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China's Radical New Space Drive
First time accepted submitter Noctis-Kaban writes "Scientists in China have built and tested a radical new space drive. Although the thrust it produces may not be enough to lift your mobile phone, it looks like it could radically change the satellite industry. Satellites are just the start: with superconducting components, this technology could generate the thrust to drive everything from deep space probes to flying cars. And it all started with a British engineer whose invention was ignored and ridiculed in his home country."
The principles behind the EmDrive have serious theoretical problems, and the original builder and designer never tested it in a vacuum chamber.
Taking a sealed container and pumping a few kilowatts of microwaves into it, chances are any thrust developed is actually air that's getting heated up and expanding out of the container. Unless the EmDrive has been put in a vacuum chamber where this can be demonstrated to definitely not be the case (i.e. low enough that their couldn't be enough reaction mass) then it's not actually working.
How about this headline: "Discredited British Engineer Finds New Scam Victims in China." His invention is "a closed, conical container which, when filled with resonating microwaves, experiences a net thrust towards the wide end." Sounds realistic.
"First they came for the slanderers and i said nothing."
The thrust is reported to be from the large end towards the small end. The entire body of this thing that's heating up from a few kilowatts of microwaves would be warming air that flowed over the surface and thus imparting energy to it and providing a source of thrust. It would easily provide continuous thrust.
From the article: "Seems to violate law of conservation of momentum". - Yup it does. Imagine putting an invisible mass-less box around the entire system. Almost nothing comes out the back (only microwave energy - more on that later). The center of mass of the box accelerates. This is a violation of conservation of momentum - one of the most well understood and best tested laws in physics. If there were some exotic high energy physics effect proposed for this at least it might be worth listening, but this is just electromagnetism - very well understood. The "group velocity / phase velocity" is just jargon that has nothing to do with this since it is the Poynting vector that carries momentum.
You CAN make a reaction drive using photons (microwaves in this case), this idea has been around for many decades. The problem is that photons carry a lot of energy relative to their momentum so it takes an enormous power source to produce any thrust. So far no one has found a practical application where there was a large enough energy (and high enough power ) source to make this practical.
There have been a lot of experiments with microwaves - I've personally worked on a 600MW pulse microwave system. There have even been attempts at microwave driven spacecraft sails. Some early experiments seemed to indicate more thrust than would be expected from momentum conservation. Eventually this was tracked down to gas absorbed on the surface being heated and released by the microwaves - essentially a conventional rocket. With very high microwave powers you can generate forces in all sorts of ways in a closed laboratory environment that would not work in space.
This will not work.
No more Anonymous Coward posts? Whatever shall we do?
The correlation between ignorance of statistics and using "correlation is not causation" as an argument is close to 1.
From TFA: Propellant can account for as much as half the launch weight of a geostationary satellite. This means that, in principle, fitting one with an EmDrive rather than a conventional drive, could halve launch costs.
That depends entirely on the power system needed to operate the drive. That's the real Achilles heel of various non chemical propulsion systems - they eat a lot of juice and the resulting power supplies negate most (if not all and then some) of the savings of not carrying conventional fuel.
The FAQ deals with conservation of momentum, allowance for bouyancy, electromagnetic effects, convection and other issues here: http://emdrive.com/faq.html. A fantastic picture of the device on this page: http://emdrive.com/.
Here are some of the FAQ answers:
Q. Why does the EmDrive not contravene the conservation of momentum when it operates in free space?
A. The EmDrive cannot violate the conservation of momentum. The electromagnetic wave momentum is built up in the resonating cavity, and is transferred to the end walls upon reflection. The momentum gained by the EmDrive plus the momentum lost by the electromagnetic wave equals zero. The direction and acceleration that is measured, when the EmDrive is tested on a dynamic test rig, comply with Newtons laws and confirm that the law of conservation of momentum is satisfied.
Q. Are there any convection currents which might affect the results?
A. Convection currents did not affect the results, as measurements were taken with the thrust vector up, down and horizontal. Test runs were also carried out using a thermal simulation heater to quantify the effects of change of coolant temperature.
Q. Have electromagnetic effects been taken into account? These include interactions between current-carrying conductors and between such conductors carrying RF currents and nearby metallic structures in which currents might be induced.
A. Stray electromagnetic effects were eliminated by using different test rigs, by testing two thrusters with very different mounting structures, and by changing the orientation by 90 degrees to eliminate the Earth’s magnetic field.
experiment (since IANAP), I do want to say that there seems to be a troubling trend amongst the best and the brightest in many STEM fields to mistake theory for reality. Theory is great and proceeds under the scientific method from empirical observation, but as we've seen throughout history, new phenomena and corner cases to arise and require theory to be amended.
It's fine to say "this is clearly unlikely to work under current theoretical understandings" but let's also refine and do the experiments to the best of our ability so that science remains scientific (i.e. nominally empirical and ultimately practical in nature). There's a difference between taking "current theory suggests this is likely to fail" as a statement of fact and mistaking theory instead to be *evidence* about experimental outcomes.
No theoretical argument can be evidence for the reality or unreality of phenomena, no matter how well-formed. That's not to say that we ought to mistake the phenomena at issue—it's obviously critical to be able to understand, rather than misconstrue, the reality that we observe—only that sometimes a generation or two of scientists seem to get complacent and imagine that they've got the world all figured out after all.
Let's continue to do, and—to the best of our ability and within reason (but with "within reason" here broadly defined—allocate resources for, actual experimentation and empirical observation of the world around us.
Not that we don't—but to my eye, the attitude that if theory doesn't support it, it's always a waste of money to test it out experimentally, is a dangerous one for the future of a science that is far less uniform, linear, and accumulative in its progress than we often tend to remember.
STOP . AMERICA . NOW
All the usual signs of pseudoscience.
Show it works (note : that is not the same as saying that you have shown it works), and I'll be interested. Until then, this goes in the cold fusion circular file.
... , and the original builder and designer never tested it in a vacuum chamber.
maybe try reading the context of a post before inserting the snark next time?
"The thrust is reported to be from the large end towards the small end. "
No, TFA says:
"... experiences a net thrust towards the wide end."
A surprisingly non-sceptical article; I'd expect a bit more critical thinking from Wired. Terms like "group velocity" and quantum theory", used vaguely, don't help you avoid the fact that conservation of momentum is fundamental to modern physics. It's just as inviolable as conservation of energy.
To put it another way, this article makes Wired look just as gullible as they would if they wrote "Scientists in China have built and tested a perpetual motion machine."
It's really the same thing as the conservation of energy. What we really have is the conservation of four-momentum, which is standard special relativity. You can Lorentz transform one (energy) into another (momentum) (within limits).
... sort of. And it is established physics. See Swimming in Spacetime: Motion by Cyclic Changes in Body Shape, Science, 2/27/2003, by Jack Wisdom.
But this mechanism relies on general relativistic effects, and only works in curved spacetime. Momentum conservation is not violated, because while the location of the object changes, its momentum (thus velocity) does not -- it simply cyclicly translates itself through space.
My first thought reading about the EmDrive was that Shaywer had found a way to reproduce this effect using a microwave cavity. But unless I'm mistaken, this does not appear to be the case, and I don't follow the arguments that Shaywer's drive should work.
It blatantly violates conservation of both momentum and energy. It's advertised as being useful for spacecraft propulsion, changing the momentum of the spacecraft without emitting anything that would carry equal momentum in the opposite direction. If Shawyer's claims were true, an EmDrive placed on end in a gravity field would be either an energy sink or source (depending on orientation) with infinite capacity. I see no reason why anything else on the site should be treated as any more trustworthy.
From my perspective, Einstein muddied the entire subject by equating reality with what is observed and using that false premise
The new scientific method is here! Make some wild guess about how the universe must work because that's how you'd like it to work, then call all previous work foolish and flawed. Done. Wait, didn't we used to do something similar to that?
I find it hard to believe that the Nation that is home to the Ministry of Silly Walks has ridiculed a scientist for his strange ideas. . .
These are my friends, See how they glisten. See this one shine, how he smiles in the light.
Start with null, not negative. Also avoid language like 'proven'. Then lecture about what is skeptical and what isn't.
Sorry, no. The whole point of skepticism is to assign a negative (false) value to anything but proven assertions.
That's a related concept properly called positivism.
It is a miracle that curiosity survives formal education. - Einstein
If you imagine that - you need to study up on your history. It was known that the earth was round and orbited the sun a long, long time before those two showed up.
It's hard to believe that's how Micronians are made. Why don't we see it right now by having you both kiss one another?
Just get one of these things and test it under rigorous scientific conditions and scrutiny.
If it works, it works; If it doesn't it's back to the drawing board and we can all move on.
Al this fucking shitbrained arguing over nitpicky sematic points is just maddening. Put up or shut the fuck up, because we don't want to hear your not-based-on-anything-that-counts armchair scientist opinions.
EM can serve as reaction mass, but it creates very little momentum.
This shows the problem :
http://en.wikipedia.org/wiki/Nuclear_photonic_rocket
PS. with antimatter/matter fuel a photonic drive would make sense.
"Sorry, no. The whole point of skepticism is to assign a negative (false) value to anything but proven assertions. You may still be in the realm of empiricism, but you are not being skeptical."
Not at all. As a skeptic, it behooves me to judge which is more likely, based on actual evidence. (And if I do the job properly it should be good, solid evidence.) But if I waited until everything was proven I'd be waiting past the heat death of the universe. As "causality" pointed out, what you advocate is positivism, not skepticism.
I'll never understand why simply saying "I really don't know, but it may be possible" is so damned difficult.
It seems to me like another silly ego game to declare something false when it has not been falsified, (ab)using the concept of positivism by taking it to an extreme just so you can tell somebody else that they're wrong. Yes, the burden of proof is indeed on the person making a claim, but hiding behind that to smugly declare that something "is false" is a roundabout way to make a claim yourself (that something is false) while excusing your own burden of proof (falsify it or admit you don't know). It's an attempt to put the other person at a disadvantage to "get even with them" for having a different inclination.
If you look deeply at human behavior, you will see for yourself that most people have a desperate need to feel superior in some way to another human being. It is not enough that someone be right; someone else must also be wrong. It is not enough that someone explains their opinion; someone else's must be bullshit. It's not enough to disagree with something; the other person must be put down or mocked or denigrated in some manner. Always there is an attempt to hide this by giving it the appearance of legitimacy.
Yes, in hard sciences positivism is a good thing. It prevents a lot of pseudoscience and weeds out a lot of false notions. But there is a distinction between "we're going to treat this as though it were false for now, but if you have other evidence please show me" and "this absolutely is false and I'm closing my mind now".
As far as it concerns Slashdot, I wish people would grow up, get some emotional maturity, deal with their petty little insecurities, and realize that the only real sense of worth human beings ever find comes from within yourself. It does not come from the relativity of making another person look worse than yourself and the attempt to do that is completely childish. Sadly it's also accepted as normal because it is so common.
It is a miracle that curiosity survives formal education. - Einstein