Explain xkcd: It's 'cause you're dumb.
This comic is a reference to the recent news of a microwave thruster which allegedly produces thrust without expelling any propellant or microwaves, a violation of conservation of momentum. This type of thruster would provide delta velocity without conventional limits. After researchers hooked their device up to a measurement apparatus in an air-filled stainless-steel chamber, applied RF input and measured changes in the apparatus, their interpretation of the results as a tiny thrust explainable under the moniker of "quantum vacuum virtual plasma" was at best controversial. An official statement by NASA's Johnson Space Center is still missing.
The title of the comic directly refers to this hypothetical new physics mechanism of interacting with the "quantum vacuum virtual plasma," a combination of physics words that don't normally go together.
The first part of the comic has Megan commenting on how the engine was, in layman's terms, "twitching," and states that with that much power she'd expect something more forceful. "Twitching" is an expected outcome for various complex systems, including biological ones, when arbitrarily large amounts of electric or microwave power is injected. The last panel is a joke about the scientific method, where equivalence between twitching and the hypothetical new physics is pooh-poohed, because Megan was not previously revealed to operate by the principle of "quantum vacuum virtual plasma," to which Megan responds that she is a complex entity and very well might have new physics inside her.
The title text suggests that the authors of the NASA paper subscribe to the principle that unexpected behaviors of complex systems should best be explained by invoking new physics rather than by making a detailed study of the complexities of the system. This runs contrary to generally accepted approach in science.
- [Cueball and Megan are walking together in the foreground.]
- Cueball: Hear about that "impossible" microwave thruster?
- [They stop walking and Cueball turns to face Megan.]
- Megan: Yeah. Let me get this straight — they pumped 20 kilowatts into a box under ambient conditions
- ...and it only twitched a little?
- Cueball: Yeah.
- [Zoomed out - they are seen in silhouette walking together again.]
- Megan: That's surprising. If you pumped 20 kilowatts into me, I'd twitch a lot.
- Cueball: But you're not pushing on the quantum vacuum.
- Megan: I might be. I do a lot of things.
- Cueball: I guess we can't be sure.
add a comment! ⋅ add a topic (use sparingly)! ⋅ refresh comments!
This is another one of Randall's knocks on pseudoscience... I've seen things like this before, where the guy puts 1000's of volts between a piece of tinfoil and a wire and is amazed that the thing (weighing a few grams) flies around. I'd search for it for reference but it's late here and I'm tired 18.104.22.168 04:41, 6 August 2014 (UTC)
Here is the article referenced: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20140006052.pdf 22.214.171.124 05:24, 6 August 2014 (UTC)
20 kW is probably not from any reference, but just to summarize the history of claims in a vivid manner. The news surge was predicated about the prestige of the NASA organization attaching to any tiny lab under the aegis even though the paper was not in a peer-reviewed top journal but the very last presentation made at a multi-day conference. The NASA abstract differs wildly from the abstract of the same-date paper (or draft). http://rghost.net/57230791 \\ Other coverage from the skeptical side goes a bit into the history of similar microwaves-in-a-funny-shaped-can claims, where the reported thrust seems to diminish as the sensitivity of the measurement. http://scienceblogs.com/principles/2014/08/04/impossible-thruster-probably-impossible/ http://blogs.scienceforums.net/swansont/archives/15155 https://plus.google.com/117663015413546257905/posts/WfFtJ8bYVya https://plus.google.com/117663015413546257905/posts/C7vx2G85kr4 And finally may I close with a reference to Tooth-Fairy-(pseudo)science. http://www.skepdic.com/toothfairyscience.html 126.96.36.199 05:41, 6 August 2014 (UTC)
What I'm missing is any reference to NASA being the third party to conduct this experiment and the third to witness these results. So while this looks an awful lot like Tooth-Fairy-science, it still raises the question of what the hell is going on there? Usually these pseudo-science experiments fail on reproduction or are only reproduced by non-scientists. - Nine 188.8.131.52 06:46, 6 August 2014 (UTC)
More than a decade ago a few weird Italian guys already demostrated more than a twitch. Italian Army officials ("Esercito") were not that impressed. Their bizarre website http://Www.asps.it mostly dedicated to pseudo-religious stuff and fighting trolls, repeatedly states that technical details won't be shared until a patent is definitely granted. - 184.108.40.206 06:58, 6 August 2014 (UTC)
- Fancy way of building an (ordinary) photon drive
A bit of context:
The idea of using virtual particles/quantum foam as your reaction mass has been around for a while. This turns out to just be an overly-complicated way of building a photon drive. If you accelerate a charge (real or virtual), it'll spit out photons. If you interact with charged virtual particles in a way that results in real thrust (by accelerating them), the photons you get out are real photons, and you pay for them in the usual manner (they cost you energy).
If you're building a photon drive, a heating element and a mirror work just as well.
As for the anomalous thrust in the experiments, there are a huge number of ways that you can get that from an experiment that isn't set up sufficiently carefully. The fact that two different experiments got vastly different measurements is a very big hint that something was flawed with at least one of them (possibly both).
Among other things, generating intense microwaves involves large electric currents. If any part of your apparatus is made of metal (and lots of this was), ordinary EM forces produce quite a few contaminating effects that are a royal pain to account for, especially if you're trying to measure an effect much weaker than they are. --220.127.116.11 09:26, 6 August 2014 (UTC)
I don't like how the sciencey posts use a lot of scientific terms without explaining them. I thought the purpose of this site was to make xkcd accessible for all people, science laymen included, but sometimes these explanations obfuscate more than they help. --18.104.22.168 10:46, 6 August 2014 (UTC)
- +1 -- I would suggest a rewrite of the explanation with that in mind. Spongebog (talk) 12:15, 6 August 2014 (UTC)
I don't see any "joke on quantum superposition". Either explain what the jokes are or remove that claim? --22.214.171.124 12:08, 6 August 2014 (UTC)
- That was a "correction" of "quantum supposition" which made more sense. Chad Orzel makes an actual joke about quantum superposition: "Most physicists I know have reacted to this with some linear combination of “heavy sigh” and “eye roll.”" Anyway, I have edited away the superposition by rewriting the description of the last panel. 126.96.36.199 16:02, 6 August 2014 (UTC)
- I don't see any joke about quantum uncertainty, just regular uncertainty and the scientific method in the last panel. The claim of thrust without exhaust or other momentum transfer is a claim of new physics, but the evidence of this claim is weak because the device was not tested in isolation and vacuum and the reported thrust was not in line with the claimed mechanisms. But Megan points out that new physics isn't created but only discovered, so she is just as likely to interact with the newly claimed physics as the Q-drive if enough power is applied. The Uncertainty Principle applies to systems not what model of physics applies so the claims of the Q-drive mechanism can't be in a superposition of true and false. 188.8.131.52 17:03, 10 August 2014 (UTC)
I see a sex joke in "If you pumped 20 kw into me, I'd twitch a lot" and "I do a lot of things". 184.108.40.206 (talk) (please sign your comments with ~~~~)
- 1. Sign your posts
- 2. Remind me never to have sex with you
220.127.116.11 14:08, 6 August 2014 (UTC)
- Not "a violation of conservation of momentum"
Please can someone senior in this community update this as I don't want to get I to an edit war. Unfortunately the media has been conflating the idea between the [|EmDrive] and a [|Quantum vacuum plasma thruster] as Roger Shawyer has been talking about both. NASA tested the idea of a Quantum vacuum plasma thruster which does not violate conservation of momentum
--18.104.22.168 15:06, 6 August 2014 (UTC)
- NASA did not test "the idea of a Quantum vacuum plasma thruster" -- In 2013, a very small group of researchers at NASA tested a pair of RF devices supplied to them for 2 days (and 6 days of setting up the tests). One was supposed to produce thrust in empty space while the other wasn't. But both devices were tested in air and very similar results recorded for both. Therefore either the test was flawed or the devices did not operate sufficiently different from each other to measure. Thus the "idea" was not tested, only the supplied devices and the testing protocol. In that the devices were allegedly designed to demonstrate designs to take advantage/not take advantage of the so-called "quantum vacuum virtual plasma," then to the extent where NASA might have tested a new physics principle, they certainly did not validate it. They also tested (in 2014) a much different Shawyer-type microwaves-in-a-can RF load, and got similar results. The details of the testing (and a misleading section on the vacuum capabilities of the chamber and a weird part on interplanetary trajectories) are in the pre-print.
- But as for conservation of momentum, the principle claim is that the "Quantum vacuum plasma thruster" imparts momentum on the microwave cavity while balancing opposite momentum goes where? Since the vacuum has no state of motion and no momentum, not here. Since no microwaves or other particles are emitted, not here. Thus the claim violates conservation of momentum. 22.214.171.124 15:55, 6 August 2014 (UTC)
- After reading both Quantum vacuum plasma thruster and EmDrive, it seems that they're the same type of device. In particular, scroll down near the bottom of the EmDrive article, and you can see that they're using "interacting with virtual particles" as one of the justifications for it working. Both articles also cite several of the same experiments in their introductions. The physical description of both devices was similar (resonant microwave cavities), differing only in specific cavity geometry.
- And yes, they would have had to be tested in vacuum for a serious test. If you have strong electric fields in air, the air will move (because you'll bleed charge into it, and it'll then be accelerated by the electric field; that's how those tinfoil "lifter" devices work). You'd also have to put it in an RF-absorbing chamber, to avoid resonant interactions with the chamber walls (which can cause your device to be displaced from what you think its neutral position should be; force only costs power while you're moving, so this would look like deflection with no net power applied after the system stabilizes). -126.96.36.199 20:17, 6 August 2014 (UTC)
- Revision weirdness
(For Dgbrt) Not meaning to start an edit war, but how is NASAWatch a better source for the breaking news than the earlier and glossier Wired UK. Also, Johnson Space Center and NASA are under no obligation to comment on the work of the Eagleworks lab under Sonny White. That's just one of the many points that Hambling and NASAWatch get wrong: "NASA" didn't validate anything, a small group of researchers employed by NASA claimed verification in a non-peer-reviewed presentation at a conference. 188.8.131.52 20:20, 8 August 2014 (UTC)
- First thanks for not doing an edit war. My reasons were:
- NASAWatch is still the most serious site to document but also criticise NASA's activities.
- The "wired.co.uk" article is available at that NASAWatch article. I decided to remove that "wired" link here because it uses a hell of external sites blocked at my browser by default (NoScript on Firefox). The site is not "wired.com", one of my favorite pages is there: Beyond Apollo.
- NASA did NOT release any official statements, only a small external publication did refer to an NASA employer.
- NASA keeps silent on this matter because they know there is no prove.
- --Dgbrt (talk) 20:29, 9 August 2014 (UTC)
- "'NASA' didn't validate anything, a small group of researchers employed by NASA claimed verification" -- This is (a) needlessly splitting hairs and (b) incorrect. When an organization employs individuals to take actions, those actions are, de facto, the actions of the organization. If the researchers were employed by NASA to verify or validate a claim, and they did so successfully, then it is said that NASA verified or validated the claim. The only way your assertion would be true is if the researchers, which just happened to be otherwise employed by NASA, conducted the validation / verification outside of their normal work hours, without any NASA facilities or equipment. This does not appear to be the case here. 184.108.40.206 22:59, 16 December 2015 (UTC)
) Your edit of
But while they hooked it up to a measurement apparatus, applied RF input and measured changes in the apparatus, their interpretation of the experiment conducted in an air-filled stainless-steel chamber as a tiny thrust only explainable in terms of new (undefined) physics under the moniker of "quantum vacuum virtual plasma" is an extraordinary claim on very weak data. This may fall under the category of "Tooth-Fairy (Pseudo-) science", trying to quantify a phenomenon before one has confirmed it exists.
But while they hooked it up to a measurement apparatus, applied RF input and measured changes in the apparatus, their interpretation of the experiment conducted in an air-filled stainless-steel chamber as a tiny thrust explainable under the moniker of "quantum vacuum virtual plasma".
isn't a sentence anymore. There is considerable tension between your justification "citation needed for any comment on the validity of the experiment)" and Lcarsos'
justification of "For the love of all that is good and holy just link to the damn link. No need to go all research paper on us with footnote labyrinths." where Wikipedia-like references were removed. The remaining links to the XKCD comic itself, John Baez
, and Chad Orzel
all support the wording of the original. There's also Corey S. Powell @ Discover Blogs
and Ethan Siegel @ Medium
as well as other links in this Talk page. 220.127.116.11
20:20, 8 August 2014 (UTC)
Did the box contain a hair dryer?--18.104.22.168 17:59, 12 August 2016 (UTC)