You may have seen an engine like this http://sec353ext.jpl.nasa.gov/ep/img/hall_thrusters/6kw_234.jpg associated with this EM Drive.
That’s an ion drive - completely different beast.
The other question to be addressed (and I haven’t seen stated anywhere) is the absolute minimum level at which their measurement apparatus could measure thrust. Very sensitive torsion pendulums can measure down to a few tens of micronewtons but only with very careful calibration and isolation. Eagleworks appears to be an essentially hobby project with some pocket change funding (residual money in some kind of discressionary budget item) so both the expertise and measurement quality may be limited. If the measurement floor on their setup is 50 micronewtons and they’re reporting a 55 micronewton average thrust level, the degree of confidence in the result isn’t very high, and especially if it oscillates rather than shows a consistent trend.
Stranger
That’s actually a Hall effect thruster; a type of ion drive that has been commercially avaiable for satellite stationkeeping applications for the last couple of decades, and used before that by the Soviets since the 'Seventies. It has a high specific efficiency (I[sub]sp[/sub] ~ 2,000 to 3,000 seconds) but low energy throughput efficiency which makes scaling up to constant thrust applications for large vehicles basically impossible (thermal cooling requirements end up dwarfing any propellant mass efficiencies). The same is true for most ion and plasma drives; they operate at high thermal and propellant mass efficiency but low energy efficiency, require a large heat sink or radiator, and often have electrode or wall erosion problems.
Stranger
For what it’s worth, I don’t think this is like cold fusion. I think that, like cold fusion, this is overwhelmingly likely to be a bust, but I believe that this guy is attempting to do good science and is just mistaken, while I have less charitable views of Pons and Fleishmann’s motivations.
This is a really stupid question, but I have missed the answer if it’s somewhere.
So, they have a couple of working, physical models of this thing, right? We aren’t talking about computer simulations? How big are these things? The science is over my head, but I can’t really get a good mental image of what we’re talking about here. The photos are cryptic. I can’t tell if they’re a meter across, or microscopic.
But it’s got to be tiny, right? Or we wouldn’t be talking about measurement error?
Some of the photos show people next to the devices. They’re of order a meter across. The possibility of measurement error comes not from the size of the device itself, but from the size of the effect (purportedly) produced by it.
Looking at some pictures and surrounding hardware and cabling I’m guessing in the neighbourhood of 12" to 18" in length.
ETA: Ninja’d by Chronos, and he may well be right. So, somewhere in the 1/3 to 1 meter in length neighbourhood.
Has there ever been a discovery that later turned out to be true where the initial detection was so small and weak scientists doubted it was anything but noise?
ETA: and I’m not counting the Cosmic Microwave Background because the signal was clear enough, they just doubted its source.
They’re fairly large; the dimensions of the cavity are usually stated in tens of centimeters, so the overall size lf the unit under test is on the order of a meter in diameter. They’re also fairly heavy, so the resulting thrust load not only has to overcome the inertia of the unit but also any reaction force needed to stabilize the unit (e.g. vibration in tethers or slings, motion of the fixture, et cetera). Combine that with the fact that you’re operating a relatively high power EM device next to a bunch of instruments and metallic support structures and the normally insignificant magnetic field effects now become more significant noise in the measurement. Also, although I haven’t seen anything resembling formal reporting, it appears that the thrust does not appear to scale up linearly with increased power throughput, which either suggests that the system does not operate in the expected manner, or the entire measurement is highly suspect. And again, even if an anomalous phenomenon is verified to be occurring with the thrust, if it cannot be scaled up to higher thrust and greater throughput efficiency, it may not be of significant practical use.
Stranger
Ok, thanks. I didn’t see any photos with any kind of scale.
Given the supposed effect is barely detectable, it kinda sounds like they made this part up.
Sure; the effect of electricity in generating magnetic fields–induction–was very slight, largely because of the very limited electrical potential available in that day (in order to “charge up a pile” tens or hundreds of gallons of electrolyte had to be distributed in jars, a laborous process) and Faraday’s suggestion that electricity and magnetism were two complementary aspects of a field that filled up all of space was not taken seriously (actually outright ridiculed by many) until James Clerk Maxwell published his treatise “A Dynamical Theory of the Electromagnetic Field”, giving the first rigorous mathematical treament of what became the classical field theory of electromagnetism. (Faraday was self-trained with almost no formal schooling and interpreted electromagnetism by intuition and visualization; despite this, his model for the lines of force of the magnetic field was qualitatively completely correct in every essential detail.)
Even after Maxwell’s work was recognized as correct it was largely treated as an esoteric curiousity because the necessary power to drive an electric motor or otherwise gain any practical utility to perform mechanical work out of electromagnetism outside of research didn’t exist in practical or portable form. It wasn’t until a decade after Maxwell’s death that Sprague’s constant speed DC motor and the develoment of a power distribution infrastructure by Edison and Westinghouse made electromagnetism practical to do real work. And until the eccentric Oliver Heaviside reformulated a reduced set of Maxwell’s equations using vector notation–the ones we see in introductory physics textbooks today–the practical theory of electromagnetism was not widely understood even in the burgening community of professional physicists. Consider this next time you hear someone complaining about the “useless science of the Large Hadron Collider”; circa 1860 and even later electromagnetism was in essentially the same degree of uselessness as high energy nuclear physics is now, and yet today we cannot even imagine a world without generators, electric motors, and solenoids of all kinds, just because we had no practical way to store and use electrical energy.
BTW, the original twenty equations that Maxwell developed were actually much more comprehensive and, in retrospect, give clear indications of leading way to non-classical field theory; unfortunately, Boltzmann’s development of statistical mechanics and suggestion of the discrete nature of energy transfer didn’t occur until after Maxwell’s untimely death, and Planck’s original formulation of quantum theory was long after Maxwell passed on. Had these ideas come just a few decades sooner–or had Maxwell lived and been productive for just a few more years–the revolution of modern physics–both quantum mechanics and the beginnings of relativity–may have been credited to Maxwell rather than those who came after him.
Anyway, if the effect of these EM resonant thrusters is genuine, there is a good reason to believe that it would be small; if the effect were more pronounced, or not dependent on a highly precise resonant configuration, we would have seen it already by accident, just as any socks you can’t seem to find usually turn up in squished in the back of the drawer. However, that doesn’t mean that the claims of this experiment should be taken as valid until they have been independently reproduced and some testable hypothesis of how the thrust is produced is proposed.
Stranger
So if a meter-size device provides thrust on the order of micro-newton, other than the importance to the understanding of underlying physics, what practical drive can be built from it?
Well it’s a net force of a micro Newton so there’s that. The real cool thing is the idea of not requiring propellant. Consider that in a chemical rocket you need to bring fuel to move the fuel that you’re burning to move forward. Removing that mass and relying on a dense energy source would allow smaller vehicles and longer “burns” for larger changes in relative velocities.
Longer? How about constant?
If you could “burn” (i.e. accelerate) at 1G for 3 days, you’d be halfway to Jupiter. 3 days to Jupiter, and within the Solar system, solar power might be enough to not require massive amounts of fuel (not reaction mass, fuel).
The reason why we can’t accelerate constantly is because we need to keep chucking stuff (reaction mass) out the back to accelerate, and we can’t bring quite enough stuff to chuck to accelerate at 1G for that long. Think about rockets - they blast off, burn for a number of minutes, and they’re done. Imagine how many rockets you’d need to keep going at the initial acceleration.
So, this is huge, if true. Then again, a perpetual motion machine would be huge, if true.
That’s probably the case for CP symmetry breaking, which only shows up in a select few particle interactions, and (depending on how you define it) is only on the order of one part in a thousand.
And it should have been the case for Einstein and Eddington’s famous eclipse observation. Both Newtonian and Einsteinian gravity predict deflection of starlight around the Sun, but by different amounts. The data from the eclipse were actually consistent with either theory, and slightly favored Newton, but was hailed as a victory for general relativity anyway (other, better proofs of GR followed very shortly).
I’ve often said that the great tragedy of Maxwell is that, of the two or three physicists in all of history who were greater than him, one happened to come along a mere few decades after him to overshadow him.
However, if it takes an enormous amount of energy–more than can be produced in a reasonably sized mobile power plant or solar array–or generates a large amount of waste heat such that giant radiators or consumable evaporative coolant are required to operate it at useful levels, it may not be practical.
The “blasting to Mars in 70 days” is just enthusiastic speculation; until an actual principle of operation is established and a workable model for real world applications is demonstrated, there is no way to predict whether or how capable a propulsion system it would be. It would be really cool if this were genuine, because even at a low but practical efficiency it would open up whole new opportunities in planetary exploration and resource exploitation, notwithstanding any “free energy” type applications which might arise from such a mechanism, but it is manifestly premature to even make any kind of prediction as to what might be possible if the anomalous thrust does turn out to be a real phenomenon.
Stranger
Ok, but let’s say you can build a drive like that that weighs 10kg. And it generates a constant thrust of a whole 10 micro-Newtons (10^-5 kg*m/s^2). So it can produce the acceleration of 10^-6 m/s^2. Constant acceleration.
Let’s say the distance to Jupiter is 610^11 m (that’s 600 million kilometers). From t=sqrt(2d/a) we get sqrt(1.210^18) seconds - or 34 years, roughly.
At 100 micro-Newtons, you’d get there in 10 years (at constant thrust. If you want to do anything other than zip by Jupiter, that will take quite a bit longer). And that’s just the drive itself getting there, not all the other stuff you’d want to send 
Really, unless this gets significantly higher than micro-Newtons kind of thrust, it will not have a practical use. May upend the physics, though, if it really violates the conservation of momentum (and not somehow transferring the momentum to the surrounding virtual foam somehow), and maybe something more practical can come out of the new physics once it is understood…
If this thing works at all, via anything except radiation pressure (which is understood but which would have a very hard time accounting for the purported effect), it’s going to revolutionize physics. That revolution, in turn, would be bound to lead to all sorts of practical effects. A practical spacecraft drive may or may not be among them, but there’d be bound to be something, and in fact a lot of something.