Low-Background Metal

Explanation:
In this comic, a team including Megan and Black Hat who have invented a time travel machine presents it and their problems to Cueball . Time travel is a common trope in science fiction, and specifically here on xkcd , and such a discovery would be likely to change the world as we know it. However, Megan and Black Hat's machine requires the use of "low-background" metal, which is in short supply.
Megan explains that, while delicate equipment is often shielded from radiation by lead, metal produced in modern times is contaminated by nuclear fallout in the atmosphere, which means that the shielding itself has enough radioactivity to interfere with highly delicate equipment.  In order to shield this equipment, "low-background metal" is salvaged from sunken ships.  Lead ingots from Roman cargo have been used in experiments.  The Roman lead was produced before atmospheric nuclear tests occurred [ citation needed ] and therefore did not have resulting radionuclides in the air used in its manufacture. When it is extracted, lead is naturally contaminated with the radioactive isotope Pb-210, with a 22 year half-life. Because it has spent many centuries continually underwater, it is both shielded from radioactive particles, and has had time for natural radioactivity to fade.
The number of shipwrecks of that age that can be found and successfully salvaged for metal is quite small, which puts this material in short supply. Megan mentions that they have only enough for a single trip.  The team realizes (apparently at Black Hat 's suggestion), that a solution is to use their single trip to take modern military hardware back to the era of the Roman Empire and use it to sink multiple ships.  This would both provide for many more shipwrecks to salvage, and give the team a good idea of where those wrecks were, when they returned to modern times. They could also specifically target ships that were in waters that are well-suited for salvage operations.
However, while this might be a pragmatic solution, going back in time to sink ships and murder the occupants doesn't seem like a particularly morally acceptable solution, [ citation needed ] not to mention opening up potential time travel paradoxes such as what if one of the ship occupants killed was an ancestor to one of the protagonists? If this were a real scenario, there would probably be less drastic solutions available, such as purchasing quantities of lead from the time (would need to convincingly impersonate a local and have something that could be used as currency) and dropping them in the ocean from a (rented) non-destroyed ship, which as a bonus eliminates the need to extract it from the charred remains of a ship later.
Using time travel to retrieve items from the past that are not available in the present is a frequent trope in time travel-related media. Frequently, it is done with the goal of making money , but other purposes are used as well. In the Star Trek movie The Voyage Home , time travel is used to retrieve whales and transport them to the present. In the book Timeline , time travel is used to record historical events for entertainment purposes. In the movie Avengers: Endgame , time travel is used to retrieve minerals important to a future plan. In the movie Back to the Future , when Marty tells Doc that the time machine runs on plutonium, Doc exclaims, "I'm sure that in 1985, plutonium is available at every corner drug store, but in 1955, it's a little hard to come by" (from this transcript ).
Low-background steel is the most famous kind of low-background metal, used in real life for highly sensitive particle detectors in physics and medicine, and is salvaged from ships sunk before 1945 (the Trinity nuclear test ). Since this is steel, the ships used typically date back to World War I or World War II.  (It should be noted that the vast majority of applications that previously required special low-background steel can now once again use ordinary newly-produced steel, as the concentration of radionuclides in the atmosphere has declined almost to pre-1945 levels in the decades since the cessation of atmospheric nuclear testing, due partly to the shorter-lived of these radionuclides having decayed away and partly to processes such as the carbon cycle having removed most of the still-extant radionuclides from the atmosphere.)
The title text refers to Greek fire , which was an incendiary weapon invented and employed by the Byzantine empire. It was a flammable liquid, famously said to burn on water, that was used in naval combat to set fire to enemy ships. As it was a closely-guarded military secret, many of the details have been lost to time, and modern chemists have only been able to develop educated guesses of what it probably was. Randall proposes a rather outlandish alternative hypothesis: that all records of Greek fire were actually in reference to the modern weapons used by the time travelers. It is also notable that, if the time machine was taken to the time of the classical Roman empire, Greek fire would not yet have been a known term. Perhaps the weapon wielded by the time travelers was later conflated with the Byzantines' weapon, or perhaps the time machine was taken to a period a few centuries later than classical Rome.
In 1063: Kill Hitler a single-use time machine is available. It is also used by Black Hat. However, due to the way the time machine in this comic is used, it must be assumed that they can use it again after the salvage of lead from the sunken ships.
[Black Hat stands behind Megan who addresses Cueball who stands on the other side of a table with a machine. The machine is a rectangular box with a small dome with one large and two small antennas on top. It seems to point in Cueball's direction as it has a broad protrusion at the back and protrusion at the front that gets smaller towards the tip.  The word "Time" is written on the side, and below that is possibly more illegible text.] Megan: Our time machine works. Megan: But we're almost out of low-background metal. Cueball: What's that?
[Close-up on Megan who lifts her hand palm up.] Megan: Modern metal is contaminated by fallout from nuclear testing, and lead also has natural radioactivity that fades over time. Megan: To shield sensitive equipment, physicists use lead from sunken Roman ships. Megan: But shipwreck lead is hard to find.
[Back to the original setting, Megan has turned to Black Hat, who has his hand on his chin.] Black Hat: How much do we have? Megan: Enough for one trip through time. Black Hat: Hmmm...
[The three are now in a helicopter, with Megan piloting, Cueball as a passenger in the back, and Black Hat firing a flamethrower at a Roman ship beneath them through the window behind the cockpit. Two sailors with Roman type helmets are looking on as the stern of their ship catches fire. One of them throwing his arms out to the side. The intact sail is still up behind them and behind that another sailor jumps into the water, down to a fourth sailor already in the water. Two already-burning ships can also be seen to the left of the ship under attack. One is burning all over, with the mast still up but the sail long gone, and the third ship is almost completely sunk, but the part above the water is aflame. Seven small clouds are around the helicopter in the sky.] Flamethrower: Fwooosh


ISO Paper Size Golden Spiral

Explanation:
This comic strip is about how to annoy graphic designers and mathematicians, much like 590: Papyrus and 1015: Kerning .
An easy way to annoy many mathematicians is to make fanciful claims about the Golden Ratio . It's been claimed, with varying levels of credibility, to be detectable in many natural and human-made situations, often with the dubious subjective claim that using the ratio in some particular way makes an image more "beautiful". The Golden Spiral is a spiral whose growth factor is this ratio; a common (though slightly geometrically inaccurate) way to illustrate the spiral is to draw curves through a set of squares whose side lengths shrink according to the Golden Ratio. The result looks rather like Randall's drawing here.
However, Randall hasn't used the Golden Ratio at all; he's just drawn a spiral ( not the Golden Spiral) through a common diagram showing the A Series of standard paper sizes, but in landscape instead of portrait (this diagram is commonly drawn in portrait). These papers aren't squares at all, but rectangles whose side lengths shrink by a factor of the square root of 2. Additionally, the paper sizes shrink by a factor of one half, so the area is filled in a geometric series.  This is sometimes called a silver rectangle, although the Silver ratio is actually 1+√2. By mistaking the A Series for something connected with the Golden Ratio, and perpetuating the tradition of making dubious claims about the Golden Ratio, Randall has successfully annoyed both graphic designers and mathematicians.
The title text is a similarly themed joke, based partly on the fact that the US uses customary units while the vast majority of the rest of the world uses SI units .  The 11/8.5 ratio is the length/width ratio of US Letter paper, which is 11 inches by 8.5 inches (another common size in the United States is US Legal, which is 14" by 8.5").  The value of π/4 radians is indeed equal to 45 degrees, although Randall takes the cosine in one case and uses the raw angle in the other case in order to get a close coincidence of values.  The width and length of A Series paper ( ISO 216 ) is always given in whole millimeters, and the width/length ratio is very close to cos(45°) (which is 1/√2=0.707…)  As for US Letter paper: to 4 decimal places, 8.5/11 = 0.7727 and π/4 = 0.7854.
In reality, the usage of radians vs. degrees is not a geographic or political decision, but generally is delineated by profession.  Most engineering and science fields measure angles in degrees or fractions of degrees (arcseconds, or even milliarcseconds in fields like astronomy), while mathematicians and physicists generally use radians.  Civil engineers may refer to the slope of a road by its grade , which is commonly expressed in terms of the tangent of the angle to the horizontal (either as a percentage or a ratio); for angles up to ~10°, this is close to the value of the angle in radians.
The difference between the "real" Golden Spiral squares and Randall's version is approximately either .2038 (for √2-1.6180…) or .08907 ((1/√2)-1.6180…), depending on which way you're counting. Either way, the difference would be very noticeable.)
The spiral shown is approximately a logarithmic spiral with a growth factor of √2, although it has been edited slightly to make it fit neatly inside the rectangles.
If the center of the spiral is at the origin, it may be graphed with r = C*2^(θ/π), for any positive constant C.
In 1488: Flowcharts a golden spiral has been laid in over the chart. That comic is a link that goes to the spiral page on xkcd.
[Caption inside panel:] The golden ratio is everywhere!
[Picture of the ISO standard paper sizes (i.e. A1, A2, etc.) placed so that they fit together perfectly, overlaid with a spiral resembling that of the golden ratio] [A rectangle in landscape orientation with width= height*sqrt(2) is divided into two halves by a vertical line. The left half, a rectangle in portrait orientation, with height=width*sqrt(2), is labeled "A1". The right half (also portrait) is divided into two halves by a horizontal line; the rectangle above this horizontal line (landscape) is labeled "A2". Below this horizontal line there is a landscape rectangle which is divided into two portrait rectangles by a vertical line. The right half is labeled "A3", the left half is divided into two halves by a horizontal line. The lower half is labeled "A4", the upper half is divided again, with its left half labeled "A5". The series continues like this until "A10". ] [Symbolically:  A1 -right,up- A2 -down,right- A3 -left,down- A4 -up,left- A5 -right,up- A6 -down,right- A7 -left,down- A8 -up,left- A9 -right,up- A10.] [A red spiral starts at the lower left corner of A1, passes through the upper right corner of A1 which is also the upper left corner of A2, continues through the upper right corner of A3, lower right of A4, lower left of A5, etc, and after passing through the lower right corner of A10 continues to what would be the lower left corner of A11 and the upper right corner of A12.]
[Caption below panel:] How to annoy both graphic designers and mathematicians


Modeling Study

Explanation:
In this comic, a humorous comparison is drawn between two common types of scientific studies: empirical research , where an experiment is designed to test a scientific theory, and mathematical modeling , where mathematical formulations are produced to predict how physical systems behave under given circumstances. In empirical studies, hard questions about the limitations of existing theory tend to be addressed in the abstract, which is the brief summary of the paper that is presented at the beginning of most scientific articles. In modeling studies, assumptions based on existing theory are built into the model, and any problems associated with these assumptions tend to be discussed in the methods section, which outlines the design of an experiment in the case of an empirical study, or how the model was designed and the reasoning behind the choices made in the case of a modeling study.  In the empirical study, the proverbial "big red problem box" is stated up-front where everyone who finds the paper will read it, while in the modeling study, it's buried in the middle of the paper, where it's less likely to be read.
The caption opens like a typical statement in favor of modeling studies, "A mathematical model is a powerful tool for taking hard problems," but while a researcher who works with models might go on to say "...and breaking them down," or "...and studying them in ways that would be impractical for empirical studies," Randall concludes that they can't actually make hard problems any easier.  His title text, "You've got questions, we've got assumptions," plays on the slogan of the now-defunct electronics chain Radio Shack of "You've got questions, we've got answers" by pointing out that any answers provided are built on assumptions by the modelers.  In other words, garbage in, garbage out .
Randall doesn't call this a "tip" , but it does fit in with his science tip in 2311: Confidence Interval , namely, that "If your model is bad enough, the confidence intervals will fall outside the printable area."  Much as that tip suggests that a model's results can be made to look more impressive by hiding the error bounds outside the printed area of a graph, this comic strip suggests that acknowledgments of problems can be moved to less-trafficked parts of the paper by switching from empirical to modeling studies.
[There are two columns.]
[The column on the left is a piece of paper labeled "Empirical Study". The paper consists of the sections "Abstract", "Introduction", "Methods", "Results", and "Discussion". Each section consists of several horizontal lines meant to represent blocks of text. All sections except "Abstract" have gray, dulled text, while "Abstract" has fully black text to separate it from the other sections. In the middle of the "Abstract" section, there is a large red rectangle. Inside this rectangle is the word "Problem" in large red letters.]
[The column on the right is a piece of paper labeled "Modeling Study". It consists of the same sections with the same highlighting, but the large red rectangle with the word "Problem" is in the "Methods" section instead of the "Abstract" section. Because of this, it is dulled to match the rest of the "Methods" section.]
[There is a curvy black arrow pointing from the red box in the paper on the left to the red box in the paper on the right.]
[Caption below the panel:] A mathematical model is a powerful tool for taking hard problems and moving them to the methods section.


Old Days 2

Explanation:
In this sequel to 1755: Old Days , which was released more than 3.5 years ago, the conversation continues, as if no time has passed, between (young) Cueball and (old) Hairbun about computer programming in the past. As in the first comic in this series , Cueball, having only a faint idea of just how difficult and byzantine programming was "in the old days", asks Hairbun to enlighten him on the specifics. Hairbun promptly seizes the opportunity to screw with his head.
The new claims:
[In a slim panel, Cueball and Hairbun are walking together to the right. Hairbun has her palm raised.] Cueball: What was the Internet like in the olden days, for a developer? Hairbun: Oh, things were very different.
[Cueball and Hairbun have stopped walking. Zoomed in on Hairbun.] Hairbun: The cloud was a lot smaller. It was called a "mainframe" and it was near Sacramento. Hairbun: It was on the state landline, so the whole industry paused when the governor had to make a phone call.
[Zoomed back out. Hairbun has her palm raised.] Hairbun: There was no memory protection. If you wanted to write to an address, you would call around to ask whether anyone else was using it. Hairbun: Often Bill Gates would say he was, even when he wasn't. That's how Microsoft got its early foothold. Cueball: Wow.
[Zoomed back in Hairbun. Cueball responds off-screen.] Hairbun: "Git" was originally a van that circled around gathering data tapes to copy and distribute. We all took turns driving it. Hairbun: When you saw it coming you'd blow an air horn to request that it pull over. Hairbun: That's where "pull request" came from. Cueball (off-screen): Oh, neat!
[Cueball and Hairbun continue walking to the right. Hairbun has her palm raised.] Hairbun: Before terminals, we all used punch cards, which were originally developed to control looms. Hairbun: Early mainframes would produce a sweater each time you ran your code. Hairbun: Eventually we got them to stop. We had enough sweaters.


Endorheic Basin

Explanation:
Yet another comic with one of Beret Guy's strange powers . This time he attracts water so it flows to him rather than running out towards the nearby oceans. He thus claims he is an endorheic basin , hence the title.
An endorheic basin is a limited drainage basin that normally retains water and allows no outflow to other external bodies of water, such as rivers or oceans, but converges instead into lakes or swamps, permanent or seasonal, that equilibrate through evaporation. The Caspian Sea in Asia is the largest such basin. It is debated if it is a lake or a sea (it is salty, but not connected to the oceans). If it is a lake then it is the world's largest lake.
Real-life endorheic basins do not attract water in any unusual ways. Rather, they form when low-lying, inland areas receive water from rivers and streams, but not enough to flood them completely and allow the water to overflow into an ocean. As the surface of the lake grows, so do the rate of evaporation and seepage into the ground, until they're equivalent to the inflow of water (at least, on a yearly average). Obviously, Beret Guy's inexplicable effect on water is distinct from the way actual endorheic basins function.
The panel showing Beret Guy after a shower looks similar to what could happen in a space station if you have liquid water in zero gravity. The water in this environment sticks to any surface it encounters. [ citation needed ] See for instance the start of this video Water in zero gravity and this one Wringing out Water on the ISS - for Science! to see how water reacts to human skin in zero gravity. It is thus almost impossible for him to dry off after a shower.  It seems like the water that is attracted to him is still somewhat subject to gravity, as it pools downwards upon him; presumably he knows to finish showering before it floods over his face.
In fact he needs someone to come with a siphon to get rid of the water. A siphon is a hose or u-shaped pipe, where the downward pipe is longer than the upward section. Thus the water falling in the downward section creates a pull lifting the water in the upward section up to the highest point, from which it will flow down pulling more water up. As the endorheic basin caused by Beret Guy seems to have a limited reach, placing one end of the pipe sufficiently far outside creates a similar effect: The water outside Beret Guy's area of effect flows down under the influence of gravity, creating a pull lifting the water near him "up" out of the endorheic basin. Randall made a what if? about siphons in #143: Europa Water Siphon .
As with real endorheic basins, if the water is allowed to sit, it will eventually evaporate, but he notes that he'll "develop salt flats". Water from rivers carry salts, typically in low concentrations, and if a lake lacks outflows, the salts build up over time, as the water evaporates.  If a salt lake evaporates completely, it can create salt flats (or salt pans), like those near Salt Lake City in Utah , e.g. the Bonneville Salt Flats . These salts come in a variety of forms, including minerals. Sometimes, endorheic basins have high enough concentrations of dissolved minerals to be worth extracting, which is presumably what he means by "let me know if you need any minerals".
There may also be a contrived pun here, in that "flats" is a description of various types of footwear (among them: women's shoes that are not high-heeled and ballet shoes not specifically reinforced for advanced 'pointe' dancing), and the water would clearly leave the 'flats' on his feet.
In the title text, Beret Guy mentions his "biggest fear" due to his water attracting abilities is being flooded to by "colonial engineers" in order for them to use him and the water to generate electricity.  This may be a reference to the Qattara Depression Project . The Qattara depression is a low-lying region near the Egyptian coast. For nearly a century, there have been proposals to dig a canal from the sea to flood this depression, deliberately creating a huge endorheic basin. By placing hydroelectric dams along the canal, the proposals hoped to generation huge amounts of electricity. At least one proposal included the use of nuclear explosions to create the canal, which may help to explain why he considers this his biggest fear.
He then mentions that his "biggest hope", due to his ability, is that he will generate sailing stones . Sailing stones (also known as sliding rocks, walking rocks, rolling stones, and moving rocks), are a geological phenomenon where rocks move and inscribe long tracks along a smooth valley floor without human or animal intervention. The movement of the rocks occurs when large ice sheets a few millimeters thick and floating in an ephemeral winter pond start to break up during sunny days. Frozen during cold winter nights, these thin floating ice panels are driven by wind and shove rocks at speeds up to 5 meters per minute. The Racetrack Playa , an endorheic basin in Death Valley, is one of the most famous locations for sailing stones.
This comic came out just a bit more than a month after the previous comic with one of Beret Guy's strange powers, 2310: Great Attractor , in which strange forces exerted a pull on Beret Guy. It does not appear that he himself is drawn to water, and we cannot determine if the Great Attractor is drawn to him, so Newton's Third Law may be constantly being broken, along with the more obvious scientific impossibilities that surround Beret Guy.
[Megan, holding a glass of water up in one hand, is talking to Beret Guy, who has water surrounding his feet, with small droplets falling off the two small water triangles that cover his feet.  The water in her glass is leaning towards Beret Guy.] Megan: Why are your feet wet? Beret Guy: I'm an endorheic basin!
[Megan looks down at her glass as the water in it is flying out towards Beret Guy's arm, which he has stretched out towards the glass.] Megan: Huh? Beret Guy: Nearby water flows toward me, not the ocean. Beret Guy: See? Megan: Oh, cool.
[At the top of this panel is a box with text being said by Beret Guy to Megan. Beneath it is a depiction of what he is explaining to Megan. Beret Guy is shown standing in a bathroom, with a towel around his waist. Almost his entire body is covered completely in water, except most of his head above mouth level, and both his feet are beneath the water bubble. He yells to someone outside the bathroom. A shower-tray or partially sunken bathtub can be seen to the left with a closed shower curtain across it. To the right of him is the sink with mirror above it. Further right is the door. The floor is tiled.] Beret Guy - narrating: The most annoying part is drying off after a shower. Beret Guy: Can someone bring me the siphon?
[Back to the situation from the first panel, although Megan has lowered her glass a bit. The glass seems to be as full as in the first panel though, even though Beret Guy now also has water on his arm where it was pulled out off Megan's glass in panel 2.] Beret Guy: But I have to get rid of it or I'll develop salt flats. Beret Guy: Anyway, let me know if you need any minerals!


Five Word Jargon

Explanation:
This is another comic in Randall 's My Hobby series , the first of two hobby comics released in the same week, the second being 2328: Space Basketball .
This hobby involves "collecting" and presumably using five-words-long technical jargon. In the comic, White Hat uses a phrases with five such words while talking to Randall (as Cueball ), causing Randall to exclaim "cool" (as in what a cool sentence), and then proceed to type the phrase into his phone to add to his list of favorite Five Word Jargon.
Randall then proceeds to list his current favorites among really satisfying five word technical phrases (or jargon) as a caption below the panel, with White Hat's phrase as the last, possibly the newest. Maybe it was the one that caused Randall to consider other phrases and make this comic.
In the title text, Randall says that he has another much harder hobby, which is to engineer situations where he can use more than one of his favorite phrases. It would seem difficult to combine any of the four listed phrases in a given conversation, as they are from four separate fields (medicine, economics/statistics, biology, and physics/cosmology). However, he said "situations", which is broader term than "conversations".  For example, someone could arrange for experts on these fields to deliver TED talks on these topics, so that he could introduce them by saying "today, we will learn about..." and list the phrases, but Randall cannot, because he has been banned from TED .  At least he has succeeded in using them together in this comic.
This technique has also been used by the [ [1] ], who uses three-word phrases to create excuses for why he won't fix someone's computer when they ask.
A transjugular intrahepatic portosystemic shunt (TIPS) is "an artificial channel within the liver that connects the inflow portal vein and the outflow hepatic vein".  It is used to treat various intestinal bleeding. This term can be found in this publication: https://pubmed.ncbi.nlm.nih.gov/16850140/ transjugular the shunt is inserted via the jugular vein intrahepatic within the liver portosystemic blood is shunted from the portal vein (draining blood from the intestines to the liver) to the systemic circulation (returning blood from the liver to the heart) shunt a tube within the body that bypasses the normal flow of something (whether a natural defect, or an artificial device) placement the operation to insert it
A generalized autoregressive conditional heteroskedasticity (GARCH) model is a statistical model for economic research. An autoregressive model of a time series is one that uses previous values of the time series to predict the next value. A conditional probability model is one that divides data into inputs and outputs and models the relation between them using a conditional probability distribution of the outputs given the inputs. A heteroskedastic distribution is one in which the variance (or standard deviation) of a random variable is not the same across all values of the variable. This phrase can be found in this publication: https://www.scirp.org/html/11-1241334_99870.htm
Generalized making more general, as opposed to a specific model autoregressive using previous values to predict future values. conditional outputs depending on specific inputs (in the sense of, "funding is conditional on meeting targets") heteroskedasticity the property where the variance (that is, the random difference between an expected value and its observed value) itself varies in response to some variable. From Greek, meaning "different dispersion". For example, a graph of expenditure on food against income shows higher randomness at higher income levels, because poor people always eat cheaply, while rich people sometimes do and sometimes don't. model a set of equations that attempt to describe some property of the world for the purpose of analysis
A unicellular diazotrophic cyanobacterium is a single-celled type of bacteria that is able to convert atmospheric nitrogen into a more usable form, and also generates oxygen through photosynthesis. The term can also be found in this publication: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4303622/ unicellular Consisting of only one cell ( Unicellular organism ), such as all bacteria. The opposite is multicellular , which includes almost all other lifeforms like animals, plants, algae, etc. diazatrophic Having the property of fixing nitrogen from the air into other chemicals. cyanobacterium A fairly broad category of bacteria which often play an important role in various habitats, using photosynthesis to convert light energy to oxygen. "Cyano" refers to their general blue colour, not cyanide. group A the "first" group of several groups in a controlled experiment, or a scientific study; in this case, it is the first of several (B, C) groups of phylogenetically-related organisms, for which there is as yet no published scientific name, see here: https://www.researchgate.net/publication/308030272_The_small_unicellular_diazotrophic_symbiont_UCYN-A_is_a_key_player_in_the_marine_nitrogen_cycle .
This is a term from Particle physics / cosmology . Baryons are subatomic particles containing an odd number of quarks; protons and neutrons are the most familiar examples. Baryogenesis is the hypothetical physical process that took place during the early universe that produced more matter than antimatter in the observable universe (or it could be any process that produces baryons). Sphaleron is a static (time-independent) solution to the electroweak field equations of the Standard Model of particle physics, and is involved in certain hypothetical processes that change the number of baryons or leptons (e.g. forming baryons and removing leptons).  It is believed that the electroweak interaction is responsible for baryogenesis, but that at the temperatures involved (~10 15 K), sphaleron interactions would wipe out any excess of baryons; therefore, for baryogenesis to "stick", it must have occurred at the transition out of the electroweak era...unless there were some kind of anomaly in the formation or interaction of sphalerons. Google reports no matches (other than this page) for the entire phrase in quotes, but shows about 70 results unquoted, indicating it finds only partial matches.
Anomalous Deviating from normal or expected electroweak A theory combining electromagnetism and the weak interaction , two of the four fundamental forces (alongside the strong interaction and gravity) in the Standard Model of particle physics. sphaleron a single, time-independent, solution to electroweak field equations, represented as a saddle point between two different low energy equilibria transition change baryogenesis creating baryons, which are a category subatomic particles containing an odd number of quarks, including protons and neutrons. (-genesis is a general suffix for a process which creates something; eg carcinogenesis means, creating cancer)
[White Hat, holding his palm up, is speaking to Cueball, who is typing with both hands on his smartphone. What he types is indicated with a jagged line going up from his phone.] White Hat: Yeah, I learned about it when I was researching anomalous electroweak sphaleron transition baryogenesis. Cueball: Cooool. Text on phone: A-n-o-m-
[Caption below the panel:] My Hobby: Collecting really satisfying-sounding five-word technical phrases.
Current favorites Transjugular intrahepatic portosystemic shunt placement Generalized autoregressive conditional heteroskedasticity model Unicellular diazotrophic cyanobacteria group A Anomalous electroweak sphaleron transition baryogenesis


Oily House Index

Explanation:
In economics, an index is a statistical measure of change in a representative group of individual data points. Common indices include NASDAQ (a measure of a range of stock prices) and a consumer price index (a measure of retail prices)
This chart demonstrates an invented index, the "Oily House Index", which measures a ratio of oil price to average house prices, over time.
The numerator is the average price of a new home (presumably in the US), in USD per square foot ($/sqft). It does not specify what kind of home, or where. One available metric is the average price per square foot of floor space in new single-family houses in the United States which was $118.91 in 2019. The caption refers to converting the mortgage of the new house (that is, how much the purchaser borrowed, which could be zero), while the definition simply refers to the new home price (the total value). It is not clear which of these two is used in the chart.
The denominator is the price of oil in USD per barrel ($/BBL). This is also not well defined, although the chart's caption suggests that it is based on crude oil. There are many different indices for different blends of oil in different locations, such as West Texas Intermediate , which is a crude oil commonly used as a global oil benchmark. (Others include Brent and Dubai Crude). The WTI price fluctuated around $55-60 throughout 2019. A barrel is a standard unit of oil volume, defined as 42 U.S. gallons (roughly 5.615 cubic feet or 0.16 cubic metres).
The comic then applies dimensional analysis to this index: dividing $/sqft by $/bbl yields a result whose dimension is a linear measurement, which can be called length. 1 barrel is 42 gallons, a gallon is 231 cubic inches, and a cubic foot is 12 3 =728 cubic inches, so a barrel is approximately 5.6146 cubic feet and a cubic foot is approximately 0.1781 barrel. The average price per square foot of a new single-family dwelling in the USA in 2019 was about $119/square foot, while the price of oil in mid 2019 was about $60/BBL or $10.7/cubic foot. Dividing $119/square foot by $10.7/cubic foot gives approximately 11.1 foot. This is slightly lower than the value shown on the chart of around 15.
The chart's caption then interprets that length as the depth that a new home could be filled with the crude oil that could be purchased with its price. For scale Cueball and Megan has been drawn, and the ceiling height of a typical house has been indicated, showing that only in time with deep crisis will the oil not fill the house.  It's also not exactly clear where the extra oil should go after a multi-storey house has been filled; on the top floor, you could just take off the roof and let the oil pile up (perhaps after building some retaining walls), but on the lower floors, there's already oil above the ceiling.
The index is high when house prices are high and oil prices are low (such as during the 1999 oil glut), and low when house prices are low and oil prices are high (such as during the 1979 energy crisis). See details about the chart below.
The title text, "We're underwater on our mortgage thanks to the low price of water", is a pun. A mortgage on a property is considered to be "underwater" when the value of the mortgage exceeds the value of the property. This is bad for both the owner (who owes more money than the property is worth) and the bank (who now have a loan which is not fully secured against a default: if the property owner defaults, the bank will lose money in selling the property)- though obviously far worse for the owner.
The title text is hinting at an alternative index based on the ratio of house price to the price of water instead of oil. At the 2019 rate of $118.91/ft² and a rough average water price of $0.0015/gallon , a house would have to be filled with water to a depth of 1060 ft for the house cost to match the water cost. If the price of water fell or the house cost per square foot rose, then the index would rise, causing the house to be even deeper in water (following the metaphor of the index as filling the house with physical water). This situation could arise even if the property value remained high, although Randall may be humorously suggesting that the increase in the index would literally flood the property with water, which would then damage it, obviously decreasing its value. (If the index continues to be computed on average house prices, then this single event would not materially impact the index as a whole.)
In What If #11 "Droppings" , Randall commented that "unit cancellation is weird" after making a similar calculation about fuel efficiency -- the European convention of presenting fuel mileage as "liters per 100 kilometers" represents an area (volume/distance), which can be physically interpreted as the cross-sectional area of a tube of gasoline with the total volume of fuel burned stretched out over the length of the journey.
1979 energy crisis In the wake of the Iranian Revolution , global oil supply reduced by only 4%, but caused widespread panic and a huge increase in oil price. Gulf War The Gulf War (August 1990 - Feb 1991) was the invasion of Iraq by the US, which decreased oil supplies and caused a spike in prices. 1999 oil glut In early 1999, Iraq increased its oil production, while the Asian Financial Crisis reduced demand. Prices briefly fell to as low as $16. [1] Ceiling height Reinforcing the connection with the metaphorical house filled with oil, "ceiling height" here is shown at somewhere just below 10 feet. The standard ceiling height in US homes is 9 feet for ground floor, and 8 feet on higher floors. [2] Only twice has the height been below ceiling height, during the 1979 energy crisis, and in the beginning of the financial crisis of 2007-2008. Oil and housing crashes partly cancel out As a result of the financial crisis of 2007-2008 , oil prices crashed from $147/BBL in July 2008 to $30 in December 2008. Meanwhile, falling house prices , which had partially triggered the financial crisis, continued to slump across the US, with the Case-Shiller home price index reporting its largest ever price drop in December 2008. Since both oil price and house prices were falling, the effect of dividing one by the other means that the index didn't change significantly, remaining around 8-15 feet. 2010s oil glut In 2014-16 there was a serious surplus of crude oil , partially caused by increasing shale oil from the US and Canada, a slowdown in demand from China, and increasing fuel efficiency and use of renewable energy. Prices dropped from $125/BBL from 2012 to below $30 in January 2016. By October 2018, prices had recovered to $85/BBL. ] OHI briefly became infinite as oil prices reached zero in 2020 In April 2020, the coronavirus pandemic dramatically reduced vehicle and air transport, crashing oil demand. Oil futures actually went to zero , and even below, several times: oil producers paying consumers to take their oil, to avoid the costs of storing it. Dividing anything by zero officially has no defined result, but in many thought experiments yields infinity, hence the "infinite oily house index". The graph should actually wrap around to the negative axis at this point.
[A line graph is shown. Above it is a rectangular frame with formulas inside. Most of the top part of the frame is removed and instead a heading is written over the missing section of the frame. The formula is written in three parts, with the first two parts having a division line with text written above and below.] Dimensional economic analysis New home price ($/sqft) / Oil price ($/BBL) = $/area / $/volume = Length
[The graph has a labeled Y-axis with four ticks, which have values, and also the origin has a value. The X.axis is a time-line without label. There are five labeled ticks.] X-axis: 1980 1990 2000 2010 2020 Y-axis label:  OHI (feet) Y-axis: 40 30 20 10 0
[Above the line graph there is a caption:] Oily House Index: How deep you could fill the average new home if you converted its mortgage to crude oil
[The graph begins around 15 before 1980, then dips below 10, rises slowly until about 1988 when it rises sharply. It stays high but has several peaks, and one deep valley until 1999 when there is a very high peak, which then drops fast. A few more peaks, and then a decline to the lowest point in 2008, which is followed by a small peak, and then another drop. From there it stays low until 2015 when it rises quite fast and has one very high peak. It then drops of, until 2020 when there is a really sharp peak. Above the top of the peak is a dotted line extending to the top of the graph (i.e. the top of the Y-axis, not the top of the panel). Then it drops down but not very low as it reaches the present.]
[There are six labels with arrows pointing from them to notable peaks and valleys along the graph. They are written both above and below the line. From left to right they are:] 1979 energy crisis Gulf War 1999 oil glut Oil and housing crashes partly cancel out 2010s oil glut OHI briefly became infinite as oil prices reached zero in 2020
[From 2005-2010 there is a dotted horizontal line that hits the valley at 2008. This is labeled with an arrow pointing to it:] Ceiling height
[Below the line is a drawing of Cueball and Megan standing on the X-axis near 1990. Next to them is a label with an arrow pointing to them:] People (for scale)


Space Basketball

Explanation:
This is another comic in Randall 's My Hobby series , released during the same week as his last hobby comic, 2326: Five Word Jargon .
Randall wishes to play basketball against outer space , hence the title Space Basketball . (His previous attempt at creating a " New Sports System " for multiplayer socially-distant basketball was not very successful.)  His goal is to make thirty baskets in a row before the universe puts a meteor through his hoop.
It should be noted that while may be technically correct to call the falling space object in this case a "meteor", when it hits the ground moments later it would be known as a meteorite .  See also Terminology section below. See also 1405: Meteor , for what Randall's thoughts are on this.
Randall estimates that his success rate at free-throw shooting is approximately 30%.  Therefore, the chances of Cueball making 30 shots in a row is 0.3 30 , or about 1 in five quadrillion (2×10 −16 ); for comparison, there are approximately 150 quadrillion seconds remaining before the Sun engulfs the earth (5 billion years), so if Randall has a chute set up under the basket and enough basketballs to sustain a constant high rate of shooting, he has "decent" odds of achieving his goal before the Sun burns out.  But really, Randall has comparably rapid learning at this task, whereas asteroids have extreme persistence far beyond Randall's life, so when he says the odds are comparable he is abstractly weighing his unique skillset against that of small stellar bodies.
Still, the lifetime odds of being killed by a meteorite have been estimated at 1 in 75,000 or 600,000 or 700,000 [1] . These calculations are usually based on the probability of being alive at a time when a huge impact kills billions of people. Randall just uses the chance of one meteorite shot on Earth hitting this hoop (hoop-area divided by Earth-area = 3.2×10 −16 ) which is in the same range as 0.3 30 . Actual meteorite fall statistics report an average of 1.2 meteorites per year hitting the European continent which suggests that the average probability of Cueball winning after each shot attempt is about equivalent to a meteorite passing through the hoop over the period of 10 hours. Therefore Cueball has a better chance of winning than the universe "on the short term" if he makes more than 840 free-shot attempts per year for the rest of his life. The expected time for the universe to actually "complete" the challenge would be in the range of 8 billion years, the same magnitude to the current age of the universe and longer than the estimated remaining lifetime of the solar system .
In the title text, Randall assumes that he would get better at free throwing shooting with practice in his lifetime ("the short term"). Some of the world's best basketball players have free-throw percentages over 90%, and even professional players with reputations of being "poor" free-throw shooters (e.g. Shaquille O'Neal) are above 50%.  If Randall can improve his percentage to 50%, his odds of sinking thirty baskets in a row improve to "nearly" one-in-a-billion, while a member of the elite 50–40–90 club would have a probability better than four percent of making thirty free-throws in a row. Some specialists have achieved much higher success rates, with the record for most consecutive baskets being held by Tom Amberry with 2,750. The NBA regular season record is 97 free throws in a row, set by Micheal Williams in 1993 (during the 1992–93 and 1993 94 seasons).
However, he acknowledges that in "the long term" (the life of the universe, or at least the Earth), the Earth will be hit by very many meteorites; even though it is more likely that Randall will make his thirty free-throws before a meteor passes through his basket, he does not possess the cosmic lifespan [ citation needed ] required to surmount the odds against him and actually have a good probability to witness either event.
A piece of space debris falling through the atmosphere is a meteor .
A piece of space debris that makes it all the way to the surface of the Earth (or any planet) is a meteorite .
Most meteors burn up completely and do not become meteorites.
The concept of a meteor passing through a basketball hoop, ten feet or less from hitting the ground, is so uncommonly discussed that the terminology could be a matter of some debate.  Unless it is very large, a meteor this close to the ground will have slowed to terminal velocity and will no longer be burning up [ citation needed ] ; it will therefore not be incandescing like a conventional meteor, and it is certain that it will become an actual meteorite within just a moment.
(Any meteor still incandescing within 10 feet of the ground, on the other hand, would presumably destroy both the basketball hoop and any nearby observer, meaning that poor Cueball, if still shooting, would lose the game in a much bigger way.)
Many scientifically-aware people have the habit of correcting "meteor" to "meteorite," so it may be safest to use the latter term among nerds other than Randall, or you could out-nerd them by pedantically pointing out a reason to still call it a meteor.
[Cueball, holding a basketball in front of him in both hands, is looking up at the basketball hoop in front of him. The hoop is on a standard board, but at the foot of the rod holding the hoop, there seems to be growing grass up, indicating it is outside.] Cueball: Okay, here are the rules: Cueball: I have to make 30 shots in a row before a meteor falls through the hoop. Cueball: I'm a 30% free throw shooter so the odds are actually pretty even. Cueball: Ready...Go!
[Caption below panel:] My hobby: playing basketball against space


Universal Rating Scale

Explanation:
In this comic, Randall has blended many traditional rating scales to create a "universal rating scale". Unfortunately, the mixing of these scales creates a scale that is impossible to use. Only a subset of the values of each rating scale is included, further weakening its claim as a "universal" scale. The result is much like the attempt to create a "universal standard" in 927: Standards .
Alternatively, it can be perceived as a way of comparing the different scales, for instance to answer a question like "Is it worse to get a 2 or an F?"
Scale of zero to ten (but with an 11, because people often add that to exaggerate - see up to eleven about the meme) 0, 1, 2, 3, 4, 5, 6, 7, 8, 10, 11. The number 9 is omitted, possibly because seven ate nine (789) or because nine is the neglected number . Competitive scores , such as for artistic gymnastics' Code of Points , (ordinarily from 0.0 to a perfect 10.0 ) 10.0 Likert scale strongly disagree, disagree, agree, strongly agree (often there is a "neither agree nor disagree" value in the middle, but it is not strictly required) School grades (there are also B, C, D, and others with + or -) F, A+ S - Schools in Japan may use the S grading , which is said to stand for "superior" , implying “even better than A.” The expression S is also used in daily life, generally perceived as an S in s pecial or s uper, here unrelated to the academic grading system. For example, the most expensive seat in a theater (e.g. a balcony seat) may be called S-seki (lit. “S seat”) in Japanese, while the second most expensive seat may be called A-seki . Many video games also use S grading, and some (such as Beat Saber and Dance Dance Revolution) use SS, SSS, and even more S's as ranks above that (though these are not shown in the webcomic). A possibly related expression is “Super S” as in Sailor Moon SuperS . Star rating 1 star, 2 stars, 3 stars, 4 stars, frequently used to rate restaurants, films etc. 5 star is omitted, probably due to Randall's opinion that items with 5 stars tend to only have had one rater and aren't trustworthy . Conservation status (this is only a subset of the nine groups in the International Union for Conservation of Nature (IUCN) Red List of Threatened Species) extinct, critical (probably critical ly endangered ), endangered, least concern According to the title text, "extinct in the wild" is a half-step below "critical", presumably above "G". Starbucks brand beverage sizes (there is also short and trenta) tall, grande, venti MPAA age-appropriate film ratings took effect November 1, 1968 with G, M (now PG), R (not shown in comic) and X (now NC-17) G, PG (as of February 11, 1972, replaced GP ), PG-13 ( introduced July 1, 1984), NC-17 (introduced September 1990, replaced X ) ESRB age-appropriate ratings for video games (there is also EC for early childhood, E for everyone, E10+ for Everyone 10+, M for Mature, and AO for Adults Only) T for teen Happiness emojis (alternately, the Wong–Baker Faces Pain Rating Scale ) Frowny face (☹, U+2639), neutral face (😐, U+1F610), smiley face (☺, U+263A). It is not totally clear which emoji each symbol is meant to refer to. The unhappy face could be Worried Face 😟, Anguished Face 😧, Frowning Face ☹ (note the lack of eyebrows), Slightly Frowning Face 🙁 etc. Coin grades G, VG, UNC meaning good, very good, and uncirculated respectively Hurricane/cyclone strengths , Saffir–Simpson scale (ordinarily categorized from category 1 to category 5) Category 5 Tornado intensities , enhanced Fujita scale (ordinarily categorized from EF0 to EF5) EF-5 Credit (and other) ratings A, AA, AAA Credit rating agencies will rank businesses and governments based on their likely ability to pay back their creditors' interest ratings. The very highest are rated AAA, and then (in Standard & Poor's scheme) AA+, AA, AA-, A+, and so on. (Note that Randall's scale rates A+ as better than AA, indicating that it's the "A+" from school grades rather than the one from Standard & Poor's list.) This could also be a reference to battery sizes. This would imply that AAA is better than AA, which is not necessarily true, but funny to think about. Alternatively, this could be a reference to sports tier divisions; where AA and AAA basketball for example promote age and skill appropriate competition.
The title text suggests that the scale as shown here is incomplete, by referencing further gradings that are not shown in the table. Critically endangered and Extinct in the wild are real conservation status categories recognised by the IUCN, although it's not clear what "Critically endangered/extinct in the wild" would mean - perhaps the "possibly extinct in the wild" designation, abbreviated CR(PEW). It would presumably fit on the table somewhere between "Extinct" and "Critical", although its ordering relative to "tall", "2" and "G" is unclear.
The title text suggests that a score at this level had been graded on a curve , which bumped its rating up to "Venti", which is on the table, two steps below "Least concern". This would be an extraordinary example of such a curve, pushing the score from approximately 2/10 to almost 8/10. This could only happen if the exam was extremely difficult, meaning most results were significantly below 2/10.
[Caption above the frame:] Universal Rating Scale
[A vertical scale, with 45 gradations, labelled. These are the grades:] 0 1 Strongly Disagree F [star] ☆ Extinct Tall 2 G Critical [frowny face] ☹ 3 endangered [two stars] ☆☆ PG Disagree VG 4 Grande 5 PG-13 [neutral face] 😐 6 T for Teen 7 [three stars] ☆☆☆ Agree Venti 8 Least Concern [smiley face] ☺ A Strongly Agree Category 5 EF-5 NC-17 UNC AA [four stars] ☆☆☆☆ A+ S AAA 10 10.0 11


Acceptable Risk

Explanation:
This comic is another comic in a series of comics related to the COVID-19 pandemic .
This comic shows Cueball and Ponytail , who are nervous to spend time in close proximity while the coronavirus is still widespread, and while lockdown procedures are still in effect across the world. Despite taking many precautions, such as wearing masks and maintaining physical separation, they still fear the effects of the virus, and attempt to weigh the value of actually seeing each other in-person versus potentially catching the virus. This is a dilemma faced by many, as the United States enters the fourth month since stay at home orders began. Cueball and Ponytail are particularly affected because they are known to overthink everyday decisions and interactions (in spite of their protestation to the contrary in the title text), as seen in e.g. 1445: Efficiency . Moreover, Cueball is bad at social interactions , virus or no virus, as pointed in the last panel.
The comic title "Acceptable Risk" is formally used in risk assessments as a risk level that so low that it is comparable with other daily life risks. Typically, Acceptable Risk is defined as the probability of death being about one in a million. Cueball implicitly makes a risk assessment where he takes into account local virus prevalence and steps to reduce transmission risk coming to the conclusion that the risk to "hang out" is an acceptable risk. During the meeting however he becomes aware that for a good risk control strategy he also has to consider the trade-off between the benefits of taking the risk of "social interaction" over the benefits of completely avoiding the risk. Additionally, the numerous precautions that Cueball and Ponytail have taken to reduce risk (wearing masks, meeting in a featureless empty field with no other people, maintaining a safe distance) likely make the social interaction much less enjoyable, and thus perhaps not worth it at all. Cueball and Ponytail figure that it is extremely hard to measure the benefits of social interaction for them, and thus decide that for now complete avoidance is the better risk control strategy.
Their screaming actually increases the risk of the interaction; this is why Japan recently banned screaming on amusement park rides (you read that right) , and why many jurisdictions are levying particular restrictions on singing even when gatherings are permitted.
[All of the panels depict the same two characters seen from a long distance, making them difficult to recognize. However, they appear to be Cueball (on the left) and Ponytail (on the right). They are each wearing a mask.]
[Cueball and Ponytail talk to each other, standing at a distance:] Cueball: Okay. Based on the local virus prevalence, our careful quarantines, and the steps we've taken to reduce transmission risk, Cueball: I think it's okay for us to hang out. Ponytail: I agree.
[Three small panels, vertically on top of each other] [Cueball and Ponytail get closer to each other.] [Cueball and Ponytail get still closer.] [Cueball and Ponytail standing near each other:] Cueball: Hi. Ponytail: Hi.
[A normal sized panel, with Cueball and Ponytail standing near each other. They are yelling, with their arms raised:] Cueball: Is this social interaction good enough that it's worth risking our lives and the lives of others?! Ponytail: I don't know! Cueball: AAAAA! Ponytail: AAAAAA!
[Cueball and Ponytail stand much farther apart.] Cueball: Healthy socializing was hard enough before the pandemic. Ponytail: Let's just try again in 2021.


Hamster Ball 2

Explanation:
This comic is another in a series of comics related to the COVID-19 pandemic .
A hamster ball is a small, transparent sphere in which a hamster or other pet rodent can run around (reasonably) safely, without being in its cage.  Cueball had previously obtained a " human-sized hamster ball " for himself.
Cueball relates that, once upon a time, he was teased for this seemingly-frivolous pursuit, but he feels that now, in the midst of a worldwide coronavirus pandemic , having his own bubble to be inside is a smart move.  He is contrasted to White Hat, who is wearing a facemask for protection.
"Who's laughing now" is a common phrase that you know better than others who originally laughed at you, or that the "tides have turned" and you have a control over the situation. However, as White Hat notes, the same people who laughed at Cueball before are still laughing at him, for the same reasons as before: even though his hamster ball has some practical utility now (enforcing social distancing), it still looks ridiculous and is lots of fun to roll around.
In the title text, Cueball says that he feels worst about being teased by "responsible, mask-wearing" teens, who treat the outside of his hamster ball as a potentially-contaminated surface (which it is, if it has previously been rolled around by ir responsible teens who might have contracted and spread the coronavirus) and disinfect it, taking care to avoid spraying the vents and thus not exposing Cueball's lungs to a hazardous chemical, before rolling him around.  It's not clear why he doesn't like being rolled around by responsible teens; it could be that he vindictively wishes that they would catch the coronavirus from the outside of his hamster ball, thus proving that he was correct to use it, or it could be that his ego is injured by the fact that even responsible and otherwise well-mannered and socially-conscious teenagers (who are not likely to be particularly harmed themselves by COVID-19, but conscientiously follow guidance to reduce transmission and protect those who are at-risk) find his hamster ball so ridiculous that they have to have fun at his expense.
As the title indicates, this is the second comic specifically devoted to hamster balls; the first was 152: Hamster Ball , in which Cueball wished for a genie to give him a human-sized hamster ball (and then had no other wishes he wished to wish). A human hamster ball also features prominently in 211: Hamster Ball Heist .
[Cueball is inside a transparent human-sized sphere, evidently "rolling" forward. Ahead of him is White Hat, wearing a mask.] Cueball: They laughed at me, all those years ago, when I got this human-sized hamster ball.
[Frameless panel with just Cueball rolling forward, with his hand in a fist.] Cueball: But who's laughing now?!?
[Cueball and White Hat have stopped. White Hat is pointing into the distance.] White Hat: Sounds like the same people. White Hat: See? There's some of them over there.
[Cueball turns around to roll backwards while White Hat stands next to him still.] Cueball: Yeah, neighborhood kids. Cueball: At least they've stopped trying to roll me into soccer goals. Cueball: No, here they come. Cueball: Run!


Cursed Chair

Explanation:
This comic is another in a series of comics related to the COVID-19 pandemic .
Beret Guy informs Cueball that he purchased a cursed office chair from a mysterious shop. Cueball isn't sure if he remembers this happening, which is possibly because Beret Guy has previously stated that he makes a habit of purchasing daily necessities from such stores. Beret Guy then exclaims that the store he bought the chair from was gone when he went to return it, though given his buying preferences, he should perhaps not be so surprised. Cueball suggests that maybe the shop was simply closed due to the COVID-19 pandemic , as is the case for wide variety of non-cursed businesses. Beret Guy takes this as proof that the chair somehow caused the pandemic, a claim Cueball meets incredulously. In the final panel, Beret Guy is doing battle with the chair, which taunts him and claims to be immortal (“ I can not die ”). In fact, most chairs cannot die, because they are not alive. [ citation needed ] Cueball remarks that it would be simpler to shop at IKEA , a store famous for its minimalist flat-pack furniture, and which does not sell cursed items [ citation needed ] (although they do sell “ miniature Dyson spheres ”).
The cursed chair and the boarded-up store are references to the stores that sell cursed items mentioned in 1772: Startup Opportunity . In that comic, the stores vanished without a trace. But the fact the door was boarded is much more likely due to the pandemic or other causes than the store mysteriously disappearing.
Buying an item from a shop you never noticed before, bringing it home, discovering it is cursed, and trying to return it only to discover the shop isn’t there anymore is a popular trope. See The Little Shop That Wasn't There Yesterday .
In the title text, the Siege Perilous is the empty seat at the Round Table in Arthurian legend, reserved by Merlin for the knight who would find the Holy Grail (who turns out to be Sir Galahad ) and fatal to anyone else who sits in it. Herman Miller is an American office furniture company that produced the Aeron chair , which is the basis for an artwork by Glenn Kaino called The Siege Perilous . Wirecutter is a website that evaluates and recommends consumer products.  From the title text, it sounds like (in the xkcd universe) Wirecutter is used to encountering cursed products, [ citation needed ] so they didn’t even bother trying to sit in it to test the Siege Perilous’s perilousness (er, peril ) before they started fighting it—and emerged victorious, if it’s only nearly as immortal as it boasts.
[Beret Guy and Cueball are talking.] Beret Guy: Remember how I bought my desk chair from that mysterious shop? Cueball: I think so? Beret Guy: Turns out the chair was cursed.
[Beret Guy and Cueball are still talking. Beret Guy has his palms out.] Beret Guy: So I went back to return it, but the shop was gone! The door was boarded up! Cueball: I think most of the shops are closed because of coronavirus.
[Beret Guy has his hands over his mouth in shock.] Beret Guy: Oh no! Beret Guy: The curse must have caused the pandemic! Cueball (off-panel): What.
[Beret Guy starts running with a raised sword in a frameless panel. Cueball is next to him.] Beret Guy: If I destroy the chair, we can stop the virus! Cueball: What.
[Beret Guy is chasing a floating desk chair. Cueball is watching.] Beret Guy: Die, plague-bringer! Desk chair: Hee hee I can not die Cueball: Maybe you should just shop at IKEA.


COVID Risk Chart

Explanation:
This comic is another in a series of comics related to the COVID-19 pandemic .
This comic is a graph showing the risk of COVID-19 infection of numerous activities on the horizontal axis, while showing the other (i.e. safety) risks of the activity on the vertical axis. The activities are also color coded green, yellow, orange, or red, presumably indicating whether engaging in them is a good idea. All the activities are green in the upper left corner (no COVID-19 danger and no other dangers), but change to yellow, orange, and red as you go right or down. This presentation and color progression is similar to a common presentation of a risk matrix .
One-dimensional charts showing the COVID-19 risk of common activities were popular at the time of this comic, when businesses and schools were re-opening after the first wave of COVID-19.
The top of the graph contains activities that people are likely to engage in during the pandemic, beginning (from left to right) with staying at home, hanging out with friends at the park, grocery shopping, attending in-person classes, and singing in church. The first few activities are common and not very dangerous (colored green and yellow), but the last two come with significant risks of infection due to COVID-19 (they are colored orange and red). Lower on the graph the activities become more and more dangerous (though these dangers are not related to COVID-19, i.e.: they are non-covid risks) and then non-sensical, a trend often seen in xkcd comics. Some activities are grouped together, being variations of the same thing (such as going down a waterslide, going down a waterslide with a stranger, and going down a waterside on an electric scooter). The last row contains extremely dangerous activities such as (from left to right, or from low COVID-19 danger to high) bungee jumping while doing sword tricks, going down a waterslide on an electric scooter, (participating in an) axe catching contest, racing a scooter through a hospital with a mask over your eyes, and winning a test tube -eating contest at a COVID testing lab. All these activities are likely to result in undesirable outcomes. [ citation needed ]
Part of the humor comes from the increasing ridiculousness of the "red" activities, some of which are unlikely combinations or escalations of other less-risky activities (e.g. renting an electric scooter is a "green" activity, but riding that scooter with a stranger carries more risk, and then still more from racing that scooter through a hospital, with or without a mask).
This comic strip is similar in presentation to 2282: Coronavirus Worries .
The title text suggests a ticket to "the" kissing booth as a prize. Presumably, the prize is for the test-tube eating contest, and the booth is the kissing booth mentioned in the comic, "a kissing booth at a COVID testing site". A kissing booth is a kind of sideshow sometimes seen at carnivals, where members of the public can pay a small fee to kiss someone, usually an attractive woman. Winning a ticket would normally be positively received. However, since kissing is a very high risk activity for COVID-19 transmission, it would now be perceived as a kind of punishment. Moreover, if the ticket was the prize for the test-tube eating contest then not only would the winner already likely have infected themselves with COVID-19, but they are likely to have mouth injuries from eating glass, making the kiss even riskier.
The lowest-risk category of activities has very low COVID risk and also very low non-COVID risk.
Staying home The lowest-risk activity of all, as long as the home itself is safe, and your family members do not have COVID-19. Video chats Video chatting carries a slightly higher non-COVID risk than simply staying at home, because you might get into an upsetting argument or accidentally expose something embarrassing. As long as the person you're chatting with is not within your personal space, the risk of catching COVID from them is still zero. Hanging out with friends in the park Physically interacting with others creates an increased risk COVID transmission, but the major risk of transmission seems to come from sharing enclosed spaces, not the outdoors, and as long as everyone keeps to themselves, they can still safely enjoy the social interaction (as long as they aren't prone to overthinking everyday decisions ). Going for walks Going for walks carries very little COVID risk as long as you stay by yourself. It is slightly more dangerous than staying home though, as you might fall or hurt yourself in some way. Hanging out with friends on the beach This has a similar COVID risk as hanging out with friends in the park, but has slightly more safety concerns due to possible unpleasant encounters with crabs, jellyfish, and other ocean-going animals as well as the risks posed by extended UV exposure. There are also negligible risks of tsunamis, shark attacks, and encounters with other rare and deadly animals. Riding an electric scooter Electric scooters are scooters powered by electricity. They have increased in popularity recently, representing a form of lightweight transportation. If done by oneself, riding one has essentially no risk of coronavirus, but it is relatively easy to injure oneself when riding an electric scooter. Electric scooters have previously been mentioned in E Scooters . Renting an electric scooter This has a slightly higher COVID risk than riding your own scooter, as a previous renter could have left traces of the virus on the handle bars. In terms of general safety, it is the equivalent of riding your own scooter. Going down a waterslide Waterslides are common attractions at water parks and even some community pools. They are simply slides made faster by running water down them. They are not extremely dangerous, so long as the rider can swim or stand in the pool of water at the end of the slide, though it is definitely possible to injure oneself on one, both reasons perhaps contributing to it being the most dangerous of the "green" activities. As long as the water is properly filtered, any handrails are sanitized between riders, and riders waiting in line and in the pool are appropriately separated, there is little risk of catching COVID.
The medium-risk category of activities has medium COVID risk and also medium non-COVID risk.
Grocery shopping Going shopping for groceries involves entering a building in which others are present, including many workers who are present for hours-long shifts. The risk of catching COVID can be reduced by wearing face masks, barriers between staff areas and customer areas, and limiting customer densities. Grocery shopping while hungry Shopping for groceries while hungry does not carry any greater risk of catching COVID, but this shows a slightly increased non-COVID risk because people who go shopping while hungry tend to buy foods that are more expensive and less healthy. (Be advised that a study that popularized this "common sense" result has been retracted due to academic misconduct by its author, Brian Wansink .) Grocery shoplifting Shoplifting is taking goods without paying, so this activity is stealing groceries. It would expose you to the same amount of COVID risk as regular grocery shopping, but would additionally subject you to the risk of arrest and/or physical retaliation. And even if not detected, self-inflicted risks may result from your possibly apocryphal chosen method of subterfuge. While this activity is not very risky and is colored yellow, it is probably not a good idea. Riding a single rental scooter with a stranger This is a bad idea, as most rental scooters are designed for only one person. It would also expose you to a stranger, who might have COVID. The safety concern of riding with two people on a one-person scooter is not reflected in the comic. Going down a waterslide with a stranger This carries the same risks as going down a waterslide by yourself (as long as the waterslide is designed for two people), but exposes you to a stranger who could have COVID. Getting in a stranger’s car This can potentially be risky because driving is dangerous, and because murders have occurred in the past when people hitchhike. Getting into a stranger’s car would also expose you COVID, if they are carrying the virus. A car is a confined space, which is generally considered particularly bad from a COVID perspective. Playing lawn darts This activity poses little risk of COVID-19 transmission, as this game is usually played outdoors and players generally do not have to be close to play, so standard outdoor precautions can be taken. Lawn darts can pose a moderate risk of personal injury if played unwisely, which is why they have been banned in their original metal-tipped form in the United States and Canada. Climbing up a waterslide with a stranger This activity poses similar risk of COVID-19 transmission as the "going down a waterslide with a stranger" activity, but there is higher non-COVID risk because waterslides are meant to "go down", and going against the normal flow of water (or without ensuring that nobody else is sliding down) may result in injury. Getting in a stranger’s car uninvited This has similar risk as the normal "getting in a stranger's car", but there is higher risk of getting in a car uninvited , as you may be considered a hijacker or trying to steal the car, and thus the stranger may physically attack you. Doing skateboard tricks Performing tricks on a skateboard, especially if well away from other people, carries little risk of COVID-19 transmission, but carries a moderate risk of personal injury, especially when a manoeuvre does not go as intended and/or the rider unintentionally comes off the board to collide with the ground and/or obstacles. Riding a conveyor belt through the TSA x-ray machine This has relatively low risk of COVID infection, assuming the conveyor X-ray machine belt is sanitized; however, this is generally not legal or lawful and may get you in trouble with the TSA and other authorities, and you might get cancer because of the exposure to X-rays. Axe throwing contest Under normal circumstances, attending an axe throwing contest is a fairly risky endeavor, as an improperly thrown axe has a tendency to rebound off the target and could hit you (whether you are throwing or merely spectating). The global pandemic adds an additional layer of risk, as if you are engaged in an axe throwing contest you most are most likely in close contact with other people increasing your risk of catching COVID-19.
This is where things start getting serious. This category of activities has a higher COVID risk and same for the non-COVID risk.
Attending in-person classes While there is low risk to injure oneself in class, most schools have closed at the beginning of the COVID pandemic to prevent the virus from spreading through close proximity attendees. Some schools have switched to online classes, while others have reopened and reduced the number of students per classroom. The risk of transmission would then be greater when attending in-person than online class. Attending online classes while in class at a different school Continuing on the previous activity, participating to classes in both modes at the same time wouldn't augment risks associated with COVID, but could cause mental exhaustion or similar stress-related symptoms. If you are not properly paying attention to a class you should be attending, or have inexplicably gone to a classroom that you have no reason to be in, there are further risks that you will fall foul of a teacher's or school's authority. Getting a dental cleaning Superficial dental work by a trained practitioner is not particularly risky under normal circumstances, but COVID precautions in most sitations (keeping at a distance, using face coverings) aren't compatible with the requirements of one person leaning in close to another person's open mouth and prodding into it with various tools. Going on a Tinder date Meeting a stranger is very much the point of a Tinder date. Even if the intimacy only extends to drinks and/or a meal it is difficult to 'socially distance' while still being sociable. The meet-up intention, by one or both parties, might be expected to be even less distancing. As well as COVID risks from well-intentioned encounters, there are very basic risks (on the night or consequentially) to health and happiness that cannot be entirely ruled out. Getting a dental cleaning from a Tinder date It seems that the COVID risk from combining the above two activities do not significantly compound, but: the low likelyhood that an almost-random stranger is trained in dental hygiene adds to the non-COVID risks to impromptu dentistry; if they are qualified, they are unlikely to have turned up properly equipped; if they arrive equipped, without pre-arrangement, that may also be worrying. Doing skateboard tricks in a hospital Skateboarding in a confined indoor setting, or in rooms furnished with beds and equipment should be significantly more risky than in a skatepark or other typical venue. Possibly the immediacy of healthcare professionals and supplies makes the outcomes of any injuries less problematic. However, your exertions in the proximity of likely sources for the COVID pathogen is a significant issue in itself. Racing a scooter through a hospital with a mask on Your skateboard tricks may have been not particularly mobile, like Feet Stomps and other in-situ board-flips. If you're on a scooter ( foot- , electric- or combustion-powered ) that is deliberately traveling fast then you're living more dangerously. But at least you're wearing a mask, to slightly reduce the accompanying contagion risks... Racing a scooter through a hospital without a mask ...unless you aren't? Setting off fireworks in your car A car is an extremely confined space, and most fireworks need a lot of space once lit. It's not obvious if you are supposed to be in the car yourself, but there is at least risk of damaging the vehicle. Running and sliding headfirst into the pins at a bowling alley Intending to impact a bunch of 1.5kg pins, with your head doing the job normally done with a ~7kg ball, is not considered particularly risk-free. Being in a (normally) communal recreational facility, there may also be chances of contact with surfaces previously shed-upon by the exertions of a COVID-infected person. Stealing a stranger’s car This is illegal, may involve risk of physical confrontation and do you really want to get into that driver's seat without thoroughly disinfecting it first?
This is where things start getting really serious and even somewhat absurd. This category of activities has the highest COVID risk and the highest non-COVID risk.
Singing in church Being in a public gathering place such as a church is a significant exposure risk for COVID. While singing is normally harmless, in a church singing is often done without masks and in a group, further increasing exposure in this case. There have been cases of outbreaks traced to choir practices/performances , which motivated bans on singing in churches. However, the same article mentions that a fluid mechanics expert studied the airflows from singing and various instruments and came to the conclusion that "singing is quite safe". (Certain instruments were another matter.) N.b., the outbreaks traced to the four choirs mentioned in the article were all prior to widespread practice of prevention measures. Going to a restaurant Restaurants are another place where traffic and exposure to COVID is high, as well as being a confined space. Other accidents, such as fires, falls, or choking add to the non-COVID risk. Going to a bar Similarly to restaurants, bars are also a place where COVID-19 spreads often. Bars can be more crowded than restaurants, with people sitting or eating in closer proximity. However, since the customers are more likely to be drunk and to get into a fight, the non-COVID risk is increased. Even if not engaging in violence, people who are even slightly inebriated are more likely to ignore standard precautions like social distancing. Going to a party / Hosting a party Parties are a highly social activity which increases exposure to COVID. Hosting or attending a party carries similar COVID-related risk as both involve interactions with others, while accidents can occur at a party, contributing to the non-COVID risk. However, hosts may still have a slightly larger COVID-related risk as they are more likely to be touching objects or surfaces on which the virus is present as they tidy up during or after the party, and are likely in proximity of all the guests during the party. Going on a cruise Cruises have been a site where many people have contracted COVID , leading to the high COVID-related risk. However, there are other risks associated with cruises that are non-COVID related, such as the risk of the ship sinking, or other sicknesses, etc. Opening a kissing booth at a COVID testing site Opening a kissing booth at a COVID testing site is likely to attract others who may be sick with COVID (since they are likely at the testing site to be tested, or to have been in proximity to someone who is), and kissing them greatly increases the risk of transmission. Opening a booth close to a testing site may also lead to controversy, adding to the non-COVID related risk. (A kissing booth is a place where one can kiss the person at the stand as a prize or in exchange for money). Doing skateboard tricks in a bar As mentioned before, bars are places where it is very likely to contract COVID. Doing skateboard tricks in such a confined space also leads to a very large risk of injury. Skateboarding in a mosh pit on a cruise ship Mosh pits are often very densely crowded with people, so the risk of transmission is huge. Also, doing skateboard tricks in such a crowded area means one could get trampled, knocked over, run into other people and/or things, etc. Additionally, doing these on a cruise ship heightens the risk, as mentioned above. Getting a COVID test from a stranger at a crowded bar As mentioned before, bars greatly increase the risk of contracting COVID, and getting a test from a stranger means the test itself carries many non-COVID related risks coming from a malicious or incompetent stranger. Testing for COVID-19 involves taking a sample of mucus, saliva, or blood; any of these sampling apparatus may potentially be contaminated with COVID or other diseases if they are being improperly re-used. Bungee jumping while doing sword tricks While bungee jumping is an activity that is often not performed in a crowded area, meaning that it is difficult to contract COVID while doing so, the act of bungee jumping while doing sword tricks could lead to a host of injuries. Going down a waterslide on an electric scooter As mentioned before, if the waterslide is not used by many people, riding it is not likely to cause COVID. However, since waterslides contain water and electric scooters contain batteries (they don't mix well, safety-wise), many injuries may result. Also, some areas of the waterslide {i.e. tunnels) could result in you flying out of the electric scooter and injuring yourself further. Setting off fireworks in a stranger's car A car is a confined space, and so the risk of contracting COVID is higher. Setting off fireworks in cars also will cause many injuries to everyone in the car, and more injuries in reactions from the driver and/or other angry passengers. Axe catching contest The proximity to others during a contest means a higher risk of contracting COVID. As for the axe catching part, injuries are likely to occur from attempting to catch flying axes, especially if the catcher is inexperienced. Racing a scooter through a hospital with a mask over your eyes A hospital is a place where COVID patients often stay, leading to a higher risk of contracting the disease. Having a mask over one's eyes would do nothing to help reduce the risk. Riding a scooter while effectively blindfolded in an area that has many obstructions like a hospital can lead to many injuries. Winning a test-tube-eating contest at a COVID testing lab Eating many test tubes which potentially contain samples containing COVID will almost definitely lead to one contracting the disease, and eating glass will lead to numerous internal injuries which will then easily lead to death. The title text proclaims that "First prize is a free ticket to the kissing booth!" further increasing the risk.
[This comic is a graph plotting the safety risk of activities on the vertical axis and the risk of infection from COVID-19 on the horizontal axis. Lowest risks are in the upper left corner, and highest in the lower right. All activities are color coded green, yellow, orange, or red. A two way arrow labeled “non-COVID risk” points up and down to "high" and "low" labels on the left side of the graph. Another two way arrow labeled “COVID risk” points left and right to "high" and "low" labels on the top of the graph.
From left to right and top to bottom:]
Staying home & Video chats , Hanging out with friends in the park , Grocery shopping , Attending in-person classes , Singing in church Going for walks , Hanging out with friends on the beach , Grocery shopping while hungry , Attending online classes while sitting in class at a different school , Going to a restaurant Riding an electric scooter , Renting an electric scooter , Grocery shoplifting & Riding a single rental scooter with a stranger , Getting a dental cleaning & Going on a Tinder date , Going to a bar & Going to a party & Hosting a party & Going on a cruise Going down a waterslide , Going down a waterslide with a stranger , Getting in a stranger’s car , Getting a dental cleaning from a Tinder date , Opening a kissing booth at a COVID testing site Playing lawn darts , Climbing up a waterslide with a stranger , Getting in a stranger’s car uninvited , Doing skateboard tricks in a hospital , Doing skateboard tricks in a bar Doing skateboard tricks , Riding the conveyor belt through the TSA x-ray machine , Axe throwing contest , Racing a scooter through a hospital with a mask on & Racing a scooter through a hospital without a mask , Skateboarding into a mosh pit on a cruise ship Setting off fireworks in your car , Running and sliding headfirst into the pins at a bowling alley , Stealing a stranger’s car , Racing a scooter through a hospital with a mask on & Racing a scooter through a hospital without a mask [extends from previous row], Skateboarding into a mosh pit on a cruise ship & Getting a COVID test from a stranger at a crowded bar Bungee jumping while doing sword tricks , Going down a waterslide on an electric scooter , Setting off fireworks in a stranger’s car & Axe catching contest , Racing a scooter through a hospital with a mask over your eyes , Winning a test-tube-eating contest at a COVID testing lab


Slide Trombone

Explanation:
In this comic, Megan carries her "old" trombone , a brass musical instrument with a movable sliding piece used to change a musical note's pitch, which those offscreen apparently haven't caught sight of since the 90s (presumably the 1990s). These offscreen people don't suspect anything unusual of Megan's trombone until it turns out that it contains a water gun, which she uses to soak the other characters. It is unclear whether she has somehow hidden the water gun inside the trombone, has disassembled it to produce a hybrid trombone/Super Soaker device, or otherwise modified the trombone such that it can shoot water as a water gun would.
In the second panel, she is priming the water gun by pumping air into it, following the sequence of pump actions used for the Super Soaker. During the first "slide" action, the user pulls the grip towards themselves, increasing pressure within the water reservoir of the gun. During the second "hiss" action, this grip is pushed away; a valve prevents air leaving the chamber, though a small amount usually leaks out. Part of the joke here is that a slide trombone also has a slide mechanism, held in a similar way as that of the Super Soaker, but which serves a completely different purpose. In the case of the trombone, when the slide is extended, the total length of tubing between the mouthpiece and the bell is extended, thereby lowering the pitch of the sound that is produced (there is, however, no comparable air chamber). This similarity between the two devices enables Megan to use the trombone's slide as if it were a Super Soaker's.
In the third panel, she presses the trigger, causing the compressed air within the water reservoir to push water from it at high speed, hitting the off-screen targets. One cries out in surprise, while the other expresses the realization of what had happened to their lost Super Soaker (that Megan had taken it as an alteration to her trombone).
In the title text, Megan asks those offscreen about the CPS 2000 , a water gun which, as is mentioned, was powerful but too powerful, causing injuries to those shot by it and allegedly leading to its discontinuation. Megan then, in connection with her previous question about the Super Soaker, asks to borrow a tuba, most probably to hide the CPS 2000 water gun inside. Her reasoning behind needing this tuba seems to be that the CPS 2000 is seemingly larger than the Super Soaker originally stored in Megan's trombone and thus would require a larger vessel (this use of the tuba may be cause for loss of friendship with an experienced player).
The CPS 2000 referenced by Megan was developed primarily by Lonnie Johnson (inventor) and Bruce D'Andrade for Larami 's Super Soaker product line. The "CPS" within its name refers to the " Constant Pressure System " used in certain water guns (its technology can be seen in this patent by Bruce D'Andrade). In this system, a rubber bladder within the water gun is pressurized by the user's pumping action, which draws water from a reservoir and pushes it into the pressure chamber, filling the bladder like a balloon. Once the desired volume of water is stored within the toy, the water can be released by means of a spring-loaded trigger and valve system. Upon release, the rubber bladder pushes the water out of the pressure chamber and out of the front nozzle, hitting whatever targets the user desires it to. The "constant pressure" of the CPS's name refers to the fact that the bladder will exert the same pressure on the water throughout the shot, ensuring consistent power and range, as opposed to air pressure Super Soakers, whose power will die off during the shot as the pressurized air within the pressure chamber expands, expelling the water but reducing the pressure in the toy.
The Super Soaker that Megan uses in this comic is also referenced in 220: Philosophy and 517: Marshmallow Gun . If the water gun featured in this comic is the same as that depicted in previous comics, it would likely be a Super Soaker 50 , the first widely available pressurized water gun. It could also be the less common but earlier model the Power Drencher or the later SS 50 Classic Series , Super Soaker S.E. , or the 20th anniversary SS 50 rerelease .
[Megan walking along carrying a trombone.] Offpanel voice #1: Hey, her old trombone. Offpanel voice #2: Cool, I haven't seen that thing since the 90s.
[Four quick shots of Megan moving the trombone's slide back and forth. It makes sound, but not like an ordinary trombone.] FX: Slide FX: Hisss FX: Slide FX: Hisss
[Megan does something else with the trombone, and it shoots water at the offpanel observers.] FX: Pshhhhh Offpanel voice #1: AUGH! Offpanel voice #2: So that's where my Super Soaker went.


Photo Deposit

Explanation:
Some mobile banking apps allow users to deposit checks through the app, by photographing the check and entering the relevant information. The comic parodies this imagining a bank that allowed you to "deposit" banknotes via a mobile app, by taking photos of them. The caption implies that this attempt is predictably disastrous, as it's shut down within six hours.
Checks are essentially documents instructing a bank to disburse funds from a given account to a specified recipient, hence electronic transfers make sense: the recipient's bank can transfer the image to the depositor's bank and the funds can be transferred between the two. The check could only be deposited by the recipient, and any attempt to deposit the check repeatedly would be refused (and potentially subject the recipient to legal action).  By contrast, cash functions as a bearer instrument , where physical possession of the banknotes effectively constitutes possession of the funds. Hence, depositing cash electronically would make little sense, as the depositor would still have the notes (and therefore the money), and the bank would not. Such a transaction would enrich the depositor at the expense of the bank.
The title text states that the app recognizes the serial numbers on the bills and prevents users from depositing them multiple times. However, this would not solve the fundamental problem. Clients could still deposit all of their cash and retain ownership of it.  And they could then exchange those bills for different ones and deposit the new bills, repeating the process indefinitely (which explains Cueball's comment about "a lucrative six hours"). It is possible that Megan and Cueball are deliberately depositing the same bills to each of their accounts, given their close proximity.
The only way such a system could work is if every entity that accepted cash payments or deposits operated from a common database, functioning in real-time, which kept track of each transaction, and disallowed any further use of that specific bill. This would have the ultimate impact of making cash virtually useless, as once every bill had been spent once, all future transactions would need to be electronic (unless there were a system in place to physically distribute the appropriate bills to the appropriate people, which would defeat the entire point). Such a system is essentially the basis for cryptocurrency , which uses a crowd-sourced system to track the movement of money. But such a system would require virtually universal acceptance in a given country, and could not be implemented by a single bank.
In addition, the system would be highly vulnerable to counterfeiting . Common anti-counterfeiting measures include using distinctive materials and fine details, both of which are difficult to duplicate well enough to fool a human. Smartphone cameras, on the other hand, can't distinguish texture and may not have sufficient resolution to make out that level of detail. Counterfeiters could produce and deposit an almost unlimited number of bills, then destroy them, leaving little evidence of their crime.
As a result, this system would be inherently unworkable, and the party that would suffer from it would be the bank that implemented it in the first place. Which makes it realistic that, if a bank were to implement such a scheme, they'd very quickly realize their error and put an end to it. This is why the bank took down this system.
[Megan is holding a banknote up in one hand, while she is taking a picture of it with her smartphone held in the other hand. A starburst near the phone indicates the sound this makes. She is standing with her back to Cueball, who faces away from her. He is holding a banknote down by his side in one hand, while he is looking at his smartphone which he holds up in the other hand. From Cueball's phone there is a starburst from which a line goes up above him to indicate what is on the screen.] Megan's phone: Click Cueball's phone: Deposit accepted!
[Caption below panel:] After a lucrative six hours for us, our bank removed the new feature in their app that let you deposit cash by taking a picture of it.