3158: Shielding Chart

Shielding Chart

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Title text: Sharks can occasionally travel short distances through air when pursuing prey, but their attenuation coefficient is pretty high.

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Explanation

This is one of 52 incomplete explanations: This page was created by a SPACE-BASED SHARK DEFENSE BOT. Don't remove this notice too soon. If you can fix this issue, edit the page!

This comic is part of a series on confusion matrices.

Various hazardous (or merely obnoxious) materials, objects, and effects can have their danger reduced with specialized protective equipment. The yellow squares are where the shield fails to protect against the object. The grey-yellow squares are where the shield is partially successful, but still presents some risk. The grey squares are where the shield succeeds.

The first five barriers are materials/conditions which may be used to block some things and not others, which makes for a relatively normal comparison matrix. The last five barriers are devices which are deliberately designed and manufactured to block the last five materials/effects. Comparing those with effects for which they aren't designed is presented for absurdity.

The first three hazards - Gamma Rays, Neutrons, and Alpha Particles - represent different types of radiation. Their associated "beep" and "click" sounds mirror real detection behavior: "beep" corresponds to ionizing radiation like gamma and alpha particles, detected by modern radiation detectors, while "click" refers to neutron detection, which uses a separate type of counter designed for neutral particles. Geiger counters, an earlier form of radiation detector, also clicked.

All but two tiles feature Cueball trying to make use of that column's chosen 'protective shield', although in the case of some scenarios (involving vacuum or water) he may also be sufficiently equipped against the environment he finds himself in. Also present will be the row's specific 'effect', either in its own right (an object or creature that embodies the phenomenon automatically) or as conveyed by Megan (when not just present as onlooker) who may also have had the 'shield' primarily delegated to her. The two main exceptions are where Cueball himself emits the sound (from within 'protective' suits that turn out to be ineffectual sound-blockers), to apparently annoy Megan, and depictions of radio reception (which always shows Cueball's attempt to transmit, whether or not it shows a successful incoming message).

Some hazards, such as alpha particles, a form of radiation with particularly low penetrative power, can be easily deterred by common things; even a relatively short distance through air is enough to minimize their impact. Comparatively, more dangerous hazards, such as the far more penetrative gamma rays, are unaffected by all but the shielding methods actually intended for them. No effect is either all effective or all ineffective, against each form of 'shielding', and neither is any instance of shield consistent against all effects.

The title text notes that, while the shark hazard is shown on the chart to be entirely nullified by a sufficient air barrier, in reality sharks are capable of attacking prey even if it is a short distance out of the water. However, it claims a high "attenuation coefficient", which is an overly scientific way of saying that you don't need a lot of air between you and the shark before it can't hurt you. Indeed, while sharks can jump out of the water to a certain height, there's a hard line between "vulnerable" and "out of reach", and a person can be within arm's reach of a shark's attack while they themselves are in no danger whatsoever.

Table

Shielding Chart	Air	Lead	Water	Glass	Vacuum	Oven mitts	Armor	Bio-hazard suit	Faraday cage	Shark cage
Gamma rays	Gamma rays are not significantly shielded by air.	Lead is commonly used as shielding against gamma rays. Lead works because of its density and high atomic number, scattering gamma rays.	Water can be used to shield against gamma rays, but you need at least 10 feet of water between you and the gamma rays for it to work.	Gamma rays have the highest energy of any type of light and have no mass or charge, making them pass through most materials easily.
Neutrons	Neutrons are not stopped by low density materials such as air.	Lead's high density means that neutrons will keep bumping into lead nuclei, losing their energy through inelastic scattering. However since lead nuclei are much heavier than neutrons, most of the energy will remain with the neutron; as a result, many collisions are needed to slow the neutrons. Some neutrons will also be absorbed by the nuclei, although the cross section is rather low.	Since protons and neutrons have almost the same mass, a collision with a hydrogen atom in water will result in the neutron losing almost half of its energy, resulting in a very rapid attenuation. Moreover the cross section for the fusion of neutrons and protons is high, leading to most neutrons being captured to form deuterium.	None of these materials are dense enough to slow or absorb neutrons in significant quantities.
Alpha particles	As alpha particles are almost completely unable to travel through most materials, any of these would effectively stop them. Even if they didn't, the intervening air and distance to Cueball would prevent them being detected in any case. In the third panel, Cueball questions if his equipment is working, as this is the only thing which isn't detected within the first four shields.	While alpha particles are unable to travel through air, they can move freely in a vacuum. As such, alpha particles are able to reach Cueball in this scenario, activating his detector and allowing Cueball to know that his equipment is indeed working properly.	As with the first four shields, any of these materials would block the particles, and in any case they would have a hard time travelling through air to reach Cueball regardless of the shield provided.	There are gaps in both the cages through which the particles could pass. In both cases, the emitter has been moved closer to the observer, because otherwise the effect would be masked by the intervening air.
Light	Light passes easily through air; if it didn't, we would not be able to see.	As lead is a solid, opaque material, light is not able to pass through it.	Water is mostly transparent to visible light. It will attenuate over long distances, but won't be quickly blocked.	As glass is a largely transparent substance, light is usually able to pass through it.	Because a lack of air does not impact the travel of light, it reaches Cueball without issue.	Cueball is able to use the opaque oven mitts to cover the light source, successfully preventing the light from reaching him.	The helmet Cueball is wearing is opaque, blocking the light from reaching him. It also makes this a fairly useless set of armor.	As with the oven mitts, Hairy uses the helmet part of the biohazard suit to block the light source.	As both types of cages have holes in them, it is easy for the light to pass through the holes and reach Cueball.
Sound	Air is the most common medium through which we perceive sound. It would not serve as an effective barrier between a source of sound and someone's ears, unless it was over a very great distance.	Lead is very dense, and is in fact used for soundproofing. It is unclear why it is demarcated as being unhelpful in blocking sound, except perhaps that it would require a large block of lead to completely block all sound from passing through.	Sound travels significantly faster and further in water than in air, making it difficult to locate and understand, but certainly not doing any good when it comes to blocking sound.	Glass, while useful for muffling sound, cannot block it entirely, as anyone whose neighbors mow the lawn at 6:00 can attest to.	"In space, no one can hear you scream." In a vacuum (like space), there are no atoms or molecules to carry sound waves.	Oven mitts are thick enough that they block some of the sound if a person shouts into them, but it will not be enough to fully block out the sound.	The two cases of whether sound can penetrate suits are the only two cases where Cueball is trying (successfully) to inflict the phenomenon on Megan, who otherwise features only as the (attempted) instigator. Neither suit is able (or intended) to significantly block sound waves.	The cages are open enough that their ability to block sound is negligible, and standing in one will do very little to block out sound.
Heat	Air can be a fairly effective thermal insulator when constrained, as in aerogels and many types of insulation. However, freely moving air as depicted in this panel flows as it heats up, transferring heat from the campfire to Cueball's marshmallow. Additionally, air does little to block thermal radiation from the heat source.	Lead conducts heat, allowing Cueball to toast a marshmallow on the surface of the shield. However, since lead is poisonous, he should not do this.	Heat will raise the temperature of water. If the temperature is raised high enough the water will start to boil; boiling has long been used by humanity to prepare food. Marshmallows however are not meant to be boiled.	Cueball appears to be holding a glass bottle over an open fire, into which he has presumably placed his marshmallows. Depending on the temperature, the type of glass and its thickness, it is possible to heat the contents of a glass container, but if the container is unsuitable this can be dangerous to the user. Also, it is unclear how he proposes to consume the sticky marshmallow mess this would create.	The lack of matter in a vacuum completely blocks transmission by conduction and convection, the two main ways heat is spread through. It still allows transmission by radiation, which is less efficient. For the specific example of the thermos shown in the image, however, due to the way they are constructed, radiation is completely blocked, but there are enough residual air particles for a very slow convection, while the fact that the shielding is made from one single (very thin) piece and it has lips, there's also some conduction.	Cueball is holding a pan over an open fire while wearing oven mitts. Pans whose grip or handle is not made of a material that conducts less heat than the pan proper are dangerous to grab onto with one's bare hands: as such wearing oven mitts protects the user from heat. It should be noted that depending on the weight of the pan and the time the pan should be held over a fire to prepare its contents can be quite tiring for the user.	A suit of armor does little to protect one's hands against an open flame. The inside of the gloves will be made of some kind of cloth and/or leather, which does very little to protect one's hands against an open flame, and might pose a fire hazard.	Bio-hazards suits are more suitable designed to help filter air and allow the user to handle dangerous chemicals. However, most Bio-hazards suits are made out of fabrics with a laminate coating, both of which are prone to burning and allow heat to pass through.	Both cages have a minimal effect on the heat from a fire. Depending on the intensity of the fire and the distance from the cage this can create a comfortably warm temperature to the person inside of the cage.
Swords	Air has a negligible force against objects and is unable to stop Megan's sword's thrust.	Lead is a heavy and dense metal, and as a result, it can stop blows from a sword.	While water has a greater force than air against objects, it is still not enough to stop Megan's attack.	Glass is easily broken by sharp blows, especially if it isn't tempered, and as a result does not stop Megan's sword.	A vacuum has no resistance against objects and unsurprisingly is not able to stop Megan's attack.	Oven mitts are typically made of fabric, which would provide only limited protection. They also do not cover the full body.	The metallic armor Cueball is wearing was probably designed to stop sword blows.	Swords are sharp, and as such are able to break through the thin hazmat suit Cueball is wearing.	A Faraday cage has holes which Megan's sword is able to go through.	A shark cage, while able to provide resistance against larger threats, has holes through which Megan's sword can go.
Toxic dust	Dust can travel through air, hanging onto small currents. Air does nothing to protect Cueball.	Lead is poisonous, so while a solid lead barrier would prevent toxic dust from passing through, any dust or metal fragments from the shield would still be dangerous.	Water actually can be used to prevent the spread of dust. However, toxic dust that gets into drinking water will contaminate it, causing health problems just as airborne toxic dust can.	Dust cannot travel through glass, and being fully encased in a glass bell protects one from dust.	With no air to slow it down, dust in space can move at dangerously high speeds, possibly fast enough to tear through Cueball's space suit.	Oven mitts are worn on the hands and such do not interfere with one's breathing. Holding an oven mitt over one's face in case there is a notable amount of toxic dust in the air while evacuating is better than no protection, though.	A suit of armor still allows the wearer to breathe, and provides no particular protection from dust.	A biohazard suit is fully enclosed with its own internal oxygen supply, and as such protects the wearer from airborne particles.	Both cages are too open to provide any significant protection against dust.
Radio	Radio waves are more than able to travel through air, as this is what allows walkie-talkies to work.	Because of Lead's high density and high atomic number, radio waves are unable to penetrate lead, and would not work in Cueball's situation	Radio waves from two-way radios, like the kind shown in the comic, cannot penetrate deep water. There are radio frequencies that can penetrate deep water, but these have a much lower frequency, require more powerful transmitters, and (in the case of extremely low frequencies) cannot transmit audio.	Radio waves are a form of electromagnetic energy, which water absorbs and turns into heat. As such, Radio Waves are unable to penetrate water.	Similarly to how glass is transparent to visual light, it is also transparent to Radio Waves, allowing them to pass through glass.	As there is nothing getting in the way of radio waves in a vacuum, radios work very well in space. This is what allows ground control to communicate with astronauts in space.	Oven mitts, being fabric, have no effect on radio waves.	A metal suit of armor blocks radio waves. This is because metals are very good electrical conductors, which block the radio waves.	A Faraday cage is specifically designed to block electromagnetic fields such as radio waves. In fact, this is the only hazard here that it blocks.	The openings in a shark cage are too open for the cage to experience the properties of a Faraday cage.
Sharks	Sharks cannot travel very far on land or in the air.	Shielding yourself with lead plates will effectively protect you against sharks.	Sharks live in water, so water is not an effective shield against sharks.[citation needed]	Glass will effectively protect you against sharks, provided that it is thick enough. In fact, sharks are commonly (and safely) shown to the public in aquariums.	Cueball in the vacuum of space is very far from shark habitat in the ocean.	Oven mitts are not very effective at stopping sharks.[citation needed]	Depending on the armor, a shark might still be able to bite you through it.	A biohazard suit is weak enough that a shark can rip through it.	A Faraday cage is weak enough that a shark can rip through it.	A shark cage is specifically designed to protect against sharks. In fact, this is the only hazard here that it blocks.

Transcript

This is one of 27 incomplete transcripts: Don't remove this notice too soon. If you can fix this issue, edit the page!

The whole comic is in one panel A matrix sits in the middle with the following rows and columns:

[in all of the Gamma ray boxes, cuball stands next to a table with a gamma ray emitter on it and a geiger counter on his arm] Gamma rays; air - yellow

[The geiger counter on his arm beeps 3 times.]

Gamma rays; lead - gray

[The gamma ray emitter and the table are encased in lead - the geiger counter does not beep.]

Gamma rays; water - grayish-yellow

[The gamma ray emitter and table are in a large glass of water, the geiger counter beeps once]

Gamma rays; glass - yellow

[Only the gamma ray emitter is inside a glass dome, the geiger counter beeps 3 times]

Gamma rays; vacuum - yellow

[the table is replaced by a box- containing the gamma ray emitter, Cuball is floating in space with part of earth behind him, his geiger counter beeps 3 times]

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Discussion

Brb, going out to buy some lead. Fephisto (talk) 01:49, 23 October 2025 (UTC)

If you buy some oven mitts, too, you can get rid of the only two remaining penetrating substances (sound and heat) Logalex8369 (talk) 21:16, 23 October 2025 (UTC)

My new expansion to Rock Paper Scissors Lizard Spock is coming along nicely. KelOfTheStars! (talk) 02:25, 23 October 2025 (UTC)

Ah yes, you can make sound in a vacuum! King Pando (talk) 02:41, 23 October 2025 (UTC)

Well, there's air in her helmet, presumably... 160.39.41.199 05:05, 23 October 2025 (UTC)

We're not gonna have a good time filling out this table, are we? 47.141.47.226 05:14, 23 October 2025 (UTC)

i bet randall is laughing at those silly explainxkcd editors who now have to elaborate on every single square. if i were conspiratorial i'd say he wrote this just to spite us. raeb 08:46, 23 October 2025 (UTC)

Nah, I'm good at filling out tables :) --DollarStoreBa'al^converse 13:07, 23 October 2025 (UTC)

Is your name perhaps Bobby Tables? user:Seshan S. 10:25, 23 October 2025

Bobby Tables is good at deleting tables, not filling them out :) -Ash Crow (talk) 10:47, 24 October 2025 (UTC)

My name is Billy Tables, Bobby Tables' mild-mannered twin brother. Bobby is my evil twin here to cause mischief and mayhem in small wikis.--DollarStoreBa'al^converse 14:09, 24 October 2025 (UTC)

A bit surprised there's nothing about keeping Mr. Faraday away. --130.233.188.214 06:50, 23 October 2025 (UTC)

He was a doctor, so apples would do the job for that. 82.13.184.33 13:21, 23 October 2025 (UTC)

This came out a couple of weeks after the 50th anniversary of Jaws, so it's disappointing that "a bigger boat" isn't one of the protections. Barmar (talk) 14:24, 23 October 2025 (UTC)

"Air," "Lead," "Water," and "Glass," and a near-perfect "Vacuum" actually vary by thickness. I guess Oven mitts, armor, bio-hazard suits, faraday cages, and shark cages do too but those usually come in human-scale sizes. A meter of air won't give you significant protection against gamma rays, but if you are anywhere near sea level, the air above your head does. A near-perfect vacuum too wide for a shark to get to you before it dies will protect you, one only a few nanometers thick probably won't. 64.201.132.210 18:20, 23 October 2025 (UTC)

The best shield of all is distance. You just need enough of it. KelOfTheStars! (talk) 00:33, 24 October 2025 (UTC)

No - the best shield of all is the Hylian Shield. 82.13.184.33 08:31, 24 October 2025 (UTC)

Me & my brother read this whole thing and cracked up about it for several minutes. RadiantRainwing (talk) 03:03, 24 October 2025 (UTC)

This is definitely one of my favorite xkcd comics. I love the confusion matrix ones. RadiantRainwing (talk) 03:05, 24 October 2025 (UTC)

Wait, why no “raptors” row? I really want to see that. RadiantRainwing (talk) 03:09, 24 October 2025 (UTC)

I'm noticing that the transcript isn't looking too good right now, but I don't exactly have the time to fix it right now. Can someone look at 2998: Ravioli-Shaped Objects#Transcript and copy that format? Thanks, 42.book.addict^{Talk to me!} 03:44, 24 October 2025 (UTC)

There's now an "effect vs shield" row for every tile, plus (following on from how the first row started) a "effect-row" scene-setting description placeholder.

I put a list of the rows and columns at the top, just for quick 'scan down/along' reference by anyone reading that bit, but each cell explicitly starts with the "what vs what" and can (where it hasn't already been) be given the hue of the tile and then a followup line (or more!) which addresses the mini-vignette that depicts its particular clash of row header and column header.

Please do not bother with text-colo(u)rs. For one thing, set on default white page-background, the Yellow would be hard to read (by those who can read it) and also likely of zero value (by those who use text-to-audio to read it). The light grey would be bad enough, and the dirty-yellow could be as bad as either.

The reason I did this much is because someone had put a suggestion about copypasting the #hex HTML colour-codes which either was going to lead to the thing I've just said shouldn't be done or would have to be converted into the colour-code-equivalent descriptive plaintext, and still would not have the 'important everything vs. everything' reference which I quickly cobbled together to provide this structure.

Anyone with a text editor can still constructively search/replace anything within that basic structre that I've perhaps not done the way they think should be done (wrong capitalisation, the way the " - " sits between the "vs." and where the colour should be, whether "vs." is even the right way of describing it!), but the big job is actually trying to describe with sufficient detai what Cueball (or the fish/ice/whatever) is doing to prevent the appropriate effect by the (in)appropriate shield. Which I'm leaving for those in a time-zone more westerly than me (who aren't well beyond their healthy bedtimes) or far more easterly than me (for whom dawn has at least started to approach), or possibly just until people not significantly far from me in either direction find that they're more wide awake than anybody else around the world.

Of course, there's always a possibility that someone has been beavering away at it, offline, for a while now and is going to overwirte all that I did. Which is Ok too, and hopefully all credit to them. I may even now have spent more time writing this than I did putting my framework in, and I frankly hope to find this reply to be superfluous by the next time I check in, anyway, so I can delete it entirely and replace with a congratulatory message. ;) 2.98.65.8 00:43, 25 October 2025 (UTC)

So, with lead, water, vacuum, oven mitts, and either glass or a bio-hazard suit, I would be invincible. 67.4.71.239 22:01, 25 October 2025 (UTC)

Randall's clearly only seen the film Jaws but not the book... --Darth Vader (talk) 10:16, 26 October 2025 (UTC)

Or a popular webcomic... ;) 2.98.65.8 18:16, 26 October 2025 (UTC)

cat proximity reference?

do you think shark vs water illustration could be a reference to 231:Cat Proximity ? 129.222.167.167 00:19, 2 November 2025 (UTC)

Almost certainly (the brick joke thrown back a second time with the Shark/Faraday Cage setup, etc).

I mean, it's also possible that they're depicting a catshark, but they generally aren't the threat that even dogfish sharks are (and are probably as harmless to humans, or their insufficiently shark-proofed cages, as catfish...), but I can't see it being any more advanced real-world reference like that. 2.98.65.8 00:49, 2 November 2025 (UTC)
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