China Claims Tests of 'Reactionless' EM Drive Were Successful (popsci.com)

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.

Comments

so is there a good theory?

[Anonymous Coward]

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?

Re:so is there a good theory?

[Anonymous Coward]

I know ethan is not loved here anymore, but: https://medium.com/starts-with...

Re:so is there a good theory?

[Anonymous Coward]

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 course explain just how exactly it works. The one thing that bothers me with this drive is that it requires a somewhat large amount of energy to work, how would we be able to produce that energy if we were to think for example of sending probes outside our solar system? Solar power won't really cut it that far away and nuclear power plants have a limited lifespan, plus they add a lot of weight to the probes, which would nullify the EM drive's point to some extent.

Re:so is there a good theory?

[Black Parrot]

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 coming out of CERN a couple of years ago.

Re:so is there a good theory?

[coastwalker]

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.

Re:so is there a good theory?

[WalksOnDirt]

Yes, the old dark matter for EM drive propulsion proposal. 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'd still rate it as unlikely, but it's a possibility to keep in mind.

Re:so is there a good theory?

[Black Parrot]

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.

Re:so is there a good theory?

[Black Parrot]

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

Re:so is there a good theory?

[TheRaven64]

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.

Re: so is there a good theory?

[Anonymous Coward]

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?

[Time_Ngler]

I would say that perpetual motion machines are kind of scary.

Re:so is there a good theory?

[peragrin]

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

Re:so is there a good theory?

[unrtst]

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?

[queazocotal]

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.

Re:so is there a good theory?

[queazocotal]

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?

[MachineShedFred]

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?

[MachineShedFred]

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.

Re:so is there a good theory?

[peragrin]

Ezcept that this does a tiny fraction of that. At the trust levels involved quantum effects will be involved

Re:so is there a good theory?

[Kiaser Zohsay]

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.

Re: so is there a good theory?

[Anonymous Coward]

I thought about a search engine and googled it. Sigh

Re:so is there a good theory?

[eggstasy]

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?

[queazocotal]

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.

Re:so is there a good theory?

[queazocotal]

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)

Re:so is there a good theory?

[dywolf]

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.

Re:so is there a good theory?

[GTRacer]

25 years ago, I thought I was so clever, inventing the "hand vacuum with long neck for getting bugs off ceiling" bug-sucker. A year or so later? Skymall. Curse you Skymall.

Re: so is there a good theory?

[king neckbeard]

Plus, I would guess that there's a good chance of substantial improvements when we actually understand how it works.

Re:so is there a good theory?

[guruevi]

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, you'd be sure as hell this would already be up to being tested in space. There were some hyped up news stories about this drive but nothing useful so far.

Re:so is there a good theory?

[queazocotal]

If that is true, then it may be essentially useless as a space drive, depending on the proportionality.

Re:so is there a good theory?

[silentcoder]

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?

[Ol Olsoc]

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.

Re:so is there a good theory?

[silentcoder]

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.

Re:so is there a good theory?

[Ritz_Just_Ritz]

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?

[Ol Olsoc]

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.

Re:so is there a good theory?

[silentcoder]

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 to a perpetual motion machine - since it generates power based on the gravitational pull of the moon. The moon is not going to run out of momentum and stop rotating around the earth in any time soon enough to matter to humans. It's as close to a perpetual motion machine as makes no difference. And we've harvested it's power - already. There's your gravity powered machine - that will run until it breaks down.

It may not be "perpetual motion" as we normally think of it, but it's as close as makes absolutely no difference. And we've just scratched the surface of what we can do when we harvest gravitational motion to power machines (partly because it's very hard - it's probably impossible to do a cyclic machine using earth gravity, but as the tidal wave generator shows - it can be done using the moon's gravity - which already varies cyclicly). Whose to say we won't find a way to have The motion of Jupiter provide the energy to get our next probe too Jupiter ?
It would be very hard and I have no idea how it could work - but there is nothing in the laws of physics that says it can't be done. It's not creating energy. It's not failing to conserve momentum. It's not lacking an existing energy source - it's just using one that is very hard to use and which we've only just started figuring out how to use (sufficiently so that I'm pretty sure the tidal wave generator is the ONLY example of a genuine gravity powered machine - but it's early days).

For all we know that's what the EM-drive is doing, it may be pushing against gravitons and propelled by "gravity" itself.

Re:so is there a good theory?

[Ol Olsoc]

I would say that perpetual motion machines are kind of scary.

That's been figured out a long time ago. Go to YouTube They have hundreds of those things.

Also how to heat your house with two tiny candles and a clay flowerpot.

Re:so is there a good theory?

[dehachel12]

> But it really sounds like they're just measuring noise.
Wouldn't it be cool that it's enough to engineer a noise-drive ?

Re:so is there a good theory?

[Maritz]

I think the bottom line is nobody still knows how it works

How is still a ways off. We have not sorted out if it works yet. The effect size is very, very, small. I can see this evaporating into fuck-all.

Re:so is there a good theory?

[Maritz]

The only scary part is that we KNOW that some part of the laws of physics are WRONG.

We don't know that.

My money is still on the EM Drive being bullshit. I'll be excited as hell if it turns out to be real, but nothing so far has convinced.

Re:so is there a good theory?

[Maritz]

They're scary in the same way that goblins are scary. Also, neither exists.

Re:so is there a good theory?

[Maritz]

I'd like a theory now to explain why this was treated as a lunatic fringe thing for a decade.

Two reasons. One, it makes an extraordinary claim (thrust without reaction mass). Second, it has not provided evidence to prove that claim.

You're acting like this is done and dusted. Not by a fucking long shot.

No one understands how gravity works, after all, but you still use it daily.

General Theory of Relativity gives a brilliant breakdown of how gravity works, despite your declaration to the contrary.

Re:so is there a good theory?

[mbone]

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.

Re:so is there a good theory?

[serviscope_minor]

You're standing on one right now.

No, the parent said perpeatual motion mechanism. There's a small but subtle difference there. With something like the Earth, it will keep rotating for a very long time, because the stored energy is vast and the rate of loss is very small. But eventually it will stop.

With a perpetual motion *mechanism* something is generating energy out of nowhere. If it is generating enough then it will be enough to overcome all the sources of dissipation (you can make those essentially negligible).

If the EM drive claims to work, one can relatively easily set up a though experiment where it goes substantially over unity.

I've no problem with a device like the drinking bird which is a very subtle mechanism for harvesting energy from the environment and punting it to a different part of the environment using very subtle means. But if the EM drive is merely a very subtle sleight of hand with existing physics, then like the drinking bird, it's got no real use except as a living room decoration and is nothing to get excited over.

For all we know that's what the EM-drive is doing, it may be pushing against gravitons and propelled by "gravity" itself.

Unfortunately, that's just technobabble. It would be fine on the Enterprise though.

Re:so is there a good theory?

[nusuth]

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.

Re:so is there a good theory?

[sycodon]

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.

Re:so is there a good theory?

[jcr]

I suspect that the measured thrust is due to some kind of interaction with the earth's magnetic field.

-jcr

Re:so is there a good theory?

[mbone]

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., when N >= 2 X / A^2. If X is 5 kg and A is ~ 5 x 10^-6 N/W (typical numbers claimed), then N needs to be ~ 4 x 10^11 seconds (12,675 years) and the device velocity will be 400 km/sec. Clearly, energy is being created and (at this relatively low velocity, 0.0013c) special relativity will not change this situation.

Whether this actually works and, if it did, whether it would be a practical means of creating energy are, of course, rather different questions.

Re:so is there a good theory?

[mbone]

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?

[silentcoder]

>No, the parent said perpeatual motion mechanism. There's a small but subtle difference there. With something like the Earth, it will keep rotating for a very long time, because the stored energy is vast and the rate of loss is very small. But eventually it will stop.

Yes, I said later in the same post. But it won't happen in any timeframe that matters. So for all matters of practicality - if you can use that to power a machine that machine has achieved the goal for which perpetual motion machines are designed -the only difference is you haven't violated conservation of energy, you're just using a very large supply.

Re:so is there a good theory?

[locofungus]

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.

You run the drive generating thrust F at power P until you reach a speed v without extracting any energy. You then extract energy such that your retarding force exactly balances the thrust provided by the drive.

The thrust provided via the drive is using constant power but the retarding force is extracting F*v watts. If F>1/c N/W (photon drive) then you can choose a velocity v such that you can extract more energy than you're putting in without the vehicle slowing down

Re:so is there a good theory?

[shaitand]

All my life brotha.

The furthest I've traveled down a road because of something was that time I invented the digital book reader, even had a custom low power linux built for it and interface made. I was inspired by my old sony clie palm counterpart and discovering what a great experience it was to read on it. I was even working on the prototype hardware when in my spare time while working at an office depot when some third party company you've never heard of (which was later purchased of course, Amazon or B&N can't remember) announced they'd developed one. I'd have beaten them by a heavy margin if I'd hadn't been trying to buy everything and live on like $300 a week even still only being able to work on it in my spare time.

Granted this more kindle fire than kindle and at the time the battery life would have been more like 6-8hrs than the 3-5 days I get with my kindle and e-ink. Had I finished it, it still probably would have taken me months more to get money together for a patent and I'd have needed to research and put together the application myself.

Re:so is there a good theory?

[Black Parrot]

I haven't googled it, but I've always wondered why physicists are so certain that dark matter is a thing and why I never read that maybe the gravitational constant isn't so constant and varies through out space. Seems like that would explain gravity abnormalities just as well without the pesky problem of "stuff we can't interact with that we just assume is there".

Positing a parameter that varies everywhere and can have whatever value it needs to explain the observations isn't likely to result in an improved understanding of anything.

Re:so is there a good theory?

[Anonymous Coward]

Sorry, but that's garbage.

All the examples you've given involve simple inertia (big spinning things keep spinning), or tapping a really tiny amount of energy out of a really huge reserve. But in every case, conventional physics lets us explain exactly what's happening, and how long it will take for the system to run down.

If the argument frequently posted by serviscope_minor and others is accurate, this "drive" becomes an over-unity device above a certain speed, producing more power than you put in. That's what people want out of "perpetual motion" -- a source of free energy. They've never gotten it, and they never will.

If you think this "drive" is tapping into some other source of power, well, we'll all be really happy if it's true, but some coherent theory would be great.

Re: so is there a good theory?

[Black Parrot]

I invented sex, but didn't patent it because I thought everyone else lived in their mom's basement too.

Re:so is there a good theory?

[stealth_finger]

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.

Doesn't stop most other app developers.

Re:so is there a good theory?

[Immerman]

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.

Re: so is there a good theory?

[saloomy]

Explanation: one of our laws was wrong or not universal. As technology improves and our experiments push against those fundamental laws, we may begin to understand the way the universe works in for fundamental and subtle ways and have a better description of those laws.

Re:so is there a good theory?

[Immerman]

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.

Re:so is there a good theory?

[jabuzz]

The argument is that you could attach a couple of them to the outside of a large wheel, they would push the wheel around and that could be used to generate electricity that would power the emdrive's.

The problem is that this all assumes that everything is lossless in the first place which clearly it is not. So as there is no known way to actually make such a device out of emdrives with known engineering they are cannot be used to create a perpetual motion machine.

The in the real world there are no spherical chickens.

Re:so is there a good theory?

[Maritz]

Let me clarify. Yes, we know some of physics has to be wrong, or at the very least incomplete.

We don't, however, know this because of the EMDrive. We don't know if the EMDrive does anything, or if we have a bunch of experimental apparatuses with anomalous thrust.

GR and Quantum Theory fundamentally disagree on many things, mainly that in GR quantities are smooth and classical, and in QM they are descrete and quantized. In most contexts the differences don't matter, but in some high-energy environments (big bang, black holes) the disagreements become huge.

I don't see an application for the EMDrive at the moment, the effect size is at least one order of magnitude too small to do anything useful with. Well within the reach of experimental noise.

Re:so is there a good theory?

[Maritz]

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.

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 sure why.

Re:so is there a good theory?

[gweihir]

What tests by credible (!) scientific organizations are you talking about? AFAIK there were none.

Re:so is there a good theory?

[xvan]

I've heard of 3 theories.
1 The law of conservation of energy is wrong.
2 Ether is real
3 There is something not being measured.

So it's obvious the scepticism of the scientific community.

Re:so is there a good theory?

[werepants]

It's not as though there is a single test article being operated on by each group though, or a single measurement technique. Each group is building their own drive, presumably with different efficiency, power, mass, etc. So if you are measuring the power output of a Honda 4-cylinder engine and a Dodge V-12, you are going to get very different number and error bars. It doesn't mean that the effect isn't there, and you wouldn't expect the error bars on the machines to overlap.

It's certainly possible that all of these experimenters are fooling themselves and EM Drive will turn out to be this generation's cold fusion, but there's no expectation at this point that differing experiments will have agreement with one another in the specific values of raw thrust, or thrust/W.

Re:so is there a good theory?

[Immerman]

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 experimenting with photonic thrust for certain applications, and the entire reason the EMdrive is attracting attention at all is because it's showing thrust/watt ratios at least an order of magnitude greater than the theoretical limits of a photon drive.

Re:so is there a good theory?

[nusuth]

Converting work and energy is not essential for the argument. If you work out the maths, you can see the same problem exists in terms of kinetic energy gain when this device is accelerating. The problem is after a certain speed you gain more energy than you put into the system. The faster it goes, the more surplus energy it generates.

Re:so is there a good theory?

[Eravnrekaree]

You don't seem to be understanding what I am saying. I do care what the truth is, the truth is the truth. I am interested in the truth, rather than science fiction. I am just saying there shoud be scientific data to back up the truth. When you test a theory about how the physical laws work, the test is valid for the context in which it was performed. But when we extrapolate the test data to contexts which we have not tested, we are making an assumption. The extrapolations can be handy in order to get something working in little time for everyday work, but at the same time it doesnt rule out that we may have undiscovered phenomena where the four forces work differently or maybe additional forces. I'm not saying we can find a way to make an anti-gravity drive, but we are far from ruling this out and it makes sense to look for it.

Re:so is there a good theory?

[fbobraga]

I love him, you insensitive clod!

Re: so is there a good theory?

[Immerman]

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.)

Re: so is there a good theory?

[WaffleMonster]

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

Except 3x that which has been claimed to have been observed with EM Drive has been demonstrated with photon rockets using mirrored surfaces.

Why does nobody bat an eye when photon rockets are shown to outperform EM drives?

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.)

All photon rockets do this... efficiency goes to plaid above the relativistic threshold. Your just not accounting for total energy properly.

Re:so is there a good theory?

[HuskyDog]

If you take the time to read Shawyer's own papers on the topic (which may of course be complete drivel) he explicitly states that his drive needs to obey conservation of energy (i.e. no perpetual motion). He then goes on to evolve equations and related explanations which suggest that the drive's thrust drops significantly with increasing acceleration and velocity (basically due to Doppler shifts inside the cavity). I seem to recall that the maximum theoretically possible values are 0.5m/s/s and 30km/s but this does rather depend on precise thruster design.

I am of course unable to say whether his explanations are true, and if the drive doesn't work at all then they are irrelevant, but the papers (mostly available from www.emdrive.com) do at least address the perpetual motion issue.

Re:so is there a good theory?

[Immerman]

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 fact I seem to recall that one of the early inventors, who claimed to achieve several orders of magnitude higher thrust/power ratio than most current experiments, also claimed that the ratio fell precipitously as soon as the drive began to accelerate. In which case it might end up being great for supporting hovercraft, but useless for acceleration or free energy devices.

Re:so is there a good theory?

[Immerman]

Other way around actually - it will slow down the rotation of the Earth while pushing the moon further away - exactly as is happening now, only at a slightly faster rate. And while I could see some particularly credulous hippies protesting on those grounds, it shouldn't be too hard to show them the numbers and point out the fact that unless we're harvesting energy at a rate to dwarf the tidal heating of the Earth, both Earth and the moon will be incinerated by the expanding sun long before it matters.

Especially effective if you immediately point out that there are far more serious and immediate things to be concerned about - such as the ecosystem damage caused by interfering with the tidal flow of water - which for many tidal generating schemes is a legitimate concern.

Re:so is there a good theory?

[HuskyDog]

I strongly recommend reading Shawyer's various papers on the drive (most can be found at www.emdrive.com). Now I will admit that I find quite a lot of their contents either incomprehensible or just plain crazy, but he does evolve some equations which relate thrust to input power, velocity (usually zero in these tests) and (vitally) the Q of the cavity.

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:so is there a good theory?

[serviscope_minor]

He then goes on to evolve equations and related explanations which suggest that the drive's thrust drops significantly with increasing acceleration and velocity

velocity relative to what?

Re:so is there a good theory?

[nusuth]

I have not read his papers. I have tried to read his basic theory but I am not a physicist and most stuff in the Shawyer's explanation is beyond me. However thrust being variable wrt. speed is also incomprehensible. What is the frame of reference for this speed and why is that frame preferred? Any external frame of reference would violate even Galileo's relativity. Since this system is at rest wrt. its parts, there is no internal speed to refer to either.

Re:so is there a good theory?

[Immerman]

>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 possible leap can be quite huge from our perspective. Take one of the earliest: the domestication of fire - the first person who discovered that you could keep a fire going indefinitely in a controlled fashion by adding more wood completely revolutionized the human condition. There probably weren't any intermediate steps to that discovery, and it immediately gave their tribe a large number of new advantages: "unlimited" heat, light, and predator deterrence (so long as someone stayed awake to tend the fire), a dramatic increase in productivity after dark, and the ready availability of fire to advance other technologies - fire-hardened spears, cooked food (+~20% accessible calories), fired ceramics, etc.,etc.,etc. A huge array of technological advances easily discovered by accident once the one "quantum leap" was made.

Re:so is there a good theory?

[rogoshen1]

I too do this, once i sent the producers of Jeopardy a bill for the answers i got right.

Re:so is there a good theory?

[Immerman]

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 increasing your inertia). The same basic reason ion drives are becoming more popular - the amount of delta-V achievable for a given amount of reaction mass is dramatically higher, provided you have a reliable power source like solar panels.

The EmDrive is especially interesting because the thrust-to-power ratios observed have consistently been at least an order of magnitude greater than those theoretically possible from photon drives (shining a radio/laser/microwave out the back), which are the only kind of "reaction massless" drives previously known. And some experiments have even observed ratios exceeding that of current ion drives, though it's admittedly far from clear that those weren't attributable to experimental error.

Pretty much the only place that absolute thrust really matters in space travel is during takeoff and landing from a planet, and in making fast fine-tuning maneuvers, such as when docking. For everything else a long slow burn is pretty much just as good. We currently mostly use powerful engines in short bursts because of those crippling reaction mass limitations - you want to get the maximum delta-v per gram of expelled mass, and for most maneuvers there's a very small window when the efficiency is notably greater than at other times (e.g. at the highest and lowest points of a Hohmann transfer orbit).

Re:so is there a good theory?

[Carewolf]

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.

True, mostly. We are actually pretty sure dark matter is both matter and dark. It is matter because it affects gravity, and it is dark because we can't observe it so it interacts very little with light, making it dark or simply transparent (which mostly is the same as dark in space). Not much else is known though.

Re:so is there a good theory?

[silentcoder]

>Except the stored energy in an EM drive is negligible, and we have to put it there.
Hundreds of kilowats to produce micronewtons of thrust is decidedly not something I would call "negligible". It needs MASSIVE amounts of energy.

>If it can act as a perpetual motion machine,
Nobody has proven that it can and you alone has suggested it, while providing no conceivable mechanism for doing so. The device as described CANNOT generate electricity, it's physically impossible. So you've gone from "this may mean there is an exception to one of the laws of physics" to insisting that it's free energy device because you seem to think it can just ignore ALL the laws of physics. I already, in my previous post, pointed out why your "wheel generator" is a fantasy and this thing cannot possibly drive one.

>then it can almost certainly be optimized a little further and made into a free energy device.
Well you still haven't given us any reason to believe it IS a perpetual motion machine. At least, not in the sense you're suggesting. In the sense that, on human timescales, the solar system is a perpetual motion machine - maybe and that's by no means guaranteed considering the huge powersource it needs. The only viable sources of that power STILL need fuel. Nuclear, the fuel is on-board. Solar - the fuel is IN the sun and it WILL stop working when that fuel runs out. All any scientists looking at this thing have suggested is that it might, possibly, be a very CHEAP energy device. Free energy ? That's something you made up - with nothing to support your claims, which are easily shown not to be possible - as a way to dismiss that possibility.

How about you let the scientists do science - test the thing, keep testing it. If it really violates the laws of physics the tests will eventually show that conclusively - and we get to answer the interesting question of *why* the previous tests seemed to show otherwise, and make better tests. Or it will keep working - and we get the fun of figuring out what is wrong in our understanding of the laws of physics and make a breakthrough.

Perhaps that breakthrough could even mean that free energy goes from proven impossible to "oh you can do it in certain conditions". I highly doubt that, it's definitely not a LIKELY scenario - but it's not impossible either. Human knowledge is not absolute - and when it comes to physics, there is no way to know what we don't know.

Re:so is there a good theory?

[HuskyDog]

Honestly, I am making most of this reply up as I go along, since I am not a relativity physicist (or indeed any sort of physicist at all) and Shawyer's entire alleged explanation relies on relativity. Having said that, one can determine one's local velocity without a need for an external reference.

Supposing that you placed the device in empty space. We could call its current speed zero. Clearly it is not zero relative to all the other objects in the universe, some of which are approaching and some of which are receding. If we mount a sensitive accelerometer on the device and then switch it on we will (allegedly) record an acceleration. If we now integrate that acceleration over time we will get a 'local' velocity and I THINK that is the velocity Shawyer is discussing. I very vaguely understand that Einstein's special theory of relativity says that different velocity relative to everything else in the universe doesn't matter and that it all comes out correct when you do all the sums, but that might be completely ignorant rubbish.

The only thing I feel able to say with confidence is that if you want an authoritative answer to your question then you need to (a) read Shawyer's papers with a damp towel wrapped round your head and (b) find a proper physicist who has also read them to discuss it with. Sorry!

Re:so is there a good theory?

[HornWumpus]

There is no problem with any data anywhere in the universe that can't be fixed by applying one of finaglers constants.

Examples of these constants: FC0 = (Data observed - answer wanted), FC1 = (Data observed / answer wanted) etc etc More complicated with more data points obviously.

The whole idea of dark matter is simply the application of FC1. Matter is missing, so it must be dark.

Re:so is there a good theory?

[Immerman]

Sure it can: Assuming that the thrust/power ratio will be constant with speed. At this point there's no experimental evidence to back that assumption, and I suspect there will prove to be caveats that make perpetual motion impossible, but if it's the case, then in theory you can build a free energy device with it:

Mount it on the rim of a big wheel that turns a generator, Then just spin the wheel up until the EmDrive is moving fast enough that thrust * radius * angualr speed is greater than the power being used. Spin it a bit faster, and you overcome the efficiency losses as well, and you can use the electricity generated to power the drive. Spin it a bit faster yet, and you're generating excess power. Doesn't matter low the thrust is, if it's better than a photon drive then there's a (theoretically) attainable breakeven point.

Re:so is there a good theory?

[countach]

It's not so much that someone predicted dark matter, and the observable universe backs up the theory. Rather the theory of gravity doesn't match the observable universe, so some scientists came up with a total fudge factor called dark matter to match up with what is observed. Bit of a difference, huh!

Re:so is there a good theory?

[countach]

Well... there are other theories out there about why it affects matter that don't involve it being matter. Faults in space time, etc etc.

Re:so is there a good theory?

[akozakie]

Another example - the TCP-based internet. The (early) TCP traffic control algorithms are an engineers creation - things that looked like a good idea. They make sense. They just were not verified mathematically. There was no guarantee that connections would share the backbone even remotely fairly. Yet the Internet did work for years. First good theoretical models I've seen that show it can plausibly work with large-scale multiplexing are all XXI century (it's NOT exactly easy to model - the early algorithms are surprisingly complex from the system model point of view). TCP moved forward in the meantime, but the fact is: for years we've been using a network without a proper theoretical model. We treated it empirically. It worked but we couldn't really say with full certainty WHY. I'm not 100% sure we know now - I've changed research fields and several algorithms are in active use...

Re:so is there a good theory?

[aXis100]

What's rarely mentioned in the media summaries is that when the EmDrive moves, the field in the microwave cavity gets consumed and you have to spend energy to replenish it. This makes it ideal for station keeping (or hover cars) where you just need to provide a balancing force.

Anyway, there is no free lunch here and energy is still being conserved. It's only momentum that is in question.

Re:so is there a good theory?

[silentcoder]

Assuming you're right... you have a free energy device that almost certainly only works in orbit... it would be less trouble to generate energy with solar panels, wind-turbines or tidal generators then. We already have all three and they are all powered by things in outer space with the bonus that we don't need to build a way to get that energy down here in a useable form, it arrives all by itself.
Any by any human measure - those *are* free energy since they require no fuel source we have to supply. Solar and wind are powered by the nuclear fuel in the sun - but we'll be extinct before *that* ever runs out.

Why would anybody care about the "free energy" dreams that violate the known laws of physics when we already have technology for free energy that doesn't ? The moment your energy production device does not require fuel - you've got it as close to free as it can get. And, as we learned, those still cost money - to build, to maintain, to build and maintain the grid. But even if you could build a perpetual-motion generator those costs wouldn't go away - so... same problem.

Anyway, building a perpetual motion machine within the current laws of physics is entirely allowed - just very, very difficult. Couple a black hole to a white hole to make a wormhole (relativity allows this - though we may be centuries from the technology to actually keep wormholes open, and before then we may discover that we were wrong and they aren't actually possible). Put the white hole above the black hole, put a water-wheel like generator between them and drop a lead ball into the black hole.
It goes through the wormhole, comes out, turns the generator - falls back into the black hole.

There's nothing in physics that prevents that - since it needs no energy to get from the black hole to the white hole. This is one reason why black holes are considered singularities -the known laws of physics break down when you encounter one.
This exact design has been proposed by serious physicists as a way to build time machines. Compared to that, running a generator is nothing.

But frankly - a solar panel does the same job by any practical measure and is a *lot* simpler and doesn't require any materials we don't already have.

Re:so is there a good theory?

[silentcoder]

Except that you clearly didn't read what I wrote.

Dark matter was a hypotheses (what you call a "fudge factor") to explain the discrepancy between observations and gravity. There are several other hypotheses to explain this.

But each of these hypotheses then lead to OTHER predictions. You can look to see if those predictions are true or not. Only dark matter's predictions are observed. That makes it the hypotheses most likely to actually be true.

In case you were wondering modified Newtonian mecanics is an even BIGGER "fudge" factor. It claims gravity changes behaviour at very large distances (to literally the opposite of what it always does all the other times) - and offers absolutely no explanation for how this could happen.

For example any theory to explain the motion of galaxies leads to predictions about the amount of redshift in the universe. The observed redshift in the universe match that predicted by Dark Matter but NOT that predicted by MOND.

No theory is locked to a single observation. A theory explains an observation - but *always* leads to OTHER predictions: if the theory is true, then we would also see x and y and z. So we can go look to see if x and y and z are the way they would be if the theory was true.

We have strong evidence for dark matter because everything predicted BY dark matter theory (not the prediction of dark matter, the predictions BY dark matter) are matching observations.

http://scienceblogs.com/starts...

Re:so is there a good theory?

[Immerman]

I like the way you think.

Re:so is there a good theory?

[gantry]

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.

Yes, last time I looked they were putting kilowatts of power into a small device. It would be surprising if differential heating did not produce a small force from convection or even radiation pressure.

My hunch is that the devil is in the experimental details, and the laws of physics will not need to be rewritten.

Re:so is there a good theory?

[angel'o'sphere]

Sorry, that is nonsense.

How do you extract the 20W exactly?
And how would that be different from an Ion engine where you "extract 20W" after moving 20M?

If you loko at the specs of the EM drive you see, it gains speed so slow (aka the force is so low), you can never extract more energy than it puts into gaining speed. To be precise: you probably can only extract something in the order of a millions of the energy you put into it: so "inefficient" is it.

So your idiotic idea about a PM is just a gigantic energy wasting device.

Re:so is there a good theory?

[angel'o'sphere]

If F>1/c N/W (photon drive) then you can choose a velocity v such that you can extract more energy than you're putting in without the vehicle slowing down
This is complete bollocks.

Re:so is there a good theory?

[nusuth]

Actually the argument is pretty generic without any referance to any particulars of the thrust generation device or getting useful work our of it. Any device that convert energy in to thrust without interacting anything else cannot possibly be more efficient than a photon thruster, If emdrive is conclusively shown to produce trust more efficiently than that, there must be a medium that it interacts with. Hopefully, it is not something mundane and useless like outer casing of the engine, Earth's magnetic field or air around the engine, but an exotic possiblity like axions. In the latter case there is both new physics and new space exploration possiblities.

Re:so is there a good theory?

[Alioth]

It's happening anyway, every last joule of that tidal energy is already being used, it's just being used up by crashing up and down shorelines rather than turning turbines. Tidal power merely extracts some of the energy that would have otherwise been dissipated on the shoreline, so there's no net effect on the moon anyway.

Re:so is there a good theory?

[angel'o'sphere]

If your math would be right, you could make a PM with every kind of drive.
As we all learned in school, that we can't, I think your math is wrong ;D

Re:so is there a good theory?

[angel'o'sphere]

The faster it goes, the more surplus energy it generates.
No it does not. Facepalm. If that was the case every other drive had the "same problem".

Re:so is there a good theory?

[angel'o'sphere]

I simply don't get it ...
We are talking about a drive that produces an incredible low amount of thrust for an incredible high amount of power used.
It is completely impossible to make with that a device that produces enough electricity to power an EM drive. And at that point all your attempts to fabulate an PM fails apart.

Your idea is as idiotic as assuming you can run an 1.5V DC motor with a 1.5V generator attached and recharge the same battery that is running the motor with the power gained from the generator.

Re: so is there a good theory?

[jcr]

You're so clever and insightful. I'll bet you have a full and rewarding social life.

-jcr

Re:so is there a good theory?

[nusuth]

No you cannot. With the only known reactionless drive we have, the photon drive, you cannot reach the breakeven point. With any normal rocket (ion drive whatever), your system is not closed. Both energy and mass is consumed. The thrust may be constant (which is only approximately true) but the mass of craft is not. The kinetic energy of the remaining rocket+fuel changes exactly in proportion to mass loss and the energy expended to expel it. So, no PM.

Re:so is there a good theory?

[cwsumner]

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.

Ha! ... You think that you are joking, don't you? ;-)

Re: so is there a good theory?

[syntotic]

But we are still not yet experiencing the benefits of emdrives. Think like biologists do, in vitro is not the same as in vivo. In vivo is to have it working and running, in vitro is just any lab. I see very suspicious that China copied this discourse also and has it all confirmed and nearly working but Occident discoverer is just asking for smooth theory and frowning. I did grow up when these kind of Science Fiction news were classified material and the core of a thriller novel and governments were always involved and the big public unaware, so these news make me feel uncomfortable. Arent we losing some kind of technological career again and again and again? Or since when these kind of block careers are no longer relevant? I do not think this helps give credibility to the drive existence but rather makes it all suspicious its turned into a budget area very similar to what happened with convenient-AIDS research for which there is not yet a cure nor vaccine but only some PrEP (surprise!), after all those millions... See how we not only fell behind in technology but ALSO theory lost credibility? Theory was the Reason we were Occident and China a place lost in Communism! Technology was the Reason we were Modern and China was Antiquity in extenso! NASA at least should be running like crazy about this, on pure chauvinist reasons. It is how this whole shebang happened ad was _started_. No guarantee modern state of affairs will lead to something BETTER and not a step behind.

Re:so is there a good theory?

[syntotic]

8-* Bioradio still does not ring a bell in your ear, figuratively speaking? As I wrote elsewhere, once is coincidence, two is bad luck, but a few decades long.... those guys were *hearing* it in their schizophrenia...

Re:so is there a good theory?

[RespekMyAthorati]

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.

That assumes that you can supply the 10W indefinitely.
But you can't: eventually the power supply (batteries, fuel, nuke, etc) will run out and acceleration will cease.

The net kinetic energy gained will be at most the potential energy stored in the power supply.
In practice, it will be less than that due to inefficiencies.

Re:so is there a good theory?

[RespekMyAthorati]

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.

Exactly - queazocotal and mbone are idiots.

Re:so is there a good theory?

[RespekMyAthorati]

If the reactionless drive is assumed to produce thrust based on the power input only

Just like a rocket or ion drive.
And just like a rocket or ion drive, the thrust will drop to zero as soon as the power supply runs out.
There is nothing "perpetual" about it.

The only difference is that the rocket and ion drive are losing mass, while the EM drive supposedly isn't, and there is no known way for that to happen.

Re:so is there a good theory?

[syntotic]

This is standard save-of-face. The assumption is that there ARE such x and y and z observation YET to be observed, and new at that. But as we advance degrees of freedom go down. I like particularly the black matter idea, but it is still sounding like all explaining Aether that cannot be felt, cannot be seen, but it explains _it_ well... I see dangers in both lack of consistency and full consistency, because we CAN have a set of theories supporting each other and still be missing the point. The point here does not seem to be a scientists matter but a matter for meta-scientists, because as far as I could see the drive does have some theory behind (EM theory proper), so what is missing is an encompassing theory, not a working theory. No one is yet using Einstein technique of jumping up to a(n intuited) principle then falling down with explanations and matches. Can we be VERY sure a Chinese working EmDrive is a real proof of facts or just a ploy to attract people in and maybe hide some budgets for a while in all sides before it all ends in just an accumulation of errors? What did you say are the predictions of theory+EmDrive we have to be looking for?

Re:so is there a good theory?

[syntotic]

Oops! We DO use such! They are called statistical error, and can be modeled, deferred, transferred, distributed.... and assume any value (within limits) (Q).

Re: so is there a good theory?

[silentcoder]

What assumptions. Were talking about known facts. The bullet cluster is colliding in a way thats impossible under MOND but exactly according to what ot would do if there is dark matter. No other theory can explain what we can see it doing.
The cosmic background radiation is exactly what you would have if about 80% of the matter produced in the big bang was dark - and wrong for every other theory.
The gravitational lensing of galaxies is exactly where it would be if tgere was a dark matter halo around them holding most of the mass far from the stars... and no other theory explains this.
The redshift in the universe is exactly as dark matter theory predicts and if any other theory was true it would have to be different.

There is no other known theory that explains the universe we observe.

Here is a key thing about science. We do not measure an idea by how well it does what it was designed to do. Explainimg the thing we invented an idea to explain is not a valid test (that would be circular reasoning). We measure a theory by what else it does. We work out what other consequences it has and then compare those to observations.
There are dozens of theories to explain the speed of galaxies. They all do it very well. No surprise bevause thats what all of them are designed to do. Dark matter however is the only one thst passes the "other things" test. Every identifiable consequence of dark matter has been observed. None of the cobsequences of any competimg theory is observed. The universe looks like one with dark matter. It does not look like one with MOND. We know what a MOND universe would look like and we do not live in one.

Re:so is there a good theory?

[nusuth]

You have to pick a mass that is worked on and a frame of reference to define work & energy. If you ignore part of the system, it is natural that you can do over unity energy gains.
A rocket has a reaction mass, initially completely in the rocket, which is accelerated by a power source and expelled. Obviously, for space travel, we are interested in the rocket only, but to do a proper energy balance, you have consider the energy balance of the expelled mass too.
For simplicity, assume that we turn on the engine in empty space in a straight line and point of "launch" is our reference point. Since the rocket's thrust is constant, the rocket seemingly gains more kinetic energy per power spent per unit time as it speeds up. However:
1) The inverse is true for reaction mass coming out of the nozzle; it has the highest amount of kinetic energy a the start and it has less and less speed relative to launch point, therefore less and less kinetic energy relative to launch point, as the rocket speeds up.
2) The rocket is heaviest at liftoff, and it has less and less mass as it speeds up.
These two balances the equation exactly, giving a constant gain in total kinetic energy per power spent per unit time.
If you pick another frame of reference, say, the rocket itself, now the expelled mass has constant kinetic energy over time, as the exhaust speed is constant. The power is also constant. The rocket does not move relative to itself, so its KE is always zero (and we do not care about it getting lighter). Again the equation is balanced exactly.
Remove the reaction mass, and it is impossible to balance regardless of frame of reference. Whether you do this as an error in calculation, as in ignoring the reaction mass in an actual rocket, or by design, as in the case of so called reactionless drive, is irrelevant. It is not possible that Energy in=Energy out without the reaction mass (in case of photon drive, you have to take into account E=mc2 to do the balance)

Re: so is there a good theory?

[MacGyverOfComputers]

Yes and I had conceptualized this engine years b4 but mine is much more complex involving nuclear physics future technology that is in my mind, cannot write it public because of its nature in which it functions creates unlimited energy capeable of power that creates a massive em gravity field that seperates its mass from our solar systems sun and its gravity this opens a temporary portal in space that allows it to travel unlimited distance instantaneously the reason I cannot write the way to make it is because it is meant for space travel and not for war which man does not now appreciate this great power and use it responsibly.

Re:so is there a good theory?

[angel'o'sphere]

Then just spin the wheel up until the EmDrive is moving fast enough that thrust * radius * angualr speed is greater than the power being used.
And how should that be possible with an EM drive when it is impossible with any other "drive"?

Re:so is there a good theory?

[angel'o'sphere]

With the only known reactionless drive we have, the photon drive,
First of all the term "reactionless" makes no sense. You mean: "without reaction mass".
Secondly: the photon drive has a reaction mass, they are called "photons".

Of course a "normal" rocket is no PM, and neither is a EM drive, that was my point.

Re:so is there a good theory?

[nusuth]

With the only known reactionless drive we have, the photon drive,
First of all the term "reactionless" makes no sense. You mean: "without reaction mass".
Secondly: the photon drive has a reaction mass, they are called "photons".

Of course a "normal" rocket is no PM, and neither is a EM drive, that was my point.

Your point seemed to be that my maths works equally well for a rocket and EM drive, so if it were correct, both would have been allowing PM. As it is already known that normal rockets do not allow PM, my maths must be incorrect.

My point is that my calculations only take into account what happens on the engine side. In the EM drive, the engine is all there is to it. It converts energy and produces work all by itself. In a normal rocket, what used to be part of the system is now expelled as reaction mass. So the calculations are complete for an assumed reactionless EM drive, but incomplete for a rocket engine. It may be the case that my maths are not correct for Em drive either, but your point for its incorrectness is not valid.

I am not saying EM drive is PM, nor am I saying that it cannot work. I am saying that it cannot be an engine that converts energy into propulsive power without interacting with any kind of matter, as assuming that allows an impossible construct, a PM machine. We just don't know where its reaction mass comes from.

Re:so is there a good theory?

[Zxern]

Turbine is a moving part. Moving parts have friction. Overcoming friction takes energy. So no this couldn't be a perpetual motion device.

Re:so is there a good theory?

[Immerman]

Photon drives don't have the thrust, and any thing else requires you to accelerate the reaction mass up to engine speed first.

Though someone above said that at currently measured thrusts at least, the EM drive falls several orders of magnitude below break-even as well, so who knows.

Re:so is there a good theory?

[angel'o'sphere]

The math works for any engine type the same.

I have an idea

[slashmydots]

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.

Re:I have an idea

[arth1]

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.

Re:I have an idea

[Anonymous Coward]

But once you have enough trust you can just tell people it's moving faster, and they will believe you.

Re:I have an idea

[serviscope_minor]

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?

Re:I have an idea

[johannesg]

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.

Re:I have an idea

[tinkerton]

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.

Re:I have an idea

[serviscope_minor]

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.

Re:I have an idea

[tinkerton]

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.

Re: I have an idea

[Anonymous Coward]

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. This is not a perpetual motion device.

Re:I have an idea

[queazocotal]

'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 win.
Even if you say 'I'm willing to wait' - it doesn't work, as you rapidly move past the point at which solar panels work well, and the higher initial thrust of the ion engine now looks even better.

Re:I have an idea

[Chris Mattern]

The main issue, and the one this solves, isn't running out of fuel, it's running out of reaction mass.

Re:I have an idea

[queazocotal]

The power density of RTGs is worse than solar.

Re: I have an idea

[swillden]

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

[jeremyp]

Photons have momentum but no mass.

Re:I have an idea

[drinkypoo]

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 :)

Re:I have an idea

[serviscope_minor]

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/

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 perprtual motion machine (if the device works as reported, then it is functionally equivalent to a perpetual motion machine---if you're prepated to listen I will happily explain how a working EM drive could be used to construct a perpetual motion machiene) then I can believe in unicorns. Why not.

Re:I have an idea

[serviscope_minor]

Photons have momentum but no mass.

They have no rest mass.

Re:I have an idea

[arth1]

Those millinewtons can be applied over a very long time though, allowing significant speeds to be achieved.

That doesn't help if the gravitational pull from nearby heavies like Earth, the Sun and Jupiter due to the added mass of the engines and its power source is larger than the force they can provide.
The forces it has to counteract act now - they don't wait to tally up the delta after immeasurable times.

Re:I have an idea

[Maritz]

I say strap it to a spaceship.

A spaceship for ants?

Re:I have an idea

[serviscope_minor]

Let's launch it on one of Japan's new "scientific" solid rocket boosters

Now, now. Japan *need* to be able to launch a "communications satellite" at very short notice from a mobile platform.

Re:I have an idea

[tinkerton]

Yeah. So now reread my post. I'm not arguing that maybe there is thrust with conservation of momentum. I'm saying that your differential diagnosis is lacking.
  You're willing to put the law of conservation of energy on your list of possibilities , ranking it that as 'outrageously unlikely' but listable.
  But the possibility that energy and momentum are getting out in a way that was overlooked, that you consider fairytale level and not even worth listing.
  It should be the other way round at least.

Re:I have an idea

[tinkerton]

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.

That's 'openended microwave generator' right, so everything gets out? Good argument.

Re:I have an idea

[serviscope_minor]

Yeah. So now reread my post.

Just did.

. I'm not arguing that maybe there is thrust with conservation of momentum.

Um OK...?

You're willing to put the law of conservation of energy on your list of possibilities , ranking it that as 'outrageously unlikely' but listable.

I listed it for the purposes of rhetoric only because it keeps coming up here.

But the possibility that energy and momentum are getting out in a way that was overlooked

The thrust is too high for it to be leaking radiation (something you suggested). If momentum is escaping in another way, such as it stripping off the inner layer of copper and ejecting it, then it's not working as an EM drive.

You could pour petrol over it and set it on fire, and I guarantee it will move, but I would not classify it as working in that case.

My argument is predicated on the claim that it is actually working.

Re:I have an idea

[tinkerton]

I don't know and I don't care. The arguments I paid attention to were valid.

Re:I have an idea

[Solandri]

If you're about to blow a spaceship's worth of cash on something [...] And would that influence your decision to blow a few tens of millions on it?

If you're going to launch something into space anyway, then the cost of adding this experiment to the spacecraft is only about $5000/kg. So if you can whittle it down to a few kg, you're not talking about much cost at all. Heck, one of the ISS crew members could request it as part of their personal allowance.

You'd lose all the fancy instrumentation you have on the ground to measure exactly what's going on. But putting one of these in orbit is probably a cheaper way to settle the question "Does this thing really work?" than all the money we've already spent testing it on the ground. It's like when I'm helping friends with computer problems - some things (e.g. reboot) take so little time and effort to do that I ask them to do it right off the bat before even trying to diagnose the actual problem.

Re: I have an idea

[Enigma2175]

No, you only need electricity to create the EM field, and you can generate that from sunlight. No need for fuel.

Sunlight is generated from fuel.

Re:I have an idea

[IMightB]

I would think it depends on how close to the star you are.

Re:I have an idea

[Dr. Evil]

The assertion of em drive is not based on theory, but alleged observation.

Conflicting measurements are evidence of experimental error. China's trying a new experiment, hopefully their measurements agree with some others. I think we both expect the outcome to be "no thrust".

It looks like a fun experiment. Not sure why they feel it's worth investigating, but maybe it's related to another project and not a high cost item for them.

If it works, you can propose your unicorn attractor constant.

Re:I have an idea

[tinkerton]

I listed it for the purposes of rhetoric only because it keeps coming up here.

Valid argument. It was not a good list of possibilities because it was not intended as such.

If momentum is escaping in another way, such as it stripping off the inner layer of copper and ejecting it, then it's not working as an EM drive.

Fine. But what the experiment tests is "it works". "This thing I set up here pushes. And I have a theory that it proves that hell will freeze over anytime now and you have to buy it together with the experiment!"

Then at least one should be able to buy the experiment without buying into the theory as well. That was this third option I mentioned.

Does that mean as a scientific investor I would think this experiment is worth investing in? I don't. Apparently some have made the calculus that 'slim chance of success but if successful yielding extremely high theoretical reward' makes it worthwhile.

Re: I have an idea

[swillden]

No, you only need electricity to create the EM field, and you can generate that from sunlight. No need for fuel.

Sunlight is generated from fuel.

Not fuel carried by the spacecraft.

Re:I have an idea

[serviscope_minor]

Fine. But what the experiment tests is "it works". "This thing I set up here pushes.

OK, I see where we disagree, and it's not contraversial!

I contend the purpose of the experiment is not to merely push since we already know how to do that, but to push without reaction mass. Therefore to "work", it has to do so without reaction mass.

If you have different criteria, that's fine and I accept that by your criteria it works.

Re:I have an idea

[WaffleMonster]

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.

What is so compelling about EM drive from a perspective of capabilities as measured thus far that requires substantial gaps in the laws of physics to explain?

Photon rockets with 3x that of the best EM drive results per watt have been demonstrated using mirrored surfaces simply by bouncing lasers thousands of times. Why are they allowed to work while EM drive is labeled "impossible".

Nobody really has a handle on what if anything EM drive is "pushing off" of. It is all just conjecturbation at this point.

Re:I have an idea

[serviscope_minor]

If you have different criteria, that's fine and I accept that by your criteria it works.

To claify: something is producing a thrust, since they're measuring it.

I reckon (we both do?) that the thing producing it is an experimental artefact and isn't interesting.

Re:I have an idea

[serviscope_minor]

Photon rockets with 3x that of the best EM drive results per watt have been demonstrated using mirrored surfaces simply by bouncing lasers thousands of times.

If it's multiple bounces then it's a solar sail, not a photon rocket, and the thing other thing you're bouncing the laser off essentially forms reaction the mass. As you gain speed relative to your other mirror the efficiency will drop.

Why are they allowed to work while EM drive is labeled "impossible".

They're "allowed" to work, because they conserve energy and momentum, because there's a reaction mass.

Nobody really has a handle on what if anything EM drive is "pushing off" of.

It's most likely pushing off the air or ambient magnetic field or something. That's neither useful nor interesting though.

There isn't just magic stuff in space you can simply push off though. If there was, then it has interesting things to say about geocentrism!

Re:I have an idea

[ceoyoyo]

You just made orbital mechanics cry.

Re:I have an idea

[Tablizer]

To get a perspective, anybody want to do the math on the following?:

Take the RTG power supply used on the New Horizons probe, attach an EM drive about the size of those used in successful tests, and add a very simple one-way transmitter capable of detection from Earth out to say 100 times the distance of Pluto. (Perhaps use capacitors to spike a periodic transmission pulse in order to get a strong but simple signal.)

Based on the lab test thrusts, what kind of speeds are we looking at with such a test probe?

Re:I have an idea

[CrimsonAvenger]

Now, now. Japan *need* to be able to launch a "communications satellite" at very short notice from a mobile platform.

Or a recon satellite. Seriously, recon sats are one of the few types of satellite that you really need to be able to launch on short notice. Sometimes REALLY short notice....

Re:I have an idea

[ceoyoyo]

The trick with the photon thrusters (they are not "rockets") is that you get an equal force on both ends. The idea is to let one of those ends be a small spacecraft carrying no fuel and the other end be a spacecraft that stays at Earth with a bunch of big lasers and conventional propulsion. Photon thrusters are really a way of efficiently "beaming thrust".

Re:I have an idea

[tinkerton]

My feeling is it isn't worth investigating. Usually the idea is that 'science should thoroughly investigate whether claims like this are true'. That's why I mentioned science as investment: in that model you can't invest in everything so you have to choose. This falls off the list.

Re:I have an idea

[HiThere]

The page I read yesterday claimed that this was entirely consistent with the conventional laws of physics, and was based on radiation pressure in a resonant cavity of an appropriate shape.

This would seem to put rather strong limits on the amount of power that could be generated by an EM drive, putting in as only slightly better than ion rockets as far as impulse (and perhaps not as good), but significantly simpler in design and only requiring electricity as fuel.

In short, if the paper was correct this is probably an improvement on current technology for certain applications, but nothing dramatic, and only useful for certain applications. If you're thinking of using a light sail (without a launch laser) or an ion rocket, you should consider this as an option.

Re:I have an idea

[angel'o'sphere]

We all would like to know how a working EM drive could be used for a 'perpetium mobile' machine!
Especially for one that fits the definition and 'creates' more energy than it consumes ... and one that is still 'perpetium' when its energy source has run out ... you might attempt on the first part and fail, the later part is impossible, hence a perpetium mobile machine with an EM drive as source is impossible.

Re:I have an idea

[johannesg]

You are comparing a well-known propulsion mechanism (ion drives) to something we aren't even sure is generating propulsion in the first place, and which according to current theory really has no business doing so even if it is. Let's assume there really is an effect here. Maybe the shape of the cavity is still highly sub-optimal. Maybe, once theory explains what is going on, we can create engines based on the effect that are much more efficient.

Also, we should look at possible future missions. Drop the solar panels; put a nuclear device there and just keep accelerating until halfway to the next star. Is such a mission even possible with ion drives?

Re:I have an idea

[johannesg]

You completely misunderstand the purpose of the experiment, then. The experiment is not "here is a crackpot theory, let's try to prove it". It's "here's a device that seems to produce an effect we cannot yet explain. Is the effect real, and what is the explanation?".

Several teams across the world claim to have replicated this result. Now, maybe it's all nonsense; maybe there is really something there we don't (yet) understand - the only thing I know is that it is too early to judge. And instead of explaining why the measurements could not have been taken, what you should be feeling is excitement at a mystery to be solved, and (very slight chance, but still) the possibility of a new extension to the laws of physics. If you really are a scientist, your job is not to close your mind and explain why everybody got it all wrong. It is to explain the effect apparently being measured.

And sure, it can be a measurement error. It can be outright fraud (unlikely, I think). It can be an overlooked conventional effect. But it can also be something new - something for which Nobel prizes are given out, something that may one day send probes to the stars. Shouldn't we at least look?

Re:I have an idea

[slashmydots]

Yeah but see you can get microwave ovens for like $3 at the thrift shops so just strap a loooootttt of them to the spaceship.

Re:I have an idea

[RespekMyAthorati]

But once you have enough trust you can just tell people it's moving faster, and they will believe you.

And if you start to doubt it, they will be able to convince you, etc.
Sounds like a trust circle to me.

Re:I have an idea

[RespekMyAthorati]

I could hypothesize that it's actually a unicorn attractor

How about a magnet attractor?
When an electromagnet picks up a chunk of steel, there is acceleration but no loss of mass.
Maybe the EM drive is interacting with the earth's magnetic field in some way, like an elaborate compass needle.

Re:I have an idea

[WaffleMonster]

If it's multiple bounces then it's a solar sail, not a photon rocket, and the thing other thing you're bouncing the laser off essentially forms reaction the mass. As you gain speed relative to your other mirror the efficiency will drop.

I guess I'm just stupid. I don't understand why this is relevant with regards to what is possible.

They're "allowed" to work, because they conserve energy and momentum, because there's a reaction mass.

What is the basis for the assumption EM drive is *required* to be any different to explain outcomes?

It's most likely pushing off the air or ambient magnetic field or something. That's neither useful nor interesting though.

There have been tests conducted in vacuum and testing in different positions to rule out similar possibilities specifically. I'm not claiming EM Drive actually works or doesn't work. I just don't get the assertion conservation laws are required to be violated to explain observed EM Drive outcomes assuming they are not just errors.

There isn't just magic stuff in space you can simply push off though. If there was, then it has interesting things to say about geocentrism!

If such magic were possible it could be sufficient to explain results without necessarily affecting conservation laws. There are other options besides assuming EM Drive is a free energy machine.

Re:I have an idea

[RespekMyAthorati]

I could hypothesize that it's actually a unicorn attractor

How about a magnet attractor?
When an electromagnet picks up a chunk of steel, there is acceleration but no loss of mass.
Maybe the EM drive is interacting with the earth's magnetic field in some way, like an elaborate compass needle

Re:How big is an EM Drive?

[Anonymous Coward]

No but the point is you can put more power through a single one. The limitation right now is availabvle power which is very low for solar panel satellites but if you made a satellite with a high density power source such as nuclear, then you have much more power avail to run the drive. That's the real holy grail all these teams are working toward inc the China team.

Hilarious

[djinn6]

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. Now that would be exciting.

Re:Hilarious

[arth1]

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 happily violates Newton III. And so does quantum mechanics.

Re: Hilarious

[Anonymous Coward]

The Lorentz force does not violate Newton's third law, and quantum mechanics is based upon Hamiltonian mechanics which is just Newton's laws expressed differently.

Re:Hilarious

[jandersen]

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 exciting. It would indicate a violation of Lorentz invariance symmetry, apparently; don't ask, I haven't spent the time understand it, but I'm sure a lot of things would look very different, if the fundamental conservation laws that follow from this were broken. No, if this works, and it does look that way, then there is something we have overlooked - there must be some momentum that is emitted in some way to produce a reaction-force.

Re:Hilarious

[little1973]

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/...

Also, Erik Verlinde talks about 'elastic back pressure' in his recent paper https://arxiv.org/pdf/1611.022... 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 this case dark energy would be the elastic energy of space. So, it's no wonder the universe is expanding.

It has also implications to the fate of the universe. I mean it may not depend on how much matter is in the universe, but rather what kind of properties space has.

Re:Hilarious

[serviscope_minor]

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 that looks remotely like the older idea of it). So if the aether existed, then Newton's third law wouldn't.

But you also might like to consider why we're seeing only thrust by pushing against it, as opposed to drag by it moving relative to us. And chances are it's moving FAST because we're not at rest in the universe. We're whirling round the earth's axis, around the sun, the galaxy and Andromeda.

Secondly, The EM cavity is more or less a reversible electrical machine, which means if it's moving relative to the ether, then you ought to be able to get power out by experiencing drag. There's no sighs of that either. One way for THAT to be OK would be for there to be significant gaps in EM theory. But, EM theory has stood up remarkably well over the years. It was formulated before relativity but actually predicted a whole bunch of relativistic results and was in fact one of the driving forces of relativity coming into being as an independent theory.

My bet is that tens of thousands of existing, peer reviewed experiments are not flawed in a consistent way, and that this one is.

Re: Hilarious

[LaszloKerekes]

Much like a solar sail, expanding on this momentum is transfered something like p=hf/c

Re:Hilarious

[serviscope_minor]

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.

Re: Hilarious

[khallow]

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).

Re: Hilarious

[slew]

How about the Casimir effect? Which of Newton's laws explains that?

Re:Hilarious

[wierd_w]

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 different goal in mind (conversion of neutrino flavor, vs simply interacting with neutrinos) and so it has different requirements for the cavity.

https://arxiv.org/pdf/hep-ex/9...

If the cavity is selectively interacting with ambient neutrinos, and imparting them with a slight change in momentum in a preferred direction, the conservation law requires the device's momentum to change accordingly. Unlike a photon, a neutrino has REAL mass. As such, significantly more momentum could be transferred to one than one gets with a photon.

For real. Take the test article to Japan, point it at the detector, and see if a small spike in neutrino flux happens. It does not need to measure thrust, or any other such stuff. Just see if there is a change in neutrino background corresponding to device activation. The device is small, so it needs to be right on top of the detector. (The detector is huge and underground, and cant be moved. The test article is much more portable.)

Re:Hilarious

[arth1]

Yeah, no. Also, well done for providing a link to an article which doesn't remotely back up your claims.

Well, yes, it does
The circular field increase/decrease is what you get instead of an opposite and immediate force.

Re:Hilarious

[slashrio]

If this idea originates from you then I'd seriously consider publishing it somewhere.
Oh, you just did. :)

Re:Hilarious

[serviscope_minor]

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

[Maritz]

Newton's laws don't posit virtual particle pairs. Just because it's incomplete doesn't make it wrong for what it is.

Re:Hilarious

[Maritz]

Well, it's kinda hard to explain the existence of matter and energy without breaking a couple of "laws"

Current thinking is that the Universe created matter as it expanded by borrowing against gravitational potential energy (which is negative). So no, you don't have to break laws just to explain where the matter and energy originated.

Re:Hilarious

[ceoyoyo]

Neutrino detectors aren't that sensitive. You'd be making a very small change in neutrino flux, if any. If your hypothesis is true, the device would change the *energy* of ambient neutrinos, not create more of them.

Testing the EM drive next to a nuclear reactor to see if you get more thrust might be a better experiment.

Re:Hilarious

[wierd_w]

At best, this article would act a bit like a gathering "lens" for neutrinos if this idea is true. The lens is "very small", and the amount of neutrinos passing through it is very small compared to the vast volume of neutrinos passing through the earth.

Purposeful generation of neutrinos for research purposes are many orders of magnitude more intense, and even with said scattering, are more like a high power search light than the tiny little magnifying glass type concentrator this device would represent by analogy.

If the new vectors of travel for the neutrinos passing through the device are not laser-like (strongly collimated, and very parallel) the neutrinos will disperse, like light being emitted from a flashlight. Get far enough away, you cannot reliably detect the light of the flashlight even with it aimed right at you.

SK2 is underneath a mountain, because the detectors are not directional per se-- (instead, they arrange the detection elements such that they can compute intersections through the grid of detectors, and use timing values to determine which side of the detector the event passed through first) and the need to eliminate other sources of excitation from cosmic particles is very real to keep confidence of signal high.

Due to the combination of factors, the best place you could put the test article is right on top of the detector, above ground. A scaled up test article to maximize ambient neutrino cross section would probably be needed.

I concur with a prior poster that testing the device near a strong source of artificial neutrinos (to get a higher rate of intersection with the device) and testing for greater thrust relative to proximity of the neutrino source is another good test. It would nicely explain some of the inconsistency in the results published on the em-drive.

There is much less distance straight down through the mountain over the top of the detector than there is passing through the earth.

Re: Hilarious

[angel'o'sphere]

The Casimir effect has nothing to do with Newtonian laws.
And surprisingly the "conservation of momentum" still holds. The sum of the momentum of the two plates used to "create" the effect is always zero.

Re: Propellantless doesn't mean reactionless

[fubarrr]

>Reactionless

Certainly not reactionary. If it was, research chief would've been standing in from of firing squad by now

Seen this before

[Anonymous Coward]

Shades here of the Cold War, when every Western technology advance was greeted by an immediate announcement from the USSR that they had discovered it years ago, been successfully using it for aaaages, and were pitying of the decadent capitalist imperialist (cont'd on page 94...) bourgeousie who had only just discovered it.
Of course China has successfully been using this. Hmm-hmm. Yeah.
Between their shameless and rampant theft of IP from the West, their cultural paranoia, and their total lack of tolerance for failure in academia or science, I doubt they've actually had an original research thought in the last 40 years.

Re:Seen this before

[cheesybagel]

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.

Re:Misleading

[arth1]

China? Intellectual Property you say?

Well, there is that. It could have more in common with the EM Drive than we think. :)

This Could be Easily Settled with an Experiment

[Anonymous Coward]

Why not construct and launch a space probe equipped with this EM drive, set in on a course to Jupiter for an interstellar slingshot to Alpha Centauri. It should be easy to calculate via telemetry whether or not the probe continues to accelerate without reaction mass for fuel. If it does, then we know the EM drive is not bogus. If not, then we found the answer and all it took was $200,000,000 dollars or so, which would be a bargain by space program standards. If the probe really can accelerate continuously in the vacuum of space then it shouldn't take too long for the probe to reach a substantial fraction of the speed of light.

Re:This Could be Easily Settled with an Experiment

[Anonymous Coward]

Because it can be verified in the lab a lot cheaper, with a lot more variations and controls. The proposal only launches one probe, right? We can benchtest a dozen configurations and try nulls for a tenth of the launch cost of that. If you can find a stupid billionaire, feel free, but they're mostly rich because they're not stupid.

Re:This Could be Easily Settled with an Experiment

[gweihir]

No, not at all. The thrust (if it is there) if far, far too low for that. Do you people even read the description of what this thing maybe does before you start to fantasize?

Re:This Could be Easily Settled with an Experiment

[cwsumner]

No, not at all. The thrust (if it is there) if far, far too low for that. Do you people even read the description of what this thing maybe does before you start to fantasize?

The thrust is what they planned for, and is the correct amount for a test of a device that we don't understand. The test NASA did was designed to detect extraneous influences. Making it more efficient and more powerful would be a very bad idea, at this point. (Or at least the point where we were, when they did the test.)

Re:This Could be Easily Settled with an Experiment

[gweihir]

Bullshit. The observed thrust is rather close to the margin or error. Nobody halfway competent plans an experiment that way. Incidentally, NASA did not do any test on this at all. NASA Eagleworks, which is not NASA, did the tests.

Bomb them!

[adjustinthings]

'Pentagon Officials' claim this could be used to beat the USA to distant resources thus threatening the american way of life. Therefore we must bomb them,obviously. (like every other fracking 'news' article lately) Or should i say Russia?

Re:Bomb them!

[gtall]

Get yer ass out of the '60's.

Re:Bomb them!

[l0n3s0m3phr34k]

Reading around in particular on this mission (SJ 17), you should have been upmodded instead. The test of this drive isn't the main mission...the main mission is probablly more along the lines of "in space Eavesdropping":The observed maneuvers provide clear clues on the intent of the SJ-17 mission as a Space Situational Awareness pathfinder, testing navigation technologies to link-up with resident objects in Geostationary Orbit – getting sufficiently close to capture optical imagery of the object and shadowing it at close distance to intercept its uplink communications.

This is a test to see if they can maneuver close enough to intercept signals. Today their targeting a Chinese orbiter...but once this tech is ironed out it will probably be set up for rapid in-orbit deployment against non-Chinese systems. I see a use of having a sat like this sit in GEO orbit nearby potential targets, but not "too close" until mission green-go. They will then use whatever electrical engines (EMDrive, conventional ion, whatever works) to get into uplink intercept range. I can even see, in case of an actual conflict, "sacrificing" and taking out a comsat.

The whole EMDrive is just icing on the cake here; it's just a means to an end for in-orbit maneuvering.

Plenty of room for thermal effects

[Anonymous Coward]

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 is this picture supposedly showing?

Re:Propellantless doesn't mean reactionless

[evanh]

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.

Re:Propellantless doesn't mean reactionless

[evanh]

There's no mass being expelled in laser propulsion either.

Re: Misleading

[Anonymous Coward]

So, please help me understand the (apparently, seemingly) typical slashdotter mindset here. What makes these guys douchebags?

Serious question. Why, given their choice of emdrive, are they therefore shown to be deserving of that?

Re:It supposedly has no exhaust, a closed system

[Calydor]

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.

Re:Misleading

[Theaetetus]

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.

Re:It supposedly has no exhaust, a closed system

[Anonymous Coward]

That guy is a moron. He uses strawman logic all over the video.

Re:It supposedly has no exhaust, a closed system

[GNious]

Thunderf00t's video reminded me of the original meaning of "to beg the question".

Re:Propellantless doesn't mean reactionless

[tinkerton]

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...

Re:Propellantless doesn't mean reactionless

[Noughmad]

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.

Re:Propellantless doesn't mean reactionless

[serviscope_minor]

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".

Re:Misleading

[Zorpheus]

Heh, they give things different names at least. Maybe EMDlive?

Re:Propellantless doesn't mean reactionless

[Herve5]

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)

Re:Propellantless doesn't mean reactionless

[serviscope_minor]

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

[thermidor]

There's a difference between mass and rest mass.

Re:Misleading

[Anonymous Coward]

No, its an OEMDrive :)

Re:Propellantless doesn't mean reactionless

[tinkerton]

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... )

Re:How big is an EM Drive?

[CrimsonAvenger]

At present, no, not near Earth's gravity well, at least. The added mass of the cavity thrusters would probably increase gravitational force more than the tiny force they produce.

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 gain enough thrust to make it worth the bother?" Answer is "probably", unless the EM drive unit outmasses the satellite it's attached to (or the satellite + multiple EM drives is massive enough that your launch vehicle can't get it up there....)

Re:how far can it be scaled up?

[Big Hairy Ian]

I suspect making it more efficient is going to be far more important than scaling it up as the bulk of the mass is going to be generating energy for it.

Re:Propellantless doesn't mean reactionless

[wonkey_monkey]

No-one really uses the concept of relativistic mass any more. Things just have invariant (rest) mass.

I love SF as much as anyone, but..

[rkordmaa]

Lets face it, in all likelihood emDrive is complete bunk, its probably just an overly complicated Crookes radiometer. But sure, test it out, worst that could happen is an cautionary tale like the one about n-rays.

Re:Misleading

[jbmartin6]

Trademark isn't the same as copyright, it only applies to similar businesses or cases where there might be confusion as to the origin. So you are free to make a Windows line of children's toys.

BULLSHIT

[110010001000]

More fake news. Go to CAST website. THERE IS NOTHING THERE ABOUT IT. And the website is in English too. Stop posting this bullshit about the EmDrive. It is this decades eCat.

Re:BULLSHIT

[NoImNotNineVolt]

Go to CAST website.

I googled. Do you mean:
Center for Applied Special Technology, something for people with disabilities?
Google Cast, now called Chromecast?
Cast software, something for SQL?
CAST LA, a group trying to end slavery?
Council for agricultural science and technology, which also has nothing to do with space propulsion systems?

In short, what are you talking about?

Re:BULLSHIT

[Maritz]

E-Cat is probably still going. The highly trustworthy Mr Rossi is getting a full career out of that bullshit.

Re:BULLSHIT

[l0n3s0m3phr34k]

I'm pretty sure I remember you have previous posts calling people "space nutters", and are pretty rabid in attacking anything outside mainstream NASA. The claim that CAST has nothing just because the English version has nothing means nothing...unless you've gone through the Chinese language version and can prove the two sites contain the same information.

I found another reference in English at http://spaceflight101.com/shijian-17-rendezvous-with-chinasat-5a/: "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 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 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.

Re:BULLSHIT

[Areyoukiddingme]

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.

More than a decade of Google Translate, and it still pulls stuff like that. I swear human Asian language translators have been trolling machine translation to Romance languages since its inception.

Re:BULLSHIT

[l0n3s0m3phr34k]

LOL, I just assumed China used some type of bovine-based measurement system...

Re:BULLSHIT

[Tablizer]

[thrust is measured to micro-cow level] Don't tell me they're still trying to model those things with spherical micro-cows

Brexit, Trump, Cubs winning, EM-Drive; anything's possible. Maybe the Spherical Cow Engine will power future interstellar ships.

"Captain, I'm giving you all the milk she has. I cannot milk any faster ... we're gonna blow!"

Re:Propellantless doesn't mean reactionless

[jeremyp]

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

[Anonymous Coward]

From the 2nd link (in Chinese), 9th paragraph, translation and emphasis mine:

Chen Yue's team began working on the EM drive in 2010. The team designed the drive's cavity based on classical EM theoretical calculations. The analysis led the the researchers to believe that the thrust was generated by the uneven distribution of the electromagnetic field inside the resonance cavity. Therefore, no traditional propellant was required for its working. Essentially, it made use of the force exerted on the matter by the electromagnetic field, which was compatible with laws of classical physics.

Re:It supposedly has no exhaust, a closed system

[drinkypoo]

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.

Re:Propellantless doesn't mean reactionless

[slashrio]

And why would the 'torch engine' not become an over-unity device?
Constant power, constant thrust, constant acceleration, time-linear speed increase (in the non-relativistic region), quadratically increasing kinetic energy.
Just like the 'EM-drive'.

I must have missed something that nobody came up with this yet. :)

Re: tests keep confirming it?

[slashrio]

I think one could better state: "Tests haven't falsified the claim, yet."
Not to say that I think it won't work, I have no idea.
But the tests were just not conclusive enough, yet, to really confirm that it works.

Re:Misleading

[slashrio]

Word goes that one day Xi Jinping belittled Obama about the state of democracy in the US:
"Hah! Evely 4 yeals and you call that democlacy? WE have best democlacy, election evely molning!"

Re:Propellantless doesn't mean reactionless

[serviscope_minor]

Photons have no mass but they do have momentum.

Yes, no rest mass.

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.

Yep and you get 3uN/kW. Anything more and you have a free energy device.

Such an engine would have no reaction mass but would not violate the law of conservation of momentum.

If you're chucking momentum out of the back, it's getting into rather fiddly semantics as to whether it matters specifically if there's rest mass or not. Remember there's a mass-energy equivalence, too. So yeah, you are indeed chucking something with zero rest mass out the back.

1. The device doesn't work

Most likely.

2. Something with momentum is being ejected but we just haven't found out what yet

Also reasonably likely, but in that case, I think that's a pretty good definition of "doesn't work". I mean if it's stripping off the inner layer of copper and hurling it out the back somehow, then it's not an EM drive, it's a rather poor ion drive. It also doesn't have any of the purported properties either. So, if you've got this one, you might as well add:

2a causes reaction against something external like magnetic fields or air.

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.

I think we're in agreement!

Re:Misleading

[arth1]

First, it's a drive, yes? And it's using electromagnetism, yes?

Yes? Do you mean to imply that a Nissan Leaf has an Em Drive?

Re:Propellantless doesn't mean reactionless

[Maritz]

No one doing the research is claiming such a violation. The journo is just making stuff up.

If they claim to have measured thrust, and nothing is coming out, then they are claiming a violation.

Not quantum

[Roger W Moore]

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.

Work done=kinetic energy

[Roger W Moore]

How exactly do you intend to use the thrust to produce energy ?

Think about the object the drive is attached to. When it starts to move that is because the thrust has done work which is converted into kinetic energy.

Re:Work done=kinetic energy

[silentcoder]

But you can't use that energy to power the thrust producer - so that does not make it a perpetual motion device. That energy has already been used (since the device is moving) there is no potential energy there.

Re:Work done=kinetic energy

[serviscope_minor]

But you can't use that energy to power the thrust producer

Sure you can, you just have to hook it up right.

so that does not make it a perpetual motion device.

No: you don't need to show how to construct a practical device. Merely showing that it's over unity is sufficient to show it's (equivalent to) a perpetual motion machine.

Look at it like this. First start with some big numbers.

Imagine it produces 1000N /kW.

So put two on the edge of a wheel 1m in diameter, and pump 1kW in. There's 1000N making whe wheel spin up. Let it freewheel util it's travelling at 1 revolution per second. Now connect it to a generator and extract enough power such that it doesn't accelerate any more, but doesn't slow down. And keep pumping that 1kW in.

Well it transpires that you'll be pulling 6.3kW at the shaft. Let's say you get a conversion efficiency of 80% from shaft power to electrical energy and 50% from electrical energy to microwaves. Well, you could use that to sump the 1kW of microwaves in and still have 3kW of electrical energy to do with whatever you liked and the machine would keep spinning and keep spitting out 3kW of energy.

Those are not unrealistic numbers for power conversion efficiency.

OK, so 1000N/kW is unrealistically high.

What about 100N/kW?

10N/kW?

1?

0.1?

0.01?

0.001?

At what point does it turn from unrealistic to realistic and why? At 0.001 N/kW, the system above won't work because there are no materials which could make a wheel that wouldn't fly apart.

But it still works if you get exotic. Imagine the device in orbit around a high mass star or black hole and using an electrodynamic tether to convert it's kinetic energy back into electrical energy.

Re:Work done=kinetic energy

[Alioth]

> Now connect it to a generator and extract enough power such that it doesn't accelerate any more, but doesn't slow down

This here is the impossible bit. Just because you can /momentarily/ extract 6-odd kw at the shaft, it doesn't mean you can keep doing it forever. You may find that any more power extracted than just the friction in the bearings will slow your hypothetical wheel down.

1000Nm torque doesn't say anything about the power you can continuously extract.

Re:Work done=kinetic energy

[serviscope_minor]

This here is the impossible bit. ...?

Yes?

I'm not sure what you're arguing here. I'm arguing that IF the EM drive works as described then you can set up the system I described and you get the absurdity of perpetual motion. Ergo, the EM drive does not work.

It's a reductio ad absurdum argument. I show that a working EM drive would yield an absurd result. Therefore the EM drive does not work.

If you're arguing that perpetual motion is impossible, I wholeheartedly agree. And that implies the EM drive is impossible.

Actually you've pointed the error at the wrong place. The bit you selected isn't the impossible bit, the impossibility comes later see:

1000Nm torque doesn't say anything about the power you can continuously extract.

Power = torque * angular velocity

If you have a prime mover (e.g. a turbine) applying 1000Nm of torque to a generator shaft at 1 revolution per second and you extract less than 6kW you'll find that the assembly accelerates. In any physical system the torque will drop off as the speed increases. But if you're putting in that much torque at that speed you most certainly can extract 6kW at the shaft. That's how every generator ever works.

The next bit is fine too. You can generate electricity and then generate microwaves just fine. That's how your domestic microwave oven works.

The problem is using those microwaves to generate thrust. Thats the bit where it gets silly. But there's not a difference between your internally and externally generated electricity. Therefore the whole EM drive can't work because if it did, the conclusions are absurd.

Re:Work done=kinetic energy

[silentcoder]

Except that the thing you described very well may not work at all.
If, indeed, the EM drive produces thrust without expelling matter - there is nothing to drive your generator - the thrust won't drive it because it's only acting on the machine itself and in the wrong direction.

You've got absolutely no proof that the thing could spin a wheel - indeed if it works the way it is said to work then the wheel will not spin. So your problem goes away. The trouble is -that violates conservation of momentum, so you're assuming there is actually something being expelled.

The only theory we have where something gets expelled though - that something is dark matter, which will pass right through your wheel and not spin it. So it's still not a perpetual motion machine as there is absolutely no way to power a generator using that thrust. Everything we know says dark matter cannot hold electrical charge or interact with normal matter - there is thus, absolutely no way, with the current laws of physics be used to produce electrical power in normal matter.

The only energy produced is kinetic and that exists ONLY on the drive. There is no evidence of any energy going the other way. Indeed the very reason we have doubts about the EM drive is because there is nothing leaving it, no energy being sent the other way. Nothing that can drive your generator.

When another poster said that was the impossible bit - he was telling you the bit you missed, you can't drive a wheel without something hitting it.

Re:Work done=kinetic energy

[serviscope_minor]

I think you've misunderstood my description.

Instead of being mounted on a spaceship, the drive is mounted to a wheel. Nothing hits the wheel, the drive pushes it, if the drive works.

PS, I'm claiming the drive can't work.

Re:Work done=kinetic energy

[silentcoder]

There's no reason to believe this drive could work in atmosphere - certainly not the way you are suggesting.

You power it up, get the wheel spinning. Immediately losses begin to appear. From friction in the bearings to the magnetic pulls in the generator to air resistence - all this slows it down again. So to keep it turning you must power the drive continuously. I assume you're thinking of - get it to a high speed, then let the momentum generate power for the next burst, to get it back up to speed.
But that is impossible. There is no way the momentum can ever generate enough power for the next burst to have as much energy as the last one had- because of those losses, sooner or later, the machine will just stop.

Even with your device- it's not a perpetual motion machine - you're making the same mistake *every* perpetual motion machine makes: you're forgetting about the losses during operation.

I'm not convinced it works. But I am sure that YOUR reason why it can't is bullshit - because you are wrong to claim what you proposed is possible if the device works, it's not. Because of losses.

Re:Work done=kinetic energy

[angel'o'sphere]

First of all the term "above unity" does not exist in physics.

Secondly:
So put two on the edge of a wheel 1m in diameter, and pump 1kW in.
When you have put 1kW into a spinning wheel with a EM drive, you already have expended GWs or TWs on energy. Regardless what you can recover from the spinning wheel, you are deep into minus with your energy balance.

Re:Work done=kinetic energy

[angel'o'sphere]

I'm not sure what you're arguing here. I'm arguing that IF the EM drive works as described then you can set up the system I described and you get the absurdity of perpetual motion.
No. You described us a system that can not work. Regardless which what kind of drive you power it. Hence the connection to the EM drive is a logical no sequitur.

Power = torque * angular velocity
That is wrong. Torque is mass times 'angular velocity'. So 'mass' times 'angular velocity' times 'angular velocity' yields angular or "turning motion kinetic energy". In other words you are mixing up the "fly wheel" _kinetic energy_ in your "construction" with power.

Forget the stupid torque, just use a sledge or a flying rock: energy is m*v^2 ... and that is not power. Your idea how to extract energy just because the "drive" is an EM drive (your idea would either work or not work with an ion drive, too, it is completely agnostic from the mechanism that powers it, facepalm) is silly at best and as you hang so much on it and don't grasp any counter argument I dare to say, it is not silly, but idiotic.

Re:Work done=kinetic energy

[serviscope_minor]

You seem to be confused/misunderstanding a number of things. Nonetheless, you seem to be arguing in good faith, so I'll do the same and write a longer explanation.

Firstly, my argument is a reductio ad absurdum. I take the EM drive as it is claimed to work and show that IF it is true, the consequences are absurd. I therefore claim that it cannot work. You are jumping straight to the end and saying "your conclusions are absurd so you're wrong".

At that point I can't actually tell if you're agreeing with me while claiming I'm wrong or disagreeing with me while claiming the EM drive DOES work.

You power it up, get the wheel spinning. Immediately losses begin to appear.

Fixating on losses makes the debate much more tedious, but does not ultimately change the conclusion (more later). But, firstly, go back and read my post. The numbers I put in allow for losses of up to 80%. I purposely picked those numbers because we can easily beat them today with standard, off-the-shelf tech. In fact just about every powerstation has fewer losses than my hypothetical system.

Now at this point onwards, you are forgetting it's a reductio ad absurdum. I'm taking an extra-juiced EM drive (1N/W) for a rhetorical purpose. It's not an idle purpose though, so bear with me.

From this point on, you need to assume the EM drive works as claimed:

You power it up, get the wheel spinning. Immediately losses begin to appear. From friction in the bearings to the magnetic pulls in the generator to air resistence - all this slows it down again. So to keep it turning you must power the drive continuously.

Yes, you are correct so far. We dump in 1kW and our magical drives are applying (still) 1kN at the edge of our wheel*. That's a lot of power and far more than the losses at this point---the wheel is only spinning at 1 rev per second after all (it's 1m across). If left unchecked, it would continue to accelerate for a while, but we don't leave it unchecked.

We're still dumping 1 kW in from an external source. And the EM drive continues to provide 1kN of thrust so 1kNm of torque.

So I say now connect it up to a brake, and keep putting in that external 1kW. If we are careful with the brake, we can stop the wheel accelerating but not slow it down. The EM drive keeps wanting to spin the wheel up, so we need to keep applying the brake. 1kW is still coming in from the outside.

So now what? Now replace the brake with a generator. From the wheel's point of view there is no difference. But given the numbers: 1N/W, 1m, 1 rev per second, there's about 6.3kW of power there. Now the "losses" come in. Let's assume we have a horrible 50% loss (easy to beat that in practice). Well, the generator will still be spitting out 3.1kW of electrical power into a load.

The wheel is still spinning and we're still putting in 1kW.

Now look at the balance. We've got 1kW of microwaves going in and 3kW electrical coming out. Domestic microwaves are about 64% efficient, so we can take 1.6kW of the electricity and generate 1kW of microwaves. and about 1.5kW of electricity is left over. We can now disconnect the external input, plumb in the newly generated microwaves and we have 1.6kW of electricity coming out all by itself.

That is absurd! Therefore the assumption that the EM drive works is wrong.

Therefore the EM drive cannot work.

QED.

And you really can't argue I've ignored the losses because they're all in there. Now, having had this argument several times, I'm going to climb on a soap box and have a rant. Fixating on losses makes these arguments massively more tedious. The thing is you're implicitly assuming there's some sort of practicality argument in that it only counts if the described machine is practical. There is none. If you can show over-unity performance with something theoretically possible but otherwise impractical then you have revealed a flaw in your physics.

It's the "perpetual motion machine" game. If your claims result in a perpetual motion ma

Re:Work done=kinetic energy

[silentcoder]

>I take the EM drive as it is claimed to work and show that IF it is true, the consequences are absurd.
But that's not TRUE. I proved that your claim of the consequences is false because it doesn't account for losses in the conversion process.

Re:Work done=kinetic energy

[silentcoder]

No saying "80%" is not "accounting for losses. It doesn't matter WHAT number you choose.

The only number where ANYTHING is a perpetual motion machine is 0%.

If it's not 0% then the thing will eventually stop unless you keep adding energy from outside.

The E.M. drive requires a continous supply of energy to function - lots of it.

If your numbers show anything except a guaranteed stop after a while - then it's your numbers that are wrong.

I am not arguing that the EM drive works OR that it doesn't - I believe that answer is unknown. I am arguing that your REASONING for dismissing it is flawed.

Re:Work done=kinetic energy

[silentcoder]

Note that nowhere is it claimed that any E.M. drive can produce more thrust than you could have gotten with the same energy using more conventional methods. It's just claimed to be using the energy directly instead of in a material fuel.

Consider this. Matter energy equivalence means it's possible to convert raw energy into matter.

If I could build a device that converts solar photons into hydrogen atoms (this is possible) - then I could build a rocket which fires hydrogen atoms out the back without putting any hydrogen on it, just my converter.
The problem is that it takes a LOT of energy to do the conversion - the same reason nuclear power provides so much, but the other way around. So to make my hypothetical device work that way I would need to have a massive battery or capacitor to store that solar energy over a very long time until there is enough of it stored to produce convert some photons into hydrogen and pump it out the back.
It's difficult - but not impossible. It's just that it would take years to produce enough to get a micronewton of thrust, then years for the next push... it's not very practical when a solar sail can also get thrust from photons without the insane delay. We know that's not how this device works - it doesn't use enough energy for it to be possible.

But it isn't doing anything the EM drive isn't claimed to be doing - getting thrust directly from energy without fuel. So that's what you need to compare it against. The best theories we have for the E.M. drive is
1) It's shape causes more photons to push out the back than push forward - and the thrust is from that, which makes it a less efficient reverse solar sail
2) It is creating one of those rare occasions where photons can interact with dark matter - and expelling the dark matter out the exhaust - in the latter case it is actually just a conventional rocket, the only difference is that it's fuel is something that is already abundant in orbit so we don't need to take it with us, we can just use it there. A bit like building a coal plant on top of a coal mine so you don't have to pay for transport of the coal.

The E.M. drive claims to convert energy to thrust. Lots of energy for very little thrust. Now thrust is work - of which energy is a component - but the energy in that small amount of thrust is FAR less than the energy that was used to produce it.
It's only a perpetual motion machine if it claims to produce more energy (or at least as much energy) as it consumes. That's almost certainly impossible. But the E.M. drive makes no such claims - it converts electrical energy into kinetic energy - at MASSIVE losses. A huge amount of electrical energy produces only a tiny bit of kinetic energy.

That is NOT a perpetual motion device. That your maths suggest otherwise proves that your reductio et absurdium numbers are merely absurd and have no resemblance to the claims. There is less kinetic energy produced than electrical energy used. Millions of times less. Hence it is not claimed to be a perpetual motion machine.

Re:Work done=kinetic energy

[serviscope_minor]

Strip out all the talk of EM drives, dark matter and losses and so on and we get this:

Me: The existence of X implies the existence of Y. Y is impossible therefore X is impossible.

You: No, Y is impossible therefore X cannot imply Y therefore X might not be impossible.

Your argument is flawed because your "therefore" above implicitly assumes X is possible. There is no reason that X cannot imply an impossible Y if X itself is not possible.

There are other confusions in your post but there is no point in addressing them until we sort out the above.

Re:Work done=kinetic energy

[silentcoder]

Not quite.

It's more like:
You: X implies Y. Y is impossible. Therefore X is impossible.
Me: X does not imply Y, your attempt to show that X implies Y is fatally flawed - not least for utterly misrepresenting the claims about X. Here is why.

I didn't say CANNOT imply Y. I proved that X DOES NOT imply Y.

In order for a device to imply perpetual motion the energy produced must be GREATER than the energy put in. In the case of this device it's smaller - in fact it's extraordinarily smaller. Smaller by 6 orders of magnitude. As an energy convertor this may be the least efficient device in history ! The steam engines designed by Hero of Alexandria 2500 years ago were 4 orders of magnitude more efficient !

If it's goal was to produce energy it would be the worst design ever conceived. Luckily, that isn't what it's for - because it would be significantly lessuseful for the purpose than trying to heat an appartment building by standing outside it and repeatedly slapping the walls with your hand. More of the energy from your food would actually be increasing the ambient temperature of the building than the kinetic energy the EM drive gets out of the electrical energy it uses.

Re:Work done=kinetic energy

[serviscope_minor]

Well if you're going to accuse me of dishonesty, then I think this is over.

I was mistake. I believed you were arguing in good faith. I have not once misrepresented the EM drive. It is claimed that it gives a force when fed with microwaves. Everything I said stems from that and that some.

You are absolutely making the error I claim. Your reasoning of nonspecific "losses" is precisely why a perpetual motion machine (And you need to stop spitting hairs over this--I'm quite clearly talking about a machine, i.e. Something that does work aka an over unity device---not merely something that runs for a long time in the absence of significant friction) cannot exist. So, you absolutely jumping to Y cannot exist, then working backwards in a logically flawed way.

You haven't disproved my claims either. You've attempted and failed to hand wave them away by claiming "losses". I've listed the losses in the system. You haven't. So either back up your arguing with something specific or abandon it. I've given actual numbers and simple equations. If I am wrong in my argument then there is an error. If you can't find it, or something equivalent then I don't think your argument has merit.

You're also compounding your mistakes by confusing force with energy and power. The steam engines of hero cannot keep applying torque to the shaft regardless of the speed because they use reaction mass. The EM drive keeps applying a force no matter the speed because it had no reaction mass. At that point it's simply a question of speed.

The fact you don't seem to understand the difference or relationship between force, speed and power and have no inclination to find out, makes me think that it's not worth pursuing this debate much further.

Re:Work done=kinetic energy

[silentcoder]

I never said you were deliberately misrepresenting it - but you still did. Force from energy is not a controversial claim - literally ever engine in the world does that.

>You are absolutely making the error I claim. Your reasoning of nonspecific "losses" is precisely why a perpetual motion machine (And you need to stop spitting hairs over this--I'm quite clearly talking about a machine, i.e. Something that does work aka an over unity device---not merely something that runs for a long time in the absence of significant friction) cannot exist. So, you absolutely jumping to Y cannot exist, then working backwards in a logically flawed way.

No I'm not, I'm saying you're still wrong even if one ignores the issue of losses. It can only be a perpetual motion machine if the output energy is not less than the input energy. We can calculate the output energy from the thrust generated - and it's 6 orders of magnitude LESS than the input energy. The fundamental definition of a perpetual motion machine has not been met - in fact this is literally the FURTHEST from a perpetual motion machine any machine ever built has ever been.

>You haven't disproved my claims either. You've attempted and failed to hand wave them away by claiming "losses".
Notice how in the last message I didn't mention that word at all ? I explained it - as in the previous paragraph by going back to basics: to what the definition of an impossible perpetual motion machine is - and how this doesn't meet that. If your numbers have output energy equalling or exceeding input energy - then they are not a fair representation of the claims. EVERY machine turns energy into force. As long as the kinetic energy in that force is LESS than the input energy required to produce it- you're safely in the realm of acceptable physics. There are things about this machine which, if it works, cannot be explained by current physics - but this is not one of them.

>You're also compounding your mistakes by confusing force with energy and power.
I did nothing of the kind. I specifically said the opposite. The thrust generated moves the device - the amount of thrust determines how much it can be accelerated by - which is the work done, from which you can calculate the kinetic energy gained. That energy is 6 orders of magnitude less than the energy required to produce it.

>The EM drive keeps applying a force no matter the speed because it had no reaction mass
So does EVERYTHING reaction mass has nothing to DO with that. If I have a rocket flying a 7Km/s in orbit, and I fire a lightweight ion engine, it will go faster. You apply a force, you get acceleration. Reaction mass has nothing to do with that and neither does the current velocity. The amount of acceleration is determined by the force applied and the mass of the object it is applied to. That's it.
The velocity (speed) also has *nothing* to do with whether or not it is a a perpetual motion machine. The ONLY thing that matter is whether the output energy is less than the input energy or not. And when you use a force to accelerate a moving object the output energy of the motor is NOT calculated based on the new speed of the object - it's calculated from the difference between it's former speed and it's current speed. The amount of acceleration achieved = the work done = the energy gained.

>The fact you don't seem to understand the difference or relationship between force, speed and power and have no inclination to find out, makes me think that it's not worth pursuing this debate much further.

I do - but you've not, at any time, given me any reason to believe that the infinitissimally small thrust claimed, could produce an acceleration that somehow means it did so much work that the energy gained is larger than the energy spent gaining it.

Ironically - the lack of reaction mass makes this LESS of a perpetual motion machine than any current rocket ! Yes LESS. Because the rocket equation works both ways. When a rocket burns fuel - it gets lighter, the remaining fuel

Re:Work done=kinetic energy

[serviscope_minor]

Of course force from energy it's not a controversial claim. I'm really not sure how you understood me so badly that you thought I said that. Force from energy without reaction mass is however.

We can calculate the output energy from the thrust generated - and it's 6 orders of magnitude LESS than the input energy.

Do so then and show your working. Unless you can get this step correct, there is no need to address your other points. Take the most recent figures of 1.2 mN/kW.

Re:Work done=kinetic energy

[silentcoder]

There's a missing number which neither of us has - the mass of the device. You need that to calculate the change in velocity which you need to calculate the kinetic energy.
My number is a best estimate given the 7 orders of magnitude difference between input energy and thrust.

Re:Work done=kinetic energy

[serviscope_minor]

No you don't. You are mistaken. It's basic physics that energy= force*distance so therefore power= force*velocity.

The mass doesn't come into it. If you do the maths with f=ma and e = mv^2/2 you will find the mass cancels out.

Now do the math and show your claim.

Re:Work done=kinetic energy

[silentcoder]

But you have no knowledge of
a, m or v.

The only factor you have is f - that's not enough. But I'm not the one making the claim (that their figures represent a perpetual motion machine) - you are, so the burden of proof is on you to do the math and show that e is bigger than 1 KW. Since watt is a measure of the rate of energy use - you actually don't even have the input energy.
You are claiming that output energy exceeds input energy - but you have no evidence to back up this (ridiculous) assertion. You just want us to accept it as a consequence of the lack of reaction mass without giving any evidence - but that is begging the question.

Now here's the clencher -the people who are testing this thing - at numerous independent labs around the world, include some pretty good scientists - their work is also being reviewed by top phycisists - people who most certainly WOULD raise a red flag if this things' output energy was higher than it's input energy. They have not done so. Nobody but you has suggested it - and the people who DO know the mass, the acceleration and the velocities certainly don't believe so.
Nobody but you believes it is possible, in fact, with ANY mass or acceleration from any velocity for this thing to produce more energy than it consumes.

The burden of proof is on you to show why you believe this claim. If you have access to the numbers for mass, velocity and acceleration then you can do so.

Re:Work done=kinetic energy

[serviscope_minor]

You have mentioned m and a again.

Are you seriously denying p=fv?

If you're prepared to accept that, I'll continue. If not, this is pointless since you've be discounting very well established physics.

Re:Work done=kinetic energy

[cwsumner]

Back when they were first considering producing electricity for power, some scientists did an analysis similar to these.

It was obvious that for greatest power transfer to occur, the impedance of the load should equal the impedance of the generator. The problem was that the power calculated in the generator woul be the same as the power calculated in the load. This obviously showed that any generators would burn up before being able to produce the greatest power levels. Therefore, no electric power distribution system would work.

Their analysis was correct. ... But their conclusions were wrong.

I reccomend you both examine your assumptions! ;-)

Re:Work done=kinetic energy

[RespekMyAthorati]

But your whole argument is based on the idea that you can use energy
to produce acceleration (delta-v) and then use that increased speed to generate more energy.
But you can't!
And that is the reason PM is impossible.

In other words, it's your bogus assumptions that defy physics, not the EM drive.

Re:Work done=kinetic energy

[serviscope_minor]

You are so close and yet so far. It's quite funny really.

PM is impossible, wet both agree.

If the EM drive worked you could indeed do what you're talking about. Ergo the EM drive is also impossible.

It's simple really. The existence of an EM drive implies perpetual motion. Perpetual motion is impossible therefore the EM drive is impossible. Your---and I use this phrase charitably---debunking is to simply bang on the "PM is impossible drum" as loudly as possible without taking the time to consider the deeper implications of that.

So well done for realising PM is impossible. When you understand how that implies the EM drive is impossible, you will have reached enlightenment. Or you know you can keep repeating the first point as if that is somehow news to me even though it is in fact the core of my argument.

NO YOUR WRONG PM IS IMPOSSIBLE

Duhhhhhhhhhhhhhhhhhh.

Re:how far can it be scaled up?

[Maritz]

It still seems too good to be true. I hope it pans out but I very much doubt it.

Re: how far can it be scaled up?

[Maritz]

The chair is pushing on the ground. Not a good analogy.

Re:How big is an EM Drive?

[Maritz]

If it works, sure. But it probably doesn't work.

Re: Propellantless doesn't mean reactionless

[guruevi]

Various measurements have shown that the shape of the box doesn't matter and the direction has been different in some of the measurements. According to Wikipedia: Of seven tests, four produced a measured force in the intended direction and three produced thrust in the opposite direction. Furthermore, in one test, thrust could be produced in either direction by varying the spring constants in the measuring apparatus.

This tells me that we're dealing with measurement errors. Sure, pumping energy into something will cause something to happen for various reasons but the forces acting upon it will be uniform in every direction thus cancelling out the energy used. It's like throwing a ball at a wall in a room. You are converting energy into forces on the ball and you are 'thrusted' in the opposite direction but then your ball hits the wall which is going to be exerting a force in the exact opposite direction (Newton figured that out a few centuries ago), even in a vacuum of space, if you have an enclosed room you can throw a ball at any wall repeatedly and it won't do shit because you're just cancelling out the forces, the only way you'll be exerting a force in any direction is by throwing balls out of an open window (expelling the mass and thus leaving you with a net thrust force in whatever opposite direction)

Re:Misleading

[Maritz]

Hmm. I bet Pons and Fleischmann are kicking themselves that they didn't get all their cold fusion trademarks in order.

In this case "rewrite" IS accurate

[Roger W Moore]

Rewriting the laws of physics is roughly as accurate as...

Not in this case. Our current laws of physics say that this is an impossible device IF it operates as claimed and is not due to some effect they have not accounted for (my money is on the latter). Hence this is one of those times when a rewrite really would be required. This device appears to violate some of the most fundamental symmetries of nature changes like that are huge...but need phenomenal evidence to support them which is so far very much lacking.

Re:In this case "rewrite" IS accurate

[Ol Olsoc]

Rewriting the laws of physics is roughly as accurate as...

Not in this case. Our current laws of physics say that this is an impossible device IF it operates as claimed and is not due to some effect they have not accounted for (my money is on the latter). Hence this is one of those times when a rewrite really would be required. This device appears to violate some of the most fundamental symmetries of nature changes like that are huge...but need phenomenal evidence to support them which is so far very much lacking.

the Good Doctor White declares this is Zero point energy doing the work. So I would suggest that the EM engine be powered by a fine Cold Fusion reactor.

Yeah, harnessing ZPE would be quite a trick. It would mean that we can extract energy from the quantum vacuum. It would also mean that QV is not indestructible, that we are warping space-time. White says the scaling frm 100 watts that gave 50 microNewtons will give us 6 Newtons at 10 KW and 1300 Newtons at 100 Kw. That would make for a wicked graph. And this thing kicks ass in simulation. Then again, many things do.

Regardless, the idea has to be researched, competition and stuff, you know. It's pretty cheap to do the experiments. And hey, if we have found a way to harvest ZPE, we've pretty much solved all of our energy problems.

I won't even hold my breath.

Re:Misleading

[Maritz]

They're unlikely to be propelling any satellites so I wouldn't worry overmuch.

Re:Propellantless doesn't mean reactionless

[Ol Olsoc]

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".

I suspect that if this thing were ever proven to work, that it won't violate any laws, because the reaction mass is coming from the outside - what hits the engine.

But the whole thing smells like cold fusion, and as you point out, it's a rubbish engine even if it does actually work.

Re:It supposedly has no exhaust, a closed system

[T.E.D.]

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 ....

Your "random Youtuber" is in fairly good company though. Among other skeptics, there's a Mathematical Physicist at UC, and Physicists and UT-Austin and Caltech who have publicly scoffed.

The produced thrust is so low that measurement or experiment error seems a quite likely explanation. Even its designer at NASA freely admitted in his peer-reviewed paper on the engine that there is no mainstream theory in Physics that can explain his reported results.

I'm not saying he's wrong. But thinking up something that shouldn't work, but you want it to, then building it, is just not how science works. If he'd found a weird result in some other experiment, didn't understand it, but decided to try to use it to build an engine, THAT I'd understand. Most of what we know about electricity came about exactly that way. This thing's history has much more resemblance to the various perpetual motion machines that somebody's always coming up with.

So I'm going to go with History and with the Physicists on this one.

Re:It supposedly has no exhaust, a closed system

[guruevi]

Even high school physics can debunk these claims. The problem is that any tests so far have been thoroughly debunked. The Chinese had a 'success' which couldn't be reproduced. NASA had a success but when moved to a vacuum chamber to account for the thermal reaction it suddenly stopped working so well, the problem being that we can't get a space-like vacuum nor lack of gravity on earth.

One of the later tests could change the direction of thrust simply by changing the springs on the measurement apparatus and half the tests have measured thrust in one direction while others have measured thrust in the opposite direction it's supposed to go.

Re:Propellantless doesn't mean reactionless

[serviscope_minor]

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.

you don't know when it fails!

[kiviQr]

If you do not know how it works you do not know when it will stop working! Sending a mission to Mars and learning that you can't go back may not be that great.

Re:you don't know when it fails!

[Immerman]

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 encounter any mysterious performance fluctuations, then it's reasonable to assume that the basic principle is sound and reliable, and more powerful drives are unlikely to be any less reliable (barring mechanical issues). And if we do see performance fluctuations, well then it will be a question of whether we can learn to predict those fluctuations (maybe thrust varies with the proximity of other masses, the slope, curvature, or depth of gravity wells, or the speed relative to any of those), and if not then it will presumably at least offer a glimpse at some other unexpected phenomena happening in our solar system, and still be useful in applications where reliable performance isn't essential - probes can mostly drift until thrust resumes, but you might want to include a backup ion drive in your space ship, or at least have such emergency "tugboats" on standby if thrust has been known to fail for long periods.

Re:For FFS it doesn't violate anything

[Maritz]

Well done you explained it. Now go and play with the worms in the garden.

Re:pulling

[Maritz]

You can't "pull" if you cannot "push" yourself. You'd imagine that'd be obvious.

Re:No, they' re doing it wrong! Idiots

[Maritz]

Just because you can, doesn't mean you should. Better to have something that you've a reasonable expectation that it will do something. This isn't there yet, probably never will be.

Re:It supposedly has no exhaust, a closed system

[T.E.D.]

My personal favorite line from its Wiki:

In 2015, Shawyer published an article in Acta Astronautica, summarising existing tests on the EmDrive. Of seven tests, four produced a measured force in the intended direction and three produced thrust in the opposite direction. Furthermore, in one test, thrust could be produced in either direction by varying the spring constants in the measuring apparatus

I suggest that this should instead be referred to as the Experimental Error Drive.

I know how they work

[goombah99]

EM drives so far have never measure continuous acceleration (that is to say creating kinetic energy and creating momentum). They have only measured static force, usually a torque.
      An electric motor has lots of torque but it will never go anywhere at all in a frictionless environment. A vibrating spring has apparent force on one end, but it's not going anywhere because the net system has a stationary center of mass. This is the same case as separated charges of electric or magnetic monopoles and dipoles.

Thus the EM drive is nonsense till you use it to go somewhere in free space. I note that a planetary orbit is not free space. There's magnetic and electric feilds ou there. We already know that charged object can feel a torque in those magnetic fields (look at the Aurora).

My guess is the EM drive is some sort of induced dipole between itself and the earth.

How they work is they don't, if were talking propulsion and not static force or vibration or rotation.

Re:I know how they work

[Immerman]

Heck, even if they work as a magnetic drive, they still work, and could be useful at least for orbit maintenance. It then simply becomes a question of whether they are more or less useful than other magnetic drives.

I agree though that testing them in interplanetary space will be the real test of whether they'll revolutionize space travel or not. I mean, even if they're pushing off dark matter or something, it's quite possible that DM clumps around planets, and that thrust will be drastically reduced in open space.

Re:I know how they work

[Alioth]

If it is an interaction with the Earth's magnetic field, that's not to say it's useless - a propellant-less means of satellite station keeping in Earth orbit would still be useful iff the effect scales up sufficiently.

Not necessarily anything with physics. magic trick

[raymorris]

> we KNOW that some part of the laws of physics are WRONG. We know that NOW

Not at all. What we know is that we don't know why this thing appears to work. Have you ever seen a magic trick? I can make a wooden stick simply vanish right before your eyes. I can make it instantly re-appear somewhere else. Your observations will directly conflict with your knowledge of physics. That doesn't mean your understanding of physics is wrong, it only means you don't know how the trick works.

Did you know there's a magical battery that never runs out of power, and chemicals in the battery never seem to change, they don't undergo any chemical reaction. The selenium battery seemed to violate the conservation of energy. It took 70 years to fully understand where the power was coming from, from the LIGHTS IN THE LAB. The selenium was turning light into electricity. There's no contradiction with the laws of physics, just an effect that was not understood at the time. That's all we have with the EM drive right now - an effect we don't yet understand. Scientists are trying to find the cause by ruling out possibilities such as reactions with the atmosphere - zinc-air batteries are commonplace, air can be an energy source.

Re:Propellantless doesn't mean reactionless

[serviscope_minor]

But you're saying we can't physically exceed it,

Yes.

, so your theory is broken somewhere.

My theory predicts the EM drive doesn't work otherewise we could go over unity.

maybe it maxes out at 1/10 c (or whatever the relativistically correct fraction would be)

At 1/10c it would be very far over unity even with the current measurement of millinewtons per kilowatt.

And besides, 1/10c relative to what? If you're proposing relative to some absolute frame of reference, then conservation of momentum has gone out of the window, so there's no need for finding reasons why it conserves momentum.

Re:how far can it be scaled up?

[gweihir]

Not at all. At this time there is a tiny chance this thing will produce a minuscule amount of thrust if fed a lot of energy. The far larger chance is that there is a measurement error that us tricky to find.

Re:Misleading

[gweihir]

Ah, so there is a second group of fraudsters trying to capitalize on the success of the first group to con the public into believing something with grossly insufficient evidence?

Re:No, they' re doing it wrong! Idiots

[gweihir]

There can be no test in orbit until you get significant thrust for a reasonable amount of energy. This thing cannot do that. It gives you a tiny trust for a lot of energy, that is if it works at all. Because the thrust is so tiny, smart people actually expect this will turn out to be an equally tiny measurement error.

My reaction?

[hoggoth]

I read the article... but I have no reaction.

Re:It isn't the aether, then

[jandersen]

If I redefine aether as "the gaseous envelope of earth", this doesn't make the aether real. And neither does redefining aether as "space-time" make aether real.

We don't know what reality is - even the best models are only models. This is true for the ether theory as well as for GR and QM. The ether theory was quite plausible for a time, but as it turned out, it was too elusive and unwieldy, and when relativity came along, it gave a much simpler and more intuitive model. But neither GR and QM are reality - both theories must in the end fail, and we already know something about where: GR's assumptions about smoothness don't hold at the singularity that is assumed to exist in the centre of black holes, for example, and QM's standard model offers no clue to what "dark matter" and "dark energy" may be.

A lot of the concepts used in physics are just placeholders for things we donÃt understand, but which we can describe phenomenologically: force fields, particles, mass, electric charge etc. This enables us to make calculations, but it doesn't really add to our understanding in the sense that is explains these things in terms of something more fundamental - only general relativity attempts that with some success, in that it replaces the force of gravity with the interaction between inertial mass and the shape of space-time.

Re:Propellantless doesn't mean reactionless

[HuskyDog]

Except that according to its inventor (www.emdrive.com) thrust is related to not only power and cavity design, but also velocity. The net effect of this is, he claims, that the device has a terminal velocity of around 30km/s which is well below "free energy" speed. Note: I don't claim this is true, it is just what Shawyer wrote.

Re:Propellantless doesn't mean reactionless

[Carewolf]

2a causes reaction against something external like magnetic fields or air.

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.

I think we're in agreement!

Wouldn't 2a mean the law of conserved momemtum in its current form is wrong? I mean if you can cause a reaction with an external magnetic field that generates thrust without projecting energy/mass in any direction, that is basically what people are claiming about the EM drive?

Execute the management of PopSci

[AbRASiON]

In front of their fucking children.

I've emailed these fucking assholes before about this.
http://www.popsci.com/emdrive-...
That link ONLY works in the United States.

As soon as it picks up an Aussie IP address, it does this.
http://www.popsci.com.au/?src=...

They don't mirror the content and it's been going on for multiple years, I'm so fucking sick of it.
Sorry but these people are moronic, it's the internet for fucks sake, there are no borders.

Does anyone with a god damn clue have some kind of contact there, how to stop these assholes doing this stupid shit?

Re: 3uN/kW

[slashrio]

How is that a fundamental upper value of the thrust-to-power ratio?
(You didn't say that cruncing the maths right would lead to this value.)
What I'm aiming at is that if the efficiency of the photon drive can be increased enough, the over-unity 'problem' could possibly return.
If it's a fundamental limit, then I guess there also must be a theoretical relationship to the law of no-over-unity-allowed (CoE? c?).

Re:It supposedly has no exhaust, a closed system

[HiThere]

You are probably incorrect to conflate "eagle-works" was it? with NASA, but several reasonably respectable groups have reported small positive results. And I'm including the "eagle-works" report in the "reasonably respectable groups". So it's likely to be correct, and it's also likely to fall within the bounds of current physics, even if nobody can really explain why just yet. Physics has a lot of stuff in it with complex interactions, so it's quite reasonable that it should include things that nobody has thought of putting together in quite that way yet which produce results that aren't what anyone expected. This is because complex systems often have unexpected interactions. If you go back 200 years nobody expected that it could explain thought. And maybe it doesn't, and we still need some more basic explanations, but that's not the way to bet.

Re:Propellantless doesn't mean reactionless

[slashrio]

Loss doesn't seem to be a fundamental theoretical concept that has to be taken into consideration here.

Re: 1/10 c

[slashrio]

1/10c relative to what?

It's origin 'of course'. That's the point of zero speed. If there weren't a point of reference, over-unity wouldn't be a problem, as we wouldn't know where to measure the speed, and kinetic energy, against.

Hmm, sounds shaky. Let me counter myself here:
Suppose a planet far far away with established zero speed relative to earth (mars at a certain point of time?), the EM Drive would crash into that planet with a higher kinetic energy than has ever been supplied by its power source...
So hmm, perpetual motion indeed if we would be able to capture and store that energy, put it in another, bigger, EM Drive and send that one back to earth and then capture that energy.

We would have free energy forever. :)
Well, ok, and then there's solar, so we don't even need it...

Re:Propellantless doesn't mean reactionless

[serviscope_minor]

30 km/s relative to what?

That's not an idle question. It's a very fundamental property of known physics that an absolute reference frame does not exist. In fact, conservation of momentum stems from that.

Re:Propellantless doesn't mean reactionless

[serviscope_minor]

Nope, it wouldn't be wrong: that's how electric motors work. That well end up as force on the thing today's generating that magnetic field, and anyway the field itself has energy and momentum.

Chances are either this is a very inefficient helicopter (it's shifting air around) or a very inefficient electric motor.

Re:Propellantless doesn't mean reactionless

[Carewolf]

Nope, it wouldn't be wrong: that's how electric motors work. That well end up as force on the thing today's generating that magnetic field, and anyway the field itself has energy and momentum.

Chances are either this is a very inefficient helicopter (it's shifting air around) or a very inefficient electric motor.

Well an electric motor does cause a reaction, it is just that the mass it projects backwards is the surface of the Earth, so it is kind of slight.

Re:Propellantless doesn't mean reactionless

[locofungus]

Except that according to its inventor (www.emdrive.com) thrust is related to not only power and cavity design, but also velocity. The net effect of this is, he claims, that the device has a terminal velocity of around 30km/s which is well below "free energy" speed.

And the solar system is orbiting the galactic centre at a speed of in excess of 200km/s. Therefore, according to its inventor, the EMDrive doesn't work.

QED.

Re:It supposedly has no exhaust, a closed system

[cwsumner]

... NASA had a success but when moved to a vacuum chamber to account for the thermal reaction it suddenly stopped working so well, ...

No, it didn't. ;-)