Cannae/EmDrive

[CptRichardson]

It is just like the faster-than-light neutrinos from a few years back. Most people who knew something about the topic expected it to be a simple error, and of course it was a simple error. This will turn out exactly as that.

Except for the repeated results being replicated by various individuals, successful modeling of the phenomenon to within 2% of test results, a whole load of other factors as they work to eliminate all possible instrumentation errors and keep getting the same results. And also because their explanation DOESN'T violate the laws of physics as we know them once they spelled it out, and while messy still fits and should clean up with more data.

Edited February 9, 2015 by CptRichardson

[PB666]

Because with infinite delta vee, they could fly to an asteroid and push it into a collision course with Earth. If they fly to an asteroid that turns out to be a rubble pile, they can just fly to a new one.

Only if that individual lived for 1000 years. 50E-6 N at 16W and given 1KW per meter at 50% efficiency for solar translates into 0.0015 N per m^2 of panel. Lets say we had a ship with 1000 x 1000 meters of panel and ignored the weight of the panel. The ship could generate 1500 newton. 15km (earth debiotizing) diameter impactor has a mass of 4/3 pi 7500^3 times d (say 3) = 5.3E12 mass. At 1500 newtons accelartion would be 3E-9 meters/second or 3E-10g. The issue of moving to intercept the asteroid itself is a problem. 1000000 meters of panel has to way many kilotons, the dV of the entry would have to be tiny to gain orbit, it might take years to arrive that that speed and approach, and then landing on the asteroid is a whole different problem. One 1 meter/second of thrust would take how long? 100 years.

Diverting objects from crossing earth's orbit is easier than making them hit the earth. First you have to find an object of size, some of then have high energy differences and planes that do no cross the earths, you would have to match planes and then cross orbits. If you're acceleration is too slow there is a good chance you will send the asteroid on a hyperbolic trajectory with earths upper atmosphere (drag would be immaterial) or on an escape orbit or collision orbit with some other body (like Jupiter).

ION drives are far more dangerous, because in theory the ion drive potential is to create particles with the energy of a baseball from a single hydrogen atom. THis is unrealistic but particles with 2 x mass gain and ISPs in the 100,000s or 1,000,000s are conceivable. For very heavy payloads that include a nuclear power supply this might be very useful. You could even eject spent fuel in the drive.

[DerpenWolf]

I have to admit I am a bit skeptical but if it works then that's absolutely fantastic! If we can get a decently powerful model working we just need to put a nuclear reactor up in orbit and away we go!!! Also I wonder if this could possibly cut down the time needed for interstellar trips by a large degree? Finally does anyone have any clue why the drive works as I would think that a equal force would be pushing on both sides of the drive despite the two different ends due to the slope of the walls?

[-Velocity-]

But there is some people here that still won't believe it works even if we have satellites being propelled by them.

No, there is no one here like that. If there is independent verification by an outside reputable source, and we start seeing some peer-reviewed journal papers, minds will change. The skeptics are skeptics because they simply don't see enough evidence. A small NASA lab who hasn't published any peer-reviewed papers on this, and some small Chinese lab are NOT reputable sources.

Also, the skeptics are skeptics because they are NOT the kind of people who let their hopes and desires interfere with what they believe. A proper scientific mindset removes your desire from the results, because the greatest desire should always be the TRUTH. And the truth is, as awesome as a reactionless drive would be, it conflicts with centuries of science. I may not be an expert in the field, but when confronted with the "explanation" on how these EM drives work, my understanding is that the real experts in quantum mechanics scoffed at the idea. I can't be an expert in every field, and so I have to trust in their judgement. I'm not one of those people who, even though I have very little (or no) education in a field of study, is dumb enough to question the judgement of the actual experts in that field, and think I could possibly come up with something that they hadn't already thought of yet. The people (not talking about any of the people in this thread) who think they can second-guess what scientists and experts have to say on a subject really irritate me. /rant off

But I think that's why we're skeptics. Until strong enough evidence is presented and/or the experts start changing their minds, the most logical conclusion is that this EM drive does not in fact work, and that this small NASA lab is not taking some factor into account or has some kind of other experimental error. To get all excited over these results is only setting yourself up for what is almost certainly going to be a big let-down.

Edited February 9, 2015 by |Velocity|

[Stargate525]

Also I wonder if this could possibly cut down the time needed for interstellar trips by a large degree?

This cuts down the time needed for anything; If this is actually a reactionless drive, you don't need to pack fuel. Payload fraction goes through the roof.

[DaMichel]

Interesting, stuff. Makes me wish i had taken those physics lectures so i could understand the virtual particle stuff. But i'm very sceptical. It sounds a lot like the aether theory, indeed. Which of course was disproved long ago.

Apparently they managed to repeat the experiment in hard vacuum. My bet is now on some electromagnetic interaction with the walls of the vacuum chamber producing the "thrust" (as already mentioned above). They cannot really refute this possibility, can they?

It is very funny if you think about it, they basically want to use a microwave oven for propulsion. Very Kerbal.

[-Velocity-]

This cuts down the time needed for anything; If this is actually a reactionless drive, you don't need to pack fuel. Payload fraction goes through the roof.

Obviously, you're still limited by your ability to generate electric power. Say you have a nuclear reactor that outputs 100 kW for 10 years. The current results are showing like 100 uN of thrust for like 16W input power. Say your spacecraft weighs 2000 kg. 100 uN for 16 W is only 6.25 uN/W. With 100 kW input power, that's still only 0.625 N. After 10 years, your delta-V is only about 100 km/s. That's good for solar system travel, but still far, far, far less than what you need for interstellar.

Now, obviously, it's likely to that the device would be able to be improved once we understood how it actually works, but- improved enough to enable interstellar travel? Probably not. Nuclear pulse propulsion would still probably be better.

[Frozen_Heart]

This cuts down the time needed for anything; If this is actually a reactionless drive, you don't need to pack fuel. Payload fraction goes through the roof.

Acceleration is still an issue. Even with unlimited fuel, if the acceleration is tiny then it will still take a long time to get anywhere.

[Robotengineer]

Acceleration is still an issue. Even with unlimited fuel, if the acceleration is tiny then it will still take a long time to get anywhere.

Yes, it doesn't really matter if EmDrive can move 100,000 tonnes anywhere in the solar system if it takes the craft a thousand years to get there.

[PB666]

Yes, it doesn't really matter if EmDrive can move 100,000 tonnes anywhere in the solar system if it takes the craft a thousand years to get there.

Thats the travelers technology paradox. If it takes 1000 years to get there in 50 years there will be a technology that gets you there 10 times as cheap and 10 times as fast.

[sal_vager]

Well if these can't be scaled up, just use more of them.

Thousands upon thousands of mass produced cheap EM drives....

[K^2]

Except they're saying that's NOT the case. They're trying to figure out how to check for it, but they believe the push modifies the virtual particles so that they do not immediately annihilate, but instead convey the thrust reaction out. They're trying to figure out how to check for a particle wake right now as part of their continuing study.

Convey to what? If net is still less than 300MW per N, then whatever it is, it has mass. In fact, mass flow is exactly sqrt(F^2*c^2 - P^2)/c^2

Anything with better efficiency than photon drive is a reaction drive. That is just basic physics. How the reaction force is conveyed can be very creative. We could be seeing a very odd sort of an ion drive, but it is not reactionless one.

[PB666]

This cuts down the time needed for anything; If this is actually a reactionless drive, you don't need to pack fuel. Payload fraction goes through the roof.

E=mc^2. Interstellars still need mass to create energy, even if you don't eject it. If you want to travel 1/10th the speed of light, then you have to perfectly convert 10% of the fuel to energy and perfectly conserve the energy in light momentum. Also, lets we forget, those light beams are wasteful, since they still carry energy as well as imparting momentum. You also need 10% of the fuel to stop. The best mass energy conversion rates outside of supercolliders is below 1% so 1/10th the speed of light is technically no possible nor even approachable.

The only potential for getting around this is having a ship that rides lasers and collects and emits the energy. Brownian motion would not tolerate success on small scales its only plausible on hideously large scales.

Consider if we increased the speed by 1 magnitude (500,000 mph) over currently possible. At that speed it takes 1300 years to travel 1 light year, the nearest planet is 4 light years so thats around 5000 light years with no hope of stopping once we go there. Thats 250 human generations.

IMO interstellar travel will require large asteroid like ships that can travel for 100,000s of years and are virtual microcosms. 97% of our own species is roughly that age, so. . . . . . Maybe the reason that aliens are not whizzing through our solar system, wait 100000 years, lol.

[sal_vager]

Are solar panels not an option here?

[N_las]

Are solar panels not an option here?

Solar panels are useful if you are extremly near the sun (like earth). But in interstellar space, the sun is but another star. It would be like using solar panels here on earth at night.

[Technical Ben]

Uh, no, because they got reverse thrust from reversing the current.

- - - Updated - - -

Uh, they've gotten as perfect as they can to vacuum. If they had seal errors, it would have been pretty obvious, and given that the test results are within something like 2% of the atmospheric tests, it seems to not be an atmosphere thing. Likewise, they did check the magnetic interactions as stated in the article, and have ruled out most, if not all such events. I will grant that the copper plate ablating is possible, but I don't know.

Addendum: Nope, copper ablation can be ruled out. A second article just posted shows that the copper housing doesn't even reach 100 degrees F.

Reverse thrust from reverse current suggests other forces. Anything apart from a perfect vacuum and/or checks on ablating suggest it's magnetic/static/propellent based, just in this case, from the copper case!

Edited February 9, 2015 by Technical Ben

[Sean Mirrsen]

Convey to what? If net is still less than 300MW per N, then whatever it is, it has mass. In fact, mass flow is exactly sqrt(F^2*c^2 - P^2)/c^2

Anything with better efficiency than photon drive is a reaction drive. That is just basic physics. How the reaction force is conveyed can be very creative. We could be seeing a very odd sort of an ion drive, but it is not reactionless one.

It's wrong to call the EMDrive a "reactionless" drive. It's not reactionless, the same way a turboprop is not reactionless, despite its exhaust having very little to do with the thrust it creates. What it doesn't have is any reaction mass, in the conventional sense. It uses its onboard energy to find something heavier and more energetic than a photon to push off of. Just because that something returns to no longer existing (or being undetectable) as soon as it leaves the thruster does not invalidate the theoretical principle.

Also yes, I'd like to also point out that even after we have satellites and interplanetary missions working with that technology, it's vital to still have skeptics and naysayers among the scientific community who will attempt to find flaws in the theory. It will be bad if it's discovered that the theory doesn't actually work. It will be worse if it only works well enough to get twenty people stranded on a transfer orbit to Mars because the effect was the result of some temporary or Earth-specific arrangement.

Edited February 9, 2015 by Sean Mirrsen

[Aghanim]

Convey to what? If net is still less than 300MW per N, then whatever it is, it has mass. In fact, mass flow is exactly sqrt(F^2*c^2 - P^2)/c^2

Anything with better efficiency than photon drive is a reaction drive. That is just basic physics. How the reaction force is conveyed can be very creative. We could be seeing a very odd sort of an ion drive, but it is not reactionless one.

Possible testing:

Aim the tail of the thruster to some sort of very small magnetic scoop, then count the amount of particles in the scoop. If it increases, then the thruster might work because it accelerates its own outgas. It it didn't, increase sensitivity until you give up and just accept new physics

[Greenfire32]

It also would mean any crazy group or person with enough money to buy a cubesat with an emdrive has the ability to easily exterminate the human race.

Because with infinite delta vee, they could fly to an asteroid and push it into a collision course with Earth. If they fly to an asteroid that turns out to be a rubble pile, they can just fly to a new one.

We already have NUCLEAR BOMBS so...pretty sure we'll survive the EMDrive.

Just sayin.

[Northstar1989]

Totally irrelevant. Even if EMDrive uses virtual particles for recoil, virtual particles must vanish. The total "exhaust" mass must therefore be zero. Massless "exhaust" is equivalent to photon drive, which has maximum efficiency of 1N/300MW. Efficiency higher than that guarantees presence of reaction mass. It's that simple.

Virtual particles are ones that propagate off the shelf. They violate E² = p²c² + (mc²)², which is true for "real" particles. Virtual particles show up in various interactions, as exchange particles, for example. Virtual photons carry electromagnetic forces, etc.

Finally, because virtual particles "temporarily" violate conservation laws, they must promptly vanish. That's a hand-wavey explanation of it, but it should do for purposes of discussion at hand.

It doesn't matter if the virtual particle promptly vanishes. As long as it was there to be acted on in the first place. Exhaust doesn't have to actually leave a reaction-engine to have generated its thrust- the moment it acted on the appropriate reaction-harvesting surface (such as the engine nozzle of a chemical rocket) its force has been transferred, and it could promptly disappear into nothingness for all anybody cared and the engine would be no worse off for it...

Regards,

Northstar

[K^2]

Just because that something returns to no longer existing (or being undetectable) as soon as it leaves the thruster does not invalidate the theoretical principle.

It does, actually, because there are conserved currents involved. Would you trust this idea if it was promising free energy to power a city? No, you'd call its inventor a crackpot, and any "working" prototype a mistake, at best.

Well, for EMDrive to have efficiency it promises without pushing from real, massive particles, it has to violate the same symmetry that protects conservation of energy. If EMDrive works, free energy is possible. In fact, it should be way easier to build a free energy generator than an actual propulsion unit based on this principle.

I understand that it's difficult for a lay person to recognize, but EMDrive can't work for exactly the same reasons that you would use to explain to someone why magnets can't be arranged to power a perpetual motion device. There is just a bit more tensor math involved.

It doesn't matter if the virtual particle promptly vanishes. As long as it was there to be acted on in the first place.

Again. Magnets pushing magnets.

But let me try explaining it from this perspective. Virtual particles can't vanish if you have acted on them. Because they now carry excess momentum that has to go somewhere. If you draw all possible diagrams of action on virtual particles, the only ones that will not cancel are ones where force is applied right back at the source. Because there is a momentum-conserving delta function in the integral. Because momentum is conserved. And net thrust is still going to be zero.

This is pulling yourself up by bootstraps with a fresh coat of paint.

Edited February 10, 2015 by K^2

[Sean Mirrsen]

It does, actually, because there are conserved currents involved. Would you trust this idea if it was promising free energy to power a city? No, you'd call its inventor a crackpot, and any "working" prototype a mistake, at best.

Well, for EMDrive to have efficiency it promises without pushing from real, massive particles, it has to violate the same symmetry that protects conservation of energy. If EMDrive works, free energy is possible. In fact, it should be way easier to build a free energy generator than an actual propulsion unit based on this principle.

I understand that it's difficult for a lay person to recognize, but EMDrive can't work for exactly the same reasons that you would use to explain to someone why magnets can't be arranged to power a perpetual motion device. There is just a bit more tensor math involved.

I rather think it's difficult for a highly conventional person to recognize. (Wait, I'm thinking of quantum physicists as "conventional", what is the world coming to?)

As an unconventional person, however, I find my train of thought hard to communicate. So try to bear with me, maybe one of us will manage to see the error in the other's thought process.

In order for conservation of energy to be maintained, the particles don't have to continue existing, much less continue to be detectable. They are undetectable in the first place, because whatever mechanism causes them to form, also causes them to disappear (either entirely, or merely "elsewhere" by whatever 'quantum shenanigans' are going on there) immediately - assuming the virtual particle theory is at work here. If this mechanism is not dependent on the particles' energy state (or the amount of energy imparted does not make an appreciable difference in their lifetime), the particle will likewise cease to exist after it's been acted upon by the thruster. The momentum the particle had either disappeared with it (wait, I think I remember a term. Entropy?) or returned to the same "ocean of quantum whatevers" that spawned it in the first place.

Think about it. How can you detect an increase of energy in the ocean if you can't detect the ocean? You put the propeller down and it spins in nothing, generating thrust but seemingly not interacting with anything.

There would probably be ways to detect the "wake" the device generates though, as you are entirely correct that, as I've already said, energy likely doesn't go anywhere. It could manifest as an increased amount of "virtual particles" being created in the area of the exhaust, if the particles' creation rate is tied to energy saturation. There are too many possibilities to account for them all here. Yes, it could still all be an error. But saying "no, it can't work because it can't work" is about the worst thing to do as far as I'm concerned.

edit: I found a way to put it into a different perspective that might be closer to conventional physics that a regular physicist might be able to wrap his head around it. Imagine that every virtual particle that is imparted with some energy and then disappears, turns into so many neutrinos.

...

Actually now that I think about it, they should definitely test for neutrinos. That's about the single most devious kind of particle, I wouldn't be surprised if it's behind all this.

edit2: oh hey, autocensor. Never thought I'd trip that.

Edited February 10, 2015 by Sean Mirrsen

[Newt]

I beleive that the thing is that you are putting energy somewhere it does not really matter where, but there has to be forece flowing into the virtual particles (if that is the case). Once they have been given that energy, they should not be able to simply vanish with it; energy must always come from, and go to somewhere, this is fairly (extrmemley) well proven and established. This is the case with your 'ocean of quantum whatevers' just as much as it is of the ocean of water particles. If the particles came from some seperate region, then they cannot cease to exist (although they do not need to be easily detectable).

If that does not answer what you are meaning Mirrsen, I am not quite sure what you are getting at.

And science is conventional -- it has to be. K^2 is (if I understand correctly) getting at the fact that really this fundamentally goes against common sense and precident. Energy does not come from nowhere, or everything we know about physics is fundamentally wrong. The principle of conservation of energy is very well understood to work, and cloaking something in a fancy spaceship engine does not avoid that main issue. There has to be something that that engine is imparting force to, or it does not work. You cannot burn a vaccum to heat your house (I am npt reffering to a vaccum cleaner, by the way).

(if spelling issues abound, my apologies, strange spellcheck behavior said that half the words were wrong, then that all are right, and the keyboard is laggy. Argh)

Edited February 10, 2015 by Newt
spelling error #1 fixed

[K^2]

In order for conservation of energy to be maintained, the particles don't have to continue existing, much less continue to be detectable. They are undetectable in the first place, because whatever mechanism causes them to form, also causes them to disappear (either entirely, or merely "elsewhere" by whatever 'quantum shenanigans' are going on there) immediately - assuming the virtual particle theory is at work here. If this mechanism is not dependent on the particles' energy state (or the amount of energy imparted does not make an appreciable difference in their lifetime), the particle will likewise cease to exist after it's been acted upon by the thruster. The momentum the particle had either disappeared with it (wait, I think I remember a term. Entropy?) or returned to the same "ocean of quantum whatevers" that spawned it in the first place.

Think about it. How can you detect an increase of energy in the ocean if you can't detect the ocean? You put the propeller down and it spins in nothing, generating thrust but seemingly not interacting with anything.

You are aware of the fact that I've done graduate work in particle theory, right? As in, this is my actual field of study?

This simply isn't how virtual particles work. Particle-antiparticle ocean is a very bad analogy for vacuum. While certain parallels between quasi particle-antiparticle systems in solid states do exist, the particles, virtual or otherwise, that we are talking about here are not quasi particles. There is no lattice to absrob the momentum. These particles are excitations in fields, and carrying momentum means having an excitation in the field.

But more importantly, if vacuum simply picks up that amount of momentum, it must gain mass. Whatever else happens, anything that carries away the momentum must be on the shell. So it either has mass, and we have regular reaction drive, or it is a null current, and what you have is a photon drive, which drains ridiculous amounts of energy. Anything else violates conservation laws in very fundamental ways.

[Sean Mirrsen]

You are aware of the fact that I've done graduate work in particle theory, right? As in, this is my actual field of study?

This simply isn't how virtual particles work. Particle-antiparticle ocean is a very bad analogy for vacuum. While certain parallels between quasi particle-antiparticle systems in solid states do exist, the particles, virtual or otherwise, that we are talking about here are not quasi particles. There is no lattice to absrob the momentum. These particles are excitations in fields, and carrying momentum means having an excitation in the field.

But more importantly, if vacuum simply picks up that amount of momentum, it must gain mass. Whatever else happens, anything that carries away the momentum must be on the shell. So it either has mass, and we have regular reaction drive, or it is a null current, and what you have is a photon drive, which drains ridiculous amounts of energy. Anything else violates conservation laws in very fundamental ways.

Oh I do believe you have a lot of experience in these matters. It's very useful experience, and like I said, it's vital that people keep trying to poke holes in the theory, as long as it does not impede actual experimentation. Because we're dealing with things that simple theorizing either fails to explain, or has too many explanations for that can't or shouldn't be valid all at once.

And if you missed the last edit in my post, consider neutrinos. What if the energy imparted to the virtual particle were to cause the creation of so many neutrinos? Just as an example, I mean. The virtual particle is massive enough to provide thrust, but dissipates into energy packets that barely interact with matter. It doesn't have to be (and likely isn't) neutrinos, but the goings-on are strange enough to potentially create some other form of exotic particle. Would that theoretically, at all be possible? If it were possible, would it potentially explain the thruster's operation?

(Also, please stop using "reaction drive" as an insult. EMDrive is a reaction drive. It just doesn't carry reaction mass.)