China Claims Tests of 'Reactionless' EM Drive Were Successful (popsci.com) 470
An anonymous reader quotes a report from Popular Science: The "reactionless" Electromagnetic Drive, or EmDrive for short, is an engine propelled solely by electromagnetic radiation confined in a microwave cavity. Such an engine would violate the law of conservation of momentum by generating mechanical action without exchanging matter. But since 2010, both the United States and China have been pouring serious resources into these seemingly impossible engines. And now China claims its made a key breakthrough. Dr. Chen Yue, Director of Commercial Satellite Technology for the China Academy of Space Technology (CAST) announced on December 10, 2016 that not only has China successfully tested EmDrives technology in its laboratories, but that a proof-of-concept is currently undergoing zero-g testing in orbit (according to the International Business Times, this test is taking place on the Tiangong 2 space station). If China is able to install EmDrives on its satellites for orbital maneuvering and altitude control, they would become cheaper and longer lasting. Li Feng, lead CAST designer for commercial satellites, states that the current EmDrive has only a thrust of single digit millinewtons, for orbital adjustment; a medium sized satellite needs 0.1-1 Newtons. A functional EmDrive would also open up new possibilities for long range Chinese interplanetary probes beyond the Asteroid belt, as well freeing up the mass taken up by fuel in manned spacecraft for other supplies and equipment to build lunar and Martian bases. On the military side of things, EmDrives could also be used to create stealthier, longer lasting Chinese surveillance satellites.
I have an idea (Score:3)
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So you flip the switch and it goes that way but we have no idea why. I say strap it to a spaceship. That's good enough for me.
Not good enough for the spaceship, though. Adding a substantial amount of mass to gain a couple of millinewtons of trust isn't too helpful.
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Re:I have an idea (Score:5, Insightful)
Not good enough for the spaceship, though. Adding a substantial amount of mass to gain a couple of millinewtons of trust isn't too helpful.
Those millinewtons can be applied over a very long time though, allowing significant speeds to be achieved. Moreover, missions to far-away objects would no longer have their lifetimes limited by running out of fuel.
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'missions to far-away objects would no longer have their lifetimes limited by running out of fuel.' - well - ...
At the NASA EMdrive recent published thrust, there are no plausible long-distance missions it could be better at than a conventional ion engine.
This is simply because the power generated per kilo of solar panels is small.
This sets an acceleration limit, because you need power to accelerate, which means you're swapping several years of fuel for a ion engine for heavier solar panels, and it's not a
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The power density of RTGs is worse than solar.
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The main issue, and the one this solves, isn't running out of fuel, it's running out of reaction mass.
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You mean they won't worry about running out of reaction mass to eject when they need to accelerate/decelerate. They still need fuel to create the EM field.
No, you only need electricity to create the EM field, and you can generate that from sunlight. No need for fuel.
Re:I have an idea (Score:4, Interesting)
Trouble is that's super expensive. There are two choices here:
1. The EM drive works, which means there is a substantial gap in the laws of physics which have already passed very many far, far more stringent tests than the one in this article, implying thousands of other unrelated experiments were flawed in a consistent way.
2. The EM drive doesn't work and there was a flaw in this and a rather tricky experiment.
If you're about to blow a spaceship's worth of cash on something, you might first want to consider how tricky the experiment is. Putting in a kilowatt (think domestic microwave) and measuring a milinewton (a grain of rice?) is hard. Think of all the confounding factors. Now consider none of the other tests have stood up to peer review yet.
Which do you think is more likely now, 1 or 2?
And would that influence your decision to blow a few tens of millions on it?
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What, no third option between the other two of 'oh yes there is an effect but we overlooked something so that it does conserve momentum'?
It's hard to know whether your math model with all of its simplifications really fits the reality.
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like what? I could hypothesize that it's actually a unicorn attractor and when it's switched on, any nearby invisible unicorns will come and give it a judge in the right direction.
Thing is, for it to conserve momentum, there's needs to be reaction mass of some sort.
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So you'll sooner consider the hypothesis that conservation of momentum is broken than consider the hypothesis that there's radiation leaking in a place they haven't looked yet. No wonder you believe in unicorns.
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So you'll sooner consider the hypothesis that conservation of momentum is broken than consider the hypothesis that there's radiation leaking in a place they haven't looked yet.
Physics, it works, bitches.
https://xkcd.com/54/ [xkcd.com]
You know we can calculate the maximum possible thrust from leaked radiation and it's 3uN/kW, vastly smaller than the amount reported. Therefore it isn't that.
No wonder you believe in unicorns. :blink:
Ya know, sure why not. If you can believe we'll fly around the solar system on a perprt
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Photons have momentum but no mass.
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Photons have momentum but no mass.
They have no rest mass.
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If you're about to blow a spaceship's worth of cash on something, you might first want to consider how tricky the experiment is.
Let's launch it on one of Japan's new "scientific" solid rocket boosters, that should help keep costs down :)
Plenty of room for thermal effects (Score:2, Interesting)
I followed one of the links, and got a picture claiming to be a 'test' at Eagleworks, and the words 'in air' (without saying exactly what is in air).
Look, the heat sink for the power amp is mechanically linked to the large end of the cavity... Doesn't it seem to anyone with even a tiny bit of experience with simple air convection from a bigass heat sink that this is the exact configuration you'd most expect to exhibit such effects, and of the reported size too?
Eagleworks are apparently smart people... what
BULLSHIT (Score:3, Informative)
Re:BULLSHIT (Score:5, Informative)
I found another reference in English at http://spaceflight101.com/shijian-17-rendezvous-with-chinasat-5a/ [spaceflight101.com]: "and debuting a Hall-Effect Thruster system for use on future Chinese GEO satellites"
Digging into this via Google Translate does provide far more information. The information your claiming doesn't exist actually DOES exist, on the stdaily.com article. It's just all in Chinese, so you have to put some effort in to translate it. My link is at translate.google.com [google.com] and https://translate.googleusercontent.com/translate_c?depth=1&hl=en&rurl=translate.google.com&sl=auto&tl=en&u=http://digitalpaper.stdaily.com/http_www.kjrb.com/kjrb/html/2016-12/11/content_357005.htm%3Fdiv%3D-1&usg=ALkJrhhkYPDNKL_9BxSu6OAkt5KIHsse9Q [googleusercontent.com] but I don't know if this link will work for anyone else.
Using Google page translation:
Chen Yue said: "We use the classic electromagnetics and electrodynamics to design several different shapes of thrusters, theoretical analysis can generate thrust thrust, and through the test of the thrust, the results in line with theoretical analysis. Science and Technology Daily Beijing December 10 " Roger Xiaoe in an interview was also asked this "eternal" problem, he made it clear that the EM engine does not violate Newton's law of mechanics: "EM engine in a direction to generate propulsion, if circumstances permit, will In another direction, the momentum of the whole process is conserved. "This explanation is considered ambiguous.
"We have successfully developed several specifications of several prototype principle, the establishment of experimental verification platform to complete the milli-level micro thrust measurement test, through several years of repeated tests and the corresponding interference factor investigation test, confirm that the type of thruster Thrust exists. "Chen Yue introduced that they have completed the test device can be used for flight test development, is in orbit verification.
"This technology is currently in the latter stages of the proof-of-principle phase, with the goal of making the technology available in satellite engineering as quickly as possible," said Li Feng, chief architect of the China National Space Technology Institute's communications satellite division. , The principle prototype volume, thrust is small, require special engineering methods, optimize the cavity design, improve the cavity quality factor, reduce the loss, the microwave energy is more effective for generating thrust. At present, the thrust is measured to micro-cow level to millennial level, at least to improve the level of 100 cents or even cattle-level satellite can be used for attitude control, orbit and so on.
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I know ethan is not loved here anymore, but: https://medium.com/starts-with... [medium.com]
Re:so is there a good theory? (Score:4, Informative)
Because his musings are now generally only available on Forbes which is not accessible if you run ad blocking software. The link above is on another site though.
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why is he not loved here anymore?
He's too dorky even for Slashdotters.
Back before I quit clicking him, he did sometimes post some good analyses.
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It's an obvious idea, and one that I thought of independently only to quickly find that I wasn't the first one to think of it.
I hate it when I think of something "brilliant" and google tells me it's already out there.
Can't think of many examples off the top of my head, but a couple of good ones are:
o dark matter is just gravity leaking in from a parallel brane.
o the name Donna Matrix
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A non-programmer friend of mine came to me all wound up about an idea he had for a mobile app. We went through all the gyrations of writing up a simple agreement and signing it, so he could tell me the idea without me being able to shut him out. The idea was for a mobile passport app to facilitate checking in at Customs in the airport. I went to the app store and found one in about 30 seconds.
He was disappointed.
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Re:so is there a good theory? (Score:5, Informative)
Because there is a lot more to cosmology than gravity and movement. There are several theories to explain the movement of the galaxies - some of which do essentially come down to gravity behaving differently in some situations (like over very long distances).
So when you have more than one explanation for an observation - how do you choose one ? Well you do some more maths - and figure out what ELSE would be observable if the theories are true - and then see if any of those things can be observed. All of the theories make a number of these "predictions" and they all turn out false.
Dark Matter's predictions have all turned out to be true. Predictions way beyond the speed at which galaxies rotate. The presence of that mass, and where it is concentrated, would affect other things - and those things we can look for, and we've found them. And gravity bends light, so if there's a huge clump of unobservable matter somewhere, it would bend light -and we should be able to see that the light was bent (we've known how to observe graviational lensing since Einstein's days). Again we can see distinct patterns of graviational lensing that fit the predictions of dark matter theory and goes against what is predicted by every competing theory.
Now it's possible that along the way we'll come up with a different theory that explains observations better - but some of the smartest people in the world are trying and of all the ideas they've had none has matched the observations better, none have made predictions that better fit the other things we can observe. Right now, dark matter is by far the single strongest theory we have for explaining the way galaxies move - and the only one where the other things you can predict would be true is ALSO being observed. It's an extremely strong theory backed up by a lot of solid observations.
There are also active experiments to try and find a way to detect dark matter - partly this is made difficult since we're not sure what to look for, some people think it's made of very large, heavy particles and others that it is made up of tiny particles (but lots more of them) called "Axions". The idea that the EM drive may be using dark matter for fuel is based on the Axion idea.
But since we don't know - and have no real way of theoretically saying one is more likely than the other - we are looking for both. Doing all sorts of complex experiments to try and create conditions where - if dark matter is present we can force it to interact with something else and reveal itself. We haven't succeeded yet, but considering how difficult it is to look - we aren't giving up yet either.
Re:so is there a good theory? (Score:5, Informative)
I haven't googled it, but I've always wondered why physicists are so certain that dark matter is a thing
Dark matter is a placeholder. It isn't necessarily dark, nor matter, or even a thing. Its more of "We're not certain exactly why some aspect of the universe isn't what we think it should be.
So you could declare everything wrong, and go back to the caves, or put in a placeholder so you can do further research and eventually figure out what the placeholder "dark matter" is.
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If you'd googled it, you would have seen galactic rotation curves, which are rather neatly explained by hypothesising invisible matter in a large spherical halo around the galaxy. You'd also probably have chanced across the bullet cluster. [wikipedia.org]
The changing g you mentioned is known as Modified Newtownian Dynamics (MOND). At present it is largely discredited, but who knows, maybe it'll make a big comeback one day.
DM is a bit like climate change on Slashdot. Lots of people get really angry about it. Honestly not
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I think the bottom line is nobody still knows how it works, which is both fascinating and scary at the same time. If it works how some scientists think it works, that would indeed rewrite the laws of physics as we know them -- and this is scary. But since early indications show it working it is extremely fascinating since it opens up so many new possibilities. It also gives new material for science fiction writers to work on.
I would like to see them be able to scale this up and boost its performance, and of
Re:so is there a good theory? (Score:5, Insightful)
If it works how some scientists think it works, that would indeed rewrite the laws of physics as we know them -- and this is scary
Why is it scary? The physical models we have now are good enough for all of the machines that we've built (indeed, many of them are fine with models a few centuries old). Stuff isn't going to break as a result of this, but stuff that we'd previously thought was impossible now might turn out not to be and physicists have a lot more work to do to create models that explain them. That's a pretty exciting, but not very scary.
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I would say that perpetual motion machines are kind of scary.
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But it isn't a perpetual motion machine it still requires input energy. Turn off the electricity and the drive shuts down. What it does do is converts electro magnetic field to thrust more directly than previous versions
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It's a perpetual motion machine.
If you have an engine that produces one newton per 10W of input power, then move it 20 meters a second, you can extract 20W from this.
At 200m/s, 200W. Leaving 10 (or 190W) of free energy output after you subtract the first.
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Ezcept that this does a tiny fraction of that. At the trust levels involved quantum effects will be involved
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Unless the thrust is 1/c newtons per watt - then the same problem arises - the exploitation simply gets harder.
Some of the earlier Chinese tests reported thrusts in the exploitable range - 1N/2000W comes to mind.
I cannot find the thrust per watt of this latest claimed chinese verification.
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How exactly do you intend to use the thrust to produce energy ?
The thing almost certainly only works if that thrust is used to move it - if you try and capture any of it to drive a turbine, the space-craft will stand still.
Not quantum (Score:3)
At the trust levels involved quantum effects will be involved
Not really. I have a colleague who pulls molecules apart with lasers using pico-newton forces. Milli-newton forces are a billion times larger so quantum effects are not likely to be significant. Even then quantum mechanics is symmetric under translations in time which is the symmetry which gives you conservation of energy.
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I don't know much about Physics but I did some quick math on the NASA results and we are talking about 5 micronewtons per watt, not 0.1 newtons per watt.
If this affects your conclusion about perpetual motion, or not, is something I am not knowledgeable enough to judge. But I would love to learn more from you!
Re:so is there a good theory? (Score:5, Insightful)
It doesn't, it just changes the numbers at which breakeven occurs to ones not easy to achieve on earth.
Unless you get to 1N/300000000W (in which case it is a well understood photon drive)
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It doesn't, it just changes the numbers at which breakeven occurs to ones not easy to achieve on earth.
Unless you get to 1N/300000000W (in which case it is a well understood photon drive)
Yes, the claimed EM drive thrusts are much larger than a photon rocket would produce for the consumed power.
Re:so is there a good theory? (Score:4, Insightful)
The grandparent used mixed power and energy units but I think the problem is easier to grasp with work and energy:
If the reactionless drive is assumed to produce trust based on the power input only, the force produced F is some constant efficiency constant, C, times the power. Let's say C=0.000005 and F=0.000005 P.
Assume we run this engine for a time period of t. Then the total energy E spent is P.t.
The work done by the engine is force it produces F times displacement s. Note that there are no time units in the calculation. W=F.s , the same amount of work is done with a given F and s, regardless of how much time displacement s takes.
You can convert work into energy and vice versa, so if you get more work than the energy you put in, you have a perpetual motion machine. That is if Net Work=F.s-P.t is greater than 0.
The problem is the energy we put in to system directly depends on time, while the work we extract from it does not. As the engine goes faster P.t drops proportionally, while F.s stays constant. The required speed for Net Work being positive is v=P/F, that is v=(P.C)/P and that is v=1/C. With the efficiency figure you have given the breakeven speed is 200000m/s. That is a a high but physically possible speed. The efficiency could have been a thousand times less, and it would still be possible to make a perpetual motion machine.
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It's a perpetual motion machine.
If you have an engine that produces one newton per 10W of input power, then move it 20 meters a second, you can extract 20W from this.
At 200m/s, 200W. Leaving 10 (or 190W) of free energy output after you subtract the first.
Agreed. Let's make this a little more rigorous.
Suppose that the device has a mass of X kg and produces A Newtons per Watt of power, with a power of 1 Watt. Turn it on. It is consuming 1 Joule / sec and producing A Newtons, so the device is (in free space) accelerated at A/X m/sec^2 and (after N seconds) is moving at NA/X m/sec, giving it a kinetic energy (1/2 mv^2) of (X/2) * (NA/X)**2 = N^2 A^2 / 2X Joules for an expenditure of N Joules.
When N^2 A^2 / 2X is >= N you break even (ignoring losses), i.e.
Re:so is there a good theory? (Score:4, Interesting)
Of course, that requires assuming a great deal about the actual performance characteristics of the device. At present we only have evidence that it generates a particular thrust when basically at rest with respect to local inertial reference frames, though the exact details of its orbital behavior may shed more light on that. If it's reacting against virtual particles, dark matter, space-time curvature, aether, or any number of other things that might have specific localized properties, then it's thrust/watt ratio might well diminish with speed to remain under the "perpetual energy" exploitable limit.
And there's also the (arguably less plausible) possibility that it's actually tapping into some outside source of energy that we simply do not yet recognize. As one example, the quantum vacuum potentially contains truly astounding energy density, and while it's generally accepted that the energy could not be directly tapped, it's far from proven. This device might conceivably in some sense be erecting a directional electromagnetic "sail" into a normally unperceived energy source, with the kinetic energy gains coming not from the energy required to maintain the sail, but from the interaction of that sail with whatever energetic medium it's in contact with.
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If that is true, then it may be essentially useless as a space drive, depending on the proportionality.
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Just because perpetual motion can't exist, doesn't mean there can't be, and aren't, things that come so close as makes no difference to humans.
You're standing on one right now.
Sure the earth can't spin forever. But it will be spinning long after we're extinct. It's a perpetual motion machine for all practical concerns.
The universe is literally filled with those.
And we can and have built machines to harness some of the energy from those things movements.
A tidal-wave power-generator is actually pretty close t
Re:so is there a good theory? (Score:4, Insightful)
I can see it now...Greens protesting about tidal power generation because it will slow down the moon and cause it to crash into the earth.
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Except the stored energy in an EM drive is negligible, and we have to put it there. If it can act as a perpetual motion machine, then it can almost certainly be optimized a little further and made into a free energy device.
But that's a big if. At present all we've seen is that is seems to generate thrust when standing still - it's quite possible that the thrust/power ratio will fall off with speed in any number of ways that could prevent it from ever coming close to driving a perpetual motion machine. In
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If it works how some scientists think it works, that would indeed rewrite the laws of physics as we know them -- and this is scary
Why is it scary? The physical models we have now are good enough for all of the machines that we've built (indeed, many of them are fine with models a few centuries old). Stuff isn't going to break as a result of this, but stuff that we'd previously thought was impossible now might turn out not to be and physicists have a lot more work to do to create models that explain them. That's a pretty exciting, but not very scary.
"Rewriting the laws of physics" is one of those buzzphrases that is used in schlock journalism, Ancient Aliens type shows and some religious folks with an oddball agenda to grind.
Rewriting the laws of physics is roughly as accurate as the same people calling a huge shift in something as a quantum leap, when in fact a quantum "leap" is incredibly small.
Should be interesting when we figure out what the placeholders are, though.
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>when in fact a quantum "leap" is incredibly small.
Except, it's not. A quantum leap is the smallest leap possible, but that says nothing about the actual size of the leap. If we're talking about an electron leaping from one orbital energy level to another, then yes, that's incredibly tiny, at least from our perspective (though the difference in orbital diameter is quite large relative to the size of the electron doing the leaping).
If we're talking instead about technological shifts, then the smallest
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No, but you can characterize its behavior and reasonably extrapolate that nothing is going to suddenly change without warning. It's a guess, but a reasonable one. We used fire for possibly millions of years without any real understanding of the mechanisms behind it. Heck, there's an awful lot of widely used pharmaceuticals whose exact method of operation isn't understood (birth control for example)
If we send EmDrive powered probes around the solar system (the likely first use, regardless) and don't encou
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The one thing that bothers me with this drive is that it requires a somewhat large amount of energy to work, ... plus they add a lot of weight to the probes, which would nullify the EM drive's point to some extent.
I don't see the connection to those points from TFS. This drive seems plenty interesting, but from a power to weight ratio, it sucks. Loads of energy in, and micronewtons of thrust out? It's still very interesting, but I don't see how this looks viable for small satellites. Hopefully I'm overlooking something obvious.
Re: so is there a good theory? (Score:2)
Well, a little thrust over a whole lot of time is still a lot of velocity. No, this won't be good for quick maneuvers, but if you pair it with a near constant energy supply (solar + battery / nuclear) you can fire this thing for a month and it will be going very far, very fast.
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You mean power-to-thrust ratio? Weight doesn't really seem to be a major issue with these drives, and could theoretically be lowered dramatically (say a microwave-reflective inner surface supported by an aero-gel frame)
The key is that power is an almost unlimited resource in space, while reaction mass is decidedly not, and comes with some horribly crippling nonlinearities in any event (achievable delta-v increases far slower than the amount of reaction mass you're carrying, since you're simultaneously incre
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I would like to see them be able to scale this up and boost its performance
oh sure.
its all fun and games, until imps and pinkies and cyberdemons overrun your research facility.
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I suspect that hauling around the means to generate electricity from a nuclear source is a LOT less mass to deal with than huge tanks of chemical propellant.
Re: so is there a good theory? (Score:2)
Just because we have an imperfect model of the physical universe doesn't mean that our understanding of things already mastered gets reset. This is how science is supposed to work. Come up with a theory, attempt to disprove; or confirm.
Re:so is there a good theory? (Score:5, Insightful)
Actually we do, for reasons that have nothing whatsoever to do with the EMdrive. For one: General relativity and quantum mechanics are fundamentally incompatible - something about requiring different vacuum energy levels if I recall correctly. Which implies that there's a flaw in one or both of those theories. And there are other such situations as well. And then there's the various observational anomalies that we can't yet explain, which strongly suggest that either something in our current theories is wrong, or that there are other forces at work that we haven't yet discovered.
All of which is perfectly normal - such incompatibilities and unexplained anomalies are the guideposts that we use to probe deeper into the rules governing the universe, and improve our theories so that they better reflect reality. If the EmDrive does indeed work, which is looking increasingly likely, then it's simply one more unexplained anomaly. It's noteworthy only because (A) at first glance it seems to violate conservation of momentum, something that has gone basically unchallenged since Newton first formulated it, and (B) it has clear immediate applications.
And perhaps also because, given (B), we may for a time find ourselves in the situation of building and optimizing increasingly powerful and expensive engines without having any solid theory of the physics that governs their operation. Which has been extremely rare in recent centuries, though you could argue that much of modern pharmacology falls in that category. For example, we have only vague and overlapping theories as to how, exactly, hormonal birth control prevents pregnancy, and much the same can be said of many other medications - proving that they do work is far simpler than understanding exactly how they're interacting with the body's incredibly complex bio-chemical systems to achieve their results. On a more "technological" front gunpowder is the most recent example that springs to mind - it was used and optimized for centuries before chemistry even existed as a formal field of study, to say nothing of having a reasonably solid theoretical basis.
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Applicability depends on which results you looks at - there's a lot of individual EM devices out there, no two identical, and some are claiming results several orders of magnitude larger than others. Maybe that's just sloppy experiments, maybe it's because they accidentally hit upon a large optimization for a poorly understood phenomenon. If/when we achieve consensus that the things actually work at all, I'm confident that optimizations will begin accumulating quite rapidly.
Besides which, we're already ex
Re: so is there a good theory? (Score:5, Insightful)
A few reference points:
The big reason the EM Drive is attracting any interest at all is that it seems to be generating thrust per watt ratios at least an order of magnitude greater than theoretically possible with a photon rocket (i.e. shining a laser/flashlight/microwave/radio source out the back end), so there's no accepted theoretical basis for the thrust it's generating, unless maybe it's actually vaporizing itself and leaking pressurized metal gas out the back end
It would also seem to break conservation of momentum, which has gone basically unchallenged since Newton first formulated the laws of motion and kick-started physics as a mathematical science. If the engine thrust imparts momentum in one direction, then something else needs to gain an equal amount of momentum in the opposite direction (e.g. the exhaust from a rocket), and within our current understanding, that doesn't seem to be happening.
Finally, conservation of energy (Ein=Eout + heat) could also be broken by a reactionless thruster as it's heavily dependent on speed. If the EmDrive generates a constant thrust for a constant energy input as it accelerates (completely untested), then its kinetic energy will increase at a steadily increasing rate, since energy increases with the square of velocity. At some point the incremental increase in kinetic energy will be larger than the incremental consumption of electrical energy, at which point you could theoretically attach it to the rim of a wheel turning a generator to produce more energy than you're consuming. (normal rockets don't face this issue since the exhaust is being slowed down while the rocket accelerates, so the total kinetic energy change remains constant.)
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It seems that every test of EM drives by credible scientific organizations so far has been successful.
I'm pretty sure that's not correct. Last time I read up on it there were reports that it worked, reports that it didn't, reports that it "worked" but didn't always thrust in the same direction, and one peer-reviewed paper reporting that it worked had to be retracted after the authors discovered errors in their analysis.
I hope it does work, and that it turns the laws of physics on their collective head. But it really sounds like they're just measuring noise.
Don't forget the report of FTL data transmission
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It hasn't been successful at all. The only tests seem to describe micronewtons of force in exchange for ~100Wh of energy consumed, a far cry from the flying car engine it's creators promised. The micronewtons aren't enough to go up against earth or sun gravity so useless to propel anything anywhere and the energy source would have to be massive.
Most of those test seem to be also both in the range of error and the results have very low confidence by the researchers themselves, if there were anything useful,
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It seems that every test of EM drives by credible scientific organizations so far has been successful. Is there some theory now to explain how and why they work?
IMHO, no.
There are plenty of theories, but not one of them would stand up to five minutes of review by a proper theorist. When JASON reviewed Sonny White's work, they were (to be euphemistic) not kind about the theories presented.
Note, by the way, that testing in orbit is not the same as confirmation in orbit, which if you read carefully they are not claiming.
If you want to read about this closer to the source in Chinese, here you go [stdaily.com].
Re: so is there a good theory? (Score:2, Insightful)
Building something better generally requires both some experimentation and some theory. Even if you don't know why it works, reality demands you know basically how it works.
Ironically QM is the "classic" example of this. We don't know why superconductors work, but as we created better working theories on how it worked, we were able to discover better materials
Re:so is there a good theory? (Score:5, Insightful)
A major, major problem with the reports is that the results vary so much, and their error bars do not overlap.
If someone says "we have conclusively measured the height of Madonna, and she's 1.8m high +-0.1m" - that is one thing. If further investigation says "1.85+-.1" - then that's great, and is a confirmation.
If the next person to measure her comes out with 47m+-10m - then they have not meaningfully replicated the measurement, and disparity of measurements by various groups is a hallmark of something being wrong.
This, combined with the fact that some people don't get it to work at all leads to it being plausible that in fact nothing is happening.
The thrusts reported don't overlap.
Re:so is there a good theory? (Score:4, Interesting)
He claims (and I certainly haven't bothered to verify this) that if you look at the various papers reporting experimental tests and take into account their reported Q values then they all match his equation to within experimental error. So, he claims that the reported thrusts do 'overlap' if you allow for the different Qs being achieved.
Re: Propellantless doesn't mean reactionless (Score:5, Funny)
>Reactionless
Certainly not reactionary. If it was, research chief would've been standing in from of firing squad by now
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Read second sentence of article - "Such an engine would violate the law of conservation of momentum ..." The author is referring to Newton's laws of motion (action and reaction).
No one doing the research is claiming such a violation. The journo is just making stuff up.
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Agreed, but to be fair it would signify a problem with the bookkeeping of the electromagnetic radiation. Now I realize this bookkeeping can at times be quite tricky but since this should be a case that can be handled fully with classical electromagnetism, it would be extraordinary if proven.
That's also why I don't believe it...
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An instance of how the bookkeeping can quickly become problematic: when an observer on earth surface sees a falling charge, does the observer see radiation? What does that say about conservation of momentum and energy? Since the observer sees an accelerating charge, is there reaction radiation slowing down the charge? ( https://arxiv.org/pdf/gr-qc/00... [arxiv.org] )
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No, the journo isn's "making stuff up". Such an engine would violate CoM (and CoE too if you set it up right) because there's no reaction mass. If there is reaction mass then all they invented is a very inefficient thruster of which we already have vastly better version and, er, not to put too finer point on it, you could point to the mass and say "ooh there it is".
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And what is the reaction mass for the pressure of light on a surface?
(In space we deal with this all the time, as a perturbation in general)
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And what is the reaction mass for the pressure of light on a surface?
If you asked google, you'd have got the answer. It's much lower. It's 3uN per kW for a photon drive. It's a bit less straightforward for reflections since relative speed introduces doppler shifts which change the momentum.
Re:Propellantless doesn't mean reactionless (Score:5, Insightful)
Photons have no mass but they do have momentum. You could, in theory, make an engine by pointing a torch in the opposite direction to the way you want to go and turning it on. Such an engine would have no reaction mass but would not violate the law of conservation of momentum.
There are three possibilities as I see it:
1. The device doesn't work
2. Something with momentum is being ejected but we just haven't found out what yet
3. The law of conservation of momentum is wrong.
Of the three, I would happily bet my house that it is not the third one.
Re:Propellantless doesn't mean reactionless (Score:4, Interesting)
And why would the 'torch engine' not become an over-unity device?
I'm glad you asked! And it turns out you can't entirely ignore relativity.
So, as you correctly pointed out, the thrust is constant, so the (non relativistic) speed increases linearly, but the energy goes quadratically.
Since the power in is constant, eventually the power due to the increasing k.e. must exceed the power in. The smaller the thrust, the higher the speed at which the cross over occurs, but crossover must occur.
Well, yes, except there's a speed limit: the speed of light. It turns out that if you crunch the maths right then for the tiny thrust from the photon drive (3uN/kW), the breakeven speed is the speed of light.
You can never reach that so you can never reach the breakeven point and you certainly can't exceed it.
For anything (the EM drive) claiming a higher thrust per unit of power, the breakeven point is below c, so you could theoretically exceed it, yielding free energy.
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There's no mass being expelled in laser propulsion either.
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But there is momentum exchanged. Photons carry momentum, even if they don't have mass. This drive, if it works as described, violates conservation of momentum.
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No-one really uses the concept of relativistic mass any more. Things just have invariant (rest) mass.
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Or maybe Newton's 3rd law isn't true in some circumstances. Now that would be exciting.
We already know it isn't always true. The Lorentz Force [wikipedia.org] happily violates Newton III. And so does quantum mechanics.
Re:Hilarious (Score:4, Informative)
We already know it isn't always true. The Lorentz Force happily violates Newton III. And so does quantum mechanics.
Yeah, no. Also, well done for providing a link to an article which doesn't remotely back up your claims.
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Well, yes, it does
Well, no it doesn't. The page makes no mention of your claims at all.
The circular field increase/decrease is what you get instead of an opposite and immediate force.
So in other words, if you incorrectly ignore a major component (the energy and momentum of the field) then you can show absurdities like violation of Newton's third law.
Re: Hilarious (Score:2)
How about the Casimir effect? Which of Newton's laws explains that?
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It'd be hilarious if this turns out to be pushing against some aspect of the normally intangible fabric of space-time, after physicists so thoroughly debunked luminiferous ether.
Well, I think the luminiferous ether perhaps didn't go away as much as it was reinterpreted in a form that was much easier to model and eventually became the space-time of GR. The ether was in many ways a sound enough idea - a kind of field of substance in which light propagated and which was sort of pulled along with things that moved. In many ways it was just one more field amongst the many we have been piling on since then to describe things we don't understand all that well.
Or maybe Newton's 3rd law isn't true in some circumstances. Now that would be exciting.
Quite so - possibly a bit too
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The possibility that it is neutrinos (Nobody ever takes the suggestion of pointing the damn thing at the neutrino detector in Japan and asking if they get a measurable increase in neutrino flux seriously, and everyone just summarily rules them out as "totally not the thing we are looking for" for this device) has some merit, (despite the above.)
See section 2 of this paper for instance, on converting neutrino flavor, using a high Q resonant cavity with strong RF signal (sound familiar?) . The paper has a dif
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If I swing back and forth on an office chair I too can move without expelling reactionary mass.
No net change in momentum means no need to expel reactionary mass from your local space. Plus, your reactionary mass for the state changes in chair motion you describe are the ground and parts of the chair you are pushing against to move. Even if you are merely rocking, shifting your body back and forth, you're pushing your body against the seat of your chair (and they are the reaction mass for each other's motion).
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Well, they debunked the luminiferous ether, but there are other aether theories out there. A 'popular' one is the Superfluid vacuum theory.
https://en.wikipedia.org/wiki/... [wikipedia.org]
Also, Erik Verlinde talks about 'elastic back pressure' in his recent paper https://arxiv.org/pdf/1611.022... [arxiv.org] concerning 'emergent gravity'.
Personally I do not think gravity is emergent, but I wonder if elasticity could be applied to space itself. That could explain observations without dark matter.
Even dark energy can be explained. In th
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It'd be hilarious if this turns out to be pushing against some aspect of the normally intangible fabric of space-time, after physicists so thoroughly debunked luminiferous ether. Or maybe Newton's 3rd law isn't true in some circumstances.
Actually the two are related, more so than you think.
The third law stems from the conservation of momentum. From Noether's theorem, conservation stems from the translation invariance of space. The latter is at odds with the translation invariance (or at least an aether tha
Re:Misleading (Score:5, Informative)
This is not an EmDrive. It's a drive of the same type as an EmDrive, resonant cavity thrusters, but EmDrive is a trade mark for one particular variant by Satellite Propulsion Research Ltd, which this isn't.
First, it's a drive, yes? And it's using electromagnetism, yes? Therefore, it's at best merely descriptive, and therefore not a protectable trademark.
Second, the ElectroMotive Designs company already has a registration on the EMDRIVE mark for converting cars and trucks to hybrids. So, Satellite Propulsion Research can go suck on the smaller end of a resonant cavity.
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No, its an OEMDrive :)
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China? Intellectual Property you say?
Well, there is that. It could have more in common with the EM Drive than we think. :)
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Re:It supposedly has no exhaust, a closed system (Score:4, Insightful)
Oh hey, random Youtuber dismissed the claims because they don't match what he learned in high school physics or something, so screw empirical testing from NASA and CAST.
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Well, he does actually do science for living, but on the other hand he's also a troll, so.. hard to say whether one should care about what he says at this point.
He doesn't work with the emdrive at all, so he has nothing useful to say about this in any case. Anything he could say could also be said by someone who isn't a troll.
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Thunderf00t's video reminded me of the original meaning of "to beg the question".
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I wouldn't call on-orbit tests of a low powered version "using it". Besides it wouldn't be the first time "the other side" picked up an ignored Western invention and took off with it. An example would be the Christie tank in WWII.
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Get yer ass out of the '60's.
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Unless you're talking takeoff from the ground, the extra mass of the cavity thrusters is meaningless. Because you're pushing in the direction of motion to reach a higher orbit (or against it, if you want a lower orbit).
The only question to be answered about "multiple EM drives" (assuming they work at all, of course) is "do we gai
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