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Old 22nd November 2016, 09:25 AM   #121
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Originally Posted by RussDill View Post
The important aspect here is that the constant force vector is attached to a rotating wheel. Conservation of momentum, angular momentum, and energy are actually really closely linked and the rotating wheel thing is just a simple mental exercise.

If you are into low level physics, just imagine an EmDrive in empty space. Energy is applied and it accelerates. Presumably some energy is lost to heat, but some energy is being converted into kinetic energy. Now, imagine some related situations. An EmDrive ship is slowly approaching, it brakes using it's drive to come to a halt. It spent energy in bringing it's kinetic energy to zero. Where did both it's kinetic energy and the energy consumed by the EmDrive go?

At the particle level, physics operates the same forwards or backwards once you flip a few signs. Play both tapes in reverse. In the first tape, you have an EmDrive that slows to a stop and converts it's kinetic energy into electrical energy. In the second tape, you have a drive that accelerates away while producing electrical energy.

A common problem to these is that whether the kinetic energy of the system is increasing or decreasing depends on the inertial reference frame of the observer. Don't forget that KE = ½mv². So the amount of kinetic energy that's being added (or removed) depends on the relative velocity of your inertial reference frame.

The problem gets much worse when you start considering non-inertial reference frames.
Thanks, I understand now.
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Old 22nd November 2016, 09:56 AM   #122
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Originally Posted by RecoveringYuppy View Post
Sure, but I don't see how that relates to BenBurch's statement.
Seems pretty straightforward to me. Interaction with the magnetic field can produce thrust, therefore that is one possible source of error that isn't eliminated by putting it in orbit.
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Old 22nd November 2016, 10:02 AM   #123
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Originally Posted by phunk View Post
Seems pretty straightforward to me. Interaction with the magnetic field can produce thrust, therefore that is one possible source of error that isn't eliminated by putting it in orbit.
I don't see how. It seems pretty difficult to accidentally attach a very long, highly charged, tether to this mission or to accidentally create anything resembling it.
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Old 22nd November 2016, 10:34 AM   #124
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Originally Posted by RecoveringYuppy View Post
I don't see how. It seems pretty difficult to accidentally attach a very long, highly charged, tether to this mission or to accidentally create anything resembling it.
The point was that it's possible to generate thrust off the magnetic field, not that it would be done exactly the same way.
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Old 22nd November 2016, 10:45 AM   #125
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Reading about it all, I ended up here:

http://www.projectrho.com/public_htm...nlessdrive.php

Which talks about the problems fiction writers will cause themselves if they write in a reactionless drive. While it's talking about such things in reference to works of fiction, there's a lot of, what seems to me, to be decent science in there leading me further and further down the 'it can't and doesn't work' route.

I really, really want it to work.

I really, really, really don't think it does.
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Old 22nd November 2016, 10:55 AM   #126
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Originally Posted by RecoveringYuppy View Post
I don't see how. It seems pretty difficult to accidentally attach a very long, highly charged, tether to this mission or to accidentally create anything resembling it.
For the EM Drive thrust levels, how long would the tether have to be at what charge? I haven't done the math (maybe later) but if you're using a typical small spacecraft 28V power system and you wind up with, say, a 0.3 meter tether to get comparable thrust, then the spacecraft's wire harness will likely have more net thrust than your EM Drive.
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Old 22nd November 2016, 11:06 AM   #127
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Originally Posted by RecoveringYuppy View Post
But is that ever an >escape< from Earth? I meant "out" literally.
Do you mean impart enough deltaV to escape Earth orbit, or park at L4 or L5? That would take an enormous amount if energy and remass.
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Old 22nd November 2016, 11:17 AM   #128
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Originally Posted by catsmate View Post
Do you mean impart enough deltaV to escape Earth orbit, or park at L4 or L5? That would take an enormous amount if energy and remass.
Enormous amount of energy? No. Earth orbit to escape velocity is in the neighborhood of 10 kWh per kilogram, obviously depending on specifically what orbit you're starting in.
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Old 22nd November 2016, 11:18 AM   #129
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Originally Posted by Horatius View Post
...But what they don't get is, real scientists don't think that way....
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Old 22nd November 2016, 11:19 AM   #130
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Originally Posted by dasmiller View Post
For the EM Drive thrust levels, how long would the tether have to be at what charge? I haven't done the math (maybe later) but if you're using a typical small spacecraft 28V power system and you wind up with, say, a 0.3 meter tether to get comparable thrust, then the spacecraft's wire harness will likely have more net thrust than your EM Drive.
Even if it did wind up to be that large wouldn't there be trivial ways to negate it? Such as routing the wires appropriately?
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Old 22nd November 2016, 12:27 PM   #131
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Originally Posted by RecoveringYuppy View Post
Even if it did wind up to be that large wouldn't there be trivial ways to negate it? Such as routing the wires appropriately?
There would be easy ways to reduce it. Whether that's enough depends on the magnitude of the problem. If a "natural" harness (a harness for which magnetic interaction wasn't a consideration) would cause about the same force as the EM Drive, then we could probably knock the harness effect down by 99% without too much trouble (shielding, twisted pairs, etc). But what if the magnetic effect was 1,000,000X the EM Drive? I suspect the shielding won't be anywhere near that good, and at those levels, there are all sorts of small or transient effects that you won't be able to ignore and will probably have a lot of trouble even measuring.

There may be other tricks if you specifically designed your spacecraft to minimize magnetic interaction. It's an interesting problem.

I'm not an expert in the field, I'm thinking about it more by analogy to RF shielding problems. And I'm no expert in that, either, but worked around it and I've even had to give a few briefings on the subject.
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Old 22nd November 2016, 12:54 PM   #132
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Originally Posted by Tolls View Post
Why do they feel that they need to launch something into space to detect this "thrust"?

Why do they think it's easier to see this effect up there than down here in a lab under significantly better controlled conditions?
One obvious cause would be gravity If the thrust effect is relatively weak, it would be much easier to detect in microgravity.

The science of the EM drive just took a significant step upward in credibility with NASA's paper on the drive effect passing peer-review and being published in the American Institute of Aeronautics and Astronautics (AIAA)’s Journal of Propulsion and Power:

http://www.dailygalaxy.com/my_weblog...-hea.html#more

Abstract here:

http://arc.aiaa.org/doi/10.2514/1.B36120
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Old 22nd November 2016, 01:12 PM   #133
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Originally Posted by dasmiller View Post
But what if the magnetic effect was 1,000,000X the EM Drive?
I'm thinking it can't be or we'd be seeing satellites wandering away from Earth due to their current wiring. A million times the numbers being reported by NASA for the EmDrive would be very significant. A million times the numbers being reported by the drive "enthusiasts" would be staggering.

Links for the numbers I'm about to cite below. Please poke holes.

NASA Eagleworks reports 50 to 100 micro-Newtons [ETA: of thrust for the EmDrive variants]. I don't know the mass of the device they are testing but that seems pretty significant for a small device, especially if you let it operate continuously.

The most reliable numbers I can come up for how that thrust might affect objects in LEO is station keeping numbers for the ISS.

ISS masses 419K Kg. It's station keeping vehicles have, at most, 8000 Newtons of thrust. They operate infrequently, such as a 15-20 minute burn once every 10 to 45 days. If I've done my arithmetic properly that works out to 19 millinewtons per kilogram when the engines are operating. Average over time it then works outs to something around 2 to 10 micro-newtons per kilogram. And that seems to square with some claims I've seen that this device, if real, would make a perfect station keeping engine.

So I'm having a hard time understanding why it's certain that a test in space wouldn't be conclusive. It all seems to hinge on whether the test satellite could be in the 10 to ~100 Kg range. And those numbers become more flexible if the test can be conducted at higher altitude.

https://en.wikipedia.org/wiki/Intern..._Space_Station
https://en.wikipedia.org/wiki/Automa...ansfer_Vehicle
https://en.wikipedia.org/wiki/Zvezda_(ISS_module)
https://www.nasaspaceflight.com/2012...r-loss-latest/
https://en.wikipedia.org/wiki/RF_res...ics_Laboratory
https://en.wikipedia.org/wiki/CubeSat
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Old 22nd November 2016, 02:18 PM   #134
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Originally Posted by RecoveringYuppy View Post
I'm thinking it can't be or we'd be seeing satellites wandering away from Earth due to their current wiring. A million times the numbers being reported by NASA for the EmDrive would be very significant. A million times the numbers being reported by the drive "enthusiasts" would be staggering.

Links for the numbers I'm about to cite below. Please poke holes.

NASA Eagleworks reports 50 to 100 micro-Newtons [ETA: of thrust for the EmDrive variants].
Fair enough. 1 million times 50 micronewtons would be 50N, and I'm certain that typical spacecraft aren't seeing anything like 50N of magnetic interaction. Or 1N, for that matter. Again, without running the math, I'd guess it's down in the millinewton range.
Quote:

I don't know the mass of the device they are testing but that seems pretty significant for a small device, especially if you let it operate continuously.

The most reliable numbers I can come up for how that thrust might affect objects in LEO is station keeping numbers for the ISS.

ISS masses 419K Kg. It's station keeping vehicles have, at most, 8000 Newtons of thrust. They operate infrequently, such as a 15-20 minute burn once every 10 to 45 days. If I've done my arithmetic properly that works out to 19 millinewtons per kilogram when the engines are operating. Average over time it then works outs to something around 2 to 10 micro-newtons per kilogram. And that seems to square with some claims I've seen that this device, if real, would make a perfect station keeping engine.

So I'm having a hard time understanding why it's certain that a test in space wouldn't be conclusive. It all seems to hinge on whether the test satellite could be in the 10 to ~100 Kg range. And those numbers become more flexible if the test can be conducted at higher altitude.
Bear in mind that in LEO, drag is a significant factor, and it's a proportionately more significant factor on lightweight spacecraft. It's also pretty erratic. ISS is in a relatively high LEO, which helps. But for a very-low-thrust thruster test, I'd definitely want to be at least a few thousand km up.

Ideally, I'd want two virtually-identical spacecraft that were starting out in near-identical orbits; each would have an EM Drive and a DummyDrive that consumed the same amount of power and distributed it similarly. I'd have one spacecraft operating the EM Drive and the other running its DummyDrive, and see how the orbits diverged. Then I'd switch 'em, and see it again. etc etc. But that's an expensive test.
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Old 22nd November 2016, 02:44 PM   #135
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Originally Posted by RecoveringYuppy View Post
I don't know the mass of the device they are testing but that seems pretty significant for a small device, especially if you let it operate continuously.
This seems like something that should be in the published paper, but a quick glance shows that they list the dimensions, but not the mass.
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Old 22nd November 2016, 05:20 PM   #136
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Great summary. Scott Manley makes all sorts of awesome videos on thrusters.

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Old 22nd November 2016, 08:32 PM   #137
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Originally Posted by RussDill View Post
Great summary. Scott Manley makes all sorts of awesome videos on thrusters.


Well, if his Kerbal Space Program videos are anything to go by, I'm convinced!

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Old 22nd November 2016, 09:36 PM   #138
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Originally Posted by Horatius View Post
Well, if his Kerbal Space Program videos are anything to go by, I'm convinced!

Check out the science playlist

The one about rocking plumbing in particularly interesting.
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Old 23rd November 2016, 01:48 AM   #139
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Originally Posted by ChristianProgressive View Post
One obvious cause would be gravity If the thrust effect is relatively weak, it would be much easier to detect in microgravity.
But you then replace gravity (which is pretty constant down here) with the various other effects we have just been talking about, from drag, to solar rays, to magnetic effects, all of which are nowhere near as constant.

Peer review is only the start. It only says "this is not utter garbage"..."there might be something here". Now that it's published we should get to see some interesting reviews, and a better idea of if there is something there.
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Old 23rd November 2016, 03:02 AM   #140
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Originally Posted by ServiceSoon View Post
No true Scotsman.
Actually, no. If you go into carrier science, it is to discover new stuff, study the law of nature, and find out more about reality.

It is not to nod and agree to old dusty equations.

This is really a case where the no true Scotsman is an idiotic fallacy to apply.
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Old 23rd November 2016, 08:08 AM   #141
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So, Eagleworks claim that the drive might work due to pilot-wave theory. I've seen this dismissed as "baloney", but I've not seen any actual counter-arguments.

Would anybody who knows more than I do about this like to throw their hat in the ring?
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Old 23rd November 2016, 09:56 AM   #142
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Originally Posted by Squeegee Beckenheim View Post
So, Eagleworks claim that the drive might work due to pilot-wave theory. I've seen this dismissed as "baloney", but I've not seen any actual counter-arguments.

Would anybody who knows more than I do about this like to throw their hat in the ring?
It's solid physics, but fringe such. Pilot wave theory is one of many interpretations of quantum theory. Essentially it says that the Schrödinger equations give the equations of motion for a wave carrying a particle, not the particle itself.

It's an example of a hidden variable theory that appears to not violate Bell's inequalities.
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Old 23rd November 2016, 11:04 AM   #143
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Originally Posted by Squeegee Beckenheim View Post
So, Eagleworks claim that the drive might work due to pilot-wave theory. I've seen this dismissed as "baloney", but I've not seen any actual counter-arguments.

Would anybody who knows more than I do about this like to throw their hat in the ring?
afaik, all the current interpretations of QM offer no testable predictions to differentiate between them. They all give the same predicted results of all the experiments we currently can run. So saying that there is some solution in pilot wave theory makes me really skeptical because you should be able to have the same solution using any other QM interpretation. Why pilot-wave specifically?

Here's a bit of the skinny:

https://en.wikipedia.org/wiki/Pilot_wave

Quote:
The de Broglie–Bohm pilot wave theory is one of several interpretations of quantum mechanics. It uses the same mathematics as other interpretations of quantum mechanics; consequently, it is also supported by the current experimental evidence to the same extent as the other interpretations.
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Old 23rd November 2016, 01:08 PM   #144
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Quote:
The de Broglie–Bohm pilot wave theory is one of several interpretations of quantum mechanics. It uses the same mathematics as other interpretations of quantum mechanics; consequently, it is also supported by the current experimental evidence to the same extent as the other interpretations.
"Sounds a bit wooish to me."

I like replicable results. I like falsifiability. If something here is replicable but unexplained, and currently unfalsifiable math models of reality aren't supplying answers in a replicable manner, then they need to be discarded from this problem.

Personally, I assert this finally proves the existence of aether.
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Old 23rd November 2016, 02:38 PM   #145
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What I find slightly dubious in Measurement of Impulsive Thrust from a Closed Radio-Frequency Cavity in Vacuum is Figure 19 in the Synopsis of Experimental Results.
They measure the forward and reverse thrust at 3 power settings to get 3 points with error bars that almost overlap. They then apply a linear fit. That implies a bit of confirmation bias, i.e. that the effect is real and will increase with increasing power. However it is just as valid to state that the effect levels off at about 90 μN with increasing power from that data. Which in turn is a hint that the effect is not real. Their "push off vacuum" speculation via pilot-wave theory should have a greater push with more power.
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Old 24th November 2016, 02:37 AM   #146
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Originally Posted by Jrrarglblarg View Post
"Sounds a bit wooish to me."

I like replicable results. I like falsifiability. If something here is replicable but unexplained, and currently unfalsifiable math models of reality aren't supplying answers in a replicable manner, then they need to be discarded from this problem.
I'm having a hard time understanding you. What "something" is replicable but unexplained? And what unfalsifiable math models are you referring to?

You'll note that the only mathematics referred to was the math of QM. As stated in the post you responded to, pilot wave theory is an interpretation of QM, and thus it's mathematics are identical to all other interpretations of QM.
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Old 24th November 2016, 03:10 AM   #147
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Originally Posted by RussDill View Post
afaik, all the current interpretations of QM offer no testable predictions to differentiate between them.
I think the point is that if the EM Drive does work, then pilot wave theory gives it a mechanism by which it could without violating the known laws of physics, which none of the other interpretations do. So, even if the theory is fringe, if there's no evidence contradicting it, and there is as much evidence supporting it as any other interpretation of quantum mechanics, couldn't the working of the EM Drive (were that ever to be demonstrated) actually count as evidence for the theory? And, if there's no evidence against it and it's just not as popular as the Copenhagen interpretation, then by what reasoning can the suggestion be considered "baloney"?

So I suppose what I'm asking is is there anything inherent in pilot wave theory that makes the idea of using the virtual particles of the quantum vacuum as a medium through which to generate thrust a nonsense? Is there any actual evidence (mathematical or experimental) against this idea?
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Old 24th November 2016, 03:50 AM   #148
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Originally Posted by Squeegee Beckenheim View Post
So I suppose what I'm asking is is there anything inherent in pilot wave theory that makes the idea of using the virtual particles of the quantum vacuum as a medium through which to generate thrust a nonsense? Is there any actual evidence (mathematical or experimental) against this idea?
It seems to me that the virtual particles that one used to generate thrust would, by virtue of that interaction, become real particles with energy and momentum. Your spacecraft would simply be emitting particles (probably photons?).

In which case you've just got a photon drive, not a reaction-less drive. You'd be able to detect the photons (or whatever particles) thus emitted.
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Old 24th November 2016, 04:09 AM   #149
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Originally Posted by Roboramma View Post
It seems to me that the virtual particles that one used to generate thrust would, by virtue of that interaction, become real particles with energy and momentum. Your spacecraft would simply be emitting particles (probably photons?).

In which case you've just got a photon drive, not a reaction-less drive. You'd be able to detect the photons (or whatever particles) thus emitted.
Okay, so it seems like it'd be worth them coming up with a protocol to test whether or not it actually does emit particles of some sort. That would go some way towards confirming their hypothesis as to method of action.
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Old 24th November 2016, 08:03 AM   #150
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I thought photons had already been eliminated as a possible thrust based on performance being "better" than expected.
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Old 25th November 2016, 06:36 AM   #151
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The published paper has been annotated with criticisms
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Old 25th November 2016, 10:17 AM   #152
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Originally Posted by Roboramma View Post
It seems to me that the virtual particles that one used to generate thrust would, by virtue of that interaction, become real particles with energy and momentum. Your spacecraft would simply be emitting particles (probably photons?).

In which case you've just got a photon drive, not a reaction-less drive. You'd be able to detect the photons (or whatever particles) thus emitted.
Yes, and of course, if you are going to use photons, you wouldn't want microwave photons.
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Old 25th November 2016, 12:55 PM   #153
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I think the idea is that the virtual particles exist long enough to generate thrust before disappearing again. It's a little hard to tell, as even quantum physicists seem to not quite be able to get their heads around what the claim is exactly.
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Old 25th November 2016, 01:57 PM   #154
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Originally Posted by Squeegee Beckenheim View Post
I think the idea is that the virtual particles exist long enough to generate thrust before disappearing again. It's a little hard to tell, as even quantum physicists seem to not quite be able to get their heads around what the claim is exactly.
The Casmir effect is real and pretty weird
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Old 25th November 2016, 02:07 PM   #155
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I'm pretty sure that it's been shown that the Casmir effect can't actually be responsible for the thrust, although some people certainly claim that it is.

I mean, of course, all of this is putting the cart before the horse, rather, since it's not yet been demonstrated that there is any thrust to explain.
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Old 25th November 2016, 02:25 PM   #156
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Originally Posted by Squeegee Beckenheim View Post
I'm pretty sure that it's been shown that the Casmir effect can't actually be responsible for the thrust, although some people certainly claim that it is.

I mean, of course, all of this is putting the cart before the horse, rather, since it's not yet been demonstrated that there is any thrust to explain.
It doesn't seem to be like the Casmir effect - and indeed, it seems to try violating conservation of momentum, so I doubt there's anything except experimental error
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Old 25th November 2016, 04:19 PM   #157
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SciShow Space have just published a youtube that explains all of this in a simple way. Some of it is a repeat of what is in this thread. I think it is well worth a watch.

You need only watch the first 2:30 minutes of it. The rest is on another, equally interesting, subject.

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Old 25th November 2016, 04:24 PM   #158
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Originally Posted by Squeegee Beckenheim View Post
I think the idea is that the virtual particles exist long enough to generate thrust before disappearing again. It's a little hard to tell, as even quantum physicists seem to not quite be able to get their heads around what the claim is exactly.
If that's true, You'd need to be giving them enough energy so that when they recombine, they would emit a pair of photons. These photons would then be the carriers of momentum and you'd likely be at worse efficiency than just a straight photon drive.

At least to me, any explanation needs to first explain in what way this is not a free energy device.
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Old 25th November 2016, 09:10 PM   #159
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Originally Posted by rjh01 View Post
SciShow Space have just published a youtube that explains all of this in a simple way. Some of it is a repeat of what is in this thread. I think it is well worth a watch.

You need only watch the first 2:30 minutes of it. The rest is on another, equally interesting, subject.

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SciShow says "it looks like the technology is legit". I don't remember them as being particularly "out there". Are they right? Is the EM drive actually looking like it might work?
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Old 26th November 2016, 12:45 AM   #160
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Originally Posted by Fudbucker View Post
SciShow says "it looks like the technology is legit". I don't remember them as being particularly "out there". Are they right? Is the EM drive actually looking like it might work?
This thread holds people with views all across the spectrum. I really think the video gave the whole thing the kid's gloves treatment in order to hop on the hype train. I certainly don't think the majority view of the scientific community is that it's legit.

The "maybe pilot wave" thing just raises a whole bunch of red flags with me. It shouldn't matter what QM interpretation you use. If you can get a result with pilot wave theory, you should be able to get the same result with copenhagen.
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