explain xkcd - User contributions [en]

Talk:1743: Coffee

2016-10-07T08:12:21Z

162.158.85.249:

For me as a non-native speaker this XKCD looks like the guests ordered Ground Coffee and Cueball didn't realize that ground might come von "grind". [[User:Gunterkoenigsmann|Gunterkoenigsmann]] ([[User talk:Gunterkoenigsmann|talk]])--

With "I'm a regular Starbuck" Megan says, she is a regular visitor of Starbuck and has learned her skills there watching. Sebastian --[[Special:Contributions/162.158.83.168|162.158.83.168]] 08:10, 7 October 2016 (UTC)

The expensive coffee filter comment might be a reference to the ridiculously high prices for vacuum cleaner bags. --[[Special:Contributions/162.158.85.249|162.158.85.249]] 08:12, 7 October 2016 (UTC)

1740: Rosetta

2016-10-04T19:49:22Z

162.158.85.249: /* Explanation */ lets be a bit more distinct ;-)

{{comic
| number = 1740
| date = September 30, 2016
| title = Rosetta
| image = rosetta.png
| titletext = I WONDERED why he kept asking whether we thought the impact speed was too low.
}}

==Explanation==
On the day this comic was posted (September 30th 2016), the ''{{w|Rosetta (spacecraft)|Rosetta}}'' mission ended with the final descent of ''Rosetta'' onto the comet {{w|67P}}. Landing Rosetta on the comet gave the scientists ([[Ponytail]], [[Megan]] and [[Hairy]]) a chance to collect extra data from very close to the comet, using the spacecraft's powerful sensors.

[[Cueball]] however [[1339: When You Assume|assumed]] that the landing was a "{{w|Asteroid_impact_avoidance#Kinetic_impact|kinetic impact}}" mission to deflect a comet that was on a collision course with Earth. A similar scenario (but using a nuclear weapon implanted inside of the asteroid to deflect it) was depicted in the 1998 film ''{{w|Armageddon (1998 film)|Armageddon}}'', of which Cueball is apparently a fan.

In reality, at the time ''Rosetta'' landed, 67P was already leaving the inner solar system and was [http://sci.esa.int/where_is_rosetta/ a long way past Earth]. It will return to the inner solar system in around 5 years time, but its orbit will not pass close of the earth in any forseeable time.

Also, as the title text hints, Rosetta's speed was only [https://astronomynow.com/2016/09/30/rosettas-final-hours/ 90 cm per second] relative to the surface at the moment of impact (or about 2 mph/3.25 km/h; the speed of a slow walk), while the comet was travelling at 14.39 km/s. Given that Rosetta only weighs a couple of tons (or [[1461: Payloads|six horses]]), and 67P weighs nearly 10 billion tons (or 22 billion horses), Rosetta's landing will have no actual measurable effect on the comet's momentum.

''Rosetta'' (and its lander, ''Philae'') were previously the subject of the comics [[1402: Harpoons]] and [[1446: Landing]], and were mentioned in [[1461: Payloads]], [[1547: Solar System Questions]] and possibly [[1621: Fixion]].

==Transcript==
:[A control room with Megan and Hairy sitting on stools in front of opposite desk with computers. Hairy has his arms in the air. Ponytail is standing between them with Cueball, she is watching Megan and he is looking at Hairy.]
:Megan: Signal lost.
:Megan: ''Rosetta'' has impacted the comet.
:Ponytail: Good work everyone.
:Hairy: ''Woooo!''

:[Zoom on Ponytail, still looking at Megan and Cueball who has turned towards Ponytail.]
:Cueball: So.
:Cueball: Do you think we deflected it?

:[Ponytail turns to Cueball as does Hairy who turns and looks away from his computer.]
:Ponytail: Huh?
:Cueball: Did we hit the comet hard enough to deflect it away from Earth?

:[In a frame-less panel Ponytail talks with Cueball.]
:Ponytail: That... Is that what you thought we were doing?
:Cueball: I just assumed...

:[Megan enters whispering in Ponytail's ear, holding a hand up to her mouth. Ponytail still looks at Cueball who raises his arms up in the air.]
:Megan: He's a huge ''Armageddon'' fan. Let him have this.
:Ponytail: Okay, fine.
:Ponytail: Yes! We did it! The Earth is saved!
:Cueball: ''Wooo!''

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring Hairy]]
[[Category:Comics featuring Megan]]
[[Category:Fiction]]
[[Category:Space probes]]

1724: Proofs

2016-08-27T07:18:59Z

162.158.85.249: removing "standard"

{{comic
| number = 1724
| date = August 24, 2016
| title = Proofs
| image = proofs.png
| titletext = Next, let's assume the decision of whether to take the Axiom of Choice is made by a deterministic process ...
}}

==Explanation==
[[Miss Lenhart]] is back teaching a math class. She begins a proof when one of her students ([[Cueball]]) interrupts her asking if this is one of those dark-magic (unclear, incomprehensible) proofs. She says no, but it soon turns out that it is; Cueball exclaims that he just knew it would be.

The proof she starts setting up resembles a {{w|proof by contradiction}}. This kind of proof assumes that a particular condition is true, and shows that this assumption leads to a contradiction, which disproves the initial assumption. For example assumption that √2 is a {{w|rational number}} means that, for some natural ''a'' and ''b'', √2=''a/b'', where ''a/b'' is an {{w|irreducible fraction}}. Yet, multiplying this equation by itself, we get 2=''a²/b²'' which in turn rearranges to 2''b²''=''a²''. Therefore ''a²'' is even (as any integer multiplied by 2 is even), which means that ''a'' is an even number, as an even number squared is always even and an odd number squared is always odd. This means, that ''a=2k'' and ''2b²=(2k)²=4k²'', meaning ''b²''=2''k²'', so ''b'' must be even too. But if both ''a'' and ''b'' are even, ''a/b'' cannot be irreducible. Contradiction means that the initial assumption is false, and √2 cannot be a rational number.

Alternatively, instead of a proof by contradiction the setup could be for a one way function. For example, it is relatively easy to test that a solution to a differential equation is valid but choosing the correct solution to test can seem like black magic to students.

The way that Ms Lenhart's proof refers to the act of doing math itself, is characteristic of metamathematical proofs, for example {{w|Gödel's incompleteness theorems}}, which, at first sight, may indeed look like black magic, even if in the end they must be a "perfectly sensible chain of reasoning" like the rest of good mathematics. While typical mathematical theorems and their proofs deal with such mathematical objects as numbers, functions, points or lines, the metamathematical theorems treat other theorems as objects of interest. In this way you can propose and prove theorems about possibility of proving other theorems. For example, in 1931 {{w|Kurt Gödel}} was able to prove that any mathematical system based on arithmetics (that is using numbers) has statements that are true, but can be neither proved nor disproved. This kind of metamathematical reasoning is especially useful in {{w|set theory}}, where many statements become impossible to prove and disprove if the {{w|axiom of choice}} is not taken as a part of the axiomatic system.

Using a position on the blackboard as a part of the proof is a joke, but it bears a resemblance to {{w|Cantor's diagonal argument}} where a position in a sequence of digits of a real number was a tool in a proof that not all infinite sets have the same {{w|cardinality}} (rough equivalent of the number of elements). This "diagonal method" is also often used in metamathematical proofs.

The axiom of choice itself states that for every collection of nonempty sets, you can have a function that draws one element from each set of the collection. This axiom, once considered controversial, was added relatively late to the axiomatic set theory, and even contemporary mathematicians still study which theorems really require its inclusion. In the title text the decision of whether to take the axiom of choice is made by a deterministic process, that is a process which future states can be developed with no randomness involved. {{w|Determinacy}} of infinite games is used as a tool in the set theory, however the deterministic process is rather a term of the {{w|stochastic process|stochastic processes theory}}, and the {{w|dynamical systems theory}}, branches of mathematics far from the abstract set theory, which makes the proof even more exotic. The axiom of choice was mentioned earlier in [[804: Pumpkin Carving]].

Although Miss Lenhart did retire a year ago after [[1519: Venus]], she seems to have returned here for a math course at university level, but continues the trend she finished with in her prior class.

==Transcript==
:[Miss Lenhart is standing facing left in front of a whiteboard writing on it. Eleven left aligned lines of writing is shown as unreadable scribbles. A voice interrupts her from off-panel right.]
:Miss Lenhart: ... Let's assume there exists some function ''F''(''a,b,c''...) which produces the correct answer-
:Cueball (off-panel): Hang on.

:[In a frame-less panel Cueball is sitting on a chair at a desk with a pen in his hand taking notes.]
:Cueball: This is going to be one of those weird, dark magic proofs, isn't it? I can tell.

:[Miss Lenhart has turned right towards Cueball, who is again speaking off-panel. The white board is also off-panel.]
:Miss Lenhart: What? No, no, it's a perfectly sensible chain of reasoning.
:Cueball (off-panel): All right...

:[Miss Lenhart is facing the whiteboard again writing more scribbles behind some of the lines from before (the first line has disappeared). The lines that have more text added are now number three and five (four and six before). Cueball again speaks off-panel.]
:Miss Lenhart: Now, let's assume that the correct answer will eventually be written on the board at the coordinates (''x, y''). If we—
:Cueball (off-panel): I ''knew'' it!

{{comic discussion}}

[[Category:Comics featuring Miss Lenhart]]
[[Category:Comics featuring Cueball]]
[[Category:Math]]

Talk:1707: xkcd Phone 4

2016-07-16T10:21:12Z

162.158.85.249: Add comment to '4' is 'IV'

The current explanation seems to assume a constant current draw of 1A without explicitly stating it.
[[Special:Contributions/141.101.95.117|141.101.95.117]] 14:04, 15 July 2016 (UTC)

The 12 headphone jacks is probably referring to the rumor that the iPhone 7 may not have a headphone jack. [[Special:Contributions/141.101.104.90|141.101.104.90]] 14:58, 15 July 2016 (UTC)

Fun fact: the Walkman II (the most popular variant) had 2 headphone jacks, so that two people could listen to music at the same time, but the second jack was removed from later designs. This has a few more than that, perhaps there is one for each voice assistant to make it "usable". {{unsigned ip|141.101.98.119}}

An alternative explanation of "onboard cloud" could be a file server that serves over WIFI, Bluetooth, and NFC, turning the phone into an effective NAS sneakernet [[User:Seebert|Seebert]] ([[User talk:Seebert|talk]]) 15:30, 15 July 2016 (UTC)

The "certified" feature probably refers to various certifications being used as marketing features. [[User:Joedetode|Joedetode]] ([[User talk:Joedetode|talk]]) 15:33, 15 July 2016 (UTC)

The Julian calendar is used by Orthodox Christians, but not astronomers. Astronomers use something called {{w|Julian day}}. --[[User:Mlv|Mlv]] ([[User talk:Mlv|talk]]) 16:27, 15 July 2016 (UTC)

"Did you know '4' is 'IV' in Roman numerals?" is probably a dig on "Mac OS X", which is supposed to be pronounced "Mac OS 10". Apparently it used to annoy Steve Jobs that it was pronounced "Mac OS EX" by many people. {{unsigned ip|108.162.210.214}}

It could be also a reference to the Samsung Galaxy Smartphones, as they were called Galaxy S (1st Version), Galaxy S II (2nd Version), Galaxy S III (3rd Version) and Galaxy S4 (fourth version, which does not use Roman numerals anymore) [[Special:Contributions/162.158.85.249|162.158.85.249]]

"The nickel–iron battery does exist, but it's terrible for most applications. Worse, this battery is non-rechargeable, meaning that it would have to be replaced to use the phone again after it is exhausted." is not supported by the link https://en.wikipedia.org/wiki/Nickel%E2%80%93iron_battery. The first line of which begins "The nickel–iron battery (NiFe battery) is a rechargeable battery ... ".--[[Special:Contributions/108.162.219.11|108.162.219.11]] 17:11, 15 July 2016 (UTC)

The comment about the Nickel-Iron battery being non-rechargable is referring not to the Wikipedia article, but the battery annotation on the picture, which states clearly that the included battery is non-rechargable. Perhaps the explanation should be amended to clear up this ambiguity. [[Special:Contributions/141.101.98.132|141.101.98.132]] 18:07, 15 July 2016 (UTC)

This explanation would be easier to read if put in a table, with the term on the left and description on the right {{unsigned|4jonah}}

The drawing may be interpreted as if "software defined" applies to part of the case (or the whole case). That would be... interesting, if useless. Doable - although probably impractical and not worth the price - with e-paper for graphical motives, for actual textures or other material characteristics maybe Nobel-worthy (and still quite useless in this application). {{unsigned ip|162.158.201.6}}

The inclusion of a parallel port may be a stab at Apple products such as iPhones. Apple seems to insist on avoiding otherwise standard connectors such as Micro USB, in favor of their own proprietary ones. [[Special:Contributions/108.162.237.168|108.162.237.168]] 06:02, 16 July 2016 (UTC)

1692: Man Page

2016-06-10T06:49:28Z

162.158.85.249: correct bug report url as written in comic

{{comic
| number = 1692
| date = June 10, 2016
| title = Man Page
| image = man_page.png
| titletext = For even more info, see blarbl(2)(3) and birb(3ahhaha I'm kidding, just Google it like a normal person.
}}

==Explanation==
{{incomplete|Initial draft/outline. As one of those comics, needs a section on each part. Needs an explanation of a man page for those unaware. Also needs fact-checking.}}
This comic shows a Unix man page for a fictional program called "blerp". It details the command line options for this program, many of which are strange, annoying, or even impossible. These options are mostly in alphabetical order.

Unix manpages are meant to provide a brief reference on the usage of a command, not verbose and well-written explanations as you may find in manuals which is another common type of documentation. This fictional manpage seems to exaggerate its crypticness, thus making fun of a common trait that many manpages have.

[[wikipedia:Command-line_interface#Command-line_option|Command-line options]], also known as flags, are typed following a program name to change how the program runs. The following is an example usage.

<code>blerp -a -d -t -p "AVIGNON"</code>

This would run blerp in attack mode, outputting to DEBUG.EXE, with tumble dry, and with POPE set to AVIGNON. In most cases, any number of flags can be used in any order, and applicable flags can be followed by arguments (such as "AVIGNON" in this example).

{| class="wikitable"
!Flag!!Description!!Explanation
|-
| -a||ATTACK MODE||Like a robot or something similar. Strange for a command line program.
|-
| -b||SUPPRESS BEES||Nonsensical option.
|-
| -—||FLAGS USE EM DASHES||Hard to tell the difference between en and em dashes. Command line options (flags) typically use en dashes (short dashes approximately the same width as the letter n). Em dashes can't easily be typed into a command line interface, so switching flags from en to em dashes is excessively difficult and nonsensical.
Also implies a paradox where if flags were to use em dashes, this flag itself would be invalid.
|-
| -c||COUNT NUMBER OF ARGUMENTS||Most likely not useful.
|-
| -d||PIPES OUTPUT TO DEBUG.EXE||Almost a standard option, but .exe is the weird part.
|-
| -D||DEPRECATED||Many programs contain legacy options to avoid breaking scripts that use them. While the option should still work, the documentation is changed to say "deprecated" to discourage further use. Eventually such options gets removed.
|-
| -e||EXECUTE SOMETHING||Vague.
|-
| -f||FUN MODE||Strange and slightly ominous.
|-
| -g||USE GOOGLE||As an actual program flag, a bit hackjob-ish, but most likely relating to googling how this program works.
|-
| -h||CHECK WHETHER INPUT HALTS||Completely impossible, by the Halting Theorem.
|-
| -i||IGNORE CASE (LOWER)||Usually, ignoring case means that a program will run without differentiating between upper- and lowercase. This flag suggests that blerp will run ignoring all the lowercase characters completely, or ignoring all the uppercase characters with -I.
|-
| -I||IGNORE CASE (UPPER)||
|-
| -jk||KIDDING||A common acronym, not a program flag.
|-
| -n||BEHAVIOR NOT DEFINED||Possibly mathematically ominous? Otherwise useless.
|-
| -o||OVERWRITE||Standard flag.
|-
| -O||OPPOSITE DAY||Strange flag.
|-
| -p||SET TRUE POPE; ACCEPTS "ROME" OR "AVIGNON"||This refers to a [https://en.wikipedia.org/Western_Schism historical schism in the Catholic Church.] In the 14th century, the Pope briefly ruled from Avingon, France, instead of Rome. After the Papacy was returned to Rome in 1377, the Church split (the so-called Western Schism) as not everyone accepted the move and the Pople who ordered it. This flag apparently allows the user to select a preferred Pope. There is actually a possible feature request here, as \"PISA\", a third Pope, should also be an option.
|-
| -q||QUIET MODE; OUTPUT IS PRINTED TO STDOUT INSTEAD OF BEING SPOKEN ALOUD||In most cases, a program will output basic information to the console, and running it in quiet mode will make it run without outputting anything. Blerp, on the other hand, outputs information through audio, and the quiet flag causes it to run like a normal program.
|-
| -r||RANDOMIZE ARGUMENTS||Pointless and possibly damaging.
|-
| -R||RUN RECURSIVELY ON <nowiki>http://*</nowiki>||The star (*) symbol is often used as a wildcard to match any string of characters. "<nowiki>http://*</nowiki>" suggests that blerp will be run on every webpage on the internet.
|-
| -s||FOLLOW SYMBOLIC LINKS SYMBOLICALLY||[Needs explanation of symbolic links]
|-
| -S||STEALTH MODE||Similar to -a.
|-
| -t||TUMBLE DRY||Perhaps useful for a program that runs on a clothes dryer. Refers to [https://img1.etsystatic.com/000/0/5254504/il_570xN.184726893.jpg directions like these].
|-
| -u||UTF-8 MODE; OTHERWISE DEFAULTS TO ANSEL||[Explanation of ANSEL necessary.] UTF-8 is rather standard. Similar in this regard to -q.
|-
| -U||UPDATE (DEFAULT: FACEBOOK)||Update usually refers to replacing an old software with a newer version. The default here suggests posting a status update to Facebook.
|-
| -v||VERBOSE; ALIAS TO find / -exec cat {}||Almost standard flag, in ordinary programs the opposite of -q. This command prints the contents of all files in the filesystem tree. However, it will never complete, as certain device files never end (/dev/urandom contains random bytes). Note that the "find" command is missing <code>\;</code> and will not run, instead complaining <code>find: missing argument to `-exec'</code> .
|-
| -V||SET VERSION NUMBER||Many programs will have a flag to view the version number. This flag changes the version number instead.
|-
| -y||YIKES||Meaningless.
|}

The bug report site, http://www.inaturalist.org/taxa/47744-Hemiptera, is a currently active webpage and inaturalist.org is a site working to extend biological research, and http://www.inaturalist.org/taxa/47744-Hemiptera does work and points to the same page as http://www.inaturalist.org/taxa/Hemiptera. [[wikipedia:Hemiptera|Hemiptera]] is the order classifying True Bugs.

blorp(501)(c)(3) is not a valid chapter reference for a manpage, it is however a slightly covert reference to the [https://www.irs.gov/charities-non-profits/charitable-organizations/exemption-requirements-section-501-c-3-organizations 501(c)(3)] section of the Internal Revenue Code of the United States, which describes the requirements for an organization to be tax-exempt.

Copyright "or best offer" is humourous, needs explanation of individual parts.

The "copyright" line references several variously open-source content licenses; GPL 2, GPL 3, creative commons, and BSD licenses are mentioned. "LIKE GECKO" is a reference to a web browser user-agent string; modern user-agent strings include a lot of text designed to let the browser pretend to be several different browsers/renderers, and "(like Gecko)" is the standard text for a browser that wants to be treated as if it were Gecko while admitting, if you look closely, that it isn't really Gecko. This copyright line, which includes a lot of mashed-together text that might appear to match any of several different licenses, resembles a user-agent string.

==Transcript==
:[A terminal screen; the background is black and the text is white.]
:{| class="wikitable"
|style="background-color:black;"|<font color="white">
;NAME
:blerp

;SYNOPSIS
:blerp {[ OPTION | ARGS ]...[ ARGS ... -f [FLAGS] ...}
:blerp {... DIRECTORY ... URL | BLERP} OPTIONS ] -{}

;DESCRIPTION
:blerp FILTERS LOCAL OR REMOTE FILES OR RESOURCES USING PATTERNS DEFINED BY ARGUMENTS AND ENVIRONMENT VARIABLES. THIS BEHAVIOR CAN BE ALTERED BY VARIOUS FLAGS.

;OPTIONS
:{|
! scope="row" | -a
| ATTACK MODE
|-
! scope="row" | -b
| SUPPRESS BEES
|-
! scope="row" | -—
| FLAGS USE EM DASHES
|-
! scope="row" | -c
| COUNT NUMBER OF ARGUMENTS
|-
! scope="row" | -d
| PIPES OUTPUT TO DEBUG.EXE
|-
! scope="row" | -D
| DEPRECATED
|-
! scope="row" | -e
| EXECUTE SOMETHING
|-
! scope="row" | -f
| FUN MODE
|-
! scope="row" | -g
| USE GOOGLE
|-
! scope="row" | -h
| CHECK WHETHER INPUT HALTS
|-
! scope="row" | -i
| IGNORE CASE (LOWER)
|-
! scope="row" | -I
| IGNORE CASE (UPPER)
|-
! scope="row" | -jk
| KIDDING
|-
! scope="row" | -n
| BEHAVIOR NOT DEFINED
|-
! scope="row" | -o
| OVERWRITE
|-
! scope="row" | -O
| OPPOSITE DAY
|-
! scope="row" | -p
| SET TRUE POPE; ACCEPTS "ROME" OR "AVIGNON"
|-
! scope="row" | -q
| QUIET MODE; OUTPUT IS PRINTED TO STDOUT INSTEAD OF BEING SPOKEN ALOUD
|-
! scope="row" | -r
| RANDOMIZE ARGUMENTS
|-
! scope="row" | -R
| RUN RECURSIVELY ON <nowiki>http://*</nowiki>
|-
! scope="row" | -s
| FOLLOW SYMBOLIC LINKS SYMBOLICALLY
|-
! scope="row" | -S
| STEALTH MODE
|-
! scope="row" | -t
| TUMBLE DRY
|-
! scope="row" | -u
| UTF-8 MODE; OTHERWISE DEFAULTS TO ANSEL
|-
! scope="row" | -U
| UPDATE (DEFAULT: FACEBOOK)
|-
! scope="row" | -v
| VERBOSE; ALIAS TO find / -exec cat {}
|-
! scope="row" | -V
| SET VERSION NUMBER
|-
! scope="row" | -y
| YIKES
|}

;SEE ALSO
:blerp(1), blerp(3), blirb(8), blarb(51) blorp(501)(c)(3)

;BUG REPORTS
:<nowiki>http://www.inaturalist.org/taxa/47744-Hemiptera</nowiki>

;COPYRIGHT
:GPL(2)(3+) CC-BY/5.0 RV 41.0 LIKE GECKO/BSD 4(2) OR BEST OFFER
</font>
|}

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