Main Page

Welcome to the explain xkcd wiki! We already have 12 comic explanations!

(But there are still 3242 to go. Come and add yours!)

Latest comic

Go to this comic

Detector

|< < Prev #3254 (June 3, 2026)

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

|< < Prev Random Explanation

Explanation

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. When Cueball asks what the machine detects, Ponytail claims it detects gas, dust, particles, light, radio waves, gamma rays, protons, neutrons, electrons, fields, forces, events, potentials, or states, all of which are obviously supposed to be detected.^{[citation needed]} However, they could have just made separate detectors, but that would ruin the joke.

Cueball points this out and Hairy says that is why it has been continuously lit since they turned it on. Ponytail is shocked when Cueball asks what would happen if the light labeled "not detected" were to shine, and Hairy claims it would be pretty bad. If that were to happen, the result would be really bad, as there would be no matter, light, forces, etc. If there is almost no reason for the not detected light to shine, they could have simply made a simple circuit board with a led and written a program so that the light is always on.

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. This might not even be a real detector, because it will continuously shine "detected."^{[citation needed]} The title text may be a reference to how medical tests and other measurements can sometimes be misleading. However, no further details are given.

Randall has recently talked about detectors before in 3249: Neutrino Project.

Transcript

[Hairy is standing next to 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]

Ponytail: Over there are our electron microscope, XRF scanner, and mass spectrometer. And this is our most sensitive detector.

Cueball: What does it detect?

[The next panel zooms in on the detector]

Ponytail: (off-screen) Lots of stuff.

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

[The next panel zooms out.]

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: What happens if it says "not detected"?

Ponytail: Oh gosh.

Hairy: That would be pretty bad, I think.

New here?

Feel free to sign up for an account and contribute to the explain xkcd wiki! We need explanations for comics, characters, themes, memes and everything in between. If it is referenced in an xkcd web comic, it should be here.

• If you're new to wikis like this, take a look at these help pages describing how to navigate the wiki, and how to edit pages.

• Discussion about various parts of the wiki is going on at Explain XKCD:Community portal. Share your 2¢!

• List of all comics contains a complete table of all xkcd comics so far and the corresponding explanations. The red links (like this) are missing explanations. Feel free to help out by creating them!

Rules

Don't be a jerk. There are a lot of comics that don't have set in stone explanations, feel free to put multiple interpretations in the wiki page for each comic.

If you want to talk about a specific comic, use its discussion page.

Please only submit material directly related to—and helping everyone better understand—xkcd... and of course only submit material that can legally be posted (and freely edited.) Off-topic or other inappropriate content is subject to removal or modification at admin discretion, and users posting such are at risk of being blocked.

If you need assistance from an admin, feel free to leave a message on their personal discussion page. The list of admins is here.

Logo

Explain xkcd logo courtesy of User:Alek2407.