3249: Neutrino Project

2026-05-23T22:55:12Z

AndyW: /* Explanation */

{{comic
| number = 3249
| date = May 22, 2026
| title = Neutrino Project
| image = neutrino_project_2x.png
| imagesize = 324x471px
| noexpand = true
| titletext = We definitely put the pool in a mine for shielding. It was absolutely not to hide it from the funding people.
}}

==Explanation==
{{incomplete|This page was created recently by a solar neutrino. Don't remove this notice too soon.}}

A {{w|neutrino}} is a type of subatomic particle that extremely rarely interacts with matter. In nearly all cases, neutrinos pass through objects, regardless of density or composition, with no effects whatsoever unless there are so {{What If|73|many of them}}. For instance, about [https://icecube.wisc.edu/news/press-releases/2017/11/first-look-at-how-earth-stops-high-energy-neutrinos-in-their-tracks/ 100 trillion neutrinos pass through your body every second] to no noticeable effect.

However, there is a very small chance that a neutrino will collide with any material, including water, which has the advantage of being transparent to the light that occurs due to that interaction. Neutrinos can thus be detected by constructing a large pool of water, shielded from as many other particles and radiations as possible, and carefully monitoring it for the small flashes of light that occur when a neutrino does interact with one of the many water molecules within the pool. {{w|Photomultiplier tubes}} are used to assist in detecting these very faint and infrequent flashes and reveal the possible nature (and direction) of the interactions that caused them.

The comic jokes that these detectors were not constructed with this purpose in mind. Instead, [[Cueball]] and [[Ponytail]], the organizers of this project, obtained funding for a “neutrino project” and then embezzled these funds for a pool party, likely primarily to buy the large swimming pool seen in the panel. They supposedly only then realize that the pool could be repurposed as an actual neutrino detector. (It is unclear what, exactly, they had claimed to be building with the funding they somehow obtained.)

It is unclear how large the pool in the comic really is. The {{w|Super-Kamiokande}} detector in Japan, one of the world’s largest and most well-known neutrino detectors, holds over 50,000 tons of water. This is approximately 20 times the water capacity of {{w|Olympic-size swimming pool}}s. The only statement made about the water capacity in the swimming pool is “huge”, which is not a precise measurement of volume or mass.{{Citation needed}} The pool appears to be between 10 and 20 meters in diameter. While the surface of the pool seems to be at most half as large as that of an olympic-sized pool, its depth could be approximately the same, since it seems to safely allow jumps from an approximately 1m high platform. Therefore, a regular pool of this appearance would be expected to hold less water than an olympic-sized one, and certainly much less than would be required for an effective neutrino detector. However, since the bottom of the pool is not visible, the physicists ''might'' just have built a pool with an appropriate volume by making it extremely deep. Assuming a diameter of 20m and therefore a surface area of approximately 314m², the pool would need to be approximately 159m deep. Constructing such a pool would be even more expensive than building a neutrino detector{{Citation needed}}, thanks to the large depth. It's more likely that the pool simply isn't circular with such a small diameter. The problem that the pool is too small is not a problem in the context of the cartoon. The final report to the funding agency would simply conclude "Would work, but we need a larger pool for the next one."

The title text elaborates on why the pool was suitable for a neutrino detector. In real life, these detectors must be heavily shielded from all other particle interactions that might drown out neutrino interactions. This generally requires them to be deep underground (like {{w|Deep Underground Neutrino Experiment|this}} and {{w|Sudbury Neutrino Observatory|this}} and {{w|Super-Kamiokande|this}}), so a surface-level pool would obviously be unsuitable for that purpose. Randall implies that the pool was built in a deep mine in order to prevent it from being noticed by the people responsible for funding the project, which could fulfill the shielding requirement but is a humorously excessive strategy for hiding a swimming pool from a small group of people.

==Transcript==
{{incomplete transcript| This transcript was written by a pool party attendee. Don't remove this notice too soon.}}

:[There is a large pool with a curved edge at the bottom of the panel, with a diving board and several stickfigures in and around it. Ponytail and Cueball are talking in the pool, two hairy Kidballs are passing a ball, a Kidball is jumping of the diving board, and a Danish and a Ponytail with a drink are walking along the outside of the pool.]

: Ponytail in pool: How much trouble do you think we'll be in when they find out we used the grant money to throw a huge pool party instead?
: Cueball: We could argue that we '''''did''''' build a neutrino detector.
: Cueball: There's a lot of water here. A solar neutrino will probably interact with it at '''''some''''' point.
: Ponytail: ...Wait. Actually, if we got some photomultiplier tubes...

:[Caption below comic:]
:How the neutrino detector was invented

{{comic discussion}}<noinclude>
[[Category:Physics]]
[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Danish]]
[[Category:Comics featuring Kidball]]

3240: Bottle

2026-05-02T00:36:04Z

AndyW: /* Explanation */

{{comic
| number = 3240
| date = May 1, 2026
| title = Bottle
| image = bottle_2x.png
| imagesize = 581x235px
| noexpand = true
| titletext = "I know it seems impossible, but the trick is that I sailed in here when I was very young."
}}

==Explanation==
{{incomplete|This page was bottled recently. Don't remove the cork too soon.}}
This comic shows a life sized ship in a bottle sailing along with other sail boats in the sea. The humor comes from the surreality of the situation.

In this comic, [[Beret Guy]] is inside a {{w|Impossible bottle#Ship in a bottle|ship in a bottle}}. A common question when one sees one is "how was it put inside the bottle", due to the small size of the opening in the bottle compared to the ship. The answer is that the ship was assembled (or at least partially unfolded, from more compact original components assembled outside) within the bottle. The title text alludes to this, by saying that Beret Guy grew up inside the bottle to fit (however, this is nonsensical, as he could likely fit into the bottle anyway, and ships do not grow as living things do).

The water level in the bottle is lower than the water outside. This is because the bottle will sink until the weight of the bottle and its contents (the water, the boat, and [[Beret Guy]]) equals the weight of the water displaced by the bottle. The weight of the missing water in the bottle is consequently equal to the weight of the bottle, the boat, and [[Beret Guy]]. If you added water to the bottle in an attempt to make the inside and outside water levels the same, the bottle would just sink deeper. This would continue until the boyancy became less than zero at which point the bottle would sink.

In practice, the bottle is horizontally unstable. The weight of the bottle is not equal along its length (it appears heavier at the neck), and the boyancy at each point will not equal the weight at that point. This is also true of the boats in the cartoon, the difference is that in the bottle much of the weight is the water which is free to move. If the neck of the bottle goes down (to increase the displacement to balance the weight), the water will move to the front of the bottle. This increases the weight at the front which will force the front even deeper. This will continue until the bottle is floating vertically. [[Beret Guy]]'s boat would appear to fit in the width of the bottle so everything will be fine. This effect (known as the 'free surface effect') has real implications for ships with open decks, such as car ferries, and has been implicated in several disasters such as the 'Herald of Free Enterprise', the 'Princes Victoria', and the 'Estonia'.

==Transcript==
{{incomplete transcript|Don't remove this notice too soon.}}

[Three small single-masted sailboats are shown, all sailing towards the right. The ones on the left and right are on the ocean, while the one in the middle is contained completely by a large bottle. On the left, Cueball and Megan are in one boat; Cueball is near the stern, possibly holding the tiller, while Megan is before the mast. In the middle, Beret Guy is before the mast in the boat that's inside the giant bottle, with a cork plugging the bottleneck. On the right, Ponytail is directly aft of the mast of the third boat. All the boats are sitting on the water with ripples on the surface, but the water level in the bottle is lower than the rest.]

{{comic discussion}}<noinclude>

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Beret Guy]]
[[Category:Comics featuring Ponytail]]
[[Category:Strange powers of Beret Guy]]

explain xkcd - User contributions [en]

3249: Neutrino Project

3240: Bottle