EmDrive - why is it being tested?

It is a bit technical to understand stuff about the EmDrive. But my question is how it came to be tested by the likes of NASA and others, and in layman’s terms.

Yes I am all for setting aside laws, including physical laws when they gets in the way of humanity. But this one, how did it happen? Was it just a different experiment that seemed to have a unexplained thrust, or some mathematical model of should in theory work? Or something else?

How did EmDrive and the theory behind it seem to get such traction?

Because of things like the light mills, the Crookes radiometer…

See http://en.wikipedia.org/wiki/Crookes_radiometer

And if you think you know what it is, update yourself Such as the 2010 Nanoscale light mill…
In 2010 researchers at the University of California, Berkeley succeeded in building a nanoscale light mill that works on an entirely different principle to the Crookes radiometer…
There’s been lots of debate about why these work…

As to the Cannae/EM drive … “Both inventors claim that their devices do not actually violate any physics, and instead take advantage of very particular but speculative aspects of existing physics. It is important to note that while both theories are being tested, Eagleworks is testing whether or not the devices work as a SEPARATE thing from WHY they work…”
And basically, Nasa would get someone to drop in to see the invention at work, and if it looks good, get it themselves to REALLY test it.
(due to the possibility of hidden tricks in the test setup that is not NASA…)

So eagleworks tested the device and found some tiny force on the EmDrive…
Um … isn’t it tiny ? Does it DO anything worthwhile in space ? Would the amount of fuel the EmDrive needs to produce such little thrust mean that it give worse mileage than rocket power ?

Still the interaction between light and matter is still very much worth investigating…

NASA Eagleworks is a lab specifically set up to test fringe ideas that may lead to breakthroughs in propulsion. They are also investigating the Albecuirre drive, even through it requires things which we don’t believe can exist (negative mass matter) to function.


Also, the fact that a Chinese lab has claimed a result may well have created a political reason to take a look at the EmDrive. No matter how unlikely, I don’t think NASA would take the chance of letting China have a huge headstart on this thing if it does work.

Presumably, if the effect were real and they could confirm it completely, there would be ways to boost the thrust developed. One obvious way would be to make the apparatus superconductive.

The EMDrive, if it works, does not consume propellant at all. So you could launch a solar powered satellite into low earth orbit with such a drive, and over months to years it would go faster and faster, presumably eventually reaching escape velocity and hurtling off into the cosmos.

However, as I pointed out in another thread, if the EMDrive works, it seems to violate either conservation of momentum or relativity, at least locally. This makes it unlikely that it works. However, reproducible experimental evidence trumps theories of physics. If it actually works, and it can be unequivocally demonstrated to work (multiple labs, testing in space, etc), those theories of physics would have to be updated accordingly.

I imagine that the main issue with most claims that go against the laws of physics is that the inventor generally refuses to actually let anyone investigate how it works nor independently verify that it does. That is because, generally, the whole thing is a hoax to start with.

If someone has a device that does something interesting and is willing to let other people tinker with it, eventually it should work its way up the ladder. To be sure, at every step, the person tinkering with it is going to expect that they’ll discover that it’s just X obvious thing. But if they can’t find X then they’re probably going to call over their friends, getting them intrigued in the device as well.

Scientists (as I understand) actually rather like things that they don’t understand.

Does anyone have an estimate of how it would comparethrustwise to a similarly pwered photonic drive? That would also not require reaction mass.

My own estimate is that emDrive would provide 10,000 (Eagleworks) to 100,000 (Chinese) times more Newtons per watt than photonic.

So what are some realistic applications for Em drive? I saw some ‘fly to the moon in 4 hours and make 0.10 of light’, but I took those as magazine fluff.

I think that if this is for real, that it would be hugely useful, even if it generates low thrust. Combine low thrust with a long term electrical supply (solar cells or thermopile) equals lots of delta v.

A satellite equipped with one might not need propellant and rockets to keep station. Probes could explore the solar sytem with significantly less propellant (used when high thrust is needed). With less need for propellant, the probes are either lighter or have more room for payload.

If this generates high thrust, all bets are off, everything changes. It would be kinda like the spacecars in Star Wars or the Jetsons (though they might need extension cords).

And of course, it seems that current explanations of the process are inadequate- so this may provide new insights into fundamental physics, leading to who knows what.

Or maybe it’s just cold fusion (and faster than light neutrinos, etc, etc) all over again. ( I have the same sense of excitement I had when I heard about cold fusion- I imagined nuclear power sock warmers!)

The EmDrive violates the laws of physics as we know them. If it pans out, then we would need to reconstruct new laws of physics before we could even begin to say what the potential applications would be. For starters, it definitely violates the law of conservation of momentum. If it does that, then it also violates at least one of special relativity, or conservation of energy. If the EmDrive works and it turns out not to violate special relativity, then we can use it to make a perpetual motion device, the implications of which are clearly staggering.

Physics guy I am not but is someone claiming it will not need any power input?

Also I agree is a questionable assertions since if it works the laws are changing in a unknown way.

Yes, Einstein is. Special relativity and conservation of energy between them imply conservation of momentum. Reactionless drives, if they exist, violate conservation of momentum. Therefore, if relativity is still correct, then conservation of energy is also violated.

Note that this is not the only way such a drive could work. Maybe, instead, it still conserves energy, but violates special relativity. In that case, it couldn’t be used to make a perpetual motion machine. This just highlights my point that we would have to figure out just what laws it’s violating before we can begin to explore the implications.

Especially since special relativity underpins quantum electrodynamics, which is the physics that underpins things with everyday consequences, like physical chemistry, electromagnetics, etc. If SR is wrong, there’s a lot else that’s wrong.

The (admittedly low level) stuff I have read includes claims that the inventor asserts that it does NOT violate conservation of momentum (ie, it’s no truly reactionless). However, the same articles state that physicists find the inventor’s physical analysis/explanation of the device incorrect/incomplete.

Specifically, there is a notion that it may interact with virtual particles in a way that gives it a push (but that virtual particles should not behave this way).

If the inventor is correct about this, it seems to me that it clears the conservation of momentum problem. I’m sure it raises other implications.

Does someone knowledgable care to comment?

Just for the sake of argument, imagine that space wasn’t really empty and there were particles you could push against. (the classic ether hypothesis)

If this was the case, you could build a spacecraft that worked kind of like a jet aircraft. It would suck in particles and accelerate them out the back, powered by some kind of energy source. You’d be immune from the rocket equation.

But (there’s always a catch), as you go faster, you begin to encounter those particles at higher and higher relative velocities. You’d need more and more energy to go faster.

In short, you’d take relativity behind the shed and shoot it. If the universe works this way, you’d be able to build a speedometer for your spacecraft that tells you your absolute speed relative to space, and the faster you go using the engine, the more energy it takes to go faster still.

Still beats the rocket equation, but no perpetual motion for you…

If this drive (somehow) pushes back virtual particles, would they remain virtual? Would you detect particle radiation in the exhaust? I suppose for that to happen, you would have to input enough energy into the system to “create” these particles?

Can I tell my absolute speed relative to the CMB?

For mind bending reasons, no, apparently not. (well, maybe, CMB isn’t completely uniform). Apparently, the fashionable theories regarding the Big Bang right now are that because space has expanded, the big bang happened “all around us”, and so there is no way to tell where we are right now relative to “where” the big bang happened.

Grains of salt. Whole salt shakers. I’m not arrogant enough to think I have a better theory, but for something as complex and far away as the origin of the universe…we’re just hairless apes who have not yet figured out how to augment our intelligence much, we only have hand built sensors that are positioned barely above our planet at best, and we’ve only even been able to research this for a few decades. And the theories keep changing. Maybe once we’re superintelligent and have much bigger and better sensors spread across many AU we’ll be able to confidently come up with a bulletproof theory.

So, while conservation of momentum hasn’t been violated in any research done in recorded history, if the empirical data says it’s just a suggestion, and that data has been confirmed to be legit, well, that’s how it goes.

Well, yes, a lot needs to be done with this yet.

The claim is more incredible than CERN’s FTL neutrinos, of which even they were dubious, so therefore needs a heavy burden of proof.

It’s still interesting to discuss the implications to both physics and to society.

Speaking of physics and the comment about favored frames of reference:

I seem to remember some discussion about movement relative to “the fixed stars” in some discussion of General Relativity I heard years ago. This smacks of a favored frame of reference. Was this for real, or was it an old fashioned view of GR, or was it merely a device to help the student better visualize acceleration? I have not heard that phrase “fixed stars” in reference to relativity in ages.

What does it mean if GR wants “fixed stars” and SR rejects them?