Impossible thrust

That EM propulsion system  that appears to defy the law of conservation of momentum doesn't seem to be going away.  I'm hoping someone (James?) can chime in.


MikeD said...

Of the ten reference links in that article, three link to other stories on the same site, two reference the same article (a freelance guest post), and two link to a conference website (one the front page, the other an article abstract presented by one of the people claiming great results for this drive).

Overall, I rate the article "sketchy" and would like to see more evidence linked from scientific sources. This smells of "cold fusion" type stuff.

And then I found this:

E Hines said...

This author also says this--and repeats it in at least one of the links: the conservation of momentum, which states that for something to be propelled forward, some kind of propellant needs to be pushed out in the opposite direction.

No. She apparently slept through her junior high science class. Nothing has to "be pushed out." The accelerated motion comes from an unbalanced force. I'd like to see her explain solar sails with her theory.

An EM drive may or may not work, but this...lady...couldn't make the argument in either direction with her level of understanding of elementary physics.

Eric Hines

MikeD said...

For something to be propelled forward, something needs to be pushed in the opposite direction. A solar sail works because (like a conventional sail on earth) the solar wind pushes against a sail propelling the craft forward. This EM Drive doesn't do that. It bounces microwaves around inside a closed chamber, and (save for some technobabble about "quantum vacuum virtual plasma" which doesn't actually MEAN anything) no one can say why this should work, or how it doesn't violate conservation of momentum.

Now, generally, fantastic claims require fantastic evidence (one of the reasons I reject AGW is that they're making the fantastic claim that the Earth is getting unnaturally hotter and that mankind is causing it, but when asked for their evidence they shout "the science is settled!" That's not science, that's hucksterism). But there's been no fantastic evidence. As XKCD points out, they've managed to create vibrations. Micronewtons of force is less force than your breath causes. And it appears that there actually has been no carefully controlled experiments that control for all outside influences. And even "friendly" articles to the drive admit that, frequently blaming the lack of funding the scientists attempting to study the device are receiving. This does not meet the burden of proof required to validate such an absurd claim.

Without some kind of actual study and an explanation that amounts to more than "I dunno... magic?" I'm going to call this one bunk.

Grim said...

So, I took a look at the Germans' paper that allegedly confirmed this. The claim they're taking seriously is that there's something about the shape of the resonance chamber that's doing the work. I can think of a 'medium sized' example that makes that intuitively plausible: if you neck down a pipe that has water traveling through it, the water pressure increases. So, the same water is producing more pressure against the walls of the pipe at one end than at the other.

The idea here is to harness the increased pressure created by the movement of the microwaves back and forth in a chamber with a narrow and a wide end. Since pressure is higher at one end than the other, it can (so is the claim) be harnessed as thrust.

Whether that works or not, I certainly can't tell you, but that's the basic idea as far as I can tell.

Eric Blair said...

Assuming that the thing is actually working as advertised, the fact that people don't seem to understand *how* it's working doesn't mean it isn't working. If you get my meaning.

Let's see somebody build something that uses the motor for motive power.

james said...

I haven't seen the full article yet; just the abstract. That wasn't claiming anything stronger than "We're not sure what's going on yet."

I'm dubious as all get out, for reasons adequately described above and in that MikeD link. If it turns out to be real, I think we can safely skip the proposed explanations (e.g. pushing against the virtual particles in the vacuum) and head for exotic realms.

MikeD said...

I can think of a 'medium sized' example that makes that intuitively plausible: if you neck down a pipe that has water traveling through it, the water pressure increases. So, the same water is producing more pressure against the walls of the pipe at one end than at the other.

But for that pressure to be higher at the narrow end than at the wider end, you need to let the water flow out of the system. If you seal the narrow end, the water pressure will equalize throughout the whole of the system.

James knows more about the physics stuff than I do. My background in physics is slipshod at best. My entire point of argument is from Occam's Razor and the Scientific Method in general. If you want to claim your device does what physics says is impossible, then you need to provide quite a large amount of proof that can be tested by others (frequently) and they need to be able to replicate your results reliably. None of that seems to have yet happened (the results in each of the tests performed provide wildly different numbers and use different controls... that's a bad sign if you're trying to prove it works).

Texan99 said...

I, too, will reserve judgment until someone can scale it up far enough that there's no question of measurement glitches. Then, if we can't argue that they're pushing against virtual particles, I guess we'll have to say they're pushing against the ether, or phlogistons, or something. Something sure would have to give.

I'm still surprised it's taking this long to sort out definitively. That's often a sign of interesting confusion.