NASA claims to have tested a "reactionless" space drive, and it works.

August 1, 2014 8:41 AM

Early days, but if true => BIG change
posted by aleph (215 comments total)

Actually, it violates conservation of momentum, which means that the testers are misunderstanding the data, rather than the device "working".
posted by Avenger at 8:49 AM on August 1, 2014 [9 favorites]

Actually, it violates conservation of momentum, which means that the testers are misunderstanding the data, rather than the device "working".


Whew! Ok. Nothing to see here.
posted by kbanas at 8:52 AM on August 1, 2014 [7 favorites]

...three sets of independent researchers who all got the same results.
posted by radiosilents at 8:52 AM on August 1, 2014 [6 favorites]

Actually, it violates conservation of momentum"

Isn't that why this would be "BIG change"?
posted by NervousVarun at 8:54 AM on August 1, 2014 [11 favorites]

Actually, it violates conservation of momentum, which means that the testers are misunderstanding the data, rather than the device "working".

Yes, it does seem infinitely improbable.
posted by Atom Eyes at 8:54 AM on August 1, 2014 [75 favorites]

Warp drive here we come!
posted by monospace at 8:55 AM on August 1, 2014

I found the abstract here. Quoting what I think is the most interesting aspect:
"Thrust was observed on both test articles, even though one of the test articles was designed with the expectation that it would not produce thrust. Specifically, one test article contained internal physical modifications that were designed to produce thrust, while the other did not (with the latter being referred to as the "null" test article). "

So, if I am reading this correctly, even when the device does not fit into his design that is supposed to use virtual plasma to push, it still works.

Can anyone find the full paper?
posted by Hactar at 8:57 AM on August 1, 2014 [2 favorites]

I tell you what: I will bet you my entire life savings that this device does not produce "reactionless" momentum. If a device can be constructed that violates conservation of momentum, then it could also double as a free-energy device as well, which means that money (and scarcity) itself would be meaningless.

Actually, it violates conservation of momentum"

Isn't that why this would be "BIG change"?
posted by NervousVarun at 8:54 AM on August 1 [+] [!]

The problem with these kinds of stories is that people always underestimate the consequences of physics-breaking devices. A reaction-less drive would not just allow us to explore space more freely, it would actually turn us into gods who can manipulate the universe at will.

Hence, it's probably not true.
posted by Avenger at 8:57 AM on August 1, 2014 [28 favorites]

> also : "Nasa"? NASA.

Copyediting in the UK permits capitalizing only the initial letter of an acronym pronounced as a word. Thus: Nasa, Fifa, Faq, etc. Examples from The Guardian's Style Guide.
posted by ardgedee at 8:59 AM on August 1, 2014 [28 favorites]

Dean Drive, it's just another Dean Drive, it's rubbish science.
posted by MartinWisse at 9:00 AM on August 1, 2014 [2 favorites]

The problem with these kinds of stories is that people always underestimate the consequences of physics-breaking devices. A reaction-less drive would not allow us to explore space more freely, it would actually turn us into gods who can manipulate the universe at will.

*goes shopping for cape and helmet*
posted by Brandon Blatcher at 9:00 AM on August 1, 2014 [26 favorites]

Actually, it violates conservation of momentum

Yeah, but thee Casimir effect "violates" conservation of energy, right? Two metal plates suddenly start moving towards each other of no accord? The implication of the Wiki article on the EmDrive posits a few possible non-classical theories by which this is not a violation of conservation of momentum.
posted by Maecenas at 9:00 AM on August 1, 2014 [5 favorites]

Also from the abstract: "Testing was performed on a low-thrust torsion pendulum that is capable of detecting force at a single-digit micronewton level, within a stainless steel vacuum chamber with the door closed but at ambient atmospheric pressure."

Now I'm no rocket scientist, but isn't the very purpose of this hypothetical "microwave drive" to provide thrust in the vacuum of space? So if the chamber is full of air, doesn't that invalidate the whole experiment? Seems if you're going to go to the trouble of getting a vacuum chamber, maybe you should evacuate it?

I don't know. If anyone can shed light on why this alone doesn't wreck the results, I'd love to hear it.
posted by Joey Buttafoucault at 9:00 AM on August 1, 2014 [2 favorites]

It's 'reactionless', Avenger, not 'powerless'. As in, no chemical reaction required. No one is saying it outputs more power (thrust) than it takes in (electricity).
posted by Frayed Knot at 9:00 AM on August 1, 2014 [10 favorites]

Actually, it violates conservation of momentum, which means that the testers are misunderstanding the data, rather than the device "working".

Or it means that our current understanding of conservation of momentum is missing some things. Newtonian mechanics has certainly been Jossed by relativity before.

I'm agnostic about the physics of this (it does seem highly unlikely to bear fruit), but I'm really, really psyched at the drive's name: The Cannae Drive. DUDE.
posted by pie ninja at 9:01 AM on August 1, 2014 [8 favorites]

Wait...if this drive was reactionless, wouldn't this thread be empty?
posted by yoink at 9:01 AM on August 1, 2014 [37 favorites]

It's powered by the opinions of amateur scientists on the internet.
posted by 2bucksplus at 9:02 AM on August 1, 2014 [61 favorites]

The drive's inventor, Guido Fetta calls it the "Cannae Drive",

I wonder what Lieutenant Commander Montgomery Scott would have to say about it.
posted by Sys Rq at 9:03 AM on August 1, 2014 [11 favorites]

Either this device is doing something, in which case we learn something, or it's not doing anything and we find something else, in which case we learn something.

So basically we win either way.
posted by truex at 9:04 AM on August 1, 2014 [18 favorites]

Avenger: Doesn't conservation of momentum apply to closed systems only?
posted by I-baLL at 9:04 AM on August 1, 2014

Yeah, it seems like this is just saying that there is some need for further testing, perhaps in a vacuum. Here's where the EM Drive people claim it should work. Something something relativity.

The problem with these kinds of stories is that people always underestimate the consequences of physics-breaking devices. A reaction-less drive would not allow us to explore space more freely, it would actually turn us into gods who can manipulate the universe at will.

Yeah, as pointed out, they're claiming to turn electricity into momentum without further chemical reaction. It sounds like it's using a bit of geometry and the relativistic speed of microwaves to get the effect. Which is crazy, but isn't a free energy device...
posted by kaibutsu at 9:06 AM on August 1, 2014 [8 favorites]

paging physicsmatt .......... physicsmatt to the press-release-de-nonsense-phone
posted by lalochezia at 9:09 AM on August 1, 2014 [9 favorites]

So what did the null test article actually do and include? It might help to understand the distinction between a device "designed with the expectation that it would not produce thrust," and, say, a banana, which also does not produce thrust.

Does that part indicate that they failed to eliminate some other input that looked like thrust to their instruments but wasn't actually coming from the device at all? Or did they somehow try to make an engine that wouldn't work and fail because they don't fully understand how this thing works. Or doesn't work.

I'm confused. Just give me a Mr. Warp Drive and spare me all this science mumbo-jumbo. y'all motherfuckers lyin' and gettin' me pissed
posted by Naberius at 9:09 AM on August 1, 2014 [2 favorites]

Faster! We must comment faster, or else someone might have enough time to go and actually read the fucking article.
posted by Behemoth at 9:10 AM on August 1, 2014 [20 favorites]

It's not reactionless. It got a reaction out of me.
posted by dances_with_sneetches at 9:10 AM on August 1, 2014 [4 favorites]

I wonder what Lieutenant Commander Montgomery Scott would have to say about it.

He'd probably say "RTFA." Captain.
posted by The Bellman at 9:12 AM on August 1, 2014 [12 favorites]

Back in the 90s, Nasa tested what was claimed to be an antigravity device based on spinning superconducting discs. That was reported to give good test results, until researchers realised that interference from the device was affecting their measuring instruments. They have probably learned a lot since then.

One would hope?
posted by Naib at 9:12 AM on August 1, 2014

It's powered by the opinions of amateur scientists on the internet.

That's nothing - Ed Begley Jr. developed a go cart powered by his own sense of self-satisfaction
posted by bitteroldman at 9:12 AM on August 1, 2014 [3 favorites]

a banana, which also does not produce thrust.

Says you. An infinite supply of bananas saved my bacon that one time I was trapped on the middle of a frictionless surface. All I had to do was squeeze and glide.
posted by Iridic at 9:12 AM on August 1, 2014 [12 favorites]

Can't speak for everyone Behemoth, but I read this yesterday and was primed and ready to slam my fingers against the keyboard like so many terrifying mobile sausages.
posted by truex at 9:13 AM on August 1, 2014 [6 favorites]

Appears we'll learn more about applying group velocity correctly from work around the EmDrive either way, sounds useful.
posted by jeffburdges at 9:16 AM on August 1, 2014

He'd probably say "RTFA."

Dammit, Scotty, I'm a doctor, not a finish-reading-the-paragraph-before-rushing-over-to-make-a-lame-joke-er!
posted by Sys Rq at 9:16 AM on August 1, 2014 [14 favorites]

I wonder what Lieutenant Commander Montgomery Scott would have to say about it.

He'd just smirk at the newb who didn't read the article.
posted by Brandon Blatcher at 9:16 AM on August 1, 2014 [1 favorite]

However, it's hard not to suspect that Star Trek's Engineer Scott -- "I cannae change the laws of physics" -- might also be an influence. (It was formerly known as the Q-Drive.)

The Q Drive, on the other hand, merely changed the gravitational constant of the universe.
posted by bicyclefish at 9:17 AM on August 1, 2014 [13 favorites]

I'm curious: Among those who are stating staunchly that the device does not and cannot work, would you suggest that further testing should stop? Should the scientific community look at the results from NASA et. al. and say "Well, that's nice, but it violates physics, so let's leave it alone and work on something else"?
posted by lore at 9:17 AM on August 1, 2014 [5 favorites]

I dunno. If this work it fits perfectly with hippybear's "Living in Hollywood Screenwriter Reality" hypothesis.
posted by Luddite at 9:19 AM on August 1, 2014 [8 favorites]

also : "Nasa"? NASA.

If this turns out to be true it should hereafter be known as
NASA!
posted by DigDoug at 9:24 AM on August 1, 2014 [3 favorites]

also : "Nasa"? NASA.

In most UK style books, acronyms aren't automatically all caps, they're initial caps if they're spoken as a word, and all caps if you say the individual letters, thus, the BBC, but Nasa. If the acronym has entered the language as an ordinary word, it's all lower case (laser, pin number, sim card.) Unless, of course, it starts a sentence.
posted by eriko at 9:25 AM on August 1, 2014 [4 favorites]

I'd suggest that when dealing with aspects of the physical world which involve quantum physics that we leave the common sense aside to some extent and take a critical look at he quality of the experiments and data in the eyes of experts, and reputation of the researchers and their organizations before passing judgement based upon common sense and college physics. If there is anything that the last 10-20-30 years have taught us about physics is that sometimes what we think we know, we really don't know even though the quality of our 'knowing' is really getting much better all the time.

IOW I mean, its physically impossible for something to be in two places at the same time, amirite?
posted by sfts2 at 9:30 AM on August 1, 2014 [9 favorites]

can it get a spaceship up to ludicrous speed?
posted by pyramid termite at 9:33 AM on August 1, 2014 [5 favorites]

Writing off improbable findings before seeing any of the data is about as helpful to the process of discovery as endorsing it. Take heart, people who find this stuff interesting, your curiosity is a good and merited thing as we await the math bits of this story.
posted by late afternoon dreaming hotel at 9:35 AM on August 1, 2014 [13 favorites]

...three sets of independent researchers who all got the same results.

All that means is that the original researchers executed their experimental procedure as written. It doesn’t show that the experimental procedure itself isn’t flawed or that the conclusions (reactionless thrust) follow from the data.

What’s more likely, three groups of researchers don’t entirely understand the phenomenon they’re observing or we’re very wrong about fundamental physics and countless scientists and experiments have failed to discover it till now?

Breakthroughs happen, but for every Geiger–Marsden Experiment there are many OPERAs or polywaters.
posted by Fongotskilernie at 9:35 AM on August 1, 2014 [1 favorite]

lore: Among those who are stating staunchly that the device does not and cannot work, would you suggest that further testing should stop? Should the scientific community look at the results from NASA et. al. and say "Well, that's nice, but it violates physics, so let's leave it alone and work on something else"?

Of course not! It's an interesting device, the results seem rather far-fetched, so people are going to keep poking at it cautiously, from a distance.

Your comment suggests two misunderstandings. First of all, "NASA et al." are the scientific community. And second, young scientists dream of finding something that violates the laws of physics! No one wants to waste time on a wild goose chase, but if there's something real there... [eaten by a bear]
posted by RedOrGreen at 9:38 AM on August 1, 2014 [2 favorites]

...it would actually turn us into gods who can manipulate the universe at will

So some sort of hyperbole drive?
posted by furtive at 9:39 AM on August 1, 2014 [34 favorites]

Among those who are stating staunchly that the device does not and cannot work, would you suggest that further testing should stop?

I think ~zero people think this. This is sort of like the time-traveling neutrino thing: the more fundamental law of physics your experiment appears to have violated the more likely it is your experiment is flawed. So you do more experiments in different ways to see what you got wrong.

The fact that the test was done in an atmosphere and the fact that the 'dummy' article produced thrust are pretty big signs pointing to the experimental setup vs new physics but we'll find out!
posted by Skorgu at 9:40 AM on August 1, 2014 [8 favorites]

The fact that it consumes energy is more encouraging to me than any concern about violating the law of conservation of momentum, and pretty much answers any argument about perpetual motion. Newtonian laws are inescapable for effects at familiar scales, velocities and levels of energy but have to be modified in ways we're barely beginning to understand when you get outside those ranges. If it didn't consume energy it would be a lot weirder.
posted by George_Spiggott at 9:44 AM on August 1, 2014

The two issues I have with the NASA research as described in the abstract. (I don't have access to the full paper.)

1) The results were done at ambient pressure. I'd like to see them replicated in vacuum.

2) Both test articles produced thrust, one of them was expected not to. This, however, wasn't a true null article, both were built by the company wanting to demonstrate the device.

But there's a lot of interesting things here that NASA can't explain offhand.

So what did the null test article actually do and include?

I suspect that detail is in the full paper. Alas, the full paper is online but not free.

Should this turn out to be real, it's a pretty big deal. Even at these low levels of thrust, the total ΔV available when you don't have to carry propellant mass is limited only by the time you can thrust - which would be limited by your power source, and the reliability of that power source and the thruster itself.

It could easily shave 60% off the mass of a geostationary satellite if they can wait a long time for the actual orbit insertion. It would still shave a goodly amount off if they carried convention propellant to get into GSO, and then used this thruster solely for station keeping.

It's very much the kind of thing that won't get you anywhere fast, but could get you about anywhere. It won't directly make getting to orbit cheaper, to get to LEO, you don't need micronewtons of thrust, you need meganewtons of thrust. But once you beaten by most of the atmospheric drag, all high thrust gives you is quick changes in ΔV. Low thrust over long time will give you the exact same ΔV.

Now, having said all of that. These sorts of papers are published when the team working on something looks at everything they can think of and can't find out what's happening. The purpose is to get a lot more eyes on the problem. Usually, this results in someone finding out either a missed force or a hidden problem with the experiment. (See the supraliminal neutrinos LHC reported.) So, don't be surprised if this turns out to be nothing.
posted by eriko at 9:48 AM on August 1, 2014 [7 favorites]

Actually, it violates conservation of momentum

Is that true? From The Article: "the drive may work by pushing against the ghostly cloud of particles and anti-particles that are constantly popping into being and disappearing again in empty space."
posted by stbalbach at 9:48 AM on August 1, 2014 [1 favorite]

Also, see maglev propulsion and railguns. Those convert electricity to acceleration without propellant.
posted by George_Spiggott at 9:49 AM on August 1, 2014

can it get a spaceship up to ludicrous speed?

Give me 1N of thrust on a 1000kg probe without having to carry reaction mass, and I get get a ludicrous number of nines close to c. It'll take a while, but it'll get there.

91mN of thrust would work too -- it would just take even longer.
posted by eriko at 9:50 AM on August 1, 2014 [2 favorites]

it's a bit confusing from the article, but there's two different drives being talked about here. Fetta's Cannae drive, whose NASA tests are documented here, is measured producing an unexplained ~0.05 millinewtons of force. Shawyer's EmDrive, which was tested by the Chinese team, was measured to have ~88 millinewtons of force, or about 2000x the Cannae drive. For context, the claimed EmDrive force is in the range of currently used ion drives. But not having to carry any propellant is an enormous advantage.

Actually, it violates conservation of momentum

Well now that we've established a random Metafilter commentor is smarter than the NASA scientists who did the experiment, let's look a little deeper.

The fine Wired article which we have all read carefully says "the drive may work by pushing against the ghostly cloud of particles and anti-particles that are constantly popping into being and disappearing again in empty space". The Linked Emdrive explanation says

The inevitable objection raised, is that the apparently closed system produced by this arrangement cannot result in an output force, but will merely produce strain within the waveguide walls. However, this ignores Einstein’s Special Law of Relativity in which separate frames of reference have to be applied at velocities approaching the speed of light. Thus the system of EM wave and waveguide can be regarded as an open system, with the EM wave and the waveguide having separate frames of reference.

I'm not equipped to evaluate the plausibility of these explanations; I don't even understand if they're equivalent somehow. But it sure sounds interesting, particularly in the context of two separate experiments verifying some sort of unexplained effect. It will probably turn out to be some previously unaccounted for measurement problem, like cold fusion or the Pioneer anomaly. But it takes more than a sophomore physics student waving his hands about Newton's laws.

pretty much answers any argument about perpetual motion

Fortunately no one is making any claims about perpetual motion. Again, from the fine article, the innovation here is "eliminating the need for the supply of propellant that occupies up to half the launch mass of many satellites."
posted by Nelson at 9:52 AM on August 1, 2014 [11 favorites]

Ok, someone just tell me this: If this is real, interstellar travel? In our lifetimes? Yes?

I've waited so long.
posted by If only I had a penguin... at 9:53 AM on August 1, 2014 [2 favorites]

"Wrap it up, guys, WeedSmoker420 debunked us by typing FAAAAAAKE! It's over."--NASA scientists.
posted by Ghostride The Whip at 9:54 AM on August 1, 2014 [24 favorites]

Avenger: “Actually, it violates conservation of momentum, which means that the testers are misunderstanding the data, rather than the device ‘working’.”

Is anybody – even the proponents of the device – actually trying to say that physics is invalid? If this happened, then there's probably an explanation that accords with the law of the conservation of momentum ("interaction with the quantum vacuum virtual plasma," &c.)

The issue here is not whether the law of the conservation of momentum is valid or not. It's whether this actually happened. And if it happened, then there's almost certainly some way in which it does accord with the law of the conservation of momentum.

I mean – if I drop a ball, and it comes back up at my face, I don't say "that's impossible, because gravity!" I say: "well, there must be some other explanation, like maybe there are magnets in the floor and in the ball, or maybe there's a hidden wire, or maybe the ball just bounced."
posted by koeselitz at 9:54 AM on August 1, 2014 [7 favorites]

> Fortunately no one is making any claims about perpetual motion.

Yes they are, in this thread:

> If a device can be constructed that violates conservation of momentum, then it could also double as a free-energy device as well, which means that money (and scarcity) itself would be meaningless.
posted by George_Spiggott at 9:56 AM on August 1, 2014 [2 favorites]

Nelson: “Fortunately no one is making any claims about perpetual motion. Again, from the fine article, the innovation here is ‘eliminating the need for the supply of propellant that occupies up to half the launch mass of many satellites."”

George_Spiggott: “Yes they are, in this thread:”

Avenger: “If a device can be constructed that violates conservation of momentum, then it could also double as a free-energy device as well, which means that money (and scarcity) itself would be meaningless.”

No. Nobody in this thread has claimed that this device actually violates conservation of momentum, as far as I can tell.
posted by koeselitz at 10:00 AM on August 1, 2014

(Nor do any of the scientists involved here.)
posted by koeselitz at 10:00 AM on August 1, 2014 [1 favorite]

Uh, this is bullshit. For example, correlation doesn't equal causation. Stupid scientists.
posted by MisantropicPainforest at 10:01 AM on August 1, 2014 [4 favorites]

No. Nobody in this thread has claimed that this device actually violates conservation of momentum, as far as I can tell.

Except maybe in those exact words in the very first comment?
posted by George_Spiggott at 10:01 AM on August 1, 2014 [5 favorites]

Momentum can be carried by electromagnetic fields; photons msot definitely have momentum. In fact the pressure from the light of the sun at Earth's distance is, if I recall, roughly 1000 times more than the pressure from actual solar wind particles. Thus the idea of a solar sail which operates by reflecting the photons from the sun and gaining thrust from them.

So this doesn't inherently violate any laws of physics, though if my math is correct you'd need about a 10 kW beam (about 10 decently powered microwave ovens worth) in order to generate 30 uN of thrust just by photon pressure alone. It looks like these tests were done at more like 20 W, so that's not a convincing explanation.

The short answer is there's any number of ways this could be interacting with the environment, none of which require violation of momentum conservation. I mean the fact that the RF device the creator said shouldn't work produced thrust, too, indicates that there's something probably perfectly ordinary going on from the perspective of classical/relativistic electrodynamics. And until they show this thing actually producing acceleration in a vacuum, they haven't really shown that it generates a steady thrust, only a static force.
posted by Zalzidrax at 10:01 AM on August 1, 2014 [2 favorites]

Say, did anybody else notice who Cannae's "Creative Lead For Media" is? Joel Hodgson. As in that Joel Hodgson.

So instead of wondering how it violates the first law of thermodynamics and other science facts, just repeat to yourself "It's just a show, I should really just relax."

Joel actually touched on his involvement with Cannae in this Nerdist Podcast interview from last year.
posted by Strange Interlude at 10:03 AM on August 1, 2014 [11 favorites]

Except maybe in those exact words in the very first comment?

Someone on MetaFilter said something that is wrong. And someone else wrongly said they didn't say it. Maybe! News at 11.
posted by stbalbach at 10:03 AM on August 1, 2014 [3 favorites]

Also, see maglev propulsion and railguns. Those convert electricity to acceleration without propellant.

They don’t differ from ordinary trains in this regard, though. They’re both firmly reaction‐based. Their propellant just happens to be the Earth.

Rockets prove that you don’t need to push against something external, but you can if you want to. Either way, you need reaction mass somewhere.
posted by Fongotskilernie at 10:09 AM on August 1, 2014 [3 favorites]

Luddite: "I dunno. If this work it fits perfectly with hippybear's "Living in Hollywood Screenwriter Reality" hypothesis."

If living in the reality branch governed by Hollywood Screenwriter Logic means we get to skip the death of the planet and go and explore the stars, well, that's fucking awesome.
posted by Happy Dave at 10:11 AM on August 1, 2014 [1 favorite]

Thanks for unwinding all that, George Spiggot.

I propose we just move on past the "this violates what I learned in high school physics" comments that derailed the discussion and move on to what the actual article and related links are saying. Which is that there's a device which appears to be generating propulsion through a new mechanism and the theory is a bit confusing, but may rely on quantum vacuum fluctuation or special relativity.

Extraordinary claims require extraordinary evidence and so far all we have are a couple of outsider engineers pushing their new engines and a few independent experiments appearing to confirm some effect. We're right where we were with cold fusion when that news first broke. It's worth looking at more closely, but I'm still skeptical it will turn out to be something.
posted by Nelson at 10:15 AM on August 1, 2014 [4 favorites]

They don’t differ from ordinary trains in this regard, though. They’re both firmly reaction‐based. Their propellant just happens to be the Earth.

My point. The fact that we don't see the reaction force doesn't mean that electric motors or railguns or solenoids violate the laws of nature. All we needed was magnetism to complete that picture.

And for this to not violate any physical laws, we just need empty space to not be empty. And nobody in physics has actually thought it is for some decades now so we should be good here.
posted by George_Spiggott at 10:17 AM on August 1, 2014

Since the device evidently depends on virtual particles, and since one theory of dark energy is that it's an effect of virtual particles, they should call it the Dark Energy Drive: DED.

Wait...if this drive was reactionless, wouldn't this thread be empty?

Well, yes -- your point?
posted by jamjam at 10:18 AM on August 1, 2014

I wonder if adding those invisible spam links to the bottom of their About page was also part of Joel's job. I guess there's some synergy there, one of them is to 'researchpapers4sale.com'.
posted by steveminutillo at 10:20 AM on August 1, 2014 [2 favorites]

There's an interesting precedent in optical (as opposed to microwave) wavelengths for this drive, called a photonic laser thruster that uses a resonant cavity to amplify radiation pressure (in the cited case, by a factor of about 3000). Of course, the ends of the resonant cavity are on different spacecraft.

I think it would a good idea to avoid standing in the axis of that microwave device. I think it leaks power.
posted by the Real Dan at 10:22 AM on August 1, 2014

me: “No. Nobody in this thread has claimed that this device actually violates conservation of momentum, as far as I can tell.”

George_Spiggott: “Except maybe in those exact words in the very first comment?”

Nope. It does not say that this device actually violates conservation of momentum. Like I said, nobody is claiming that.
posted by koeselitz at 10:22 AM on August 1, 2014

(On reading your other comments, George_Spiggott, I gather we're both getting at the same thing. The claim that "this can't work, because it violates the conservation of momentum" is a canard a bit like "airplanes can't work, because they violate the law of gravity" – that is, assuming that this must violate a fundamental law of physics and therefore can't be happening is hasty and ignores the fact that there are a whole lot of variables in any experiment we don't know about and haven't explained yet. If this is actually happening the way it seems to be happening, it's almost certain that it's happening well within the law of the conservation of momentum.)
posted by koeselitz at 10:25 AM on August 1, 2014 [1 favorite]

First of all, "NASA et al." are the scientific community. And second, young scientists dream of finding something that violates the laws of physics! No one wants to waste time on a wild goose chase, but if there's something real there... [eaten by a bear]

In this case, by "NASA et al." I meant "those who replicated the experiment." Clearly they're part of the scientific community, but they're not the entirety of it.

More to the point, I wasn't asking if the scientific community will continue to look into it, or if scientists, young or otherwise, want to replicate it. I was asking if the people here on Metafilter who are stating, without looking at the actual data - that it does not and cannot work - most of whom I suspect are armchair scientists, not actual researchers -- think that the scientific community shouldn't look into it.
posted by lore at 10:26 AM on August 1, 2014 [1 favorite]

Ahh, something I missed on the NASA experiment.

There were *three* test devices, not two. Two were build by Cannae LLC, one of them was expected not to work, but did. The third was an RF load they pumped the same amount of energy into, to see if that energy was reacting with the torsion balance to create force, it did not create any.

So, that's why the fact that the 2nd test article did produce thrust didn't kill the experiment -- a pure RF load in the same place produced no thrust at all.
posted by eriko at 10:29 AM on August 1, 2014 [1 favorite]

As much as I lkke the Cannae Drive, I suggest that, since it can apparently run on anything that produces electricity and isn't dependent on a chemical reaction, "Indifference Engine" would also be a good name.

The Indifference Engine doesn't care that you don't think it works.
posted by 1adam12 at 10:33 AM on August 1, 2014 [17 favorites]

So to sum up, if it doesn't violate conservation of momentum it's boring. If it does, it doesn't exist.
posted by edd at 10:35 AM on August 1, 2014 [6 favorites]

The Indifference Engine doesn't care that you don't think it works.

The Honey Badger Drive.
posted by ChurchHatesTucker at 10:41 AM on August 1, 2014 [6 favorites]

But I want to be a god, godammit.
posted by Guy_Inamonkeysuit at 10:46 AM on August 1, 2014

The Indifference Engine doesn't care that you don't think it works.

The Honey Badger Drive.

Don't you mean the Honey Babbage Drive?
posted by Mei's lost sandal at 10:48 AM on August 1, 2014 [6 favorites]

Or the Honey Barbara Drive, which compels you to plant trees.
posted by George_Spiggott at 10:50 AM on August 1, 2014

I mean – if I drop a ball, and it comes back up at my face, I don't say "that's impossible, because gravity!" I say: "well, there must be some other explanation, like maybe there are magnets in the floor and in the ball, or maybe there's a hidden wire, or maybe the ball just bounced."

You forgot the devilish "I'm hanging by my feet from the ceiling" gambit.
posted by Celsius1414 at 10:53 AM on August 1, 2014 [3 favorites]

And then there's the Hanna-Barbera Drive, which is a reactionless form of locomotion employed by Flintstones characters which involves running in place above the ground for a moment then suddenly launching forward with a "sproing" without your feet ever touching the ground.
posted by George_Spiggott at 10:53 AM on August 1, 2014 [6 favorites]

More than giving us godlike visages, or allowing us to flout the laws of physics, this
will stimulate the economy!
posted by Chitownfats at 10:57 AM on August 1, 2014

Not to mention the Hannah Montana Drive, which CAME IN LIKE A WRECKING BALL.
posted by Strange Interlude at 10:59 AM on August 1, 2014 [2 favorites]

If it turns out that this thing actually works, could it be used in land-based vehicles?
posted by showbiz_liz at 11:00 AM on August 1, 2014

Direct full-text PDF link here. Hopefully that works without authentication.

It's only a one-pager, should be a quick read for anybody who wants to see the whole thing.
posted by zug at 11:03 AM on August 1, 2014 [2 favorites]

could it be used in land-based vehicles?

To kill everything in its wake, yes.
posted by Mei's lost sandal at 11:13 AM on August 1, 2014 [3 favorites]

If only I had a penguin...: “Ok, someone just tell me this: If this is real, interstellar travel? In our lifetimes? Yes?”

Interstellar? It's roughly a decade round-trip (Earth-time) to Proxima Centauri at 1g. This doesn't seem to be providing that much acceleration. Interplanetary? Totally doable. Even at 0.01g a Titan round-trip is only 5 months.
posted by ob1quixote at 11:14 AM on August 1, 2014 [1 favorite]

Or the Honey Barbara Drive, which compels you to plant trees.

Omigod. My day cannot get any better, I'm in a state of Bliss.
posted by DoubtingThomas at 11:18 AM on August 1, 2014

Interstellar? It's roughly a decade round-trip (Earth-time) to Proxima Centauri at 1g. This doesn't seem to be providing that much acceleration. Interplanetary? Totally doable. Even at 0.01g a Titan round-trip is only 5 months.

Huh...well I don't see how staying in our own solar system will save humanity when the sun burns out, or help us meet other civilizations and found the Federation, or any of the cool stuff I am hoping to do. I realize it's 10 years round trip is a bit much for touristing purposes, but it seems possibly feasible for colonizing, right? Anything around there we can colonize?

I don't know what a G is. How many Gs fast is this thing likely to go? ANd if it only takes to microwaves worth, can't you just put in 100 microwaves and go ten times faster?
posted by If only I had a penguin... at 11:20 AM on August 1, 2014

Oh, the link sort of explains Gs. I thought it was just a citation on the time. So I see even the centre of the Galaxy is only 20 years. We should go there. Check it out.

I just looked it up and Earth is pretty much on the edge of the Galaxy, which means travelling the galaxy end to end would take about 40 years. Why did Voyager initially think it would take them 75 years to get back from the Delta quadrant?
posted by If only I had a penguin... at 11:27 AM on August 1, 2014

I think that should be "c" -- as in the speed of light -- not "g". Proxima Centauri is about 4.2 light years away, so if you were moving at the speed of light, it would appear to observers on Earth that a round trip took a little more than 8 years. But your own experience of the thing would be very different. If you were traveling at 0.9c, for example, from Earth, it would look like it took you about 4.7 years to make the trip. But from the ship, it would look like it took only about 2 years. At 0.99c, you're down to 6 or 7 months from the perspective of the ship. My point being that if you want interstellar travel and don't care about coming back to a world more or less as you left it, then getting close enough to the speed of light makes it doable.
posted by Jonathan Livengood at 11:29 AM on August 1, 2014

G. Harry Stine, doubtless influenced by his experience investigating the Dean Drive, wrote a novel (pseudonymously) called "Star Driver" about the development of a "sky hook' which essentially used a standing RF sawtooth wave in a plasma which produced propulsion because science. In the novel it passes the "pendulum test", a way of ruling out resonant frictional effects and the like which of course the Dean Drive didn't. The novel has the protagonist mounting it mid-fuselage in his Cessna 182, and then turning off his engine at altitude and flying on the "star drive" alone. A fun, silly read, which I knew nothing of the context of until this post, which motivated me to to a little background reading.
posted by George_Spiggott at 11:30 AM on August 1, 2014

Nope, scratch that first bit. I should have actually read the link. The rest is right, though.
posted by Jonathan Livengood at 11:31 AM on August 1, 2014

You forgot the devilish "I'm hanging by my feet from the ceiling" gambit.

Also the "I am a hapless cartoon coyote" one.
posted by XMLicious at 11:34 AM on August 1, 2014

I just looked it up and Earth is pretty much on the edge of the Galaxy, which means travelling the galaxy end to end would take about 40 years. Why did Voyager initially think it would take them 75 years to get back from the Delta quadrant?

Probably because they wanted to get back in less than a billion years as measured on Earth. The idea of Warp Drive is that there's no time dilation effect because you're not 'moving' in a conventional sense. So you get to have both interstellar travel and a TV show about it that has story lines accessible to humans in 1966.
posted by George_Spiggott at 11:35 AM on August 1, 2014

I don't know what a G is.

The g is "Gravitation acceleration (Earth)" -- that is, an acceleration the same as the acceleration created by Earth's gravity at the surface. It's roughly 9.8m/s². We use 1g as a reference because that's what we experience here on Earth. Similarly, we define planetary distances by Astronomical Units (AU), which is based on the average distance between the Earth and the Sun.^*

How many Gs fast is this thing likely to go?

Wrong unit. Gees are a unit of acceleration, which is change in velocity over time. Actual velocity is measures in meters per second (m/s) rather than meters per second per second. (m/s²)

The faster your acceleration, the quicker you'll get to something near light speed. Light speed in a vacuum (represented by the letter c) is the absolute fastest you can go in the universe.

1G acceleration is a fair amount. A fast but not incredibly expensive car can accelerate around .5g. The Bugatti Veyron, one of the fastest production cars in the world, can accelerate at 1.55g. You can see much higher accelerations under turns and braking -- many cars can brake at more than 1g, and an F-1 race car will see over 5g in some turns.

You can see much higher accelerations, but only over very short time scales. A soccer ball kicked by a professional striker accelerates at around 300g for a fraction of a second. A baseball on a full contact hit sees 3,000g. Human beings have survived 100g accelerations for very short intervals of time, but usually they won't, 100g is considered the lethality limit in most crashes. The simplest way to reduce the gees felt is to increase the time over which that force is applied. So, a car hitting a wall at 60mph pulls about 100g, but the airbags and seat belts mean you experience that force over a much longer time period, pulling only 10g during the event.

A typical parachute hits you with about 20-40g for a very brief instant when the canopy pops open. During WWII, when the chute opened on the stiff end of that range, there were many cases of paratroops blacking out when the chute opened, and it occasionally happens today.


* It's now defined as exactly 149,597,870,700 meters.
posted by eriko at 11:38 AM on August 1, 2014 [12 favorites]

This violates the laws of physics, grammar, and decency.

So it's probably true.
posted by blue_beetle at 11:39 AM on August 1, 2014 [1 favorite]

> If this is actually happening the way it seems to be happening, it's almost certain that it's happening well within the law of the conservation of momentum.

If this really is a "reactionless" drive, then it is breaking the law of conservation of momentum.

If you claim it isn't breaking that law, somewhere else, something has to be losing the moment you have gained. Given the description of the experiments so far, what would that "thing" be?

That said, The Law of Conservation of Momentum is just a name for "a lot of observations so far all showed..." And breaking it wouldn't have the ramifications of breaking other laws like the Conservation of Mass/Energy.

I'm already thinking about how you would change dynamics with this, and it just wouldn't be a problem. You'd create imaginary "momentum sources" that simply added momentum to the system. Everything would still work out to zero....

"Extraordinary claims" of course. But these seem reputable scientists. I'm eager to see...
posted by lupus_yonderboy at 11:53 AM on August 1, 2014

Should probably read the rest of the thread. If it's electromagnetically "pushing against space", in a manner vaguely analogous to a maglev train or a railgun pushing against coils without actually touching them, then it's not reactionless. We just have to suppose that the interesting properties of "empty space" that are currently being investigated include something that can be pushed against.
posted by George_Spiggott at 11:56 AM on August 1, 2014 [2 favorites]

So you get to have both interstellar travel and a TV show about it that has story lines accessible to humans in 1966.

Pretty sure Voyager has story lines that are accessible to humans in 1995 or so. It would be shocking if they were accessible in 1966, but perhaps they are powered by this new drive and thus violate the space-time continuum.
posted by hippybear at 11:59 AM on August 1, 2014

> If it's electromagnetically "pushing against space", in a manner vaguely analogous to a maglev train or a railgun pushing against coils without actually touching them, then it's not reactionless.

That is not correct. If it isn't breaking the law of conservation of momentum, then something else has to change to make up for the extra/missing momentum, and that has to be something with mass (by the very definition of momentum) - and empty space, being massless, is not a candidate.
posted by lupus_yonderboy at 12:00 PM on August 1, 2014

If it's electromagnetically "pushing against space", in a manner vaguely analogous to a maglev train or a railgun pushing against coils without actually touching them, then it's not reactionless.

You're entirely missing the use of "reactionless" here.

Basically, every engine we use for space travel is based on chemical reactions to produce thrust. This requires fuel, chemical fuel of varying sorts, which gets used up over time.

This drive, if it actually does what it seems to do, does not use chemical fuel at all. It uses electricity, converted to microwaves, to create thrust.

Exactly how or why it is maybe creating thrust remains to be investigated. It is possibly pushing against something, yes, but that is not a "reaction" in the way they are meaning in this context.

The ability to use electricity as fuel is an exciting one, because you could collect energy via solar panels and then burn that energy to create thrust. You wouldn't require a chemical reaction or expendable fuel, you would just need photons streaming out of a nearby star, something which is really plentiful in this particular region of space.
posted by hippybear at 12:04 PM on August 1, 2014 [2 favorites]

A typical parachute hits you with about 20-40g for a very brief instant when the canopy pops open. During WWII, when the chute opened on the stiff end of that range, there were many cases of paratroops blacking out when the chute opened, and it occasionally happens today.

Military parachutes are designed to get you to the ground as quickly as safely possible, while civilian ones are typically designed to let you linger a bit more. Does that mean civy parachutes pull more Gs?

and empty space, being massless, is not a candidate.

It's a candidate now.
posted by ChurchHatesTucker at 12:05 PM on August 1, 2014

The assumption is space is not empty, but contains quantum vacuum virtual plasma. In fact we know this is true, but possibly it can be made useful, which would be neat.

Sort of a Maxwell's demon situation for momentum instead of thermodynamics?

Some details already on the always trustworthy wikipedia
posted by pseudonick at 12:08 PM on August 1, 2014

Not sure the people who study such things believe that space is actually empty anymore, for any number of reasons and theories. Dark matter, dark energy, spontaneously generated bits and pieces of matter and anti-matter...

There's a lot more going on in the places which look black to us than simply nothing.
posted by hippybear at 12:10 PM on August 1, 2014

This is a scifi side note but If only I had a penguin don't forget when doing the math on interstellar travel for purposes of actually colonizing somewhere to include the need to decelerate. Otherwise you shoot past whatever your destination is. Even assuming this fancy new drive idea works it still needs to spend energy decelerating equal to that which it spent accelerating (though I suppose you could cheat a bit by aerobraking if your destination had an atmosphere).
posted by Wretch729 at 12:14 PM on August 1, 2014 [1 favorite]

You're entirely missing the use of "reactionless" here.

I was just about to say something similar.
posted by roystgnr at 12:14 PM on August 1, 2014

Obviously it's pushing against the luminiferous aether.
posted by Pyry at 12:20 PM on August 1, 2014 [5 favorites]

and empty space, being massless

This is an example of commensensical language being fairly useless for these sorts of discussions. If you mean some sort of platonic empty space which not only contains no particles or energy, including dark energy, virtual particle/anti-particle pairs, and which you basically define as massless in order to call it "empty space" then yes, it's not only massless but a tautology to say so.

But if you're saying that that's what the actual space in our universe is, then please show your work.

You're entirely missing the use of "reactionless" here.

The article is using it wrong, that's for sure. Not expelling a carried propellant != "reactionless", and therefore not necessarily impossible even in conventional physics.
posted by George_Spiggott at 12:23 PM on August 1, 2014

> You're entirely missing the use of "reactionless" here. Basically, every engine we use for space travel is based on chemical reactions to produce thrust

I hate to keep correcting people, but that is also not correct.

Reactionless has nothing whatsoever to do with chemistry.

First, not every existing drive uses chemical reactions to produce thrust. We already have tested ion drives, though not particularly finalized. Space elevators are perfectly consistent as an idea, though it's unknown if they are technically feasible.

A drive that doesn't use chemical reactions isn't surprising and it doesn't break any laws.

But we aren't talking about "chemical reactions" - we're talking about Newton's Third Law, "For every action there's an equal and opposite action."

That breaks laws - Newton's Third Law, and the Law of Conservation of Momentum, which is basically the explanation of Newton's Third Law.
posted by lupus_yonderboy at 12:24 PM on August 1, 2014 [2 favorites]

> But if you're saying that that's what the actual space in our universe is, then please show your work.

The burden of proof is on you - I'm claiming your idea is impossible. If you're telling me that you're "pushing against space", please show me where the momentum is going! :-)

To say, "the momentum is going into empty space" isn't a meaningful idea as far as I can see - you're basically saying, "Momentum is not conserved."
posted by lupus_yonderboy at 12:26 PM on August 1, 2014 [1 favorite]

Physicists are still at a loss to explain Morrissey, who gets closer the more he is ignored.
posted by dr_dank at 12:29 PM on August 1, 2014 [4 favorites]

Rockets work in space. What are they pushing against?
posted by ChurchHatesTucker at 12:29 PM on August 1, 2014

I wonder what Lieutenant Commander Montgomery Scott would have to say about it.

I wonder what Hannibal would have to say.
posted by kirkaracha at 12:30 PM on August 1, 2014

lups_yonderboy, your presumption that momentum must only be in the form of solid matter is wrong. Electromagnetic fields carry energy and momentum.
posted by Zalzidrax at 12:31 PM on August 1, 2014

> Rockets work in space. What are they pushing against?

They aren't. It's Newton's Third Law.
posted by lupus_yonderboy at 12:31 PM on August 1, 2014

The burden of proof is on you - I'm claiming your idea is impossible. If you're telling me that you're "pushing against space", please show me where the momentum is going! :-)

I've made no claim to prove. I don't know that this thing works. I'm saying that the counterarguments are uninformed supposition based in part on the inadequacy of mundane language. As far as empty space being empty, a good popularizer to start with would be Lawrence Krauss. "If you removed all of the particles, all of the radiation, absolutely everything from space and all that remained was nothing, that nothing would weigh something."

Rockets work in space. What are they pushing against?

The propellant that they carry. Stand on a skateboard in a gym and throw a medicine ball hard.
posted by George_Spiggott at 12:32 PM on August 1, 2014 [3 favorites]

Rockets work in space. What are they pushing against?

You are about to get piled on by like six people who will tell you some convenient fiction like that rockets push against their own exhaust. But I'll tell you the Truth that we all known in our hearts: rockets push against the aether.
posted by Pyry at 12:32 PM on August 1, 2014 [5 favorites]

From the FAQ:

Q. Is the thrust produced by the EmDrive a reactionless force?
A. No, the thrust is the result of the reaction between the end plates of the waveguide and the Electromagnetic wave propagated within it.

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.


posted by bellastarr at 12:32 PM on August 1, 2014 [7 favorites]

> lups_yonderboy, your presumption that momentum must only be in the form of solid matter is wrong. Electromagnetic fields carry energy and momentum.

Sure, that'd be fine too. If you told me that this machine worked by using existing electromagnetic fields and pushed against them, that could be convincing. But I'm not seeing that that's what they're claiming at all.
posted by lupus_yonderboy at 12:32 PM on August 1, 2014

Lupus_yonderboy. Read the article, the brief abstract, or the wikipedia page.

Empty space is not empty, it is a sea of temporary particles. Allegedly this drive pushes against that sea. Whether this works, I don't know, it does sound like Maxwell's demon to me in a lot of ways. This would lead to an abnormal distribution of quantum fluctuations as a 'wake' maybe?

These aren't crackpots, and freshman physics isn't a surprise to any of them.

CHT: Rockets throw out material behind them, that pushes them forward.
posted by pseudonick at 12:33 PM on August 1, 2014 [3 favorites]

ardgedee: Copyediting in the UK permits capitalizing only the initial letter of an acronym pronounced as a word. Thus: Nasa, Fifa, Faq, etc. Examples from The Guardian's Style Guide.

Surely you mean "Copyediting in the Uk...". ;)
posted by IAmBroom at 12:34 PM on August 1, 2014 [6 favorites]

Having a bit of trouble here: the microwave creates thrust when its radiated out and when its absorbed again. Are they reflecting the microwave without the microwave acting on the reflecting thing and sending it straight back up to 'act' in the original direction of movement? Is it somehow just generating more force on absorption that it created in the opposite direction on emission? The primary articles are behind a pay wall.
posted by Slackermagee at 12:34 PM on August 1, 2014

Even assuming this fancy new drive idea works it still needs to spend energy decelerating equal to that which it spent accelerating

That's why nearly all real proposals about interstellar travel involve the vehicle turning around about halfway through its journey and applying the drive which got it up to whatever speed it is traveling toward braking for the second half of the journey.

First, not every existing drive uses chemical reactions to produce thrust. We already have tested ion drives, though not particularly finalized. Space elevators are perfectly consistent as an idea, though it's unknown if they are technically feasible.

We have no spacecraft currently in service which is not using chemical drives.

Wikipedia suggests to me that most ion drive systems are going to use xenon gas or some other element as fuel, converted to ions (a chemical reaction), which will end up being depleted over time. Perhaps I'm misunderstanding something here?

A drive that doesn't use chemical reactions isn't surprising and it doesn't break any laws.

I never said anything that put me on the side of "this is breaking a law or it isn't breaking a law". I'm actually on the side of "this is probably a new thing which is fully consistent with physics and while we don't understand it yet it is worth further exploration because if it actually is doing what it looks like it is doing it is going to be Very Useful".
posted by hippybear at 12:35 PM on August 1, 2014

> I've made no claim to prove.

That's fine, but I'm pretty sure my claim is logically true:

If this drive works then either:

1. the momentum has to come from somewhere, or
2. the law of conservation of momentum is broken.

To say, "It pushes against empty space" doesn't say where the momentum is coming from. Does "space" have an unlimited quantity of momentum in any direction you can just pop out if you please? Surely that makes for a distinguished frame of reference - surely special relativity prevents this from happening?
posted by lupus_yonderboy at 12:35 PM on August 1, 2014

The word reactionless has nothing to do with chemistry.
posted by lupus_yonderboy at 12:37 PM on August 1, 2014

To say "it pushes against the coils in the tracks" "doesn't say where the momentum is coming from" in a maglev train either, and yet it works. Try not recapitulating this whole thread, read it and a few of the links. And by the way, I didn't use the phrase "it pushes against empty space".
posted by George_Spiggott at 12:39 PM on August 1, 2014

> To say "it pushes against the coils in the tracks" "doesn't say where the momentum is coming from" in a maglev train, either and yet it works.

That is absolutely not correct.

The tracks are connected to the Earth, and that's what's getting the momentum. If the Earth were very small or your train very large, you'd indeed see the reaction, but because your train weights a few hundred tons and your Earth a few sesquitons, you don't see it.

The train pushes against the track, the track pushes against the Earth, you experience delta momentum, the Earth experiences the inverse reaction, the negative delta of your momentum.
posted by lupus_yonderboy at 12:43 PM on August 1, 2014 [1 favorite]

While I want this to be true, my guess is that they will find that they forgot to account for the earth's magnetic field, or the air in the cavity heated at resonance or something classical physics oriented.

But then again, they are really smart people and I didn't even read the paper.
posted by bottlebrushtree at 12:52 PM on August 1, 2014

Look, there are a lot of possibilities for how such a thing could work without breaking conservation. It could rely on existing electromagnetic fields; it could be something like Mach's Principle.

But there are a lot of problems with a device that pulls against space, and the relativity objection is an obvious one. If you can "pull against virtual particles in space" then that creates a distinguished "not moving" frame of reference.

Or, if you can "pull against virtual particles in space" in any intertial frame of reference ("when travelling at any speed") with exactly the same results, then it's impossible to make the law of conservation of momentum work any more unless you just consider "all of empty space" to be an infinite source/sink of momentum, which is basically giving up the law entirely.
posted by lupus_yonderboy at 12:53 PM on August 1, 2014

The tracks are connected to the Earth,[...]

Yes, i know that, but "doesn't say where the momentum is coming from" is the phrase you used, which is not a meaningful statement of the problem, and I was demonstrating that by applying it to something well understood.

Many people have pointed out that your notion of "empty space" is similarly unuseful. Might want to look into that. As I said, Lawrence Krauss is a good starting point for the non-physicist.
posted by George_Spiggott at 12:54 PM on August 1, 2014

If electrical energy alone can be converted to thrust, it would not violate any laws I am aware of. They are both manifestations of energy, but so far we have been unable to connect them.

I don't work for NASA. Even if it is too good to be true, it is likely that new knowledge will emerge from the research.
posted by Repack Rider at 1:00 PM on August 1, 2014 [1 favorite]

> Lawrence Krauss is a good starting point for the non-physicist.

I'm a bit beyond that - thanks anyway.

I'm well aware that "empty space" is a complex concept - I did not in fact use this phrase initially, and was pointing out it seemed wrong - but the relativistic objection against the idea seems hard to refute no matter how you slice it. Let's see the math, please? (A sketch is more than fine, but the more the better...)
posted by lupus_yonderboy at 1:00 PM on August 1, 2014

Surely you mean "Copyediting in the Uk..."

Did you say that just for uks?
posted by howfar at 1:06 PM on August 1, 2014 [2 favorites]

Let's see the math, please?

Um, the math for what? The math for "your lay objections to an experimental finding of physicists is based mainly on the limitations of conversational terms for things and not reading the articles?" Again, I have made no assertions of fact about the finding. You're saying they're wrong which is an assertion.
posted by George_Spiggott at 1:07 PM on August 1, 2014 [2 favorites]

George_Spiggott: are you a physicist?
posted by lupus_yonderboy at 1:08 PM on August 1, 2014

I'm not a physicist myself, but I have several grad courses in dynamics and over a decade of experience as an applied mathematician, so I can do the math...
posted by lupus_yonderboy at 1:10 PM on August 1, 2014

Look, I'm sorry this became less than cordial. It really does appear to me that any concept of "pulling against space or virtual particles" seems to be incompatible with relativity, but I'm really interested in an explanation as to why that it not the case... if you know, lay it on me!
posted by lupus_yonderboy at 1:13 PM on August 1, 2014

I think anyone asking about "seeing the math" should probably pony up the fee to get access to the actual published paper, because nobody here in this thread actually HAS any of the math associated with this particular set of experiments.

Sharing here, probably in brief quoted form, is undoubtedly considered Fair Use as long as you aren't quoting lengthy passages from the paper.
posted by hippybear at 1:14 PM on August 1, 2014 [1 favorite]

eriko: "Should this turn out to be real, it's a pretty big deal. Even at these low levels of thrust, the total ΔV available when you don't have to carry propellant mass is limited only by the time you can thrust...

Wait. I think I figured it out... Delta-V you say? That can only mean that certain squarewaves are being pushed by ... something, or...

Someone.
posted by symbioid at 1:17 PM on August 1, 2014

From the description, the published paper doesn't do the math either:

But the Nasa team has avoided trying to explain its results in favour of simply reporting what it found: "This paper will not address the physics of the quantum vacuum plasma thruster, but instead will describe the test integration, test operations, and the results obtained from the test campaign."

posted by lupus_yonderboy at 1:17 PM on August 1, 2014 [1 favorite]

If it turns out that this thing actually works, could it be used in land-based vehicles?

Very slow nuclear-powered land vehicles, maybe. The most appropriate transportation application I can think of this side of space is a Zeppelin.

I'm going to assume it works by accelerating dark matter, because I always wanted something that did that, nobody can disprove it with easy appeals to relativity and conservation of momentum, and it seems to make at least as much intuitive sense as pushing on virtual particles.
posted by sfenders at 1:23 PM on August 1, 2014 [1 favorite]

i think all physics threads should be fighty.
posted by el io at 1:24 PM on August 1, 2014 [9 favorites]

Look, I'm sorry this became less than cordial.

I in turn apologize for starting a reply with "Um", which is deeply obnoxious and rightly frowned on.

I'd distill this down to, basically:

Experimenters: "We produced a result which seems to suggest we're able to push against empty space. Damn, that's an interesting and unintuitive result, more research is indicated."

Objectors: "It is unintuitive to push against empty space."

Experimenters: "Yeah, we said that already. We'd like to know what this is."

As you probably rightly surmise, I am not a physicist. But I do share a key quality of a good scientist, that of being acutely aware of the scope my own ignorance. I do not know what empty space is. All my reading makes clear that nobody else does either, yet, but they're throwing massive effort at it and so far the only thing that's really clear is that it isn't anything you would imagine based on the placeholder term "empty space", and they freely admit that terms like "dark energy" are themselves placeholders. I'm interested in this result, would love to know more, the end. I'll probably stop pushing back against the disputations I see here because it doesn't seem like a good use of time.
posted by George_Spiggott at 1:24 PM on August 1, 2014 [2 favorites]

But there are a lot of problems with a device that pulls against space, and the relativity objection is an obvious one. If you can "pull against virtual particles in space" then that creates a distinguished "not moving" frame of reference.

the Emdrive people don't even claim to be pushing against space... but then, their whole thing smells like an elementary wave-guides theory error.
posted by ennui.bz at 1:25 PM on August 1, 2014 [1 favorite]

> Pretty sure Voyager has story lines that are accessible to humans in 1995 or so. It would be shocking if they were accessible in 1966

Not so shocking when you realize that Gilligan's Island started in 1964.
posted by George_Spiggott at 1:35 PM on August 1, 2014

This drive, as stated, is reactionless. The inventor can make any claim he wishes to about how it uses quantum or relativistic effects to explain a violation of conservation of momentum, but quantum mechanics, special relatively, general relatively, and their intersections (quantum field theory and UV completions like string theory) all respect momentum conservation. So any appeals to these theories to explain a violation of momentum conservation is simply incorrect on a theoretical basis -- which is not to say that an experimental result is incorrect (though it pretty clearly is in this case, in my opinion), merely a statement that momentum-conservation violating effects would be evidence of physics outside those theories. If said new physics overrules relatively and quantum field theories, the new physics must also explain every other physical phenomenon as well as GR and QFT, or explain why the new physics reduces back to the known laws of physics in every experiment other than the ones that claim to have a new effect. This is known as the correspondence principle; special and general relatively, for example, contain within themselves Newtonian physics, once you take the limit of low speeds, low curvatures, and small masses. Quantum mechanics as well contains familiar classical mechanics; in the limit of large action (large compared to \hbar), trajectories follow extremum of actions to arbitrarily high precision, which is what we observe in our classical existence. All attempts to explain this drive by resorting to dark energy, dark matter, vacuum fluctuations, and the like are doomed to failure: we only know of these odd results due to the application of theories of physics that this drive must violate. Appeal to ignorance if you must (and of course physicists do not know all that there is about the Universe), but please do not use physical concepts that have actual meaning and significant experimental evidence unrelated to this "drive" to buttress your arguments. For no other reason than that it annoys me personally.

Allow me to explain why the drive cannot be "pushing against spacetime," assuming that our theoretical understanding of spacetime and relatively and physics is correct. Again, I am not saying that this theoretical argument invalidates the experimental result (the experimental result is in my opinion certainly not evidence of a Magic Space Drive (TM), but that's separate from the theoretical argument). The claim is that such a drive takes energy in the form of electricity and converts it into thrust. Not only will this device violate momentum, it will violate energy conservation. Consider an actual working rocket. In a real rocket, energy is used to throw material (reaction mass) in one direction, and the remaining rocket moves in the other, as expected by conservation of momentum.

Such a drive also conserves energy. Consider the original rest frame of the rocket - call it Frame A. I see the rocket and the reaction mass, sitting at rest. I see the potential energy stored in the rocket. This might be in the form of chemical propellant (which will leave as reaction mass), or nuclear fuel rods (which will heat water or gas to expel as reaction mass), in the form of chemical energy in the food I eat and then use to power my muscles to physically pick up a rock and hurl it in the direction opposite the one I want to go, or just in the usual form of Hollywood-style glowing blue energon cubes. Because we all know that energy is just a free-floating thing, and it definitely glows blue. Unless it's evil energy, in which case it is red, purple, or green. The rocket turns on, energon cubes are consumed, reaction mass goes left, rocket goes right. I see where the energy went: into the kinetic energy of the reaction mass and the kinetic energy of the rocket. Energy is conserved. This is the situation imagined by the proponents of the magic space drive here: electricity is consumed, and turned into kinetic energy.

Now, imagine that instead of sitting at rest relative to the rocket, I am moving past it in the frame of reference that the rocket will end up in after it finishes firing (that is, I start seeing the rocket move past me, and after the rocket fires, I will see it at rest relative to me). Call this Frame B. In a real rocket, energy is still conserved. Initially there was kinetic energy of the rocket (moving relative to me) and potential energy in the fuel, afterwards there is no rocket kinetic energy, no fuel energy, but the reaction mass appears to be moving faster (relative to me) than it would appear to be moving in Frame A, conserving energy. So, according to me, it appears that all the fuel energy and rocket kinetic energy was used to throw the reaction mass very fast, and the rocket stopped "dead in the water" relative to Frame B. Momentum is of course also conserved here. This little thought experiment (momentum and energy conserved in all frames), demonstrates Galilean invariance. No matter where you are, or how you move, everyone agrees on the fundamental laws of physics, which we assume includes energy and momentum conservation. All Einstein did (and I say all with appropriate levels of theoretical deprecation, this is a massively important idea), is recognize that the speed of light is a law of physics that everyone has to agree on, and later recognized that a free-falling observer is following a geodesic (this gives you special and general relatively, respectively. If you're Albert "Bad-Ass" Einstein).

Now, this is the problem with the Magic Space Drive (TM). In Frame B, the drive violates energy conservation. The drive starts with kinetic energy, it starts with fuel. It consumes fuel, and in doing so comes to rest relative to Frame B. There is nothing moving opposite the drive (no reaction mass), so there is nothing to "carry away" both the momentum or the energy.

Now, if you want to say that this drive is "pushing against spacetime," it should be clear from my thought experiment above that you are privileging a particular reference frame in spacetime. In that one particular reference frame, whatever it is, you get to say energy is conserved. However, that simply cannot be the case in all reference frames. Someone gets to see energy violated, because someone gets to see electricity consumed and the rocket come to rest. There is no Lorentz invariant way to get this idea to work in all frames of reference.

So, you have two choices. First, you can say that there is a special reference frame, and Einstein's theories are just wrong as the correct explanation of the laws of Nature. OK, I have no problem with that -- though I am not going to bother to work on the idea at the moment, because it violates enough concepts I know work well that it judge it not worth my limited time on this Earth to pursue. There are many such ideas, and everyone has the responsibility to select where their personal cut-off is. I'm just telling you mine. Prove it, clearly and unambiguously, and then we'll work on figuring out how to fix our understanding of physics to accommodate this new result. Second, you can say that your reaction mass is equivalent to massless particles (i.e. you have a photon drive sans photons), which eliminates the problem. By the way, this requires about 300 MW of power for a sustained thrust of 1 Newton. Good luck with that.

Further, the idea that this drive is working by emitting radiation from one end of a cavity that then imparts a force to the other end of a cavity that causes the cavity to move is beyond ridiculous, modulo Magic Space Drive (TM) effects. Emitting radiation from one side of the cavity will cause the cavity to recoil in the direction opposite the radiation emission direction. Then, when the radiation is absorbed on the other end, the cavity will recoil again, returning it to rest. Removing one end of the cavity and letting the radiation stream out gives you a photon drive. Which requires 300 MW of energy for 1 N of thrust. Good luck with that. Again, not saying that I'm disregarding legitimate experimental results, if proffered, I'm just saying the proffered explanation is not correct.

Now, looking at what is being offered as experimental results, I see a 1 page "paper" with no figures, no detailed description, and doing several things that I consider somewhat foolish for such an experiment. Several "reactionless" drives "work" in particular laboratory conditions, usually by pushing cleverly against the lab set up. If you want to see a reactionless drive of the type that often have been claimed in the past, take a rolling chair on a carpet, and inch along by throwing your weight side to side. You apparently violate momentum because you are using the friction of the rollers against the carpet and moving slowly in one direction to avoid overcoming the frictional force, followed by a quick motion in the other to get motion. Thus, the fact that this experiment was done in an airfilled room attached to the walls in some unspecified way makes me suspicious.

Sorry, this is just not up to anything resembling a standard I can trust. It just smells of bad science, of the type that happens quite often and grabs attention when it does. I understand the reason people are exciting, I get the desire for something awesome that will give us great things. I dreamt (and still dream) of stardrives and spaceships. I'm just saying you should take this with a massive, massive grain of salt, understand the enormity of the claim being made, and recognize that better results should be demanded. In my opinion, these NASA scientists should have known better, and constructed an experiment that addressed the obvious concerns.

I don't have much more to add, beyond this. There is plenty of really interesting stuff about conservation laws and Noether's theorem that could be discussed in the realm of real physics, but I don't have the time to really get into it, and it's far beyond the scope of the present discussion. I realize that there will likely be some pushback to my contribution in the thread, as I am taking the side of the Man in this. I urge people to take the opportunity to read and think critically, and to understand that it gives very few scientists any particular pleasure to act as the agents of dream-crushing. The Universe is as it is, and it appears to be constructed in such a way as to prevent many "magic" concepts that readers of sci-fi would love to have. Reactionless drives, faster-than-light travel and communication, cheap ground-to-orbit launches, cold fusion, lightsabers, and easy zero-g sex are only a few of them. Disappointing as I know this is to all of us, the laws of physics as they are are truly beautiful and amazing, and the more I learn of them, the less I can imagine a consistent Universe built any other way. No one promised us easy access to the Universe, and it would be a real shame if we let dreams of the impossible blind us to the hard work of what needs to be done, be it interplanetary travel or providing cheap energy for life on Earth.
posted by physicsmatt at 1:37 PM on August 1, 2014 [88 favorites]

Not so shocking when you realize that Gilligan's Island started in 1964.

Are you suggesting a link between the Castaways and the crew of Voyager? That is something which was never even hinted at in the brilliant Gilligan's Wake (which if you haven't read, you should stop whatever you are doing right now and start reading, because fucking wow).
posted by hippybear at 1:39 PM on August 1, 2014 [1 favorite]

i don't know... the more I think about it there this story illustrates how moribund the whole military-space industrial complex is. I *guarantee* there is a team of people at Lincoln Labs or JHU's APL that do nothing but exotic wave-guide theory. And someone from that team could go to the whiteboard and explain why this was a dumb experiment to do or an interesting one. *And* the optics of the story suggests that they did go and explain that it was a dumb experiment to do, but the lure of super-technology was too strong for the political-military administration.

It shows you how non-science driven the whole business is. So, I guess I'm betting that there isn't anything here.
posted by ennui.bz at 1:46 PM on August 1, 2014

If you want to see a reactionless drive of the type that often have been claimed in the past, take a rolling chair on a carpet, and inch along by throwing your weight side to side. You apparently violate momentum because you are using the friction of the rollers against the carpet and moving slowly in one direction to avoid overcoming the frictional force, followed by a quick motion in the other to get motion. Thus, the fact that this experiment was done in an airfilled room attached to the walls in some unspecified way makes me suspicious.

The Dean Drive was never subjected to the pendulum test, which would have all but ruled out e.g. mechanical resonance phenomena.

So yeah, until you can do it in microgravity and a hard vacuum and not in any non-negligible magnetic field (so basically not anywhere in the vicinity of Earth for a start), your experimental results are going to be somewhat limited in value without a testable theory behind them.
posted by George_Spiggott at 1:51 PM on August 1, 2014 [1 favorite]

> I realize that there will likely be some pushback to my contribution in the thread,

On the contrary, I suspect your obvious expertise will win the day.

> It shows you how non-science driven the whole business is.

Not at all. There are apparently repeatable results. There needs to be an explanation. Almost certainly the result will be "a subtle phenomenon from known physics" but even in that case human knowledge is expanded. Occasionally, the rest will be a new physics. It's really really unlikely this time but you can't ever tell for sure.

It's like buying science lottery tickets. Most of the time you get phlogiston or Lamarkism but one in a million pays off with relativity or quantum mechanics. The payoffs are so good that it's really worth buying all the tickets and scratching them off one at a time...
posted by lupus_yonderboy at 1:52 PM on August 1, 2014 [4 favorites]

easy zero-g sex

These 10 Quick Tips...
posted by ryoshu at 1:55 PM on August 1, 2014 [1 favorite]

Luddite: "I dunno. If this work it fits perfectly with hippybear's "Living in Hollywood Screenwriter Reality" hypothesis."

Every so often a movie comes along that sounds like a fake movie in a heavy-handed Hollywood satire. "A CG-heavy, 3D adaptation of The Great Gatsby starring Leonardo DiCaprio? Oh, come on!"

So there's some supporting evidence right there.
posted by brundlefly at 1:56 PM on August 1, 2014 [4 favorites]

Mind you, you can proceed to engineering and even build an entire industry without a decent theory. For most of the history of flight, aeronautical design was based on empiricism and a lot of the prevailing theory was silly, only accidentally of value and occasionally flat out wrong. Knowing that might have kept a lot of people from getting on planes, so just as well they didn't know it because as long as you build within the constraints of empiricism you're probably going to be all right, even if you don't really know why it works.
posted by George_Spiggott at 2:09 PM on August 1, 2014 [2 favorites]

I've followed this story in a few places, and when I commented upthread I was on a low battery iDevice with the benefit of the knowledge that physicsmatt was probably around the corner and about to plonk the kind of awesome post he always does into such threads, so I stuck to a one-line snark.

I want to say this: almost everywhere there's been some discussion of some kind of 'cheat', a change of frame of reference, a dumping into some quantum mechanical zero-point field, whatever. One of the really great things about physics is the way it has all these amazingly general rules to it. Conservation rules like momentum and energy are way up amongst those as being fantastically powerful.

(This analogy is probably Feynman's btw) If you were playing chess and had a bishop on the board you'd know if it started off on a white square, you'd always see it on a white square. That's a kind of conservation rule - the colour of the square a bishop is on in is conserved. It never changes. If someone's claimed to see a bishop change the colour of the square you know one of three things:
* they made a measurement error
* they weren't paying attention and the bishop got captured and a pawn got upgraded
* chess is following some funny rules you didn't know about
In no circumstances do you ever think there was just some funny configuration of pieces on the board that according to the rules you know allowed that bishop to change colour square. It just can't happen. In the same way it doesn't matter what shape the cavity in the EmDrive is or whatever - according to the rules it just can't happen. It doesn't matter if you involve quantum mechanics, fiddle with relativity, or what, because all those have the one rule of momentum conservation embedded right into their hearts.

Now it could be that momentum isn't conserved, but we have really good theoretical reasons (which are part of how we can literally prove that if the universe works the way we think it does momentum must be conserved - physicsmatt mentioned Noethers Theorem, which tells us if the laws of physics are the same everywhere, we must be able to come up with something called momentum that is conserved) why it should be, and we'd properly fall off our chairs in shock if it weren't. It'd take a lot of evidence to swing any sane-minded physicist that way. So we can sensibly discount that.

So either it isn't working as a drive, or it is using something as a propellant. We can fairly easily write down rules for how propellants must behave like this, and you can either chuck matter out the back, which this thing explicitly isn't, or you shoot photons or something behaving like them out the back, in which case you can do it without all the fuss as we're quite good at manipulating photons these days.

Physics is a great fun tool to work with, because it lets you shortcut so much stuff. Sure, it lets you calculate precisely the trajectory of your cannonballs or whatever, but it lets you write down rules about physical systems that have to be obeyed no matter what, and let you bundle up complex things into 'black boxes' that must obey rules in a very general fashion, and there are literally no ways to shortcut it without throwing out the rules altogether.
posted by edd at 2:16 PM on August 1, 2014 [7 favorites]

Appeal to ignorance it is then! I think there is some evidence that this is not actually the advent of a Magic Space Drive in the fact that the EmDrive concept has been around for some 14 years or more, they ought to be pretty simple to build, and yet we're still not actually using them to fly around in space.
posted by sfenders at 2:22 PM on August 1, 2014 [2 favorites]

Thanks to physicsmatt and edd for explaining this better than I could.

The rest of this thread (and all MeFi threads which involve perpetual motion/warp drives/free energy) is kinda depressing on account of gullibility.
posted by Avenger at 2:22 PM on August 1, 2014

(and all MeFi threads which involve perpetual motion/warp drives/free energy)

Neither perpetual motion nor warp drives nor free energy is the subject of this FPP.
posted by hippybear at 2:25 PM on August 1, 2014 [2 favorites]

physicsmatt actually explains how a device which violates conservation of momentum would be indistinguishable from a free-energy device.
posted by Avenger at 2:32 PM on August 1, 2014

Yes, he does. But whatever is going on with this particular set of repeatable experiments remains to be explained, and so there is no way to say whether anything has been violated or not.
posted by hippybear at 2:35 PM on August 1, 2014

Should I? Oh, why not.


MetaFilter: kinda depressing on account of gullibility
posted by blurker at 2:39 PM on August 1, 2014

physicsmatt actually explains how a device which violates conservation of momentum would be indistinguishable from a free-energy device.

Kinda strawmanny there: I don't recall anyone suggesting otherwise, and that's not the the least of what physicsmatt did. He took a swing at the "spacetime traction" supposition and provided some sustenance for lupus_yonderboy's reference frame arguments for a general audience, which I greatly enjoyed reading. If anyone here seriously suggested that this result meant "yay, momentum doesn't have to be conserved", I must have skipped over it.
posted by George_Spiggott at 2:42 PM on August 1, 2014 [1 favorite]

The rest of this thread (and all MeFi threads which involve perpetual motion/warp drives/free energy) is kinda depressing on account of gullibility.

Then you may enjoy this thread where MeFites were excessively—and incorrectly—skeptical. "Perpetual motion" claims abounded. (Three years later there was considerably more clarity. Spoiler alert: no conservation laws were harmed.)
posted by Mapes at 3:33 PM on August 1, 2014

In addition to the reference frame argument (sorry lupus_yonderboy, I guess I needed it spelled out a little more) what I found useful in physicsmatt's response was invoking the correspondence principle for both relativity and quantum theory:

This is known as the correspondence principle; special and general relatively, for example, contain within themselves Newtonian physics, once you take the limit of low speeds, low curvatures, and small masses. Quantum mechanics as well contains familiar classical mechanics; in the limit of large action (large compared to \hbar), trajectories follow extremum of actions to arbitrarily high precision, which is what we observe in our classical existence.

So invoking spacetime or QM effects as an escape hatch for classical constraints at classical scales doesn't work. You apparently can't, for example, get free energy from the universe by being quick enough to steal particles from quantum fluctuation before they have a chance to annihilate. Black holes do that at their event horizon, but the result, in the form of Hawking radiation, is dissipative; the black hole loses mass/energy as a result of this radiation and will shrink accordingly, unless it's pulling in more mass from its surroundings by gravity. So QM doesn't let you flout Newton just by being clever.

It'd be nice to think that the universe is full of something which, apparently, ordinary masses pass through without resistance, but which something we're capable of creating can get traction on, and ride to the ends of creation, but I'm not saying I actually believe it.
posted by George_Spiggott at 3:34 PM on August 1, 2014 [2 favorites]

Whatever the results, the UFO nuts are going to be over this like teachers on free alcohol, using it as an explanation for how UFOs work. If it's (almost certainly) disproved, then they'll claim its a conspiracy to silence The Truth. In the unlikey event something comes of it, they'll claim the government is releasing a small piece of UFO technology.

Either way, i'm sure there's going to be some highly profitable kickstarters and investment opportunities to come out of this.
posted by happyroach at 3:51 PM on August 1, 2014

"highly profitable kickstarters and investment opportunities"

Men in Black Ink. (Or "Inc.", I guess).
posted by Chitownfats at 4:03 PM on August 1, 2014

MetaFilter: i'm sure there's going to be some highly profitable kickstarters and investment opportunities to come out of this.
posted by hippybear at 4:09 PM on August 1, 2014

Appeal to flatulence: cosmic prawns are life forms composed of weakly-interacting dark matter which pervade space, travelling in parsec-long shoals. The electrical activity created by these experimental drives interact with the special structures in the prawns' digestive systems (they have four stomachs that permit the ingesting of normal matter in extraordinary circumstances, during the once-per-billion-years droughts in their normal food sources) and it is the resulting farts of the cosmic prawns which provides thrust, unnoticed because momentum is imparted to WIMP flatulino particles.
posted by XMLicious at 4:24 PM on August 1, 2014 [2 favorites]

Surely you mean "Copyediting in the Uk...". ;)

England isn't in the Uck, it's in the you kay. Neener.
posted by eriko at 4:38 PM on August 1, 2014

Quantum mechanics doesn't let you flout Newton just by being clever.

Can we staple this to the forehead of every single journalist & blogger on the planet?

Please?
posted by aramaic at 5:27 PM on August 1, 2014 [1 favorite]

I share the skepticism of everyone here, but I've realized that the real shame of it is the reason our skepticism is so well founded. We live in an era of singular stagnation for fundamental physics. Over much of the last few centuries, there was a decent chance that a shocking result from a well-conducted experiment might actually contradict known physics in a way the led to new physics, or at least revealed a surprising new implication of known physics. Sure, most experiments with crazy new results have always turned out be flawed in some way. But certainly for the last two centuries, the Bayesian prior that theory is correct and the experiment likely to be wrong has never been higher. It doesn't mean that we won't find something that overturns the Standard Model someday or even soon, but after watching four decades of new hints fizzle one after the other, there's good reason to be skeptical of this one. Which is too bad for those of us raised on Faraday and Einstein and Heisenberg and the SF they gave rise to, hungry for something really new. Because if recent history is any guide, this won't be it.
posted by chortly at 5:54 PM on August 1, 2014 [1 favorite]

take a rolling chair on a carpet

But I'm still trying to get with child a mandrake root, and also take a flying fuck at a rolling donut AND at the moon.

Seriously, the explanation about Galilean invariance and appealing to a privileged frame of reference was very helpful to my slacker's understanding of physics, physicsmatt, beyond this reactionless drive discussion. Thanks for taking the time.
posted by thelonius at 6:50 PM on August 1, 2014

I don't think it's so much the lack of shattering new discoveries that people are disappointed by, but the lack of discoveries that will give us FTL. In fact, FTL seems to contradict the basic nature of the universe, and people raised on Star Trek and Star Wars have a hard time dealing with that.

There's plenty of bizarre, wonderful stuff that we've discovered. But no Starship Enterprise, sorry.
posted by happyroach at 6:51 PM on August 1, 2014 [1 favorite]

You know, even if someone built a quantum vacuum plasma thruster, I don't think it'd actually be a reactionless drive.

Virtual particles work because they annihilate nearly instantly after forming, so they don't create permanent mass-energy and violate energy conservation. If you grab them and chuck them out the back of the spacecraft, they're not going to annihilate each other anymore. While it should be possible in principle to do this (see Hawking radiation) and this solves the conservation of momentum problem, I bet anything it would work out so that you had to put enough energy into the engine to completely 'pay' for the mass-energy of the particles it emits (like the black hole does for Hawking radiation).

If it worked that way, such a device wouldn't violate conservation laws at all. It would basically convert energy to mass and then chuck that mass out the back of the spacecraft. However, it would also totally defeat the point. No matter how good your power source is, you can't create more mass in the thruster than you converted to energy in the ship's reactor. So, while I think it could actually function, it would be useless in practical terms.
posted by Mitrovarr at 7:48 PM on August 1, 2014 [1 favorite]

The rest of this thread (and all MeFi threads which involve perpetual motion/warp drives/free energy) is kinda depressing on account of gullibility.

Indeed. All these threads full of people saying "Of course it isn't perpetual motion. On the other hand, here's how it could work without violating the existing laws of physics" show the deep naivety of the Metafilter crowd.

Fortunately we have people capable of setting us straight by repeating something that no one is arguing about over and over.
posted by Tell Me No Lies at 7:50 PM on August 1, 2014 [1 favorite]

In no circumstances do you ever think there was just some funny configuration of pieces on the board that according to the rules you know allowed that bishop to change colour square. It just can't happen.

This aspect of physicists -- and in my experience it's very true that physicists think this way -- has always baffled me a bit.

I work on software systems that are massively complex, but at their core have perfectly understood and executed rules. I live in a constant state of worry that I've missed some basic implication of how these rules interact, and history shows I'm right to do so. It's very rare that messy reality slips in: 99% of the weirdness I see is due to me not being able to predict the perfect execution of rigidly logical rules.

I look at physics and I think "This is a much more complex system where we have some fairly large gaps in our understanding. How can they so blithely assume they understand the implications of even the rules that they're sure of?"

As a practical matter however this approach appears to work. I suspect it's because they only have one system and have had thousands of people vetting the implications over long periods of time. I've got a new system every year that about 20 people total understand.
posted by Tell Me No Lies at 8:12 PM on August 1, 2014 [2 favorites]

It works, but the power companies will bury the patents, and hide all the devices in Area 51.

The Truth is out there, but They won't let you find It.
posted by mule98J at 8:24 PM on August 1, 2014

And breaking it [Conservation of momentum] wouldn't have the ramifications of breaking other laws like the Conservation of Mass/Energy.

Actually, it would. Conservation of momentum comes directly from conservation of energy and Galilean relativity. (Yes, that Galileo. Described almost 500 years ago.)

Let's say I have a battery powered device. It weighs one kilogram. If I turn it on, it accelerates away from me at 1 m/s^2 for five seconds and continues away at 5 m/s forever. It does so without pushing anything back the other direction. How much power does it use?

Well, an easy answer is that as it weighs one kilogram and moves 5 m/s, the high-school-physics answer is that it has 12.5J of kinetic energy. Whatever else it does, it can't convert less than 12.5J from its power source into kinetic energy.

Now, let's say I get on an airplane with this device. While moving 300 m/s, I activate the device. After five seconds, it's moving 305 m/s, and it keeps going until it bumps into the cockpit door. How much energy did it require?

The same high-school-physics equation tells me that to go from 300 m/s to 305 m/s requires 1512.5J from its power source. Whatever else it does, to accelerate a 1kg object from 300 m/s to 305 m/s requires at least 1512.5J.

So, why can I walk forward on an airplane? After all, I'm going from 300 m/s to 305 m/s, and I'm certainly not feeling bogged down like I have to work a hundred times as hard as I would to walk on land.

The reason is that in order to walk forward, I have to push back on the airplane. Doing that causes it to move slightly slower, giving up an enormous amount of kinetic energy, which all gets concentrated into me.

This happens invisibly and most of us never really think about it. This is Galilean relativity, the fact that accelerating and decelerating an object by pushing against another object doesn't change based on how fast the system is moving. If two objects exert force on each other, all observers will agree on how much their relative speed will change. All observers will agree that a certain amount of energy needs to be expended to cause that change to happen, but they won't agree on the invisible answer of how exactly that energy got distributed into and from kinetic energy.

But any device that can accelerate without pushing on something else breaks Galilean relativity, because no two observers can agree on how much energy in needed to do what it did.
posted by Hatashran at 9:40 PM on August 1, 2014 [11 favorites]

Crap. Missed physicsmatt's comment. I'll leave my alternative explanation here anyway.
posted by Hatashran at 9:43 PM on August 1, 2014

Hatashran: no, it's good. We got to the relativity part later, and physicsmatt's comment was very strong, but yours is very clear!
posted by lupus_yonderboy at 10:29 PM on August 1, 2014 [1 favorite]

I'm a physicist of the experimental kind, and I looked through the full 20-page paper from NASA. It was submitted to a conference, which means it's barely peer-reviewed, and it reads like the report from an ambitious diploma project. They focus is on the technical aspects of the measurement setup, and use phrases like "Test schedule constraints prevented multiple data points to be gathered in the reverse orientation [...]".

As others have pointed out, a proper experiment should be done under vacuum, and they actually rigged their apparatus in a vacuum chamber. I think they just didn't have enough time to pump it out.

My biggest concern is with the geometry and materials of the setup though. The microwave power enters the propulsion resonator through a fixed copper tube that sticks into it from one end, along the axis of the force. The outer chamber is also small and the resonator mounted asymmetrically inside it on an aluminum construction. Based on these things, my best guess is that they measure a magnetic force between the fixed and suspended parts, caused by eddy currents in the metals. When the force you study corresponds to the weight of two mosquitos, artifacts like that show up easily.

This is all to say that the paper doesn't approach the rigor required to support an important scientific result. It seems like the main author got carried away with the conclusions and that the seniors let it be since conference papers aren't seen as very important. Now that the story has taken off, I'm not sure everyone involved feels comfortable about it.
posted by Herr Zebrurka at 1:56 AM on August 2, 2014 [9 favorites]

I look at physics and I think "This is a much more complex system where we have some fairly large gaps in our understanding. How can they so blithely assume they understand the implications of even the rules that they're sure of?"


It took a bit of thought to answer this, and this is the best I came up with. This is after a number of margaritas, so bear with me:

Unlike a computer system, which uses a set of arbitrary rules to create a desired outcome, science is based off of observing the universe, and trying to discern the rules behind it. So any new theory that comes along, also has to match what we already see. Einsteiin's theories have to encompass Newtonian physics, which had to match Kepler, who based his theories off of observations of the planetary orbits, and so on. So really, science is pretty much the opposite of programming- in a real sense instead of setting the rules and observing the products, we're looking at the results, and trying to figure out the rules.


The problem with the device being a reactionless drive- if it works, it contradicts Relativity, which is backed by a huge amount of observational data. Which is possible of course- there may be some exception to observations that shows we need a newer, more encompassing theory. But then again, it's bucking a huge amount of observations about the universe, so I wouldn't bet money on it. In fact, I'd bet money against it- you can probably find some suck er, takers on that.
posted by happyroach at 2:12 AM on August 2, 2014

Since the thrust measured by NASA is orders of magnitude less than the a priori claim, it should be labeled "failed to confirm."
posted by SemiSalt at 7:52 AM on August 2, 2014

Tell Me No Lies: I understand the concern. This is not so much like someone claiming to have written a piece of computer software that does something apparently very impressive that you can't understand though, or which utilises unexpected behaviour of the language. It's more like the programming equivalent of someone claiming to have written code to solve the halting problem, or to access some piece of hardware the kernel you are running on should prevent you from reaching.

I mean, the halting problem is proven impossible, and breaking the known laws of physics only breaks the known laws and isn't logically impossible, but it is broadly the same in that in the context of assuming certain laws hold then some situations are proven impossible, no matter how you combine the allowed ingredients.
posted by edd at 8:43 AM on August 2, 2014

ITT: everybody is smarter than NASA apparently
posted by young_son at 11:24 AM on August 2, 2014 [2 favorites]

Smarter than WIRED, maybe.
posted by sfenders at 12:52 PM on August 2, 2014 [1 favorite]

OK, so if we assume this device works, then what's the simplest way to turn it into a perpetual motion machine?

If you bolt this magic device to the edge of a flywheel and apply constant power, then it should produce a constant force that accelerates the flywheel at a constant rate (i.e. the flywheel gains K rpm per second as long as power is applied to the magic device). This is much more interesting than your average electric motor which would need linearly increasing power to sustain a constant force on an accelerating flywheel.

So you have constant input power producing a constant acceleration. The kinetic energy of a flywheel is proportional to rpm^2. This flywheel energy has a quadratic relationship to the input energy, with some proportionality constant that depends on the efficiency of the magic device.

Given the way quadratic equations work, at some rpm, the flywheel's kinetic energy will be increasing faster than than the input energy is consumed. We'll call this the break-even rpm. Once you exceed the break-even rpm, you can put a generator on the spindle to feed electricity to the reactionless drive, and still have some surplus left over for powering other stuff.

Am I missing anything here? Not only will this device let you skip carrying around propellant, but you can ditch the spacecraft power plant as well! In fact, if you have 3 or 4 of these devices (which you'd want for redundancy anyway), you can even use them as reaction wheels for attitude control!

Truly, this invention will revolutionize spaceflight.
posted by ryanrs at 2:19 PM on August 2, 2014 [10 favorites]

The wife says:

It's probably just a Crookes radiometer. At atmospheric pressure and assuming the thing is of order 10x10cm, you only need a temperature differential around 0.1 milliKelvin to get the claimed thrust. They're dumping 20 W of power into the thing, and even admit to having a "reduced reflection coefficient at one end plate." First, they should prove it's not this. There's always plenty of reaction mass around when you're in an atmosphere.
posted by sebastienbailard at 5:30 PM on August 2, 2014 [12 favorites]

ITT: everybody is smarter than NASA apparently

I'm sure NASA is one of the best places to go look for people who don't think this device is working. You don't have to be a rocket scientist to see that the published tests fall short of proving it.
posted by Herr Zebrurka at 9:42 AM on August 3, 2014 [3 favorites]

As others have pointed out, a proper experiment should be done under vacuum, and they actually rigged their apparatus in a vacuum chamber.

I seemed that way to me too. I was wondering how the idea it wasn't in a vacuum wandered into this thread.

I think they just didn't have enough time to pump it out.

Seems as good as any reason.
posted by Tell Me No Lies at 12:35 PM on August 4, 2014

You don't have to be a rocket scientist to see that the published tests fall short of proving it.

Which makes me wonder: Was it the experimental design or execution that was flawed? And what experiment would need to be executed to make people believe the propulsion effect is real even if we haven't quite connected the dots of how it might fit into the existing physics framework?
posted by Tell Me No Lies at 12:38 PM on August 4, 2014

Was it the experimental design or execution that was flawed?

Possibly. This was what graphic designers call a "quick and dirty." There's something going on. Further investigation will find out what. It may be a revolution in physics, or a cautionary tale in experimentation.
posted by ChurchHatesTucker at 12:42 PM on August 4, 2014

The reason I heard it wasn't a vacuum was because the magnetron uses electrolytic capacitors. I think that's from the Ars Technica thread on it, but I'm not sure.
posted by ambrosen at 3:16 PM on August 4, 2014

Here's John Baez's fantastic post on the matter.
posted by kaibutsu at 7:51 PM on August 4, 2014

Considering that the paper itself says that "This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States," I have no qualms sharing this Scribd link to the full paper.

Regarding the reason for not pumping down, the "future work" section on the last page of the paper states: "Vacuum compatible RF amplifiers with power ranges of up to 125 watts will allow testing at vacuum conditions which was not possible using our current RF amplifiers due to the presence of electrolytic capacitors." So there's the source for the electrolytic capacitor theory....

Strangely, this is the only place that the full article mentions that a vacuum wasn't pulled. Unlike the conference abstract, the full paper does not mention that the measurements took place in a "vacuum chamber with the door closed but at ambient atmospheric pressure." Instead, they describe a measurement apparatus that can pump down to 5E-6 Torr (see pg 4), leading the reader to believe that that's how the measurements were made. The only disclosure that the experiment wasn't done at a vacuum comes from that line about the caps on the very last page. Considering how important the vacuum is to the validity of their claim (or even to the demonstration of the measurement apparatus as described), the omission of any discussion about it leaves a bad taste in my mouth.... (As it would have in any reviewer's, had it been reviewed to the same level of stringency that journals use.)

I know it's too much to ask, but I do wish Wired and its ilk would wait for peer-review publications before getting all excited. There's just so much that doesn't pass the sniff test here, but even if it did, the whole point of peer-review is to catch mistakes (ones that even the best sometimes make) before a bad result gets out in the wild.
posted by Westringia F. at 7:52 PM on August 4, 2014 [5 favorites]

Less unflattering explanation for the omission: they originally did it at ambient and wrote both the conference abstract and the paper accordingly; they then obtained the vacuum compatible RF amplifiers, repeated the measurements, and updated the paper, forgetting to remove that line on the last page. Since abstracts usually have deadlines before the articles, one can imagine how an preliminary non-vacuum abstract might be paired with a final full-vacuum paper, with an odd preliminary non-vacuum line that wasn't pumped out.

I don't think this is what happened, but as a scientist I feel compelled to offer an alternative explanation for what I said above!
posted by Westringia F. at 8:17 PM on August 4, 2014

Oh, but Tell Me No Lies, this may be a misunderstanding: They put the equipment in a vacuum chamber, but they did not pump out the air. From what I understand, the experiments were done under atmospheric pressure.

ambrosen: It seems you are right. They say this in the summary of the paper: "Vacuum compatible RF amplifiers with power ranges of up to 125 watts will allow testing at vacuum conditions which was not possible using our current RF amplifiers due to the presence of electrolytic capacitors."

Tell Me No Lies: And what experiment would need to be executed to make people believe the propulsion effect is real [...]

In general terms, the more spectacular your claim, the stronger the proof has to be for people to believe it. I'm making this up on the fly, but for important discoveries in physics it goes something along these lines:

If there is an accepted theory that explains the result of your experiment, you have a relatively light burden of experimental proof. You still have to take every precaution not to introduce any artifacts, but people are inclined to believe the soundness of your work. An example could be Millikan's oil drop experiment to establish the quantization of charge. Finding the Higgs boson in the energy range where it was expected is another example. That experiment was done with extraordinary rigor though, enough to be trusted even if it had come up with something that didn't comply with standard theory.

The next step up is if there is no existing theory for the effect you observe. Then you need to be able to address any "what if" that makes even remote physical sense, and you should not expect to be believed until others have confirmed your results. An example of that would be Kamerlingh Onnes' discovery of superconductivity. It didn't break any rules exactly, but it was strange and unexpected and remains a rather curious phenomenon.

Further up the ladder, we have experiments that cannot be explained without introducing a whole new line of thinking. One example would be if you demonstrated wave-particle duality in a double-slit experiment, before quantum mechanics had been developed. A modern equivalent might be to find a particle that gives rise to human consciousness. Those things go at right angles with previous thinking but maybe not entirely against it.

I'm not sure if we need another step on this ladder, the line gets blurry between this one and the one below. But if we decide to define a fourth step, that's where you end up if your results go against all observations made in the past and the consequences rip up established theory by the roots. Examples could be demonstrations of faster-than-light travel, perpetual motion, or the existence of ghosts. The burden of proof becomes almost impossible here, because Occam's razor puts you at a disadvantage compared to the craziest of things. A global conspiracy of scientific fraud is at least as plausible as, say, a functional time machine.

With the disclaimer that I don't work with cosmology and fundamentals, I think a violation of momentum conservation on this macroscopic scale would fall into the fourth category. There are a few conservation laws, and they tend to be treated as axioms in theoretical research. In that sense, those laws are what physics is built from. If this one was to crumble, it would take an immense amount of theory with it, and we would probably postulate a new elemental particle or give the Aether a second chance sooner than we'd give up momentum conservation in a general setting.

Having said all that, I feel that there is one important thing to add: The authors of the NASA paper did not bassoon outrageous conclusions to the world. They say the following in the abstract: "Test campaign results indicate that the RF resonant cavity thruster design, which is unique as an electric propulsion device, is producing a force that is not attributable to any classical electromagnetic phenomenon and therefore is potentially demonstrating an interaction with the quantum vacuum virtual plasma". This comes after an explicit disclaimer that they will not treat the feasibility of the concept. Given how fantastic this would be if it was true, that sentence is well on the optimistic side, but on the other hand, it's quite natural to get a bit too enthusiastic about the stuff you work on. This is especially true when you finally see the results you've been hoping for, and even more so if you are a student or a young scientist. The senior authors should probably have caught this and toned the wording down even more. Realistically though, it's an obscure conference paper and those aren't supposed to have any high stakes. The normal sequence of events would have been for the first author to give his presentation at the conference and get some polite criticism, and for all of it would fit in as part of his scientific education. Now the authors have to respond to a different and much bigger audience, and may get derided because they bring discredit to NASA. I'm not saying they did everything right, but Wired should know that a paper like this is not the same as an official proclamation of truth. It would have been decent of them to talk to the authors before running the story.
posted by Herr Zebrurka at 11:55 PM on August 4, 2014

>>Tell Me No Lies: And what experiment would need to be executed to make people believe the propulsion effect is real [...]

>In general terms, the more spectacular your claim, the stronger the proof has to be for people to believe it.

True enough, but there is nothing spectacular about saying that when you apply power to this device in a vacuum it moves without losing mass. It is a simple binary proposition. The implications of it working may be hugely problematic, but the experiment itself seems rather straightforward to set up and reproduce.

A lot has been written here about how poorly the experiment was executed and written up. My question is: how would the experiment have to be run for the result -- presumably negative but you never know -- for it to be accepted as valid?
posted by Tell Me No Lies at 1:57 AM on August 5, 2014

Oh, but Tell Me No Lies, this may be a misunderstanding: They put the equipment in a vacuum chamber, but they did not pump out the air.

Ah, right you are.
posted by Tell Me No Lies at 2:03 AM on August 5, 2014

> A lot has been written here about how poorly the experiment was executed and written up. My question is: how would the experiment have to be run for the result -- presumably negative but you never know -- for it to be accepted as valid?

They would have had to investigate and eliminate all reasonable alternative explanations that would explain their result under the present theory. In the case of a result that appears to violate laws of conservation of momentum or energy, those alternative explanations are "you transfered the momentum or energy elsewhere" (eg, 'pushing off' the atmosphere a la a Crookes' radiometer because you haven't pulled a vacuum) and "your measurements are experimental artifacts that do not yield the same result when the experiment is repeated" (far from 'validating' the previous findings, they got force values that were orders of magnitude smaller than what was reported previously). They did not address, let alone eliminate, either of these simpler explanations.

Having done so, they also would have had to provide a new theory (or at least an explanation that could be developed into a theory) for what was happening. Importantly, that theory would need to give testable predictions that could be falsified experimentally. In this case, that means offering a new theory that not only explains the thrust seen in the slotted device, but also the thrust recorded in the unslotted null device. (Indeed, the fact that it was seen in the null device is exactly the sort of experimental falsification of their prior theory -- that it was the asymmetry of the slots that made it work -- that I'm talking about.) They do not offer any testable explanations or predictions.
posted by Westringia F. at 4:53 AM on August 5, 2014 [1 favorite]

(And the less one is able to offer a new & falsifiable theory, the greater the need to eliminate all alternative explanations under the existing theory. If one claims that one cannot explain the result -- that it's truly New Physics -- then one had damn well be certain one can't. They're shying away from making a claim this strong -- Wired &al have been really trumpeting the "new physics" part -- but not as much as they should, and their own apparent lack of skepticism is why there's such vigorous skepticism about it from the community.)
posted by Westringia F. at 5:10 AM on August 5, 2014

Okay, I feel like we're talking past each other here, and maybe it is a cultural thing with physicists and engineers. At the moment I don't care about the physical principles behind the thing, I just care if it works or not.

From my perspective the "how" is something you worry about only after you've settled that the "what" is really happening. Having a plausible theory up front definitely makes it much more attractive to put resources in and do experiments on, but ultimately the important thing is whether you have something useful.

So having written that, yeah, a bit of an engineering bias there. I suspect I'm asking my question in the wrong forum.
posted by Tell Me No Lies at 9:39 AM on August 5, 2014

Today's xkcd cartoon seems relevant.
posted by RedOrGreen at 7:58 AM on August 6, 2014

10 questions about Nasa's 'impossible' space drive answered
posted by crayz at 4:59 AM on August 7, 2014 [1 favorite]

10 questions...

Well now I have no idea what to think.

...except to say that any test rig capable of detecting the force from waves in the Gulf of Mexico from 25 miles away is pretty slick.
posted by aramaic at 6:48 AM on August 7, 2014 [1 favorite]

10 questions about Nasa's 'impossible' space drive answered

While the original abstract says that tests were run "within a stainless steel vacuum chamber with the door closed but at ambient atmospheric pressure", the full report describes tests in which turbo vacuum pumps were used to evacuate the test chamber to a pressure of five millionths of a Torr, or about a hundred-millionth of normal atmospheric pressure.

So, there's something, I guess?
posted by Nonsteroidal Anti-Inflammatory Drug at 7:32 AM on August 7, 2014

Great Scott!

A superconducting version of the EmDrive, would, in principle, generate thousands of times more thrust. And because it does not require energy just to hold things up (just as a chair does not require power to keep you off the ground), in theory you could have a hoverboard which does not require energy to float in the air.

posted by ChurchHatesTucker at 8:08 AM on August 7, 2014 [1 favorite]

That Wired list of questions has quite a point-of-view despite trying to sound authoritative.
posted by smackfu at 9:12 AM on August 7, 2014 [1 favorite]

This is the actual paper with photos and infos and all.
posted by crayz at 9:13 AM on August 7, 2014

The near term objective is to complete a Q- thruster breadboard test article that is capable of being shipped to other locations which possess the ability to measure low thrust for independent verification and validation (IV&V) of the technology. The current plan is to support an IV&V test campaign at the Glenn Research Center (GRC) using their low thrust torsion pendulum followed by a repeat campaign at the Jet Propulsion Laboratory (JPL) using their low thrust torsion pendulum. The Johns Hopkins University Applied Physics Laboratory has also expressed an interest in performing a Cavendish Balance style test with the IV&V shipset.

Your move, skeptics!
posted by crayz at 9:25 AM on August 7, 2014

It certainly does sound like the actual scientists are taking this more seriously than a lot of people in this thread?
posted by Justinian at 12:32 AM on August 8, 2014

2. Thrust was also measured from the 'Null Drive', doesn't that mean the experiment failed?
No, but it probably means all the theories about how it's supposed to work are utter nonsense.

3. They didn't do it in a vacuum, so how do we know the result is valid in space?
Someone mentioned the Crookes radiometer. Searching the web seems to indicate that the claim on Wikipedia that the effect goes away below 1 millionth of a Torr might be about right. That's five times less pressure than the vacuum NASA would have been using if they had been able to test the thing in a vacuum, which it appears they weren't. The paper mentions that they can achieve that pressure, but as mentioned somewhere above the only reference to actually doing so in this test is to say they couldn't due to electrolytic capacitors.

4. Why didn't they test Shawyer's EmDrive design as well as the Cannae drive?
According to WIRED, they did! And got positive results for it too! Which is more evidence that their test procedure for these things is somehow flawed.

7. What's this about hoverboards and flying cars?
I guess it's from some ridiculous crap on the EmDrive web site, which claims that with the addition of some superconductor magic these things could produce lots of force, so long as you don't try to convert any of it into kinetic energy. It says "An average velocity of only 0.1 m/sec will reduce the specific thrust to 0.93 Tonne / kW." Velocity relative to what, you might ask. Why couldn't you switch the thing off and then on again to instantly restore its thrust at the new velocity? WIRED would compare it to the chair using no energy to hold me off the ground. Well, that chair is connected to the earth through well-known forces. If it's anything like that, I guess they have invented anti-gravity in addition to reactionless drive. Perhaps the reason they don't say as much is that people have already heard of too many anti-gravity devices being revealed as scams and delusions.
posted by sfenders at 5:11 AM on August 8, 2014

It certainly does sound like the actual scientists are taking this more seriously than a lot of people in this thread?

Everyone has an agenda, "actual scientists" included.
posted by smackfu at 7:17 AM on August 8, 2014

True, this is a big chance to get your name in the papers even if you're almost certain the thing is not going to work.
posted by Justinian at 8:08 PM on August 8, 2014

While the original abstract says that tests were run "within a stainless steel vacuum chamber with the door closed but at ambient atmospheric pressure", the full report describes tests in which turbo vacuum pumps were used to evacuate the test chamber to a pressure of five millionths of a Torr, or about a hundred-millionth of normal atmospheric pressure.

The paper appears to contradict Wired's claim: "Vacuum compatible RF amplifiers with power ranges of up to 125 watts will allow testing at vacuum conditions which was not possible using our current RF amplifiers due to the presence of electrolytic capacitors."

Just leaving this here to save people having to search through the paper, which almost looks like it might actually be deliberately misleading about what was done.
posted by howfar at 1:39 AM on August 24, 2014 [1 favorite]