EMDrive and other reactionless propulsion claims

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Re: NASA scientists report positively on propellant-less dri

Postby stoppedcaring » Fri Aug 01, 2014 2:46 pm UTC

My first guess would be that the orientation of the reflectors results in an asymmetric magnetic field which induces current in something nearby, making the whole thing act basically like a solenoid. Which could explain why different experimental designs are getting such vastly different thrust.

Although, if that's not the case, this is interesting. Is there any reason why the right design couldn't be pushing against virtual particles? Virtual particles are, AFAIK, emitted in random directions, but if the right geometry caused virtual photons moving in one direction to be deflected preferentially, I imagine thrust could result.

When we bounce virtual microwave photons into existence using an electromagnetically-vibrating mirror, what does the conservation of momentum in that system look like?

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Re: NASA scientists report positively on propellant-less dri

Postby gmalivuk » Fri Aug 01, 2014 2:53 pm UTC

If this is the same "propellant-less" drive I've seen mentioned for years, it's just a glorified photon drive possibly combined with a solar sail of some sort.

It's true that solar sails don't use propellant, but that doesn't make them a breakthrough revolutionary technology or whatever people want to claim for this.
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Re: NASA scientists report positively on propellant-less dri

Postby stoppedcaring » Fri Aug 01, 2014 3:29 pm UTC

gmalivuk wrote:If this is the same "propellant-less" drive I've seen mentioned for years, it's just a glorified photon drive possibly combined with a solar sail of some sort.

It's true that solar sails don't use propellant, but that doesn't make them a breakthrough revolutionary technology or whatever people want to claim for this.

If real, the breakthrough would come from being able to get more momentum out of a single photon's energy. Emit a photon (or bounce a photon off a single solar sail), and the amount of momentum you get is very low compared to the amount of energy you're using up. That's why bouncing a laser beam back and forth between two reflectors is vastly more energy-efficient for the thrust produced. If there's a way to do the same thing using virtual particles as your secondary reflector, well, that's awesome.

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Re: NASA scientists report positively on propellant-less dri

Postby eSOANEM » Fri Aug 01, 2014 4:35 pm UTC

elasto wrote:
eSOANEM wrote:The fact that they predict velocity-dependent thrust (and therefore acceleration which is invariant) is very worrying and strongly suggests to me that something has gone very wrong somewhere


That would mean it could accelerate through the light barrier, right? (Well, become a black hole first I guess)

That seems rather implausible to say the least :p


According to their graph (not that I follow the derivation of it), the thrust becomes negative above about 0.8c so no.

Again, what frame that's in doesn't seem to be defined so it's not clear what that actually means but it shouldn't be able to break c.
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Re: NASA scientists report positively on propellant-less dri

Postby stoppedcaring » Fri Aug 01, 2014 4:45 pm UTC

Thrust, or at least energy, is velocity-dependent, thanks to the Oberth effect. I imagine that this sort of novel propulsion, if it works, could be particularly sensitive to the Oberth effect.

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Re: NASA scientists report positively on propellant-less dri

Postby eSOANEM » Fri Aug 01, 2014 5:25 pm UTC

An object's kinetic energy isn't lorentz invariant though. Its proper acceleration is though. This means that the scalar thrust of the engine shouldn't be velocity dependent if we're not to break SR. The paper is suggesting that it is.

Essentially, the Oberth effect is a different thing.
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Re: NASA scientists report positively on propellant-less dri

Postby gmalivuk » Fri Aug 01, 2014 6:11 pm UTC

Merged this with the existing EmDrive thread. Good to keep all our conservation-of-momentum-violating crackpottery together in one place.
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Re: China Picks up the EMDrive

Postby Izawwlgood » Fri Aug 01, 2014 6:20 pm UTC

Is the general consensus that there was an error in NASA's testing/
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Re: China Picks up the EMDrive

Postby stoppedcaring » Fri Aug 01, 2014 6:29 pm UTC

Izawwlgood wrote:Is the general consensus that there was an error in NASA's testing/

How much energy is actually involved? I'm sure that with any appreciable current, it would be easy to miss some induced magnetic interference.

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Re: China Picks up the EMDrive

Postby gmalivuk » Fri Aug 01, 2014 6:33 pm UTC

It is always funny (in a depressing way) how persistently people continue to think basic magnetism is able to violate the laws of physics.
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Re: China Picks up the EMDrive

Postby stoppedcaring » Fri Aug 01, 2014 6:53 pm UTC

gmalivuk wrote:It is always funny (in a depressing way) how persistently people continue to think basic magnetism is able to violate the laws of physics.

Not sure if you were replying to me or not, but that's not what I was implying. I had suggested earlier than an induced current could have produced an unanticipated magnetic interference between the "engine" and the table/measuring devices, producing a false result.

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Re: China Picks up the EMDrive

Postby Izawwlgood » Fri Aug 01, 2014 7:04 pm UTC

Surely though there are ways to separate out forces, either by building another 'test' machine that is shaped differently, and/or by... I dunno, doing whole thing in a... faraday... cage...?

Wasn't part of the shtick with this drive that it was shaped asymmetrically, and that was responsible for the directionality of the thrust?
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Re: China Picks up the EMDrive

Postby stoppedcaring » Fri Aug 01, 2014 7:08 pm UTC

Izawwlgood wrote:Surely though there are ways to separate out forces, either by building another 'test' machine that is shaped differently, and/or by... I dunno, doing whole thing in a... faraday... cage...?

Oh, I'm sure. Just trying to think of what mistakes the NASA team could have made.

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Re: China Picks up the EMDrive

Postby gmalivuk » Fri Aug 01, 2014 8:02 pm UTC

stoppedcaring wrote:
gmalivuk wrote:It is always funny (in a depressing way) how persistently people continue to think basic magnetism is able to violate the laws of physics.

Not sure if you were replying to me or not, but that's not what I was implying. I had suggested earlier than an induced current could have produced an unanticipated magnetic interference between the "engine" and the table/measuring devices, producing a false result.

No, I was more building on your same point: this "drive" may induce some kind of magnetic effect, and because the people making devices like this still don't understand how magnetism works, they interpret it as some sort of free energy or momentum.
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Re: China Picks up the EMDrive

Postby Frenetic Pony » Fri Aug 01, 2014 10:23 pm UTC

gmalivuk wrote:
stoppedcaring wrote:
gmalivuk wrote:It is always funny (in a depressing way) how persistently people continue to think basic magnetism is able to violate the laws of physics.

Not sure if you were replying to me or not, but that's not what I was implying. I had suggested earlier than an induced current could have produced an unanticipated magnetic interference between the "engine" and the table/measuring devices, producing a false result.

No, I was more building on your same point: this "drive" may induce some kind of magnetic effect, and because the people making devices like this still don't understand how magnetism works, they interpret it as some sort of free energy or momentum.


And usually they then shout at investors about "unlimited free energy!" Usually "investors" meaning rich inherited wealth type people, possibly from the middle east or etc.

While I do remember a paper on a theoretically practical drive that would push against vacuum energy, I don't remember it being anything like the above nor being energy efficient nor being tested.

Still, if this is a new way to get in on the "magnets = free unlimited energy" scam I should check it out. Why should these guys be the only ones getting money from this stuff?

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NASA scientists report positively on propellant-less drive

Postby WarDaft » Sat Aug 02, 2014 12:42 pm UTC

Of rather significant importance in the NASA release, is that in the two apparatuses they built, both produced thrust... even though one of them was not supposed to.

I will be following this, just in case it's not a huge mistake, but I'm not expecting anything.
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Re: EMDrive and other reactionless propulsion claims

Postby Minerva » Sun Aug 03, 2014 2:14 pm UTC

When they document the method and experiment in detail allowing it to reproduced and it is accepted by a credible, peer-reviewed scientific journal and published, then at that time we've got N = 1 positive results claimed. And then other scientists can try and reproduce that single claimed positive result with all the information needed to properly reproduce the experiment, and we'll go from there.

As far as I'm aware, nobody, including the NASA group, has actually published all the details and results to allow an independent analysis and reproduction of the experiment.

And I can just smell the cries a mile away... "We've got a car that runs on water, but we can't publish the details to allow the device to be reproduced, because then Big Oil (Big Hydrazine in this case?) will steal the technology!"
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Re: EMDrive and other reactionless propulsion claims

Postby stoppedcaring » Mon Aug 04, 2014 5:06 pm UTC

Apparently, the difference between the "should work/shouldn't work" models was some sort of baffle or groove or slot on the inside which the original inventor had claimed was necessary for the device to function. That they measured the same thrust regardless of whether those slots were present means that the original inventor clearly doesn't understand the system...but we already knew that, because his "relativistic reflection" claim is junk science.

Though the Chinese test apparently didn't have those slots either. So perhaps they really are picking up something real.

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Re: EMDrive and other reactionless propulsion claims

Postby drachefly » Mon Aug 04, 2014 6:49 pm UTC

It can't be pushing off the quantum vacuum. If you want to get anything out of the quantum vacuum, you need to provide all of the energy and momentum yourself.

If this is somehow real, it would be the most surprising result since quantum mechanics, counting everything from the photoelectric effect up to the Aharonov-Bohm effect as one big discovery, and as out-of-the-blue as muons. This does not speak well for the likelihood of its being the case.

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Re: EMDrive and other reactionless propulsion claims

Postby johnny_7713 » Tue Aug 05, 2014 7:31 am UTC

Minerva wrote:When they document the method and experiment in detail allowing it to reproduced and it is accepted by a credible, peer-reviewed scientific journal and published, then at that time we've got N = 1 positive results claimed. And then other scientists can try and reproduce that single claimed positive result with all the information needed to properly reproduce the experiment, and we'll go from there.

As far as I'm aware, nobody, including the NASA group, has actually published all the details and results to allow an independent analysis and reproduction of the experiment.

And I can just smell the cries a mile away... "We've got a car that runs on water, but we can't publish the details to allow the device to be reproduced, because then Big Oil (Big Hydrazine in this case?) will steal the technology!"


Actually the NASA team has published their test set-up and results: http://arc.aiaa.org/doi/abs/10.2514/6.2014-4029

Per the final section of that paper, they're also working on a device that can be shipped off to other laboratories for independent testing.

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Re: EMDrive and other reactionless propulsion claims

Postby stoppedcaring » Tue Aug 05, 2014 2:23 pm UTC

drachefly wrote:It can't be pushing off the quantum vacuum. If you want to get anything out of the quantum vacuum, you need to provide all of the energy and momentum yourself.

How exactly did conservation of momentum work when we knocked virtual photons into real photons with a superconducting quantum interference device? Where did the momentum of the new photon come from? Was the mirror itself infinitesimally deflected in the opposite direction? Or were the photons created only in pairs with zero total momentum?

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Re: EMDrive and other reactionless propulsion claims

Postby Rococo » Thu Aug 07, 2014 2:29 am UTC

stoppedcaring wrote:
drachefly wrote:It can't be pushing off the quantum vacuum. If you want to get anything out of the quantum vacuum, you need to provide all of the energy and momentum yourself.

How exactly did conservation of momentum work when we knocked virtual photons into real photons with a superconducting quantum interference device? Where did the momentum of the new photon come from? Was the mirror itself infinitesimally deflected in the opposite direction? Or were the photons created only in pairs with zero total momentum?

I haven't studied the dynamical Casimir effect in detail, but looking at the paper it appears to be the former. If you have two mirrors and shake one of them, it always takes a little extra work compared to the classical expectation because you have to overcome the Casimir force. If you shake it slowly, you add energy to the vacuum smoothly and don't see any change, but if you shake it very quickly you add energy faster than the vacuum can respond and create excitations.

It's quite analogous to a situation where you have closed chamber with water, and you push one of the walls in slowly or quickly. In that case, vacuum energy is represented by the gravitational potential energy of the water, which rises and falls as you push on it. If you push on it very quickly, the water can't settle to its equilibrium height, but instead just sloshes around. The difference, of course, is that in the quantum case the water 'height' is not observable, only the waves.

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Re: EMDrive and other reactionless propulsion claims

Postby Izawwlgood » Thu Aug 07, 2014 1:28 pm UTC

Sorry, the 'background virtual plasma' or whatever has a tensile modulus?
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Re: EMDrive and other reactionless propulsion claims

Postby drachefly » Thu Aug 07, 2014 2:31 pm UTC

stoppedcaring wrote:
drachefly wrote:It can't be pushing off the quantum vacuum. If you want to get anything out of the quantum vacuum, you need to provide all of the energy and momentum yourself.

How exactly did conservation of momentum work when we knocked virtual photons into real photons with a superconducting quantum interference device?


I dunno, but my ignorance on this question is ignorance of the setup, not of quantum mechanics.

From what I know of the renormalization group, though, if you dislodge a particle from something's renormalization garbage-can, it's going to have to fill in that hole. So, I'd guess the momentum would end up in whatever was creating the Casimir effect.

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Re: EMDrive and other reactionless propulsion claims

Postby jewish_scientist » Fri Aug 08, 2014 5:47 am UTC

I have been reading and I have to admit, 90% of this stuff is going right over my head. It is simply to complex for me, but I am going to ask my question anyway.

Even if a propulsion system has no net acceleration, the system can still move. I know this because of a simple thought experiment:

Put a cannon, a cannon ball and gunpowder in a very large, closed box. This box rests on a friction-less plane. The box is at rest. Load the cannon and fire it at the opposing wall. The cannon ball pushes on the cannon, which in turn pushes on the box. The box will accelerate. Some time will pass before the cannon ball reaches the other wall. When it does, the force it exerts on the box will made the box stop moving. But during that time in between the launching and the landing of the cannon ball, the box was moving. There is no net change in the box's velocity, but there is a net change the box's position. If you make the box so big that you can reload and fire the cannon before the cannon ball hits the wall, then the velocity vector would have a constant direction (although its magnitude would fluctuate quite a bit) until you run out of gunpowder and/or cannon balls.

This proves that even if a propulsion system cannot create a net force, it can still do work (it moved a mass, so work must have been done). However, everyone here is talking about whether or not the EMDrive can produce thrust, a force. But that is irrelevant because it may still be able to preform work even if it cannot produce thrust. So why is everyone discussing the wrong thing?
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Re: EMDrive and other reactionless propulsion claims

Postby Tub » Fri Aug 08, 2014 6:34 am UTC

jewish_scientist wrote:This proves that even if a propulsion system cannot create a net force, it can still do work (it moved a mass, so work must have been done).

Has it really? Then tell me: What's the center of gravity of the whole system (including cannonball) before and after the firing?

All you're really doing is shifting mass around inside the box, but you're not moving.

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Re: EMDrive and other reactionless propulsion claims

Postby Eebster the Great » Fri Aug 08, 2014 7:08 am UTC

Yeah, you're moving the geometric center of the box but not its center of gravity, so you're not doing any work. Even if you were, the reaction force would push the box back to its initial position, so the total displacement (and thus work) would end up being zero.

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Re: EMDrive and other reactionless propulsion claims

Postby johnny_7713 » Fri Aug 08, 2014 7:44 am UTC

jewish_scientist wrote:I have been reading and I have to admit, 90% of this stuff is going right over my head. It is simply to complex for me, but I am going to ask my question anyway.

Even if a propulsion system has no net acceleration, the system can still move. I know this because of a simple thought experiment:

Put a cannon, a cannon ball and gunpowder in a very large, closed box. This box rests on a friction-less plane. The box is at rest. Load the cannon and fire it at the opposing wall. The cannon ball pushes on the cannon, which in turn pushes on the box. The box will accelerate. Some time will pass before the cannon ball reaches the other wall. When it does, the force it exerts on the box will made the box stop moving. But during that time in between the launching and the landing of the cannon ball, the box was moving. There is no net change in the box's velocity, but there is a net change the box's position. If you make the box so big that you can reload and fire the cannon before the cannon ball hits the wall, then the velocity vector would have a constant direction (although its magnitude would fluctuate quite a bit) until you run out of gunpowder and/or cannon balls.

This proves that even if a propulsion system cannot create a net force, it can still do work (it moved a mass, so work must have been done). However, everyone here is talking about whether or not the EMDrive can produce thrust, a force. But that is irrelevant because it may still be able to preform work even if it cannot produce thrust. So why is everyone discussing the wrong thing?


While the initial and final velocities may be the same, I'm pretty sure the velocity of the box in between the time that the cannon hits the wall and the time that the ball hits the wall has a different value.

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Re: EMDrive and other reactionless propulsion claims

Postby WarDaft » Fri Aug 08, 2014 10:30 pm UTC

Eebster the Great wrote:Yeah, you're moving the geometric center of the box but not its center of gravity, so you're not doing any work. Even if you were, the reaction force would push the box back to its initial position, so the total displacement (and thus work) would end up being zero.

Aren't there patters of movement like in the Falling Cat Problem that produce a net displacement?
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Re: EMDrive and other reactionless propulsion claims

Postby notzeb » Fri Aug 08, 2014 11:05 pm UTC

WarDaft wrote:
Eebster the Great wrote:Yeah, you're moving the geometric center of the box but not its center of gravity, so you're not doing any work. Even if you were, the reaction force would push the box back to its initial position, so the total displacement (and thus work) would end up being zero.

Aren't there patters of movement like in the Falling Cat Problem that produce a net displacement?
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Re: EMDrive and other reactionless propulsion claims

Postby drachefly » Mon Aug 11, 2014 11:25 am UTC

johnny_7713 wrote:While the initial and final velocities may be the same, I'm pretty sure the velocity of the box in between the time that the cannon hits the wall and the time that the ball hits the wall has a different value.



The velocity of the box alone does change. But the velocity of the system of the box, cannon, and cannonballs? That remains constant throughout.

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Re: EMDrive and other reactionless propulsion claims

Postby jewish_scientist » Tue Aug 12, 2014 12:33 am UTC

Tub wrote:
jewish_scientist wrote:This proves that even if a propulsion system cannot create a net force, it can still do work (it moved a mass, so work must have been done).

Has it really? Then tell me: What's the center of gravity of the whole system (including cannonball) before and after the firing?

All you're really doing is shifting mass around inside the box, but you're not moving.
Eebster the Great wrote:Yeah, you're moving the geometric center of the box but not its center of gravity, so you're not doing any work.


I feel quite embarrassed. What is interesting though, is that when I asked my physics teacher this he did not point that out. He basically told me that because acceleration is conserved, it does not matter if work was done.
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