Finnish Scientist Provides Another Explanation For The 'Impossible' EM Drive (examiner.com)

MarkWhittington quotes a report from Examiner: Ever since the EmDrive entered the news about a year or so ago, it has sparked considerable controversy. The device is alleged to work by using microwaves that produce, in some fashion as yet unknown to science, thrust. Many scientists suggest that the EM drive is impossible as it violates known physics. However, a number of tests conducted in Great Britain, Germany, China, and at NASA's Eagleworks at the Johnson Spaceflight Center have resulted in thrust that cannot, as yet, be explained by experimental error. The International Business Times reported that a Finnish scientist has published an article in a peer-reviewed science journal with a possible explanation as to how the drive works. International Business Times writes, "A new peer-reviewed paper on the EmDrive from Finaland states that the controversial electromagnetic space propulsion technology does work due to microwaves fed into the device converting photons that leak out of the closed cavity, producing an exhaust. The research, entitled "On the exhaust of electromagnetic drive," is published in the journal AIP Advances 6 and is the brainchild of Dr Arto Annila, a physics professor at the University of Helsinki; Dr Erkki Kolehmainen, an organic chemistry professor at the University of Jyvaskyla; and Patrick Grahn, a multiphysicist at engineering software firm Comsol."

Comments

If this is correct it should be easy to check

[Crashmarik]

Unless the photons are perfectly out of phase and co linear you will get interference patterns on all three axes. Seeing as they are microwave photons that should make them nice large and obvious.

Re:If this is correct it should be easy to check

[flyingfsck]

Well, maybe you should read the article. They postulate that the exhaust is indeed paired photons, which are impossible to observe. I'm just not convinced that such an EM drive will be more efficient than simply placing a lump of decaying matter at the focus of a reflector and using ordinary infrared photons as the drive.

Re:If this is correct it should be easy to check

[jeepies]

That's not how destructive interference works in the EM field. The photons at a point of destructive interference are diverted to area of constructive interference. They don't continue on as an unobservable photon pair. A point of destructive interference in a wave means the photons aren't there. In terms of the wave equation it means the probability of finding a photon at that location is 0. That's not because photons masking each other, it's because physically they are never present at that point.

Re:If this is correct it should be easy to check

[silentcoder]

Assuming the theory is correct, you may be right. But this is a new theory - and key to it is that it means the EM-drive does, in fact, have an exhaust - it's just that the exhaust is mass-less photons rather than matter. But the whole reason we have the name 'photon' is because light behaves so much like a particle to begin with - and photons are known to have momentum after all.

That said, since it's apparently able to convert something like sunlight into useful thrust without fuel - it could, in theory, keep providing thrust for many centuries (well until something hits or damages it). Your decaying matter will be useful only as long as the fuel remains(but may provide more thrust since the particles it exudes have mass which hugely increases their momentum). Then again - depending what you use, quite a lot of decaying matter have half-lives in the thousands-of-years category.

All that said - assuming both technologies prove viable, you can expect more prosaic and immediate concerns to dominate the decision - like what happens if something goes wrong and the damn thing crashes to earth. Space agencies tend to be rather reticent about putting things in orbit which, if they crash, could spread highly reactive material around the area they land in. This is why RTG's tend to only be used on long-range space-probes, the only risk of spreading that plutonium on the planet is if it crashes during launch.

Having said all that - if we imagine an EM-drive which uses solar-power to produce microwaves to produce photons to produce miniscule levels of thrust - well magnetrons are fairly heavy, and the parts in there are quite pricey... would you not be able to do it more cheaply for about the same weight (if not volume) by skipping all the intermediary steps and just fitting the satelites with solar sails ?

Re: If this is correct it should be easy to check

[Weaselmancer]

Your signature line is funny, considering the nature of your post. ;)

That being said, you should read McCulloch's paper on his emdrive theory. It isn't a complete rewrite of physics, just an additional term added in to momentum. It struck me as very similar to when Einstein amended momentum with the gamma factor. Everything we saw up to Einstein's time was correct for p=mv. Mostly because velocities near the speed of light hadn't been considered yet. If McCulloch is correct, we get another gamma-like term added in for small accelerations in the form of quanta. If he's correct, of course.

He might be, and he might not be. But I think his paper is pretty interesting and it doesn't seem to me like it would take a massive rewrite of everything we know. It feels more like the transition from Newtonian physics to relativistic physics. More of a "Oh, for these unique and less common cases, here's another thing you need to consider." No magic necessary.

Re:Good

[BitterOak]

Finns get a lot of media considering it is an icey wasteland.

An icy wasteland that gave us Linux!

Must be a first for slashdot RTFA skimmed summary

[Crashmarik]

Recent reports about propulsion without reaction mass have been met on one hand with enthusiasm and on the other hand with some doubts. Namely, closed metal cavities, when fueled with microwaves, have delivered thrust that could eventually maintain satellites on orbits using solar power. However, the measured thrust appears to be without any apparent exhaust. Thus the Law of Action-Reaction seems to have been violated. We consider the possibility that the exhaust is in a form that has so far escaped both experimental detection and theoretical attention. In the thruster’s cavity microwaves interfere with each other and invariably some photons will also end up co-propagating with opposite phases. At the destructive interference electromagnetic fields cancel. However, the photons themselves do not vanish for nothing but continue in propagation. These photon pairs without net electromagnetic field do not reflect back from the metal walls but escape from the resonator. By this action momentum is lost from the cavity which, according to the conservation of momentum, gives rise to an equal and opposite reaction. We examine theoretical corollaries and practical concerns that follow from the paired-photon conclusion.

Relevant portion of abstract bolded

Re:This could be exciting

[wierd_w]

There's one problem though...

I seem to recall that the net thrust exhibited by the em-drive is greater than the photon pressure of the microwaves. if the thrust was being produced by cancelling photon pairs escaping the system, then it would be some fraction of that potential, not greater than.

I can see this explaining SOME of the thrust, but the deal breaker is the thrust being higher than the photon pressure of the microwaves it runs on. (Else, it would be easier and more efficient to just aim the magnetron's waveguide out the back of the ship.)

Shawyer's non-peer reviewed "quantized inertia" explanation that abuses unruh radiation is more likely to explain the greater thrust values (and also makes some testable predictions.)

No No No

[Greyfox]

Clearly running the microwave creates a virtual quantum burrito. As long as there's a burrito in the microwave, thrust is guaranteed to be generated,shortly!

Re: Must be a first for slashdot RTFA skimmed summ

[wierd_w]

More, photons are massless, and only interact strongly with matter because they are the force mediating particle for electromagnetism.

Photons are their own antiparticle, so when they interact strongly with each other, the force drops to zero, so the pair doesnt interact with anything else. This allows them to pass through the wall of the cavity like it wasnt even there. They still have energy, and a mathematical equivalent of momentum, so when they leave the system, an equal and opposite change in momentum of the system occurs.

That's my layman's understanding anyway.

The problem is that this is just a convoluted form of light pressure. The thrust exhibited by the em-drive is supposedly higher than the expected momentum change from simply radiating the microwave photons, and only some of the photons bouncing around inside the cavity will perfectly pair up to form neutral photon pairs that can escape the system. That means this mechanism cannot explain the anomalous nature of the thrust.

Kinda sounds like how a LASER works

[fzammett]

You've got a cavity. Inside you pump some energy. The energy is nominally trapped and bounces around. Eventually, some of it finds its way out in a coherent way. Seems like the paper is describing a similar explanation as to how LASERs work, roughly-speaking. Sounds plausible for sure.

Re: Must be a first for slashdot RTFA skimmed summ

[jeepies]

The author of that paper clearly does not understand how constructive and destructive interference work in the EM field. He's correct that the photons do not simply disappear when there is destructive interference, however they are diverted to areas of constructive interference and this would not allow them to leave the cavity of the device if they otherwise couldn't.

What they wrote in the paper may sound good to someone who has a passing knowledge of EM fields and constructive/destructive interference in waves, but to someone who understands this more clearly it makes about as much sense as asking a mechanic to change your blinker fluid.

Re:But what if we fed it more power?

[Required Snark]

No, it's different the cold fusion. The people who discovered this do not claim any magic sauce. No information is being withheld.

This is proceeding the way that scientific progress normally works. An experimenter found an effect that did not fit in the current paradigm. Other experimenters found similar results. Now theoreticians are coming up with hypothesis that may explain the result. Other theoretical types will either agree or disagree. Other experiments will be done to test the hypothesis. Eventually a general consensus will emerge. It's all completely normal.

Remember it was 100 years ago that Einstein predicted gravity waves, and they were just detected. Eventually can be a long time.

Re:Good

[nicnet]

He's not Swedish, just comes from a Swedish speaking family in Finland (very common).
According to your principal 50 million Americans are "actually Spanish".

Re:This could be exciting

[c9brown]

For anyone interested, the "quantized inertia" explanation was proposed by McCulloch, and is here: http://dx.doi.org/10.1209/0295-5075/111/60005

Re:But what if we fed it more power?

[silentcoder]

>Remember it was 100 years ago that Einstein predicted gravity waves, and they were just detected. Eventually can be a long time.

And worth noting that, in science, 100 years can be enough for the "laugh-you-out-of-the-room" crazy idea to become the mainstream consensus theory. A perfect example:
1912 - Wegener proposes continental drift. He gets laughed out of the room. Firstly he's not a geologist but a botanist and he basis his ideas on the agreement of the fossil records between Africa and South America but he has no real explanation for what can move a whole continent. He suggests forces in the mantle but every geologist "knows" those forces are far too weak (today we have a completely different model of those forces that's more than capable of it).

1930s - Arthur Holmes proposes an early version of plate-tectonics theory that at least makes Wegener's ideas sound a bit more plausible. Most geologists remain unconvinced to say the least.

1955 - Two scientists show up at a geology conference to rehash Wegener's idea. But they are armed with two key new weapons. One - they didn't used the land-shorelines but the shorelines about 50miles into the sea where erosion is less prevalent. Two, they used a computer to model the pieces - and the fits were just too damn perfect to ignore. They also propose a new mechanism for what could actually provide the force to move the continents - the theory we now call plate tectonics, basically an updated version Holmes's ideas. The conference ends up just as divided but, somehow, moving continents are now the consensus theory.

1990s - the new theory of plume tectonics explains most of the remaining questions about the subject, and what has long been mainstream science with a lot of unanswered bits suddenly makes tremendous sense. This is the prevailing theory today.

But look at that timeline - in a matter of about a hundred years an idea that probably occurred to many people over the centuries but was dismissed as fantasy by any serious scientist goes from ridiculous to mainstream - because we develop ever better technologies to gather data and test theories in simulations which gives us information not previously available. Now we've even got strong evidence that plate tectonics happen on other planets (notably Mars).

Re:Good

[quenda]

They are no more Swedish than the entire population of Switzerland is German.

Come on - the Swiss are even more German than the Germans. Swiss visitors to Germany complain about the inefficiency, lawlessness and excessive frivolity.