3053: KM3NeT
| KM3NeT |
 Title text: Unfortunately, KM3NeT led to the discovery of the Pauli anglerfish, which emits Cherenkov radiation to prey on neutrino researchers. |
Explanation[edit]
KM3NeT is a telescope under the Mediterranean Sea. As Ponytail explains, its goal is to detect neutrino interactions with the seawater. Neutrinos mostly originate from the sun and cosmic radiation. Neutrinos interact with solid matter only very rarely, so a telescope looking for them needs a lot of matter, in this case seawater, to spot collisions in. When such a collision happens, it can release a spray of other particles moving at close to the speed of light in a vacuum (typically denoted c). In seawater, however, the speed of light is slower, and particles moving faster than it cause the emission of a type of light called Cherenkov radiation, which the telescope detects as a blue flash.
When Cueball questions the rationale by pointing out the existence of bioluminescent fish, which might also produce blue light, Ponytail responds with a pun. Since fish move much slower than the speed of light, they are "under-c" life, as well as being "undersea" life, since they live under (or more accurately, in) the sea. Cherenkov radiation is produced only by particles exceeding the speed of light in the local medium, so could not be produced by the movement of fish. However, this ignores the point of the question of other sources of light, like fish, possibly being confused for Cherenkov radiation, which doesn't require the light they produce to actually be identical or produced by the same source or mechanism.
The title text claims that the KM3NeT telescope discovered a type of fish that emits Cherenkov-like radiation: the 'Pauli anglerfish'. Anglerfish have specialized organs that emit flashes of light to attract or startle their prey. Supposedly the (mythical) Pauli anglerfish uses its radiation emissions to prey on neutrino researchers, which is why the discovery is described as 'unfortunate'. In actuality, anglerfish are smaller than humans and do not prey on researchers.[citation needed] The Pauli anglerfish is presumably named after the theoretical physicist Wolfgang Pauli, who first proposed a neutrino-like particle, in part to preserve angular momentum during nuclear decay.
Transcript[edit]
- [Ponytail is pointing behind her towards a drop down screen as she adresses Cueball and Megan in front of her. On the screen is a panel showing a side view of a deep-water telescope. It shows four series of circles stringed together attached to the rough bedrock, so the circles are floating above the bedrock, but far beneath the surface. Waves are drawn just beneath the top of the panel on the screen, indicating the surface of the ocean.]
- Ponytail: The KM3NeT deep-water telescope detects the flashes of Cherenkov light from neutrino interactions.
- Cueball: How do you know you aren't just seeing bioluminescent fish?
- Ponytail: Cherenkov radiation is only emitted when things exceed the local speed of light, so it can't be produced by under-c life.
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For future context, this array has risen in notoriety thanks to the recent detection of the highest energy neutrino yet, but sadly I need to take this occasion to note how the deadliest thing in the strait of Sicily are not superluminal alien fish, but human traffickers moving people on botched up vessels from the north African coast for the past fifteen years, often resulting in shipwrecks in the waters right above KM3NeT. --172.70.216.67 22:39, 19 February 2025 (UTC)
I heard about this last week from a BBC Podcast (Inside Science?). The telescope is only part complete*, and consists of photo-multipliers (can detect a single photon) in glass spheres on a string rising from the sea floor to create a 3D grid (as illustrated). As the decay results in further luminescent particles the direction can be determined and the muon was travelling tangentially to the surface. *As with LIGO, the observation was made when the facility wasn't fully commissioned, so they had to carefully check for other light sources (possible joke source) that they weren't being 'swallowed' by bioluminecence? RIIW - Ponder it (talk) 08:13, 20 February 2025 (UTC)
So... excuse my naivité, but how do they, in reality, ensure bioluminescent fish are not confusing the neutrino detectors? 162.158.155.101 19:33, 20 February 2025 (UTC)
- As it depends upon a 'track' of light, you can work out how likely it is that a set of bioluminescent fish happened to spontaneously 'flash' (in a line, in sequence and at a superluminal velocity for the medium) that coincidentally looks like the non-fish detection signature that they're looking for. (That and/or other factors, looking for particular wavelengths, without known bioluminescent sources, etc.) 172.69.195.229 20:54, 20 February 2025 (UTC)
- They just discount anything that looks a bit fishy.172.71.178.78 09:31, 21 February 2025 (UTC)
- Cerenkov radiation, at any time, looks like a giant cone with the tip at the position of the generating particle. So I assume they can track the progress of the detections with time and dismiss anything that's not compatible with that geometry and time dependency. Nomentz (talk) 15:34, 21 February 2025 (UTC)
- You can't 'see' the cone, in the way the diagram indicates, but you could infer it from your exacting recordings of when the cone/piled-up-wavefront crosses your various detectors. And it is unlikely that a set of flashes happened, from separate but linearly-aligned sources, that happened to so similarly coincide into an identically constructive "shockwave of light"/'photonic boom'...
- PS, you (and others, if interested) might like to use the ready-templated form of wikipedia linking that we have here,
{{w|Cerenkov radiation}}, saving the effort of the 'full link'. Just paste any wiki page's major header in after the "w|". With, whenever necessary, the option of adding another "|" and text you want to appear instead of the straight page-title. (It has a flexibility regarding initial capitalisation, and adding a plural 's', or similar trivial suffix, after the {{}} shortcuts the need to do{{w|Singular|plural}}in most cases, and similar tricks. See how {{w}} is used in pretty much any Explanation source, and you might pick up more of the useful subtleties.) 172.70.160.216 22:28, 21 February 2025 (UTC)
- The other answers have some good general explanations. The actual way that it's done on-the-ground (in-the-sea?) at KM3NeT is mostly based on time correlation of the signals from different parts of the detector. If a true particle track is detected, it should look like a very brief, almost-simultaneous spike seen by a significant number of detector elements (PMTs). The duration of this spike, and the time difference between the spikes seen by different detector parts, is on the order of nanoseconds. In contrast, a bioluminescence event takes place on the order of miliseconds (~6 orders of magnitude longer!), so it's very easy to tell one from the other. Another factor is that, for an event to be really interesting, it needs to hit multiple parts of the detector (that are physically far from each other) almost at the same time - a bioluminescence event usually doesn't reach that far. A more significant source of background is the decay of radioactive elements in the water, but the light flashes from this also don't reach far enough to be a problem, and can actually be really useful for detector calibration. I worked on KM3NeT as a student intern many years ago, and I'm so excited to finally see them in the news again!162.158.245.161 13:14, 27 February 2025 (UTC)
Please,[citation needed] for "undersea life does not move at the speed of light"? It's mildly humorous, but in contrast to the mission of this site to EXPLAIN xkcd and just sheer ignorance, we do not need a cite for any life, undersea or not, travelling at less than the speed of light! Cuvtixo (talk) 21:27, 20 February 2025 (UTC)
- you may find it was added by a bot. 162.158.39.130 11:59, 21 February 2025 (UTC)
I feel that Randall missed a chance at a "Cherenkov Angle" pun in the title text 172.70.134.237 23:40, 20 February 2025 (UTC)
Woah! Was that a Dad Joke? 162.158.168.161 11:55, 21 February 2025 (UTC)
I don't think that the explanation of the title text is incomplete (but I'm a Physicist with a diploma); which part do you want to be explained further? Nomentz (talk) 15:25, 21 February 2025 (UTC)
- Looking at the revision history, it appears there's a glitch in the matrix. The incomplete tag was removed, nobody reinstated it, but then several edits later it reappears in the pre-edit version.141.101.99.69 16:50, 21 February 2025 (UTC)
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