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.
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.
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.)
They also conserve both energy and momentum.
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.)
This is probably stupid to anybody that knows about physics, but I had to ask :)
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.
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.
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.
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.
(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?
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.
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.
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.
"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
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.
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'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.
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.
Thank you. That led me to learning about:
https://en.m.wikipedia.org/wiki/Alcubierre_drive
And:
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.
"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."
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.
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).
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.
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.
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.
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.
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.
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.
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]"
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.
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.
There seemed to be a measurable effect going on, so they tested it.
A big ask for a group of people who's best technical achievement so far is to fly a plane into a building.
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.