ah.clem and infodragon write:
This story from a Wired article: NASA is a major player in space science, so when a team from the agency this week presents evidence that "impossible" microwave thrusters seem to work, something strange is definitely going on. Either the results are completely wrong, or Nasa has confirmed a major breakthrough in space propulsion. British scientist Roger Shawyer has been trying to interest people in his EmDrive for some years through his company SPR Ltd. Shawyer claims the EmDrive converts electric power into thrust, without the need for any propellant by bouncing microwaves around in a closed container. He has built a number of demonstration systems, but critics reject his relativity-based theory and insist that, according to the law of conservation of momentum, it cannot work.
NASA states... "Test results indicate that the RF resonant cavity thruster design, which is unique as an electric propulsion device, is producing a force that is not attributable to any classical electromagnetic phenomenon and therefore is potentially demonstrating an interaction with the quantum vacuum virtual plasma"
The real test will be whether it works outside the Earth's magnetic field. A lot of these sorts of "inexplicable" devices end up obeying conservation rules by degrading their own magnets, basically harvesting energy stored during the magnet's manufacture and leaving the magnets electrons in a less ordered state. If this thing were placing a minute drag on the spin of the Earth's core to balance the equations, I doubt we'd be able to detect it.
How long till the Kerbal mod for it comes out?
I'm skeptical as well.
Back in the 90s, Nasa tested what was claimed to be an antigravity device based on spinning superconducting discs. That was reported to give good test results, until researchers realised that interference from the device was affecting their measuring instruments. They have probably learned a lot since then.
The torsion balance they used to test the thrust was sensitive enough to detect a thrust of less than ten micronewtons, but the drive actually produced 30 to 50 micronewtons -- less than a thousandth of the Chinese results, but emphatically a positive result, in spite of the law of conservation of momentum
I'd like to see it tested in space as well, and if NASA thinks it really is viable I'm sure it will be on a rocket sometime headed outside the magnetic field for testing. It could ride piggyback with some other instrument; we have a lot of scientific equipment outside the magnetic field already and there will surely be plenty more.
But I don't see how it would violate the laws. It isn't like perpetual motion; you're not getting free anything with this, you have to feed it electrical energy which it allegedly converts to kinetic energy. Personally, I prefer ion propulsion.
If it does work, imagine a vessel with them in huge arrays fed by fusion generators!
The point is that it would, according to the article, violate conservation of momentum. Just because it doesn't violate the laws of thermodynamics doesn't mean it doesn't violate any laws of physics.
Well, actually, if it indeed works, it quite obviously doesn't violate the laws of physics; however, we might then have to update our idea about what the laws of physics are.
Speaking as a genuine physicist, my biggest pet peeve of the science world is that while non-scientists misunderstand what is meant by "theory", scientists mis-understand (or at least mis-construe) the meaning of "law". Laws in science are not like laws in government, though sometimes they can be as arbitrary. A scientific law is simply a mathematical equation that describes some process--nothing more, nothing less. There is nothing that requires a scientific law to be correct, or have any bearing in reality. As a result, the laws of the game of science can be as meticulous as chess, or as crazy as Calvin ball. Though often I feel like they are now so convoluted that, along with the degree of obsession people have over them, it feels more like D&D.
There are three things I wish everyone understood better: statistics, compassion, and the fallibility of all fields. We'd all be much better off if our response to statements like this were, 'Huh, that's interesting... How can we test this?' rather than turning up our nose at and ignoring any idea that doesn't fit perfectly into our particular mindset.
While I think there are many other things that could have generated the measured force (pushing against the air in the chamber? It wasn't a vacuum. Maybe it created an electromagnet and pushed against earth's magnetic field?), if it does work it still conserves momentum. They think it was pushing against the vacuum quantum plasma, the virtual particles that continuously pop in and out of existence even in vacuum. If so, the virtual particles become the propellent, accelerated away from the drive, providing thrust. Momentum is conserved.
Yes, the article points that out but adds that much having to do with particle physics seems to violate Newtonian laws while following relativistic laws. This seems to work on the principle that waves added in phase with each other double amplitude, while waves added out of phase cancel them out, making it only seem to violate conservation of momentum without actually doing so.
Nobody's saying it's free energy. What's interesting about it is that it provides thrust without propellant. The only way to move in space (besides solar sails) is to throw something in the opposite direction of your desired travel. We generally do this violently, with rocket engines. Even the ion drive you like uses propellent. It works by excitation of the electric field, accelerating an ion (generally xenon) and propelling it out the back.
What would be neat about this, if it worked, is that you wouldn't have to carry propellent, just fuel to generate electricity (or solar panels). That's huge, because the mass of the propellent is the real limiting factor on how fast we can move through space. The faster you want to go, the more propellent you have to carry, and the more propellent you have to carry, the more propellent you need, etc, etc. And then you have to carry all the propellent you need to slow down.
If this works, it would basically be using vacuum quantum plasma as the propellent. The microwaves bounce around in the chamber and push against the particles that spontaneously pop in and out of existence. Momentum would still be conserved.
However, this test doesn't seem conclusive. First, they didn't even have a vacuum in the test setup. They had it in a vacuum chamber, but it was at atmospheric pressure. Ummmmm maybe it was pushing off, I don't know, the air? It's also in Earth's magnetic field. Perhaps it just created an electromagnet and pushed against Earth's magnetic field. Also, they built another machine that was supposedly designed to *not* produce thrust, and yet it did. Something weird is going on here, but it's a big leap to say "Oh, it must be pushing against vacuum quantum plasma!"
More study is needed. First produce thrust in a vacuum. If that still works, do it away from the Earth's magnetic field. Then we're talking. If that works, then...damn depending on the efficiency, a real reactionless drive can get you to the stars. A small but constant acceleration will eventually get you a significant fraction of the speed of light, without needing to accelerate the mass of propellant needed to accelerate and decelerate.
Damn, I have mod points but I can't mod you up because I commented in this thread.