Talk:EmDrive
This article is amazingly content-free. The only cites to modern science support the idea, and the article offers nothing besides hand-wavey insults to debunk the idea.
I'm thinking of putting a "delete" template on it shortly. ħuman
04:27, 8 June 2009 (UTC)
- Don't diss our resident "science-wiz". - π 04:31, 8 June 2009 (UTC)
- Argh, I never want to relive those days. Except for the stealing commas from Wikipedia part, anyway. "Human, I'm no idiot. And I know a great deal more about cat species, and indeed zoology in general, than anyone else on this site." Crickets and tumbleweeds come to mind. ħuman
05:01, 8 June 2009 (UTC)
- Argh, I never want to relive those days. Except for the stealing commas from Wikipedia part, anyway. "Human, I'm no idiot. And I know a great deal more about cat species, and indeed zoology in general, than anyone else on this site." Crickets and tumbleweeds come to mind. ħuman
Rather than delete, it's worth looking into. http://www.emdrive.com/ I think is the main page for it and http://en.wikipedia.org/wiki/EmDrive can act as a decent starting point. Snark is one thing, but we do need to make the articles accurate first and then go on to the funny parts, not the other way around.
narchist 14:31, 9 June 2009 (UTC)
- Very interesting that New "Darwin Was Wrong" Scientist picked up on it and published it.
narchist 14:33, 9 June 2009 (UTC)
- Let's not delete. This article is an example where we can do better than wikipedia. From what I have read it seems that the EmDrive does not work. It would great to present a coherent argument for this case. Or, in the event we determine that it might work, we could argue the opposite. What I'm getting at is that Wikipedia is constrained to present well-sourced published views from experts. We are not constrained in this way. I have studied math to PhD level and mathematical physics to masters level so I'm willing to have a go at this. Does this sound reasonable or is this sort of thing outside the scope of RW? JoeDuffy 14:39, 9 June 2009 (UTC)
- I've looked at reactionless drive on wikipedia and am wondering if any RW minded people have been at it. It's very much in the style of an RW rather WP article, quoting ProjectRho and making snarkastic references to "Big Science" in only the third paragraph. Reads much better than most of WP's drier stuff.
narchist 15:04, 9 June 2009 (UTC)
Contents |
[edit] Reversion
I reverted BoN's recent additions/subtractions because it seemed to be all based on a YouTube video displaying a "working" model EmDrive. The edits made the page read exactly opposite from its direction. Aboriginal Noise with 4 M's and a silent Q 00:18, 12 December 2009 (UTC)
- Is that a toaster I see to the left of Nacelle B? ħuman
01:40, 12 December 2009 (UTC)
- I've readded the link anyway. If it's a claim that it works, we can't ignore it. Even though it looks as conclusive as... well, I'll have to think up an appropriate similie but it doesn't particularly look impressive compared to, say, the clip of VASIMR working.
narchist 14:54, 12 December 2009 (UTC)
- I've readded the link anyway. If it's a claim that it works, we can't ignore it. Even though it looks as conclusive as... well, I'll have to think up an appropriate similie but it doesn't particularly look impressive compared to, say, the clip of VASIMR working.
- Speaking of things going the wrong direction...am I the only one who's noticed that the video appears to show it rotating toward the narrow end of the cavity...the opposite of the direction of the claimed thrust? Cjameshuff (talk) 22:18, 5 July 2012 (UTC)
- This one? No, it's hard to tell what direction it's supposed to be turning from that set up. But those most recent comments remind me why you don't discuss physics on YouTube.
gnostic 23:39, 5 July 2012 (UTC)
- There's more pictures and video here and here which more clearly show the setup and the orientation of the cavity. There's videos at the latter link which may be somewhat better quality than the YouTube video. It definitely looks like it's rotating toward the narrow end, not the large end of the cavity.
- Another bit...it supposedly works best when "stationary relative to their thrust", a phrase that is physically meaningless (he's not referring to inertial, non-accelerating motion, as Earth's gravitational acceleration is somehow not an issue...guess that whole equivalence principle thing was really more of a guideline). Shawyer's papers are generally muddled and confused about reference frames and seem to be assuming a universal rest frame. In his update from September of 2012, he even seems to claim it can act as a generator while decelerating. Given that a deceleration is just an acceleration in a particular direction...wouldn't just turning it around turn it into both an energy source and a reactionless drive? (For extra irony, the page is titled "Conservation of Energy"...) --Cjameshuff (talk) 02:19, 3 November 2012 (UTC)
- This one? No, it's hard to tell what direction it's supposed to be turning from that set up. But those most recent comments remind me why you don't discuss physics on YouTube.
[edit] Latest results
The Chinese are now reporting thrust of .72N (about 2.5 ounces) from their latest 2.5kW device. That's pretty meaty. See this Aviation Week article for more. -- 68.144.54.246 (talk) 06:15, 29 November 2012 (UTC)
- On the Chinese involvement: two papers have been published, the most recent was submitted in mid 2011, Yang Juan doesn't even mention it on her faculty page, and there's been nothing else since. Looking over the version of the paper on the emdrive.com site reveals rather obvious problems...they used a stationary magnetron coupled to the cavity via a flexible waveguide. The force measured may simply have been the force between the cavity and the magnetron, transmitted mechanically or electromagnetically via the waveguide...there's nothing to indicate they tried different cavity orientations or symmetrical cavities to exclude this. Also, the thrust measured is in the opposite direction to that claimed by Shawyer, from the large end to the small end of the cavity. And contrary to the recent edit by 24.70.185.204, the claimed behavior does violate conservation of energy: a device on end in a gravity field would be an infinite energy source or sink. Cjameshuff (talk) 19:40, 2 February 2013 (UTC)
- There's another article by the same author (David Hambling) at Wired, just as mindlessly accepting and ignorant of the reasons for criticism as the previous one. "Criticism was unsophisticated: Newton said it was impossible, therefore he must be a fraud. Even the most advanced theoretical critique, produced by John Costella, a PhD in relativistic electrodynamics, amounted to arguing about the direction of an arrow on one of Shawyer's diagrams." What difference could the direction of one little arrow make, right? And he says it doesn't violate conservation laws, and he's the inventor so he must be right, right? Cjameshuff (talk) 22:06, 8 February 2013 (UTC)
- Both the theoretical work and the experimental evicence have been published in peer-reviewed papers, and it's been replicated independently. There has been no critique fo the Chinse theory paper. Sounds like science. biohazard
[edit] Seems that this article may be wrong
Nasa tested the drive and found it produces a net force... http://ntrs.nasa.gov/search.jsp?R=20140006052
Weird — Unsigned, by: 96.224.207.29 / talk / contribs 06:49, 2 August 2014 (UTC)
- The described tests and measurements were rather flawed (they did their tests in a vacuum chamber, and described in detail the design and operation of that vacuum chamber...and then they did their tests with the door shut, but at ambient atmospheric pressure), and they also measured an apparent thrust from a null test article that had been modified to not produce thrust. The force measured was just 30-50 micronewtons, easily measurement error due to air currents or some other factor.
https://plus.google.com/117663015413546257905/posts/WfFtJ8bYVya
https://plus.google.com/117663015413546257905/posts/C7vx2G85kr4
http://space.io9.com/a-new-thruster-pushes-against-virtual-particles-or-1615361369 Cjameshuff (talk) 23:35, 5 August 2014 (UTC)
Have to agree. There's a long way to go before Roger Shawyer's hypothesis is proven, but this page needs to be updated now that there are several positive results from reputable sources. The primary debate should be about test methodologies, but this is starting to look less like pseudoscience and more like a possibility based on NASA's latest findings. Definitely not in the same category as Time Cube anymore. — Unsigned, by: 208.70.28.165 / talk / contribs 20:37, 6 August 2014 (UTC)
Science scepticism is about as "rational" as religion. Science needs to be open to new ideas and theories, and liberals who want knowledge to stop evolving are a funny sect. — Unsigned, by: 213.229.76.12 / talk / contribs 13:05, 8 August 2014 (UTC)
- The experiments were complete crap, though. In the Chinese experiment, the force per watt is ridiculously high but points the wrong way and there was an ample opportunity for classical forces. NASA's forces per watt are much much smaller, with drifts of comparable magnitude visible in the graphs as measured, because it was done in the air. It's obvious what needs to be done: dual suspension that measures force and torque independently (and which will not react to minor bending of cables under load), equipment and electronics in a sealed container with a battery, made of permalloy to shield magnetics and electrostatics, the whole thing under high vacuum. But they don't want the equipment to be shielded in a box, they want a vacuum rated RF amplifier, which is expensive, and will outgass producing reaction forces and screwing up the measurements to the point where they'll produce more publicity yet. Dmytry (talk)
- Can someone look at this? It details some test methodology that the NASA abstract didn't mention (which addresses some issues brought up by the previous comment). I can't seem to find the full report from NASA's experiments though.
- http://www.wired.co.uk/news/archive/2014-08/07/10-qs-about-nasa-impossible-drive
- I may not be a scientist, but NASA definitely isn't new at testing propulsion systems. I don't know how many of you here are actually experts in the relevant firlds, but may be we should be careful about dismissing all these experiments as "crap". — Unsigned, by: Lorien / talk / contribs
[edit] Let's talk about conservation of energy and relativity
Why isn't anyone mentioning that EmDrive necessarily violates either conservation of energy or the lack of an absolute reference frame, regardless of whether or not it violates conservation of momentum?
Let's suppose that we have a spaceship with a mass of 1 million kilograms, and it accelerates at 1G, or 9.8 m/s2, and it is powered by an EmDrive with a thrust of 10N/kW. Therefore, it will require 981 MW, or 980.7 MJ per second. (Lower efficiencies will delay the spaceship's transformation into a free energy machine, but it will happen sooner or later unless it is equal to or less efficient than a photon rocket, which is a hideously inefficient method of propulsion.)
After one second, the ship will be traveling at 9.8 m/s. Its kinetic energy from a reference frame in which it is traveling at 9.8 m/s is 48 MJ. It will have spent 980.7 MJ.
After two seconds, it will be traveling at 19.6 m/s. Its kinetic energy from the same reference frame as the first is 192.1 MJ. It will have spent 1,961 MJ. The kinetic energy has quadrupled, despite the velocity only doubling, and the expended energy only doubling.
After ten seconds, it will be traveling at 98 m/s. Its kinetic energy from the same reference frame is 4,808 MJ. It will have spent 9,807 MJ. The kinetic energy is 100x what it was the first second, but it has only spent 10x that amount of energy.
After 100 seconds, it will be traveling at 980 m/s. Its kinetic energy from the same reference frame is 480,886 MJ. It will have spent only 98,066 MJ. Oops.
This tends to be hand-waved away, saying that the device becomes less efficient at higher speeds. But that requires a reference frame (which a reactionless propulsion device doesn't have); otherwise, there is no difference between a stationary object and a moving one. But perhaps Einstein was wrong. But that's still an extraordinary claim, and we all know what that means. EmDrive and friends deserve every bit of skepticism it was met with 10 years ago, and it will continue to deserve every bit of skepticism until they get a lot more thrust than 116 µN. Show me a completely sealed EmDrive floating in a vacuum, and then we'll talk. —ShapeshiftingLizard ~▲~ hear me roar ~▲~ 22:40, 8 April 2015 (UTC)