> 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.
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.
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.
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?
>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.
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
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.
crazy person X has found a bronze alloy that almost seems like antigravity
You're using words like "almost seems" that just don't match up to the results seen, especially considering the flawed testing methods used.
"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.
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
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.
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.
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.
But Ether Wind was disproved by Special Relativity theory, not by Quantum Theory. I see no conflict between Quantum theory and Ether theory. But, if you wish, let accept that there is Quantum Field, ...
The conflict is simple: quantum fields are conservative, which means you can't arrange mass/energy in one way, and then rearrange it another way, and end up with more energy than you started. Gravity is conservative: if you drop a ball, friction aside, it will bounce back into your hand. It can't go higher, and there's no magic you can do by arranging matter to come up with a path where it ends up with more energy than it started with (unless you steal the energy from elsewhere).
Any such effect that exists, would not be called the "Casimir effect" because it would have to obey completely different laws than the actual observed Casimir effect seems to. The Casimir effect is actually evidence against such an effect, insofar as it's perfectly explainable in terms of conservative forces.
I see no word "Ether" in your post. LIGO (which is basically Michelson–Morley experiment at much higher scale and precision) already demonstrated waves in Ether/QF(Quantum Field)/PV(Physical Vacuum)/Space caused by merges of black holes, so I see no point to play this word game anymore.
I'm unsure about why you think that laws of conservation will not hold for Ether, AKA Quantum Field, AKA physical vacuum. If we will be able to get energy from QF, QF will lost that energy and will cool down, so Casimir effect will be smaller until it will vanish. However, there is no shortage of PV in space, and Sun is pretty good at heating it.
However, because of wave-particle duality, and because waves are propagating without moving, and because waves are propagating at speed of light, Casimir effect may be unaffected by rotation even when exposed to raw vacuum for speed less than 50% of speed of light.
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.
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."
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.
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.
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:
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.
> 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:
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.
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).
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.
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.)
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.
> 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.)
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!":
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.
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 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 :)
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.
>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. ;)
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:
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 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.
