), as that has already degenerated into name calling.

          8. To prove it another way, we can also note that (F=ma) and (v = at)

            Therefore (P=Fv) is actually (P=ma^2t)

            That indicates that the power of the device must increase linearily with time in order to maintain acceleration. Therefore, to maintan constant power, we must either lose mass linearily over time, or lose thrust.

          9. Did you read the rest of his reply?

            And even if you didn’t, you just reiterated that constant force gives constant acceleration – counter to what you’ve been trying to claim all along.

          10. “You’re really seriously claiming that in a vaccum, the force required to accelerate an object by a constant amount depends on its current velocity?”

            Yes. Maintaining constant acceleration relative to some object does require ever-increasing power.

            This is basic Newtonian physics. Take for example the kinetic energy formula (E = ½mv^2). Increasing your velocity by a constant amount requires increasingly large amounts of energy the faster you are already going.

            You just have to remember that the rocket is not the only object that is moving. You’re leaving behind mass which loses speed as you gain speed.

          11. In which case, can you tell me how much force (or power, if you’d prefer) would be required to increase the velocity of a 1 kilogram object in a vacuum by one meter per second? If so, why doesn’t the answer depend on how fast it’s already going (relative to what, too?)

          12. “In which case, can you tell me how much force (or power, if you’d prefer) would be required to increase the velocity of a 1 kilogram object in a vacuum by one meter per second?”

            In a space with no other object, it is meaningless to say that we are moving in any direction because we lack a reference frame, so the question itself has no physical meaning.

            “If so, why doesn’t the answer depend on how fast it’s already going (relative to what, too?)”

            Exactly. “Relative to what?”.

            If you and the object are the only things in this space, the speed that it is “already going” before you throw it is zero. If you had a second object to throw, and toss it at the same relative speed from yourself as the first one, it suddenly appears that the first object speeds up as well as if by magic, because by the reaction principle you accelerate away from it by throwing the second object.

            Whether you move or it moves, the two cases are indistinguishable because there’s no fixed frame of reference. From your point of view then, you are accelerating all the objects instead of just the object you’re throwing. It takes the same force over the same distance and time to throw the object, but the kinetic energy in the system of objects you’ve previously thrown seems to increase at an accelerating rate with each throw, and therefore your own kinetic energy relative to them seems to increase more than the energy you spend.

            This seems like a violation of the conservation of energy – except for the fact that you’re also losing 1 kg of mass every time you throw one, so the extra energy actually comes from your own kinetic energy. This is called the Oberth effect: https://en.wikipedia.org/wiki/Oberth_effect

          13. Relative motion might be meaningless without any other objects, but acceleration isn’t. Regardless, let’s make things more obvious. Suppose the 1KG object in question is accompanied by two other objects. One is motionless relative to it at the beginning, and the other is moving away from it at one meter per second. Now can you answer the question?

          14. “In which case, can you tell me how much force (or power, if you’d prefer) would be required to increase the velocity of a 1 kilogram object in a vacuum by one meter per second? If so, why doesn’t the answer depend on how fast it’s already going (relative to what, too?)”

            You can’t. You’re missing information.

            For force, you need the time that the force is operating. Let’s say 1 second. Then the answer is easy: 1 N in 1 second causes a 1 kg object to change its velocity by 1 m/s.

            For power, you need the *distance* over which the force operates, since energy is force times distance. Which, if the object is moving, means it depends on the object’s speed! If the object was moving at 0 m/s in the reference frame, accelerates to 1 m/s in 1 second, that takes a total of 0.5J (it moved 0.5 m), averaged over 1 second is 1 W. If the object was moving at 1 m/s in that reference frame, accelerates to 2 m/s in 1 second, that takes 1.5J (it moved 1.5 m).

            WTF, you say, it takes 3 times more energy! Yes, it does. So how is that possible? Because in vacuum, conservation of momentum says if you gain 1 kgm/s, something else *lost* 1 kgm/s. For a rocket, that “something” is the exhaust, and that momentum change of 1 kgm/s in the rocket corresponded to a bigger decrease in its kinetic energy (in absolute terms). Which went into the rocket.

            So yes, a constant acceleration does require ever increasing kinetic energy transfer as the object’s velocity increases. How do you avoid having a preferred reference frame, then? Conservation of momentum.

          15. I have a RC boat that turns power into thrust without shedding mass. And it’s speed is limited only by friction. BLDC motor spins propeller really fast, that sucks water on one end and shoots it faster on the other. Energy stored in batteries is converted into thrust, which causes acceleration up to mechanical limit of both the propulsion system and hull design.

            Ever heard of Bussard ramjet? The same Bussard as in Star Trek’s Bussard collectors? That one converts energy into thrust too by using electromagnetic fields to collect hydrogen molecules, compress them enough to cause thermonuclear fusion and release them from the other end of the ramjet. With constant mass, constant thrust and constant drag force caused by particles that are in vacuum of space, the only thing that will change is velocity. And if the crew of hypothetical space craft needed extra boost, they could vent out that unlucky guy in red shirt from the aft airlock.

          16. An RC boat still conserves momentum. It throws *the water* behind it. It just happens to travel in this medium with a free supply of stuff to throw behind it.

            A Bussard ramjet still conserves momentum. It throws *the fused hydrogen* behind it. It just happens to travel in this medium with a free supply of stuff to throw behind it. Same deal.

          17. One problem might arise with many assumptions regarding conservation of momentum: Newtonian Physics are – if there is an effect – not the domain of this matter (cogh…). I.e. as the microwaves travel with considerable velocity/speed.

          18. This is not a hard problem to solve. Dax is clearly confusing conservation of energy with conservation of momentum. Conservation of energy is not obviously being broken, while conservation of momentum is. It also seems like a lot of you (mind bogglingly) are confusing terms like energy, power, force and acceleration. If any of you are any sort of engineers, you should be deeply ashamed. Here are the facts:
            Constant force on an object of constant mass results in constant acceleration.
            The energy required to exert a constant force depends on the mass (which changes in a rocket) and the speed (which changes most of the time).
            Using the rocket equation on something that isnt a rocket (or something that doesnt lose mass) is fairly meaningless
            If you use 1kw of power to move something for 1 second, whatever form that power is in, it will increase its speed by sqrt(2000/M) (assuming 100% efficiency etc). Obviously this device does not claim to be 100% efficient in that sense.

            Maybe the problem is that you guys immediately went into a long technical discussion, and it took 7 posts for someone to mention conservation of momentum, which is the important part.

          19. “Conservation of energy is not obviously being broken, while conservation of momentum is. ”

            … Kindof.

            It’s important to realize that conservation of momentum is just saying “there’s no preferred direction to the Universe” and conservation of energy just says “there’s no preferred location in the universe.” Adding in conservation of angular momentum gets you “there’s no preferred direction in the universe,” and you combine them all to get “no preferred reference frame.” You can actually start from those, do a bit of math, and get back conservation of momentum/energy. They’re totally equivalent.

            What’s funny about those laws is that at first glance, they’re obviously crap. There are 2 obvious preferred frames in the universe: the rest frame of the CMB (frame in which the CMB is isotropic) and the rest frame of the Hubble flow (frame in which the Hubble flow is isotropic).

            So people then hedge their bets and say “well… we just mean that the physics doesn’t care about it. The actual Universe might.” Except that, well, physics is what actually generated the CMB and the Hubble flow. Not some local thing in the Universe. So what’s the deal? What’s going on is that the Hubble flow and the CMB were generated by *physics we currently don’t understand* (whatever caused the Big Bang, and whatever caused inflation). Those two things “broke” conservation of energy/momentum/etc. because we don’t know where the energy came from. When people *do* figure out how inflation works, for instance, the CMB rest frame will then just be caused by some symmetry-breaking constant in the math, and energy/momentum conservation comes back – the energy came from “magic inflaton field,” or whatever. For reference, the concept of “missing energy” being interpreted as “something we can’t see” is like, the basis for huge amounts of particle physics.

            So in this case, they’re not actually claiming violation of conservation of momentum. Which would be silly, because it’s not so much of a conservation law as a tenet: something that physicists *start* with, and build everything else around it.

            What the JSC guys are actually claiming is that they’re “distorting the quantum vacuum” to produce thrust. You make the quantum vacuum dense behind you, and chuck photons into it. The photons impart *more* momentum change because they’re resisted more by the denser vacuum out the back (you can frighteningly also view this as locally reducing ‘c’ in that area). So where does the momentum in the end come from? The vacuum: you’re distorting it a little bit, and presumedly that distortion ripples out through physics you don’t know, carrying momentum, and hey! In the end, momentum gets conserved.

            Or they might be pushing off the voodoo magic field. Both equally likely in my mind.

          20. Crap, crap. Mucked things up there. Conservation of energy is “no preferred time.” Conservation of momentum is “no preferred location.” Conservation of angular momentum is “no preferred direction.”

        1. The mass of a rocket decreases, and the velocity of the exhaust increases. That’s what makes up the difference.

          That being said, they’re not claiming a constant acceleration. They’re claiming a constant force, in a fixed frame corotating with the Earth. The only way you get an (apparent) reactionless drive is if there’s some kind of exhaust you’re missing: the only question is what’s the exhaust that you’re missing. It’s either something stupid that the testers are missing, or they’re pushing against the voodoo magic field. (Or gravity, like the linked paper says, but hey, both of those are probably equally likely).

          1. The constant force cannot be “thrust”, because “thrust” implies that it remains over distance and creates the conservation of energy problem, yet “thrust” is what they claim.

            There’s a multitude of ways in which a microwave cavity can create a static force, such as eddy currents in the metal or in the gas inside, which create a magnetic field, which interacts with nearby metallic objects or the earth’s magnetic field and causes the pendulum to turn.

          2. “The constant force cannot be “thrust”, because “thrust” implies that it remains over distance and creates the conservation of energy problem, yet “thrust” is what they claim.”

            1) Jet engines provide a thrust in an atmosphere. Try to fly them out of an atmosphere and thrust disappears (because the air disappears, but that’s the point). Same deal here. They might get a thrust in that setup. That doesn’t mean it continues once you’re anywhere else.

            2) Being fair, it really could be thrust. See above voodoo magic field. OK, the scalar portion of a scalar-tensor theory of gravity, but it’s the same deal. No matter what, they’re pushing against something. It’s either exhaust they haven’t found, or they’re pushing off of something they haven’t identified. Local metal objects (through magnetic fields), the Earth’s magnetic field, the atmosphere, or a previously undiscovered fundamental field. (Guess which one is the least likely.)

            I mean, there *are* fundamental fields you could imagine always pushing against with magic unknown physics we don’t currently have. Dark energy, the Higgs field, whatever the hell dark matter is, etc. But I do not believe ‘random aerospace engineer’ has managed to tap into magic unknown physics with a copper box.

            “such as eddy currents in the metal or in the gas inside, which create a magnetic field, which interacts with nearby metallic objects or the earth’s magnetic field and causes the pendulum to turn.”

            Yeah, I filed that under “something stupid they’re missing.” However, pushing against the Earth’s magnetic field is easy to rule out, and I believe they did do that: just turn the entire setup. Similarly you could just move the thing around inside the room, and if the force stays the same, that’s also not likely to be a magnetic-type reaction.

            I think they’ve done that too, but actual results from the NASA group are few and far between. It’s really sketchy science. Information release through Internet message board isn’t an improvement over peer review.

        1. Just because it’s not yet fully understood doesn’t mean it’s pseudoscience. In fact, the process it’s going through in order to prove or disprove the device are literally the definition of science.

          1. No, because the argument from ignorance asserts “this is true because it hasn’t been proven false”. In fact, you are the one proposing an argument from ignorance, insisting the device is invalid because it hasn’t been proven valid.

          2. No, it’s the fact that the EMDrive is equivalent to a perpetual motion machine that make it pseudoscience. It cannot produce more thrust than a laser of equal beam power without violating the conservation of energy.

          3. Sure, but lasers are incredibly inefficient. If you built a device as effective as a laser, but far more efficient, that’d be an innovation worth having.

          4. Nono, it’s not the efficiency of the laser that matters. That only makes the problem worse.

            A photon of energy E thrown out the back imparts a momentum change of E/c to the ship. So if you do that in time “t”, the power is E/t, the rate of momentum change – e.g. the *force* is E/ct.

            If the efficiency of photon generation is “e” (so e less than 1), then the efficiency of any photon-type drive is 3.33e nN/W. That’s *nano-newtons*. So 3.33 nN/W is the upper limit of any photon-type drive.

            And these guys are claiming micronewtons/W, or a thousand times greater than any photon drive can generate.

          5. If that’s the case then, yes, it does cause me to reassess my own estimate of the whole thing’s plausibility down rather a lot. The fact that legitimate scientists have done legitimate science and come up with inconclusive results means that I’m quite happy to wait on further information before labelling it “pseudoscience”, though.

          6. “The fact that legitimate scientists have done legitimate science”

            This is probably the biggest problem I have with people outside the scientific community. There’s a ton of absolute crap out there that looks like it was done perfectly fine. So why isn’t it immediately shown to be crap? Because it costs money to try to repeat something. And to try to eliminate a tiny effect, it costs a *lot* of money. And scientists *do not get paid* to attempt to eliminate somebody else’s crap. So tons of “inconclusive” results or wacko-stuff results just sit out there, without being disproven, because the legitimate scientists don’t have money to waste.

            In this case, though, this is different. This isn’t legitimate science. This is crazy hairbrained science. It falls under NASA’s “it’s okay to spend small amounts of money on crazy hairbrained schemes if the potential reward is huge” program (Breakthrough Propulsion). Everyone knew this was almost certainly crazy. The problem that NASA has now is that you really needed a skeptic in charge, and I don’t think White is a good enough skeptic.

          7. I was using “real science” as a shortcut; I’m happy to spout the scientific method terminology if you want.

            The corollary of what you call NASA’s “it’s okay to spend small amounts of money on crazy hairbrained schemes if the potential reward is huge” scheme is that when it produces positive or inconclusive results, the rational thing to do is withhold judgement in favor of more and more robust testing – not to dismiss it as pseudoscience because it seems crazy and hairbrained.

            While I’m sure not every scientist at NASA is as brilliant as their best, I’m pretty confident that they’re smart enough to understand the basics of their field, and if it could be dismissed as simply as some commenters think, that they would have avoided it altogther, or pointed that out themselves.

        2. ” insisting the device is invalid because it hasn’t been proven valid.”

          We aren’t even at that step yet – we’re still at the stage of proving that the experiment is valid and does actually measure the effect its supposed to, which hasn’t been done. So we have an unverified experiment producing uncertain results, and we are supposed to accept on these grounds that there exists positive evidence for the device?

          Your argument from ignorance is that we have something here because we don’t understand what’s happening, when in reality we have nothing but a bunch of junk data, and trying to speculate on junk data is called pseudoscience.

          1. > and we are supposed to accept on these grounds that there exists positive evidence for the device?

            I don’t think anyone’s suggested that – I certainly haven’t. The article itself takes a pretty balanced “it’d be cool if it works, but evidence is weak so far; more science required” view.

            > when in reality we have nothing but a bunch of junk data

            My own opinion of NASA’s ability to do science is evidently higher than your own, then.

          2. “My own opinion of NASA’s ability to do science is evidently higher than your own, then.”

            NASA is a very big organization. There are very smart, detail oriented people who do super-careful experiments. There are also complete hacks. How can such a wide range of talent all continue to get funding? Welcome to government science funding!

          3. “There are also complete hacks. ”

            Exactly. This sounds exactly like one of those cases where someone put the new guy on the job because someone in the management found this really cool thing that absolutely must be tested, and none of the reputable researchers want anything to do with the crank stuff.

            Kinda like the scientific equivalent of “fetching the left handed hammer”.

          4. Actually it sounds much more like the wacko group at JSC – the guys who were trying to observe space being bent using a tabletop laser. Oh wait! It is those guys.

          5. To believe one cant be ignorant is pure ignorance in itself. First off, its a written article. Its purpose is to get noticed, read, and spread. Please understand that when taking shots at its verbage. Bit of trollage if you ask me. Second, Ill be the first crack pot to toss out the conspiracy that the cone shape is pretty damn close to the “ice cream cone” theory behind the movement of large masses in ancient Egypt. Funny enough, it was thought it was some how sound induced. Having the attitude that said possible future progress is unobtainable due to currently known restrictions is beyond understanding to me in this community. Im also the type to believe we hear and read what were supposed to. So this generalized “pipedream” feeling im getting from posters, is it intended? Lets say ANY country perfected it…why would they let us know, or believe that it was real??!!! Or am I the only one that believes that war applications would trump all other in the eyes of ANY government?

          6. Would you believe that the government has tech that can scan a vehicle(rather,anything) and read off ALL materials making up said vehicle or structure in seconds..They do. Yes, that means they can do soooo many violations of privacy and youll never know. Also means they should be able to mass produce and make every port have flawless security… but they wont. My point being is everyone seems to be taking this article and dismissing it based on limited information. Everyones being ignorant to how filtered this information is.

          7. “Would you believe that the government has tech that can scan a vehicle(rather,anything) and read off ALL materials making up said vehicle or structure in seconds”

            WabbaWabba take this from a person that doesn’t trust governments you need to stop going to conspiracy sites. there is no such technology like that, it’s not even physics possible, even if you could magically get all atoms to talk to you (without vaporizing the object in question) you could not get a clear picture of what molecular they make up.

            that’s kind plays into of why no one is afraid of governments hiding this or any other tech.

            the only thing that controls tech and science as a whole is the laws of physics and the collective humans understanding of it. no government or group have a monopoly on that Knowledge so anything they can make everyone else can to. if so many people can make it not even half of them would stay quite about it ( it’s not human nature.)

      3. Ontop of the 2 comments already given (both of which are very valid) im actually walking around this subject with the idea that ‘what we think we know’ about energy isn’t actually correct, or is incomplete, yes, if you take an EM Drive trough certain thought experiments it just doesn’t add up, but that can just as well mean our understanding of the subject is flawed?

        Like how we where sure the earth was flat, the sun and the moon where at the same distance from us, we where the center of the universe, quantum mechanics where a hoax, pluto wasnt a planet (and apparently may be considered one again now), the higgs boson was a funky sci-fi idea that couldnt be right, etc etc, science is (in part) about disproving what we think we know, the only way we can do such a thing is to let people try (for lack of a better term) ‘silly stuff’.

        I just hoped that the centuries of science performed so far would’ve taught us to be open to new ideas, science didn’t stop at 1955 (Einsteins passing) exceptionally smart people are still born every day, and it would be great if everybody could just accept that and try be open to new ideas. (And no, i’m in no way thinking that i would be one of those people, in case anybody gets the wrong idea from this comment)

        1. Everybody wants to think they’re being resisted because they know something the rest of the world doesn’t.
          The difference between al‐Hāʾim, Keppler, Galileo, Boltzmann, Hubble, Higgs, &c is that they made hard predictions. They didn’t just come up with a crazy, revolutionary, idea, they developed it to it’s final point and used it to make predictions. Most importantly, these predictions were verified, and continue to be verified.

          EM drive may indeed be a possibility, but when we can’t even design a method to properly test it how can we know? To date the results claimed have not been replicated, nor excluded experimental error. Like they say on Mythbusters “..The difference between science and screwing around is writing it down.” and so far R&D into the EM ‘drive’ has just been screwing around. Shoddy record keeping is the bane of all science (and a huge problem in academia). IF results are only replicated in one lab by one team it suggests two possibilities: 1)They aren’t reporting the critical factor in their experiement and until it is captured the experiment won’t be replicated or 2) EM’drive’ is a farce and deserves to be ridiculed.
          Getting ‘some reaction’ doesn’t count as replicating results. They should get -the same- results.

          The likelyhood that the misunderstanding is of our current description of physics and the universe rather than of how the device operates, assuming it does, are pretty low. Until there are consistent widely repeatable results I’m not getting excited.

          PS: Pluto is a bad example. “Planet” is a completely arbitrary human term that continues to be redefined. The definition is only an aid to connotate characteristics and shorten discussions. Planetary status plays no role in space exploration.

          1. Even the great fall sometimes.

            Galileo couldn’t resolve the difference between the Copernican (heliocentric) and Tyconian (geocentric) systems because both made equal predictions about the phases of venus or moon, etc. The only practical difference was whether the earth or the sun moves.

            So Galileo set about to prove that it’s the Earth that moves by arguing that it’s the motion of the earth that causes the tides, and by motion he meant that tides are caused by the sloshing of water when the earth moves relative to the static firmament – exactly like the sloshing of water in a bucket that is being moved in a circle around a point without rotating it.

            The problem was that according to that hypothesis, there should be only one tide per 24 hour day, when in fact there are two – Galileo explained the problem away by declaring that the shape of the oceans must cause a secondary wave – but he could never explain how it works. He was just so adamant that he was right, that he wouldn’t hear any other way, and that’s part of the reason why he was locked up in house arrest. Galileo had no proof, yet he went around preaching heliocentrism which was at the time considered implausible by other astronomers because they didn’t have Newton’s theories yet. They had no theory to show that something as heavy as the Earth could possibly move around, and every reason to think that it didn’t.

            So ironically, the man was both a genius and a crank by modern standards. He went against the best scientific knowledge of the day with poorly concieved theories and ideas, and persisted despite being shown that his theories didn’t work. Ultimately, we know that Galileo was wrong anyways: there’s no center to the universe.

            So he wasn’t actually the sort of martyr for science as Neil De-Grasse Tyson would like you to believe. As a scientist, he was pretty low tier. He was just on the right side of the debate between church and science in today’s popular narrative.

        2. I wouldn’t use the flat earth example if I were you. Contrary to popular belief it was never widely accepted by the educated populace. By the time of Columbus almost no one in the scientific community believed it.

      4. One thing for sure: you didn’t read the NASA paper. You mixed information up, about the various drives tested at Eagleworks: the RF tapered cavity aka EmDrive, the slotted and unslotted Cannae drives, and the experimental control device.

        The EmDrive produced thrust. The RF load didn’t show thrust, as expected. The Cannae drive show thrust both in the slotted and unslotted version (that was the point of the articles you refers to).

        Your information is out of date and finds its bogus source in incomplete preliminary web articles whose authors hadn’t read the full NASA paper, only the misleading and incomplete abstract from NTRS server. Even Wikipedia has this story right.

        The full paper : http://www.libertariannews.org/wp-content/uploads/2014/07/AnomalousThrustProductionFromanRFTestDevice-BradyEtAl.pdf

      5. Just as a thought. If the device relies on a RF source to theoretically create thrust in a method that we are not completely aware, there is another source of RF that *could* provide additional energy.

        Technically there is a lot of background RF noise within the universe. We consider this the threshold frequency of sending a signal. That is any signal that you want to send over RF must be stronger than the background RF radiation in order to be received. There have been a few projects that send the signal below the threshold (I saw them on here) but their not my focus.

        What if this background radiation is adding energy to the system and that provides the additional energy for the *thrust* that is being seen? We could measure this by taking measurements of the background RF and adding it to the input power to see if it makes up the difference.

        This would solve the problem because the device is then making use of energy that is everywhere in our universe as an additional power source. It may not be enough to get us to Mars but it could be the source of this thrust especially for the “OFF” case.

        I know it’s a long shot but it is a possibility. However if I’m wrong, and I very well could be as my degrees are in medical sciences, I will accept it and move on. I was just pondering the possibilities and that popped into my head.

        1. I think you’re confused: there is *not* a lot of background RF noise within the Universe. There’s the cosmic microwave background, and that’s it.

          Thermal noise, which is what you’re talking about for the “any signal must be stronger than this” is generated by anything at a given temperature, including the Earth itself, or your receiver. But if you avoid the Earth, and operate in a frequency range where the atmosphere is transparent (otherwise you’re seeing the atmosphere), the only real “background” you see is from the CMB.

          “What if this background radiation is adding energy to the system and that provides the additional energy for the *thrust* that is being seen?”

          2 problems with this.

          1) The CMB’s energy density is way, way too low for this.
          2) It would be asymmetric. You’re already moving way fast with respect to the CMB: like, 600 kilometers per second. If you unfurled a giant microwave sail in space, the CMB would actually provide some pathetic thrust (towards Aquarius, actually). But it would be ludicrously tiny, like 1 femto-newton (10^-15!) per meter squared, and it would only work in that one direction (facing Aquarius) – turn it 90 degrees and poof, the thrust vanishes.

      6. “..and constant acceleration requires constant increase in power proportional to v^2 whereas the input power of the device remains constant.”

        This is the part that confuses me. Who is claiming this? They haven’t even definitively proven that the device produces thrust at all, let alone is able to produce a constant acceleration at constant power input. It seems like an odd assumption to make about a device with no theory of operation.

        So for the device (or for the sake of argument, any device that could convert energy to kinetic energy without conserving momentum) to be real, all that has to happen is for the device to satisfy the 1/2mv^2 formula. So this device would require increasing power input to have a constant acceleration, or at a constant power input the acceleration would slowly drop off.

      7. ” and constant acceleration requires constant increase in power ”

        No it doesn’t. Constant power will accelerate you forever assuming no force counters your force. You dont need the power levels to be constantly *increasing.*
        (assuming everything else is equal and your not approaching C)

        It requires no force at all to keep going in a friction-less environment. Force is only ever needed for the *change* in speed.
        Thats why even a Ion-drive can reach great speed eventuality – as long as your supplying enough to counter any frictional forces you will keep getting faster and faster and faster.
        (again, assuming your not near C)

        1. It will accelerate you forever, but it wont provide constant acceleration.
          P=Fv, F=ma, P=vma.
          Assuming a is constant and m is constant (not the case in rockets, but its unlikely that it balances out perfectly with the v increase), the increase in v from the acceleration means that the power must be increasing all the time.
          acceleration is not the same as “keep[ing] going” (i.e. constant speed and 0 acceleration).

          1. Math doesn’t work like that. Can’t divide by 0 and magically get infinity.

            For an object that’s not moving, the instantaneous power (rate of change of work done) is zero, yes. If you throw a ball up in the air, when its at the very top, the instantaneous power of gravity (rate of change of work done) is zero. In fact, before it hits the top, the power is negative, at the top, it’s zero, and as it falls, it becomes positive.

            Power isn’t “F*v”, it’s the rate of change of the integral of the force over the path. It’s only F*v if the force is constant over distance and time, so the derivatives/integrals are trivial. If the power changes, then you need to integrate properly, and in those cases you don’t get infinity.

          2. Sigh, yes, I knew someone would sieze on that. Yes, dividing by zero does not get you infinity. But what you’re saying would imply that a nearly stationary object can be accelerated extremely rapidly with only a small force. For instance, a 1 kilogram object moving at one centimeter per minute would only require watt of power to accelerate at 6000 meters per second squared. Forgive me if that seems a little… counterintuitive.

          3. “For instance, a 1 kilogram object moving at one centimeter per minute would only require watt of power to accelerate at 6000 meters per second squared. Forgive me if that seems a little… counterintuitive.”

            No. A 1 kilogram object, accelerating at 6000 meters per second squared (from a force of 6000 N), moving at 1 cm/minute, is *having 1 Watt of power delivered to it* – or said another way, is having work done on it at a rate of 1 Joule/sec.

            That says *nothing* about the power required to *generate* that 6000 N force. Just the rate of change of the kinetic energy of the object the force is acting on. That’s all.

            Pick up a 100 kilogram weight and hold it over your head. That weight is having exactly zero watts of power delivered to it, but damn you’re still getting tired.

          4. A watt is literally a measure of power. Now you’re handwaving and saying “well, it’s power, but it’s not the right sort of power”? What would you say is the theoretical power requirement to produce that effect, then?

          5. What are you talking about? I’m saying exactly what it is: accelerating an 1 kg object moving at 1 cm/s at 6000 m/s^2 requires doing work on it at 1 Joule/second, which is 1 Watt. There is no physics here. This is all definition.

            So how do you do work on an object? You apply a force to an object, over a distance. Again, this is definition. So what is force? It’s a change in momentum. So to do work on an object, you need to change its momentum, over some distance: change in momentum over a distance is an “impulse.”

            So how is energy and momentum related? In classical physics, they are not in the slightest bit. There’s no way to accelerate with energy alone (without mass). This entire idea that it takes “energy” alone to move things is relativistic. So don’t complain about relativity coming along here – you can’t accelerate things with energy alone without it, because you *cannot conserve momentum* without it. Special relativity gives E^2 = (pc)^2 + mc^2.

            Great! So now we can convert energy to momentum. Which means we can convert power to force. Which is just what you wanted. Now let’s assume 2 cases:

            1) You throw photons out the back (m=0).
            2) You throw 1 kg out the back (m=1kg).

            Divide both sides by t, and plug stuff in.
            1) To generate 6000N with photons takes 1.8 terawatts.
            2) To generate 6000N with 1 kg of mass takes 18 megawatts. About 100,000 times better! Neat, huh? Oh wait – we also had to consume about 10,000 terawatts to *create* the 1 kg. Because that’s the only way you can convert energy into momentum.

            So let me be clear here: in order to *deliver 1 Watt of kinetic energy* to this 1 kg object, to accelerate it at 6000 m/s^2, it requires at a *minimum* 1.8 terawatts.

          6. Wait, how do you arrive at the figure for ejecting the mass? Doesn’t that take you back to square one? And if we’re supposing that the energy required to impart a given acceleration depends on your current velocity, wouldn’t it require more energy to eject the projectile, too?

          7. “Wait, how do you arrive at the figure for ejecting the mass?”

            6000 kgm/s forward = 6000 kgm/s backwards in the ship’s frame (v=0), so 1 kg mass must gain 6000 m/s, and at the end of the day, 1 kg @ 6000 m/s is 18 MW. I don’t care *how* the mass was accelerated – no matter what it had to cost *at least* 18 MW over that second (e.g. it took 18 MJ). In other words, this “magic rocket” has a specific thrust of 0.33 uN/W, way higher than the photon rocket. Way easier to accelerate with mass.

            But that’s in the ship’s frame. What about in Earth’s frame, where the ship is moving at 1 cm/minute? It sees it thrown out at *less* than 6000 m/s, because it was already moving at 1 cm/minute. So Earth sees that the power dumped into the exhaust is *less* than 18 MW. How much less? 1 Watt less.

            I’m not being terribly careful here because the sudden change of acceleration and how the mass gets accelerated out the back would require you to integrate. But regardless, doing it carefully would give you an identical answer: Earth sees the exhaust gain 1W less than the total power consumption.

            So you spent 18 MW, and from Earth’s point of view, 17.999999 MW went to the exhaust, and 1 W went into KE, which corresponds to P=F*v.

            What about the 10,000 TW number? That’s the cost of creating the mass in the first place (mc^2). If you *have* the mass, that’s free. But if you *don’t*, obviously, creating mass to throw it out the back sucks. But if you have the mass, using more and more mass makes that momentum transfer more and more efficient. 100 kg thrown out the back at 60 m/s takes only 1.8 kW! And if you have an arbitrarily large mass thrown out the back – so that it’s functionally *stationary* in the ship’s frame, it would take… 1 W.

            “And if we’re supposing that the energy required to impart a given acceleration depends on your current velocity, wouldn’t it require more energy to eject the projectile, too?”

            Minimum power required for 1 kg at 6000 m/s^2 @ 1 cm/minute = 1 W. That’s conservation of energy, and depends on velocity, and holds up until relativistic speeds. It doesn’t matter whether you use photons, 1 kg, or pink rabbits to accelerate.

            Minimum power required to generate 6000 N = 18 TW. That’s conservation of momentum + relativity’s energy-momentum relation. It *does not* depend on velocity. But if you have mass to shed, then you can trade a large portion of that 18 TW for rest mass (inefficiently, mind you, relativity is an ass).

            You have to meet *both* of these, but conservation of momentum is almost always the limiting factor. Space sucks because there’s no place to dump momentum.

            From Earth’s point of view, at low speeds, all of your energy is being dumped into the photon rocket, and only a pathetic fraction is going into KE. (Same argument as before – Earth sees the light out the back redshifted, so it has less energy – that difference is equal to your change in KE). At high speeds, almost all of the energy goes straight into KE.

            As the ship accelerates, it takes more, and more, and more power to accelerate. When it’s moving at 2 cm/minute, it will take 4 W. And guess what? For the photon rocket, Earth will see 18 TW… minus 4 watts. So it will see more, and more, and more power dumped into KE. Energy’s all conserved: it always sees an 18 TW output (at the rest frame of the ship).

            This is the point. Can you accelerate forever with a constant power output and no mass loss? Sure. But without a place to dump momentum, you can’t exceed 3.33 nN/W. Anything past that and you’re violating conservation of energy.

            These guys are exceeding that by 1000.

            So when people say “they’re not violating conservation of energy, just momentum” – this is wrong. Relativity connects energy and momentum, by 1/c, which is that 3.33 nN/W. Can’t have one without the other.

          8. Thanks for the very detailed explanation. But it seems that in the case of the photon rocket you’re saying that what changes from the stationary observer (earth’s) perspective is the proportion of the energy that ends up as kinetic energy vs the proportion that it sees in the emitted photons. Doesn’t that mean that from the POV of the accelerating object, it’s putting in a constant energy and getting out a constant acceleration? Whether or not the energy required for a given acceleration depends on velocity was the original point of contention.

          9. “Whether or not the energy required for a given acceleration depends on velocity was the original point of contention.”

            Again, there are *two requirements* that you can build up here. One from conservation of momentum. One from conservation of energy. You have to satisfy *both* of them in vacuum (well, everywhere, but you don’t usually think about the momentum change of the Earth when you walk). And the net effect, in the end, is that an observer at rest sees a ship with a constant power drive *not* have a constant acceleration.

            From conservation of energy, the energy required for a given acceleration grows depending on the time, which means it grows depending on the velocity. Again, this is nothing more than the definition of KE.

            For a 1 kg mass, accelerating at 1 m/s^2
            t=0: KE=0 J, v=0, a=1 m/s^2, x=0 m
            t=1: KE=0.5J, v=1 m/s, a=1 m/s^2, x = 0.5 m
            t=2: KE=2J, v=2 m/s, a=1 m/s^2, x = 2 m
            t=3 KE=4.5J, v=3 m/s, a=1 m/s^2, x = 4.5 m

            From time t=0->1, you gained 0.5J, which means your KE increased at 0.5W. Average v=0.5 m/s.
            From time t=1->2, you gained 1.5J, which means your KE increased at 1.5W. Average v=1.5 m/s.
            From time t=2->3, you gained 2.5J, which means your KE increased at 2.5W. Average v=2.5 m/s.

            So the power ‘required’ to keep increasing your KE at a rate consistent with conservation of energy grows with velocity. ‘Required’ is in quotes here because it’s not like you have to satisfy the conservation of energy demon. This is more like “power that went into your KE.” But obviously that power had to come from somewhere, so that’s why you would say that’s the power required.

            From conservation of momentum, though, the ‘energy’ required is constant, but your specific thrust is either 3.33 nN/W, or you’re shedding mass, which obviously means you cannot accelerate forever with constant power.

            So you have two cases:
            1) You’re accelerating with mass, which means you’re making it up because your mass is decreasing over time.
            2) You’re accelerating with energy, in which case your thrust is 3.33 nN/W. (At some point the apparent ‘KE required per unit time’ will exceed the ‘power required from relativity’ but if you do the math, the apparent velocity that that happens at is the speed of light. Obviously well before that you need to be careful about time in each reference frame, but what I can say is that the short answer is that the observed acceleration at Earth *decreases* over time. Same thing. No long term constant acceleration, as observed from Earth.

            Another way you could think about it is imagine if you have a laser beam on Earth that you can perfectly focus towards a ship, which collects all of it, and reflects it. This is actually *more* efficient than throwing photons out the back: you get a thrust (initially!) of 6.66 nN/W. (Why? Because the photons reflect, so the momentum change is 2x).

            But as the ship accelerates, the beam looks weaker and weaker, so your acceleration goes *down* with increasing velocity. Constant power, decreasing acceleration, because the velocity’s going up. Same deal.

      8. “1) If the drive was real, it would break the conservation of energy principle of physics: A force applied to a mass causes constant acceleration, and constant acceleration requires constant increase in power proportional to v^2 whereas the input power of the device remains constant. Energy must appear out of thin air – therefore it’s bogus.”

        I’m sorry but this is nonsense. f=ma Constant accelleration requires a constant force. In a regular rocket engine, which delivers a constant force, acceleration increases, but only because the rocket burns fuel and gets lighter. If you chose to ignore this, a constant force (and thus constant power) leads to a constant rate of accelleration. (eg increasing velocity) I am assuming that we are traveling at non relativistic speeds, btw.

  3. Well probably there is a easier way to do it than kicking up your microwave generator, well it all depends
    The interessting thing is that when a gyro wheel goes arround it doesn’t pulls outward it just goes arround. Somehow the flywheel force is missing. When you swing around something it pulls outward from the center whenn it is not rotating. But when the rotating flywheel is swung arround it doesnt pulls outward from the center. This can be used.

    Here they made a interessting prototype.
    https://www.youtube.com/watch?v=nstIIZZadAM

    Dont worry you dont have to believe it or understand it right away. -> i think nobody really does, i mean to a full extend.
    for example look at the following video:

    https://www.youtube.com/watch?v=GeyDf4ooPdo

    they just concentrate on the upward force, but miss that it’s not pulling outward from the center

    Just wanted to share this info.
    take care

    1. Nothing you’ve shown is particularly inexplicable or even difficult to describe. In the case of your first video, the static friction of the ping pong balls on the table is only overcome by your device’s sudden movements, but not by its gradual turns. As far as I can tell, the flywheel doesn’t serve any purpose at all.

      Why would a spinning flywheel pull ‘outwards’? Which direction would that even be?

      1. Yes you are right all ” i’have” shown is that i can post two internet videos and write some words. And its not my first video as you are posting inexplicitly or explizitly it is someone elses video i was refering too. And yes i also make mistakes.

      2. It is actually a bit more subtle, but you are absolutely correct that the static friction, especially on what appears to be a billiard table, is key. The flywheel does serve a purpose, as the rotation of the frame is due to precession due to the external force due to gravity. The total angular change int he phi-direction (change of tilt for the plane of rotation) is quite small and not visible in the video. I had to look at it a few times before I realized that this was the point. The device is clever, tremendously impractical and inefficient, and useless without an acceleration normal to the path it is going to travel, such as that due to gravity, and friction against the external frame for the precession torque to react against at the center of the device.

        1. I see what you’re saying; there’s no motor rotating that frame. It’s a result of the slight angle of the gyro generating a rotating force. That said, the gyro still seems a bit useless. Couldn’t the same effect be generated by actually using a motor to rotate the frame rather than rely on the gyro? Then it’s just a matter of suddenly accelerating mass to generate movement.

          I do understand that this would impart a moment on the platform that could cause it to rotate, but at sufficiently low speeds the friction between the platform and the table would be enough to prevent it.

          1. Absolutely could use a motor to rotate the frame, and drives that do that have been built. Many people think that because the motive force for rotation comes from the precession here that there is no need for external forces. They are mistaken. In fact, the net of the external forces is the same for this as if a motor just turns the frame, but there is no directly applied external torque to oppose the rotation, other than the small friction in the bearing which, in this case, is in the same direction as the rotation rather than opposing it. Of course, there is an external torque, in the end, that is as if it were driven by a motor. I leave this as an exercise to the reader.

            The thing with this one is that is seems like magic to most people, even those conversant with elementary physics. I refer you to https://xkcd.com/332/ for further details.

      1. Get rid of the friction from the balls and table and it would look pretty silly oscillating back and forth. It would probably be much more obviously useless if they had put it on an air-hockey table.

    1. I think the text is wrong too: “He’s amazingly accurate for a medieval archer, but he just can’t hit the target.”

      Man, how do these kind of basic errors keep happening in the blog posts on HAD? You’d think at some point they’d finally start proofreading.

  4. After all the talk about accuracy and precision, the captions for the figures (and a few other places in the article) are backwards. Accuracy can’t get ‘better’ if you’re not hitting the target, regardless of precision.

  5. 30kN of thrust with 1kW seems way too good to be true. 6 of those would equal the thrust of an F-35’s engine, running on the amount of power a motor scooter’s engine puts out.

    1. Agreed, with numbers like that I feel like if you could put one on a windmill tied to a generator it would produce more energy than it consumes. I don’t think this is a few notches up from a crazy guy in his garage claiming he has a perpetual motion machine. I think it is a crazy guy in his garage claiming he has a perpetual motion machine. [Sigh…](http://reddit.com/r/EmDrive)

    2. I think the “μ” key is close enough to the “k” on the keyboard to cause some confusion.
      Perhaps the author should work on increasing the accuracy of his typing, along with the precision of his proofreading.

  6. There can be no power to thrust relationship, otherwise you end up with something that will contain more kinetic energy than the “thruster” energy put into it. The only way I could see this drive having an effect is if it lost thrust as you accelerate exactly conserving energy, but I’d have to work that out, still seems bogus.

    Here is an interesting article I found that talks about similar devices and claims (albiet more mechanical) from last century:
    http://www.projectrho.com/public_html/rocket/reactionlessdrive.php
    It really makes you think about serious issues that could arise if this sort of technology were possible.

  7. Wouldn’t building a small craft and depositing it in space show some unaccounted for movement if the drive was “powered”? Nothing better than actually building a prototype and putting it to use.

    Anyone besides crackpot inventors and armchair sleuths have an answer for that?

    1. Given the forces involved, it would be difficult to make sure it was absolutely stationary relative to your own reference frame when you started. And other forces, such as black body radiation from a hot surface, or input from the sun, could cause effects that interfere with the experiment. Not to mention, getting stuff into orbit is expensive – better to come up with cheaper simpler tests you can do here on earth until you’re pretty confident.

  8. “Bad science” is dismissing a fact because it doesn’t fit existing theories. « It can’t be true, it violates the law of XXX », « If they knew basic science, they wouldn’t have tried that » « This can be safely ignored, this is most likely an error of measurement ».

    Good science is investigating until either finding out the cause of the error, or figuring out the new phenomena enough to amplify it. And even in the former case, there’s no need to slap a pejorative label onto it. Bad science have historically been the dogmatic naysayers.

      1. The actual scientists investigating this aren’t making extraordinary claims, they’re testing claims. If it turns out that the tests prove positive we will have some extraordinary evidence, but discovering what that evidence means is even more work.

    1. It’s not an efficient use of resources for good scientists to construct experiments to disprove conclusions made from measurement errors all the bad ones come up with when it’s pretty clear from the start what the outcome will be.

      Just let the bad ones muddle on as long as they don’t consume too much resources doing so.

  9. “Bad science” is dismissing a fact because it doesn’t fit existing theories. « It can’t be true, it violates the law of XXX », « If they knew basic science, they wouldn’t have tried that » « This can be safely ignored, this is most likely an error of measurement ».

    Good science is investigating until either finding out the cause of the error, or figuring out the new phenomena enough to amplify it. And even in the former case, there’s no need to slap a pejorative label onto it. Bad science have historically been the dogmatic naysayers.

    1. An interesting sociological phenomenon; accurate science isn’t aided when vocally supported by a small lunatic fringe. Constructive debate is easily derailed by nonconstructive conspiracy theorists, which makes them their own worst enemy!

  10. This can’t work, at least not as explained on diagram. If it could, then by using same reasoning a ‘frustum’ filled with high-pressured gas would have to create trust too, because F(small end) = Pressure * S(small end) < F(large end) = Pressure * S(large end), and we know that it isn't happening. And while we are at it, why then not eliminate small end and use a pointed proper cone instead of frustum? Surely we would have a better yield, with no opposite force at all!

    1. The troubling thing is that it all depends on the mechanism at play. If it’s a matter of the RF energy imparting a force on each end, it’d never generate a thrust as all the forces are contained within the device.

      Think of it like a pair of opposing hydraulic cylinders (of different sizes). If the base ends were attached to earth and the rod ends attached to the same platform, an equal pressure to both cylinders would cause the platform to move. This is because one cylinder is applying less force than the other, leading to an imbalance that allows a force to be applied between the earth and the platform.

      Now let’s attach the base end of the cylinders to the same platform as the rod. Because all the forces are being imparted on the platform, nothing moves. The platform gets stressed, but there’s no external force applied to generate movement.

      But, once again, that’s assuming the RF energy is imparting a force on the ends of the EM drive and not that the RF energy is somehow imparting a force against an outside mechanism.

  11. Plain old radiation pressure alone will generate a few micronewtons from a kilowatt. No fancy microwave generator or funny frustums needed: Just use a radiant heater. A flashlight is a thruster with an exhaust velocity of 3e8 m/s (or specific impulse of 3e7 seconds if you’re american). Not a lot of deltaV out of a pair of D cells, but that’s what a nuke plant (or antimatter) is for.

  12. This article is ridiculous on the face of it. I don’t have the slightest clue where the numbers or concepts come from. Setting aside whether the EM drive works or not and the whole accuracy/precision thing, the rest of the assertions made here are flat out FALSE.

    1) The thrust the article claims from a drive is 5 full orders of magnitude higher than what experimenters claim to be seeing. It’s not 30N/W (the sane way of saying “30kN per 1kW”…) or anywhere near. A comment claims that this figure comes from emdrive.com, but I can’t find that anywhere on the main page. What I *do* find there is a reference to the Chinese experiment in 2012, which claims to have achieved a thrust of 720mN from a 2.5kW “engine”. That comes to 0.000288N/W, which is a factor of 100,000+ lower than the article asserts.

    2) A pitiful misunderstanding of basic physics units: a Newton does not “hover” 1kg. A Newton (as per wikipedia) is the force required to accelerate 1kg of mass by 1 m/s. Thus, it takes 9.81 Newtons of upward force in order to counteract the gravity of the planet [Earth] and make that mass hover.

    3) If we re-run the numbers from the “helicarrier” example: The Nimitz has 2 A4W reactors each rated at 550MWt each. If one redirected all of that into electricity generation rather than steam turbines (which is afaict where the 208MW number came from, except there are 4 of those and they’re MW*t* steam engines for the propellers), and you get an efficiency similar to that of civilian reactors , you get approximately 360MWe. Based on the Chinese experiment, that gives 103,680N of force, which translates into the ability to “hover” 10,568kg of mass. That’s actually *really* cool, but the Nimitz actually weighs approx 90,800,000kg.

    Somebody please tell me this was a gullibility test?

    1. I agree the thrust numbers are ridiculous. But they are definitely taken from Emdrive.com. Question 18 on their FAQ page says:
      “Q. How can the EmDrive produce enough thrust for terrestrial applications?
      A. The second generation engines will be capable of producing a specific thrust of 30kN/kW. Thus for 1 kilowatt (typical of the power in a microwave oven) a static thrust of 3 tonnes can be obtained, which is enough to support a large car. This is clearly adequate for terrestrial transport applications.”

      This is clearly a theoretical number, but it’s difficult to believe based on the currently measured forces in experiments, even assuming they are measuring a real effect.

      1. OK, looks like you’re right. I think where I missed the decimal is that when I read it this morning [blurry] I saw 3kN and used those in my initial mental calculations, combined with the fact that the article uses *10* as g instead of 9.81. That’s still only one order of magnitude out of the equation.

        As for the claim of 30N/W, I’d love to know where the FAQ actually gets *it’s* data. For a device that’s supposedly producing 0.3mN/W now, generating 10,000 times that sounds like pure fabrication. As near as I can tell, it’s based on the assumption that there’s a magic frequency at which all the thrust is generated, and the Q factor of the microwave emitter is thus the limiting factor: the lower the Q the lower percentage of total goes into that particular frequency. I can’t think of any other mechanism by which the claim of increasing Q factor results in increasing thrust makes any sense.

        I see all kind of other things wrong with this, but I’m not trained in the relevant fields, so I’ll just let the experiments play out.

        I’d love for those claims to be real, but I just don’t see it. At best I see an improvement to long-haul spaceflight.

        1. I agree, the experiments I have seen show tiny amounts of thrust that are so small they could be attributed to things like the earth’s magnetic field or the radiated heat from the back end of the thrustum. Not sure how they arrived at the 30 N/W.

          I do think this topic is fun and totally legit to write/talk/dream about, Brian qualifies everything he wrote with that fact that nothing has been proven. These numbers are just fun to plug in and think about what if scenarios.

  13. Hi, I’m also working on this.
    The claimed “hovercar” would depend on using a superconducting cavity for high (ie 10exp6*) Q factor.
    As for the claims it breaks CoE, as Shawyer clearly shows accelerating causes a drop in efficiency so this would be ideal for a hover-drive and satellite fine tuning but not so useful for space launches.
    In fact in terms of efficiency a simple model helicopter based on Li-Ion is 10,000* more efficient than the basic copper/brass system using a 22% efficiency magnetron so unless someone invents a room temperature superconductor with half-decent Jc tomorrow this still won’t hit the market much before 2025 at the earliest assuming the system is based on Y123 or BSCCO and a closed circuit cryocooler.

  14. This article shouldn’t have been done.

    Give the EM people a year or two to prove their design. If it fails and they eat crow so be it. If it works to some degree we should be elated.

  15. Definitely not a hack. Since when did HAD start posting psuedo-science and free energy nonsense? What’s next, the timecube guy? It’s a little over the top to suggest you need a master’s in physics or RF engineering to understand this, a freshman physics course would be more than sufficient to make it plainly obvious that this will not work. If whatever milli/micro newton thust they are seeing in the lab is actually an electromagnetic effect is it probably due to some unaccounted for stray currents/fields produced by RF leakage that they failed to notice. If wouldn’t be the first time someone claimed an amazing discovery based on data that hadn’t been thoroughly checked (in recent memory…see the tachyonic neutrino’s result from the OPERA collaboration).

  16. Hey Brian,
    You sold me on your new awesome implausible and unsubstantiated technology again! You know I can’t resist you.
    Can you give me the link to the kickstarter so I can support this EM drive? Thanks!

      1. All they need is $800 more so they can be 10*420, representing the amount of devil’s lettuce they had to smoke to believe this idiotic idea. Tajmar’s paper is trash, ya dinguses.

      2. All they need is $80 more so they can be 10*420, representing the amount of devil’s lettuce they had to smoke to believe this idiotic idea. Tajmar’s paper is trash, ya dinguses.

  17. Hi everyone.

    I have a question.
    I don’t know nothing about the math and theory about this.
    If you have energy going in. Cant you have some sort of matter coming out.
    It kind of makes sense to me.
    I don’t see the perpetual motion if you have something going in and something going out and getting motion out of the deal. But saying that I think the output is way to high and not possible.
    I guess I could ask my kids they are gifted, but I don’t want to hear them ramble on for days about it.

    I have read all the comments here I did under stand some of it, but all the math is over my head.
    Could I get a semi easy answer? If it’s possible.
    Thank you very much.

    1. @Perry, forget the math and theory for now, bottom line is NASA is testing it.
      “space com 26713 impossible-space-engine-nasa-test” the article is from August 1st of 2014

      As far as perpetual motion yes it is possible HOWEVER there is only two and only TWO examples of this in effect: The Universe itself.

      Even then we may get 3 bad outcomes if it isn’t:
      a.) the big crunch
      b.) the heat death
      c.) a bubble universe will be born inside ours and overtake everything (ours)

      And the orbit/spin of an Electron.

      For a brief overview consider that wikipedia article on Magnetohydrodynamic_drive is valid and working. now before the hair spliting occurs yes it applies to liquids HOWEVER since most of the scientific articles and experimentation notes are behind DAMNED PAYWALLS there is very little in the way of hard/concrete “DIY EMDrive”. Give it a couple of years and you’ll probably see youtube videos on it.

      As it stands now, plenty of DIY railgun/coilgun vids.

      A few more article of note.
      “wired uk news archive 2014-07 31 nasa-validates-impossible-space-drive”

      The semi-easy answer is look at the very bottom of the “Magnetohydrodynamic_drive” wikipedia article.

      Additionally wikipedia Spacecraft_propulsion has a nice table that breaks-down the force and newtons.

      With a huge power-plant yes, helicarriers are legit. However these EM drives aren’t REALLY *hand wobble motion* designed for that typical “1/4 impulse power” the are more along the lines of accelerate to ~90% speed of light efficiently. (Or that is what I got from it…)

    2. The semi easy answer is that this thing runs on an unlimited supply of bullshit, you can’t see it, you can’t touch it but it goes on and on like perpetual motion. In this case it’s probably good for another 94 comments as people get caught up in the ” I can piss higher than you” contest. Watch this ” Is Schrodinger’s cat dead or alive?”

      1. @Vic – Both, until you adopt one at which point Rick and Morty would show up and well things would get really messed up.

        Unlimited Bullshit doesn’t exist. Human Stupidity of which Einstein mentioned would make a remarkable power source.

        I’d imagine the entire town of Kitty Hawk,NC or Fairville,OH fought like hell not to believe it, then fought like hell to own it.

        So, The most obvious issue is do the orbits of electrons around a proton and/or neutron atom ever decay or stop? I mean the are in movement & forever so, Yes? Sorry, Bad Troll is Bad. And as far as the universe goes we still don’t know what dark matter is only that the Universe is comprised of 90% of it (and it’s a show on syfy as well right?), can it re-aggregate and become a hydrogen atom once more?

        Honestly I hope we will have a twinkling idea of what it is in our lifetimes. But, we can’t dispute the fact that Bohr, Dirac, Planck, Coulomb, Fermi, Heisenberg, Ampère, Coulomb, Gauss, Heaviside, Henry, Hertz, Lorentz, Maxwell, Volta, Weber, Ørsted (Yes, I left out the most obvious science lengends from the list as that would have been too cliche) had to deal with the fact that the general populace as well as their fellow peers were hurling Unlimited Bullshit their way.

        It’s irrelevant considering the current record is having 1 photon being present in two places at the same time with 143 Km distance between them. What does this have anything to do with the EM drive?

        Arthur C. Clark’s Three Laws:
        1.)When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong.
        2.)The only way of discovering the limits of the possible is to venture a little way past them into the impossible.
        3.)Any sufficiently advanced technology is indistinguishable from magic.

        I really like that 3rd law.

        But I really don’t get how the HaD thread/comments/conversation went from basiclly a-fancy-radio-transmitter-with-a-unusual-antenna-that-can-push-stuff to a insane clown posse perpetual motion machine discourse.

        -=-=–=-=-=-=-
        The double quotes that I throw in my posts are not without purpose, I use them to not waste the time of the moderators as full web-links thereby shortening or bypassing -your comment awaiting moderation- that way if you are interested you can use the text between the dub-cues since I am unable to lmgtfy.

    3. “If you have energy going in. Cant you have some sort of matter coming out.”

      Not necessarily. You could put energy in and get energy out. The EM drive doesn’t claim to be a matter energy converter.

      I can see a few possible explanations for the small (really small) amounts of force. Number one would be an interaction between the microwaves and the external environment (magnetic field, quantum effect, etc). Number two would be a small unnoticed heating of the chamber, causing an unbalanced force due to the different amount of radiative areas(although the experimental data shows a reversible thrust if I remember correctly).

      To anyone saying this violates CoE, NO!. There is energy being constantly injected to the system. and a VERY small reaction being produced from that. Lots of energy in versus little energy out does not equal a violation of CoE. That energy has to be going somewhere and doing something.

      The acceleration factor of this would be equivalent if not smaller than an Ion based drive. It would take months(years) of acceleration to get to any appreciable speed. The only possible advantage of this, if it works, would be the lack of reaction mass. the whole spiel of ” we can get hover cars from this” really neglects the fact that the energy to reaction ratio is terrible.

  18. How hard is it anyway to test this thing? Just make a 1kW model, place it on a cart that is air-cushioned to reduce friction and power it up. If it works it should start moving. Even if the thrust is really small. If it’s bulls***t, it won’t move at all. And by making multiple tests with the same setup, some under power and some not, it should be fairly easy to prove it works. And by measuring, how fast it moves it would be easy to calculate some basic parameters of this drive.

    For me it sounds too much like typical Free Energy/PM/Solar Roadways/Batteriser crap to be true. So I’ll wait for scientists to finish testing this thing.

    1. Many labs have now tested it, including NASA.

      Of course, these tests are often partial or essential fails.

      The promoter of e-cat claims otherwise, but NASA for instance said they cannot be certain they are measuring thrust vs instrument error.

    2. It needs to be tested in a ferrite isolation enclosure to remove interfering magnetic fields, an anechoic isolation box to remove interfering electric fields, a vacuum to remove force from convection, and have a heatsink to rule out radiative heat force in the expected direction of thrust all at the same time. The levels of thrust produced are very small unlike what is said in the article.

  19. Not sure where you’re getting those force values from…

    via wiki;

    “…a net mean thrust over five runs was measured at 91.2 µN at 17 W of input power. ”

    That works out to ~0.005 N for 1kW ….

  20. Ugh. The longer this drags on, the more similar to the E-Cat it sounds.

    The e-Cat is certainly an outright scam.

    I feel bad for the scientists who get conned into being stagehands for that particular magician.

    The EM-Drive has a VERY SIMILAR man at it’s core – and I would be surprised to find he isn’t a magician (opportunist
    ).

  21. I want this to be real.
    I don’t think that it is real.
    If it does turn out to be real how can it be explained?
    My best guess is that it would mean the the aether is real and it is pushing against it.
    I don’t believe in the aether.
    But if this were real I might have to think again about that.
    I would be very happy to be wrong!

  22. In order to see how it works as a perpetual motion machine imagine you put one of these drives on a bar that is extended out from an electrical generator, so as it applies thrust the generator spins.

    The power output from the generator is governed by the torque (amps) and the speed (voltage) given by what is turning it.
    Power = amps * volts

    The force produced by this drive is fixed and does not vary with speed, as such you can increase the power output simply by letting the generator spin faster and faster producing higher and higher voltages. At some point you will be producing more power than the drive consumes, you have a perpetual motion machine that is generating surplus power.

    A chemical rocket will run out of fuel, so not perpetual motion. Laser thrusters decrease in efficiency at a rate such that you only achieve break even when the thruster itself hits the speed of light. (Before you fall down the same rabbit hole I did of thinking oooh mirrors and stuff, your laser will be red shifted every bounce losing energy)

    1. A generator will not continue to run faster and faster with a constant applied force.

      At least I don’t believe the generators at Hoover Dam are constantly gaining speed with a constant force.

    2. “The force produced by this drive is fixed and does not vary with speed”

      I keep seeing this, but it seems an odd assumption to make about something most people don’t event believe to be real.

      “Laser thrusters decrease in efficiency at a rate such that you only achieve break even when the thruster itself hits the speed of light.”

      Why couldn’t such a thing be true of the EM drive as well?

      1. “I keep seeing this, but it seems an odd assumption to make about something most people don’t event believe to be real.”

        The inventor claims that it produces thrust without reference to the outside universe, as such the force would be independent of its external speed, IE it is a “reaction less drive”

        “Why couldn’t such a thing be true of the EM drive as well?”
        Mostly because the thrust/power numbers given are far in excess of a photon thruster, implying the breakeven point would be significantly lower than the speed of light. A photon thruster is not reaction less, the photons it emits have mass (well sorta, that whole E=MC^2 thing)

  23. Just because it appears to violate known established beliefs doesn’t make it not work.

    Take the Earth Battery, effectively harvesting planetary forces for small gain.
    I suspect at the end of the day having an electromagnetic propulsion system inside a giant magnetic field will play a part in this.

    IE Lets say for the sake of argument that the power emitted in RF bounces around inside the metal device the fields interact at some point with the metal creating (or something else) some sort of heat or eddy current / field, now lets say that somehow couples with a magnetic field from earth/sun what ever and is pushed or pulled along it then you could see a “thrust” effect on a minuscule scale all because we didn’t fully understand the size of such a system. We might be looking so hard for ejected particles and forgetting that if we had a strong enough and light enough magnet we could interact with earths field on a usefull scale.

    Or a second thought, have you ever seen a radiometer, the device works in a partial vacuum due to some neat forces crated by light. This simple “toy” took some time to fully understand how it worked.

    In the end I think there is something going on but like the above examples upon further investigation it will turn out the gains just are not there to be useful enough and likely won’t work in space. Just my 2 cents. I won’t even claim to understand the pseudo science and actual physics involved. The skeptic in me just says this is too good to be true.

  24. If we could build this nuclear-powered emdrive helicarrier then one could use it to cause an extinction level event. Since the helicarrier has to apply a force of more than it’s weight, it is capable of accelerating at g. So if we fly off into space(you don’t even need to put it into orbit!) get it something like 2900 Au from the Earth(transit time 34 days following a brachistochrone trajectory) and accelerate straight at the Earth for about 108 days you could cause massive damage. The helicarrier would have as much kinetic energy as the asteroid that killed the dinosaurs.

  25. Side lining stuff, they may not have been helicarriers, but we did have the USS Akron and USS Macon for flying aircraft carriers. I know a guy who saw the Akron in flight. Amazing thing.

  26. If the thrust is real, and not a result of inaccurate measurement, then it would likely be due to the RF energy causing some particles to be knocked away from the copper frustum. The net thrust would result from the big end emitting more particles than the small end, simply because it has more surface area to catch the RF radiation.
    This suggests a couple things:
    1) The copper is essentially consumable. Momentum is conserved.
    2) The amount of RF energy required to generate a useful amount of thrust would be hazardous to anyone in the in the vicinity, especially in the “exhaust path”.

      1. NASA scientist and multiple-trips to space astronaut Dr. Franklin Chang-Diaz said on September 29, 2009: “In fact, with the power close to what a nuclear submarine generates, you could use VASIMR to fly humans to Mars in 39 days.. A chemical rocket makes the trip in 8 months. That’s 8 months of exposing your astronauts to debilitating cosmic radiation and weightlessness. By the time they get to where they’re supposed to work, they’re gonna be in bad shape—almost invalids! They’ll have to spend a big chunk of their time just recovering from the trip. That’s simply not a smart way to conduct an exploration program. By not addressing the key problems of limited power and propulsion, NASA is forced to work with extremely complicated and expensive mission architectures that are very limited in capability.”

  27. 1 Newton = force to accelerate 1kKilogram by 1 meter per second in 1 seconds time.
    1 Newton-meter = force required to move 1kg 1 meter.
    1 G = Force of Gravity = Acceleration due to gravity = 9.8 meters/sec/sec.
    Hovering in mid air on Earth = 9.8 newtons/kg
    1 Watt = 1 Joule/Second
    1 Watt = 1 newton-meter
    Thrust/PowerInput ratio of “emdrive” according to article: 30 kilonewtons/kilowatt
    Uh… 1000 watts = 30 kilowatts?
    Say What? Write up error!

  28. I’ve been following em drives for a few years now and my conclusion, as an educated but not professional scientist, is that it smacks of being a snake oil fueled PM machine.
    Not that I wouldn’t love it to be true. I really really would. But common sense and facts just stop it getting any traction as a useful device.

  29. Would the RF signal of a nuclear helicarrier with EMDrive not be strong enough to basically kill every single electrical or electronic device near its flight path? We would probably not care too much once the ship leaves our solar system, but every other dreamed up terrestial or near orbital application would have to be banned because of the massive RF noise the drives would generate.

  30. I just realized… if a light, be it a flashlight or a laser, provides a miniscule thrust… at the very least, microwaves should do something demonstrably similar. Small enough RF wavelengths produce measurable photons, after all.

    It’s not in the magnitude that the article is suggesting, but it is better than “this shouldn’t do ANYTHING.”

  31. This has been some of the most interesting reading I’ve browsed through on here in some time. The somewhat bickering tone, I could do without. But such is the nature of discussion over topic this interesting. I am not versed in the laws of physics. I’m not an engineer of any sort either. I just like to think about things that are out of the normal, everyday subjects. I mainly wanted to thank all of the people who have been commenting so passionately with such vast amounts of information. My opinion, uneducated as it may be, is that the laws of physics are quoted as to be definite. Because those laws have not been dis-proven does not mean that they can not, without a doubt, be broken. We just have not discovered a way of doing so, yet. If you think, invent, build or live inside a set of rules that you think are unbreakable, then you will never achieve anything beyond the confines of those rules.

    1. Since you are “not versed in the laws of physics. … not an engineer of any sort either” you sure have a strong feeling on this stuff. Just understand that while you spent your time learning to do whatever you do, other people dedicated their time to learning science and physics and engineering. While you may have a gut feeling that you need to express on the internet and really really really want stuff like this to be true, the real scientist and physicists and engineers actually understand WHY they know what they know and can back what they know up with facts and logical reasoning. Are they 100% confident in everything? Of course not, but if there is overwhelming evidence to support something, and no evidence to disprove it then you are a fool to believe it’s not true. There is a difference between being scientifically skeptical and believing ANYTHING is possible. This isn’t the time of thinking the world might be flat. The depth of human understanding is staggering in this day and age. Your problem is that you have a fundamental misunderstanding of how to think scientifically.
      If you want your mind blown, go learn about quantum electrodynamics and then come back and say that the physicists don’t know what they are talking about and might be wrong about everything. QED makes the most accurate predictions about the physical world that humans have ever made and since you are a self professed science layman there is absolutely no way you will ever really understand it (I won’t ever if that makes you feel any better). All you can ever do is trust there are people who do and because those people can defend their position with facts and evidence they know what they are talking about. The evidence that the real scientists and physicists and engineers actually know what they are talking about is really simple to see. The computer you are using, and the cell phone in your pocket with their 4G data radio connections, and the satellites beaming your TV and GPS data down are all real and all work. That’s all you need to know. Tell the guys that made all the technology you interact with on a daily basis that they don’t really understand anything and watch them punch you in the face.

      1. My statement, as was sufficiently explained, was my opinion. Your comment, “and since you are a self professed science layman there is absolutely no way you will ever really understand it (I won’t ever if that makes you feel any better)” only lets me know you make assumptions of others while having a most likely higher then realistic view of your own intelligence since you think that it would somehow comfort me that even someone with such an elevated intelligence as yourself cannot grasp QED theories so I shouldn’t feel bad. The dismissive nature of your response, especially telling me that “The computer you are using, and the cell phone in your pocket with their 4G data radio connections, and the satellites beaming your TV and GPS data down are all real and all work. That’s all you need to know.” may be the most condescending blurb I’ve ever read on these forums. So you can keep your “scientifically skeptical” view. I’ll stick with anything is possible.

        1. I have a degree in space science.
          Members of my community all think that the thrust this thing is producing is an artefact in some form.
          90% of them preface or P.S their statements with “but I really hope it works though”

          Don’t take the HAD community as representative of the science community. Much like the Italian experiment that was saying neutrinos were travelling faster than light we are all pretty sure that its not the case the question becomes what is going on in the experiment. So people are going to replicate the experiment in different ways and see if they do or don’t see the effect.

          The biggest issue with this particular thing is it violates the laws of thermodynamics, that whole “no perpetual motion machines” thing seems to be one of the really fundamental laws of the universe so it being wrong, would be like discovering radiation and e=mc^2 again, its a really quite giant claim to make. It would invalidate pretty much all of physics, even the basic stuff.

          1. “90% of them preface or P.S their statements with “but I really hope it works though””

            That’s completely the opposite of my experience. In my experience, most scientists say “why the *%!% is this crap getting funding when the rest of NASA’s budget’s getting slashed?”

            Keep in mind JSC did not *build* these things. They got them from an external company. It should not be NASA’s job to attempt to prove that some random aerospace engineer’s crazy idea doesn’t work. They don’t need to. Let private industry show that, or better yet, let the fact that no one wants to give the guy money show that.

            “Much like the Italian experiment that was saying neutrinos were travelling faster than light we are all pretty sure that its not the case the question becomes what is going on in the experiment.”

            My response to OPERA’s mistake was similar, too. You don’t report crap like this to the public, because *you know* it’s crap. You let an undergraduate or graduate student report it at a conference, and you report it by treating the “observed signal” as an “unknown systematic error”, and put limits on the observed effect, and you have the student then also *postulate* what could cause it as a *real* effect.

            Then, at a conference, people from that experiment sit down with others, talk about it, make some ideas as to what’s going on, figure out new ways to test it, and quietly figure out what the heck had gone on *without* wasting money looking like a fool.

            Science nowadays is way too much “science by press release,” and it’s awful, because it just completely screws up any hope of fair funding.

        2. HA! Go try to fly off the top of a building Mr. Anything Is Possible. You know gravity is just a theory, and could possibly be wrong. Let me know how that turns out.
          To make my previous point again:
          Leave the physics to physicists. And more importantly, SHOW SOME RESPECT for the people (scientists, physicists, engineers) who actually put in the work to understand and make the things you obviously take for granted.

          1. “SHOW SOME RESPECT”

            Excuse me, but isn’t that exactly what HE F*CKING DID by saying things like, “this is some of the most interesting reading I’ve browsed through on here in some time,” and, “mainly wanted to thank all of the people who have been commenting” ???

            Like the OP, I’ve enjoyed the hell out of the comments on this post, until now.

            Go away asshole.

  32. Wonder how long before the US government totally discredits the inventor and his ‘hoax’, and he mysteriously, though predictably, dies of an accidental gunshot wound in a Paris tunnel?

  33. If the EM-drive is real, then everyone should be terrified, depending on the state of the QED vacuum.
    If the QED vacuum has some frame of reference against which the drive is pushing, then relativity is wrong,
    but you can’t violate energy or momentum conservation.

    But if relativity remains correct, then we can always push against the vacuum no matter what velocity we’re going.
    You can use this to violate momentum conservation and energy conservation in turn.

    Here’s where it gets scary, pair the two. A reaction-less spacecraft powered by a perpetual motion generator can accelerate to any velocity, given enough time. Want to destroy a country in such a way that is practically unstoppable?
    10% light speed is only 10 years at 0.1g, a 1 tonne spacecraft colliding at this speed would release the equivalent of
    ~5 kilograms mass-energy, or an explosion of ~100 Megatons of TNT.

    1. “If the QED vacuum has some frame of reference against which the drive is pushing, then relativity is wrong,
      but you can’t violate energy or momentum conservation.”

      No, no, no, no. The Universe can generate a preferred frame of reference even though the underlying physics has none, through spontaneous symmetry breaking.

      Effectively, this means that conservation of energy and momentum are more axioms than laws. If you find a situation that violates it, you reframe the problem to define some kind of external field which provides or absorbs said energy/momentum. Does it seem like cheating? Kindof. But we’ve had to do this for other things, too: namely inflation – for inflation, they called it the “inflaton field,” and that’s the entire basis for modern inflationary cosmology. What preferred frame do you get from that? The cosmic microwave background (the frame in which the CMB has no dipole). The only way you can get a CMB that everyone in the universe can agree on is if the Universe expanded superluminally – hence, universal CMB = inflation.

      What preferred reference frame would the quantum vacuum have? The frame in which the Hubble flow is isotropic.

      So no, if this turns out to be real (which it won’t) it won’t violate conservation of momentum, energy, or relativity. You can’t really violate those things – they’re like Newton’s second law. Not really a law, more of a definition. “We define the action acting on particles to be time, location, and rotation invariant”, etc. And the world will not blow up.

    1. While I agree that a device that seems to violate what we know about physics is implausible, it’s not automatically impossible; by that conclusion, before relativity Mercury was impossible because the precession of its orbit couldn’t be adequately explained.

  34. If the EM should actually work, it would not only violate the conservation of momentum law, but also the 1 thermodynamic law of conservation of energy.

    So imagine an EM drive in space. Starting velocity 0m/s. Now microwave energy is switched on and creates a constant accelerating force, that might even be incredible small. That causes a constant acceleration of a incredible small number in meters/s every second.

    At first, the EM drive is incredible inefficient, because the spaceship has no kinetic energy and you waste much more microwave energy than you gain in kinetic energy, because kinetic enery increases by velocity^2

    Now as the spaceship has gained velocity, the change of kinetic energy per second is incredible great, even if the accelerating force is very small.
    https://en.wikipedia.org/wiki/Oberth_effect

    At a certain speed (relativistic effects also work for you at a certain speed), the kinetic energy gain (very small change of m/s^2 still causes an extreme change in energy at high velocity) is greater than the microwave energy dumped into the cavity. This is when the EM drive starts to violate the first law of thermodynamics.

    1. “If the EM should actually work, it would not only violate the conservation of momentum law, but also the 1 thermodynamic law of conservation of energy.”

      That’s not true – at least, it’s not necessarily true. Let’s assume they’re actually performing voodoo magic and manipulating the quantum vacuum. So that means that the vacuum has a preferred reference frame – namely the one where the Universe is expanding uniformly around you (Observationally this is basically equivalent to the CMB rest frame, but from a physics point of view it doesn’t have to be. From what we know right now, the Big Bang and inflation don’t have to have been caused by the same thing). Doesn’t have to be that, though, it could also be something related to the relative mass in your nearby vicinity. Just depends how the voodoo magic works. (You can tell how much I think this is real.)

      In order to push against the vacuum, it needs to be mutable – which means that there must be a portion of it that gets denser as you move relative to its rest frame. Doesn’t have to be all of it – if it *was* all of it, you’d expect physics to be vastly different at different parts of the Universe. Which means the effect of your distortion would get weaker as you get faster (relative to it), which means no violation of conservation of energy. Effectively, the quantum vacuum starts braking you, and you actually would hit a steady-state velocity.

      This isn’t wacko-speak talking, either. The CMB provides a braking force to anything moving against it, obviously, which is the exact same idea. It just happens to be ridiculously tiny when we’re moving so slow compared to it. At super-relativistic energies (still below c!), the CMB becomes universally destructive. If you imagine a proton in a giant electric field, for instance (which would normally generate a constant KE energy gain) you’d also be able to derive a steady-state maximum energy due to CMB braking.

  35. I don’t understand why this is controversial, correct me if I’m wrong (which I probably am)

    But why does this violate the conservation of momentum? When the electrons hit the wall… are they not transferring their energy into it? I’m not a physics buff

      1. Okay, that makes sense, just read a little more.

        Has anyone analysed the electronics that hit the tapered face? because I think there should be more then two forces in the system… When they hit the tapered face, they should reflect and break into two components, one reflecting and the other contributing to a force parallel to the two forces on the flat parts?

        http://www.masinaelectrica.com/emdrive-independent-test/

        That’s cool as well.

  36. Where did the data on the power to thrust ratio come from? I think someone misplaced a decimal point somewhere, because I remember it being some like a few megawatts per lbf. of thrust.

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