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NASA presents evidence that microwave thrusters seem to work (wired.co.uk)
406 points by jchesters on July 31, 2014 | hide | past | web | favorite | 198 comments

Wow. My gut tells me something is wrong here, and that this is being mismeasured. However, this would be an enormous breakthrough if it pans out, even at the low levels NASA has seemingly confirmed.

We're very good at generating power in space; solar is basically infinite in the inner parts of our solar system, and we have a lot of experience with RTGs and other power generation mechanisms. If we can directly turn power into thrust without burning fuel in the process, this truly changes everything.

But as I said, I think this will end up not panning out for one of these reasons: 1) The microwaves bouncing around cause a small amount of material to be lost and be sent out of the device, causing the thrust. 2) The RF in play is throwing off detection (this, to me, seems most likely -- it could explain the thousandfold difference in detected thrust levels between the Chinese and US tests). 3) Some sort of effect that is linked to gravity. No idea what, though.

I really look forward to further testing.

Edit: Given that I'm terrible with the scale of small numbers, I decided to do some quick math. If you were to use that thrust of 50 micronewtons to drive the Voyager spacecraft (722kg) full out for one year from a starting velocity of 0m/s, you would end up at 0.0911259m/s at the end of the year. By comparison, Voyager is currently traveling at 17km/s.

Given that it has so far been detected as working by two independent organisations that tried very hard to get the test right, some new science has clearly been done here. We don't yet have clear evidence that it's a new propulsion technology, as it's possible that what has been discovered is an entirely new mechanism for confounding measurement instruments, but that does not lessen the scientific value of this discovery.

There is new knowledge here. Perhaps new physics. I slightly wish I was a physicist so that I could go and find out.

The Chinese tests did not include testing in a VACUUM. Not a sealed chamber, but an actual, airless, gasless, box of some sort.

The power levels involved in these devices are 10-20 kW - that much power into anything is capable of heating air and producing currents from convection alone. A microwave cavity is exactly the sort of thing which would make a great make-shift reaction chamber for a very inefficient, very ordinary jet engine of some sort.

I note the Wired article here also makes no mention of whether they tested the device in a vacuum chamber. Its the only test which matters, and no one ever does it, meanwhile they're pumping enough wattage to flash boil water around things.

EDIT: From the NASA abstract as well - "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."

Given what this thing claims to do, and how you have to operate it (allegedly) and the scale of the forces involved (tiny), not testing in an actual, evacuated vacuum chamber is absurd.

That much current would also create a magnetic field radiating out from the wiring. Maybe the force is that of the interaction between the earth's magnetic field and the microwave.


They tested with an RF load to look for that kind of effect.

If it ain't tested in a vacuum, it's almost certainly simple coronal discharge.

Even if in a vacuum, you can get multiplication.


Except that they also tested a dummy unit with the resonance chamber futzed, so any gross physical effects from coronal discharge, convection etc, should have shown up on that as well.

I don't believe this means much of anything, other than, "the working unit probably had coronal discharge, and the dummy didn't."

That's certainly a lot easier to believe than the result they got. If, on the other hand, they observed the same sized effect in a decent vacuum, I would be more inclined to believe it. The fact that this test didn't take place in a vacuum, despite already being in a vacuum chamber ought to make people wonder a bit.

Having fed microwaves into vacuum chambers my own self: if the torsion pendulum was already in there, there is absolutely no reason this experiment wasn't run in at least a rough vacuum. I can understand not going to UHV if the cavity things are dirty or have crap which outgasses, but there is no excuse for not running this experiment in a rough vacuum.

There is actually a history of "antigravity" researchers measuring coronal discharge. http://blazelabs.com/l-intro.asp

According to the abstract of the paper they found a similar but smaller effect on the dummy unit.

If the microwave chamber is sealed air tight, they might need to construct a special one before they can test it in vacuum. But yes, they should get on that!

>two independent organisations

Sorry, but one of them being Chinese, I would say that there is only one reliable source, and the chances that they made a mistake are high.

Are you saying that no good science can be made in China purely because it's China? USSR sometimes lied about their results,but they had scientists just as good as the US did. I have little doubt that good science can be done in China too.

Here is a great paper that shows that more than 99% of Chinese clinical trials show a positive result. Either null results are being suppressed or data is being fabricated.


Good science certainly comes out of China, but a lot bad science comes along too.

It should be noted that the paper (as I've read in the abstract) extrapolates from MEDICAL data. There's a huge prevalence of pseudomedicine and mysticism which receives incorrect confirmation (as evidenced by the aforementioned paper), but a poor publication record in medicine journals isn't necessarily a good predictor of physics journals.

US journals aren't big on publishing null results either.

Nope, I am saying that Chinese science is not reliable. I'm not saying that they lie about all their science, or that no good science is done in China.

But when you have to go with your gut, and there are only two sources and one of them is Chinese, I would never reach a conclusion such as: "some new science has clearly been done here"

>>Nope, I am saying that Chinese science is not reliable

Why not?

From the Chinese graduate students and professors that I have talked to the problems seems to be that it is really is to commit fraud and get a way with it.

In particular in some fields you can get rich writing grants, getting a considerable amount of money and writing fake papers.

There is a heavy temptation for many to do the same when all of their colleges are able to buy multiple houses and live an extravagant life style. An example from ~5-9 years ago would be a Chinese professor flying to California and buying a multi million dollar vacation house in cash. This is an extreme example and was uncommon even at the time.

My understanding is that this is not the case in all fields, it is easier to get a way with fraud in the less hard sciences supposedly. I also have read about several efforts over the last several years to try and correct matters.

It is also the case that many papers written by non-native english speakers suffer from grammar and spelling errors. Unfortunately incorrect grammar and or spelling often has a negative halo effect for many on the scientific content of the paper.

There is plenty of good science that comes out of China, however it suffers from a negative halo effect from the above sources.

I know some phd's here in the states... it's not much better. Seriously.

Lots of back scratching that goes on behind closed doors and lots of bogus papers that re-use old results or "recombine" old data in order to get funding for an actual project... really a lot of hogwash and bad science.

Nothing directly to cause fraud where I am tho. Tho I'm sure some publications are better about that than others.

There's cultural incentive to report results that are favorable even if they are wrong.

This has the unfortunate side effect that research coming out of China needs to be taken with a grain of salt and extra doubly carefully verified.

It's nothing the scientific method can't handle (we're seeing the start of the verification steps here), but knowing that lots of research coming out of China is misrepresented it introduces another layer of healthy skepticism that it needs to be verified before being accepted as a thing.

Suppose University of Shanghai produces a result, and the University of Beijing confirms it. Rather than accept the result, it's likely that before it's declared "SCIENCE!" a NASA or MIT or whoever is going to want to have verification from someplace that doesn't have a long history of misrepresenting scientific claims.

This is going to be treated differently than if the original work was done at say...CERN and the confirmation was done by CalTech.

I don't think NASA has the same credibility as an MIT or Caltech. From their arsenic-based lifeforms [1] to their D-Wave "quantum computer," [2] NASA seems to work on a lot of fringe science.

[1] http://science.nasa.gov/science-news/science-at-nasa/2010/02...

[2] http://www.nas.nasa.gov/quantum/

"There's cultural incentive to report results that are favorable even if they are wrong."

Indeed, but unfortunately in western capitalism there is sometimes a financial incentive to report results that aren't favourable even if they are wrong. A bit like what happened with the banks, or with tobacco companies.

I don't know much about the physics field, but in economics all that davorak says applies [0]

[0] https://news.ycombinator.com/item?id=8115275

In economics, given things like the Reinhart and Rogoff paper on debt, that would seem to apply to places like Harvard as well.

It would alter our understanding of physics, so it would be both scientific and technological. From what I understand it would move our understanding of everything even further from classical Newtonian physics and deeper into the relativity/quantum dichotomy realm. This thing could only have a relativistic macroscopic explanation and a quantum mechanical microscopic one. Classically it's impossible.

One immediate consequence of a massless drive is that interstellar flight becomes far more "thinkable." It's not like we could build a starship tomorrow, but if this worked and if you could build a power plant (fusion?) capable of running a big one long enough, you could practically accelerate to meaningful fractions of the speed of light. Hell... I wonder if fission would be sufficient if you no longer had to take propellant? All that propellant mass could be plutonium instead, and you "burn" it slowly and jettison the spent fuel to progressively reduce your mass and increase your acceleration.

Side note: if this keeps getting confirmed, the Fermi paradox becomes even more paradoxical. "They should be here." The impracticality of interstellar flight disappears as an excuse. If this effect is possible, something is clearly wrong. Either life itself is edge-of-impossibility improbable and most of the cosmos is sterile, we are the most advanced/complex life in the galaxy, or they are here and they're not communicating with us, or something even weirder.

Once you get up to speed reaction mass might be effectively free with something like this: http://en.wikipedia.org/wiki/Bussard_ramjet

One thing I've wondered about with respect to bustard ramjets: they work by collecting hydrogen from the quite rarified interstellar medium and fusing it for energy release.

Collection of hydrogen for fusion means that collected hydrogen atoms need to be in close proximity with one another for fusion to occur.

This in turn means that interstellar hydrogen, essentially at rest with respect to the ramjet-equipped spaceship ploughing through the medium, has to be accelerated pretty much from the rest frame to the velocity of the ship as part of the collection process. This acceleration of hydrogen to ship velocity requires energy.

At what ship velocity would more energy be expended collecting hydrogen than it would yield in ship reference frame when fused? This would seem to be an upper limit for Bussard-type propulsion systems.

It's the same with jet engines, for similar reasons. (Although in practice your maximum speed is largely dictated by "melting the engine is considered shortsighted".)

The theoretical upper-bound exhaust velocity of a Bussard ramjet is something like ~0.12c, assuming you start with 4 hydrogen and end with 1 helium. As such, the theoretical upper-bound speed limit relative to the interstellar medium of a Bussard ramjet is also ~0.12c. In actuality, it will be quite a bit lower, as quite a lot of the energy is carried off in the form of energetic photons and neutrinos.

Personally? A Bussard ramjet will never work, even assuming we get the scoop part figured out. The lower bound on how fast it has to go before it can start working and the upper bound on how fast it can go are too close. Not to mention the Lawson criterion for hydrogen burning (4xH -> He), or, alternatively, the problem of containment of the catalyst and the beta-decay steps of the CNO cycle.

If you crunch the numbers, it turns out the bad news is a Bussard ramjet won't work as an engine.

The good news is, it will work as a brake. That takes care of the deceleration half of your delta-V requirement, which is better news than it sounds: thanks to the rocket equation, it doesn't just halve your required mass fraction of fuel, it square-roots it.

Assuming proton-proton fusion, the speed limit is about 12% c, relative to the interstellar medium (http://www.projectrho.com/public_html/rocket/slowerlight.php). That depends, however, on the assumption that the initial kinetic energy of the incoming hydrogen is completely wasted- that the ramjet does not have "regenerative braking", so to speak, that can recover some of the pre-existing kinetic energy. That's a pretty reasonable assumption from an engineering point of view, but physics theoretically allows us to do better.

This engine does not change the energy needed for interstelar travel, only reaction mass, and reaction mass is often free with an energy generator, because all of them waste some mass. If this thing is confirmed, it will be a much more significative scientific breakthrough than a technological one.

That said, there is no reason for interestelar travel not to be viable. It's just too expensive for us with our current tech.

Reaction mass is definitely not free. You can get a lot of energy by a number of means, but the need to haul an ever increasing quantity of reaction mass for every bit of delta-v you want is the limiting factor.

If you did not have to haul any reaction mass, then delta-v is limited solely by energy. Which means you can take some solar panels and thrust indefinitely up to light speed, with a vessel weighing a couple of kilos as opposed to megatons.

That would not work for several reasons. The energy produced from the solar cells would be negligible compared to the force of photons hitting the panels. If you instead of an engine just used a very large thin sail with a proportionately small cargo then you could theoretically reach c, but only close to stars. If you instead removed the sail and used antimater as an energy source, that would also work. The problem with all ideas is the interstellar medium, particles, photons. Drag from interstellar medium would damage and slow down the ship, even at lower percentages of c. Close to c everything would behave as shot from a particle accelerator and even photons from background radiation would be blueshifted to high energy gamma rays.

I wasn't commenting on using photon reaction - I was commenting on using this hypothetical reactionless drive (which would, presumably, produce more thrust then photon force - which the claimed device does from relatively small amounts of power).

If you had a reactionless drive, then the solar sail force would be negligible compared to the drive.

Even if the thrust from reactionless drive would be higher, it cannot be higher than the pressure produced by the photons on the solar cell, which you use to power the drive. If the developers claim that it does, then you have basically infinite energy.

I wonder which speed should a spacecraft have so that cosmic microwave background will be as bright as Sun from earth.

This may explain "where is everybody", btw. Why do you need a Dyson sphere when there's free sunlight.

We have no technology for carrying energy that does not waste more than enough mass for using in reaction. Reaction mass is free with the carried energy.

Well, except for solar pannels, of course. But you can't move near lightspeed and stay near the Sun.

No, look up the rocket equation.

Let's say your rocket is a mass driver, throwing rocks out the back end with electromagnets. You need two things: one is an energy source to power the electromagnets, like some kind of nuclear reactor, and the other is a big pile of rocks.

The big problem for a rocket is that it's not just carrying the payload and reactor fuel, it's also carrying that big pile of rocks. For a given exhaust velocity, the faster you want to go, the bigger that rock pile has to be, which is even harder to push, and the challenge just multiplies. If you're trying to get to another star it's practically impossible.

A reactionless drive would still have the nuclear reactor, but it gets rid of the big pile of rocks. Now higher speed no longer means you need a bigger rock pile, it just means you run the nuclear reactor longer. You'll need more reactor fuel but with the mass driver you needed that plus the bigger rock pile. Now you just need more reactor fuel, and that's relatively minor.

So yeah, it'd be a huge technological breakthrough, if it actually works.

I don't know where you got those numbers from. Momentum of an object is equal to mass times velocity. Change in momentum is equal to impulse, which is force times time. Therefore f * t = mv, and change in v = f * t / m. Plugging in the numbers, (0.00005 N) * (3600s/hour * 24 hours * 365 days) / (722 kg) = 2.18 m/s

Voyager used gravity assist to achieve its current velocity, so the comparison isn't 100% fair. A craft with this drive can certainly avail itself of that technique as well.

Other deep-space spacecraft make use of non-trivial delta-v, around 200/300 m/s for some maneuvers: https://space.stackexchange.com/questions/4054/delta-v-of-de...

Oh, for sure. It's by no means an apples-to-apples comparison (just being in orbit around Earth before you start your journey out gives you a huge jump on that), just gives you a sense of scale.

Let's not forget a similarly ellusive case which lasted quite long:


Although admitedly this thruster can undergo much more testing.

It's not a breakthrough in science at all, honestly. It is already well known that you can propel something just by generating photons (generally using nuclear power to heat an element, just like a light bulb). Microwaves are just a different wavelength. It is just too inefficient to matter at the moment. The only breakthroughs to be made are in efficiency. Photons still have energy and momentum, just no rest mass, and there is even such a thing as electromagnetic pressure created from photons transferring momentum.

It's true you can generate thrust by throwing photons out one end, but that's not what this device does. It bounces microwaves around inside a closed, superconducting chamber, with one end wider than the other.

Oh, it's that device? The one that was on the cover of New Scientist at some point? We (i.e. the lecturer) mocked that in physics lectures (mostly on a "look at the shit New Scientist publishes..." sidetrack). It may also have claimed perpetual motion, while it was at it.

If there really is some quantum interaction, then this becomes interesting, but from momentum alone the contributions from the sides of the box always exactly cancel the resultant from the mismatched plates (by definition of a closed box).

If you've got constant thrust from constant energy input, that pretty much implies perpetual motion, since energy input increases linearly with time and kinetic energy with the square of time.

If you want to say you get less thrust as velocity increases then you run into trouble with the principle of relativity.

So I'm skeptical too, though I think it's worth continuing experiments.

Sure, you can only find the mistake while repeating the experiments (perhaps, as someone else suggested, in a vacuum might be a plan).

I hadn't noticed the constant thrust problem you mention, I'm now recursing back through the equations I remember to try and work out why it costs more energy to push something that's already moving fast... wait, force applied was never anything to do with energy to start with, impulse/power were. Brain-fart resolved.

What if you had an ideal electric car driving on flat ground with no friction losses (i.e. if you turn off the motor, it coasts forever.)

If you draw constant power from the batteries, is it impossible to maintain constant acceleration?

Oh right, that makes sense; constant acceleration implies constant force, and work is force*distance. As the meters tick by more rapidly, the motor performs the same work in less time, and thus the required power increases.

Which means, "a reactionless drive is like a car in space" would be a nonsensical concept without a preferred reference frame.

Wait, I get what you're saying (0.5mv^2), but isn't it relatively straightforward to get constant thrust from constant energy in other situations? Laser --> lightsail, for example.

To reply to myself, the thrust you'd get from a laser that shoots at you would in fact diminish as you accelerate away from it, as the light would redshift and thus carry less energy to you.

Argument from Authority is a thing.

indeed, my PhD supervisor is often wrong about stuff. I don't believe my lecturers per se, but rather I remember the argument about cancelling edge effects (which certainly seems to apply here.)

It's already a kind of well known concept in SciFi to bounce the photon back and forth a lot, getting a little hit of momentum each time (and draining its energy, thus changing its wavelength). Keeping the reflecting pair on the rocket and trying to use asymmetry to pull more off on one side than the other seems a pretty straightforward thing to try.

Exactly right. It's an apparent violation of Newton's Third Law, unless the photons are pushing against virtual particle pairs as suggested in the article.

It's not a violation from the reference frame of the rf - just yours.

Considering that photons have a force, I wonder if the force of the photos hitting a craft propelled by an EmDrive would be able to approach a star. The craft with an EmDrive would likely need solar panels to sustain the EmDrive which would increase the craft's surface area to encounter more photons and other energy particles.

There's no need of a solar panel for big spacecraft, US and USSR have designed compact enough nuclear reactor that can generate Mw of power for various submarines,like here http://en.wikipedia.org/wiki/Alfa_class_submarine. There has been time that a single US submarine was able to power the entire Hawai island after a natural disater http://news.google.com/newspapers?nid=1755&dat=19821128&id=E...

Voyager is only traveling at 17km/s because of orbital maneuvers. These thrusters would probably not be used for delta-v. However, they would be great for reliable attitude control. Currently attitude is controlled with reaction wheels, small fuel based thrusters or magnetorquers or some combination. Reaction wheels fail, fuel based thrusters run out of fuel, and magnetorquers are weak.

NASA is running out of fuel (Plutonium) for RTG's and no new fuel is produced.


The plutonium shortage in NASA really has nothing to do with technology or science, but just politics. We simply stopped producing the stuff, but we could start again at any time; as the article you linked mentions, we're planning on doing so.

There's enough plutonium to make 10,000 nukes stored in the Sellafield facility in Cumbria, England


So, there is no storage.

It isn't that simple:


Of course a program could be spun up to actually do the separation, but I think it might be sort of expensive.

I've been there as a child, if I'd have known that, I probably wouldn't have gone.

I know I read an article about 2 years ago saying that more was being made. Now I have to find it.

EDIT Got it! http://www.spaceflightnow.com/news/n1303/20pu238/#.U9qX5fldX... The date is six before the other story.

"For the first time in 25 years, the United States is producing plutonium fuel to power spacecraft on missions beyond Earth, replenishing a dwindling stockpile to supply NASA's next Mars rover and other proposed probes."

It's impossible to run out of plutonium so long as uranium fuelled reactors are running. It's a common by-product of the fission process.

It maybe be harder or impractical for them to get it or process it, but saying "no new fuel is produced" is false

That's like saying we won't run out of oil because we are producing carbon and oxygen... if it's not in useful form, it's perfectly sensible to say that no new fuel is being produced.

Normal uranium reactors produce a mix of plutonium isotopes, which are hard to separate and end up as nuclear waste. NASA needs pure Pu-238, which has to be made in specialized reactors.

Iirc, all Canadian CANDU reactors produce large amounts of weapons-grade plutonium.

Which is exactly the problem. RTG needs Pu-238, and can't use weapons-grade plutonium, which is mainly Pu-239.

That design has also been altered by India to consume the plutonium by-product, using it as fuel.

Combining with the comments below, there is a note that the test worked even when they changed a vital configuration (seemed to be a control test).

When a control fails, the conclusion is that the experiment is buggy and you need to rethink things. Unfortunately, it seems from the article, the conclusion was that some new physics was at work here.

19 thousand years.

Woops, you're right! I was doing some ballpark math a couple orders of magnitude higher thrust, to see what would be practical if this were scaled up.

(For context, my original post said that matching Voyager's velocity would take 19 years.)

Your first explanation was my immediate thought -- but I assume they at least checked for this (if it's obvious to a high school physics type such as myself).

I would assume that an actual thruster would be a bit bigger than the test unit!

What happens after two, five and ten years?

It should increase linearly.

Keep in mind that a linear speed increase is still a non-linear distance increase over time.

So, it seems from reading the paper's abstract that they did measure thrust both from the real propulsion test device and from the dummy test device. That's not very promising:


> 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).

I'm not as certain. They don't mention measuring thrust from when they replace the test article with an RF load (whatever that means), or when they reverse the test article. Then they end on this note: "Test 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. Future test plans include independent verification and validation at other test facilities."

So that makes me think that maybe they just don't know why it works, so the modified one still works for the same unknown reason. Probably not though. Like they say, they need more tests.

And they did the experiments in a vacuum chamber but at atmospheric pressure so that I can easily imagine that they just accelerated polar molecules or something like that.

Yes, or maybe something like a plasma actuator.

Meh. If that's true then Wired shamelessly went for click bait. :P

Well, I'd love to be wrong really.

Pretty please, somebody confirm my reading comprehension skills are complete garbage? :)

It doesn't say how much thrust the null article "produced." If there's a significant difference, that's still very suggestive.

My next suspects for error would be that the device is propelling itself through heat dissipation or electrostatic ally by throwing off charged particles. Both of those possible confounding factors are testable, either by measuring heat via IR imaging and computing what propellant effect that heat would have of by dummying up the null device to produce and dissipate an identical amount of energy to the non-null device.

But honestly, I'm a hacker. I'd go rent me a vacuum chamber and put it on a whirlygig and see if it makes it spin. If it spins faster and faster and faster until it flies apart (well okay maybe I'd turn it off before loss of structural integrity), something is definitely off in our understanding of physics and God really will let us have hoverboards. So give me a hoverboard.

if the drive is propelling something to get tens of µN, you could float strips of thin plastic film across the supposed path of reaction matter and it'd be visibly accelerated by collisions with that something, at least if my math is right.

Would have been nice if the scientists didn't know which device they were testing - blind.

In the majority of physical experiments doing a blind test is not that helpful, since it will not change the physical data. It can happen that blind testing is helpful, but most of the time it is a sign that the protocol or equipment needs to improved.

Most of the time bias creeps in at the analysis stage. In my experience. Deciding what data to keep and what to reject, deciding which fitting algorithm is working correctly, etc.

The purpose of blind testing in medicine is to eliminate the possible effects caused by different patient-doctor psychological interactions.

If we find out that inanimate objects behave differently if the operator does/doesn't believe in their success (as patients do), then that'd be much bigger news than engine development.

Blind testing is still very important in physics; go look up N-rays.

Third replication then?

This stuff has been hovering (pun intended) at the edge of detection for some time: spinning superconductors, this thing, etc. all claiming to provide evidence of tiny amounts of thrust in apparent violation of standard conservation of momentum. Obviously skepticism is in order, but either something is very wrong with all these experiments or there's something here.

What's interesting about this one is that the original inventor has something resembling a theory. It may not be a complete theory, but it tries to explain it via relativity in a way that makes physical sense.

I'm always really skeptical of these things, but not in the knee-jerk total dismissal sense. I just say show me the replications. They're doing the right thing. Now we need more people to build these and test them under different conditions.

The ultimate test would be to launch one, since you can't really screw up detection of a big delta-V change in space.

Not sure this counts as a replication, yet. This is an un-refereed conference paper, I'd really want to see a proper publication.

The other strange thing in the paper, but not mentioned in the article, is that the 'null device' produced thrust:

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).

I'm not a physicist and I can't debunk this theory point by point, but actually, you don't need to know much physics to see how this must be wrong. Special Relativity requires conservation of momentum, in every observer's frame of reference. If someone claims to explain supposed non-conservation of momentum by invoking "Special Relativity", they are just attempting to trick you.

(As far as crackpot theories go, I'm actually surprised they didn't throw in a "quantum" or two for good measure.)

(Edit: I'm not saying that the experiment itself is invalid. It might be, I don't know. What I'm saying is the supposed theory[1] is necessarily wrong, because you can't get non-conservation of momentum out of Special Relativity without suggesting new laws of physics, which is not at all discussed in the "paper" I linked below.)

[1] http://www.emdrive.com/theorypaper9-4.pdf

But they did throw in a "quantum" or two. This is basically what they are shooting for: http://en.wikipedia.org/wiki/Quantum_vacuum_plasma_thruster

Like I said, the best test would be to put one in space. If you fire the thing up an the satellite's orbit changes, that's kind of a hard measurement to screw up. (Let it orbit with the drive off for a while as a control.)

If you fire the thing up an the satellite's orbit changes, that's kind of a hard measurement to screw up.

Caution: a re-reading of the Pioneer Anomaly is in order before you start assuming things in microgravity move because of new physics ...

No idea why you're being downvoted for this. You're completely correct as to why this device's claimed physics are bunk (and why, as I note above, the way it always gets tested is highly suspect).

Not being very familiar with the the topic, what would it cost to build a usable version of this? How massive would it be?

Constant thrust using only solar power and no propellants says to me that one could certainly shut the skeptics up by flying a microsatellite to Mars and back.

Constant thrust using only solar power and no propellants is already possible. Just shine a light backwards, or better yet turn that solar panel into a mirror. What makes this so strange is that it is emission-less even counting photons.

It would be a lot cheaper to lock one in a vacuum chamber and see if it still works.

I think most people think that by far the most likely thing is that they missed something and this isn't doing what they "claim". While quietly hoping it does :P

This is one of these things which is just a few percent less crazy than it sounds.

The issue is that special relativity isn't quite compatible with quantum gravity, see


What it comes down to is that quantum gravity has a length scale and a time scale, both of which are unthinkably tiny. However, special relativity says there is nothing special about any particular space or time interval because if somebody was going fast enough, an interval that looks like a planck interval to most people could get expanded or shrunk to something big like a kilometer or an hour.

But following that line of reasoning is problematic if there is no special reference frame, since for all I know I already am going incredibly fast relative to some imaginary observer.

Doubly-special relativity manages to preserve the invariance of the speed of light under ordinary conditions but also preserve the invariance of plankian quantities under extreme conditions. Related theories also bring in the idea of a special reference frame which means you might be able to "push" against the vacuum.

The main trouble jiving that with these experiments is that the energy scale at which DSS effects come into play is huge, way out in grand unification country, so it's hard to believe it could be probed by these experiments.

I've always thought it was unfair that this is impossible. It's not like you're getting something for nothing - you are still required to expend energy. So why does the universe have to be such a dick about converting electricity directly into motion?

The universe isn't really a dick. It just cares deeply about the conservation of momentum.

Following the Noether theorem, conservation of momentum follows from uniformity of space (translation symmetry), i.e. for an experimental result it doesn't matter whether it takes place here or some light years away. Although we have some astronomical hints for that and it is a compelling hypothesis (in light of Occams razor) this is not necessarily the case. Finally, the concept of conservation of momentum is a theory for which we have compelling evidence in that nobody has been able to falsify that. But this doesn't necessarily mean that this holds for all times.

And entanglement.

Where can I read more about how/why this is impossible? Isn't it just the reverse of a solar sail to send out the photons yourself rather than catching them? It seems like shining a flashlight in one direction should produce thrust in the other. Is that not true or is it something different at work here?

>> It seems like shining a flashlight in one direction should produce thrust in the other. Is that not true or is it something different at work here?

That is absolutely true. Electromagnetic radiation effectively has momentum. Take the energy in joules and convert it to mass via E=mc^2 and then plug it in the momentum equation p = mv but using c as the velocity and you get p = E/c. Change in momentum over change in time is force, so we can then get to F = P/c. I believe the units are Newtons, Watts, and meters/sec. So with 300 Megawatts you can produce a whole Newton of force!

I used this on a physics final once, but hid the work because the prof expected us to use formulas for radiation pressure derived from electromagnetics and I had missed that lecture. Later I derived the general case of my approach and it matched the EM derived formulas. 50/50 if he would have appreciated it or marked it down. The question was "a 50mW laser is reflected off a mirror, what force is exerted on the mirror due to the beam?". Note that the change in momentum is doubled for reflection vs emission or absorption.

> the prof expected us to use […] and I had missed that lecture

You just gave me a wave of nostalgia. That’s how I survived all of my math and physics classes. If you develop an intuitive understanding of the material, you can derive things as needed from a few core principles you do remember. A bit sad when learning is the way to subvert an educational system, though.

That's how I passed quite a few math exams that I couldn't be bothered to study for.


Yes, charged batteries have more mass per e=mc². That means that a good AA battery weighs ~100 picograms more than a dead one.

I am not sure that I buy that. Charging the battery moves molecules from one electrode to the other. The number of atoms in the battery doesn't change. Do they really get heavier by virtue of changing their arrangement?

If you use that logic (and maybe it is right) then it seems to me as though pushing a rock up a hill makes it ever so slightly heavier too.

Maybe that's my complete lack of intuition about non-classical stuff though.

Yes, they do get heavier by virtue of changing their arrangement. And yes, pushing a rock up a hill makes it - well, the rock will get slightly lighter in weight by virtue of being further from the Earth (classical inverse square law of gravity) - but the total mass of the rock-Earth system (assume you used solar power so you didn't take the energy from a terrestrial source) will slightly increase.

This is my understanding: say you have a spring which is just two positive particles. When you compress it, bringing the particles closer, you're storing energy in the EM field (E²+B²) near the particles. When you accelerate the spring, you're also accelerating the energy, which requires extra energy. This feels the same as the spring becoming heavier.

This is just a microscopic explanation for the general principle that energy has mass. I've never done the math to confirm that the extra energy to accelerate the compressed spring corresponds to the extra mass from stored energy.

Chemical binding energy.

When oxygen combines with hydrogen to form water, it gives off energy equivalent to the change in mass (water molecules are oh-so-slightly less massive than their constitute oxygen and hydrogen atoms). A battery produces power by converting molecules into different molecules with more binding energy (i.e. lighter molecules that have given up more energy/mass).


When you do all the math, photons have mass/momentum etc. which all keeps everything copacetic.

> Isn't it just the reverse of a solar sail to send out the photons yourself rather than catching them?

No, that'd be the case if it were open but it isn't. As I understand it, it's an entirely closed system. That's what's controversial, there's nothing coming out of this "thruster", not even photons.

There's an image on page 3: http://www.emdrive.com/yang-juan-paper-2012.pdf

(disclaimer, I only have a hazy understanding of what this is supposed to be)

Wouldn't it be relatively straightforward to repeat the Chinese test in a garage? We're talking a whopping 70 millinewtons here, so equivalent to the weight of 7 grams. Some shrews are lighter than that.

Microwave science has this strange aura, since the stuff that happens in cavities etc is not exactly obvious at first sight. http://en.wikipedia.org/wiki/Cavity_magnetron

I checked again. Some insider said the Chinese machine does produce 80 millinewtons, but it's less efficient than the NASA one since they take way more power input.

sorry to disappoint you, but it's actually 30~50 micronewtons, which is only 0.04g.

> As I understand it, it's an entirely closed system.

You got the gist correct. The microwaves are supposed to be completely contained.

> It seems like shining a flashlight in one direction should produce thrust in the other. Is that not true or is it something different at work here?

Yes, there does seem to be something else. Classical mechanics cannot explain thrust from shining a flashlight inside your spaceship. But "the EmDrive converts electric power into thrust ... by bouncing microwaves around in a closed container"

I think that when you send out photons, there is energy in them. Like, energy you would have rather have converted into momentum. ...IANAP.

The momentum those photons are carrying implies a change in momentum to the emitter that is equal and opposite. Conservation of momentum applies even though the emitted substance is electromagnetic radiation, not matter particles.

What's weird about this device is that the radiation chamber is completely closed---the microwaves emitted are then re-absorbed by the chamber, but the claim is that the net momentum of the chamber has changed... Somehow. If it is true, it'd be a violation of conservation of momentum (unless the microwaves are somehow passing momentum to something else, which is why people are talking about quantum mechanics possibly coming into play).

We're well beyond my physics knowledge here. (See IANAP above!) So, I have questions.

Is momentum the only type of energy a photon has?

By allegory: Suppose a cannonball can be red hot, or cool. Separately, it can be flying or at rest. So, there are four cannonball types: hf, hr, cf, and cr.

The hot, flying cannonball has the most energy and the cool, resting cannonball has the least. Yet, the momentum of both flying cannonballs is equal--temperature is orthogonal.

Is all that right?

If it is, then... I thought photons contain some energy that is similarly orthogonal to momentum.

...I guess I don't recall learning that, so maybe I just made it up. But, I have seen videos of laser pointers that can burn paper--they don't seem to have recoil. If the energy that is burns that paper is ... momentum, then I've clearly misunderstood the SCALE of mechanical energy vs. thermal energy. But if the thermal (or something?!) energy is ... separate, then... Well, then we're back to the original point: most of the energy you use to create a photon isn't translated into momentum, so light isn't the propellant you're looking for.

NB I don't have a comment about the microwave chamber other than "NFW.".

IAAP, so let me take a stab at answering it.

Each photon can be completely described by three values. Where is it? Which direction is it traveling? What is its energy? For photons, unlike the cannonball, there are no additional places to store energy.

So, what does that mean for the laser example? Because you are absolutely right that lasers can ignite paper. Photons carry both energy and momentum, but the two cannot be separated. If the paper takes the energy, it must also take away the momentum. The key equation for light is "E = pc", energy equals momentum times the speed of light. The more the energy, the more the momentum. Reduce the energy (or transfer it into the paper

Let's start playing with some numbers. I like drinking tea, and I don't like waiting very long for the water to boil. So, I take out my 1 megawatt laser, and bring a cup of water to boil in about 0.5 second. The lasers you have seen igniting paper are usually 50 milliwatt, so we are talking 20 million times stronger. If there is an effect, surely it would be visible here.

So, that E=pc formula still works here. Because I am transferring energy to my cup of water, I must also be transferring momentum. The question is, how much momentum? To determine this, I rearrange the formula to p = E/c. Using the magic of google to handle the unit conversions, I find that I have about 0.001 pounds of force. The friction of the cup against the table is far, far more than enough to keep the cup from showing any reaction whatsoever.


You are asking absolutely great questions. It is fun to hear somebody not accepting things at face value, comparing to known experiences, and figuring out how to make them fit. Keep up the great work.

Thank you for this.

Let's see, I think a million watts is a bit more than we need to 235 mL of water in 0.5 seconds.

A calorie (not a Calorie) is the amount of energy it takes to raise 1 ml of water 1 deg C. Suppose 15C water (pipes run through the ground which is cool).


Is that right? While a megawater later is overkill for your cup of tea, it is NOT overkill for ten cups of tea (in half a second)?

For some reason, I always thought of a megawatt as BIGGER. Or, I guess I thought of boiling water as SMALLER.

In any case, there's still something I don't get here.

Obviously if you are trying to change the velocity of your spacecraft and all you have is a cup of water and a megawatt laser, you're not going to point the laser into space, you're going to point it at the cup. (Which happens to be roughly and conveniently conical.)

Picture this: point your megawatt laser at your friend's spacecraft and her cup of water... She'll get delta-V when her water boils, but that's AFTER you already got a little (very little) recoil from firing the laser.

I guess I don't understand the relationship between momentum and mass when mass is zero.

You are correct, and I was wrong in the amount of energy necessary to bring the water to a boil. I was using wolfram alpha, "energy to boil a cup of water", which probably then gave me the energy needed to boil it all away, not just to bring it to a boil.

It takes a tremendous amount of energy to heat things, overall. For example, compare the energy in a bullet to the energy in a warm cup of water. A 20g bullet moving at 400 m/s has 1600 joules of energy. That amount of energy, when used to warm a cup of water, would only warm it by less than 2 degrees Celsius.

Let's start with your last statement, on the relationship between energy, momentum, and mass. The most common formula is E=mv^2/2. This works for objects with mass that are moving slowly. Now, by "moving slowly", I mean "relative to the speed of light". The fastest object made by man, the Juno spacecraft, moves at about 140,000 km/hr, which is a paltry 0.00013c. This formula still works here.

If we want to know what happens at faster speeds, we need to dip into special relativity. There are some messy derivations, but one critical formula that comes out of it is E=sqrt(m^2c^4 + p^2c^2). If you imagine a ninety-degree triangle where the shorter sides are the mass of an object and the momentum of an object, then the long edge is the energy. Increasing either mass or momentum will increase the energy.

Suppose we start dialing down the momentum in this equation. After some math, (http://en.wikipedia.org/wiki/Binomial_theorem ), we arrive at E=mc^2 + mv^2/2. This is the origin of the famous E=mc^2. We now have two terms, the rest energy, and the kinetic energy. Note that the other term is the more familiar form of kinetic energy, which is why it works in everyday life.

Now, suppose we go the other route and set m=0. Then we get E=pc. Even though one side of the triangle (mass) has been reduced to zero, the other side (momentum) still gives it a non-zero energy. I apologize if that is more math than you had been hoping for, but eventually one always runs into some math.

A few things on the spaceship. You are absolutely right on the thinking of it. As soon as the laser switches on, it starts applying force. If my friend's spacecraft is one light-second away, I don't need to wait one second for the laser to reach her before feeling anything, because the light itself carries momentum away. In fact, if I wanted, I could just fire the laser out into space. I get propelled one way, and to balance out the momentum, the photons are travelling in the opposite direction.

> Is momentum the only type of energy a photon has?

Well, momentum is not a type of energy.

But then, for photons and any other massless thing, the momentum is a function of the particle's energy. It's mass that make it possible[1] for the momentum to vary.

[1] IANAP and don't know the exact causation relation here. Talking about causation probably does not even make sense, but I'm not sure of that.

Not quite. It's the ability to travel at different velocities that allows the momentum to vary for particles with mass. But massless particles like photons always travel at the speed of light, so that option is not open to them. Therefore, their energy and momentum are always proportional.

I guess a related question is "why does a flashlight in space not propel itself". And I don't know the answer to that.

Edit: Ok. That makes sense. I guess it's just not a practical source of propulsion.

A flashlight in space does propel itself, but that's not really a related question. A more related question is why does a flashlight in a fixed mount inside of a windowless spacecraft not propel the spacecraft (or, similarly, why does a fan inside of a sealed, ventless housing attached to an airplane wing not function as an engine.)

Of course, if there's some way this does work despite what we think we know about physics, its a pretty gigantic breakthrough (well, at least, understanding and practically applying it would be -- otherwise its just an anomaly that provides a pretty gigantic question mark...)

A flashlight in space would propel itself, since photons have momentum.

It does. But the propulsion is really, really tiny.

For all those saying this is impossible because of X, I think the great Richard Feynman put it best:

"If it disagrees with experiment, it's wrong"


Experiments this delicate are very difficult to get right.

And it is very difficult to overstate just how much established physics would have to be scrapped if momentum conservation turned out to be violated. (Just for starters, relativity implies that non-conservation of momentum in one frame must always involve non-conservation of energy in another.) Why would quantum field theory calculations match experiment to ~12 digits of accuracy if its basic foundations were flawed? (Those calculations are affected by literally every possible quantum vacuum effect, so why wouldn't introducing some new set of momentum violating interactions completely throw off the results?)

This is an astoundingly extraordinary claim, and it should thus require tremendously compelling evidence. I'm not at all convinced that these experiments are clean enough or consistent enough to even approach that standard.

Of course, but there's still a lot of things consistent with the experiment that are less improbable than reactionless thrust.

This is still an important experiment, though -- if your testing methods are discovering 'impossible' effects, they are discovering effects that are possible but wrong, too. This is something worth getting to the bottom of. Every contradiction is a discovery, even if it's not the discovery you want.

Assuming you can perfectly rule out measurement, experimental design, etc. flaws, of course.

You want to apply Bayesian reasoning to this. Conservation of momentum is a very well-tested, long-established physical law. Our priors going into this experiment should be "it is impossible to produce thrust without throwing mass or energy out the back of your thruster!" at something like 99.99999%

So now this experiment has happened! That should indeed reduce our belief in the above. But there are other explanations, like, "the experimenters screwed up." So previously our beliefs were:

There is no way to get thrust without blowing mass or energy out the back end of a thruster (and if you do it as energy, it's a completely enormous ridiculous amount of energy): 99.99999%

There is a free lunch: 0.00001%

Now we think:

There is no way to get thrust without blowing mass or energy out the back end of a thruster (and if you do it as energy, it's a completely enormous ridiculous amount of energy) (and those experimenters screwed up): 99.99998%

There is a free lunch: 0.00002%

> "If it disagrees with experiment, it's wrong"

Sure. But if a small number of easy-to-misconfigure experiments appear to disagree with the conclusion of a large number of experiments of various difficulty all pointing in the same direction, its not unreasonable to suspect that the most likely explanation is an error in the setup or interpretation of the small number of experiments.

Isn't this drive using relativistic effects similar to what allows a magnet falling down an aluminium tube to produce an opposite magnetic field and slow down? I mean, clasically speaking that effect is also impossible.

Previous discussion, from six years ago: https://news.ycombinator.com/item?id=314297

Some interesting comments, and much skepticism

So it produced 720 mN of thrust the first try, but under more careful conditions it produced 30 uN? This smells like a spurious result, but I suppose more investigation is in order.

Two different devices, Shawyer's "EmDrive" was the 720mN device, Fetta's "Cannae Drive" was the 30uN device.

Wanted to jump in and ask, does anyone remember a site that went through the math of two magnetic rings being charged and discharged out of sync, utilizing the delay in the speed of light between the rings to create a net force? Imagine a craft shaped like a dumbbell, with the rings where the weights are:



The idea was that you'd create a strong magnetic field in ring 1, and then the wave would travel outward both directions (one away from the ship, and one along it) and interact with ring 2, which has the opposite polarity. Ring 2 would be attracted to the magnetism from ring 1, and pull the ship to the left. Then ring 1 would turn off, and by the time the wave from ring 2 reached it, there would be no interaction. So the craft would feel a net thrust to the left. The process would repeat over and over again at high frequency, propelling the craft faster and faster.

I believe the site said the process was 25% efficient, and didn’t violate any laws of physics. The difficulty lies with hysteresis because it takes a comparatively long time to charge a magnetic field, compared to the time it takes light to span the distance. So it went off on a tangent about using lasers to charge a superconducting ring.

But I’ve always wondered if resonance could somehow be used to take the coils out of sync automatically, a bit like a tesla coil but with an imbalance the puts one ring slightly behind the other in time with respect to their frames of reference. As they move more out of phase, the net force on the coils should get stronger and stronger. This sounds similar in some ways to the the way a magnetron works, so if it can be put out of phase in a similar way, then I’m not entirely surprised by NASA’s result. If it’s true that the time delay in the speed of light can be converted to a propulsive force, then it’s going to change, well, pretty much everything about space travel. I really wish I had the link to that site.

My approach as a physicist doing fundamental research is: I put a mental black box around the device. I don't want to know how it looks like and what it does internally. To me it's just a box into which some quantum numbers go in and some quantum numbers go out. I don't care about the complexity of your device. It doesn't matter, because that complexity tells me nothing about how the damn thing interacts with the outside world.

Now when you speak about magnetic fields, inductors and resonances you're essentially using a lot of words to describe something that has been known for over 100 years and put to practical use in millions of devices: Radio Antennas. The one ring acts like a radiator element and the other ring is an actively driven director. Other names for this are phased array antennas. This is absolutely nothing new under the sun.

And yes, this thing produces net thrust, because electromagnetic radiation carries momentum.

I bet that if you actually work out what's happening, at best it's equivalent to just emitting photons, which you can do by just aiming a flashlight out the back.

"Efficiency" isn't a well-defined quantity, though. What you are looking for is thrust/power, and even a device that converts energy to photons with 100% efficiency produces preciously little thrust per power used.

Conservation of momentum dictates that the momentum gain follows from the net momentum of emitted photons, so it really should be simply a matter of shinning light away. dp=dE/c (and since magnets have histeresis losses as mentioned, they radiate energy isotropically due to heat, lowering efficiency).

That's what I'm saying. But P/c is very little momentum compared to what you get from taking that power to throw anything with rest mass out the back.

Ya that's definitely true. You might check out JLN labs, they have a bunch of over unity and reactionless rocket experiments drawing from the work by TT Brown:


Some of the more fascinating ones are in near-vacuum. I remember reading that asymmetric fields might be able to propel virtual pairs or interact with the interstellar medium, but unfortunately the effect seems to fall too quickly in relation to density.

There was another article about how since cooper pairs are delocalized in a superconductor, they may not interact with gravity. It was trying to explain things like the electrogravitic effects near spinning superconductors:


I keep thinking that if any of these do stray from physics, it will be interesting to see how they reconcile it. So far it hasn't happened but days like today make me wonder if it's just around the corner.

Was it something like this? http://arxiv.org/html/physics/9908048v2/conclusion.htm

> Then ring 1 would turn off, and by the time the wave from ring 2 reached it, there would be no interaction.

That sounds like the magic part. "Magically, nothing will occur." IANA physicist, but it sounds like Lenz's law might be relevant.

> I believe the site said the process was [...] didn’t violate any laws of physics.

Well, there's the rub. It sounds like it directly violates conservation of momentum and Newton's third law.

That's not the one, but it's along similar lines. The site had lots of graphics and was written in layman's terms. I think I first read it around 1999 or 2000, and then lost it.

I agree with the others that any force above light pressure would appear to violate Newton’s laws.

However, I have never seen an analysis or simulation that incorporates the delay in the speed of light. Ring 1 would be limited to light pressure, and be symmetrical, but ring 2 would dissipate one half of the wave by canceling it, so technically only 3/4 of the energy would be emitted if we thought of the whole system as a black box. The other 1/4 would have to go somewhere, probably mostly heating the rings but some of it could go into the box as kinetic energy.

I think an easier way to run the experiment might be to set up a square wave with a duty cycle of 25% and a period equal to the time it takes for light to propagate between the rings. Then it would just be a matter of varying the phase on one of the rings and seeing if there’s a net force on the setup. With a spacing of 10 centimeters, there would only be 0.33 nanoseconds to build a magnetic field, and it’s going to fall by the square of the distance between coils, unless we could use the long wire approximation for large coils which falls linearly by distance:


The forces might be small but they should be measurable, and if they are even a fraction of a percent above light pressure, it’s a really big deal. Maybe the duty cycle should be 33% or 50%, maybe the period should be double or half this, maybe another waveform would be more efficient, but you get the idea.

Blah what I wouldn’t give to have the disposable income to work on this and the hundred other half-baked ideas laying around the house. It’s a special kind of hell to toil away one’s life making rent while watching the wondrous breakthroughs of the world spring forth from other people’s minds.

I wish this had an ELI5. Anybody out there that can help us mere mortals?

To boil it way down: The root claim is that there is a way to craft a special closed box that when you apply electricity to it, the box starts moving (linearly) without either pushing off of anything or throwing anything out. If that were true, it'd mean an awful lot for space travel; changing direction in space requires a ship to either crash into something or throw bits of itself away until it runs out of bits. If this thing works the way it is claimed to, a spaceship using it could control its motion forever, powered by merely the light of the nearest star.

(... it probably doesn't work the way it's claimed to, because if it does, there's a lot of interesting things we should already have seen by now in the "closed boxes moving around as if by magic" category; the universe is a big, big place of big, big possibilities. But lack of observation doesn't make it impossible, just unlikely).

> we should already have seen by now in the "closed boxes moving around as if by magic" category

I agree if it's true such phenomena must be quite likely. But maybe not in the amperage range that we witness here on earth. There are places in the universe that see amperages 10 billion times higher than what we see here. Perhaps you might see some box-ish things moving out there as if by magic.


Makes me wonder if it could somehow convert the energy to mass and throw that off, as it were. Though it's probably something more exotic, assuming it's not an error of some type.

"Convert energy to mass" does not make much sense. If you throw light away, it'll propel you.

I was thinking electrical energy, but you raise a good point that photons have momentum.

"...therefore is potentially demonstrating an interaction with the quantum vacuum virtual plasma..."

This could be extremely big news, like the biggest news of the last 50 years. Depends on whether it's true -- and how much it can be optimized. Field propulsion is a game-changer in humanity's relationship to the universe.

Lots remain to be seen, though. Wait-and-see is the appropriate response.

Still pretty neat. And it sounds like something that could easily be reproduced in college-level labs worldwide.

There's no mystery to producing thrust with microwaves. Photons have a momentum of E/c, so if you make photons with a power P and send them in one direction, you'll get a thrust of P/c.

I think the issue is that they claim to a) not emit anything, and b) claim many orders of magnitude more thrust than could be achieved by just emitting photons.

Pedantic, but NASA is an acronym. Am I unaware of a British English composition rule that permits writing it "Nasa"?

The Guardian/Observer style guide specifically uses Nasa as an example: http://www.theguardian.com/guardian-observer-style-guide-a

> Use all capitals if an abbreviation is pronounced as the individual letters (an initialism): BBC, CEO, US, VAT, etc; if it is an acronym (pronounced as a word) spell out with initial capital, eg Nasa, Nato, Unicef, unless it can be considered to have entered the language as an everyday word, such as awol, laser and, more recently, asbo, pin number and sim card. Note that pdf and plc are lowercase.

That's really interesting. Thanks for the clarification.

pin number


The operative phrase there is "considered to have entered the language as an everyday word". The acronym "PIN" has morphed into the term "pin number" meaning "A personally-identifying number usually associated with financial transactions".

Yes, it's redundant, but the point is that it's not being used as an acronym, but as a separate part of the lexicon with its own meaning.

I've never heard of that way of handling acronyms before.

The site is WIRED UK. Maybe it's a UK thing?

My first reaction was, "That's not how you write NASA; This author/editor is an idiot. How can I trust anything they've written here?" I doubt that's the reaction they want.

Now I just feel sorry for the author whose writing is forced to look weird to many readers.

Over time, maybe people will just come to recognize it as "a British thing" just like they recognize aluminium as the British spelling.

Aluminium/aluminum is less British/American than you might think. Humphry Davy initially called it alumium, then aluminum, then it was decided by others to call it aluminium, which became the dominant spelling (which it still is, internationally).

Then, just to confuse matters, Charles Martin Hall promotes it as aluminum on his marketing posters, but himself calls it aluminium on his technical documents, so some people think that the predominance of aluminum in North America may just be down to a typo.

edit - Looking at the New York Times, I notice that while they write 'NASA' and 'NATO', they also tend to write 'Unicef' and 'Norad'. I wonder if they have a four letters or less capitalisation rule for acronyms.

Wasn't it settled as aluminium to be consistent with spelling of other elements (~80 end 'ium'); selenium, rhenium, rhodium, sodium, ...

In my perception, USA don't seem to care so much for consistency with others; cf use of imperial measures.

> people will just come to recognize it as "a British thing"

When it comes to the English language, the English have a pretty valid claim.

I feel sorry for USAian authors whose writing is forced to look weird to many readers...

Does "NASA" actually look weird to anybody? That's how NASA themselves write it... so do you Brits think that everything NASA publishes with their name on it looks weird?

I say defer to however the organization in question writes it. That should surely lead to the least confusion and weirdness. It would certainly help UK news organizations with consistency:

* "CARE International": http://www.theguardian.com/lend-with-care/entrepreneurs-seek...

* "Care" _and_ "CARE": http://www.theguardian.com/lend-with-care/tackling-the-root-...

* "Nasa" _and_ "NASA" (But "Ladee" rather than "LADEE"): http://www.theguardian.com/science/video/2013/sep/07/nasa-la...

In logos I agree but in normal writing it always looks like unwanted emphasis too me.

I think there's a cultural difference here, USAian papers kept up the many founts with underlining, etc thing long after it had become unfashionable in the UK.

The norm is the norm - whatever you're used to.

...which is what my previous post was supposed to highlighting. Somebody took it personally :-(

You dare accuse The Grauniad of inconsistency?

(That'sh Private Eye's job. Ed) http://www.private-eye.co.uk

Yet 'USAian' looks weird everywhere.

That's probably down to the brightly coloured shorts.

No, but I've seen the BBC do this extensively. They turn CERN in Cern all the time. Perhaps Wired UK are just copying this style.

I've never seen the BBC call the BBC the Bbc though...

That's because BBC is an initialism (each letter is pronounced separately) rather than an acronym (pronounced as if it were a word).

CERN is an acronym and BBC is only an initialism. There is a linguistic trend to using title-case for acronyms; particularly companies seem to be turning their acronyms in to the company name. Perhaps using "Cern" is simply following that trend.

British publications have been using titlecase for acronyms for a very long time, its not a recent trend.

Probably the same thing that turned "L.A.S.E.R." into "laser".

The A in laser (Amplification) really should be an O for Oscillation. You can work out the rest...

You prefer light oscillation to stimulate emissions?

This is why I changed it for the link title on here

The top comment (on the actual article) suggests that the effect may be a result of dark matter resonance:


Which is way over my head, but interesting.

Is anyone reminded of http://www.bibliotecapleyades.net/tesla/occultether/occultet...? Which is complete pseudoscience but...

Is this the stuff Miklos Borbas was working on? https://www.youtube.com/watch?v=RbOc6R-95kk

Could the electromagnets involved in microwave generation be interacting with the Earth's magnetic field?

Anything's possible, so they really need to do the experiment with Helmholtz coils inside a Faraday cage:



It's logical when you think about it. Since particles pop in and out of existence all the time and the time these particles exist are > 0, then it should be possible to move those particles before they disappear. So law of conservation of momentum is not violated, neither any other law of physics. It is just counter intuitive, like most stuff related to quantum world.

I’m not quite convinced. If I understand you correctly, what you’re saying is the following:

Suppose we send out one photon ν of momentum p_ν. We hence gain momentum -p_ν. This photon then randomly hits a particle X of a particle-antiparticle pair and transfers its momentum/energy to the particle X, creating/altering it into a particle X'. When X' and ¬X collide again, this momentum/energy is lost and doesn’t hit the opposite wall of the cavity (where it would be transferred onto us again, causing us to lose the previously-gained momentum -p_ν).

But this would require that when X' and ¬X annihilate each other, the extra momentum of X' is also annihilated. Intuitively, I’d expect it to be sent out as a photon – with momentum p_ν.

How do you imagine annihilation of the extra momentum?

I don’t.

So why you expect it to happen?

I don’t. That’s why I wrote:

> But this would require that when X' and ¬X annihilate each other, the extra momentum of X' is also annihilated. Intuitively, I’d expect it to be sent out as a photon – with momentum p_ν.

I.e. annihilation of the extra momentum would be required for this to work on the basis of background fluctuations (in my understanding), but I don’t think that this happens.

Quantum mechanics, dreams stuff is made of.

Although unrelated, the title reminded me of a certain Improbability Drive..."Not again..."

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