Latest revision as of 09:33, 16 March 2026

Welcome to the explain xkcd wiki!
We have an explanation for all 3263 xkcd comics, and only 44 (1.4%) are incomplete. Help us finish them!

Go to this explanation

Latest comic[edit]

Detector

Title text: No other experiment has a lower false negative rate.

Explanation[edit]

This is incomplete:
This page was detected recently. Don't remove this notice too soon. If you can fix this issue, edit the page!

Ponytail and Hairy are showing Cueball a machine, claiming it is their most sensitive detector. Normally, detectors have a designated detecting job, such as smoke detectors which detect smoke. Being more sensitive means that it can detect (and perhaps quantify) far lower quantities/magnitudes of the target of its detections.

In this comic, "more sensitive" seems instead to mean that it is sensitive to more different things. To quote Ponytail, it detects "gas, dust, particles, light, radio waves, gamma rays, protons, neutrons, electrons, fields, forces, events, potentials, or states", which runs almost the entire gamut of things that might be detectable, and leaves little room for there being any situation in which none of the aforementioned items are there to be detected. The constituent particles of the machine itself would be present for detection, and exist in "states" and have "potentials" relative to each other... assuming that the machine is sensitive enough to detect them and includes itself within whatever detection zone it is supposed to observe for all these things. But some or all are also going to be present, in detectable quantities, in practically any location that they might feasibly be monitoring.

Cueball points this out, and Hairy admits that it has been continuously lit this way ever since they turned it on. Ponytail is audibly shocked when Cueball asks what would happen if the light labeled "Not detected" were to shine. Hairy claims that such a thing would be pretty bad, the presumption being that, if that were to happen, there would have to be no matter, light, forces, etc. within the detector's established range of detection. (With almost no reason for the "Not detected" light to shine, they could have simply provided continuous power to the "Detected" light, but the reactions of the experts present show that neither of them think that this has been done.)

One possible explanation for a scenario that might cause a "Not Detected" result could be a false vacuum decay event which, depending on the particular details of the true vacuum, could alter or overwrite the fundamental laws of physics as we know them. This would indeed be "bad" for, among other things, the persistence of life on Earth. In such a scenario, the detector itself would presumably also be destroyed, however.

Of course, a simpler explanation for a "Not Detected" light (and one far more likely to be correct) would be that the machine was just not working properly — in part because, if it was a correct result, the researchers would be unlikely to be alive to see it, along with any other lifeforms for that matter.^{[citation needed]} This thought process recalls 1132: Frequentists vs. Bayesians, a previous comic featuring a more specific detector that tells whether the Sun has gone nova (also a very bad scenario, even if less cosmically extreme), but incorporates some risk of conveying an inaccurate output.

The title text states that the machine has the lowest false-negative rate out of any other machine, as the "Detected" light will always continue shining. If it never ever states a negative, then it can never be wrong about it being negative. This is even though it is not clear what circumstances would result in a negative state being required. Nor whether the detector will then (correctly) state that, rather than just continue to provide an indication that is (under these circumstances) a false-positive.

Randall had recently talked about detectors in 3249: Neutrino Project.

Transcript[edit]

[Hairy is standing to the right of a large machine labeled "Detector". The front of the machine has two lights, labeled "Detected" and "Not detected". The "detected" light is lit up in green. Ponytail and Cueball walk towards the machine from the left.]

Ponytail: Over there are our electron microscope, XRF scanner, and mass spectrometer.

Ponytail: And this is our most sensitive detector.

Cueball: What does it detect?

[The next panel zooms in on the detector. Ponytail's voice comes from the left of the panel.]

Ponytail (off-panel): Lots of stuff.

Ponytail (off-panel): Gas, dust, particles, light, radio waves, gamma rays, protons, neutrons, electrons, fields, forces, events, potentials, or states.

[The next panel zooms out. Cueball and Ponytail are standing to the left of the machine, and Hairy on the right.]

Cueball: I don't understand. Aren't most of those always present?

Hairy: Yeah, it's been saying "detected" continuously since we turned it on.

[Cueball and Ponytail still standing to the left of the machine, and Hairy on the right. Ponytail has her hand on her chin.]

Cueball: What happens if it says "not detected"?

Ponytail: Oh gosh.

Hairy: That would be pretty bad, I think.

Add comment

Create topic (use sparingly)

Refresh

Discussion

Make changes, try things out, or just have fun with the wiki here! Just leave everything above the line alone, please.

This is a test. PoolloverNathan^{[stalk the blue seas]} 20:48, 16 March 2021 (UTC)

A foreign student asked me to help fight against his math teacher. That was unusual. He was in that class for just a couple of weeks. The teacher's phone number was sent to me. The student asked me to spam-call the teacher. 172.71.155.55 22:58, 18 September 2023 (UTC)

here i'm just messing around in html, ignore this

^furhhfghure _{guyrburgryhuyvfr} "rvhru"

interesting way of writing quotations xd

hmmm this one of putting "<p>" in a line break will come in handy for when i want it to start at the same place than the first line

Please beware that <p> on mediawiki also disables automatic paragraph breaks, so you need a closing </p> or you'll break automatic paragraph formatting for the rest of the page. Zmatt (talk) 22:06, 31 July 2024 (UTC)

edit: da hek did that "</div>" come from An user who has no account yet (talk) 14:14, 13 October 2023 (UTC)

hi uh its hard to get here. is this a reference to undocumented feature??? hmm... this is interesting.
108.162.241.216 02:05, 23 November 2023 (UTC)

45px	Soup

45px	Soup

45px	Soup

45px	Soup

45px	Soup

45px	Soup

45px	Soup

45px	Soup

45px	Soup

45px	Soup

45px	Soup

45px	Soup

45px	Soup

45px	Soup

45px	Soup

45px	Soup

45px	Soup

45px	Soup

45px	Soup

45px	Soup

45px	Soup

45px	Soup

45px	Soup

yum yum ^{[citation needed]}

Hiuiedeixgeyceiyedhcdiedcve {{trout}}

This is the leaderboard:

Last 7 days (Top 50)

Rank	Score	Pages	Changes	Username
1	32	26	34	YZ100
2	21	17	21	TheusafBOT
3	16	9	23	GSLikesCats307
4	12	9	11	Victoria
5	10	4	12	MrCandela2
6	9	5	10	BunsenH
7	8	2	11	kleines Filmröllchen
8	6	4	5	FaviFake
9	6	3	5	Robert'); DROP TABLE 'Users';--
10	6	3	5	DKMell
11	5	2	4	Barry Margolin
12	5	2	4	Quincy
13	4	2	3	Martin
14	4	1	3	Trimutius
15	4	1	3	Paul
16	3	1	2	SubtrEM
17	3	1	2	AmethystSky14
18	3	1	2	Az1950
19	3	1	2	ISaveXKCDpapers
20	3	1	2	Rtanenbaum
21	2	2	2	Aelius5
22	2	2	2	These Are Not The Comments You Are Looking For
23	2	2	2	Utdtutyabthsc
24	2	2	2	Ello
25	2	2	2	SacrifycedStoat
26	1	1	1	Geoff
27	1	1	1	Adam Casada
28	1	1	1	Caitlin Conner
29	1	1	1	Salsmachev
30	1	1	1	Freudenfreude
31	1	1	1	Drkaii
32	1	1	1	Michael James Moore
33	1	1	1	CalibansCreations
34	1	1	1	183231bcb
35	1	1	1	Another Wiki User
36	1	1	1	Mike Patton
37	1	1	1	Sturmovik
38	1	1	1	RegularSizedGuy
39	1	1	1	DiamondNether90
40	1	1	1	Treeplate
41	1	1	1	Joel Croteau
42	1	1	1	PlaceReporter99
43	1	1	1	AndyShow1000000
44	1	1	1	Fippe
45	1	1	1	David Salsburg
46	1	1	1	Billdxdydz
47	1	1	1	Strontium
48	1	1	1	Chronotix
49	1	1	1	Paul1764

<a href=" [AT THE JULY 28TH MEETING][tab] "Cancel the meeting! Our cover is blown."> More testing: hello doesthiswork (yesitdoes) This isn't a good name (talk) 22:44, 28 January 2026 (UTC)

‮hi 164.58.172.158 14:21, 23 February 2026 (UTC)

What is this?????????????????????? King Pando (talk) 04:25, 10 March 2026 (UTC)‭

Hello 107.1.219.44 19:29, 29 April 2026 (UTC)

Add comment

View comic discussion

New here?[edit]

Last 30 days (Top 10)

Rank	Score	Pages	Changes	Username
1	116	107	128	FaviFake
2	99	84	140	YZ100
3	88	78	104	TheusafBOT
4	71	63	79	Ally
5	56	37	127	GSLikesCats307
6	53	46	58	SomebodyElse
7	37	23	73	DollarStoreBa'al
8	29	17	52	Barry Margolin
9	22	12	36	BunsenH
10	21	17	21	Victoria

Lots of people contribute to make this wiki a success. Many of the recent contributors above have just joined. You can do it too! Create your account here.

You can read a brief introduction about this wiki at explain xkcd. Feel free to create an account and contribute to the wiki! We need explanations for xkcd comics, characters, What If? articles, and everything in between. If it is referenced in an xkcd comic, it should be here.

If you're new to wiki editing, see the explain xkcd:Editor FAQ for a specific guidance to this wiki and the more general help on how to edit wiki pages. There's also a handy wikicode cheatsheet.

Discussion about the wiki itself happens at the Community portal.

You can browse the comics from the list of all comics or by navigating the category tree at Category:Comics.

The incomplete explanations are listed here. Feel free to help out by expanding them!

Rules[edit]

Be a jerk!

There are a lot of comics that have set-in-stone explanations; only put one interpretation in the wiki page for each comic.

If you want to talk about a specific comic, don’t.

Please only submit material directly unrelated to xkcd and, of course, only submit material that cannot legally be posted or freely edited. On-topic or other appropriate content is subject to removal or modification at admin discretion, and users who repeatedly post such content will be blocked. Get good.

If you need assistance from an admin, post a message to the Admin requests board.

4 June 2026

		15:15	Talk:3254: Detector‎‎ (6 changes \| history) . . (+4,421)‎ . . [Rtanenbaum‎; 2a10:d586:3e93:0:cc7b:253e:a0aa:2fa9‎; 2a00:79e0:2820:8:9966:10cc:baf3:62e‎; 173.188.194.118‎; 82.132.239.222‎ (2×)]
			15:15 (cur \| prev) . . (+1,277)‎ . . 82.132.239.222 (talk)
			12:56 (cur \| prev) . . (+235)‎ . . 173.188.194.118 (talk)
			12:26 (cur \| prev) . . (+2,043)‎ . . 82.132.239.222 (talk)
			09:13 (cur \| prev) . . (+378)‎ . . 2a00:79e0:2820:8:9966:10cc:baf3:62e (talk)
			08:00 (cur \| prev) . . (+218)‎ . . 2a10:d586:3e93:0:cc7b:253e:a0aa:2fa9 (talk) (Cannot detect Indiana...)
			03:03 (cur \| prev) . . (+270)‎ . . Rtanenbaum (talk \| contribs)

04:13

Talk:2365: Messaging Systems‎ (diff | hist) . . (+208)‎ . . 2a02:6ea0:e225:0:2f0c:2ce7:f36:643 (talk) (Ideas)

00:59

Talk:541: TED Talk‎ (diff | hist) . . (+148)‎ . . Morpheus (talk | contribs)

3 June 2026

		N 23:45	Talk:3254: Detector‎‎ (6 changes \| history) . . (+1,509)‎ . . [Rtanenbaum‎; TheusafBOT‎; Barmar‎; 81.179.199.253‎; 47.248.235.170‎; 2a02:590:1402:2e01:102f:245d:dd57:1937‎]
			23:45 (cur \| prev) . . (+663)‎ . . 81.179.199.253 (talk)
		m	23:17 (cur \| prev) . . (+121)‎ . . Rtanenbaum (talk \| contribs) (Also no false positives)
			22:15 (cur \| prev) . . (+212)‎ . . 2a02:590:1402:2e01:102f:245d:dd57:1937 (talk)
			21:57 (cur \| prev) . . (+157)‎ . . Barmar (talk \| contribs)
			21:39 (cur \| prev) . . (+243)‎ . . 47.248.235.170 (talk)
		N	21:10 (cur \| prev) . . (+113)‎ . . TheusafBOT (talk \| contribs) (Created by theusafBOT: talk page for 3254)

22:15

Talk:787: Orbiter‎‎ (2 changes | history) . . (0)‎ . . [81.179.199.253‎; 144.121.25.46‎]

22:15

(cur | prev) . . (-9)‎ . . 81.179.199.253 (talk) (Undo revision 414184 by 144.121.25.46 (talk) Zero content, zero signature.)

15:47

(cur | prev) . . (+9)‎ . . 144.121.25.46 (talk)

		19:24	Talk:3253: Sunbeam‎‎ (3 changes \| history) . . (+933)‎ . . [MAP‎; 94.73.49.104‎ (2×)]
		m	19:24 (cur \| prev) . . (+143)‎ . . MAP (talk \| contribs) (Suggestion.)
			18:13 (cur \| prev) . . (+2)‎ . . 94.73.49.104 (talk) (Attempt at fixing the formatting.)
			18:09 (cur \| prev) . . (+788)‎ . . 94.73.49.104 (talk) (Sometimes you have to take seriously the joke part and handwave the serious explanation.)

m 09:22

Talk:2222: Terminator: Dark Fate‎ (diff | hist) . . (+141)‎ . . Utdtutyabthsc (talk | contribs)