explain xkcd - User contributions [en]

2343: Mathematical Symbol Fight

2020-08-08T21:52:12Z

162.158.123.47: /* Explanation */ delta

{{comic
| number = 2343
| date = August 7, 2020
| title = Mathematical Symbol Fight
| image = mathematical_symbol_fight.png
| titletext = Oh no, a musician just burst in through the door confidently twirling a treble clef.
}}

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

This panel imagines which {{w|List of mathematical symbols|mathematical symbols}} would be good in a fight if they were made corporeal in two (or three) dimensions. Generally, objects with longer reach and pointier ends wind up on the right ("more useful") side of the scale, and symbols with less reach and more curves tend towards the left ("less useful") side.

The comic invokes [[wikipedia:surreal humour|surreal humour]] by suggesting that mathematical symbols could be handled as physical objects in the real world. Another component of the humor is the implication that it is useful to prepare to use mathematical symbols in a fight, even though mathematicians, who use mathematical symbols, usually do not conduct their debates violently {{Citation needed}} (though some stories suggest that {{w|Hippasus}} was killed by his fellow Pythagoreans for his proof that irrational numbers exist), and even if they did, they wouldn't use large reproductions of their symbols as weapons.

{| class="wikitable"
! Symbol
! Meaning
! Notes on using in a fight
|-
|ℝ
|The set of [[wikipedia:real number|real number]]s
|Megan seems to be struggling with a giant version of this symbol.
|-
|θ
|[[wikipedia:Theta#Mathematics_and_science|Theta]]
|This symbol is not very sharp, and [[White Hat]] is unable to use it in combat. It would not work as a good shield due to the hole in the symbol, but it possibly could be thrown. (The later version of Xena's chakram had a bar in the middle.)
|-
|∅
|[[wikipedia:Empty set|Empty set]]
|Similarly shaped to theta, but identified as being slightly more useful, presumably because the parts of the bar that extend beyond the circle can be used as thrusting weapons.
|-
|∞
|infinity
|-
|>
|Greater than
|-
|∝
|[[wikipedia:Proportionality_(mathematics)#Direct_proportionality|Direct Proportionality]]
|-
|∪
|{{w|union (set theory)}}
|-
|∈/ϵ
|{{w|Element (mathematics)|member of}} (set theory) or the "lunate" lowercase {{w|Epsilon#Symbol|epsilon}}
|Cueball is holding this in the manner of a Klingon "{{w|Bat'leth}}" from the ''Star Trek'' franchise. The Bat'leth is [https://youtu.be/VsElSDXPgSA infamous] among swordfighters for being rather impractical, and that the Klingon warrior race would have been better suited using swords like humans. It seems Randall agrees, as the ∈ is quite far on the left of the chart.
|-
|π
|[[wikipedia:Pi|pi]]
|-
|∀
|"{{w|Universal quantification|for all}}"
|Could be held by the crossbar clenched in a fist, and then used as a {{w|push dagger}}, with the legs acting as a guard. Or could be held by the legs.
Compared to the similar Δ (delta) the point is sharper, the grip is closer to the point so it would be easier control (keep the weapon from twisting). Unclear why it is listed as much less effective than the delta. Perhaps the guard legs are too long?
|-
|∂
|{{w|∂}} ([[wikipedia:Partial derivative|partial derivative]] or [[wikipedia:Boundary_(topology)|boundary operator]])
|It's not clear why Randall ranks this symbol as so much less effective than the similarly-shaped 𝜌, but the curl in the "tail" of the ∂ would give it a shorter lever arm when swung and would disrupt the balance.
|-
| +
|[[wikipedia:Plus_and_minus_signs#Plus_sign|Plus]]
|Maybe thrown like a {{w|shuriken}}?
|-
|Ψ
|[[wikipedia:Psi#Mathematics|Psi]]
|It could be used as a slightly-less-functional trident or pitchfork, with a shorter handle. More particularly, it resembles a {{w|sai}} (which, funnily enough, is how "Psi" is pronounced).
|-
|≠
|not equal sign
|-
|~
|[[wikipedia:Tilde#Mathematics|tilde]], meaning "approximately", equivalent, or several transforms of a function
|A potentially dangerous throwing weapon. Could also be similar to a wavy bladed dagger ({{w|Kris}}) or a sword ({{w|Flame-bladed sword}}).
|-
|#
|[[wikipedia:Cardinality|Cardinality]], [[wikipedia:Connected_sum|connected sum]] (knot theory), or [[wikipedia:Primorial|primorial]].
|Blondie uses this symbol.
|-
|Δ
|[[wikipedia:Delta_(letter)|Delta]]
|Could be held with one bar clenched in a fist, and then used as a {{w|push dagger}}. Unclear why listed as much more effective than ∀. Also, delta could be thrown like a star.
|-
|⇒
|[[wikipedia:Material_conditional|Material consequence]] or [[wikipedia:Logical_consequence|Logical consequence]], meaning "implies"
|The point is nice, but having two poles (or one board-like thick handle) would be difficult to wield. A collection of them might make a nice defensive pike line.
|-
|⋅
|multiplication sign
|If thrown, this could be a dangerous projectile weapon, or it could be scattered on the ground as a trip hazard. Three of them stacked together would make a "{{w|therefore sign}}", which might at least conclude the ''mathematical'' portion of the fight in the user's favor.
|-
|ζ
|{{w|Zeta#Mathematics_and_science|Zeta}}
|Could be sharpened into a scythe or curved saber, depending on the curvature and length of the 'tail' at the bottom.
|-
|ℵ
|[[wikipedia:Aleph_number|Aleph number]]
|Could be brandished or thrown in the manner of a shuriken.
|-
|Γ
|uppercase Greek letter {{w|Gamma#Uppercase|Gamma}}
|If this letter is formed with {{w|serif}}s, it could be used as an axe or hook, and if it is made {{w|sans-serif}}, it would make a powerful pick or war hammer.
|-
|√
|{{w|square root}} sign
|Randall has drawn this sign with a long overbar, which makes it useful like a {{w|Pole weapon|pole arm}}. Black Hat has chosen this symbol.
|-
|''ρ''
|{{w|Prime_constant|italic rho}}
|Ponytail is brandishing this symbol against Danish, apparently using it like a club or hammer and striking with the curve.
|-
|∮
|{{w|contour integral}}
|This symbol is drawn with a very tight center, giving it an almost identical figure to the regular integral symbol. Presumably, the added bulk for marginal additional use earns it a rating of 'less effective'.
|-
|∫
|{{w|integral}}
|Could be used in the manner of a shepherd's crook, or as a {{w|Bill (weapon)|billhook}}. Could be used as a {{w|spear thrower}}, combined with ⋅ or ⇀.
|-
|→
|Implies; X→Y means that if X is true, then Y is also true
|Danish is brandishing this symbol against Ponytail, apparently using it like a spear or other polearm.
|-
|⊥
|{{w|up tack}} or falsum, indicating a false proposition in logic or the bottom element in a partial order
|Used as a {{w|war hammer}} (held by the long stem), the opponent would be struck with either leg of the top of the T. Held by the short legs (like a wishbone), could be used as a two handed sword.
(If tipped with a knapped stone head, it could become a {{w|Folsom point|falsum point}}.)
|-
|⇀
|{{w|Vector notation}}
|A single-barbed spear.
|-
|⎯⎯
|{{w|Fraction#Vocabulary|Fraction bar}} (division) or {{w|Overline#Math_and_science|overline}} (complex conjugate or mean).
|Hairy is brandishing this symbol against Black Hat. The single shaft would allow it to be used in the manner of a {{w|quarterstaff}}, {{w|bō}}, or other {{w|stick-fighting}} weapon. Of the symbols shown in the comic, Randall considers this one the most useful in a fight, presumably because of its greater reach than the vector arrow and its simplicity compared to the square root symbol.
|-
|𝄞
|{{w|Treble clef}}
|Mentioned in the title text; this is not a mathematical symbol, but a musical symbol. The treble clef is a much more complicated symbol than those used in mathematics, hence the musician's "confidence" in his weapon. The curve at the bottom could be used as a hook, the upper curl could be used as a blunt weapon, and the tight curl of the center would serve as a better defensive shield than theta.
|}

A straight line is farthest to the "more dangerous" side, which could possibly be a reference to the dangers posed by lines in "Flatland", because their infinitely-sharp endpoints could be difficult to see (particularly their rear end, which does not contain a gleaming eye as their front end does) and would fatally pierce whoever they chose to stab. However, taking a more literal view of the drawings, the straight line does not appear to be any thicker or thinner, or pointier, than any of the other lines.

The title text refers to a {{w|Treble clef}}, which is not a mathematical symbol but rather a {{w|List of musical symbols|musical symbol}}. The note of concern in the text suggests musical symbols may be viewed in such fights as exotic or especially dangerous.

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

Mathematical Symbols

[Subheading]

by how useful they would be in a fight

more useful

⟶

ℝ ∅ > ∝ π + Ψ ~ ⇒ ⋅ Γ √ ∮ ∫ ⇀
θ ∞ ∪ ∈ ∀ ∂ ≠ # Δ ζ ℵ ''ρ'' → ⊥ ⎯

[Below the (number?) line, eight characters fight each other, using some of the symbols mentioned above as weapons.]

[The characters hold more "useful" weapons from left to right, correlating with the chart.]

[Megan is awkwardly handling a giant "ℝ".]

[White Hat is holding a "θ" with both hands, as a shield.]

[Cueball is holding an "∈" in both hands, with its "tines" pointed towards Blondie, who is swatting at him with a "#".]

[Ponytail is leaping at Danish, swinging a "''ρ''" like an axe, while Danish is leaning back and thrusting a "→" back at her.]

[Black Hat is swinging a long "√" like a polearm at Hairy, who is holding a long "⎯" defensively.]

-
List of symbols from left to right (by rightmost edge):

ℝ θ ∅ ∞ > ∪ ∝ ∈ ∀ π ∂ + ≠ Ψ # ~ △ ζ ⇒ ⋅ ℵ Γ ''ρ'' √ → ∮ ∫ ⊥ ⇀ ⎯

Note: Where two symbols had similar right-most edges, the overlay grid on an ASUS pro-art display was used to decide which one went further right.

{{comic discussion}}
[[Category:Math]]
[[Category:Music]]
[[Category:Charts]]
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Danish]]
[[Category:Comics featuring White Hat]]
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Blondie]]
[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring Black Hat]]
[[Category:Comics featuring Hairy]]

Talk:2343: Mathematical Symbol Fight

2020-08-08T21:51:02Z

162.158.123.47:

Can I get aleph-null aleph-shaped throwing stars? [[User:LunarNapolean|LunarNapolean]] ([[User talk:LunarNapolean|talk]]) 20:18, 7 August 2020 (UTC)

Apologies to whoever added the "citation needed" that I stepped on. -- brad

That zeta looks conspicuously bad. I wonder if this comic will get a cleaned-up version uploaded. [[Special:Contributions/108.162.237.16|108.162.237.16]] 20:51, 7 August 2020 (UTC)

[[Megan]] usually has shoulder-length hair, so the person being attacked by Ponytail is probably not Megan... except in so far as all brunettes in this comic are called 'Megan'. [[User:LtPowers|LtPowers]] ([[User talk:LtPowers|talk]]) 20:53, 7 August 2020 (UTC)
:Is one of them [[Danish]]? And one of them Megan? [[Special:Contributions/172.69.33.121|172.69.33.121]] 22:49, 7 August 2020 (UTC)

I think Randall is underestimating the weapon utility of psi. There's a real-world martial arts [https://en.wikipedia.org/wiki/Sai_(weapon) weapon] that looks somewhat like it.[[Special:Contributions/172.69.68.197|172.69.68.197]] 22:04, 7 August 2020 (UTC)
:I think he’s also seriously underestimating the value of keeping your fingers attached to your hand. Swords have guards for a reason. I’d pick the contour integral over anything else there.

Considering the title text, a bass clef looks pretty formidable, close to a bat'leth. [[User:Nutster|Nutster]] ([[User talk:Nutster|talk]]) 00:31, 8 August 2020 (UTC)
:Yes, but the treble clef is the one in the title text, and that’s nothing like a Klingon {{w|bat'leth}}. I removed the comment from the table. [[User:Adam1729|Adam1729]] ([[User talk:Adam1729|talk]]) 02:09, 8 August 2020 (UTC)

These “weapons” seem strangely appropriate for xkcd’s stick figures... -cpl

Are we sure White Hat is holding empty set? There don't appear to be points extending outside the circle in which case I think he's actually holding Theta -jc

Can I use the LaTeX mathwitch? [[Special:Contributions/141.101.98.26|141.101.98.26]] 10:03, 8 August 2020 (UTC)

First time editor here,hope I get the notation right! Question on the pi link to wikipedia: I put in the double link to the main page and the disambiguation because unfortunately https://en.wikipedia.org/wiki/Pi_(disambiguation)#Mathematics doesn't include the mathematical constant definition (though it is listed at the top of the page). Thoughts? [[User:Alan g|Alan g]] ([[User talk:Alan g|talk]]) 10:38, 8 August 2020 (UTC)

I think that’s the is proportional to” symbol rather than just alpha. They are similar but have different Unicode symbols. Thoughts?--[[Special:Contributions/141.101.98.222|141.101.98.222]] 12:01, 8 August 2020 (UTC)
:You're definitely correct. (They don't even look that similar...) It's the direct proportion symbol, not the symbol for Alpha.
:[[User:ProphetZarquon|ProphetZarquon]] ([[User talk:ProphetZarquon|talk]]) 18:03, 8 August 2020 (UTC)
I don't think → is "implies", particularly as we've had ⇒ earlier. → is often used for "maps to", as in f: x → f(x) [[Special:Contributions/141.101.107.166|141.101.107.166]] 19:24, 8 August 2020 (UTC)

Are we sure that is the multiplication sign (center dot)? The placement makes it seem more a decimal point. [[Special:Contributions/162.158.123.47|162.158.123.47]] 21:51, 8 August 2020 (UTC)

Talk:2336: Campfire Habitable Zone

2020-07-26T14:49:38Z

162.158.123.47:

Amazingly how similar my aborted (edit-conflicted) edit matched what I found had gazumped me within the prior few minutes. Almost paragraph-for-paragraph on the same topic, with very similar details. Great minds think alike! (Fools never differ...) [[Special:Contributions/162.158.159.100|162.158.159.100]] 01:58, 23 July 2020 (UTC)
:Same thing happened to me. This was my first time trying to submit the main explanation. [[User:Barmar|Barmar]] ([[User talk:Barmar|talk]]) 02:11, 23 July 2020 (UTC)
Since the marshmallow's axis of rotation (i.e. the stick) is parallel rather than perpendicular to its orbital plane, it cannot be tidally locked in terms of its rotation. However, for the same reason, one side of the marshmallow, that which is closest to the end of the stick, does always face the campfire. [[Special:Contributions/162.158.62.75|162.158.62.75]] 02:43, 23 July 2020 (UTC)

Take note of how Ponytail is toasting the Marshmallow above the fire with the stick nearly horizontal. In this orientation, the marshmallow typically becomes too gooey inside to maintain traction on a skewer or smooth stick. Rotating the skewer/stick becomes futile as the marshmallow spins relative to the skewer/stick but remains in the same direction relative to the fire, which will be with the heaviest part down due to the earth's gravity. In maintaining the analogy, the more massive side of the marshmallow is attracted to the fire... it has become tidally locked and cannot escape, preventing even toasting of the marshmallow. [[User:Dodgo|Dodgo]] ([[User talk:Dodgo|talk]]) 04:14, 23 July 2020 (UTC)
:you cannot toast marshmallows on a single tip skewer, you need to use a marshmallow fork (which for linguistic reasons that escape me is called a fork despite having only two prongs). Care still must be exercised that the insides don’t become so gooey that the marshmallow falls off, but with a fork you can rotate and brown all sides evenly.[[Special:Contributions/162.158.78.128|162.158.78.128]] 04:20, 23 July 2020 (UTC)
:(A fork in the road has only two 'tines', or is liable to puncture a tyre if it was just a joke set-up. Four-pronged forks for general dining only became common in the early 1800s, and all kinds of contemporary forks, for given purposes, have three or two tines. The earliest forks were indeed ''just'' two-forked, as they do the basic job of doubly-impaling, whereas modern ones have to partly act as 'shovel', or even 'rake', so need more prongs. Though rarely >4.) [[Special:Contributions/162.158.159.14|162.158.159.14]] 12:01, 23 July 2020 (UTC)
:: Tuning forks also only have two tines.[[Special:Contributions/162.158.75.62|162.158.75.62]] 12:02, 24 July 2020 (UTC)

How long a stick would we need to roast marshmallows with the sun? [[User:Probably not Douglas Hofstadter|Probably not Douglas Hofstadter]] ([[User talk:Probably not Douglas Hofstadter|talk]]) 06:25, 23 July 2020 (UTC)
:Don't know about marshmallows, but from a [https://www.bbc.co.uk/programmes/m000kv7j recent radio show (first item)] I learnt that a (cylindrical, so marshmallow-shaped) burrito should be placed 60 million km sunwards. Assuming "no additional equipment", but plenty of other caveats. No discussion of how you get your snack back to you while still ''only'' cooked and before it cools down. Obviously marshmallows (on sticks, solving one issue) are a different prospect, but maybe start with that and experiment a few times? [[Special:Contributions/162.158.159.14|162.158.159.14]] 12:23, 23 July 2020 (UTC)
:Maybe this question could revive "What If?" and in addition to tackling "roasting" the marshmallow it could address how fast you'd have to retrieve it before it radiated away enough heat to no longer be "gooey"[[Special:Contributions/162.158.74.167|162.158.74.167]] 12:30, 23 July 2020 (UTC)

Am I the only person thinking that Cueball left the habitable zone because Megan, trying to get her marshmallow to toast, has just poked him in the face with her stick? [[User:Angel|Angel]] ([[User talk:Angel|talk]]) 09:03, 23 July 2020 (UTC)

According to my research, not all campfires possess a habitable zone. A few are too small to roast marshmallows; some are large enough that you cannot comfortably stand within marshmallow-roasting distance; and others just had some of that colored-fire gunk thrown in them and you don't want to roast food over whatever that gives off. [[User:GreatWyrmGold|GreatWyrmGold]] ([[User talk:GreatWyrmGold|talk]]) 13:39, 23 July 2020 (UTC)
: I doubt that. Since you can roast a marshmallow on a candle flame just fine I can't imagine a campfire(!) being too small for that. And as for the problem with too big fires it all depends on the length of the stick you are using. But again, we are talking about campfires - these are generally meant to be used for cooking. If you want to actually eat that marshmallow is indeed dependent on the stuff you are burning, on that I agree. [[User:Elektrizikekswerk|Elektrizikekswerk]] ([[User talk:Elektrizikekswerk|talk]]) 13:54, 23 July 2020 (UTC)

I've found that the habitable zone can get compromised by the smoke direction. [[Special:Contributions/162.158.159.66|162.158.159.66]] 16:32, 23 July 2020 (UTC)

Is it too far fetched to think that "Campfire habitable zone" is a much more direct 1:1 reference on the term "Circumstellar habitable zone". According to the Wikipedia article the first scientific definition of habitable zone from Dole (1964) was the range of 0.72 A.U. to 1.24 A.U. If the same horizontal scaling is applied to the green zones in the comic, then the position of Ponytail pretty precisely corresponds to the distance of planet Earth, the position of Cueball pretty precisely corresponds to the position of Planet Venus and Meghans position quite well corresponds to the position of Planet Mars? [[User:Farnsworth|Farnsworth]] ([[User talk:Farnsworth|talk]]) 20:12, 23 July 2020 (UTC)

Please note: There may be a misspelling in this panel. See the claimed distinction between "marshmallow" (in the panel) and "marshmallow." https://www.askdifference.com/marshmellow-vs-marshmallow/ [[User:JDAddelston|JDAddelston]] ([[User talk:JDAddelston|talk]]) 14:36, 24 July 2020 (UTC) JDAddelston
: I have looked at the current page, the image, and some way back in page history, and I only see "marshmellow" (noted within as incorrect) in that URL you give. Maybe I have missed the point, or it has changed without my noticing, in which case maybe you perhaps should clarify. (I also noted, while checking this, that one historic edit was for a couple of "-ise"->"-ize" changes. But I could point out other changes where international/anglicised usages could be americanized, if this is at all important.) [[Special:Contributions/162.158.159.66|162.158.159.66]] 19:47, 24 July 2020 (UTC)

Can we delete the incomplete tag now? I think we have explained everything.--[[User:Some user|Some user]] ([[User talk:Some user|talk]]) 00:25, 26 July 2020 (UTC)

Some amateurish Googling indicates that the more craters on the far side of the moon are not because it’s tidally locked, but because volcanoes on the near side obliterated many. I’m removing the “as a consequence, the far side of the moon has many more craters caused by impacts“ assertion, but noting it here in case I’m wrong ... [[Special:Contributions/162.158.123.47|162.158.123.47]] 14:49, 26 July 2020 (UTC)

2335: Photo Deposit

2020-07-20T21:40:32Z

162.158.123.47: /* Explanation */

{{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. 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; enabling a determined person to arbitrarily lower the purchasing power of existing money significantly, without issuing any new money.

This comic is also related to {{w|fractional reserve banking}}, where banks create money through lending the same money multiple times.

==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]]