The SpaceDrive Project – First Results on EMDrive and Mach-Effect Thrusters(researchgate.net)
researchgate.net
The SpaceDrive Project – First Results on EMDrive and Mach-Effect Thrusters
https://www.researchgate.net/publication/325177082_The_SpaceDrive_Project_-_First_Results_on_EMDrive_and_Mach-Effect_Thrusters
158 comments
Testing of propellantless propulsion concepts
requires a highly sophisticated thrust balance that
must be able to reliably detect very small thrust with
a resolution down to the nano-Newton range, block
electromagnetic interactions as much as possible
and limit any balance-vacuum chamber wall
interactions.
The thrust, if any, is so weak it's down in the noise. For a propulsion system, that's a big problem. It's like cold fusion in that way.
The thrust, if any, is so weak it's down in the noise. For a propulsion system, that's a big problem. It's like cold fusion in that way.
Nano-Newtons. For comparison, the tiny rockets used for attitude control on satellites have a thrust of about four Newtons. Falcon 9 booster, about 7,000,000 Newtons. This thing, if it works, maybe 0.00000001 Newton.
I'm still convinced EMDrive is the latest cold fusion, perpetual motion, panacea, whatever they are calling it these days.
Damn, the picture "killing of glorious idea by disgusting facts" again.
Sigh, will wait for the next "deformator of space/time curvature" device for the human race to reach stars ...
Sigh, will wait for the next "deformator of space/time curvature" device for the human race to reach stars ...
I always doubted the reactionless drive aspect of this, but has anymore research gone into the apparent spacetime warping effect that one NASA group discovered? Even if it can't do anything more than disort light more effectively than lots of magnetism doesn't make it useless
I think everyone that hopes for a bright future wishes the EM drive worked--an Epstein Drive in our own time! Alas, wishes do not make it so...
Reactionless drives are even "worse" than Epstein drives, since they break conservation of momentum entirely. Epstein drives just have wildly implausible characteristics- while they might break all known laws of, say, material and nuclear science, they don't break conservation laws since they require reaction mass.
If I remember correctly the authors stated it was based off of the theoretical limits of efficiency for a reaction mass drive (e.g. if we could turn mass into acceleration with very little waste energy). Which is a really great conceit in my opinion because it stays hard sci-fi where it matters (e.g. besides the aliens) while still being close enough to our time to be interesting.
Given what appears on screen, the Epstein Drive doesn’t even have that problem. It “only” acts like an electrostatic confinement fusion reactor with a hole in the confinement, slight enough for only the fusion products to escape, where the nozzle points.
(Edit footnote: only seen s1/2, anything surprising in s3 is unknown to me).
(Edit footnote: only seen s1/2, anything surprising in s3 is unknown to me).
The "Eros incident" does imply that the aliens have an interesting relationship with momentum, since ordinarily accelerating something that big that fast would grind everything to a pulp.
I thought when they were "flying teakettle" they were using water as a reaction mass, and the Epstein drive was an unexplained reactionless drive? At least in the books, haven't seen the TV show.
Iirc, there's some mention of pre-Epstein fusion ships that needed even more water.
Iirc, there's some mention of pre-Epstein fusion ships that needed even more water.
It's left intentionally vague, but at some point they do refuel the drive. It's meant to be an improbably efficient fusion drive.
The alien forces demonstrably have a reactionless capability though (see: Eros) that utterly outmatches the Epstein drive.
The alien forces demonstrably have a reactionless capability though (see: Eros) that utterly outmatches the Epstein drive.
you can read the novella Drive online: http://www.syfy.com/theexpanse/drive/prequel.php where it appears to be some sort of issue that occurs to his failing fusion drive, so definitely a more efficient fusion drive.
djsumdog(4)
Damn it. The Epstein drive is a fusion drive. It's far more plausible than this voodoo quackery, the only thing keeping it out of reality is the fact that nothing that size could handle the wattage without becoming a rapidly expanding cloud of plasma.
Everyone that hopes for a bright future would absolutely love a reactionless drive. I'd love it. But it's not real. We've seen lots of very bad methodology and things like researchers ignoring the fact that a null setup still produces the same thrust even though the drive has been modified not to work. With forces of this tiny order of magnitude it's incredibly hard to get accurate readings, and readings within the margin of error of the instrumentation should not be reported to sensationalist media as promising.
This is just another one of those ufo antigravity quacks you see on youtube, but somehow they got their day in court. I can't explain how much I'd love to be proven wrong, but reactionless drives are physically ludicrous in every single way we understand the universe. Is it possible for us to be wrong? Sure. Is it possible that we're wrong about literally every observation we've ever made in the history of physics? I very much doubt it and it's going to take more than a badly set-up experiment featuring a microwave stuffed into a tuba to convince anyone of that.
Everyone that hopes for a bright future would absolutely love a reactionless drive. I'd love it. But it's not real. We've seen lots of very bad methodology and things like researchers ignoring the fact that a null setup still produces the same thrust even though the drive has been modified not to work. With forces of this tiny order of magnitude it's incredibly hard to get accurate readings, and readings within the margin of error of the instrumentation should not be reported to sensationalist media as promising.
This is just another one of those ufo antigravity quacks you see on youtube, but somehow they got their day in court. I can't explain how much I'd love to be proven wrong, but reactionless drives are physically ludicrous in every single way we understand the universe. Is it possible for us to be wrong? Sure. Is it possible that we're wrong about literally every observation we've ever made in the history of physics? I very much doubt it and it's going to take more than a badly set-up experiment featuring a microwave stuffed into a tuba to convince anyone of that.
Wasn’t the Epstein drive not “new” physics but rather he just fumbled into making a “standard” fusion drive extremely efficient?
Given that reactionless thrust is even less plausible on a theoretical basis than superluminal neutrinos, I really hope this doesn't come as much of a surprise to anyone.
No one involved seriously thought it was reactionless. There were plenty of theories, such as a focused catalyst for dark matter decay, that would have made it perfectly compliant with Newton’s third law.
Not a surprise, but certainly a disappointment. It would have violated our understanding of physics, but it's not like that's never happened before.
> It would have violated our understanding of physics, but it's not like that's never happened before.
I've heard this sentiment a lot when it comes to the EMDrive, but honestly I think it really misunderstands how science progresses in general. For EMDrive to be real, virtually everything we know to be true about physics would have to be false: if you're saying conservation of momentum can be violated, or conservation of energy can be violated, then basically all of modern physics would have to be wrong.
When science, and especially physics, advances, it is very rarely, if ever since Newton's time, that the settled physics is 100% wrong. Instead, the "old" physics tends to be an approximation under most conditions, or there is a new phenomenon that can be explained without really violating the old rules. For example, conservation of momentum still holds under special relativity, it's just that we discovered things without mass can have momentum.
Thus, the only explanation that would really be plausible is if there is "something else" going on with the EMDrive where momentum and energy are still conserved, just that there is something happening beyond our current understanding of "energy" or "momentum". I haven't seen any explanations that even try to postulate what that could be. All I ever have seen is "but the old physics could be wrong!" without an explanation of how it could be wrong.
I've heard this sentiment a lot when it comes to the EMDrive, but honestly I think it really misunderstands how science progresses in general. For EMDrive to be real, virtually everything we know to be true about physics would have to be false: if you're saying conservation of momentum can be violated, or conservation of energy can be violated, then basically all of modern physics would have to be wrong.
When science, and especially physics, advances, it is very rarely, if ever since Newton's time, that the settled physics is 100% wrong. Instead, the "old" physics tends to be an approximation under most conditions, or there is a new phenomenon that can be explained without really violating the old rules. For example, conservation of momentum still holds under special relativity, it's just that we discovered things without mass can have momentum.
Thus, the only explanation that would really be plausible is if there is "something else" going on with the EMDrive where momentum and energy are still conserved, just that there is something happening beyond our current understanding of "energy" or "momentum". I haven't seen any explanations that even try to postulate what that could be. All I ever have seen is "but the old physics could be wrong!" without an explanation of how it could be wrong.
I've got a limited understanding of physics, but what I understood from the em drive website, was that basically it did not violate ths conservation of energy, the em-drive was more of a direct energy-momentul convetsion tool.
So, supposedly, if em drive worked, you could produce a flying car that could hover without new energy input (it was supposed to use superconducting materials in the cavity). As soon as you started mooving the energy in the cavity started to decrease - so you would be transfering the energy/momentum of photons in the cavity to your ship?
Anyway, my physics gut told me this was all bullshit, but I wanted to believe sooo much, if this worked, it would have been the greatest invention in human history.
So, supposedly, if em drive worked, you could produce a flying car that could hover without new energy input (it was supposed to use superconducting materials in the cavity). As soon as you started mooving the energy in the cavity started to decrease - so you would be transfering the energy/momentum of photons in the cavity to your ship?
Anyway, my physics gut told me this was all bullshit, but I wanted to believe sooo much, if this worked, it would have been the greatest invention in human history.
One problem is that we actually already have a direct energy to momentum generating "EM" drive. It is called a laser; light possesses momentum (in some sense, it is nothing but momentum) and emitting light asymmetrically produces thrust. The "EMDrive" claims to be orders of magnitude more efficient than laser propulsion (as well as not incinerating anything in it's wake), which is why it was both interesting and probably impossible.
Conservation of momentum is almost as important as conservation of energy, and indeed, if you have a reactionless drive you can extract unlimited energy:
"applying a constant force results in a constant acceleration, the kinetic energy of a mass driven by such a device increases quadratically with time, while the energy input increases only linearly with time. Thus, at some point, the kinetic energy of the device-driven mass exceeds the energy input, and if this energy is collected via decelerating the mass (via regenerative electromagnetic braking, for example), then there would be a net gain in energy."
https://arxiv.org/abs/1506.00494
"applying a constant force results in a constant acceleration, the kinetic energy of a mass driven by such a device increases quadratically with time, while the energy input increases only linearly with time. Thus, at some point, the kinetic energy of the device-driven mass exceeds the energy input, and if this energy is collected via decelerating the mass (via regenerative electromagnetic braking, for example), then there would be a net gain in energy."
https://arxiv.org/abs/1506.00494
I still believe it’s possible and even likely that there are aspects of our universe that are totally undiscovered, much like radio was a thing no one knew about until it was discovered. It seems reasonable to me that we might discover ways to create gravity on demand, or to contort spacetime in other ways using electrical devices. Any of this would upend our understanding of physics to a large degree. But nothing will falsify existing observations - apples will always fall from apple trees. That doesn’t mean there can’t be more out there.
The less you know, the more likely all those things seem. People who know nothing about chemistry believe you can make a car that uses water or air as fuel (but big oil is suppressing it). Children wouldn't be the least bit surprised to learn that momentum was not conserved in space or in nuclear reactions or in aeroplanes because they didn't even know it was supposed to be conserved in the first place or that those things were known to follow the same laws as their toys.
So I think being skeptical of accepted physics in any specific way isn't something a layman has much business doing. Of course there will be things we think we know that turn out to be wrong, but a layman can see such things everywhere, not just the places they will actually appear.
So I think being skeptical of accepted physics in any specific way isn't something a layman has much business doing. Of course there will be things we think we know that turn out to be wrong, but a layman can see such things everywhere, not just the places they will actually appear.
Eh, I don’t think it’s just about ignorance. I had a fantastic science teacher for chemistry and physics in high school, then took another few quarters of chemistry and physics in college, and I am fascinated by cosmology today. I’ve read Steven Hawking and I love lectures by Lawrence Krauss. I’ve watched probably every Feynman lecture on YouTube. I’m still perhaps a lay person (I am an engineer by trade), but I DO have an understanding of physics and chemistry. I don’t think there’s science people know that they’re keeping from us. I just think it’s naive to think we’ve discovered almost everything there is to know about the universe. I’m not trying to build a straw man, but I’m saying either there’s “just a little bit more” to know or there’s a whole lot. I’m inclined to believe there’s a whole lot left to discover when it comes to things that will have a big impact on our world.
And to be clear, I’m not being skeptical of accepted physics. When radio was discovered it didn’t change the accepted body of knowledge so much as it added new things we could do.
And to be clear, I’m not being skeptical of accepted physics. When radio was discovered it didn’t change the accepted body of knowledge so much as it added new things we could do.
I don't have knowledge about this phenomenon specifically, so you might be right that even an educated person would see hope, but I suspect it's more like whatshisface's two comments here which I think are very insightful:
https://news.ycombinator.com/item?id=17098795
https://news.ycombinator.com/item?id=17098873
We would expect new discoveries to be outside the range of what we've already tested, not randomly in the middle of it. For example, special relativity becomes significant at high speeds that nobody had ever studied before, not at some odd speed between a horse and a train.
But if you didn't know what has already been tested, you wouldn't know where "outside" is. The fact that the original device used a magnetron from a microwave oven suggests it was well within what we've already studied. Maybe the novel aspect is the very tiny effect which nobody measured accurately enough to notice before.
https://news.ycombinator.com/item?id=17098795
https://news.ycombinator.com/item?id=17098873
We would expect new discoveries to be outside the range of what we've already tested, not randomly in the middle of it. For example, special relativity becomes significant at high speeds that nobody had ever studied before, not at some odd speed between a horse and a train.
But if you didn't know what has already been tested, you wouldn't know where "outside" is. The fact that the original device used a magnetron from a microwave oven suggests it was well within what we've already studied. Maybe the novel aspect is the very tiny effect which nobody measured accurately enough to notice before.
The problem with this view is, it ignores that some of what we learn are very strong constraints, such as conservation laws and how they're connected to physical symmetries of systems.
Strictly speaking, all we know boils down to probabilistic statements. So yes, in some absolute sense, we might discover we're all totally wrong about something really fundamental. But we also know the bound on that probability is very, very, very, very, low.
Strictly speaking, all we know boils down to probabilistic statements. So yes, in some absolute sense, we might discover we're all totally wrong about something really fundamental. But we also know the bound on that probability is very, very, very, very, low.
> if you're saying conservation of momentum can be violated, or conservation of energy can be violated, then basically all of modern physics would have to be wrong.
Conservation is not a fundamental law, but an emergent property of a deeper principle called Noether's Theorem:
https://en.wikipedia.org/wiki/Noether%27s_theorem
https://www.youtube.com/watch?v=04ERSb06dOg&t=594s
And it is constantly violated.
Conservation is not a fundamental law, but an emergent property of a deeper principle called Noether's Theorem:
https://en.wikipedia.org/wiki/Noether%27s_theorem
https://www.youtube.com/watch?v=04ERSb06dOg&t=594s
And it is constantly violated.
> Noether's Theorem
Right, and we have determined the exact local symmetry with which we can use Noether's Theorem to show a set of exact conservation laws, and expect it to apply everywhere in the universe (and we test against that assiduously).
Concretely, we have ample direct experimental evidence that everywhere accessible in the solar system, to extremely high precision, at length scales of microseconds (and light-microseconds), spacetime has an exact local symmetry group SO(1,3), which is the Poincaré group. The exact symmetries of the Poincaré group include invariance of systems under rotations and translations. Colloquially, it doesn't matter whether your laboratory is laid out east-west vs north-south if you're testing Poincaré invariance wholly within the laboratory, i.e., you're not deliberately testing something much larger, like the Earth's magnetic field, or solar neutrinos, and it doesn't matter if you run your tests in northern hemisphere spring or northern hemisphere winter (notably the planet is at a very different point compared to other solar system bodies at both times, so this is a full spacetime translation).
That is, the results of locally-determinable non-gravitational experiments do not depend on position in spacetime, or orientation with respect to some distant object.
The rotational invariance, via Noether, gives us conservation of angular momentum.
The translation invariance, via Noether, gives us conservation of energy-monentum. With any reasonable splitting of 4-spacetime into three spatial and one timelike dimension, we take the resulting spatial translation invariance and get conservation of linear momentum, and the resulting time translation invariance and get conservation of energy.
In General Relativity, we are guaranteed a patch of flat spacetime around every point in the manifold. Far from massive objects, that patch can cover a fairly large region of spacetime (>> microseconds or light-microseconds). The metric of flat spacetime directly maps to the Poincaré group; more formally, the Poincaré group is the local group theory of Minkowski space, and the Lorentzian metric on the whole spacetime guarantees Minkowski space in small regions.
So even though we must bring in the equivalence principle when doing so, we fully preserve Poincaré invariance at laboratory scales even when on the surface of the various massive bodies in our solar system. This has already been tested experimentally to high precision against several different planetary objects other than the Earth, and several objects which aren't in approximate hydrostatic equilibrium (and thus not planets).
Everywhere we observe (on Earth, elsewhere in the solar system, and with astronomical observations) we see evidence for local Poincaré invariance (up to strong gravity, which is hidden behind event horizons anyway) from emissions and absorptions spectra, and various other observables.
Note, though, that while everywhere-flat spacetime -- the setting of Special Relativity, and in fact what makes the theory Special -- has global Poincaré symmetry, that is not true for spacetime which is not everywhere flat. The global symmetries of the FLRW model of the standard cosmology, for instance, are not time-translation invariant. Therefore there is no correspondence via Noether to a conservation of energy. However, the "swiss-cheese" approach lets us replace a comoving speck of the standard cosmology's expanding dust with a smaller-than-Megaparsec scale region of flat spacetime (corresponding to a region of spacetime far outside any galaxy clusters) or a smaller-than-Megaparsec scale region of Schwarzschild(-like) spacetime (corresponding to a region of spacetime in which there is some collapsing mass, like a galaxy cluster). This is a "sewing" or "stitching-in" process which is described in various places like Misner-Thorne-Wheeler's section on the Israel junction conditions. The standard cosmology gives us a slicing into spatial and timelike dimensions. Thus within in the two examples of "stitched-in" regions, we would the local symmetries in each such spacetime to apply, with appropriately conserved quantities per Noether's Theorem.
Indeed, we test to see whether building up the solar system by sewing together small patches of Schwarzschild(-like) and Minkowski spacetimes accords with the previously mentioned observational tests of General Relativity, at the level of numerical relativity. They do.
So, there is no escaping conservation-of-energy within the solar system theoretically. Tests of the fundamental pieces of this (which are ultimately tests of the equivalence principle under some very light assumptions, and tests of the Standard Model of Particle Physics, which incorporates the Poincaré group directly into it's formalism) support this to many decimal places.
Thus,
> it is constantly violated
is not true anywhere within the solar system, nor anywhere within the local group of galaxies back to when it first started forming stars. That is a rather large volume of spacetime.
However, after one moves sufficiently far away from that region, spacetime is no longer well modelled by a Schwarzschild-like solution, but is instead well-modelled by a Robertson-Walker metric (conversely, within the Milky way, nowhere is space well-modelled by a Robertson-Walker metric). In faraway regions of the universe which matches the observables of Robertson-Walker, one should expect a failure of the global symmetries of Schwarzschild(-like) spacetime.
Finally, even with an expanding Friedmann-Lemaître-Robertson-Walker (FLRW) model, and without "swiss cheese-ing" it, there is still at every point a small patch of spacetime in which the local symmetries are experimentally indistinguishable from Poincaré. Thus, to observe a violation of conservation of momentum (or energy) in our standard expanding spacetime with the observed value for the cosmological constant, you need a separation of millions of lightyears. This is why we see a cosmological redshift from distant galaxies but no cosmological redshift from nearby ones.
Right, and we have determined the exact local symmetry with which we can use Noether's Theorem to show a set of exact conservation laws, and expect it to apply everywhere in the universe (and we test against that assiduously).
Concretely, we have ample direct experimental evidence that everywhere accessible in the solar system, to extremely high precision, at length scales of microseconds (and light-microseconds), spacetime has an exact local symmetry group SO(1,3), which is the Poincaré group. The exact symmetries of the Poincaré group include invariance of systems under rotations and translations. Colloquially, it doesn't matter whether your laboratory is laid out east-west vs north-south if you're testing Poincaré invariance wholly within the laboratory, i.e., you're not deliberately testing something much larger, like the Earth's magnetic field, or solar neutrinos, and it doesn't matter if you run your tests in northern hemisphere spring or northern hemisphere winter (notably the planet is at a very different point compared to other solar system bodies at both times, so this is a full spacetime translation).
That is, the results of locally-determinable non-gravitational experiments do not depend on position in spacetime, or orientation with respect to some distant object.
The rotational invariance, via Noether, gives us conservation of angular momentum.
The translation invariance, via Noether, gives us conservation of energy-monentum. With any reasonable splitting of 4-spacetime into three spatial and one timelike dimension, we take the resulting spatial translation invariance and get conservation of linear momentum, and the resulting time translation invariance and get conservation of energy.
In General Relativity, we are guaranteed a patch of flat spacetime around every point in the manifold. Far from massive objects, that patch can cover a fairly large region of spacetime (>> microseconds or light-microseconds). The metric of flat spacetime directly maps to the Poincaré group; more formally, the Poincaré group is the local group theory of Minkowski space, and the Lorentzian metric on the whole spacetime guarantees Minkowski space in small regions.
So even though we must bring in the equivalence principle when doing so, we fully preserve Poincaré invariance at laboratory scales even when on the surface of the various massive bodies in our solar system. This has already been tested experimentally to high precision against several different planetary objects other than the Earth, and several objects which aren't in approximate hydrostatic equilibrium (and thus not planets).
Everywhere we observe (on Earth, elsewhere in the solar system, and with astronomical observations) we see evidence for local Poincaré invariance (up to strong gravity, which is hidden behind event horizons anyway) from emissions and absorptions spectra, and various other observables.
Note, though, that while everywhere-flat spacetime -- the setting of Special Relativity, and in fact what makes the theory Special -- has global Poincaré symmetry, that is not true for spacetime which is not everywhere flat. The global symmetries of the FLRW model of the standard cosmology, for instance, are not time-translation invariant. Therefore there is no correspondence via Noether to a conservation of energy. However, the "swiss-cheese" approach lets us replace a comoving speck of the standard cosmology's expanding dust with a smaller-than-Megaparsec scale region of flat spacetime (corresponding to a region of spacetime far outside any galaxy clusters) or a smaller-than-Megaparsec scale region of Schwarzschild(-like) spacetime (corresponding to a region of spacetime in which there is some collapsing mass, like a galaxy cluster). This is a "sewing" or "stitching-in" process which is described in various places like Misner-Thorne-Wheeler's section on the Israel junction conditions. The standard cosmology gives us a slicing into spatial and timelike dimensions. Thus within in the two examples of "stitched-in" regions, we would the local symmetries in each such spacetime to apply, with appropriately conserved quantities per Noether's Theorem.
Indeed, we test to see whether building up the solar system by sewing together small patches of Schwarzschild(-like) and Minkowski spacetimes accords with the previously mentioned observational tests of General Relativity, at the level of numerical relativity. They do.
So, there is no escaping conservation-of-energy within the solar system theoretically. Tests of the fundamental pieces of this (which are ultimately tests of the equivalence principle under some very light assumptions, and tests of the Standard Model of Particle Physics, which incorporates the Poincaré group directly into it's formalism) support this to many decimal places.
Thus,
> it is constantly violated
is not true anywhere within the solar system, nor anywhere within the local group of galaxies back to when it first started forming stars. That is a rather large volume of spacetime.
However, after one moves sufficiently far away from that region, spacetime is no longer well modelled by a Schwarzschild-like solution, but is instead well-modelled by a Robertson-Walker metric (conversely, within the Milky way, nowhere is space well-modelled by a Robertson-Walker metric). In faraway regions of the universe which matches the observables of Robertson-Walker, one should expect a failure of the global symmetries of Schwarzschild(-like) spacetime.
Finally, even with an expanding Friedmann-Lemaître-Robertson-Walker (FLRW) model, and without "swiss cheese-ing" it, there is still at every point a small patch of spacetime in which the local symmetries are experimentally indistinguishable from Poincaré. Thus, to observe a violation of conservation of momentum (or energy) in our standard expanding spacetime with the observed value for the cosmological constant, you need a separation of millions of lightyears. This is why we see a cosmological redshift from distant galaxies but no cosmological redshift from nearby ones.
Can you give an example of how it is "constantly violated"? One not involving a "perpetual motion machine"?
The linked video mentions the expansion of the universe, and relativity.
Just to follow-up on my longer reply above: the solar system is not expanding. So within the solar system, there should be exact conservation of energy. (And we do test this in many ways, and it holds up).
The metric expansion only operates on scales much larger than that of the solar system (and even larger than that of the Milky Way and its collection of nearby neighbours).
(One can take a theory other than General Relativity and finely-tune the expansion of the solar system to match the null results on measures of it, and this is done in some quintessence and other models, but this won't help one do away with exact conservation of energy at scales of EmDrives; or give much room to have more energy moving into (or out of) a boundary drawn outside the solar system and the wider universe).
The metric expansion only operates on scales much larger than that of the solar system (and even larger than that of the Milky Way and its collection of nearby neighbours).
(One can take a theory other than General Relativity and finely-tune the expansion of the solar system to match the null results on measures of it, and this is done in some quintessence and other models, but this won't help one do away with exact conservation of energy at scales of EmDrives; or give much room to have more energy moving into (or out of) a boundary drawn outside the solar system and the wider universe).
The section of the video dealing with Noether's Theorem and The Symmetries of Reality actually ends at t=594s :/ so just the main link is needed: https://www.youtube.com/watch?v=04ERSb06dOg
If one or another of these so-called fundamental laws is being apparently broken by the EmDrive then that would make it a very very unusual object. Consequently there would need to be repeatable verifiable evidence that it does so and at least the beginnings of a theory as to how in fact this breakage is occurring–Noether's theorem notwithstanding.
If one or another of these so-called fundamental laws is being apparently broken by the EmDrive then that would make it a very very unusual object. Consequently there would need to be repeatable verifiable evidence that it does so and at least the beginnings of a theory as to how in fact this breakage is occurring–Noether's theorem notwithstanding.
To say there are NO theories as to how this can operate and NOT violate conservation laws is incorrect. Laymen just don't comprehend that there are possible theoretical paradigms they have not considered or are not aware of, so their knee jerk reaction is "not possible!":
https://en.wikipedia.org/wiki/RF_resonant_cavity_thruster
"Vacuum energy
Main articles: Zero-point energy, Quantum vacuum thruster, and Pilot wave Harold White, the lead scientist in the NASA investigations, suggested in 2014 that their model could be an example of a quantum vacuum thruster (QVT). This is a theoretical system that would use magnetohydrodynamics to generate thrust, similar to conventional plasma thrusters, only using the fleeting vacuum quantum fluctuations of the zero-point field as an extremely low-density plasma.[82][23][83][84]
White's 2016 paper states that pilot-wave theories, non-mainstream interpretations of quantum mechanics based on the de Broglie–Bohm theory, may help explain how QVTs could "push off of the quantum vacuum and preserve the laws of conservation of energy and conservation of momentum.".
In 2017, a Portuguese team published a paper proposing pilot-wave theory as a possible explanation to the EmDrive thrust, that would not break conservation laws. The principle is that a sufficiently strong asymmetrical electromagnetic field could act as a pilot wave. The cavity would then be attracted toward regions of higher electromagnetic intensity. The researchers propose to increase thrust by shaping the cavity with an exponential form like that of a trumpet bell instead of a frustum.[85][86]"
https://en.wikipedia.org/wiki/RF_resonant_cavity_thruster
"Vacuum energy
Main articles: Zero-point energy, Quantum vacuum thruster, and Pilot wave Harold White, the lead scientist in the NASA investigations, suggested in 2014 that their model could be an example of a quantum vacuum thruster (QVT). This is a theoretical system that would use magnetohydrodynamics to generate thrust, similar to conventional plasma thrusters, only using the fleeting vacuum quantum fluctuations of the zero-point field as an extremely low-density plasma.[82][23][83][84]
White's 2016 paper states that pilot-wave theories, non-mainstream interpretations of quantum mechanics based on the de Broglie–Bohm theory, may help explain how QVTs could "push off of the quantum vacuum and preserve the laws of conservation of energy and conservation of momentum.".
In 2017, a Portuguese team published a paper proposing pilot-wave theory as a possible explanation to the EmDrive thrust, that would not break conservation laws. The principle is that a sufficiently strong asymmetrical electromagnetic field could act as a pilot wave. The cavity would then be attracted toward regions of higher electromagnetic intensity. The researchers propose to increase thrust by shaping the cavity with an exponential form like that of a trumpet bell instead of a frustum.[85][86]"
> Laymen just don't comprehend that there are possible theoretical paradigms they have not considered or are not aware of, so their knee jerk reaction is "not possible!"
Skepticism about the EmDrive from Physicists has been nearly universal. There's always a few contrarians and heretics, but the consensus is what it is for good reason: it's best supported by the evidence.
This is not about "laymen" lacking comprehension, and the condescension doesn't help your case.
Skepticism about the EmDrive from Physicists has been nearly universal. There's always a few contrarians and heretics, but the consensus is what it is for good reason: it's best supported by the evidence.
This is not about "laymen" lacking comprehension, and the condescension doesn't help your case.
> Skepticism about the EmDrive from Physicists has been nearly universal.
So what?
Skepticism and status quo consensus does not push any field forward into new territory. The vast majority of physicist I would argue are simply refiners of areas pioneered by a scant few others, or working in the industry (myself included). Like it or not, these refiner types aren't the ones earning Nobels. You see this in almost all fields. Current AI advancement originated with maybe 3 researchers pioneer theories, its didn't spontaneously manifest from the consensus Computer Science crowd. Its the open minded mavericks on the outskirts types looking for a way to walk the line or even circumvent current understanding that stumble upon possible breakthrough science where others can move in and refine.
Sorry, but it really bugs me when I see relatively smart (but still not Physicist) techy types (relative physics laymen in my mind) defaulting to "it cant be therefor it isn't" logic. This is the Argument from Ignorance logical fallacy. Have they even bothered to read the alternative explanations that might explain the experimental result? You can read a few in my wiki link above. If not then what the F do they know then! Sure it could be just measurement error, or it could be the biggest breakthrough in space travel we've seen and may lend credence to an obscure theory such as pilot waves and quantum vacuum flux. Better not look under that rock through because it might upset the consensus who says there's nothing there. /s People don't realize how closed minded that sort of mindset really is. Armchair know-nothings looking for anything to shoot down and pat themselves on the back for deserve condescension.
So what?
Skepticism and status quo consensus does not push any field forward into new territory. The vast majority of physicist I would argue are simply refiners of areas pioneered by a scant few others, or working in the industry (myself included). Like it or not, these refiner types aren't the ones earning Nobels. You see this in almost all fields. Current AI advancement originated with maybe 3 researchers pioneer theories, its didn't spontaneously manifest from the consensus Computer Science crowd. Its the open minded mavericks on the outskirts types looking for a way to walk the line or even circumvent current understanding that stumble upon possible breakthrough science where others can move in and refine.
Sorry, but it really bugs me when I see relatively smart (but still not Physicist) techy types (relative physics laymen in my mind) defaulting to "it cant be therefor it isn't" logic. This is the Argument from Ignorance logical fallacy. Have they even bothered to read the alternative explanations that might explain the experimental result? You can read a few in my wiki link above. If not then what the F do they know then! Sure it could be just measurement error, or it could be the biggest breakthrough in space travel we've seen and may lend credence to an obscure theory such as pilot waves and quantum vacuum flux. Better not look under that rock through because it might upset the consensus who says there's nothing there. /s People don't realize how closed minded that sort of mindset really is. Armchair know-nothings looking for anything to shoot down and pat themselves on the back for deserve condescension.
I could be wrong, but I believe the postulation was along the lines of a quantum effect utilizing virtual particles from quantum vacuum fluctuations to generate microthrust. If that were true, it wouldn't really be a violation of the standard model - more of an addendum like a lot of things involving quantum mechanics.
If virtual particles are the ones I know from Feynman diagrams, then momentum is still conserved at every vertex (interaction element). Unless the person who speculated that meant something else by "virtual particles," I don't see in the slightest how they could be used to obtain momentum or squirrel it away.
Besides, virtual particles have to go away at the end of every diagram... They can act as conduits between other particle fields but if a new particle remains after the interaction it will be just another reaction product (nothing virtual or spooky). Some go so far as to say that virtual particles don't particularly exist, but that's a philosophical statement I guess (they do indeed lack many properties of other things that exist). However I can't say much about that as the arguments for this-or-that nonintuitive ontology usually emerge from advanced theoretical research that is beyond my knowledge. (I.e. in momentum space virtual particles don't even remotely seem to exist, but maybe the picture seems more reasonable when you write it all down some other way.)
Besides, virtual particles have to go away at the end of every diagram... They can act as conduits between other particle fields but if a new particle remains after the interaction it will be just another reaction product (nothing virtual or spooky). Some go so far as to say that virtual particles don't particularly exist, but that's a philosophical statement I guess (they do indeed lack many properties of other things that exist). However I can't say much about that as the arguments for this-or-that nonintuitive ontology usually emerge from advanced theoretical research that is beyond my knowledge. (I.e. in momentum space virtual particles don't even remotely seem to exist, but maybe the picture seems more reasonable when you write it all down some other way.)
Virtual particles are particle-antiparticle pairs that are constantly being created and annihilated in empty space due to quantum ground-state variations. Supposedly their effects can be observed at the event horizons of black holes, giving rise to Hawking radiation, though this may be a simplification for the layman.
They also conserve both energy and momentum.
They also conserve both energy and momentum.
> though this may be a simplification for the layman
It's almost the opposite of that: a simplification for professionals' sake. You can set up an eternal black hole and enjoy the simplifications its time-invariance permits, but then you have to match the outgoing Hawking radiation flux (as seen at infinity) with an ingoing one.
With a collapsing-matter black hole you lose time-invariance, because, coarsely, there is a region of spacetime where there is spread out matter and no trapping surface ("event horizon", or whatever, let's be agnostic about that), there is a region of spacetime where there is a trapping surface, and finally there is a region of spacetime where the trapping surface is gone and there is a gas of thermal radiation. But on the bright side, then you don't need any ingoing flux to balance the outgoing Hawking radiation. Instead you look at non-trivial Bogoliubov transformations between these different regions, which model how observer in region-with-horizon sees particles that observer in region-with-uncollapsed-matter ("no horizon yet") does not. (You can additionally change the speed of collapse, which changes the difference in particles that the later observer sees: sufficiently slow collapse means no Hawking radiation at all.)
(Professionals even make other simplifications, like dealing with a free-as-in-linear scalar quantum field rather than realistic interacting matter; it won't matter much since "real" Hawking radiation would be almost only photons anyway, and the stark problems around the border between the region with the horizon (and Hawking radiation outside it) and the region with only Hawking radiation (and no horizon) likely do not depend on the precise content of the hottest Hawking radiation.)
It's almost the opposite of that: a simplification for professionals' sake. You can set up an eternal black hole and enjoy the simplifications its time-invariance permits, but then you have to match the outgoing Hawking radiation flux (as seen at infinity) with an ingoing one.
With a collapsing-matter black hole you lose time-invariance, because, coarsely, there is a region of spacetime where there is spread out matter and no trapping surface ("event horizon", or whatever, let's be agnostic about that), there is a region of spacetime where there is a trapping surface, and finally there is a region of spacetime where the trapping surface is gone and there is a gas of thermal radiation. But on the bright side, then you don't need any ingoing flux to balance the outgoing Hawking radiation. Instead you look at non-trivial Bogoliubov transformations between these different regions, which model how observer in region-with-horizon sees particles that observer in region-with-uncollapsed-matter ("no horizon yet") does not. (You can additionally change the speed of collapse, which changes the difference in particles that the later observer sees: sufficiently slow collapse means no Hawking radiation at all.)
(Professionals even make other simplifications, like dealing with a free-as-in-linear scalar quantum field rather than realistic interacting matter; it won't matter much since "real" Hawking radiation would be almost only photons anyway, and the stark problems around the border between the region with the horizon (and Hawking radiation outside it) and the region with only Hawking radiation (and no horizon) likely do not depend on the precise content of the hottest Hawking radiation.)
I have no understanding of physics, but given that 70% of the known mass isn't measurable, couldn't something like the EMDrive "just" (lol) send dark matter one way, and get momentum the other way?
This is probably stupid to anybody that knows about physics, but I had to ask :)
This is probably stupid to anybody that knows about physics, but I had to ask :)
We don't think that there's very much dark matter in our immediate vicinity. If there were, we'd probably have an easier time detecting it. Even though there's (according to theory) a lot of it in the universe, it clumps much less strongly than regular matter, so it's diffuse.
And the characteristic of dark matter is that it interacts very weakly or not at all to electromagnetism. It would be very odd if it interacted so strongly with the EM drive that the EM drive could generate noticable thrust from such a diffuse medium.
Finally, dark matter, if it has inertia, should have an inertial frame of reference. That frame is unlikely to be "at rest relative to the surface of the Earth." Therefore, if the EM drive is pushing off dark matter, we'd probably expect it to work more strongly in some directions than others. Think of it as a sail in a ghostly wind.
And the characteristic of dark matter is that it interacts very weakly or not at all to electromagnetism. It would be very odd if it interacted so strongly with the EM drive that the EM drive could generate noticable thrust from such a diffuse medium.
Finally, dark matter, if it has inertia, should have an inertial frame of reference. That frame is unlikely to be "at rest relative to the surface of the Earth." Therefore, if the EM drive is pushing off dark matter, we'd probably expect it to work more strongly in some directions than others. Think of it as a sail in a ghostly wind.
>we'd probably expect it to work more strongly in some directions than others.
According to the paper, the EM drive did actually quit working when rotated. However the dark matter wind seems less likely of an explanation than the Earth's magnetic field. ;)
According to the paper, the EM drive did actually quit working when rotated. However the dark matter wind seems less likely of an explanation than the Earth's magnetic field. ;)
When rotated relative to the Earth!
The Earth is changing orientation in the galaxy as it spins, around itself and the Sun. Unless it was done exactly once, this experiment was performed at many orientations relative to the galaxy.
The Earth is changing orientation in the galaxy as it spins, around itself and the Sun. Unless it was done exactly once, this experiment was performed at many orientations relative to the galaxy.
That's a perfectly astute guess, and it sounds more plausible than the original theory behind the EM drive. However photons in a cavity, at these energies, are unlikely to be producing many particles - the effect you're describing is known and can happen (not even with dark matter, photons can directly produce regular matter and antimatter), but we have a good idea of how much is produced and it's not enough to thrust anywhere. (It would be easier just to shoot the photons out the back of the rocket - they're massless and therefore carry momentum with the highest possible energy efficiency.)
Although much more plausible than reactionless thrust, and I don't think your comment deserves downvotes, this is still highly unlikely. Raattgift posted a good comment explaining why in the last big EmDrive discussion:
https://news.ycombinator.com/item?id=13003811
https://news.ycombinator.com/item?id=13003811
Horsefeathers. To name two examples. The Einstein-Podolsky-Rosen's paper on entanglement “Can Quantum Mechanical Description of Physical Reality Be Considered Complete?” (Einstein et al. 1935) ignored as trash for decades. The Casimir effect was predicted from quantum theoretical calculations, but again, no-one did the experiment for decades because they felt it was a trash prediction that couldn't be true 'cause it ignored basic physical laws that everyone knew had always held and always would. Empty space just couldn't do that. And on and on and on - I've just covered this century a tiny bit, not all the time since Newton. Dark energy anyone?
Knowledge of the mechanisms behind X doesn't always precede discovery of X (why would anyone think it would always do so?) Lack of a known mechanism was why John Newlands version of the periodic table was greeted with contempt, and Mendeleev didn't find it easy sledding at first, either. But the contempt was unjustified. Birds were able to fly before the airfoil was discovered or airflow understood. Electricity was a broad field of study (Maxwell's equations, etc) long before the electron was discovered. The how usually trails the what in the history of science.
I won't be shocked if the Emdrive is a wrong turn, but the idea we could know that in advance is sciencism - the satanic inversion of science - not empirical science.
Knowledge of the mechanisms behind X doesn't always precede discovery of X (why would anyone think it would always do so?) Lack of a known mechanism was why John Newlands version of the periodic table was greeted with contempt, and Mendeleev didn't find it easy sledding at first, either. But the contempt was unjustified. Birds were able to fly before the airfoil was discovered or airflow understood. Electricity was a broad field of study (Maxwell's equations, etc) long before the electron was discovered. The how usually trails the what in the history of science.
I won't be shocked if the Emdrive is a wrong turn, but the idea we could know that in advance is sciencism - the satanic inversion of science - not empirical science.
There is still some place for using theoretical predictions to guide experiments. For example, I have developed a rune that may be used to cast Fireball - it consists of three triangles carved in to a very expensive gold-titanium laminate. If that test fails, I suppose we also ought to try four triangles, a triangle and a circle, the word 'fireball' engraved on the perimeter of a hexagon, three triangles engraved onto a momentum-nonconserving cone...
More seriously, there was a good reason to strongly suspect that the EM drive wouldn't overturn physics: we have probed electromagnetic interactions at energy densities far higher (gamma ray scattering) and far lower (radio telescopes) and everything in-between, and they all seem to be points on a continuous surface defined by Maxwell's equations applied to quantum mechanics. A working EM drive would actually be very close to the magic rune I described above: a wildly noncontinuous point where the laws of physics became massively different for one particular arrangement of matter, and then go right back to normal if you step in any direction around it.
More seriously, there was a good reason to strongly suspect that the EM drive wouldn't overturn physics: we have probed electromagnetic interactions at energy densities far higher (gamma ray scattering) and far lower (radio telescopes) and everything in-between, and they all seem to be points on a continuous surface defined by Maxwell's equations applied to quantum mechanics. A working EM drive would actually be very close to the magic rune I described above: a wildly noncontinuous point where the laws of physics became massively different for one particular arrangement of matter, and then go right back to normal if you step in any direction around it.
The general use of experiments in science (as opposed to a Homo Erectus experimenting with rock types when making hammers) is to test what we think we know, to see if it's really so. IIRC the "inventor" of the Emdrive had a theory of his own to go by that led him to his device. We probably agree that it's the use of theory to preempt and prevent any experimentation that is pernicious.
(reply to below comment) While not all experiments are equal, there's no right answer, and plenty of room for good and bad luck. The marketplace of ideas ensures enough variety that we don't miss toooo much (maybe.) Yet very often, it's those with the most eccentric and false ideas, such as Keplar, who stumble onto the right path because at least they're looking where nobody else is, for correlations no-one else thought to! So my bias is toward the most novel experiments that are still extremely likely to fail, as I think you agree.
Just this week I was reading up on the Stern-Gerlach Magnet experiment, which discovered spin; something the experimenters absolutely weren't looking for. The idiots (or recipients of blind luck) win a lot of rounds in science, 'cause they're at least trying something genuinely new.
Slightly different alloy = slightly different string theory?
(reply to below comment) While not all experiments are equal, there's no right answer, and plenty of room for good and bad luck. The marketplace of ideas ensures enough variety that we don't miss toooo much (maybe.) Yet very often, it's those with the most eccentric and false ideas, such as Keplar, who stumble onto the right path because at least they're looking where nobody else is, for correlations no-one else thought to! So my bias is toward the most novel experiments that are still extremely likely to fail, as I think you agree.
Just this week I was reading up on the Stern-Gerlach Magnet experiment, which discovered spin; something the experimenters absolutely weren't looking for. The idiots (or recipients of blind luck) win a lot of rounds in science, 'cause they're at least trying something genuinely new.
Slightly different alloy = slightly different string theory?
>We probably agree that it's the use of theory to preempt and prevent any experimentation that is pernicious.
So, there's a point about philosophy of science to be made here. If you test one bronze alloy for antigravity, and then test a slightly different bronze alloy for antigravity, and so on, finding all of them to fall when dropped, how can you know when it's reasonable to stop testing bronze alloys for antigravity? Presumably, you should eventually say "this idea has already been tested," and then stop. However there will always be a new ratio of metals to try: the only way to say "this has been tested" or "this hasn't" is to establish enough of a theory to make predictions about the effect of gravity on every bronze alloy, and then trust it when it says it will not become negative (at least, trust it enough to let it rule out potential experiments from grant approval.) When we say, "a new arrangement of photons will still conserve momentum," we are performing exactly the kind of interpolation from other experiments involving photons in cavities that, previously, stopped us from making more and more bronze bars in the search for antigravity.
So, there's a point about philosophy of science to be made here. If you test one bronze alloy for antigravity, and then test a slightly different bronze alloy for antigravity, and so on, finding all of them to fall when dropped, how can you know when it's reasonable to stop testing bronze alloys for antigravity? Presumably, you should eventually say "this idea has already been tested," and then stop. However there will always be a new ratio of metals to try: the only way to say "this has been tested" or "this hasn't" is to establish enough of a theory to make predictions about the effect of gravity on every bronze alloy, and then trust it when it says it will not become negative (at least, trust it enough to let it rule out potential experiments from grant approval.) When we say, "a new arrangement of photons will still conserve momentum," we are performing exactly the kind of interpolation from other experiments involving photons in cavities that, previously, stopped us from making more and more bronze bars in the search for antigravity.
Sure, but is that line of reasoning similar to the situation with the EMDrive? I thought the interesting part was that there was an actual as-yet unexplained result / measurement. So, going back to the bronze alloys, it's more like "crazy person X has found a bronze alloy that almost seems like antigravity, and it seems to break all fundamental laws of physics". Should we disregard, or humour it look into it? It was always very likely to be some kind of error, but it's a fundamentally less silly exercise.
there was an actual as-yet unexplained result / measurement
You're using words like "almost seems" that just don't match up to the results seen, especially considering the flawed testing methods used.
1. "actual" isn't that actual if enough independent
scientists aren't duplicating it using scientifically
accepted testing procedures.
2. "actual" isn't that actual when the quantity is down
at around noise level.
You're using words like "almost seems" that just don't match up to the results seen, especially considering the flawed testing methods used.
[deleted]
"Experiments of destroying Mites by several Fumes: of the equivocal Generation of Insects: of feeding a Carp in the Air: of making Insects with Cheese, and Sack: of killing Water-Newts, Toads, and Sloworms with several Salts: of killing Frogs by touching their skin, with Vinegar, Pitch, or Mercury: of a Spiders not being Inchanted by a Circle of Unicorns-horn, or Irish Earth, laid round about it."
[Thomas Sprat: from The History of the Royal Society, 1667]
You're misunderstanding my post, so I'll try to put it another way. Suppose I tell you I have proof I created a perpetual motion machine. You'd probably laugh me off as a crank, or at least demand an extremely high level of evidence, to even listen to me.
The EMDrive breaks the known laws of physics as much as any potential perpetual motion machine would, so for it to be correct would imply as much is wrong as our knowledge of physics as the existence of a perpetual motion machine would.
The EMDrive breaks the known laws of physics as much as any potential perpetual motion machine would, so for it to be correct would imply as much is wrong as our knowledge of physics as the existence of a perpetual motion machine would.
And indeed, you can build a perpetual motion machine out of a reactionless drive.
"any device with a thrust-to-power ratio greater than the photon rocket would be able to operate as a perpetual motion machine" https://arxiv.org/abs/1506.00494
"any device with a thrust-to-power ratio greater than the photon rocket would be able to operate as a perpetual motion machine" https://arxiv.org/abs/1506.00494
The Casimir effect already produces perpetual motion (in that sense.)
Which raises the specualtive question of whether the Emdrive exploits the Casimir effect to obtain a tiny thrust (in which case a drive subdivided into a vast number of really small trapesoidal sections might produce much more thrust.
Which raises the specualtive question of whether the Emdrive exploits the Casimir effect to obtain a tiny thrust (in which case a drive subdivided into a vast number of really small trapesoidal sections might produce much more thrust.
You misunderstand the Casimir effect. It's a relativistic analogue of the van der Waals interaction, with a very curious alternative derivation from zero point energies. It is not free/negative energy, it is not free momentum, it was never a controversial subject, we only didn't have the practical means to measure it.
Exploiting the Casimir effect can't give free momentum, because the derivation of the force is rooted in quantum field theory, which like any other physical theory of the last 400 years contains conservation of momentum at its very core.
Exploiting the Casimir effect can't give free momentum, because the derivation of the force is rooted in quantum field theory, which like any other physical theory of the last 400 years contains conservation of momentum at its very core.
There's a simple way to get free energy out of a working em-drive: "at some point, the kinetic energy of the device-driven mass exceeds the energy input, and if this energy is collected via decelerating the mass (via regenerative electromagnetic braking, for example), then there would be a net gain in energy." How do you get a net gain in energy out of the Casimir effect?
Vibration is continuous. Free energy you can get - whether we'll ever harness it to obtain thrust or electric power I don't know - but endless minor amounts of heat, yes.
How do you produce vibration with a force that makes two metal plates stick together? Once they're stuck together, the force goes away. There's no repulsive Casimir effect, and insofar as they bounce, they will quickly come to rest. It's like trying to extract free energy by dropping a ball to the ground.
Let accept that there is Ether, and Ether is like water. In such case, Casimir effect may depend on the flow of Ether, so if plates are in free space and exposed to unbound Ether, then Casimir effect may happen when plates are oriented perpendicular to flow (as usual), and may NOT happen when plates are parallel to flow (my prediction).
The Casimir effect was both predicted by quantum field theory and observed to behave more or less exactly as predicted, so there's very little room for supposed etheric effects. If they were observable, we probably would have seen them just by accident already.
> The Casimir effect was predicted from quantum theoretical calculations (...)
Thank you. That led me to learning about:
https://en.m.wikipedia.org/wiki/Alcubierre_drive
And:
https://en.m.wikipedia.org/wiki/Krasnikov_tube
Thank you. That led me to learning about:
https://en.m.wikipedia.org/wiki/Alcubierre_drive
And:
https://en.m.wikipedia.org/wiki/Krasnikov_tube
Not a surprise and not a disappointment either, when it was clear from the start that all results are within measurement error bars, so that there was neither experimental nor theoretical reason to expect to see something.
It wasn't clear from the start or there never would have been follow-ups.
There seemed to be a measurable effect going on, so they tested it.
There seemed to be a measurable effect going on, so they tested it.
Still, would have been nice to find a real effect. And by nice, I mean it would have changed the future of space travel.
It also would have literally meant the end of the world in a short period of time. Reactionless rockets with little to no cost or requiring high technical capability would lead to a terrorist shortly speeding up a hunk of lead to near lightspeed and slamming it into a earthside target, and that would be that.
We've had a few thousand nukes, many secured with the password 0000, lying around for a few decades now in a dozen countries, and that hasn't materialized. For some reason, we seem to be much better at imagining ridiculous scenarios for terrorists than they are at implementing them.
Well first that need to get it into orbit and outside of the suns gravity well. Then they'd have to get it far enough away that the lead could get up to light speed before hitting it's target, you can't do this in solar system because you can't change trajectory that fast. Finally they have to aim it correctly at earth from that distance.
A big ask for a group of people who's best technical achievement so far is to fly a plane into a building.
A big ask for a group of people who's best technical achievement so far is to fly a plane into a building.
We could witness the great filter firsthand
At least we learn from the mistake and what kind of strange things can cause this errors like this.
A lot of these things are often scams, but in this case i think everyone involved was genuine and believed they had found something great.
A lot of these things are often scams, but in this case i think everyone involved was genuine and believed they had found something great.
Agreed. There's nothing more exciting in science than finding out that our widely-held beliefs about something are wrong.
With some exceptions, depending on how you define reaction-less:
https://en.wikipedia.org/wiki/Pioneer_anomaly
That's not a reactionless situation, there is an asymmetry of photons causing the acceleration.
Yes, of course, but there is no finite propellant being consumed.
The photons come from the decay heat of the plutonium in the radioisotope thermoelectric generator, so that is a finite propellant being consumed.
A theoretical EM-drive would run on electricity, as well, so thus wouldn't be propellant-less?
Well, assuming one can violate only one law of physics at a time, this is just semantics.
Well, assuming one can violate only one law of physics at a time, this is just semantics.
No, it is different. Photon drives are like a reactionless drive in that you are not expelling matter, but photon drives are emitting mass/energy in one direction and moving in the other and conserve momentum.
Reactionless drives just produce force, pushing off "nothing." They violate conservation of momentum and break physics as we know it pretty conclusively.
Reactionless drives just produce force, pushing off "nothing." They violate conservation of momentum and break physics as we know it pretty conclusively.
They push off the whole Universe. They go in one direction, the Universe - much slower, in the opposite, and thus momentum is conserved :)
I am not sure if you are joking...but one should not imagine the situation like a tiny space ship inside an egg pushing against the egg shell from within.
There is nothing coming out of the EM-drive, it just creates a force, which is why it would be awesome.
I think you do have a good point. Of course it's not reactionless like the EM drive, but in practice, what's the difference? Both require a power source and both can continue providing thrust forever without running out of reaction mass as long as they have that power source. Even the EM drive, if it works, would still need an RTG or solar panels or something to power it, and that would still limit its use for interstellar travel.
The photons would be the "finite propellant". (However strained a term that is.)
Reactionless thrust is less plausible, yes, but it is strictly impossible. Not all explanations for it involved reactionless thrust. NASA indicated that pilot wave theory might be involved (where the vacuum acts as the propellant). This research is pretty conclusive: it doesn't work. That being said, just because you don't have any reasonable explanation for an effect does not mean that it does not exist.
Flight would have been considered reactionless thrust before it was understood that air had substance.
Flight would have been considered reactionless thrust before it was understood that air had substance.
> NASA indicated
Last time I looked it, this EM Drive research was not NASA project. They just gave a NASA engineer a warehouse to pursue his ideas on his own time like good research organization does.
The "Eagleworks Laboratories" or "Advanced Propulsion Physics Laboratory" is just what Harold G. White calls the warehouse. It has no website or staff from NASA.
Last time I looked it, this EM Drive research was not NASA project. They just gave a NASA engineer a warehouse to pursue his ideas on his own time like good research organization does.
The "Eagleworks Laboratories" or "Advanced Propulsion Physics Laboratory" is just what Harold G. White calls the warehouse. It has no website or staff from NASA.
Thanks for the correction, I had completely misinterpreted what Eagleworks was.
It was not "NASA" who indicated something, but a couple of guys working for NASA. Also, the "pilot wave theory" stuff is just idle speculation on topics of which the authors did not appear to understand much.
I really do not understand how people could say something like this (and also things like "GR is one of the most confirmed theories ever").
"Theoretically" 95% of the universe is made of invisible, unexplained stuff...
"Theoretically" 95% of the universe is made of invisible, unexplained stuff...
Then you do not know and/or understand the huge body of work around these theories that support them. These are hard to understand for people not familiar with physics. But especially for GR there are experimental confirmations that are absolutely spectacular (Mercury's apsidal precession computed precisely, time delation by gravity measured by placing atomic clocks on mountaintops and airplanes, etc., observed gravitational waves, gravitational lensing...). And noone was so far able to create an experiment that managed to falsify that theory (it is a perfectly falsifiable theory), but not for lack of trying.
>"And noone was so far able to create an experiment that managed to falsify that theory (it is a perfectly falsifiable theory), but not for lack of trying."
It was falsified by the aberrant rotation curves way back in the 1930s, the "dark matter" save was allowed for awhile but still no other evidence has been found for that. The only evidence is that GR predicts the wrong thing. It doesn't matter how many successes your theory has when we are talking about taking it as fact, only whether there is a single fail.
Regarding your individual examples:
>"Mercury's apsidal precession computed precisely"
- GR was designed to fit this, which is great.. but doesn't count as a confirmation.
>"time delation by gravity measured by placing atomic clocks on mountaintops and airplanes"
- Looks like they had to modify the original predictions to fit the data, ie Einstein didn't anticipate accounting for the rotation of the earth: http://www.conspiracyoflight.com/Hafele/HafeleKeating.html
So, like the case of mercury's precession it is more a post-diction.
> "observed gravitational waves"
- There still hasn't been one independently verified, they need to detect a GW, calculate the coordinates, then tell other people where to find a GRB, kilonova, etc. So far this has not happened.
>"gravitational lensing"
- This idea predates GR: https://arxiv.org/abs/1206.1165. Also, don't the quantitative predictions here rely on the dark matter fudge factor?
It was falsified by the aberrant rotation curves way back in the 1930s, the "dark matter" save was allowed for awhile but still no other evidence has been found for that. The only evidence is that GR predicts the wrong thing. It doesn't matter how many successes your theory has when we are talking about taking it as fact, only whether there is a single fail.
Regarding your individual examples:
>"Mercury's apsidal precession computed precisely"
- GR was designed to fit this, which is great.. but doesn't count as a confirmation.
>"time delation by gravity measured by placing atomic clocks on mountaintops and airplanes"
- Looks like they had to modify the original predictions to fit the data, ie Einstein didn't anticipate accounting for the rotation of the earth: http://www.conspiracyoflight.com/Hafele/HafeleKeating.html
So, like the case of mercury's precession it is more a post-diction.
> "observed gravitational waves"
- There still hasn't been one independently verified, they need to detect a GW, calculate the coordinates, then tell other people where to find a GRB, kilonova, etc. So far this has not happened.
>"gravitational lensing"
- This idea predates GR: https://arxiv.org/abs/1206.1165. Also, don't the quantitative predictions here rely on the dark matter fudge factor?
>>"Mercury's apsidal precession computed precisely"
>
>- GR was designed to fit this, which is great.. but doesn't count as a confirmation.
How can you claim this? GR is derived from first principles only. It also does not need any new physical constant to describe Mercury's apsidal precession. There are no adjustable parameters. It fits precisely even without the cosmological constant which you seem to hate with a passion.
>- This idea predates GR: https://arxiv.org/abs/1206.1165
What?! How can you possibly claim that work published in the 1930s predates GR, which was published in 1915 (Hilbert) and 1916 (Einstein himself). An incomplete version of the theory was published by Einstein in 1912.
How can you claim this? GR is derived from first principles only. It also does not need any new physical constant to describe Mercury's apsidal precession. There are no adjustable parameters. It fits precisely even without the cosmological constant which you seem to hate with a passion.
>- This idea predates GR: https://arxiv.org/abs/1206.1165
What?! How can you possibly claim that work published in the 1930s predates GR, which was published in 1915 (Hilbert) and 1916 (Einstein himself). An incomplete version of the theory was published by Einstein in 1912.
>"How can you claim this? GR is derived from first principles only. It also does not need any new physical constant to describe Mercury's apsidal precession."
You can derive many theories from first principles but they need to be checked against observation to be useful physics... explaining the orbit of mercury was one of the main checks of any theory. All theories that could not explain that better than Newton were filtered out. My point is only this does not count as a prediction, which needs to be on new data.
>"What?! How can you possibly claim that work published in the 1930s predates GR"
This is something you've made up? The source I provided quotes Henry Cavendish on this from ~1800:
"To find the bending of a ray of light which passes near the surface of any body by the attraction of that body"
You can derive many theories from first principles but they need to be checked against observation to be useful physics... explaining the orbit of mercury was one of the main checks of any theory. All theories that could not explain that better than Newton were filtered out. My point is only this does not count as a prediction, which needs to be on new data.
>"What?! How can you possibly claim that work published in the 1930s predates GR"
This is something you've made up? The source I provided quotes Henry Cavendish on this from ~1800:
"To find the bending of a ray of light which passes near the surface of any body by the attraction of that body"
Dark matter and energy are irrelevant, no matter what percentage of the "stuff" in the universe are made of them. Greater than 99% of the things you or I experience from day to day are the result of the electromagnetic force. We experience gravity pulling us down all the time, but that's like one continuous note contained within a symphony. Some of our electricity is produced by nuclear power, but that's hard to pick out from anything else. A few people have lived through a nuclear explosion, which probably had a profound emotional impact on them. Perhaps you've seen the glowing, radioactive paint that they used to use on watch-hands to make them glow in the dark (probably from behind glass in a museum, if you have). But everything else, all of the things you can detect with your senses, comes from the interactions between electrons and photons.
Dark matter doesn't interact with either electrons or photons, and neither does dark energy. So they're irrelevant; they can't be used to explain the behavior of the EMDrive, because the EMDrive is made of matter.
Dark matter doesn't interact with either electrons or photons, and neither does dark energy. So they're irrelevant; they can't be used to explain the behavior of the EMDrive, because the EMDrive is made of matter.
> Given that reactionless thrust is even less plausible on a theoretical basis than superluminal neutrinos, I really hope this doesn't come as much of a surprise to anyone.
You can achieve what looks like reactionless thrust by swimming in spacetime, according to GR:
http://science.sciencemag.org/content/299/5614/1865.full
So I think your statement is only true in the strictest sense using the words literally, but the spirit of the claim is actually false: theory actually predicts the existence of reactionless motion.
You can achieve what looks like reactionless thrust by swimming in spacetime, according to GR:
http://science.sciencemag.org/content/299/5614/1865.full
So I think your statement is only true in the strictest sense using the words literally, but the spirit of the claim is actually false: theory actually predicts the existence of reactionless motion.
Don't have full text access right now, but do they assume a source of "negative mass"?
Cached version: http://webcache.googleusercontent.com/search?q=cache:vxJs6kC...
No negative mass, translations can occur purely by mechanical deformations in a curved spacetime.
No negative mass, translations can occur purely by mechanical deformations in a curved spacetime.
Ahh. Looks like the affect is proportional to the spacetime curvature. So not particularly effective for interstellar travel. Also, you wouldn't be able to measure a thrust, because there would be none; there would only be translation. Very interesting, though.
The tldr for emdrive: having verified that changing the direction of the engine the thrust direction also changed, but when they attenuated the power to just the drive component, which should have changed the thrust, but it did not. Therefore the thrust being seen was not being produced by the drive itself.
For the piezo one the predicted thrust was below the noise threshold in their final tests (specifically below center of mass movements that were also - to my reading - due to the control electronics)
For the piezo one the predicted thrust was below the noise threshold in their final tests (specifically below center of mass movements that were also - to my reading - due to the control electronics)
Edit: Title has been changed, leaving this for posterity.
Apologies for formatting, but the title doesn’t match the conclusion of the paper.
“First measurement campaigns were carried out with both thruster models reaching thrust/thrust-to- power levels comparable to claimed values. However, we found that e.g. magnetic interaction from twisted-pair cables and amplifiers with the Earth’s magnetic field can be a significant error source for EMDrives.”
There was no experimental validation of this, just speculation based on their observations. They propose a simple fix, run the experiment in a magnetically shielded environment. They suggest Mu metal for maximum shielding, which would be good, but I’m a little skeptical that the vacuum vessels used in previous tests would have allowed a substantial flux of earths magnetic field through the environment. Using my phone's basic magnetometer, I get an order of magnitude reduction in field strength by placing it ~8" inside my oven and leaving the door open.
In any event they are probably on to something here. Certainly a more plausible explanation than any of the alternatives.
Apologies for formatting, but the title doesn’t match the conclusion of the paper.
“First measurement campaigns were carried out with both thruster models reaching thrust/thrust-to- power levels comparable to claimed values. However, we found that e.g. magnetic interaction from twisted-pair cables and amplifiers with the Earth’s magnetic field can be a significant error source for EMDrives.”
There was no experimental validation of this, just speculation based on their observations. They propose a simple fix, run the experiment in a magnetically shielded environment. They suggest Mu metal for maximum shielding, which would be good, but I’m a little skeptical that the vacuum vessels used in previous tests would have allowed a substantial flux of earths magnetic field through the environment. Using my phone's basic magnetometer, I get an order of magnitude reduction in field strength by placing it ~8" inside my oven and leaving the door open.
In any event they are probably on to something here. Certainly a more plausible explanation than any of the alternatives.
There was kind of. When they turn the EMDrive on its side the thrust doesn't come from the cone anymore it comes from an angle meaning that the angle at which the EMDrive/cone is placed has no relevance to the thrust's vector.
Imagine turning a rocket from horizontal to vertical and finding it still goes up, despite the exhaust from the engine going sideways.
Imagine turning a rocket from horizontal to vertical and finding it still goes up, despite the exhaust from the engine going sideways.
We changed the title to that of the article. Submitted title was 'EMDrive “thrust” caused by magnetic interaction from electric cables'.
Submitters: the site guidelines say "Please use the original title, unless it is misleading or linkbait. Don't editorialize." Please follow the rules when posting here.
https://news.ycombinator.com/newsguidelines.html
Submitters: the site guidelines say "Please use the original title, unless it is misleading or linkbait. Don't editorialize." Please follow the rules when posting here.
https://news.ycombinator.com/newsguidelines.html
Why do you let people choose the title? Wouldn't it be easier to grab it from the page's title tag automatically?
I'd say while this might help, titles need editing by the submitter more often than not, be that for removing some extra tags/snippets/etc from the title, simplifying/abbreviating long titles, etc. (which is usually ok if you don't editorialize)
That alas is the sort of thing that works 80% of the time and fails the other 80% of the time.
What about a feature where the title is automatically populated and the user can modify it if incorrect?
The HN bookmarklet (in the footer) does that:
https://news.ycombinator.com/bookmarklet.html
https://news.ycombinator.com/bookmarklet.html
Then half the submissions here would be “Github.com”.
Quick comment on your oven test: The your oven's shell is probably some low-grade, magnetic steel. Vacuum chambers are typically stainless, aluminum, or titanium (if you want to break the bank) so non-magnetic. Their shielding effects would be much smaller.
Very good point! I tried adding a caveat to my comment but can no longer edit. Confirmed negligible impact in aluminum pot and large stainless bowl.
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Yeah, it's odd that they make stronger claims in the middle of the paper (e.g. "This clearly indicates that the “thrust” is not coming from the EMDrive but from some
electromagnetic interaction.") than in the conclusion.
Why not just replace the magnetron with a resistor. That keeps the DC effects while removing the RF.
Nevermind, they are not using a magnetron like the original concept.
Nevermind, they are not using a magnetron like the original concept.
Oh, they did that in a previous emDrive experiment. It still produced the same thrust. They ignored it. This is par for the course with reactionless drive "research."
Yep. This is going to be the next cold fusion - the device will soon be debunked, but we will still be hearing about it from conspiracy theorists for decades.
The title is well supported by a statement in the paper (section 2.1, next to last para): "This clearly indicates that the “thrust” is not coming from the EMDrive but from some electromagnetic interaction." I think the conclusion is written in carefully understated scientific style.
The only thing they measured was that the thrust vector was decoupled from the cavity orientation and did not decrease when power to the cavity was heavily attenuated (fig 10). They therefore concluded that the forces measured are not thrust from the EmDrive. Everything else is (likely correct) speculation.
I am surprised that nobody has yet to attempt the "simple" solution for testing something like this.
The simple solution being to put it in space, turn it on, and see if it 'stays' in space.
The claimed amount of thrust is significant enough that it will either obviously succeed or fail if you actually put it in space.
The simple solution being to put it in space, turn it on, and see if it 'stays' in space.
The claimed amount of thrust is significant enough that it will either obviously succeed or fail if you actually put it in space.
That's not "simple". It's very, very, very expensive to put things in space. Trying to figure it out on the ground first makes sense for a number of reasons.
They should have asked Elon to toss it in the back of his roadster.
Damn it, that would have been a great idea. We could have gotten rid of this silly concept for good. Musk, it's time to launch another car!
Well, to be fair, Elon _did_ offer a free payload to NASA but they were too old and grumpy to accept the generous offer so Tesla nailed a car to it at the last minute instead.
Electromagnetic tethers work in space... well, in Earth orbit anyway. So do solar sails. Neither carry propellant and neither are reactionless drives, so it's not a great test.
One does not simply...
LEO has loads of stuff to interact with, and building a test article that won't drift due to, eg, materials outgassing is a specialist challenge.
The Planetary Society have will be testing their lightsail later this year and it's been years, one launch failure, one engineering demonstrator, and now an actual test bird with its companion (so it has something to measure distances against). And that's for something which has physics on its side and is adored by Sagan-era enginerds.
First demonstrate the thing in a lab. Otherwise nobody will take a launch request seriously, except maybe a non-expert bitcoin billionaire.
LEO has loads of stuff to interact with, and building a test article that won't drift due to, eg, materials outgassing is a specialist challenge.
The Planetary Society have will be testing their lightsail later this year and it's been years, one launch failure, one engineering demonstrator, and now an actual test bird with its companion (so it has something to measure distances against). And that's for something which has physics on its side and is adored by Sagan-era enginerds.
First demonstrate the thing in a lab. Otherwise nobody will take a launch request seriously, except maybe a non-expert bitcoin billionaire.
Your proposed test would not be conclusive because magnetic fields are a thing which can be pushed against.
Who cares?
That would still be an extremely useful invention.
I was thinking about this more from a practical perspective. And what matters is "does it work", and much less so "how does it work".
I guess if it based on magnetic fields, then it wouldn't be useful for long range space travel but it would still be extremely useful for planet scale space travel!
That would still be an extremely useful invention.
I was thinking about this more from a practical perspective. And what matters is "does it work", and much less so "how does it work".
I guess if it based on magnetic fields, then it wouldn't be useful for long range space travel but it would still be extremely useful for planet scale space travel!
Satellites already use Earth's magnetic field for stabilization and manoeuvring, but we do it using devices which are orders of magnitude simpler and cheaper than the "EMDrive". They also generate more thrust. On the other hand, because they work by the known and proven laws of physics, rather than hand-waving, we already know that they'll only work in orbit of a planet with a magnetic field, and not deep space (or if you prefer, we can calculate just how useless they'll be in deep space, because there is an ambient magnetic field out there, even if it is tiny).
> That would still be an extremely useful invention.
already invented, already in use, not as great as you'd hope.
https://en.wikipedia.org/wiki/Magnetorquer
> I guess if it based on magnetic fields, then it wouldn't be useful for long range space travel but it would still be extremely useful for planet scale space travel!
turns out it isn't that effective. which can be determined with a sophomore-level understanding of physics and magnetic fields.
already invented, already in use, not as great as you'd hope.
https://en.wikipedia.org/wiki/Magnetorquer
> I guess if it based on magnetic fields, then it wouldn't be useful for long range space travel but it would still be extremely useful for planet scale space travel!
turns out it isn't that effective. which can be determined with a sophomore-level understanding of physics and magnetic fields.
We can already propel things in a magnetic field. If that's all the EM drive is doing, then who cares?
We would care because the claimed forces of the EM drive are quite high (for space at least).
Explain, please? That doesn't make sense to me. What's so special about 'space' that makes you think the forces would increase there relative to here?
No, I am saying that there are observable effects of the EM drive, right now (which, might be due to experiment error).
And these observable effects are large when you compare them to OTHER forms of space travel.
IE, if you can have a propellant less method of travel in space, of the amount that the EM drive supposedly does, this is a BIG DEAL.
The effect doesn't increase in space. Instead, the "small" effect when compared to earth methods of transportation, are extremely useful in space.
And these observable effects are large when you compare them to OTHER forms of space travel.
IE, if you can have a propellant less method of travel in space, of the amount that the EM drive supposedly does, this is a BIG DEAL.
The effect doesn't increase in space. Instead, the "small" effect when compared to earth methods of transportation, are extremely useful in space.
Because space is big and there’s no friction. Your 0-60 time is not as relevant as here on earth.
0-60 in 1 hour is actually not so bad in space! That’s 10,000mph per week.
0-60 in 1 hour is actually not so bad in space! That’s 10,000mph per week.
There's no friction, but there's gravity almost everywhere you've got a magnetic field. And gravity accelerates things pretty hard.
Even from a practical perspective, how it works is infinitely, infinitely more important, because learning this is the only way we can make dramatic improvements in our ability to use it.
There goes my hunch that it was rectified DC currents in the cavity.
Since you can launch cubesats for comparatively little money these days, someone should actually launch one.
Unfortunately it would have to be a little further from Earth's magnetosphere to get a good test. Cubesats are kind of atmosphere skimmers.
Poor title. It is sad to see academic descend into click-baitness. Even the abstract does not tell you the key point of the paper. The most one gets from the abstract is:
Our results show that the magnetic interaction from not sufficiently shielded cables or thrusters are a major factor that needs to be taken into account for proper µN thrust measurements for these type of devices.
Reading the paper one can finally get to what we want to know, "Do these thrusters work?" The answer is no and/or can't tell yet.
Under the EMDrive section:
This clearly indicates that the “thrust” is not coming from the EMDrive but from some electromagnetic interaction.
Under the Mach-Effect section:
This again indicates that there must be some electromagnetic interaction or thermally induced center of mass shift that is masking any real thrust value.
Edit - I did not read the whole paper but skimmed for these descriptions of if they found any real thrust signal.
Our results show that the magnetic interaction from not sufficiently shielded cables or thrusters are a major factor that needs to be taken into account for proper µN thrust measurements for these type of devices.
Reading the paper one can finally get to what we want to know, "Do these thrusters work?" The answer is no and/or can't tell yet.
Under the EMDrive section:
This clearly indicates that the “thrust” is not coming from the EMDrive but from some electromagnetic interaction.
Under the Mach-Effect section:
This again indicates that there must be some electromagnetic interaction or thermally induced center of mass shift that is masking any real thrust value.
Edit - I did not read the whole paper but skimmed for these descriptions of if they found any real thrust signal.
I want to believe the same way I suspend disbelief when I read S.F. -Its temporally applied. Stop reading the S.F.? no time travel or FTL.
So my wishes aside, I feel like this is very tenuous, and is going to come down to "better measurement isolated an effect causing this" more then "there is now a tractable reactionless drive at scale for big things"
So my wishes aside, I feel like this is very tenuous, and is going to come down to "better measurement isolated an effect causing this" more then "there is now a tractable reactionless drive at scale for big things"
The fact that no-one has conclusively disproven this yet gives me hope.
My desperate desire for this to be real has nothing to do with that hope whatsoever.
I feel like, if this is real, it's one of those sci-fi MacGuffin technologies. Literally changes everything.
I feel like, if this is real, it's one of those sci-fi MacGuffin technologies. Literally changes everything.
I think it's reasonable to speculate that the air force is already carrying out live tests. The reason for this is that NASA went through a substantial amount of effort to trial and test the EM drive to their greatest ability, and it came out on top with everything they could throw at it. And it's just been a black out since then. That was about 1.5 years ago.
In the interim the air force has sent up the classified X-37 [1]. They've stated it's mission purpose is "risk reduction, experimentation, and operational concept development for reusable space vehicle technologies, in support of long-term developmental space objectives". That's certainly a horoscope style description, but at the same time it does seem to fit quite well for live testing of propellantless drives, even if not as a primary mission.
Furthermore, if the EM-drive did work, it would have a beyond revolutionary impact on everything and so it would not be surprising that it would end up getting classified after passing the initial slew of tests thrown at it.
[1] - https://en.wikipedia.org/wiki/Boeing_X-37
In the interim the air force has sent up the classified X-37 [1]. They've stated it's mission purpose is "risk reduction, experimentation, and operational concept development for reusable space vehicle technologies, in support of long-term developmental space objectives". That's certainly a horoscope style description, but at the same time it does seem to fit quite well for live testing of propellantless drives, even if not as a primary mission.
Furthermore, if the EM-drive did work, it would have a beyond revolutionary impact on everything and so it would not be surprising that it would end up getting classified after passing the initial slew of tests thrown at it.
[1] - https://en.wikipedia.org/wiki/Boeing_X-37
First, someone proposed a design that violates both conservation of momentum and conservation of energy, but that's cool because you know, fuck physics. Then there was a hoax and yellow journalism and in the end, several experiments failed to confirm/reproduce the effect, but that's cool because we have this awesome theory we are trying to confirm, right?
By the way, I am looking for a team of physicists that will confirm my revolutionary Tooth Fairy Drive(tm).