Or, why passing peer review doesn’t suddenly mean that a technology is either validated or useful.
I just saw an article in Universe today claiming that a paper on the EM Drive is forthcoming. As you may remember from my previous post, the EM Drive is a piece of crank technology that is The One To Bring Them In and In Darkness Bind Them of the crank technology world. As they all know, it is about to change everything! (Or so they say.)
The device is an assymetrical microwave cavity which will apparently generate thrust when microwaves are injected into it without producing an apparent exhaust stream. The creator, Robert Shawyer, repeatedly invokes a crazy wrong interpretation of Special Relativity in order justify why his doodad works and makes grandiose claims about the capabilities of the device. Guido Fetta, a chemical engineer turned speculative technology wonk, has also jumped out into the public about his grand claims to test the device on a cubesat in orbit soon… Fetta’s description of why his “Cannae Drive” works is somewhat more reasonable than Shawyer’s is, but still a bit iffy…
The Cannae Drive also features an asymmetrical cavity, but is flatter than the EmDrive. According to Fetta, it works by deriving force from a reduced reflection coefficient at one of the device’s end plates, due to imbalances in the Lorentz force (a combination of electric and magnetic force on a point charge due to electromagnetic fields). Nasa Eagleworks, on the other hand, suggests that the Cannae Drive works by the cavity pushing against a “quantum virtual plasma” of particles that shift in and out of existence.
This description is actually not terribly aphysical because it’s essentially describing exactly what happens in a laser. Believe it or not, the NASA description is the crankier version since it seems to be invoking something along the lines of Casimir force. I’m not a huge fan of Eagle Labs because they skirt the ragged edge of being cranky themselves sometimes. (If it all works, I will gladly eat my words.)
I think that the one word that may be useful in this mess is the word “propellantless”… I mention this here because there could actually be a big difference in utility between claiming that the drive is “reactionless” (which is impossible) and “propellantless,” but this comes back to one’s definition of the substance of “propellant.”In the end, if the justification for the drive is simply that you don’t need to take along a huge quantity of reaction mass to make it work and can instead use a nuclear plant to power it, that is not necessarily a bad thing.
Still, house needs to be cleaned.
First, the device must be described to work in a way that matches physics. No insane invocations of Special Relativity. This paper coming out is actually a nice first step toward doing just that. Passing Peer Review is a way of saying “Yes, science is being done! We have made measurements by accepted methodology and here are our results!” Which is actually much more impressive than anything that has come out of either Shawyer or Fetta for the last decade.
Making and reporting measurement is really all there is to experimental science: we may not have the interpretation right just yet, but we have numbers that can be compared to everything else in the field. How does the efficiency actually compare to a chemical rocket? Spin the numbers! It is all to show that the methodology is sound and the numbers are honest. And, those numbers will have to ultimately say that momentum and energy are conserved. The device is not… I repeat NOT… a reactionless drive. If it has a propellant, the substance is probably in photons, not gas or plasma like in conventional chemical rockets or ion drives.
The second thing that must happen is that the device should be engineered. The core of engineering is tweaking the physical parameters of the system to optimize the functioning of the device, which requires a model of the behavior… whether you understand the physical rationale behind it or not. Again, this Peer Reviewed paper is a terrific first step because it starts to characterize the actual observed behaviors of the system. If the rumored thrust is actually 1.2 mN/kW, great! A millinewton is a higher thrust than I was estimating in my previous writing, but how big of a powerplant does that require? A nuclear submarine can carry a 500 MW reactor, which would theoretically give hundreds of Newtons of thrust, which is not insignificant at all if the rumored numbers reported by Eagle Labs are true. Now, explain why and begin to tweak the envelop. If it is just a big microwave flashlight, fine, start plugging the physics into that and tell me what the actual performance limits are.
I will admit that my previous post may have been somewhat in error: it may turn out that this research is not a waste of time, but we’ve got to get away from the cranky hopefulness and start figuring out what we’ve actually got so that we can make it better.
Now, I have made something of a shift of stance in my writing of this post. Previously, I flat out called the EM Drive a waste of time. For a very long time it looked like a vanity obsession of a garage crank with delusions of popular fame. As long as it has that air, I won’t have much nice to say. Mutilating physics to build a miracle machine is crankery and there’s way too much of that happening in our world right now. What has changed now is simple: if there is a real, explicable physical phenomenon to measure, steps forward can be taken to find a real thing. It would be nice if there’s a world-altering discovery lurking in here, but that isn’t what we have yet. It really ultimately doesn’t matter to me where the idea came from, whether it came out of somebody’s garage or some rocketry lab… millions of ideas come from everywhere all the time: the point of the science is to sort through and find which observations are actually useful so that we can discard the ones that aren’t.
We’ll at least see if there’s something useful here and hopefully have a real guess about why it works. If the numbers are not reproducible or if there is some huge other way to interpret what has been seen, then it becomes time to discard the EM Drive. I guess that’s kind of the weird thing about frontier science: it always may not survive the meat grinder, no matter the source.
Since I was just thinking about this, I thought I might update this topic.
Recently, a German group made a very thorough test of the EM Drive in a very carefully built testing rig. They determined that the force everybody keeps discovering coming from the EM Drive is actually being generated by a wire supplying power to the EM Drive’s horn and is dependent on a reaction to the Earth’s magnetic field (iirc).
If that’s true, it isn’t a good sign for the viability of the EM Drive.