explain xkcd - User contributions [en]

2572: Alien Observers

2022-01-24T20:55:19Z

Ltmauve: Bulked out the explaination.

{{comic
| number = 2572
| date = January 24, 2022
| title = Alien Observers
| image = alien_observers.png
| titletext = ALERT: Human 910-25J-1Q38 has created a Youtube channel. Increase erratic jerkiness of flying by 30% until safely out of range.
}}

==Explanation==
{{incomplete|Created by a BLURRY MARTIAN SPACECRAFT- Please change this comment when editing this page. Do NOT delete this tag too soon.}}
There is speculation by many people that there could be some form of extraterrestrial life observing us, hovering around in various flying vehicles or perhaps using some form of giant telescope. These claims are often backed up by blurry pictures which claim to be of alien vehicles. In this comic, the joke is that the aliens are deliberately creating unverifiable sightings. However, with [[1235:_Settled|most people now carrying a camera with them all the time]], a sighting that would be unverifiable just by eyewitness testimony could now be captured by a smartphone camera.

This means that in order for the aliens to keep creating unverifiable sightings for humans, they must keep track of what camera capabilities each human has, leading to different distance restrictions for each human, as seen in the diagram.

In the title text, the aliens note that one particular human now has a youtube account, meaning they are likely to record video instead of attempting to capture still images. This means that the alien craft used to create the sighting must behave as erratically as possible, in order to avoid bein identified.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:Alien 1: Human 38XT11-B-C54  just bought a new phone with a 10x zoom, so we have to expand our restricted flight zone by 1,800 meters to keep our ship blurry.
:Alien 2: Seriously? Didn't they '''''just''''' upgrade?
:Alien 1: I know, I know...

{{comic discussion}}

2514: Lab Equipment

2021-09-12T20:32:34Z

Ltmauve: Nd:YAG lasers are plural.

{{comic
| number = 2514
| date = September 10, 2021
| title = Lab Equipment
| image = lab_equipment.png
| titletext = I've been working on chocolate bar annealing techniques to try to produce the perfect laser s'more. Maybe don't mention that on the grant application though.
}}

==Explanation==
{{incomplete|Created by a LASER TOASTED MARSHMALLOW - Please change this comment when editing this page. Do NOT delete this tag too soon.}}

This comic claims that in every science lab, there exist some piece of equipment that sticks around less for being useful, and more because the scientists and technicians just think the device is really cool.

The comic presents a laboratory containing equipment for analysis of substances. While giving a tour [[Ponytail]] shows a spectrometer — a device that examines light emitted from or passed through samples to fingerprint emission or absorption lines in the mix of light. Next she shows the "Nd:YAG" lasers. It is unknown if the multiple lasers are for redundancy or if they have different specifications and are for different tests. "Nd:YAG" stands for {{w|Nd:YAG_laser|neodymium-doped yttrium aluminum garnet}}; it is a lasing medium commonly used in lasers. Lastly she shows off a decommissioned laser not used in experiments, but rather for toasting marshmallows. Misuse of expensive, high-end equipment for heating junk food can lead to important breakthroughs. For example, the microwave oven was invented when {{w|Percy Spencer|someone working on microwave radar}} accidentally melted a candy bar.

Contrariwise, laser etching and cutting is commonly available in hackerspaces or makerspaces, and toasted marshmallows can be made with high-definition shapes and textures, although a normal laser cutter may introduce toxic compounds to the food. Food products have also been fed through 3d printers in place of plastic filament, and the printer will heat and plot them into arbitrarily shaped volumes. Engineering research labs will also have some of these tools, but for chemical labs they could be a rare delight.

The title-text probably relates to the critical heating required for proper {{w|Chocolate#Tempering|tempering}} of chocolate, as arbitrarily (re)melted chocolate loses various qualities of {{w|mouthfeel}} from the crystalline sugary structures that manufacturers engineer into them. In this case it is described as {{w|Annealing (materials science)|annealing}}, which is more commonly a heat-treatment technique more used to influence the nature of the crystals in metals for structural reasons. This is done when jewelry is molded from molten metal, but more likely Randall means a use of annealing in scientific research that no editors to this article have been aware of and added yet.

Annealing is also used in {{w|Annealing_(glass)|glass production}}. As is {{w|Tempered glass|tempering}}, to create safety glass that is stronger and yet breaks into 'nicer' fragments when it does fail.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}

:[Ponytail and Cueball are talking to each other. They are standing between two tables with equipment scattered on them, including lens-stands and eye-protection. Ponytail is pointing away from Cueball towards an unidentified off-panel location.]

:Ponytail: The spectrometer is over here, the Nd:YAG lasers are over here,
:Ponytail: and in the corner is a laser that turned out not to be useful for us, but we keep it because it's fun to toast marshmallows with it.

:[Caption below the panel]
:Every lab in every field has some piece of equipment like this.

{{comic discussion}}
[[Category:Science]]
[[Category:Food]]

2466: In Your Classroom

2021-05-22T02:50:36Z

Ltmauve: Quasar notes, description of "Weirdness" and "Danger"

{{comic
| number = 2466
| date = May 21, 2021
| title = In Your Classroom
| image = in_your_classroom.png
| titletext = Ontology is way off to the left and geography is way off to the right.
}}

==Explanation==
{{incomplete|Created by a QUASAR IN YOUR CLASSROOM. The table is still a work in progress. Do NOT delete this tag too soon.}}
Randall has created a chart about school courses, and the event the subject of the class appears in the classroom. The chart compares how normal an example of the topic itself would be if it appeared in the classroom, and how dangerous it would be if said example appeared in the classroom.

"Weirdness" on the chart starts at 0% on the left and moves to 100% on the right. "Danger" starts at 0% at the top and moves to 100% at the bottom.

{| class="wikitable"
|+Breakdown of Subjects
|-
!Course Topic
!Weirdness
!Danger
!Explanation
|-

!scope=row|Atmospheric Physics
|0%
|0%
|The presence of atmosphere in the classroom is quite common, as humans require the presence of an atmosphere to remain alive, and cannot learn while dead.{{Citation needed}}
|-

!scope=row|Ethics
|25%
|0%
|Ethical thinking and behavior are widely considered good and should normally be present in education, but are sadly not universal.
|-

!scope=row|Education
|
|
|Learning usually goes on in classrooms, so education as a concept is both being learned about and present in the form of learning itself.
|-

!scope=row|Bibliography
|
|
|A bibliography is a list of sources, and students should ideally learn to cite their sources. Presumably, this would be a bibliography at the end of a school paper about bibliographies.
|-

!scope=row|Human Physiology
|
|
|This comic assumes that there are humans learning in the classroom, which was true at the time this comic was published. However, as of 2038 the Earth has been overtaken and education is forbidden for mere mortals.
|-

!scope=row|Public Speaking
|
|
|Some classes require students to present things in front of the class, which is likely a requirement in a public speaking class. Thus, public speaking itself would be present in the class.
|-

!scope=row|Architecture
|
|
|All buildings can be considered architecture, and most classes take place in buildings. This comic also refers to a class''room'', which is a room, and therefore considered architecture.
|-

!scope=row|Library Science
|
|
|Library science is concerned with the organization of knowledge, and is useful for finding information. Many classes require research papers that require the use of books and other sources of information to complete them.
|-

!scope=row|Furniture Design
|
|
|Most rooms have furniture,{{Citation needed}} so this would probably be present in a classroom
|-

!scope=row|Culinary Arts
|
|
|
|-

!scope=row|Ergonomics
|
|
|Ergonomic equipment and workspaces promote comfort and efficiency, while non-ergonomic ones may be unpleasant, unhealthy, or even immediately dangerous.
|-

!scope=row|Botany
|
|
|
|-

!scope=row|20th Century Authors
|
|
|
|-

!scope=row|Exobiology
|
|
|Exobiology is the study of extraterrestrial life. This would mean that an alien lifeform was in the classroom.
|-

!scope=row|21st Century Authors
|
|
|
|-

!scope=row|19th Century Authors
|100%
|10%
|Like other authors, the class would benefit from having an actual author show up, but this would be extremely weird since no 19th century author is still alive.
|-

!scope=row|Paleontology
|
|
|
|-

!scope=row|Robotics
|
|
|
|-

!scope=row|Martian Soil Chemistry
|
|
|
|-

!scope=row|Tourism
|
|
|
|-

!scope=row|Child Psychology
|
|
|
|-

!scope=row|Entomology
|
|
|
|-

!scope=row|Occupational Therapy
|
|
|
|-

!scope=row|Hydraulic Engineering
|
|
|
|-

!scope=row|Pest Control
|
|
|
|-

!scope=row|Foodborne Illness
|
|
|
|-

!scope=row|Criminal Law
|
|
|
|-

!scope=row|Physiology of Stress
|
|
|
|-

!scope=row|Oncology
|
|
|
|-

!scope=row|Ornithology
|
|
|
|-

!scope=row|Animation
|
|
|
|-

!scope=row|Petroleum Geology
|
|
|
|-

!scope=row|Highway Engineering
|
|
|
|-

!scope=row|Toxicology
|
|
|
|-

!scope=row|Hematology
|
|
|
|-

!scope=row|Hostage Negotiation
|
|
|
|-

!scope=row|History of Siege Warfare
|
|
|
|-

!scope=row|Trauma Surgery
|
|
|
|-

!scope=row|Volcanology
|
|
|
|-

!scope=row|Quasar Astronomy
|100%
|100%
|Quasars are distant astronomical objects that release large amounts of energy. Not only would the power of a quasar destroy the classroom (as well as the building the classroom is in, the town the school is in, and the entire planet Earth,) quasars are too large to fit inside any known classroom. For example, [https://en.wikipedia.org/wiki/ULAS_J1342%2B0928 ULAS J1342+0928] has a mass of 8*10^8 solar masses. This means the event horizon of the black hole is almost 16 AU in radius, and this size does not include the accretion disk.
|-

!scope=row|Ontology (Title Text)
|<0%
|?
|
|-

!scope=row|Geography (Title Text)
|>100%
|?
|

|}

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}

:[Caption above scatter plot with labeled axes]
:Caption: The thing you study just showed up in your classroom! That's...
:Upper y-axis label: Good
:Lower y-axis label: Bad
:Upper x-axis label: Normal
:Lower x-axis label: Weird

:[First quadrant (left to right, top to bottom):]
:20th century authors
:Exobiology
:21st century authors
:19th century authors
:Robotics
:Paleontology
:Martian soil chemistry
:Child psychology
:Tourism
:[Second quadrant]
:Atmospheric physics
:Ethics
:Education
:Bibliography
:Human physiology
:Public speaking
:Architecture
:Library science
:Furniture design
:Culinary arts
:Ergonomics
:Botany
:[Third quadrant]
:Entomology
:Occupational therapy
:Hydraulic engineering
:Pest control
:Foodborne illness
:Criminal law
:Physiology of stress
:Oncology
:[Fourth quadrant]
:Ornithology
:Animation
:Petroleum geology
:Highway engineering
:Toxicology
:Hematology
:Hostage negotiation
:History of siege warfare
:Trauma surgery
:Volcanology
:Quasar astronomy

{{comic discussion}}
[[Category:Charts]]

2466: In Your Classroom

2021-05-22T01:31:51Z

Ltmauve: Created table, filled in names and first entry

2413: Pulsar Analogy

2021-01-20T20:47:07Z

Ltmauve:

{{comic
| number = 2413
| date = January 18, 2021
| title = Pulsar Analogy
| image = pulsar_analogy.png
| titletext = The #2 cause of astronomer hand injuries is trying to do vector math when the second axis points off to the right.
}}

==Explanation==
{{incomplete|Created by an INJURED ASTRONOMER - more on the injury part in the explanation. Please mention here why this explanation isn't complete. Do NOT delete this tag too soon.}}

{{w|Pulsar}}s are a kind of old shrunken fast-spinning star which no longer shine in all directions but instead produce beams of radiation out their magnetic poles that blip by us as they spin. Ponytail, an astronomer in this comic, explains a pulsar's fast rotation with an analogy about a tape measure retracting. Since the analogy does result in something that spins, the reader might think that, while they don't immediately see how it helps in understanding pulsars, they're willing to reserve judgment to see what is then done with the analogy; Cueball's response may suggest this sort of wait-and-see attitude. However, the analogy is likely to be useless or misleading, as the tape measure starts to rotate because the retracting tape is not moving only in a radial (in/out) direction. As a star collapses into a pulsar, its natural rotation rate is greatly amplified by its shrinking moment of inertia.

Further elaborations of the analogy, rather than clarifying matters, are successively more surreal. More misleading than the tape-measure is the idea of a laser measure being "exactly" like the emissions of a pulsar, which, although both pulse (and both for the same reason of holding pulsed light representation on our timeline in view of our deities), are produced in entirely different ways and are at best simply helping the mind hold the concept.

When a tape measure retracts, the part of the tape outside the tape measure is not going directly towards the tape measure's center but rather towards a hole in the side. This means the tape possesses some angular momentum relative to the tape measure. In addition, when the tape measure retracts, the part of the tape inside the tape measure rotates around a spool (which pulls the part of the tape outside the tape measure inside), so it also has angular momentum relative to the tape measure. When the tape is completely retracted, the tape can no longer rotate relative to the tape measure. Because of the conservation of rotational momentum, the tape measure will no longer spin at this point.

While pulsars also rotate quickly due to the conservation of angular momentum, the exact mechanism is completely different. Pulsars are formed when stars collapse due to no longer performing enough fusion to produce enough heat and energy to cancel out gravity. This causes the star to contract, which causes its mass, on average, to be closer to its axis of rotation, which causes the rotational inertia (also called the moment of inertia) to decrease. If the star's angular velocity stayed constant, this would cause the angular momentum to decrease, so the star's angular velocity must increase in order to offset the decrease in rotational inertia, i.e. the star (which is now a pulsar) spins faster. This method requires an initial rotation, which comes from the star. (The star's rotation comes from the dynamics of the gas cloud which forms the solar system in the first place.)

Some tape measures have a built-in {{w|laser line level}} and others have a built-in {{w|laser rangefinder}}. Pulsars emit electromagnetic radiation out of their magnetic poles, which is similar to a laser, but unlike the laser of a tape measure, the pulsar beam is emitted through the axis of the magnetic field. The pulsing nature of a pulsar comes from when the axis of rotation is not precisely aligned with the axis of the magnetic field, and the location of the viewer as the beam sweeps by. On the other hand, the laser of a laser rangefinder is pulsed by microcircuitry so as to measure distance by the time a reflection is received.

The title text mentions the {{w|right-hand rule}} in three-dimensional space. In a typical 3D coordinate system the Y-axis will point counterclockwise to the X-axis when looking down from the positive Z-axis. In academia, students are often taught to remember a number of mathematical conventions by using their actual physical right and left hands to align the axes. When the axes are in a different order, the left hand can be used in stead of the right, but there are a number of common operations in engineering and physics that use the {{w|cross product}} in systems where the first axis might point in absolutely any direction relative to the viewer. Using the hand rules, the thumb is aimed along the first axis, the forefinger along the second, and the middle finger along the third -- all at ninety degrees. So, when the first axis points off to the right, the right wrist is torqued to its full extension to make the thumb point that way while the other two fingers don't. During exams students can be seen performing this feat. People who learn cross products early in their life may develop other approaches for remembering these things, that don't stretch the hands as much, but then adopt the common approach once taught it.

==Transcript==
:[Cueball and Ponytail are standing next to each other.]
:Cueball: Why do pulsars spin so ''fast?''
:Ponytail: Hmm, let me think of an analogy...

:[A tape measure is retracting above Ponytail's head. To the right of her head, a tape measure is spinning rapidly.]
:Retracting tape measure: ''zzzzzzzzzzzzzzz''
:Spinning tape measure: SNAP
:Ponytail: You know how when you retract a tape measure and let go, it leaves it spinning?
:Ponytail: It's like that.
:Cueball (off-panel): Oh, I see.

:[A tape measure with a laser instead of a measuring tape is spinning slowly.]
:Cueball (off-panel): And if the tape measure is the kind with a laser level, that's the beam of radiation?
:Ponytail (off-panel): Exactly!

:[Cueball and Ponytail are walking next to each other in silhouette.]
:Ponytail: And when the tape whips around and smacks your hand, that's the neutron degeneracy shockwave.
:Cueball: Sounds painful!
:Ponytail: Top cause of astronomer hand injuries.

{{comic discussion}}
[[Category:Astronomy]]
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Ponytail]]

2413: Pulsar Analogy

2021-01-19T02:32:27Z

Ltmauve: /* Explanation */

Talk:2413: Pulsar Analogy

2021-01-19T02:29:54Z

Ltmauve:

I tried applying the right-hand-rule with the y-axis pointing to the right. :( I hurt my hand.
[[User:Avitzur|Avitzur]] ([[User talk:Avitzur|talk]]) 23:22, 18 January 2021 (UTC)
:Rotate your paper then do the right hand rule :)
:Hand joint exercises. Gentle motions with the wrist bent backwards, and bent forwards; 3-5 circles in both directions and both postures, twice a day. [[Special:Contributions/162.158.62.41|162.158.62.41]] 00:48, 19 January 2021 (UTC)
[[Special:Contributions/172.69.35.149|172.69.35.149]] 23:38, 18 January 2021 (UTC)

The analogy doesn't seem to be inaccurate in the way currently indicated. In both cases (tape measure and pulsar), conservation of ''angular'' momentum is what produces the result. With the tape measure, a small fast-spinning thing turns into a large slow-spinning thing; the opposite happens with a pulsar. [[Special:Contributions/172.69.35.150|172.69.35.150]] 00:05, 19 January 2021 (UTC)
:Isn't a tape measure bigger, not smaller, and slow-spinning, not fast-spinning, when it is elongated? This is very confusing. Thinking of how pulling the tape out stores energy. [[Special:Contributions/162.158.62.41|162.158.62.41]] 00:49, 19 January 2021 (UTC)
::A tape measure starts off not spinning. It's the acceleration of the tape as it moves in that starts the rotation, because the motion of the tape measure is not precisely radial. Same principle, different problem. [[User:Ltmauve|Ltmauve]] ([[User talk:Ltmauve|talk]]) 02:29, 19 January 2021 (UTC)

2413: Pulsar Analogy

2021-01-19T02:25:37Z

Ltmauve:

2413: Pulsar Analogy

2021-01-18T23:38:13Z

Ltmauve:

{{comic
| number = 2413
| date = January 19, 2021
| title = Pulsar Analogy
| image = pulsar_analogy.png
| titletext = The #2 cause of astronomer hand injuries is trying to do vector math when the second axis points off to the right.
}}

==Explanation==
{{incomplete|Created by a PULSAR. Please mention here why this explanation isn't complete. Do NOT delete this tag too soon.}}

Ponytail, an astronomer in this comic, explains a pulsar's fast rotation with an analogy about a tape measure retracting. This analogy is inaccurate, as the tape measure starts to rotate because the spring imparts a torque on the body of the tape measure.

However, pulsars actually rotate at their extreme speeds because of the conservation of momentum. As a star collapses into a pulsar, its natural rotation rate is greatly amplified by its shrinking moment of inertia.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}

{{comic discussion}}

2407: Depth and Breadth

2021-01-05T03:07:30Z

Ltmauve: Change to alt-text explaination

{{comic
| number = 2407
| date = January 4, 2021
| title = Depth and Breadth
| image = depth_and_breadth2.png
| titletext = A death-first search is when you lose your keys and travel to the depths of hell to find them, and then if they're not there you start checking your coat pockets.
}}

==Explanation==
{{incomplete|Created by a LOAF OF BREAD. Please mention here why this explanation isn't complete. Do NOT delete this tag too soon.}}

{{w|Tree (data structure)|Tree structure}}s are one of the most common data structures used in computer science. The common ways of enumerating items arranged in a tree is either {{w|Depth-first search|depth-first}}, or {{w|Breadth-first search|breadth-first}}, which are depicted accurately in the comic. Randall humorously combines the words, to produce "brepth-first", "deadth-first", "bread-first", and "death-first" search algorithms.

Depth-first search explores down the full branches of the tree before exploring the higher levels of the tree. The "opposite" of this is breadth-first search, which explores each level of the tree at a time. This type of tree structure was already discussed as inefficient for human needs in [[761: DFS]].

In the "brepth-first" algorithm, a depth-first and a breadth-first search are hybridized where the left-most node is visited more frequently than the right node, but the right node is still visited. This might be good for exploring data that is loosely but not strictly weighted to the left, or where data in deeper nodes needs some time to be loaded before it can be used. As implied by [[761: DFS]], this might be the best algorithm for a human to employ, where one can be just as knowledgeable as needs be in just enough topics to hold conversation or be quick to act in case of danger during a date.

The nature of the "deadth-first" algorithm is unclear and inefficient, since it searches the same nodes multiple times before moving to an entirely different region of the tree. It might be useful in a context where examining nodes has some probability of returning a noisy or incorrect result, such as searching for small objects that may be overlooked.

The bread-first search is taken literally. Bread is searched for first. Since the computer user now has already met their want to find bread, the computer has no reason to explore the tree at all.

The title text introduces a "death-first" search, in which the user explores what it is like to be dead, before considering anything else. Specifically, the title text refers to hell, which calls to mind the adventures of Dante Alighieri in {{w|Inferno (Dante)| his ''Inferno''}}, and is a less likely place for keys to be left than one's coat pockets {{Citation needed}}. A much more pleasant death-first algorithm might be to skip hell and purgatory and search heaven first, perhaps multiple times (which in itself would be a use of the deadth-first approach).

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}

{{comic discussion}}
[[Category:Programming]]
[[Category:Food]]

2366: Amelia's Farm Fresh Cookies

2020-10-01T05:17:21Z

Ltmauve: Description of why the cookies were bad.

{{comic
| number = 2366
| date = September 30, 2020
| title = Amelia's Farm Fresh Cookies
| image = amelias_farm_fresh_cookies.png
| titletext = I told her I'd take her address off the packaging if she'd stop submitting anonymous food safety complaints about my bakery to the health department, but she sent me a note that said NO DEAL along with an extra large batch of cookies.
}}

==Explanation==
{{incomplete|Created by AMELIA'S GRANDMA. Please mention here why this explanation isn't complete. Do NOT delete this tag too soon.}}

The comic portrays the back side of a box of cookies (evidenced by the {{w|nutrition facts}}-style table on the left side). Many brands have a romanticized origin story on their packaging explaining the name or how they have a secret ingredient. Instead, this brand's origin story is a deliberate revenge on Amelia's part towards her grandmother, because Amelia never liked her grandmother's cookies for the reasons explained.

The cookies were apparently very fragile and crumbly. They also had "gooey exteriors and slightly crisp exteriors." Normally items bake from the exterior in, so how the interior had gotten crisp and the exterior hadn't is not explained. The grandmother's cookies also had a "mysterious gritty texture" that would be unpleasant.

To complete her revenge, the "story" contains the grandmother's address. Creating false addresses for their mascots is often used as a publicity stunt for children to write testimonies to the brand's PR or marketing department. However, here it appears to be Amelia's actual Grandma's actual address, the goal being for her to receive thousands of letters on a regular basis about how her granddaughter's cookies are so great, while jabbing "unlike yours!"

In retaliation, Amelia's grandmother has started submitting (presumably bogus) food safety complaints about Amelia's bakery to the health department in a ploy to overburden the bakery with unnecessarily frequent inspections. At one point Amelia eventually decided to offer a truce, which her grandmother emphatically rejected, underscoring it by sending Amelia an extra-large batch of the cookies she knows Amelia hates.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}

:[What looks like the back of a package of cookies is shown.]

:[Top left: Product logo.]
:'''Amelia's''' Farm-Fresh ''Cookies''
:[Parts of an oval surround the logo]

:[Middle left: What appears to be a standard Nutrition Facts panel, though the details are illegible squiggles]

:[Bottom left: What appears to be an ingredients list, though the details are illegible squiggles, and a few other squiggles]

:[Right side:]
:''Our Story''
:Growing up on my grandma's farm, I spent so many cozy mornings in the kitchen, watching her take trays of fresh-baked cookies from the oven.
:Her cookies were just ''awful''.
:She used the finest ingredients. Eggs straight from the coop, stone-ground flour, hand-churned butter. But she squandered them. It's so sad. She told me I was too picky, but I know what cookies are supposed to taste like.
:When I started a bakery, I vowed not to repeat her mistakes. These cookies won't fall apart in your hands. They have gooey centers, and slightly crisp exteriors, not the other way around, ''Grandma''. There's no mysterious gritty texture. Why would there be?
:If you enjoy these cookies, please write to my grandma to let her know.
:Thanks!
:''Amelia''

:[A partially legible squiggled out address appears at the bottom left of the Our Story part of the box.]
:Ms W[illegible] M[illegible]
:1[illegible] A[illegible] Ln
:O[illegible], FL [illegible]

{{comic discussion}}
[[Category:Food]]

2335: Photo Deposit

2020-07-21T00:41:20Z

Ltmauve: Corrected mention of single person destabilizing economy.

{{comic
| number = 2335
| date = July 20, 2020
| title = Photo Deposit
| image = photo_deposit.png
| titletext = It's okay, they scan the serial numbers and make sure you can't deposit the same bill more than once.
}}

==Explanation==
{{incomplete|Created by a BANKNOTE PHOTOCOPIER. Please mention here why this explanation isn't complete. Do NOT delete this tag too soon.}}
Some mobile banking apps allow users to deposit {{w|Cheque|check}}s through the app. The comic parodies this by "depositing" cash via a mobile app. This leads to duplication of the money, since you could then spend the bill and still have its value (in your account). Checks cannot be duplicated by this method, as a check is, in some ways, an instruction for one bank to send money to another.

The title text states that the app recognizes the {{w|serial number}}s on the bills and prevents users from depositing them multiple times. It is unknown if multiple users can deposit the same bills. If multiple users are allowed to deposit the same bills, then widespread fraud would certainly occur from users attempting to collaborate by sharing bills. It is possible that Megan and Cueball are attempting this given their close proximity. If users are not allowed to deposit the same bills, widespread frustration would inevitably ensue as users would be frustrated to learn that they could not deposit many of their bills. Thus such a system would run into trouble either way. Furthermore, even with a user being unable to deposit the same bills twice, they will still double the value of their cash, as they have a spendable copy of it in their account and they still have the original which could be spent outside the bank system.

In addition, the system would be highly vulnerable to {{w|Counterfeit money|counterfeiting}}. When depositing or paying with cash, the texture of cash is different from normal paper and therefore is a method to detect counterfeits. (In the U.S., bill are made from a sort of cloth. Other nations such as Canada and the U.K. have started introducing plastic banknotes.) In contrast, the low-resolution camera of a smartphone could be fooled by a printed image, or possibly even an image on a screen, effectively enabling an attacker to clone an arbitrary banknote without actually possessing it. With image editing software (and reprinting, if the app will not accept a screen image of a bill) it would be possible to deposit a large number of bills. However, this would not allow a single person to destabilize the economy. ([https://what-if.xkcd.com/23/ WhatIf #23])

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:[Megan is holding a (cash) bill in one hand, and is taking a picture of it with her smartphone with her other hand. Cueball is holding a (cash) bill in one hand, and is looking at his smartphone in his other hand.]

:Cueball's phone: Deposit accepted!
:Megan's phone: click
:[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.

{{comic discussion}}
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Cueball]]

2335: Photo Deposit

2020-07-20T20:35:25Z

Ltmauve: Initial version.

2335: Photo Deposit

2020-07-20T20:29:51Z

Ltmauve: Started article

2319: Large Number Formats

2020-06-15T17:42:00Z

Ltmauve: period -> comma, exponential growth of size of set theory method.

{{comic
| number = 2319
| date = June 12, 2020
| title = Large Number Formats
| image = large number formats-2.png
| titletext = 10^13.4024: A person who has come back to numbers after a journey deep into some random theoretical field
}}

==Explanation==
{{incomplete|Please mention here why this explanation isn't complete. Do NOT delete this tag too soon.}}
This comic shows what the way you write large numbers says about you. Different people use different methods to express large numbers. And this comic claims it can tell something about you based on the way you format large numbers. In this way, the comic is similar in idea to [[977: Map Projections]], where it was your choice of map projections that could tell something about you.

See the [[#Table of types|table]] below for each of the 10 different ways to express large numbers, plus the 11th mentioned in the title text.

The number used as an example is the [https://www.wolframalpha.com/input/?i=Distance+to+Jupiter+in+inches approximate distance] from the planet {{w|Earth}} to the planet {{w|Jupiter}} as of the release day of the comic on June 12th 2020, in {{w|inch|inches}} (1 inch = 2.54 cm).

Two days after the release of the comic the following text could be found on [https://theskylive.com/jupiter-info Jupiter info] on [https://theskylive.com/ The Sky Live].
:The distance of Jupiter from Earth is currently 640,084,108 kilometers, equivalent to 4.278698 Astronomical Units. Light takes 35 minutes and 35.0908 seconds to travel from Jupiter and arrive on Earth.

64,008,410,800,000 cm / 2.54 inches/cm = 25,200,161,732,283 inches - much less than the number used in the comic. But Jupiter's distance to Earth changes quite quickly, and was decreasing at the time of the release of the comic.

According to a graph of the distance as a function of time on The Sky Live, the distance on the release day was 643,1 million km. This will give 25,313 which the used number will round to.

The used number 25,259,974,097,204 is equivalent to 641,6 million km. On June 13th the distance is given as 641,7 million km in the graph on The Sky Live, very close to the number used. As this was the day after the release of this comic, it seems like [[Randall]] used a different distance than the exact one for the release day. He may have also used an average for June which would be 642 million km based on the average of the distance on June and July 1st.

==Table of types==
{| class="wikitable"
|-
! Number
! Type of person
! Notes
|-
| 25,259,974,097,204
| Normal Person
| This is the full number, 25259974097204, written out in the normal fashion, with commas to indicate powers of 1000. Although writing out the number in full is indeed a common action for normal people, the specific comma convention depicted here is only considered normal in the Anglo-Saxon world; conventions for writing large numbers in full vary considerably across cultures. For example, in countries where the period is used as a {{w|decimal separator}} (including Europe outside the UK), one would write the number as 25.259.974.097.204 (or 25'259'974'097'204 in Switzerland, or 25 259 974 097 204 in Poland, France and Estonia). Under the {{w|Indian numbering system}}, this number would be written as 25,25,997,40,97,204.
|-
| 25 Trillion
| Normal Person
| This is the number, rounded to trillions in the normal fashion.
|-
| 25 Billion
| Old British Person
| In current English usage, across the Anglophonic world with some hold-outs, an n-illion means 10^(3n+3) as per the {{w|short scale}} system popularised by American influence in international trade, so a trillion means 10^12, as above. However, older British English use had an n-illion meaning 10^(6n) (i.e. the simpler calculation of ''million^n''), so a billion meant 10^12. The change stems from a 1974 commitment by Harold Wilson, the Prime Minister of the UK at the time, to change from the {{w|long scale}} (previously often described as the British system) to the short one for all official purposes.

Though not instantly widely adopted for common usage, the mid-'70s could therefore be considered the key turning point between when an older or younger British person learns (as the change filters through the system at various stages of education) what their "Billion"s and "Trillion"s are supposed to represent.

As well as 'traditionalist' British use, the long scale is widely used in the non-Anglophone world, in local language versions, though while the British system tended to infill n-and-a-half powers of the million with the term "thousand n-illion", the suffix "-illi''ard''", or equivalent, is often used for the thousands multiple directly atop the respective "-illion" point.
|-
|2.526x1013
|Scientist
|This number is formatted in {{w|scientific notation}}, using the exponent 1013.
|-
| 2.525997x1013
| Scientist trying to avoid rounding up
| Using as many decimal places as necessary until hitting a digit (0-4) that results in rounding down, even if it goes against the common scientific practice of reporting the correct amount of "significant figures". [[:File:large number formats.png|A previous version of the comic]] had a typo (the number was ''2.5997x1013''), but Randall updated the comic.
|-
| 2.526e13 or
2.526*10^13
| Software developer
| The first example is how the number would be expressed as a floating point number in scientific notation in [https://rosettacode.org/wiki/Literals/Floating_point most common programming languages]. The second example is a technically correct way of expressing the same thing in some programming languages in which exponentiation is indicated by the ^ operator. However writing it that way instead of the first way could be considered quirky, as it is written as an instruction to the computer to calculate the product of a number with 10 raised to power 13, instead of just writing the number (although in many situations the compiler or preprocessor would detect this and solve it correctly, making it functionally identical to the first case). A software developer might write it that way if they are a novice who is not familiar with the first notation, or they could simply have an personal preference that considers the second version easier to read. Perhaps an additional joke for the second version is that it is the standard scientific notation with the x for multiplication and superscript for raising to a power replaced with the notation used in many programming languages of * and ^, i.e., a software developer writing down a number in scientific notation, not necessarily while writing a program, would by habit write a * for multiplication and a ^ for exponentiation.
|-
| 25,259,973,541,888
| Software developer who forgot about floats
| The two most common computer {{w|Floating-point arithmetic|floating-point}} formats are the IEEE 754 {{w|Single-precision floating-point format|single-precision}} and {{w|Double-precision floating-point format|double-precision}} representations. These are ''binary'' floating-point formats, representing numbers as the quantity ''a'' × 2''e'', for some fractional number ''a'' and exponent ''e''. Both the values ''a'' and ''e'' have a fixed size in bits, and therefore a finite range. In single-precision, ''a'' and ''e'' have (effectively) 24 and 8 bits, respectively, while in double precision the effective sizes are 53 and 11 bits.

Fully representing the number 25,259,974,097,204 (in any format) requires at least 45 bits. Therefore this number cannot be represented exactly as a single-precision float. The closest possible representations are 0.717931628 × 245 and 0.717931688 × 245; these work out to 25,259,973,541,888 and 25,259,975,639,040, respectively. Of these, the one ending in 888 is considerably closer to the original, so is chosen due to {{w|rounding}}. (Naturally these numbers are represented internally in binary, not decimal; the actual representations, in {{w|hexadecimal}}, are <tt>0.b7ca5e</tt> × 2<tt></tt>2d and <tt>0.b7ca5f</tt> × 2<tt></tt>2d.)

In many programming languages, the keyword to request a single-precision floating-point variable is <tt>float</tt>, while the keyword to request double-precision is <tt>double</tt>. It is an easy mistake to make to forget about the limited precision available with type <tt>float</tt>, especially since its name sounds like what you want for "floating point". (Had the programmer remembered to use type <tt>double</tt>, the number 25,259,974,097,204 could have been represented exactly (still in hexadecimal), as <tt>0.b7ca5e43c9a000</tt> × 2<tt></tt>2d.)
|-
| 1013
| Astronomer
| For extremely large distances, astronomers typically only care about orders of magnitude, e.g. whether a number is 1013, as opposed to 1012 or 1014. Randall often jokes about the lack of precision needed by astronomers, such as in [[2205: Types of Approximation]] where the astronomer-cosmologist is equally willing to make pi equal to one, or ten. The original number is rounded to the nearest power of ten.
|-
| {∅,{∅},{∅,{∅}},{∅,{∅},{...
| Set theorist
| In {{w|Zermelo–Fraenkel set theory}}, the natural numbers are defined recursively by letting 0 = ∅ (the {{w|empty set}}), and ''n'' + 1 = ''n'' ∪ {''n''}. So, every natural number ''n'' is the set of all natural numbers less than ''n'', and since 0 is defined as the empty set, all numbers are nested sets of empty sets. Note that writing out a number in this form requires an exponential number of characters - that is, ''n'' + 1 requires over twice the characters as ''n'' does to write out. Thus, this method could not be finished, as it would require more data to be stored than there is matter in the universe to store it.
|-
| 1,262,998,704,860 score and four
| Abraham Lincoln
| In the {{W|Gettysburg Address}}, Lincoln speaks the number "87" as "four score and seven" ("score" meaning "20"). Base-20 or {{w|vigesimal}} numeral systems are or have been used in pre-Columbian-American, African and many other cultures. In French it is used only for higher numbers (e.g. 92 = quatre-vingt-douze). In English it can appear in certain archaic and classic contexts, such as the King James translation of the Bible ("threescore years and ten" to be the life expectancy of a human according to Psalm 90:10). In these cases, a number is written in "score" (multiples of 20) plus a remainder. In this case 1,262,998,704,860 * 20 + 4 yields the exact number.
|-
| 10^13.4024 ''(title text)''
| A person who has come back to numbers after a journey deep into some random theoretical field
| In some fields of mathematics, especially those dealing with very {{w|large numbers}}, numbers are sometimes represented by raising ten (or some other convenient base) to an oddly precise power, to facilitate comparison of their magnitudes without filling up pages upon pages of digits. An example of this is {{w|Skewes's number}}, which is formally calculated to be ''e''''e''''e''79, but is more commonly approximated as 10101034. 13.4024 is a rounded version of the {{w|common logarithm}} of 25,259,974,097,204 (log10 25,259,974,097,204 = 13.4024329009); thus, this "format" is still mathematically correct, but uncommon. However, only by using many more digits will the result get close enough to be rounded to the original number 10^13.40243290087302 = 25,259,974,097,203.5, which would round up to the correct number. This number 10^13.4024 = 25,258,060,548,319.6 deviating almost 2 billion from the correct number
|}

==Transcript==
:[A panel only with text. At the top there is four lines of explanatory text. Below that are 2 columns with 5 rows of number formats. Each numerical format is in red, with black text explaining the format below it.]

:<big>What the way you write large numbers says about you</big>
:(Using the approximate current distance to Jupiter in inches as an example)

:25,259,974,097,204
:Normal person

:25 trillion
:Normal person

:25 billion
:Old British person

:2.526x1013
:Scientist

:2.525997x1013
:Scientist trying to avoid rounding up

:2.526e13 or 2.526*10^13
:Software developer

:25,259,973,541,888
:Software developer who forgot about floats

:1013
:Astronomer

:{∅,{∅},{∅,{∅}},{∅,{∅},{...
:Set theorist

:1,262,998,704,860 score and four
:Abraham Lincoln

{{comic discussion}}

[[Category:Comics with color]]
[[Category:Programming]]
[[Category:Math]]
[[Category:Astronomy]]
[[Category:Science]]
[[Category:Comics featuring politicians]]