explain xkcd - User contributions [en]

Talk:2857: Rebuttals

2023-11-21T00:52:19Z

172.69.79.142:

Ok, so...
#"...new evidence" (yes, possibly we can start with "...evidence", but let's start with the first contrarianism).
#"...inconvenient..." (so there's something we're saying is ''wrong'' with that new evidence?)
#"...led researchers to ignore..." (maybe could fold in with the inconvenience, but arguably ''ignoring'' is a 'third way' step in sidelining it, not even disagreeing)
#"...the prevailing consensus..." (another layer of implied position-taking where there ''is'' something to disagree with)
#"...the backlash against..." (to which others firmly took up the contrary)
#"It's become conventional wisdom that..." (and this is a counter-contrary perspective)
#"However..." ("...and ''I'', for one, think that they're wrong about the whole thing!")
...well, by a very quick and dirty deconstruction. But, then again, I fully expect to be shown wrong in my delayering! [[Special:Contributions/162.158.74.25|162.158.74.25]] 00:31, 21 November 2023 (UTC)
:Wouldn't the inconvenient new evidence be the justification for the backlash against the prevailing concensus, not the reason why the new evidence is ignored? I'm not going to try to explain this comic, I'm lost already. [[User:Barmar|Barmar]] ([[User talk:Barmar|talk]]) 00:46, 21 November 2023 (UTC)

I impressed myself by correctly remembering that the author of "Structure of Scientific Revolution" was Thomas Kuhn. It was assigned reading in a philosophy of science class I took over 40 years ago, but I haven't had to think about it much since then. [[User:Barmar|Barmar]] ([[User talk:Barmar|talk]]) 00:43, 21 November 2023 (UTC)

Looking for a way to depict the Title Text: "The mainstream dogma sparked a wave of dogmatic revisionism, and this revisionist mainstream dogmatism has now given way to a more rematic mainvisionist dogstream." Too garish? [[Special:Contributions/172.69.79.142|172.69.79.142]] 00:52, 21 November 2023 (UTC)

2687: Division Notation

2023-11-18T19:08:14Z

172.69.79.142: Undo revision 329252 by 172.70.91.236 (talk) Numerous strange editing errors. (Perhaps a couple of geniuine bits. Not including a change of at least one word to UK English from US.

{{comic
| number = 2687
| date = October 19, 2022
| title = Division Notation
| image = division_notation_new_2x.png
| imagesize = 235x310px
| noexpand = true
| titletext = Science tip: Scientists hardly ever use the two-dot division sign, and when they do it often doesn't even mean division, but they still get REALLY mad when you repurpose it to write stuff like SALE! ALL SHOES 30÷ OFF!
}}

==Explanation==

In this comic there is another one of [[Randall|Randall's]] [[:Category:Tips|Tips]], this time a [[:Category:Science tip|Science Tip]], however, it is only mentioned in the title text. See below for more.

This comic pokes fun at some of the ways to write the {{w|Division (mathematics)|division}} operation in math. In this comic, [[Randall]] has used A as the dividend (the number being divided) and B as the divisor (the number that A is divided by). Division is the fourth simplest arithmetic operation in mathematics, after addition, subtraction, and multiplication.[https://plato.stanford.edu/entries/principia-mathematica/#PartIVRelaArit]

The first two of the seven notations shown are the {{w|division sign}} (÷) and the {{w|long division}} notation used for {{w|short division}} and {{w|long division}} in beginning arithmetic. (Note: division typography is only used in some countries, and there are [https://en.wikipedia.org/wiki/Long_division#Notation_in_non-English-speaking_countries different notations in the non-English speaking world]). These methods of division are often used by school children because the ÷ sign is what most people use when first learning division, and the short division format is usually the first algorithm learned for dividing arbitrary dividends, typically starting with the easier abbreviated short division form.

The expression on the third line, A/B, is the way division is usually written in software code. The four simple arithmetic operations in programming usually are +, -, *, /. This line was not in the [[media:division_notation_2x.png|first version]] of the comic. This is most commonly seen in regular mathematics as it somewhat saves space, and is easy to type with the slash key. Additionally, it uses standard {{w|ASCII}} characters instead of sophisticated notation. A notable exception is {{w|APL_(programming_language)|APL}}, which uses an idiosyncratic character set modeled after traditional arithmetic.

The expression on the fourth line, A/B, is how division is usually written by hand{{Actual citation needed}}. It is nearly identical to the fraction notation that follows, but the diagonal line allows each number to be bigger while still fitting into a single line of text. The third line's representation is the best approximation of this line's notation on a computer, without using more obscure Unicode characters. The Unicode character set can be used to accurately represent division as on the fourth line in plain text, using a small set of precomposed fractions (⅔, ⅕, etc.), regular numerals and [https://unicode-explorer.com/c/2044 U+2044 FRACTION SLASH] (e.g. 22⁄7, provided font support exists), or superscript and subscript numerals (e.g. ²²/₇, or ²²⁄₇ with the fraction slash). Using any of these requires a greater knowledge of Unicode, and the know-how (and, possibly, patience) to type them, so it is likely that only a Unicode enthusiast would type division like this, rather than an alternate or equivalent format such as 22/7 as rendered in HTML.

The fifth notation is the way division is written in science and intermediate and higher mathematics: <table style="display: inline-table; line-height: 0.75em; vertical-align: middle; font-size:10pt; text-size-adjust: none;"><tr><td>A</td></tr><tr><td>B</td></tr></table>, i.e. the dividend on the top of the expression, over the divisor on the bottom with a horizontal line separating them. This is how a {{w|Fraction|fraction}} would be written. It has the advantage of clearly separating the numerator and denominator when they are longer expressions, such as polynomials, without needing to add parentheses. This format is mostly used in written and professionally typeset math, as it can't be typed without something like {{w|MathML}}, {{w|LaTeX}} or HTML tables.

The sixth, "fancy," notation uses a negative exponent. The exponent -1 is equivalent to {{w|Multiplicative inverse|reciprocation}}. It can be used to keep an entire division expression on one line. Note that AB-1 is equal to A/B only if A and B are in a commutative ring (and B has an inverse). If A and B are, for example, matrices, AB-1 is not the same in general as B-1A (and the notation A/B is never used in this case as it would be ambiguous). The AB-1 format is also often used to express physical units.

The final form of notation declares a function. The writer defines a new function, F, that takes in the parameters A and B, before listing out the function's definition (trailing off in increasingly smaller text). Defining things as functions is very normal for mathematics, but likely not very efficient at all to commonly do for the simple operation of division. Occasionally a highly formalized definition such as this could be a setup for an elaborate and extensive proof, hence Randall warns the reader they should escape while they still can. Integer division can be defined in terms of multiplicative inequalities and the remainder, or modulo ('%' in most programming languages) operator. This situation is likely to occur in many sorts of algebra, where one might have to define what "division" means for two elements of a mathematical object such as a group, ring, or magma. One example would be an object G, such that, for two elements A and B of G, "A divided by B" is defined as an element C such that CB=A, or alternatively as an element C such that BC=A. These definitions will differ if multiplication in G is not commutative. Furthermore, if such a C is not unique, the function F(A,B) will need to include a method to select a unique value for "A divided by B" for each A and B. Thus, the F(A,B) in the comic might not even refer to a uniquely defined operation, but simply to the property of a function F(A,B) that is a valid division operation on G, given some definition of division. You were warned.

The title text is a [[:Category:Science tip|Science Tip]]. It discusses how the division sign (÷) has fallen out of favor in most professional contexts (the ISO-80000 guidelines even specify the symbol "should not be used") yet has resisted all efforts to repurpose it as a new function. Specifically, it pokes fun at how similar the division sign is to a {{w|percent sign}} (%). A scientist might be really mad at the use of the division sign as an alternative to a percent sign because it is the wrong symbol in that context, ever though they never use it for the original meaning any more. The use of ÷ instead of % is something that may appear on signs for discount offers.

==Transcript==
:[The transcript has both formatted text for visuals and a description at the start of the line.]
:[Underlined text:] Division notation

:[A [Division sign] B is above, B [Long division symbol] A is below. They are connected by a close brace.] <table style="display: inline-table; line-height: 1em; vertical-align: middle; font-size:10pt; text-size-adjust: none;"><tr><td>A÷B</td></tr><tr><td>B⟌A</td></tr></table>}
:[Label on the right:] Schoolchild

:A/B
:[Label:] Software engineer

:[A/B except the A is slightly above and the B is slightly below, and the slash is more diagonal to fit them.] A⁄B
:[Label:] Normal person or Unicode enthusiast

:[A fraction with A on the top and B on the bottom.] <table style="display: inline-table; line-height: 0.8em; vertical-align: middle; font-size:10pt; text-size-adjust: none;"><tr><td>A</td></tr><tr><td>B</td></tr></table>
:[Label:] Scientist

:[AB with -1 in superscript.] AB-1
:[Label:] Fancy scientist

:F(A, B) [text gets smaller] such that [text gets smaller] F(G)= [Text is too small to read]
:[Label:] Oh no, run

{{comic discussion}}

[[Category:Math]]
[[Category:Science]]
[[Category:Programming]]
[[Category:Science tip]]

1395: Power Cord

2023-10-22T21:24:11Z

172.69.79.142: Undo revision 326804 by 172.69.22.195 (talk) If you're putting in multiple Citation Neededs in one go, you don't appreciate the necessary subtlety.

{{comic
| number = 1395
| date = July 16, 2014
| title = Power Cord
| image = power_cord.png
| titletext = In this situation, gzip /dev/inside to deflate, then pipe the compressed air to /dev/input to clean your keyboard. Avert your eyes when you do.
}}

==Explanation==
In this comic, we see [[Beret Guy]] walking in from the left, as [[Cueball]] is sitting on a couch, typing on a {{w|laptop}} on his {{w|lap}}, with its {{w|power cord}} unplugged. Instead of connecting it to the {{w|wall socket}}, Beret Guy picks it up and blows air into the loose end of the cord, as if inflating a balloon — and the laptop inflates. It then floats away, making Cueball grab for it as Beret Guy casually walks away. (See an instance where Cueball inflates something in a similar unexpected way in [[1798: Box Plot]]).

It is not possible to inflate a laptop like this{{Citation needed}}, and (with [https://www.youtube.com/watch?v=ugVRY-Cv7Ng&t=401s rare exceptions]) it is not possible to inflate ''anything'' by blowing down a power cord. Beret Guy has previously demonstrated several [[:Category:Strange powers of Beret Guy|supernatural abilities]], for instance with power cords, such as in [[1293: Job Interview]].

In general, human breath should not be buoyant enough to lift much in an atmosphere of ordinary air. The only chemical difference between dry air and dry exhaled breath is the conversion of oxygen (molecular weight = 32) to carbon dioxide (MW=44), not counting substances in such low concentrations that their effect on the average molecular weight of the air (MW=29) is negligible. A change of concentration of the CO2 from [https://www.engineeringtoolbox.com/air-composition-d_212.html 0.04%] to about [https://en.wikipedia.org/wiki/Breathing#Composition 4%] is typical. This increases the average molecular weight. However, exhaled breath is also usually much more humid than air, increasing the concentration of water (MW=18) from a typical value of 1% to approximately 5%, which decreases the average molecular weight. The two changes approximately cancel each other.

{| class="wikitable" style="text-align:right;"
|- style="font-weight:bold; text-align:center;"
! style="text-align:right; font-weight:normal;" |
! MW
! style="background-color:#efefef;" | Dry air
! style="background-color:#efefef;" | Fractional MW 
! Air with 1% water
! Fractional MW 
! style="background-color:#efefef;" | Exhaled composition dry
! style="background-color:#efefef;" | Fractional MW 
! Exhaled composition with 5% water
! Fractional MW 
|-
| style="font-weight:bold;" | N2
| style="text-align:left;" | 28.01
| style="background-color:#efefef;" | 78.08%
| style="background-color:#efefef;" | 21.87
| 77.30%
| 21.65
| style="background-color:#efefef;" | 78%
| style="background-color:#efefef;" | 21.85
| 74.10%
| 20.76
|-
| style="font-weight:bold;" | O2
| style="text-align:left;" | 32.00
| style="background-color:#efefef;" | 20.95%
| style="background-color:#efefef;" | 6.70
| 20.74%
| 6.64
| style="background-color:#efefef;" | 17%
| style="background-color:#efefef;" | 5.44
| 16.15%
| 5.17
|-
| style="font-weight:bold;" | Ar
| style="text-align:left;" | 39.95
| style="background-color:#efefef;" | 0.93%
| style="background-color:#efefef;" | 0.37
| 0.92%
| 0.37
| style="background-color:#efefef;" | 1%
| style="background-color:#efefef;" | 0.40
| 0.95%
| 0.38
|-
| style="font-weight:bold;" | CO2
| style="text-align:left;" | 44.01
| style="background-color:#efefef;" | 0.04%
| style="background-color:#efefef;" | 0.02
| 0.04%
| 0.02
| style="background-color:#efefef;" | 4%
| style="background-color:#efefef;" | 1.76
| 3.80%
| 1.67
|-
| style="font-weight:bold;" | H2O
| style="text-align:left;" | 18.01
| style="background-color:#efefef;" |
| style="background-color:#efefef;" |
| 1.00%
| 0.18
| style="background-color:#efefef;" |
| style="background-color:#efefef;" |
| 5.00%
| 0.90
|-
| style="font-weight:bold;" | Total
| style="font-weight:bold; text-align:left;" |
| style="background-color:#efefef;" | 100.00%
| style="background-color:#efefef; font-weight:bold;" | 28.97
| 100.00%
| style="font-weight:bold;" | 28.86
| style="background-color:#efefef;" |
| style="background-color:#efefef; font-weight:bold;" | 29.45
| 100.00%
| style="font-weight:bold;" | 28.88
|}

Because humans are warm-blooded, human breath is slightly warmer than the surrounding air, and therefore has slightly fewer molecules per unit volume. This is also true of hot air balloons, but they operate at much higher temperatures than human breath and are therefore able to obtain a greater amount of net buoyancy. There is a standard cartoon convention that {{tvtropes|AllBalloonsHaveHelium| inflating something with breath}} nonetheless makes it lighter than air. Also, given Beret Guy's many manifestations of inexplicable phenomena, it is not too far fetched to believe his body is, in fact, expelling some form of lighter-than-air gas, similar to the character Rigel on Farscape who could "fart helium".

The title text involves some jokes on {{w|Unix}} systems. On Unix, {{w|everything is a file}}; even most of the hardware can be referenced by a (virtual) file. These virtual files usually are in /dev or another virtual filesystem like /sys or /proc. While /dev/input really exists and points to the input system (mice, keyboards, gamepads, etc.), /dev/inside doesn't. {{w|gzip}} is a common tool to compress files. The first joke is to compress the air inside the laptop (with the command <code>gzip /dev/inside</code>) in order to deflate the laptop back to normal size. It is a pun with the literal meaning of "deflate", which is also the {{w|DEFLATE}} algorithm used by gzip (compressing files is also called "deflating"). Another joke is "{{w|Pipeline (Unix)|piping}}", the act of using the output of one operation as the input to another. As the output of the gzip command would be compressed air, a ''physical'' pipe could be used to direct the air somewhere useful. The output of a command can also be redirected to a file. Since the hardware is a file, the suggestion is to direct the air to /dev/input (which, in this case, means the keyboard, but would actually be a directory on real system, which can't normally be piped into) to clean it, similar to "compressed air" dusting cans. The complete command would be <code>gzip /dev/inside | /dev/input</code>. As this might cause a spray of unpleasant detritus (compare [[237: Keyboards are Disgusting]]), the reader is advised to avert their eyes.

==Transcript==
:[Beret Guy enters to find Cueball on a chair typing on a laptop. Cueball's power cord is unplugged from the wall.]
:Cueball typing: Type type

:[Beret Guy picks up the power cord. Cueball continues typing.]
:Cueball typing: Type type

:[Beret Guy blows into the plug end of the cord. The laptop abruptly inflates and Cueball jerks back.]
:Beret Guy: '''PBBBBT'''
:Laptop: '''FOOMP'''

:[Beret Guy walks away, leaving Cueball climbing up his chair to retrieve his inflated laptop which is now floating away.]

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Beret Guy]]
[[Category:Strange powers of Beret Guy]]
[[Category:Computers]]
[[Category:Linux]]