The 'impossible' EmDrive could reach Pluto in 18 months?

http://www.wired.co.uk/news/archive/2015-07/24/emdrive-space-drive-pluto-mission

by jonbaer • 11 years ago

105 110 11 years ago

wired.co.uk

dicroce• 11 years ago

"WIRED understands that there are multiple labs around the world working on their own EmDrives, although Tajmar's is the only new one willing to go public so far."

I'm very curious about this bit. I wonder who is working on it?

Thorondor• 11 years ago

NASA has a group working on it: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/2014000...

The Northwestern Polytechnical University in China is testing a version of the EmDrive: https://dx.doi.org/10.1088%2F1674-1056%2F22%2F5%2F050301

Finally, a number of amateurs are interested as well: http://emdrive.wiki/Building

foobarian• 11 years ago

I wonder how they rule out the effects of the Earth's magnetic field. I can see there being some small effect due to some kind of eddy currents pushing ions into one direction. Maybe they turn the apparatus at multiple angles and check the bias to north-south?

jboggan• 11 years ago

I seem to recall that they could not find any variance in the force by orienting the apparatus in different directions. Some good work has been put into finding the cause of this, and most of the easy and obvious errors have been tested and found to be unrelated to the effect.

idlewords4• 11 years ago

Has any independent laboratory confirmed this effect and published on it in a peer-reviewed journal?

tlarkworthy2• 11 years ago

"Roger Shawyer is encouraged by Tajmar's work, which he says validates his own theoretical predictions as well as his experimental results. Shawyer has often been dismissed because of his own lack of peer-reviewed scientific publications. That looks to be changing very soon; a paper Shawyer presented at the International Astronautical Conference in Toronto in 2014 is in the final stages for peer-review for publication. This describes an advanced EmDrive-powered spaceplane."

idlewords4• 11 years ago

You're referring to an unpublished paper by the author, which appears to be a design for a space vehicle. I asked about independent tests of the claimed effect.

gilgoomesh• 11 years ago

Not exactly a journal but NASA reproduced the Cannae and EmDrive style devices and documented it:

http://ntrs.nasa.gov/search.jsp?R=20140006052

Turning 17 watts of microwave power into 40-91 micronewtons of thrust isn't exactly stunning, though.

idlewords4• 11 years ago

Another data point: my kitchen microwave has been getting 32 millimeters to the hot pocket.

baq• 11 years ago

from the wikipedia ion thruster article:

Ion thrusters have an input power spanning 1–7 kilowatts, exhaust velocity 20–50 kilometers per second, thrust 20–250 millinewtons and efficiency 60–80%.[1][2]

3 orders of magnitude less thrust than for not needing to accelerate any fuel all the way into orbit? i'll tell you space companies will send trucks full of money to anyone who can make a reliable one.

Niten4• 11 years ago

It's good to see that someone finally got around to testing this in a vacuum. Here's the paper mentioned in this story:

http://arc.aiaa.org/doi/abs/10.2514/6.2015-4083

High levels of skepticism are still warranted, as much as I would love for this to pan out. Every time this gets tested—presumably more and more carefully—the measured force gets smaller. The original test at Chinese Northwestern Polytechnical University measured 720 mN; this latest test in a vacuum chamber, only 20 μN. This is so tiny that a test anomaly would seem a much more plausible explanation than a violation of the conservation of momentum.

Of course the ultimate test would be to put one of these in space and try accelerating something with it, in the same way that the ultimate test of a perpetual motion machine would be to make one perform macro-scale net work.

idlewords4• 11 years ago

From the abstract: "We identified the magnetic interaction of the power feeding lines going to and from the liquid metal contacts as the most important possible side-effect that is not characterized yet. Our test campaign cannot confirm or refute the claims of the EMDrive..."

Given that this is a 700W microwave oven putting out a tiny amount of thrust, and that a positive finding would invalidate a basic conservation law, my money is on those wires.

rndn2• 11 years ago

On the other hand, the current theory of the EmDrive predicted exactly that amount of thrust for the given configuration.

saalweachter• 11 years ago

Smaller effect size as studies improve is the classic sign of a non-event. ESP and the like went through similar cycles - impressive early studies followed by a series of more rigorous studies with diminishing effects until people got bored and moved on to the next big thing.

api4• 11 years ago

In this case different tests have occurred at different power levels. Has anyone normalized the results? Of course with only a couple replications its early for a meta study.

Natsu2• 11 years ago

What would it take to get one of these into space?

lawlessone• 11 years ago

from the looks of how testing is going, a good old fashioned rocket.

PhasmaFelis3• 11 years ago

At least $4000 per kilogram, based a quick google.

I'm sure someone will put the cash together eventually if the dirtside experiments look promising, but there's no sense in risking the money until we're pretty sure.

MattPearce• 11 years ago

The Chinese test used kilowatts rather than watts of power:

http://www.you-tech.it/index.php/content/download/12369/1124...

mizzao• 11 years ago

All the more possible for small extra forces to slip through the cracks from magnetic fields or whatever.

Niten4• 11 years ago

To be clear, the Chinese test used 2500 watts, and this latest test used 700 watts. That is a decrease, but it's within a factor of 4.

On the other hand, the decrease in effect size is closer to a factor of 40,000.

api4• 11 years ago

Why the assumption that if it works it must violate a conservation law? That's the last thing I would suggest after exhausting every other possibility, even weird ones like space time distortion thst would still operate within known conservation laws.

teraflop• 11 years ago

The whole reason the EmDrive is supposedly so revolutionary is that it's claimed to produce thrust without requiring any propellant. If conservation of momentum isn't going to be violated, something with mass-energy has to be carrying that momentum away from the spacecraft, and if it's not matter, it has to be radiation. But the claimed efficiency is about 5 orders of magnitude higher than radiation pressure could possibly produce.

Animats• 11 years ago

"Every time this gets tested—presumably more and more carefully—the measured force gets smaller."

Uh oh. That's a classic sign of a bogus effect. It's like physicists at Stanford trying to replicate the Pons-Fleischmann cold fusion experiment. At first, they were enthusiastic, and expected big results. They started out with the apparatus surrounded with radiation alarms in case it generated dangerous amounts of neutrons. After a while, they discovered that the effect was at most twice background radiation. Since humans have water in them and water is a neutron reflector, just moving around the equipment could produce effects at that level. Then they moved the equipment to the inside of a cube of lead bricks, to eliminate external neutrons. No more neutrons, background or otherwise.

Anjin2• 11 years ago

No it is because the Chinese test dumped kilowatts of energy into the test item but the NASA test used only miniscule power. The guy you replied to presented the facts in a misleading way.

Anjin2• 11 years ago

The difference in measure thrust is due to different test articles and testing done in different labs. The 720 mN result was from China and they dumped a ton of energy into it. The smaller 20 μN result was from NASA's testing which used far less power, so the resulting thrust measure was also smaller.

Niten4• 11 years ago

You're incorrect, 20 μN was measured in the Dresden test at 700W.

DenisM2• 11 years ago

Let's cut to the chase:

5. 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.

[http://emdrive.com/faq.html]

So, the momentum simply "builds up". That's an exceptionally weak explanation.

yincrash• 11 years ago

Can anyone explain electromagnetic momentum? I thought that em waves (photons) are massless. How can they have momentum (mass * velocity)?

nerd_stuff2• 11 years ago

One derivation starts with E = mc^2, which is a special case of E^2 = m^2c^4 + p^2c^2 but with velocity set to zero. In the second equation if you instead set the mass to zero you get p = E/c (momentum equals energy divided by the speed of light) for massless particles.

The deeper reasons are above my pay-grade.

gizmo686• 11 years ago

Because photons travel at the speed of light, we need to consider relativistic effects. Under special relativity, classical momentum (mass * velocity) is not actually conserved. To achieve conservation of mass, we consider the "inertial mass" of an object instead of the classical mass, where the intertial mass is given by:

    m'=ym
    y=1/sqrt(1-(v/c)^2)

As you can see, y>1 and y approaches infinity as you speed approaches the speed of light. This is why we say that the mass of an object increases with its velocity, and that any object with mass traveling at the speed of light will have infinite mass.

Now consider the momentum, p, of a photon. We have:

     p=m*y*v
     m=0
     y=infinity
     v=c

this gives us p=0*infinity, which is indeterminate, so we cannot use this equation to determine the momentum of a photon.

Instead, we can use the engery-momentum relationship, which states:

    E^2 = (mc^2)^2 + (pc)^2

(This is a generalization of the famous E=mc^2 equation to also consider the momentum). In this equation m refers to the rest mass, not inertial mass. Because we are dealing with a photon, we have m=0, which gives us:

    E^2=(pc)^2
    p=E/c

Indicating that the momentum of a massless object is proportional to its energy.

nerd_stuff2• 11 years ago

So they "build up" momentum out of nowhere? I think that just moves the breaking of conservation of momentum to a different place.

I'm glad they're testing this until it's proven one way or the other but if it somehow works I doubt that'll be the explanation.

n0us• 11 years ago

The worlds biggest unsolved mystery about microwaves has still not yet been answered; how exactly does one microwave on HIGH?

jdmichal3• 11 years ago

While your comment doesn't add much to this discussion, I won't turn down a chance to educate.

Conventional microwave ovens only have two states: on and off. (I won't rule out the possibility of some exotic build having multiple powers, but the ones you interact with on a normal basis don't.) So, power levels cannot change the output level of the magnetron. Instead, the power levels control what percentage of time the magnetron is on. A power level of 50% means the magnetron is on for roughly 50% of the indicated time. These off periods will typically result in more even heating at the cost of time. The off periods give the heat a chance to conduct through the food and balance, reducing the lava-and-ice problems seen when heating frozen things in microwaves.

HIGH just means 100% power level.

eropple2• 11 years ago

I won't rule out the possibility of some exotic build having multiple powers, but the ones you interact with on a normal basis don't.

Mine does, and it cost $120.

http://www.amazon.com/Panasonic-Countertop-Microwave-Technol...

(I don't find that it actually makes a difference when using it, though.)

aaron695• 11 years ago

Reddit has a sub forum that seems pretty active -

https://www.reddit.com/r/EmDrive/

ChuckMcM• 11 years ago

Seriously, it isn't that expensive to get a shot on a possibly blowing up test rocket that is going into orbit, launch something and fly it out to mars and back. We'll believe you then.

duskwuff• 11 years ago

Making projections like "this drive could get a probe to Pluto in 18 months" seems kind of premature, given that scientists still aren't certain that the drive works at all, let alone how efficient it actually is.

Semiapies• 11 years ago

I'd say science reporting is a sad ghetto of journalism, but that's giving too much credit to the profession as a whole.

searine• 11 years ago

I've been following this story pretty closing for several months now. So here's the opinion of an actual research scientist.

Q. Does the Em drive produce thrust?

A. Undetermined. Several tests from multiple independent labs have reported thrust, including in a vacuum. However several of the labs that reported positive thrust come from a sketchy background.

Q. Does it violate conservation of momentum?

A. Undetermined. There are several competing theories trying to explain the phenomenon, but we lack raw data. I think the last thing anyone wants to see here is "new physics".

Q. Roger Shawyer seems like a scummy kook?

A. Yes. This is why more testing is really important.

Q. What about more tests?

A. A few dozen people have taken it upon themselves to hack together emDrives and test them. The first couple so far were plagued by poor construction, RF interference, and poor experimental design. However, the hacking community is slowly getting its shit together.

Q. Pluto in 18 months?

A. If it works. My intuition screams "its cold fusion all over again", but there is still a chance.

javert4• 11 years ago

Thanks, nice summary.

I think the last thing anyone wants to see here is "new physics".

I really want to see new physics, because I want to see us get off this rock and far away. I think most people want to see new physics. I think that's why this topic is so popular.

That said, I can understand physicists not wanting to see new physics.

Wait. In a way, that sentence is crazy. In a way, physicists should want to see new physics more than anybody.

Where does the "not wanting to see new physics" sentiment come from? Just not wanting to be wrong?

homborg• 11 years ago

I read it as: we want a better explanation, than just: "new physics!"

davesque• 11 years ago

Maybe not wanting to see new physics before seeing rigorous, reproducible experimental results? Kind of a cart before the horse thing? Just guessing.

thaumaturgy6• 11 years ago

Laymen tend to underestimate the very vast body of research which supports current physical models. "New physics" would imply that something has been fundamentally wrong with physics for a long time, and that is unlikely.

cabinpark• 11 years ago

I'd love to see new physics! Every physicist I know loves new physics.

But if you claim to violate the conversation of momentum, everyone is going to be skeptical and not believe it. We have hundreds of years of experiments and observations that support the law and have looked in many places from small to large and not seen violations. This is what makes people not believe it and thus physicists are going to assume you are wrong and not physics. It's not so much a negative concern, but more of a practical one. But should it be tested in a rigorous manner and reproduced, then physicists will believe it. It's just it hasn't and thus we are going to stick with the established very well understood and tested theory. Like are you sure you have properly counted all the initial momentum? Are you 100% you are not introducing energy to the system? The possible explanations is long and a good experiment will eliminate as many of these as possible.

As an example, look at the OPERA experiment which found to have superluminal signals. New physics? Nope, just a faulty piece of equipment. BICEP showing gravitational waves? Nope, just poor data interpretation and neglecting interstellar dust. So if you want to claim new physics, be damned sure you have ironclad proof.

DenisM2• 11 years ago

99.99% of the time when "new physics" is invoked, it amounts to crookery or kookery. Nobody wants to see that, because it takes energy to disprove even the obviously flawed claims, and the energy is taken away from more promising endeavors, that are usually less appealing to the public.

"Free Energy" is very appealing, so is "10x better batteries", "10x more flash storage", "momentum-defying space thruster", and so on. These modern-day fairy tales are gaining press simply because people want them to be true, not because they actually show a path for progress.

Similarly, a promise of a "miracle cure" is very appealing to the public, and so it may seem cynical to downplay any such claim right away, but it has absolutely nothing to do with actual advances in medicine.

eevilspock2• 11 years ago

I think the last thing anyone wants to see here is "new physics".

The article's responds with the nonsensical "Some damage to our theories of physics is an acceptable payoff if we get a working space drive."

EDIT: Let me clarify why it's a nonsensical statement:

First, I think it meant to say "cost", not "payoff". Second, there would be no cost. None of the things we were able to do with our existing theories would be lost. We'd only be pushed to refine the theories (or in rare cases come up with an entirely new theories) that would be at least as accurate as the prior theories and cover phenomenon the old didn't. If anything, we'd be able to go back and do better at all the things to which we'd applied the old theories.

It's like saying "Some damage to Newtonian physics is an acceptable cost if we get a working understanding of relativity and gravity." Einstein did no "damage" to Newtonian physics. He made it better.

evincarofautumn• 11 years ago

Well, it’s improbable, not nonsensical. If someone goes and implements a technology that trounces our working theories, we certainly need to update those theories. It’s just that that’s exceedingly unlikely to happen.

nsxwolf• 11 years ago

Not sure what is to fear from new physics. Sounds like something new and exciting to work on. Aren't physicists tired of perpetually iterating over string theory and making no new discoveries?

p1mrx• 11 years ago

EmDrive and Cold Fusion are the perfect complementary technologies. Next someone should claim to invent a cooling system that doesn't reject heat, and we can start building Stargate Puddle Jumpers.

leni5365• 11 years ago

Conversation of momentum is strongly tied to the conservation of energy through relativity theory. If it actually works (I doubt it) it has really strong implications.

repsilat• 11 years ago

Conservation of momentum is a much bigger deal than conservation of energy. We already know of situations in which energy isn't conserved (like the energy of a photon decreasing when there is metric expansion where it is.)

Conservation of momentum is a consequence of the translational symmetry of physics via Noether's theorem, so that's what we'd need to give up to hope to see it broken.

leni5365• 11 years ago

Much like conservation of energy is a consequence of time translation symmetry. If you mix spatial and time coordinates through relativity theory you can see that these are strongly coupled.

Your photon example works because there is no time translational symmetry in the case of metric expansion and it's a general relativity model. In general relativity there is no conservation of momentum either. It would be hard to even define since coordinate systems change from point to point. We can only say that the energy-momentum vector is going through parallel transport, which is like conservation in the local coordinate system.

seesomesense• 11 years ago

"They laughed at Columbus, they laughed at Fulton, they laughed at the Wright brothers.

But they also laughed at Bozo the Clown."

stillsut• 11 years ago

Question: why did someone build this drive if theory predicts it won't work? Were they just tinkering or did they have an alternative theory from which they could deduce it might work?

The 'impossible' EmDrive could reach Pluto in 18 months?

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