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

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

[rgbatduke]

Oh, I was just being facetious. As you say, physics has undergone multiple "complete rewrites" (not really, but yeah, aristotelian->newtonian, newtonian->quantum, galiliean->lorentz are at the very least very, very serious revisions of the way we think even if they do eat their predecessors and continue to support their successful results).

However, the law of conservation of momentum is one of those things that it is difficult to muck with, without requiring a pretty complete rewrite. If you put this thing in deep space and it just moves (accelerates) without shooting mass/energy/momentum out in some form, it would make me -- and physics -- pretty sad. I have to put it in the same category as the prior reports of transluminal neutrinos and the like. Always possible that they are true, but claims that will change everything require the most solid of evidence, and so far this is in the category of any number of famous "marginal" results that turned out to be accidents of one sort or another.

At the end of the day, of course, physics is KNOWN to be incomplete. Maybe the damn thing is acting as a darkon drive and is through a process we do not understand converting microwaves to darkons to momentum through some unknown resonance process. Maybe it is evidence for a dual universe where charge and spacetime are reversed, and the cavity somehow couples the two so it is pushing off against its shadow twin. Maybe we can make up a dozen theoretical explanations for it -- eventually, if necessary.

But for the moment it, like transluminal neutrinos, is still in the "probably magic" category pending extraordinary evidence to back up the extraordinary claim. Maybe if NASA launches one into orbit with its own solar power system and runs it for a few years, during which time it promotes its orbit in unmistakable ways. It doesn't look like it needs to mass more than a few hundred kilograms total, solar panels ought to be able to provide it with at least a kilowatt or three, so getting a thrust of around a newton should be possible. A newton may not sound like much pushing 100+ kg, but an acceleration of 1 mm/sec^2 over a day adds 84600 mm/sec, or roughly 90 m/sec, or (multiplying by 9/4) roughly 200 mph. It wouldn't take many days to make a clear, unmistakable alteration in the orbit. With modern instrumentation, I would think "one" (or even less) would suffice. Even 20 m/sec/day acceleration at a tenth of this ought to show up almost immediately.

In space, there is nothing nearby to push against. One can actually use the observed thrust itself to measure the mass of the satellite and see if it varies over time (eliminating the possibility that mass is being thrown out somehow assuming that it does not, as it should not). With solar cells with a cross-sectional area of at most a few square meters, radiation pressure is utterly incapable of producing this acceleration because you have at most Pr = S/c to work with, and S is order of 1400 W/m^2 and by the time you divide by c you have basically nothing left (as observed elsewhere in the thread).

At that point, if it accelerates as advertised, Classical Electrodynamics is dead as a doorknob, and QED is walking wounded as it still works off of CED and at the microwave level and high power, "photons" ought to be irrelevant anyway. Note well: you are converting a substantial amount of incoming electromagnetic energy directly into work "with no other effect" if it works as advertised. So even the second law of thermodynamics is going to be very sad. I'm tempted to quote Eddington:

"The second law of thermodynamics holds, I think, the supreme position among
the laws of nature. If someone points out to you that your pet theory of the
Universe is in disagreement with Maxwell's equations - then so much the worse
for Maxwell's equations. If it is found to be contradicted by observation -
well, those experimentalists do bungle things up sometimes. but if your theory
is found to be against the second law of thermodynamics I can give you no hope;
there is nothing to do but to collapse in deepest humiliation."

There's some wisdom there...

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.

Not making any sense to me

[goombah99]

Their claim, to my ears, is even more ludicrous than the EM drive itself. What they say is that if two photons co-propogate with opposite phase they exist in the sense of carrying momentum and energy but they can't intereact with anything like say the wall. Isn't his bananas? the dark nodes of an interference pattern don't contain any ray-like photons. they seem to be saying it does. Now one can argue what's a photon? ie. can we really talk about ray-like photons (photons going along an axis), or do we need to talk about full 3D modes which are the eigen modes of the cavity. However in either case this seems bananas to me. if two photons are canceling it's the same as no photons. the energy didn't disappear, it just was reflected at the time you injected the second photon. you do not get two photons co-propagating out of phase like they claim.

Some one please explain this seeming madness.

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?

[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:But what if we fed it more power?

[angel'o'sphere]

An experimenter found an effect that did not fit in the current paradigm.
Actually that is not what happened regarding the EM drive.

One guy thought it out and published his thoughts.

Now plenty of research labs are building prototypes: and all found unexplainable thrust

Right now the race is to either find flaws in the experiments and also to find simpler explanations than the ones the original guy(s) had to present (Roger Shawyer, Guido Fetta).