explain xkcd - User contributions [en]

2809: Moon

2023-08-01T04:43:07Z

172.70.85.93: /* Explanation */ Typo. And rephrased for precedence and to make better subject/verb non-disagreement.

{{comic
| number = 2809
| date = July 31, 2023
| title = Moon
| image = moon_2x.png
| imagesize = 313x402px
| noexpand = true
| titletext = I mean, it's pretty, but it doesn't really affect us beyond that. Except that half the nights aren't really dark, and once or twice a day it makes the oceans flood the coasts.
}}

==Explanation==
{{incomplete|Created by a STRANGE ORB FLOATING IN THE SKY. Do NOT delete this tag too soon.}}

The Moon is a celestial body orbiting Earth first formed approximately 4.51 billion years ago while the solar system was still forming. As of July 31st, 2023, the Moon is still orbiting the Earth{{Citation needed}} at a distance of 384,400 kilometers, or 238,900 miles.

This comic points out how weird it is to have such an enormous celestial body near to us. The second nearest, Venus, is approximately 46.576 million kilometers away at its closest. The Moon is close enough that we can see the craters and other stuff on the surface with our naked eye, though a telescope would help.

There are other planets with moons,{{Citation needed}} but Earth's moon is very big compared to Earth - Mars's moons are way smaller and the biggest moon in our solar system, Ganymede, is just twice as massive with 1.5 the radius despite orbiting Jupiter, which is 317x more massive than Earth with 11x bigger radius.

In human history, we have landed twelve people on the moon in the Apollo missions from 1969 to 1972. Despite advancements in technology since then,{{Citation needed}} we have yet to land another person on the Moon, though plans are being made.

The title text refers to the saying "The Moon is beautiful, isn't it?" which is a way of saying, "I love you," which originated from the Japanese Novelist Natsume Soseki overhearing a student of his awkwardly translating the phrase. More information can be obtained by googling the term or directly from [https://www.wikihow.com/The-Moon-Is-Beautiful-Isn%27t-It wikihow]. The title text also refers to the lunar cycle, in which the Moon's orbit is roughly half the time on the opposite side of the Earth from the Sun and (being visibly at least half illuminated, whilst there, except briefly during rare eclipses) provides a low but significant amount of reflected illumination that nature (as well as humanity) has found a nocturnal use for. Lastly, the title text also refers to the tides, a very nearly twice-daily cycle where the Moon's gravity (modified by the Sun's) subtly pulls upon the Earth and dragging the waters of the seas and oceans around to periodically increasing the sea levels in most places.

==Trivia==
Earth's moon is weird for an addtitional two reasons. First, it's largest and most massive moon relative to its parent planet. Secondly, our moon is the only moon in the solar system to not have a name. Not even a jumble of letters and numbers. It's simply called "The Moon".

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
[Ponytail points to something in the sky, presumably the moon. Cueball stands nearby]

Ponytail: That thing hanging in the sky is a second nearby world. It's close enough that you can see its surface as it passes overhead.

Cueball: Wow. Isn't that... weird?

Ponytail: I dunno, it's just always been there.

[Caption below the panel:]

If it didn't exist, the moon would sound like such an outlandish sci-fi concept.
{{comic discussion}}

2801: Contact Merge

2023-07-13T11:38:15Z

172.70.85.93: /* Explanation */ Major rewrite/up-padding/speculation to deal with perceived holes in prior version.

{{comic
| number = 2801
| date = July 12, 2023
| title = Contact Merge
| image = contact_merge_2x.png
| imagesize = 353x429px
| noexpand = true
| titletext = I actually kind of feel like John and Surf King wouldn't like each other, which is a lot to unpack.
}}

==Explanation==
{{incomplete|Created by YOUR OTHER FRIEND WHO EDITS EXPLAINXKCD - Please change this comment when editing this page. Do NOT delete this tag too soon.}}

[[Cueball]] is in contact with someone in a some typical text-chat context, who uses the nickname of "Surf King". His phone also knows of a person called John, which seems to be the real name of the same person, although Cueball appears to have been unaware or forgetful of that fact.

Some algorithm that manages the contact-list has been offering (or trying) to merge the contact details into a single entry, as having the same core details, which intruiges Cueball but without him understanding why. Instead he directs a comment about this to "@Surf King", who apparently did not deign to respond (leaving just a hanging ellipsis).

Cueball's follow-up comment is clearly prompted by the realisation that his 'two' contacts both share an interest in surfing, perhaps having been in separate group conversations with both John and Surf King personae in the interim, and he decides to revist the issue. But from Surf King's response it looks like gap of time between the start of this 'conversation' and it being added to was on an order of several years. Exactly how this happened depends a lot on the text-chat system in use, but it's not unknown for a persistive messaging system to keep a thread of contact 'open' to new posts perpetually. It might be expected to see a timestamp upon contributions (e.g. a time of day or how many seconds/minutes/hours ago, with perhaps "just now" or similar for the most recent and a day-/etc count or full datetime once old enough to make that more practical), or even an automated prompt that the conversation has been idle for so many days when one tries to {{wiktionary|necro#Verb|'necro'}} such an historic channel of communication. Either Cueball's interface does not feature these things or we see it only as Cueball does, seemingly oblivious to the passage of time.

The title text implies that Cueball (still oblivious to the reality of the sitution) has had second thoughts about the compatability of Surf King/John with himself, having picked up further cues from either/both of his chats with him (outside of this particular channel) that reduce the apparent social compatability. This could be explained by John being far more (or differently) extrovert when interacting via his pseudonym, or else by having subtly changed attitudes and interests over time while not using one or other identity. Either of these can be explained by perhaps having let the Surf King account of his youth go mostly idle, instead reverting to his given name to be taken more seriously in professional contexts. For Cueball, [[1674: Adult|being Cueball]], all the details of this (whatever they might ''actually'' be) probably continue to go completely over his head.

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

[Cueball chatting in DMs]

Cueball: @Surf_king Weird my phone keeps trying to merge your contact with John's

Surf_king: ...

Cueball: Hey you two should meet up-He's into surfing too

Surf_king: Oh my God

Surf_king: Are you serious

Surf_king: You've been in this chat with me for '''four years!'''

[Caption below the panel:]

I wonder who holds the record for accidentally doing this the longest

{{comic discussion}}

Talk:2781: The Six Platonic Solids

2023-07-10T09:20:39Z

172.70.85.93: Forgot this still needed doing...

Does he know about Homestar Runner? [[Special:Contributions/172.70.131.137|172.70.131.137]] 06:02, 27 May 2023 (UTC)
:Yes. http://www.hrwiki.org/wiki/Webcomic_Sightings#xkcd [[User:Trogdor147|Trogdor147]] ([[User talk:Trogdor147|talk]]) 01:07, 29 May 2023 (UTC)

Why Jorb? Only thing I can find is [https://en.wiktionary.org/wiki/jorb Jorb on wikitionary] just meaning spelling of bad pronunciation of Job. And yes the episode of Homestar Runner [https://homestarrunner.com/toons/a-jorb-well-done A Jorb Well Done] comes up. Also this episode that is the top meaning of jorb on [https://www.urbandictionary.com/define.php?term=Jorb Urban dictionary]. Would really like there to a better idea than that Plato did a great Jorb making a sixth solid to rule the mathematicians. --[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 07:18, 27 May 2023 (UTC)

: I agree. We should ask for our money back. -- [[User:Dtgriscom|Dtgriscom]] ([[User talk:Dtgriscom|talk]]) 17:19, 27 May 2023 (UTC)

What if there're much more of them, like a [https://xkcd.com/2657 Ď̩̰odec̭ähedron], but our minds can't properly comprehend their shape?
: There are a bunch of other regular polyhedra besides the Platonic solids. Most notable are the triangular, square, and hexagonal tilings (which are planar and infinite) and the four Kepler-Poinsot polyedra (which are nonconvex). And there are dozens more if you don't require faces to be planar. [[Special:Contributions/172.70.178.234|172.70.178.234]] 09:44, 27 May 2023 (UTC)
::See https://youtu.be/_hjRvZYkAgA for an overview of every regular polyhedron in Euclidean 3-space. [[Special:Contributions/162.158.146.40|162.158.146.40]] 09:59, 27 May 2023 (UTC)
:::I had never seen this channel before, and I'd very much like to thank you for introducing it to me. [[Special:Contributions/162.158.167.8|162.158.167.8]] 21:39, 29 May 2023 (UTC)
: Some of the proofs of the theorem that there are exactly five platonic solids do not require our minds to "comprehend their shape", because they only rely on their algebrical properties. In fact, the Group theory proof works in any dimension (≥3), despite our minds being very bad at picturing what stuff looks like in higher dimensions. In fact, it's a bit of the opposite: lower dimensions (2 and 3) are "special cases", because all other dimensions have exactly 6 such platonic solids. [[User:Jthulhu|Jthulhu]] ([[User talk:Jthulhu|talk]]) 15:41, 27 May 2023 (UTC)

I think this is a reference to how the Utah Teapot is nicknamed “the sixth Platonic solid” due to its presence beside real Platonic solids in demonstrations of 33D rendering. [[Special:Contributions/172.68.118.133|172.68.118.133]] 08:52, 27 May 2023 (UTC)
:...yeah, but you need to render that 33D shape on a proper 32D monitor, ideally, because even on a 31D monitor the two different forced perspectives/projections you need to collapse the extra dimensions down tend to look confusing. [[Special:Contributions/172.70.162.229|172.70.162.229]] 10:46, 27 May 2023 (UTC) *insert winky-face as necessary*
:: Thanks, that predates my claim in https://arxiv.org/abs/2103.00090, so I won’t claim priority:
::: ‘By this conception, the claim that there is a Russell Set is simply wishful thinking, analogous to wanting the phrase “sixth Platonic solid” to have a referent, while not actually intuiting which shape this might be.’
:: — [[User:FlashSheridan|FlashSheridan]] ([[User talk:FlashSheridan|talk]]) 12:33, 31 May 2023 (UTC)

Should we think about Jorb, perhaps, as "J orb," which might lead us to think about (''i'',''j'') coordinates, i.e. notational systems where ''j'' is the square root of minus 1? (blah blah engineering vs. mathematics, what does ''i'' mean, &c., &c., &c.) Maybe not! [[User:JohnHawkinson|JohnHawkinson]] ([[User talk:JohnHawkinson|talk]]) 10:41, 27 May 2023 (UTC)

When I naively imagine further platonic solids, my approach to cheating is usually to imagine arbitrarily non-euclidean space. It’s somewhat pleasant that the jorb looks a little like that —- it’s only platonic if the coordinate system it’s in bends and stretches to make it so. I imagine the name and depiction are simply to be intentionslkynvague or confusing about what it actually is. It’s a lot harder to do real innovation nowadays and tasks like inventing a jorb can readily crop up to nerds (the nerd snipe kind) who are looking for sufficiently hard and harmless puzzles. A sixth platonic solid seems to mostly happen outside the norms of what people usually consider in a pretty significant way. [[Special:Contributions/162.158.155.99|162.158.155.99]] 02:30, 28 May 2023 (UTC)

I asked GPT-4, "Why could Sauron control the Nazgûl when not in possession of the One Ring?" The response:

:''Sauron was able to control the Nazgûl even when he didn't possess the One Ring because of the nature of the rings they received and the relationship these rings had with the One Ring.''
:''Sauron, disguised as Annatar, the "Lord of Gifts," helped the Elven smiths of Eregion, led by Celebrimbor, forge the Rings of Power. Unknown to the Elves, Sauron had instructed them to forge the rings in such a way that they could be controlled by one master ring - the One Ring. He secretly forged the One Ring in the fires of Mount Doom, uttering the famous verse: "One ring to rule them all, one ring to find them, one ring to bring them all and in the darkness bind them."''
:''When he gave the nine rings to Men, these rings corrupted them over time and turned them into the Nazgûl, also known as the Ringwraiths. Because these nine rings were still under the influence of the One Ring, Sauron was able to control the Nazgûl even when he did not possess the One Ring himself. The One Ring's power was inherent and didn't need physical proximity to exert control. The Nazgûl were bound to the will of Sauron as their wills were dominated by their rings, which were in turn dominated by the One Ring.''
:''The link and dominance were so strong that even when the One Ring was lost, the Nazgûl remained under Sauron's control. It's also worth noting that Sauron held the Nine Rings the Nazgûl originally received, which could also contribute to his ability to control them.''
:''It's a complex network of influence and control established by Sauron, making him a powerful Dark Lord even in the absence of his master ring.''

Well. I'm glad <s>someone</s> something understands that. Lol. [[Special:Contributions/172.69.22.145|172.69.22.145]] 06:11, 28 May 2023 (UTC)

Looks suspiciously like a bicycle saddle to me. And as anyone who's parked their backside on one for any distance or time, it is DEFINITELY a solid. [[User:RAGBRAIvet|RAGBRAIvet]] ([[User talk:RAGBRAIvet|talk]]) 07:25, 28 May 2023 (UTC)
:(Well, there's all kinds of saddles, and the [https://www.brooksengland.com/en_uk/swallow.html golden era of leather saddles] were actually not that bad (that link states a 10 year guarantee for the current output, but I personally know of a couple used regularly for 60+years and were still doing well), though with the advent of more synthesised materials they've had to go creative with the texture/covering to give it back the 'give'. Which no doubt makes more an 'impression' on the more modern saddle purchaser, in more ways than one.)
:Reminds me of one of the more abstract 'elemental' {{w|Henry Moore}} pieces, or possibly one of his contemporaries/'inspired-by's. And you could certainly find painters and other art-form creators who have gone into 'abstract blob' shapes, either to represent something real in a novel way or to deliberately represent nothing real at all, and I suspect that's Randall's aim... (Like "xkcd" made to not look enough like anything else, or so intended). It certainly shows no sign of ''any'' symmetry at all. [[Special:Contributions/172.70.86.32|172.70.86.32]] 12:29, 28 May 2023 (UTC)

Based on the shape, ribbing, and a different definition of "platonic" I think this could be referring to the Roman artefact that was recently re-classified as a dildo. Platonic solid? [[Special:Contributions/172.70.111.111|172.70.111.111]] 16:06, 28 May 2023 (UTC)

Not gonna lie, this feels like a Cow Tools comic to me. Sometimes mathematicians discover new things, wouldn't it be weird if they discovered something impossible? End of joke. Everything else regarding the shape and name is an inkblot test (until the title text which is actually a LOTR reference of course). [[Special:Contributions/172.70.82.59|172.70.82.59]] 17:04, 28 May 2023 (UTC)

Is it worth mentioning that the dodecahedron and isocahedron have their names switched? [[User:C.h.ninnymuggins|C.h.ninnymuggins]] ([[User talk:C.h.ninnymuggins|talk]]) 21:00, 28 May 2023 (UTC)
:It would be if they were (a common error), but... they aren't. (See {{w|Platonic solid|here}}.) [[Special:Contributions/172.69.79.196|172.69.79.196]] 21:33, 28 May 2023 (UTC)

Ok whoever added that jan misali link that's super cool of you nice [[Special:Contributions/172.71.82.147|172.71.82.147]] 03:50, 29 May 2023 (UTC)Bumpf

I feel that there's a joke missing here, especially with the LOTR connection made in the alt-text. After all, Plato might have gifted the solids to the mathematicians, but thanks to Gary Gygax, it was the gamers who found a use for them....
[[Special:Contributions/172.70.86.7|172.70.86.7]] 06:37, 29 May 2023 (UTC)

Plato did a a great jorb ruling the mathematicians by forging the impossible... plato got a gold star at his job review... was that really it?--[[User:4til7|4til7]] ([[User talk:4til7|talk]]) 20:33, 29 May 2023 (UTC)

I kind of feel sorry for the platonic solids. Condemned to the friend zone for eternity; or at least until the end of this universe. [[User:These Are Not The Comments You Are Looking For|These Are Not The Comments You Are Looking For]] ([[User talk:These Are Not The Comments You Are Looking For|talk]]) 22:54, 29 May 2023 (UTC)

You've all been nerd sniped. [[Special:Contributions/172.70.42.43|172.70.42.43]]

Also the Gömböc comes to mind from the name, the shape and the novelty of Jorb.
[[Special:Contributions/162.158.182.115|162.158.182.115]] 18:51, 2 June 2023 (UTC)
: Added link to "{{w|Gömböc}}", as that is immediately what I thought of when seeing this comic. Randall's Jorb looks designed to have Gomboc-like properties: if starting on the long thin facet seen on the top edge, it would be gently pulled down by the large round egg-like "end" and then presumably roll onto one side or the other i.e. rotating around its long axis until reaching the position shown. If the Jorb were indeed a mono-monostatic shape, then like the known Gömböc design it would be a "polyhedron" with one (albeit curved) "facet", and like the Platonic solids it can rest on any one of its facets, trivially true as there is only one facet. [[User:Mrob27|Mrob27]] ([[User talk:Mrob27|talk]]) 05:50, 12 June 2023 (UTC)

So, I think this explanation is under-focused on the actual joke. The core humor here is the idea that "Platonic Solid" means "Solids Plato made" and not regular polyhedra at all. "Mathmetitions long believed there were five platonic solids, all regular polyhedra" So the jorb is explicitly a platonic solid that is not a regular polyhedra. Our explanation should point out then, things like the fact that the platonic solids predate Plato.

There is no doubt that the cube is the most common, but today a strange force made a lot of tetrahedron objects appear. This happens every year. [[User:ConlangGuide]] {{unsigned|CategoryGeneral|02:08, 10 July 2023 (re-posted)}}
:I'd like the answer to two questions:
:# What is CG even talking about?
:# What is the person who keeps removing CG's comment even complaining about? (Something about Cultural Misappropriation, but ''which'' culture(s)?)
:...maybe the answer to one will answer the other, but I've a feeling they're entirely unconnected. Perhaps one (or both?) just trolling. Yet, unless 7/7 is International Dungeons&Dragons™ Day, or something, neither even close to what I'm imagining it's about. [[Special:Contributions/172.71.242.96|172.71.242.96]] 10:50, 9 July 2023 (UTC)
::That post first appeared in June. [[Special:Contributions/172.71.154.17|172.71.154.17]] 23:45, 9 July 2023 (UTC)

I wonder if this is relevant: http://www.hrwiki.org/wiki/A_Jorb_Well_Done {{unsigned ip|162.158.62.141|3:47, 2 July 2023}}

Talk:154: Beliefs

2023-07-07T14:54:57Z

172.70.85.93: Undo revision 317394 by FaviFake (talk) Revised undo... Don't change people's Talk words for them.

Doesn't the girl have too long hair to be Megan? The official transcript just calls them 'girl' and 'professor'. –[[User:St.nerol|St.nerol]] ([[User talk:St.nerol|talk]]) 17:43, 22 June 2013 (UTC)
::Actually she looks more like Danish to me. {{unsigned|BruceJohnJennerLawso}}
:::They're just generic humans, stop trying to say "her hair is wrong for [character]". It's really dumb. -Pennpenn [[Special:Contributions/108.162.250.162|108.162.250.162]] 04:27, 9 July 2015 (UTC)
::::The girls is definately not [[Danish]]. Danish has some special personality traits (being mean and clever and not caring a thing about other). The hair is just a small thing. Also children are neither Megan nor Cueball as these are adults. I have removed reference to Danish. Actually it is the professor that looks like Megan! --[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 11:01, 28 December 2015 (UTC)
::::Randall definitely uses a specific cast of characters, each of which repeat characteristic behaviors & are recognizable primarily by consistent depiction of individual hairstyles. I encourage everyone to continue attempting to identify & thereby more fully understand each character, based upon their relative hairstyles & attitudes. (... "~ how are they connected? Hairstyles & attitudes, how do they relate? How well do we use our freedom to choose, the illusions we create?" - Timbuk 3) [[Special:Contributions/108.162.221.16|108.162.221.16]] 18:39, 27 May 2016 (UTC)
Actually, my question is whether the girl on the left is [[Science Girl]]. [[User:Hdjensofjfnen|Hdjensofjfnen]] ([[User talk:Hdjensofjfnen|talk]]) 19:53, 25 September 2018 (UTC)
::Almost has to be [[Science Girl]], or a prototype of her at least. [[User:Nitpicking|Nitpicking]] ([[User talk:Nitpicking|talk]]) 19:58, 17 August 2021 (UTC)
:::Reference to future readers: [[User:FaviFake]] has now granted Science Girl the name of [[Jill]] and converted various of the links to that (or to [[Hairbun]], but that's another story). As there should be no changes to other people's valid Talk contributions, this needs pointing out (more than it needs 'correcting'). [[Special:Contributions/172.70.85.93|172.70.85.93]] 14:54, 7 July 2023 (UTC)

What needs to be pointed out more is that science is a system of working toward finding the truth, that requires its adherents to remember that they never actually know for certain. A lot of modern "scientists" follow the same bad methodology as adherents of the geocentric model and astrology once did. Cosmology and quantum mechanics are full of epicycles, deferents, positivism, and static projection. Einstein and Schrodinger were correct to be horrified by that. —[[User:Kazvorpal|Kazvorpal]] ([[User talk:Kazvorpal|talk]]) 14:31, 29 September 2019 (UTC)

User talk:FaviFake

2023-07-06T13:59:17Z

172.70.85.93: /* I disagree with Oxford commas. */ new section

{{TOC}}<big><big><big><big><big>Hey there, feel free to '''[https://www.explainxkcd.com/wiki/index.php?title=User_talk:FaviFake&action=edit&section=new send me a message]''' :)</big></big></big></big></big>
== Objects table ==
Thanks for replying. The current table in the main text looks good, but still it is a ''description'' or just ''enumeration'' of game objects, not an ''explanation'' (or in some cases: partly an explanation). Supposing we keep the current structure, it is possible to add explanations for the planet names in the '''Explanation''' column. For example, first sentence of the second paragraph is a good ''explanation'' for the Uzumaki planet's name. On the other hand, Andal has only a ''description'' (what it looks like and what features are present on the surface) and no ''explanation'' (that it refers to Animorphs series of books). There's also a question where one should put explanations of items and messages. Some do not need an explanation ('You found a stick'), but most do: what they mean and what they refer to, both in xkcd context (such as when there's a comic about the thing) and in general context. I hope you understand the difference between ''description'' and ''explanation''. Maybe there's also some misunderstanding resulting from a language barrier; English is not my native language.

What is also missing in the table are many structures or objects found on the planets and, most importantly, dialogues or monologous of the characters, which contain many puns and references, and also hints for the player. There's simply no place for them in the current structure. Making more columns may be messsy. That's why I proposed making several tables covering different aspects.

Please take my remarks as proposals to improve the structure and not as a criticism or request for you to make everything right and fill every cell of the table. I think we need to create a clear structure for everyone else to fill in with details; but also to provide good examples to follow.

Technical remarks:
* In my opinion, the filename column is not needed, it does not appear anywhere while playing, it's in source code only. Better remove it to have more horizontal space for the rest. The names given to the planets by the editors of the explanation page shown in the Description column are fine.
* Coordinates are also not useful for a regular player, who does not use some Javascript addition/cheats, maybe remove it as well; textual directions in '''Explanation''' column are sufficient.

-- [[User:Malgond|Malgond]] ([[User talk:Malgond|talk]]) 19:59, 2 May 2023 (UTC)
:> Thanks for replying. The current table in the main text looks good, but still it is a ''description'' or just ''enumeration'' of game objects, not an ''explanation'' (or in some cases: partly an explanation). Supposing we keep the current structure, it is possible to add explanations for the planet names in the '''Explanation''' column. For example, first sentence of the second paragraph is a good ''explanation'' for the Uzumaki planet's name. On the other hand, Andal has only a ''description'' (what it looks like and what features are present on the surface) and no ''explanation'' (that it refers to Animorphs series of books).
:Hey! Yeah, that's the state of the table ''right now'', and I 100% percent agree with everything you're saying here. All planets and items that need an explanation should be explained and not just described. I mostly just copied and pasted the "planet description/explanations" from the old list to the table: creating the table was way more painful than i thought. I was actually surprized to see that nobody explained what Andal referred to, but I don't know anything about it so more knowledgeable people will have to chip in on that

:>There's also a question where one should put explanations of items and messages. Some do not need an explanation ('You found a stick'), but most do: what they mean and what they refer to, both in xkcd context (such as when there's a comic about the thing) and in general context. I hope you understand the difference between ''description'' and ''explanation''.
:I do! And I wish other people could help here. I'm not sure if you've seen it, but this is the banner i put above the table:

----
'''ALL ITEM EXPLANATIONS NEED TO BE TRANSFERRED FROM THE OLD PLANET LIST TO THE NEW TABLE''' 
We are currently switching from a disorganized list (below, inside the green banner) to the new organized table, but the explanations for specific items are missing from the new table. Please help by copying the item explanations from the old list and adding them to the new table ''in this format:'' 
<code>The item message &ndash; <nowiki>''Where to find it &ndash; Explanation, such as references etc''</nowiki></code> 
Example: You found a cheese platter (Your tanks recharge faster) – ''Next to the cell tower – The cheese is a reference to [https://example.com 1234: Cheese]''
----
'''OTHER ISSUES:'''
* upgrades that end in "???" need to be replaced by the exact upgrade message shown to the user.
* the "Tiles (X, Y)" column for planet coordinates is empty

:As you can see, the explanations should be put right next to the items and messages. Unfortunately no one has started to add them to the table yet

:> Maybe there's also some misunderstanding resulting from a language barrier; English is not my native language.
:Your English is excellent :)

:> dialogues or monologous of the characters, which contain many puns and references, and also hints for the player. There's simply no place for them in the current structure. Making more columns may be messsy. That's why I proposed making several tables covering different aspects.
Almost all the dialogues are on the [[2765: Escape Speed/Transcript]] page, so I guess they should be added there. I don't know if they're already here, I haven't looked at it enough
:: The transcript is not the place for explanations. Puns and references shall be explained elsewhere. I continue working on the transcript but there's still quite a way to go. -- [[User:Malgond|Malgond]] ([[User talk:Malgond|talk]]) 5 May 2023

:> Please take my remarks as proposals to improve the structure and not as a criticism or request for you to make everything right and fill every cell of the table. I think we need to create a clear structure for everyone else to fill in with details; but also to provide good examples to follow.
:Yeah; i totally get everything you said. In my last reply I think I was a bit too rude for some reason, maybe it's because I just finished the table and was tired.

:>* In my opinion, the filename column is not needed, it does not appear anywhere while playing, it's in source code only. Better remove it to have more horizontal space for the rest. The names given to the planets by the editors of the explanation page shown in the Description column are fine.
:* Coordinates are also not useful for a regular player, who does not use some Javascript addition/cheats, maybe remove it as well; textual directions in '''Explanation''' column are sufficient.
I was heavily inspired by the table in the [[2712: Gravity]] explanation, which included these. I kind of agree that the filename could be removed, and the filenames could be added to the planet name or explanation, i didn't think about that. About the tiles, someone might use them someday, but if the column keeps remaining empty, i don't mind seeing it disappear

:I really liked your ideas, if you don't mind I'll copy and paste this discussion in the actual comic discussion page and see what others think --[[User:FaviFake|FaviFake]] ([[User talk:FaviFake|talk]]) 21:37, 2 May 2023 (UTC)

::Update: I found a way and added all the coordinates, and moved the planet filenames to the Planet Name column to make more space for the other columns :)

::: Hi, what about dividing planets and objects like in [[User:Malgond/Drafts/Escape_Speed|my experiment]]? There's plenty of horizontal space for explanations and the entries are quite compact vertically. I also think about color-coding the different Types of game objects. -- [[User:Malgond|Malgond]] ([[User talk:Malgond|talk]]) 5 May 2023

::::Hmm, I think it looks a little messy and maybe too complicated. Do any other comics have two different tables? Also, I'm personally not a fan of mixing items, landscapes, and people. I think most people reading the table are there to get an overview of the planets and what they contain. Do we really have to explain everything in such detail? [[User:FaviFake|FaviFake]] ([[User talk:FaviFake|talk]]) 14:09, 6 May 2023 (UTC)

:::::We do not have to follow other explanations too closely, we could use a new form if it seems clearer and better. The current form has no place neither for explaining items nor for dialogues/monologues. More columns could be problematic (specifically in today's world of high and narrow screens of smartphones). Should we explain everything? Well, it us up to collective "us". Personally, I would like someone explain a few puns/dialogues I do not understand.
:::::For now, there's only a handful of people still interested in somehow finishing the explanation for this huge comic. Maybe if we two can agree on some format we could put it in discussion page and ask for votes. (Discussion needs a cleanup, BTW). -- [[User:Malgond|Malgond]] ([[User talk:Malgond|talk]]) 22:00, 7 May 2023 (UTC)

:::::Hey, I'm back. I see you're enhancing your example table, and iI was wondering, do you plan to move your edits to the actual article after you're done and use the test to see how the formatting looks? Isn't it easier to just add them to the main page directly? Just wondering. If you want I can help you port them over :)
:::::Keeping the contents of the table on your talk page and then porting them over afterwards could lead to a loss of information added after you started editing your user page [[User:FaviFake|FaviFake]] ([[User talk:FaviFake|talk]]) 13:11, 13 May 2023 (UTC)

::::::I'm back too. Yes, I intend to put it in the main article, but I am a bit shy to replace a lot of your work; I've asked for opinions in the talk page. Let's see how it sorts out. Maybe someone has a still better idea. -- [[User:Malgond|Malgond]] ([[User talk:Malgond|talk]]) 21:50, 13 May 2023 (UTC)

::::::Oh. I think the structure of the current table in the article is better than the one you've been working on: for example, it's easier to sort for items, is more compact, and is just one. Why don't you just add a "transcript" column like the table on [[2712: Gravity]] to put what things and people say, and add the rest of the information on the respective columns? Personally, I think you're making it a little bit too complicated. [[User:FaviFake|FaviFake]] ([[User talk:FaviFake|talk]]) 15:26, 14 May 2023 (UTC)

== Typo? ==

Rephrasing, yes, but I don't think [https://www.explainxkcd.com/wiki/index.php?title=1828:_ISS_Solar_Transit&curid=20102&diff=313177&oldid=285814 this] fixes a typo, or any other error. No problem with the change, but weird reason. [[Special:Contributions/172.71.242.87|172.71.242.87]] 16:21, 15 May 2023 (UTC)
:Yeah you're right, I think I just didn't want to type a long reason for such a small change. [[User:FaviFake|FaviFake]] ([[User talk:FaviFake|talk]]) 16:39, 15 May 2023 (UTC)

== Haltones ==

"They're not **predominantly** gray, the two main colors are just white and black. Sometimes he uses the gray color just like when he uses any other color" ... It didn't say that they were predominantly grey(/'gray'), any more than it said that they'd be predominently black (as [[:Category:Comics with inverted brightness]], often, in preference to white). The point being that even the most "black and white" images aren't monochrome, but have degrees of grey at the boundaries, with smoothly antialiased boundaries between the full black of the line (or filled area) and the full white of the background (or inverted detail). You'll see this if you zoom in, with your favourite image editor. And very often in images with a default RGB colourspace, even if the effective pallette employed covers just greyscale values. But greys actually do feature a lot, too (often the first choice of non-black-and-white, for slight lessening of prominence, as opposed to 'red pen' ''increased'' visibility). So it's technically inaccurate to describe them as pretty much monochrome. But how to convey this in <...counts...> less than 157ish words? [[Special:Contributions/172.71.242.173|172.71.242.173]] 16:35, 17 May 2023 (UTC)
:The wiki page says
::::"xkcd comics are usually plain, predominantly black-and-white line drawings, but sometimes they make use of hues beyond the usual monochrome colors, even if it is just red-penned annotations.
:I think it's enough, since, even if grey is more used than other non-monochrome colors, I don't believe it's so important that it needs to be included as a "third" main color. If Randall uses many bright colors, that he will obviously also use simpler hues of grey when needed. What do you think? [[User:FaviFake|FaviFake]] ([[User talk:FaviFake|talk]]) 16:51, 17 May 2023 (UTC)
:Aside from the antialising edging gradient, I just used the Random Page link and landed on [[1301: File Extensions|something with functional greys]], [[734: Outbreak|an unusual use of 'Post-It' yellow]], an unremarkably "just black pen" comic and then [[1788: Barge|more functional grey]]. I'd argue against "monochrome" as a description, as clearly there is more than just #000000 and #FFFFFF, often enough, in an actual fill-colour/broad-brush context. Even if that's #808080 or another no-hue shade. (I was expecting to land on a "grey pen" comic to assess, after enough clicks but, having seen what I got in the random first handful, I saw no need to go on.)
:And "monochrome" can be/often is coloured. Sepia photographs or "night vision" green displays are perfect examples of monochrome (with or without halftones/dithering/whatever). As is [[267: Choices: Part 4]] (other Choices comics may be considered "duotone", in different ways).
:Maybe "...are often drawn as black shapes on white, or occasionally white shapes on a dark background, but may feature at least one additional highlighting shade or an even fuller colour pallette." Does that sufficiently cover that whole breadth of use? [[Special:Contributions/172.70.86.154|172.70.86.154]] 19:48, 17 May 2023 (UTC)

== Childish slang. ==

Agree with you on the recent change that you (generic 'you', not ''you'' 'you'!) sound infantile, any which way, upon use of the words mentioned. Which is how it was still said before the revert in that version of edit. But with <code>"pretty gay" and "retarded" are infantile and offensive slang for "foolish" or "contemptible"</code>, you miss the point. Foolishness is just one distant contender for what "pretty gay" is often intended to mean (even if not actually being used for someone/something 'effeminate'). And "retarded" is more in the whole "thick, stupid, dumb" line of insult than "contemptible" (which is more "horrible, dislikable, repulsive"..?).
 Personally, I also thought it better with not actually defining insults (correctly or otherwise), as it adds power to them. I can call someone a "numpty" in jest, for example, and colloquially that might be understood as the low-level insult (if that) which it is intended to be. But if I start to bandy around its {{wiktionary|numpty#Scots|dictionary definition}} then it becomes more of a seriously accusatory description.
 Just my opinion. Not really understanding the latest revert when it had seemed to be improved (if anything) in the version you reverted away. Just putting it there. I know you're doing a lot of editing (good stuff!) just wondering if you considered this one carefully enough in your obvious zeal. [[Special:Contributions/172.71.182.89|172.71.182.89]] 16:31, 28 May 2023 (UTC)
:Addendum. Meant to say, if you decide to undo/reform your own revert (I won't do it, but on the offchance you see my point), I'd have not said "''commonly'' used". They're used in slang, but I don't think we can say how frequently they pop up. They're "used in slang" (and also not in slang, or at least not insulting slang, where "gay" has a long history of just meaning "happy", whilst "retarded" is often to do with decceleration/minimised acceleration of physical systems) but I'm not sure they're no more than minority words in the whole world of such language. They depict a subset of insult-givers (like the character in the comic, for whom it adds a certain additional characterisation) amongst all the many and varied insult-givers, and Randall surely chose such semi-bowlderised terms to not have to write any of all the far worse words he might also have done. [[Special:Contributions/172.71.94.31|172.71.94.31]] 16:46, 28 May 2023 (UTC)

== IP page to delete ==

I didn't see your thinking about why the Deletion category was not needed there. And, believe me as an IP myself, I've never known anything useful being said on an IP's User or User Talk page. With that example not breaking the pattern any. [[Special:Contributions/172.70.85.131|172.70.85.131]] 00:41, 22 June 2023 (UTC)
:I just don't think there's a reason to delete it, it's useful to have a previous talk page if the IP continues to edit and people want to communicate with them [[User:FaviFake|FaviFake]] ([[User talk:FaviFake|talk]]) 10:51, 30 June 2023 (UTC)
::"The IP" is whichever one of 'us' happens to land on that particular Cloudflare route.
::I'm not going to go back and find out which IP it represents, to check if it's in their current stock of connected gateways, but it might not be. Or it was even (depending on date) a pre-Cloudflare 'straight' access unproxied and thus no longer seen, even if the exact same editor on the exact same IP lucked on ''their'' initial gateway.
::Certainly it won't map to a meaningful 'user', chances may even be that it doesn't map to ''any'' user. IP-version User/User Talk pages are anachronisms pretty much as soon as they're created. Or before, if based upon trying to contact an author of an older edit. I was on 172.70.85.131, above, but who knows (before I submit it) what this reply's sign-off will say.
::And a one-shot editor may never ever see the results of any conversation that was tried to be started. Whereas I ''might'' see any response, anywhere, that contextually makes it plain that they're talking about an edit I once made.
::Honestly, I think it'd be worthwhile checking ''every'' IP-focussed namespace page and archiving anything truly interesting that found itself in there in some other central location then condemning them all to deletion. Maybe, if possible, prevent their creation too. But I don't have the ability to do anything (except sift through them for any of the very rare gems of quality, but I wouldn't be able to do anything about it from there on in, so...
::...not gonna do anything more about it (I can't, other than reinstate the To Be Deleted membership, whch I won't bother with), but I hope you understand my perspective on this. I've seen you become a very useful member of the community, who I generally respect for your input and tweaks to the site, and don't expect you to take instruction from li'l ol' me (not even working with an established identity). Just consider this as food for thought, and leave it at that if you wish. [[Special:Contributions/162.158.34.19|162.158.34.19]] 20:12, 30 June 2023 (UTC)

== RTL/LTR: "...but I think it refers to me" ==

Yeah, it does. The point being that we might not do anything about the smartarses who vandalise knowingly (and I don't see a problem with what you otherwise did), but when someone thinks ''they'' have unique and funny joke (along the lines of putting "Citation needed"s ''everywhere'') they might spot the comment and then realise how we've seen it all done before so refrain from the prank. I can't even recall how many times we have had to revert things, but best to put off the casual comedian, and it won't change the outcome either way for the dedicated vandal with their blood up and looking to cause trouble. [[Special:Contributions/141.101.98.107|141.101.98.107]] 20:00, 29 June 2023 (UTC)
:I guess you're right, I just thought it was very clear for everyone that rendering an entire article unreadable was an act of pure vandalism, but I guess an editor comment doesn't hurt. [[User:FaviFake|FaviFake]] ([[User talk:FaviFake|talk]]) 10:53, 30 June 2023 (UTC)

== The reason "the image size wasn't there"? ==

...because it didn't need an image-size restriction, originally? Compare the [https://www.explainxkcd.com/wiki/index.php/File:Miss_lenhart.png previous and current version sizes]. Nice to have a (''huge!'') high-res headshot, no doubt, but clearly that's why you found that it now needs artificially constraining... No actual mystery. [[Special:Contributions/172.70.85.63|172.70.85.63]] 17:16, 5 July 2023 (UTC)

:Yeah you're right, I just assumed every comic had the image size to be future-proof. The weird thing was that the "imagesize: " part was already there, but there was no value. Anyway, nothing important.

: Just out of curiosity, are you the same IP guy from [[#IP page to delete]]?--[[User:FaviFake|FaviFake]] ([[User talk:FaviFake|talk]]) 18:43, 5 July 2023 (UTC)

== I disagree with Oxford commas. ==

"For breakfast I had some bread, toast, and jam." - A legitimate(ish) case of ", and ". Or "I created the world, and saw that it was good." I otherwise prefer to suscribe to replacing all non-final conjunctions in sequence with commas but ''not'' adding one before the ultimate (remaining) conjunction. That's like having "Fish, and chips", where it isn't an actual afterthought. And best to rephrase or repunctuate (e.g. with super-listing semicolons to separate) if you have confusing comma-breakout clauses that ''so'' easily clash (or lead you down funny garden paths) with Oxford Commas. My opinion, but this is why syntax is clearer when leaving out OCs. [[Special:Contributions/172.70.85.93|172.70.85.93]] 13:59, 6 July 2023 (UTC)

2798: Room Temperature

2023-07-06T12:55:09Z

172.70.85.93: /* Explanation */

{{comic
| number = 2798
| date = July 5, 2023
| title = Room Temperature
| image = room_temperature_2x.png
| imagesize = 299x352px
| noexpand = true
| titletext = They're also refusing to fund my device that demonstrates uncontrolled hot fusion.
}}

==Explanation==
{{incomplete|Created by a LUKEWARM FUSION REACTOR. Do NOT delete this tag too soon.}}

In this comic, Cueball presents a room-temperature {{w|Semiconductor|semiconductor}}, consisting of layered silicon crystals. He enthusiastically describes the properties of his "discovery", namely that it can be tweaked to amplify or switch the flow of electric currents, but his audience is not impressed. This might be because silicon crystal semiconductors are already widely in use as a {{w|Semiconductor_device|key component of electronic systems}}.

It appears that Cueball has confused semiconductors with {{w|Superconductivity|superconductors}} - materials that have no electrical resistance, meaning the flow of electrons is not slowed down at all (resistance can be thought of as the electrical equivalence of friction). Superconducting properties are extremely desirable since they allow for the lossless flow of electric current, as opposed to regular conductors like copper which have a low but non-zero resistance so the electric current decreases over time and distance, and this may also lead to them having interesting magnetic properties. However, the known superconductors only work at extremely low temperatures close to 0 °K, so their practical use is very limited. The discovery of superconductors that work above the boiling point of nitrogen (77 °K or -196 °C) was a big deal because it meant that relatively cheap liquid nitrogen could be used as coolant rather than liquid helium. The discovery of a superconductor that works at room temperature (293 °K) would be a much bigger deal and would likely earn the discovering scientist(s) a Nobel prize.

In the title text, Cueball talks about a device that produces “uncontrolled {{w|Nuclear_fusion|hot fusion}}” which is also not met with enthusiasm. Again, this is likely due to the fact that it has already been discovered and used - in the form of {{w|Thermonuclear weapon|hydrogen bombs}}. This is likely why no one wants to fund the device - not only is it not novel, but it is extremely dangerous; though clearly he also hasn't excited those people who typically ''want'' something dangerous. ''Controlled'' hot fusion could be useful as an {{w|Fusion_power|alternative power source}} for nuclear reactors (which currently use nuclear ''fission''); however, {{w|Tokamak|current implementations}} still require more energy than they create. Cueball probably confused this with {{w|Cold_fusion|''cold'' fusion}} which is a purely hypothetical nuclear reaction that would take place at room temperature. If real, this process could provide large amounts of cheap energy, but so far all experiments that were claimed to have achieved cold fusion were found to be severely flawed and the results could not be replicated.

It should be noted that both "discoveries" presented in the comic were in fact very big and important discoveries back in their day. The proposal that nuclear fusion is what powers stars earned {{w|Hans_Bethe|Hans Bethe}} the Nobel prize in Physics, and semiconductors are what allow modern electronic devices to be so small, as their properties make it possible to selectively steer the flow of electrical current, {{w|Integrated_circuit|even over an extremely small area}}.

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

:[A single frame with a table in the middle. A device consisting of multiple components and electrical wires is on the table. A Cueball stands to the left of the table, and facing him, Ponytail and another Cueball stand to the right of the table.]
:Cueball: My layered silicon crystals can amplify or switch current while sitting right here on the table!
:Ponytail: Uh huh.
:Another Cueball: I see.

:[Caption below the panel:]
:No one is impressed by my discovery of room-temperature semiconductors.

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Ponytail]]
[[Category:Multiple Cueballs]]
[[Category:Physics]]

Blue Eyes

2023-06-27T14:46:41Z

172.70.85.93: Better place for the caveat/exception statement.

''Due to the way the template is created, the link to the comic does not operate properly. Please click [http://imgs.xkcd.com/comics/xkcd_ufs.jpg here] to view it.''
{{comic
| date = October 11, 2006
| title = Blue Eyes
| image = Blue Eyes.jpg
| before = The Hardest Logic Puzzle in the World
| lappend = blue_eyes.html
| extra = yes
}}
{{TOC}}
==Explanation==
xkcd's [http://xkcd.com/blue_eyes.html Blue Eyes] puzzle is a logic puzzle posted around the same time as comic [[169: Words that End in GRY]]. [[Randall]] calls it "The Hardest Logic Puzzle in the World" on its page; whether or not it really is the hardest is up to speculation.

The page contains two comics. On the top is [[82: Frame]], and at the bottom is [[37: Hyphen]]. These particular comics may have been chosen intentionally, as 82 involves a mind screw (and formal logic can be pretty mind-screwy to the uninitiated) and 37 involves linguistic ambiguity, which Randall has explicitly gone out of his way to avoid (interestingly, [[169]] involves the infuriating ambiguity caused by misquoting riddles). That said, Randall could have simply picked those comics out of a hat to plug for his comic (which he also does explicitly), and the date of release could also be completely random.

Randall cites "some dude on the streets in Boston named Joel" as his source for the comic idea (although he's rewritten it).

==The Puzzle==

A group of people with assorted eye colors live on an island. They are all perfect logicians -- if a conclusion can be logically deduced, they will do it instantly. No one knows the color of their eyes. Every night at midnight, a ferry stops at the island. Any islanders who have figured out the color of their own eyes then leave the island, and the rest stay. Everyone can see everyone else at all times and keeps a count of the number of people they see with each eye color (excluding themselves), but they cannot otherwise communicate. Everyone on the island knows all the rules in this paragraph.

On this island there are 100 blue-eyed people, 100 brown-eyed people, and the Guru (she happens to have green eyes). So any given blue-eyed person can see 100 people with brown eyes and 99 people with blue eyes (and one with green), but that does not tell him his own eye color; as far as he knows the totals could be 101 brown and 99 blue. Or 100 brown, 99 blue, and he could have red eyes.

The Guru is allowed to speak once (let's say at noon), on one day in all their endless years on the island. Standing before the islanders, she says the following:

"I can see someone who has blue eyes."

Who leaves the island, and on what night?

==Solution==

Randall's solution is at [http://xkcd.com/solution.html xkcd.com/solution.html].

Here are some observations that help simplify the problem.

No one without blue eyes will ever leave the island, because they are given no information that can allow them to determine which non-blue eye color they have. The presence of the non-blue-eyed people is not relevant at all. We can ignore them. All that matters is when the blue eyed people learn that they actually are blue-eyed.

There are two ways in which blue-eyed people might leave the island. A lone blue-eyed person might leave on the first night because she can see that no one else has blue eyes, so the guru must have been talking about her. Or an accompanied blue-eyed person can leave on a later night, after noticing that other blue-eyed people have behaved in a way that indicates that they have noticed that her eyes are blue too.

The problem is symmetrical for all blue-eyed people, so this means they will either all leave at once or all stay forever.

'''Theorem:''' If there are N blue-eyed people, they will all leave on the Nth night.

'''Dual Logic.'''

Blue eyed people leave on the 100th night.

If you (the person) have blue eyes then you can see 99 blue eyed and 100 brown eyed people (and one green eyed, the Guru).
If 99 blue eyed people don't leave on the 99th night then you know you have blue eyes and you will leave on the 100th night knowing so.

'''Intuitive Proof.'''

Imagine a simpler version of the puzzle in which, on day #1 the guru announces that she can see at least 1 blue-eyed person, on day #2 she announces that she can see at least 2 blue eyed people, and so on until the blue-eyed people leave.

So long as the guru's count of blue-eyed people doesn't exceed your own, then her announcement won't prompt you to leave. But as soon as the guru announces having seen more blue-eyed people than you've seen yourself, then you'll know your eyes must be blue too, so you'll leave that night, as will all the other blue-eyed people. Hence our theorem obviously holds in this simpler puzzle.

But this "simpler" puzzle is actually perfectly equivalent to the original puzzle. If there were just one blue-eyed person, she would leave on the first night, so if nobody leaves on the first night, then everybody will know there are at least two blue-eyed people, so there's no need for the guru to announce this on the second day. Similarly, if there were just two blue-eyed people, they'd then recognize this and leave on the second night, so if nobody leaves on the second night, then there must be a third blue-eyed person inspiring them to stay, so there's no need for the guru to announce this on the third day. And so on... The guru's announcements on the later days just tell people things they already could have figured out on their own.

It's obvious that our theorem holds for the "simpler" puzzle, and this "simpler" puzzle is perfectly equivalent to the original puzzle, so our theorem must hold for the original puzzle too.

Another way of looking at it is to use selective attention. Although each blue-eyed person can see each other blue-eyed person on the island, she doesn't need to. The only thing she needs to know in order to determine whether to leave on night N is whether or not she can see an Nth person with blue-eyes. On night 1, she only needs to see 1 other blue-eyed person to not leave; on night 2, she can see 2 other blue-eyed people, so she doesn't leave; and so on and so on until night 100 when she can't see a 100th blue-eyed person, and then leaves.

'''Formal Proof.'''

To prove this more formally, we can use mathematical induction. To do that, we'll need to show that our theorem holds for the base case of N=1, and we'll need to show that, for any given X, *if* we assume that the theorem holds for any value of N less than X, then it will also hold for N=X. If we can show both these things, then we'll know the theorem is true for N=1 (the base case), for N=2 (using the inductive step once), for N=3 (using the inductive step a second time) and so on, for whatever value of N you want.

Base case: N=1. If there is just one blue-eyed person, she will see that no one else has blue eyes, know that the guru was talking about her, and leave on the first night.

Inductive step: Here we assume that the theorem holds for any value of N less than some arbitrary X (integer greater than 1), and we need to show that it would then hold for N=X too. If there are X blue-eyed people, then each will reason as follows: "I can see that X-1 other people have blue eyes, so either just those X-1 people have blue eyes, or X people do (them plus me). If there are just X-1 people with blue eyes, then by our assumption, they'll all leave on night number X-1. If they don't all leave on night number X-1, then that means that there is an Xth blue-eyed person in addition to the X-1 that I can see, namely me. So if they all stay past night number X-1, then I'll know I have blue eyes, so I'll leave on night number X. Of course, they'll also be in exactly the same circumstance as me, so they'll leave on night number X too."

This suffices to prove our theorem. The base case tells us the theorem holds for N=1. That together with the inductive step tells us that it therefore holds for N=2, and that together with the inductive step again tells us that it holds for N=3, and so on... In particular, it holds for the case the original puzzle asked about, N=100, so we get the conclusion that the 100 blue-eyed people will leave on the 100th night.

==Randall's thought-provoking questions==

After giving his solution, Randall posed three questions for further thought about the puzzle. (We'll answer them in a different order than he asked.)

'' '''Question 2.''' Each person knows, from the beginning, that there are no less than 99 blue-eyed people on the island. How, then, is considering the 1 and 2-person cases relevant, if they can all rule them out immediately as possibilities?''

Blue-eyed people can't see their own faces, so blue-eyed people can see one less blue-eyed face than non-blue-eyed people can. Even though I can see that there are at least 99 blue-eyed people, I don't know that they can see that, so I need to imagine people who see only 98, who would base their actions in part by imagining people who can see only 97 who would base their actions in part by imagining people who can see only 96, and so on... All the levels are relevant. (It's like [https://www.youtube.com/watch?v=U_eZmEiyTo0 the Princess Bride scene] where Vizzini is trying to think about what Wesley would choose in part based upon Wesley thinking about what Vizzini would choose in part based upon... "So clearly I cannot choose the one in front of me!") Each layer of thinking about what someone else might be thinking about can decrement by 1 the number of blue-eyed people visible to the lattermost imagined person, so it turns out that even the base case with N=1 blue-eyed person is relevant. As the days go by, some of the more far-fetched "he might be thinking that I might be thinking that he might be thinking that I might be thinking that..." hypotheses get ruled out. But it's only after night N-1 that the blue-eyed people rule out all the possibilities in which they have brown eyes, whereas the brown-eyed people only learn on night number N that they don't have blue eyes.

It might help to think of all the different situations people might be in. (Remember brown-eyed people always are situated where they can see one more blue-eyed face than blue-eyed people can.)

'''Situation 0.''' If I see 0 blue-eyed people, I can leave right after the announcement on night 1.
'''Situation 1.''' If I see 1 blue-eyed person, then she might be in situation 0 and about to leave on night 1; or else she might be in situation 1 just like me, in which case we'll both leave together on night 2.
'''Situation 2.''' If I see 2 blue-eyed people, they might each be in situation 1 watching to see whether anyone in situation 0 leaves the first night (I know nobody will leave that night, but they wouldn't know this), in which case they would leave together on night 2; or else they might be in situation 2 just like me, in which case we'll all leave together on night 3.

:
:
:
'''Situation N.''' If I see N blue-eyed people, they might be in situation N-1 watching to see whether any people in situation N-2 leave on night N-1 (I know nobody will leave that night, but they wouldn't know this), in which case they would leave together on night N; or else they might be in situation N just like me, in which case we'll all leave together on night N+1.
:
:

Even though I start out in situation 99, I need to worry that the blue-eyed people might be in situation 98, so I need to wait long enough for people in situation 98 to figure out what's going on, and then see whether they act like they are indeed in situation 98. But if they're in situation 98, then they're worrying about whether all the blue-eyed people might be in situation 97, so they're going to need to wait long enough for people in situation 97 to figure out what's going on. Of course, that requires waiting long enough for people in situation 96 to figure out what's going on, and so on, down all the way to situation 0. All the levels are relevant, and it takes a separate day to eliminate each level, which is why the whole process takes N days.

'' '''Question 3.''' Why do they have to wait 99 nights if, on the first 98 or so of these nights, they're simply verifying something that they already know?
''

Consider an analogy. I've heard that miners used to take canaries down into mines because canaries pass out more quickly in poor air than miners do. Suppose you know the canary will do fine for 98 or so seconds, and then pass out if the air is bad. As you watch the canary for those 98 seconds, there's a sense in which you're just verifying something you already know (it'll do fine), but it seems more accurate to say that your best detector for the quality of the air takes 98 seconds to give you a reading, and you're waiting 98 seconds to see what that reading is.

When the blue-eyed people wait 98 or so days to leave, that's because their best available detector of their own eye-color takes 98 or so days to give a reading. (This detector involves watching what the other blue-eyed people do, and of course they themselves are waiting on a detector that takes 97 or so days to yield its result...) There's a sense in which they're "simply verifying something that they already know", but it seems more accurate to say that they're waiting for their best available detector of their own eye-color to deliver its reading.

'' '''Question 1.''' What is the quantified piece of information that the Guru provides that each person did not already have?''

Before the Guru speaks, the hypothetical chain of A imagining B imaging C imagining D...imagining Z seeing N blue eyed people cannot terminate uniquely. Z seeing no blue eyed people can consider whether or not they are blue eyed. This means it is not {{w|Common knowledge (logic)|common knowledge}} that there are blue eyes. Once the guru makes their pronouncement it is common knowledge and every chain of reasoning must terminate at 1 blue eyed person and Z above would have to conclude that they had blue eyes. From then on every midnight the common knowledge that there are N blue eyed people increments by 1 as everyone sees nobody leaving on the ferry.

Stated another way, there's only one stable set of beliefs for the blue eyed people that would allow them to have so many exist on the island indefinitely. That is if each blue eyed person believed not only that they have brown eyes, but also that every other blue-eyed person believed, incorrectly, that they had brown eyes. Logic reduces this to "all blue-eyes believe that all blues-eyes have brown eyes". The Guru eliminates that particular possibility.

Another simple way to understand why the Guru's information is important is thus. Each blue-eyed person knows two sets of information: what the actual situation is on the island (both now and in the past), and what would happen in a hypothetical situation. Each blue-eyed person then needs only to compare the actual situation to a known hypothetical one, and if it matches up, then they take the corresponding action. Consider this: If there were only one blue-eyed person, and the guru never made the announcement, she would not leave on day 1 because she would not know that N is greater than or equal to 1. Now let's add a 2nd blue-eyed person. Blue-eyes 2 would not be able to inductively determine whether or not to leave on night 2, because blue-eyes 2's knowledge of whether or not to leave on night 2 is dependent on what blue-eyes 1 does on night 1 if and only if blue-eyes 1 knows what to do on night 1. If blue-eyes 1 doesn't know that N is greater than or equal to 1, then blue-eyes 1 doesn't know what to do on night 1. So her lack of leaving gives blue-eyes 2 no new information, since it was an uninformed action and blue-eyes 2's inductive reasoning was dependent on blue-eyes 1 knowing what to do, and so the inductive process never takes off for the hypothetical situation. This means a hypothetical situation for N people cannot be induced. As such, blue-eyes 100 does not have certain knowledge of the hypothetical situation that would occur on nights 99 and 100, and so even though she knows N = either 99 or 100, she can't take action on either of those nights, because she has no certain hypothetical situation to compare reality to, and as such cannot have certainty about the actions she should take.

==Trivia==
*The web page which contains the puzzle has no {{w|CSS|style sheet}}. The font size of the heading and subheading is increased with deprecated HTML tags, rather than the heading tags. The way the page is displayed therefore depends on the browser's settings. Despite this fact, due to a similarity of default settings between computers, most computers will by default display the page similarly to the way it is displayed in this page's screenshot, with a white background, black text and the {{w|Times New Roman}} font or a similar one. However, it has two line breaks after every paragraph instead of HTML paragraph breaks, meaning that paragraph spacing will not vary between browsers, relative to the font size.

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