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The 'Impossible' EM Drive Being Tested By NASA May Finally Be Explained (technologyreview.com)
MarkWhittington writes: The EmDrive, the so-called "impossible" space drive that uses no propellant, has roiled the aerospace world for the past several years ever since it was proposed by British aerospace engineer Robert Shawyer. In essence, the claim advanced by Shawyer and others is that if you bounced microwaves in a truncated cone, thrust would be produced out the open end. Most scientists have snorted at the idea, noting correctly that such a thing would violate physical laws. However, organizations as prestigious as NASA have replicated the same results, that prototypes of the EmDrive produces thrust. How does one reconcile the experimental results with the apparent scientific impossibility? MIT Technology Review suggested a reason why.
We'll eventually find out we really live in a simulation...
Great job lets not even try to attempt to summarize the article, instead lets post this like its a trailer for the 11 o'clock news!
Really appreciate the complete lack of even a whiff of the explanation in the summary.
Don't disappoint your bird dog. Go to the range.
https://en.wikipedia.org/wiki/...
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I was honestly expecting to find an explanation of some subtle source of experimental error that covered it, not a possible theory explaining why it (maybe) works. I'm really looking forward to experimental testing of the improvements predicted by the theory. Who knows? With a decent explanatory theory, it might even be possible to turn it into a practical thruster. That would be awesome.
Have they tried analyzing this thing with an E-meter?
Most scientists have snorted at the idea, noting correctly that such a thing would violate observed physical laws.
The EM drive was discussed at length on other sites, and few posts were able to shine any light on the issue. Some items of note:
First, if your understanding of physics does *not* predict the Casimir effect, then you probably shouldn't be blithely dismissing the theory. The EM drive is based on a theory of physics that's more sophisticated than simple "momentum is conserved". It supposes an hypothesis that's different than what is currently accepted, but in a subtle way that is difficult to detect.
It's similar to relativity: most of our tests validate Newtonian physics, but you find relativity when you go looking for it.
Second, if you want to appeal to Noether's theorem, note that the theorem refers to smooth manifolds. If space is quantized, then Noether's theorem doesn't apply (despite being true). It's possible that Noether's theorem will break down at small scales. (If space is smooth, ie *not* quantized, then the true location of any particle is a [mathematical] real number with infinite entropy and it's action is non-computable. Not that having a non-computable universe is a problem, but...)
All in all, I get the impression that everyone commenting on the EM drive should probably keep quiet and let the experts sort it out.
I don't have any comment on either the theory or the experiment, but it's an interesting proposal.
From the Wikipedia page:
This is analyzed by Rothman and Boughn[32] who point out that the standard theory of radiation pressure is more complicated than the simplified analysis suggests.
NASA tested it in vacuum chamber to prevent this issue.
Architectural plans are like computer source code with a couple of differences: You only compile once.
The problem was that even with all you just said the thrust was higher than they expected. Hence the big issue with the drive and why people said it couldn't work. Yet it kept working in real world tests.
we are all invisible unless we choose otherwise
The ship stays where it is and the engines move the universe around it
I don't think there's a nozzle.
Play Command HQ online
No, it cannot mean any of that, because the amount of thrust provided is minimal. Even if you made the engine weightless(which you can't), you'd not be able to get enough thrust to lift anything off the ground.
The reason this is interesting for space is that in space, even tiny amounts of thirst are useful. Very slow acceleration is still fine, when you are not fighting planet like gravity: You just need to apply thrust for a long time, as opposed to what we do now, which is to turn on far more powerful drives for very short periods of time.
It's true that a lot of comets are made of ice, but still I don't see the connection...
The summary of the article is very wrong, there is no nozzle. If it had a nozzle it would be easy to explain, anything with a nozzle will operate as a rocket regardless of the wavelength you produce (Newton's law about action/reaction) and laser/microwave drives with nozzles have been built, we already use ion drives after all.
This 'engine' is completely closed. It's basically a closed cone in which you send microwaves and somehow you get acceleration. In Newtonian physics this would make no sense because it's a closed system, there is no "action" on the outside (basically the sum of all vectors of force generated come out to 0). However there seems to be something happening at the quantum level (the sum of all vectors is not 0 perhaps because at some quantized level there are hypothetically 'rounding errors').
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The amount of thrust they're seeing, even at microNewtons, is far higher than could be produced by the radiation pressure of simply emitting photons at those energy levels. If it wasn't, there wouldn't be all this fuss.
NASA measured an average of 91 microN with 17 W, or 5.3 microN/W. The Chinese measured 720 milliN at 2500 W - about 300 microN/W. By contrast, expected radiation pressure would be closer to 0.003 microN/W.
Why would anyone engrave "Elbereth"?
A theoretical physicist should go around all the time and say: According to Theory T, this should be impossible!
It looks like nonsense because it treats photons as if they were Newtonian particles and with ignorance of Maxwell's equations and relativity.
Start with section 2. It treats photons as particles with some momentum m*v. I mean, what? That's just wrong. Photons are relativistic p = E/c and quantum mechanical, E = 2\pi hbar f.
I mean take a look at this:
"Normally, of course, photons are not supposed to have inertial mass in this way,
but here this is assumed. It is not clear what the size of this mass is, but it is
clear for example that light inside a mirrored box produces a kind of inertial mass
for the box. "
So in orthodox physics, photons are not supposed to have inertial mass, but also in orthodox physics light makes inertial mass and it's clear that it's so.
The second statement, about light inside a mirrored box, is so because of relativity and the assertion of the equivalence principle. Electromagnetic fields are part of the stress energy tensor (following Maxwell) which feeds into the source term of general relativity. So yes, there is some sort of inertial contribution, but in fact it can be computed pretty exactly, and it's extraordinarily tiny, and really mostly related to the energy density of the EM field.
So relativity sometimes, but not other times? WTF?
And if the non-standard theory that inertia comes from matter interacting with Unruh radiation, how exactly does that work with photons? Photons don't interact with photons. Zero cross section until the point that they are so energetic they can pop out electron/positron pairs from the vacuum, which is so far not an experimentally accessible regime.
Presumably the idea is that the Unruh radiation inside the cavity is quantized in a particular way different from free space, but wouldn't that mean that inertia of (presumably charged) particles inside that cavity would be altered? But he was talking about the non-sensical 'inertial mass' of the photons themselves. WTF?
I don't mind non-standard theories and their exploration at all, but it's necessary to be clear which standard axioms are being rejected and which others are preserved, and follow that consistently. I just saw very unclear physics.
"...has no fuel..."
Keep in mind that the EM drive DOES require energy (to generate the microwaves). Perhaps from a nuclear reactor, radioisotope thermoelectric generator, or other efficient, long term, source. What it does not require is "propellant". I.e mass to throw out of the vehicle at high speed. It is a "massless" drive. That is what makes it special.
Why would it be a problem?
Maybe "the speed of light" is a misnomer, c is just a maximum speed defined by the universe, and photons travel at speeds that are extremely close to this cosmic speed limit. It would then be perfectly possible for them to have a tiny amount of mass. No laws break down (at least not in GR), you just have to replace Einstein's flashlights by hypothetical devices that transmit information slightly faster than light, with precisely the speed c.
Turns out "faster than light" is possible after all (but not faster than c).
What I don't understand is what the size of the observable universe has to do with anything. As far as we know, the universe itself is unbounded. The size of the observable universe is just the distance light has been able to travel since the big bang. Why would the wavelength of Unruh radiation be bounded by that? I don't see any physical reason for that.
So you've recreated this experiment and proved this? Have you published your results to spare everyone the waste of time of further environments?
The main trouble with all this talk is it doesn't mention amounts. One may be able to have all kinds of funny effects like Casimir and radiation behind the horizon and what not and it's interesting to figure out how momentum is conserved but to go from a measurable effect to 'let's use it for propulsion' is outright silly. The effect will be in the wrong ballpark and you'll be much better off by just using removing the back and using the actual microwaves for propulsion.
Every test performed on GR has shown it to be correct.
Including the description of velocity addition at velocities close to c.
Basically particles with mass are unable to reach c.
I don't mind the "what if" questions, but they do need to be grounded on some established knowledge to some extent.
You should strap it to a cat.
systemd is Roko's Basilisk.
Why would there be one and only one universe?
By the definition of universe. Multiverse theories do exist, but are not germane to the discussion of how many wavelengths fit into the universe.
What is you definition of universe?
Any event that could create one could create two or 3 or N universes.
...this assumes the universe was "created" in an "event", and that the concept of multiple universes is even sensible. Even assuming that, it's an unsupported assertion. It could very much be like saying "anybody who can discover the Theory of General Relativity can discover two or 3 or N Theories of General Relativity."
Indeed it would have to have something very special to make one and then stop. Something that does not exist in other branches of physics.
What?
If there's more than one, then space is continuous and there's no limit on the wavelength of Unruh radiation.
What? The number of universes has nothing to do with whether space is continuous, and as best I can tell, nothing to do with Unruh radiation.
Did you even read my post? I'm not questioning the validity of GR, in fact I was arguing that there needs to be no contradiction between GR and the possibility that photons could have a tiny amount of mass and travel slightly slower than c.
The speed "c", commonly but perhaps erroneously called the "speed of light", remains the ultimate speed limit. Velocity addition remains valid, particles with mass still cannot reach c, etcetera.
I'm just saying that maybe photons travel at speeds slightly slower than c, and that would be OK.
Short version: photons seem to have inertial mass after all.
You cannot just rewrite fundamental physics to fix one issue without also looking at the implications of your theory for other predictions which is it likely to change. Worse it seems that nobody has tested these drives for the emission of charged particles. A far, far simpler explanation is that this drive works by electron emission. There are a variety of way this can work which all work in a vacuum but whic would unfortunately not work in space where you are electrically isolated and would eventually build up a counter charge and cause the thrust to reduce to zero over time. This all uses established fundamental physics so it would be nice to see this ruled out BEFORE coming up with crazy new physics. It might be less exciting but it is better science.
The lopsided nature of the cone causes the Ether Turtle's shell to become warmer than its belly. This difference is uncomfortable to reptiles and makes it shift around a bit, causing the turtle underneath to adjust to compensate, in turn triggering a similar re-shuffling of the turtle below it, and so on all the way down, causing the universe to shift position relative to the probe.
Table-ized A.I.
I agree that in principle the speed of light does not have to be the same as the limit speed and that they tend to be confused. Only even the tiniest mass of light particles would easily be measured and experiments have been made that are extremely sensitive to this 'nonzeroness' , mainly because they would strongly affect how electrostatic forces depend on distance. So the mass would have to be ridiculously small. ('ridiculous' differs orders of magnitude from 'extreme' ).
You obviously didn't read the article with the talk of testing in 'qualified facilities'. It says specifically that six major groups have tested this:
"In 2012, a Chinese team said it had measured a thrust produced by its own version of the EmDrive. In 2014, an American scientist built an EmDrive and persuaded NASA to test it with positive results."
"And last year, NASA conducted its own tests in a vacuum to rule out movement of air as the origin of the force. NASA, too, confirmed that the EmDrive produces a thrust. In total, six independent experiments have backed Shawyer’s original claims."
As for the theory... Well this is one of the possible tests to prove the concept of the theory, the results so far closely match the results the theory predicts. Though the theory creates some other problems that have to be worked out to fit into the larger physics framework.
we are all invisible unless we choose otherwise
You misspelled "Slurm"
> If you bounced microwaves in a truncated cone, thrust would be produced out the open end. Most scientists have snorted at the idea
I can see why porcine scientists would snort with approval. After all, if you bounce refrigerators around in a truncated cone (nozzle), they'll produce thrust as they exit the narrow end. If you bounce toasters around, they'll produce thrust out the nozzle. Same with coffee makers. Therefore, if you bounce microwaves around a nozzle ...
The laws are more what you'd call "guidelines" than actual rules.
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I try, but as a non-physicist/non-mathematician, all I can really get out of this saga is:
1. Some guy builds and runs a funky apparatus in his lab/garage, and gets some strange results. He reports these excitedly to the world at large.
2. He's obviously smart but possibly deranged, since he claims that the apparatus violates the conservation of momentum, which is a classic crackpot move.
3. Any reputable scientists who have these results brought to their attention uniformly and immediately dismiss them as obvious crackpottery.
4. One night, while drunk, a small group of reputable scientists build the apparatus in their own lab, as a joke, and observe the same strange results.
5. Repeat steps 3-4 a bunch of times.
6. ???
7. Space probe to Alpha Centauri in my lifetime?
What should be most telling was that this "engine" produced more "thrust" when it was turned off than when it was turned on. That should tell you how stupid this thing is but everyone is so caught up in the "I want to believe" moment that they ignore all the warning signs.
I think you have demonstrated how stupid you are with that statement. They found thrust in the NULL experiment, not when it was off. The null experiment used a different shaped reflector that they felt would cancel out the acceleration. If they don't understand the theory of how the acceleration is created, then they could very well have failed to create a null experiment and instead created another shape that works as an EM drive. Once they understand how the trust in generated correctly then they can successfully create a null experiment that works correctly and produces no thrust.
The "thrust" measured by every study is so tiny that it's equivalent to the gravitational attraction of the contraption to your body. There are thermal effects that could explain this tiny thrust. So when the contraption was cooling off, the thermal effects were enough to push the air in a non-symmetric way that it produced a tiny push on the sensors. You could have measured more thrust just blowing on the stupid thing.
They also tested it in a vacuum so there is no air to push off of.
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This "thing" shows the interesting interaction between the engineering community and the scientific community. This is why you should take scientist statements with a grain of salt.
Engineers: look, this works!
Scientists: that violates the laws of science and is impossible.
Engineers: who gives a sh*t what you think? Here's the data
Scientists: the data must be wrong
Engineers: you try it
Scientists: we have no f*cking idea what's happening, but it's happening
Engineers: f*cking pinheads
Scientists: oh, maybe this is what's happening
If you take scientists too seriously, you never get past step #1.
Well that's just silly. Why would the wormhole opening be traveling at the same speed as the ground, rather than at the speed of the wormhole generator? They're both completely arbitrary reference points after all, and if the generator can impart a relative velocity, then there's no reason you couldn't just stand still and generate a wormhole coming at you at 88mph, or 200, or whatever was convenient.
Plus, there's the little matter that, if it were actually employing a wormhole, *and* somehow shielding the car itself from the extreme tidal forces that would otherwise liquefy it as it approached the event horizon (something impressive enough I'm sure ol' Doc would have mentioned it), how would you avoid liquefying the surrounding area once your shielding mechanism had passed through it?
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