explain xkcd - User contributions [en]

3147: Hiking

2026-06-29T14:37:45Z

82.132.236.191: /* Explanation */ The link, as given, went to a ballet-term page. Luckily, I found the true intended wikilink to easily add in. ;)

{{comic
| number = 3147
| date = September 26, 2025
| title = Hiking
| image = hiking_2x.png
| imagesize = 740x456px
| noexpand = true
| titletext = Every downhill walk is a waterslide that might have been.
}}

==Explanation==
On-demand delivery is a type of service where you can order a product and it will be delivered to you within hours, or possibly even minutes when the source is sufficiently local. The most well-known of these are food delivery services like {{w|DoorDash}} and {{w|GrubHub}}, where near-immediate delivery is highly preferred. Larger and less time-critical goods have similar services, such as {{w|amazon_(company)|Amazon}}, which can deliver many items well within the same day or by the next morning for most destinations that aren't particularly remote.

In the comic there's a vendor of {{w|waterslides}} that provides on-demand delivery using {{w|drones}} that fly the waterslide to a location you specify in the order, apparently complete with a water supply tank, and with a response time of minutes despite apparently being delivered to a wilderness landscape. While hiking through a terrain with lots of hills, [[Cueball]] and [[Megan]] order one whenever they're on their way up a hill, so that it will be delivered to the downhill side by the time they arrive at the summit, and they can have fun sliding down.

While theoretically possible (even the water tanks could be managed with a sufficient number of [https://pilotinstitute.com/heaviest-drones/ heavy-lift quadcopter drones]) such a system would be wildly impractical. The cost of such a program would be enormous, the timescale would be implausibly short, and installing a water slide, particularly in a way that would make it safe and stable, would require extensive site selection, planning, engineering and construction. Conducting such a project rapidly, remotely and on-demand at a specified location simply wouldn't be feasible. The strip also implies that installation (and possibly the design work) is fully automated, which is beyond current technology.

The title text suggests that [[Randall]] considers walking downhill to be a waste, as that process could have been done by waterslide if only one were present. This may reference the fact that walking downhill is often surprisingly tiring and arduous, as well as being relatively unrewarding compared to the uphill climb, even though gravity is now on your side, and may be considered a chore to be performed after the more tangible sense of accomplishment gained from reaching the top of the hill. The practice of {{w|Glissade (climbing)|glissading}} is often used to ameliorate this when on ice-covered mountains, but is significantly less practical on non-frozen surfaces.

This strip continues a long theme of comics where Randall imagines a process or piece of infrastructure that would be wildly impractical in real life, but would be a lot of fun (for certain values of 'fun') if it could be achieved. Examples include [[260: The Glass Necklace]], [[2935: Ocean Loop]] and [[2973: Ferris Wheels]].

==Transcript==
:[This scene is in a mountain with many bumps. Everything is in one panel. The consecutive actions and speech text proceed roughly from left to right.]
:[Cueball and Megan are both facing right, facing a hill. They are both wearing a backpack.]
:Cueball: Okay, we're nearing the next downhill segment. I'll put in the order.
:Cueball: ...confirming start and end points...
:Cueball: Submitted!
:[A waterslide with drones attached to it, flying down and to the right, with a wavy, dotted line heading down to the slide from the top, showing the direction it has arrived from. Megan and Cueball are standing together. Megan is pointing at the waterslide. Megan and Cueball are moved slightly forward from their last appearance, and on a side of the hill.]
:Megan: Look, here it comes!
:[The slide is on the downhill slope, with drones above it. Megan and Cueball are shown sliding down with dots around them, most likely showing the splash of water around them. Possibly riding on, or in, a long inflatable of some kind, whose front and rear ends are seen angling up out of the waterslide trough that also hides the two character's lower bodies. Some drones are near the waterslide.]
:Cueball and Megan: Wheeeee
:[The slide now is flying up and to the right with drones and another wavy dotted line, this time showing that it has been heading away from the point of use.]
:[Cueball and Megan are depicted walking, ahead of their last appearance.]

:[Caption below the panel:]
:On-demand waterslide delivery has really improved the whole hiking experience.
{{comic discussion}}<noinclude>

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Drones]]

1580: Travel Ghost

2026-06-29T14:27:57Z

82.132.236.191: /* Explanation */ I think the broader point was missed here. Ghosts get selected for optimality, mostly towards a more rapid ideal, but the 'better' version in lovemaking reverses that trend. (To a point, but from a likely less than adequate 'original'.)

{{comic
| number = 1580
| date = September 21, 2015
| title = Travel Ghost
| image = travel_ghosts.png
| titletext = And a different ghost has replaced me in the bedroom.
}}

==Explanation==
In {{w|Racing video game|racing games}}, a "{{w|Time attack#Video games|ghost}}" is a visual representation of a player's previous performance - usually the best one they've achieved so far. It is typically represented in-game as a translucent, intangible image that precisely reproduces what the player did previously. Effectively, it is a virtual racer that players can use to challenge themselves. Some games also allow you to compete against the ghosts of other players, providing a multiplayer experience without requiring all players to be present at the same time. Certain models of cycling also use this concept to motivate athletes while training.

A mapping app, such as {{w|Google Maps (mobile application)|Google Maps}}, attempts to plan the fastest route from one place to another, using a combination of pathfinding algorithms and real-time traffic data to predict the best route. However, there's no way to be sure that this is actually the fastest route unless you actually take it and compare it to other routes.

Thus, [[Cueball]] has combined these two concepts to create an app that does essentially that. Instead of predicting the best route, his app creates simulated "ghost" versions of himself using the real-time data, sends them on different routes, and compares the results. Additionally, the app can also record his own movements and create ghosts from his past journeys, allowing him to compete against his ghosts like a racing game.

However, the comic takes a turn for the absurd when it turns out that these ghosts are somehow visible to other people, rather than just being simulations on his phone. Worse, since ghosts always reproduce the same performance exactly, they have perfect punctuality. Thus, he is soon fired from work because one of his ghosts is more punctual than he is. Even worse, his children apparently comes to prefer the more punctual ghosts over him as this version of daddy never misses their games. (The girls could be the same as those in [[1659: Tire Swing]]).

In the title text, this is taken to an even more absurd degree when it turns out his sexual partner has also rejected him in favor of a ghost, specifically a different one from the one(s) that supplanted him in the rest of the comic scenarios. The implication being that, wheres those ghosts were better than him because they consistently did everything quicker, this ghost took ''longer'' than Cueball, presumably presumably delaying any ejaculation long enough to also satisfy the partner's own needs. (How an intangible ghost is able to engage in physical intercourse is not addressed.)

It should be noted that this app would not guarantee the minimum travel time. The user doesn't find out which route was fastest until after the first ghost has arrived. But as the current traffic situation will have changed by then, that route will not necessarily still be the fastest — it is still possible for Cueball to beat the ghost by getting a more favorable traffic situation. Over many journeys, however, the ghosts will become increasingly harder to beat.

==Transcript==
:[Cueball, holding a smartphone, is talking to White Hat.]
:Cueball: Lots of apps let you plan your trips using real-time bus, train, and traffic data. They try to predict which route will be faster, but aren't always right.

:[Cueball continues to talk off-panel. The text is above a map showing three possible routes with an overlaid Cueball on each; the top and the bottom route and Cueball are faded, and the middle is black up until the black Cueball. After that, this route is also faded. A black point on the right indicates the destination.]
:Cueball (off-panel): Instead of just ''planning'', my new app lets you send "ghost" versions of you along different routes, simulating their travel using the real-time data

:[Cueball, again talking to White Hat, holding the smartphone down.]
:Cueball: That way, you can see which route turned out to be faster in practice,
:Cueball: You can also race your past selves.

:[Cueball is getting out of his car holding his smartphone in one hand and a briefcase in the other; A faded out Cueball bicyclist is in front of him to the right. At the top there is a caption in a frame:
:Soon...
:Cueball: Ugh, lost to the bike ghost ''again.''

:[Cueball with his briefcase is outside a door, holding a key card up to a key reader. On the inside of the door Ponytail is facing the door and points toward the faded version of Cueball also holding a briefcase.]
:Cueball: Hey, my key won't work
:Ponytail: I'm sorry, but we've decided to replace you. This floaty guy is much more punctual.
:Cueball: But...

:[Jill and another girl with wavy long hair, is holding faded out Cueball's hands. The real Cueball is standing to the right, next to his briefcase on the ground. He is holding his hands out towards his kids.]
:Jill: Our ''new'' dad never misses our games!
:Cueball: ''Nooo!''

{{comic discussion}}
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring White Hat]]
[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring Jill]]
[[Category:Multiple Cueballs]]
[[Category:Smartphones]]
[[Category:Comics featuring children]]
[[Category:Ghosts]]

Talk:1433: Lightsaber

2026-06-29T14:09:26Z

82.132.236.191: Undo revision 415343 by Aprilfoolsupdate! (talk)

I seem to remember seeing somewhere that lightsabers are actually not lasers but rather plasma held in that shape by some sort of force field. I think it should be in the explanation if it is true. [[User:Athang|Athang]] ([[User talk:Athang|talk]]) 06:11, 13 October 2014 (UTC)
:I'd just like to know what "real laser"s have to do with lightsabers. (Other than little kids using the wrong name.) [[Special:Contributions/103.22.201.120|103.22.201.120]] 11:55, 13 October 2014 (UTC)

Most of "scientific" explanations of lightsaber (and blaster bolts) says about plasma contained in magnetic field. For example check this SE http://scifi.stackexchange.com/questions/6478.
Endless "laser sword" pun was also used in http://www.collegehumor.com/video/6704463/troopers-laser-sword, without Luke but with massive hull breach. [[Special:Contributions/108.162.231.214|108.162.231.214]] 06:38, 13 October 2014 (UTC)PTwr

One joking "explanation" of the light sabre conjured long ago on a newsgroup I was on had used the Fourier analysis. It proposed that the "handle" emits multiple beams of light with very well defined frequencies and amplitudes, corresponding to a Fourier series for a pulse wave with a low duty cycle - so the waveforms emitted cancel themselves after a short distance. The joke went on, saying that since the sum of the Fourier series is periodic, someone practicing the sabre on the Earth can accidentally chop off the head of someone walking on the Moon. [[Special:Contributions/108.162.254.29|108.162.254.29]] 07:26, 13 October 2014 (UTC)

I don't think this has anything to do with the Hull Breach card game. The sentence "Hull breach all along sector five" does however sound like something from Star Trek and not like Star Wars.[[User:Condor70|Condor70]] ([[User talk:Condor70|talk]]) 12:07, 13 October 2014 (UTC)

There is a XKCD What If discussion on infinite lasers at http://what-if.xkcd.com/109/ [[Special:Contributions/141.101.99.113|141.101.99.113]] 12:17, 13 October 2014 (UTC)

"'''Because Vader slightly tilts the active lightsaber, the beam ends up slicing straight through the hull of a large section of the Death Star. '''" Wouldn't it would cause a breach the moment he turned it on, not waiting until he tilts it? [[User:Lomky|Lomky]] ([[User talk:Lomky|talk]]) 15:07, 13 October 2014 (UTC)
:Yes, but the breach would be highly localized (the same diameter as the blade) until he tilts it. If he does so in the center of the sphere, leverage means that a slight angle change in the emitter means a huge change at the other end of the beam.[[User:Seebert|Seebert]] ([[User talk:Seebert|talk]]) 15:34, 13 October 2014 (UTC)
::Darth Vader may be more machine than man, but don't you think you're overestimating his ability to hold his hand steady? You seem to be suggesting his hand wouldn't tremor enough to cause even the tiniest perturbations in the angle.[[User:Diszy|Diszy]] ([[User talk:Diszy|talk]]) 19:29, 13 October 2014 (UTC)
:::How far are they from the hull? The original breach would still be relatively localized (on the order of 1-2% of their distance from the hull), so if they're within a few hundred meters from the boundary it shouldn't be particularly large. (That's even assuming they're on the Death Star in the first place, as the IP below me helpfully points out; could be that the original vector simply didn't intersect the Death Star at all.) Or of course it could be the original - it's only been several seconds or so, maybe they only noticed it that moment anyway. A cool calculation I don't have time to do right now: assuming the blade covered a plane sector of, say, 15 degrees (I'm ignoring the twitches for a moment, though it's easy to see that they don't change the answer much), and assuming it didn't hit any nearby planets such as Endor, approximately how many planets it would've hit on its way from the galaxy? Same question for stars (though I suppose a lightsaber blade won't do much to a star). [[Special:Contributions/141.101.64.23|141.101.64.23]] 06:51, 14 October 2014 (UTC)
::::They're on Endor (in the movie, at least). https://www.youtube.com/watch?v=WDnoczxzQyg If the beam intersects the Death Star, it would be many hundreds of KM away. Any perturbations would be HUGE at that distance. Also, the XKCD What If book actually addresses the question of the likelihood that a beam hits anything. [[User:Diszy|Diszy]] ([[User talk:Diszy|talk]]) 12:03, 15 October 2014 (UTC)
:::::I was basically saying that the beam ''didn't'' intersect the Death Star until being moved in panel four. As for the book, if you're referring to What If #109, it involves a stationary (or single-burst) laser; numbers for a moving laser (that sweeps through a section of a plane) would be different. I'm also ignoring the speed of light (which is kind of important when we're talking about interstellar distances). Estimating based on [[1276: Angular Size]], seems that the chance of hitting a star would be roughly (laptop size/Earth size)*(galaxy size/Proxima distance)*15/360, which comes out to one in several thousand. Which is less than I expected, actually. [[Special:Contributions/141.101.64.23|141.101.64.23]] 15:16, 15 October 2014 (UTC)

The scene referred to in Return of the Jedi, actually takes place on the surface of Endors moon. There are trees in the background: https://www.youtube.com/watch?v=WDnoczxzQyg [[Special:Contributions/141.101.81.222|141.101.81.222]] 15:20, 13 October 2014 (UTC)

Actually, the title text says "A long time in the future, in a galaxy...", not "ago". [[Special:Contributions/108.162.216.26|108.162.216.26]] 12:25, 13 October 2014 (UTC)
: Who said otherwise? "'''The Star Wars opening crawl''' starts with the text "A long time ago..." {{unsigned ip|199.27.128.117}}

When I first read this, I took it as a game of one-up-manship. I build something, you build something better, I build something even better, you build something cooler, etc in an ever escalating spiral of coolness. So, here, Luke has built a long sabre as a way of one-upping his father, who then asks "where does [this competition] end?" Luke's response is taht the competition, like his laser sword, never ends. That also seems to fit in neatly with Randall's penchant for puns. OTOH, I could just be making up stuff inside my head :D JonS

<GASP> We now have one of the two variables needed to find the Death Star! We have direction, now all we need is distance! {{unsigned ip|108.162.217.137}}

"'''an unusual gamma ray burst in 2008, visible to the human eye'''" - I know what is ''meant'', but perhaps a rewording? [[Special:Contributions/141.101.99.118|141.101.99.118]] 12:56, 15 October 2014 (UTC)
: Done.[[User:Iggynelix|Iggynelix]] ([[User talk:Iggynelix|talk]]) 13:43, 18 October 2014 (UTC)

"not the place for humour" uh yeah, big fate {{acn}} on that one
--[[Special:Contributions/172.71.242.70|172.71.242.70]] 14:06, 20 March 2024 (UTC)

Talk:102: Back to the Future

2026-06-29T14:06:12Z

82.132.236.191: Rude to alter others' Talk comments like that. If you wanted to respond with 'new info', you could just fully add your own words of wisdom to the conversation.

I noticed the character on the right has hair in the first two frames, but is bald in the last frame... Two persons? [[User:Rikthoff|Rikthoff]] ([[User talk:Rikthoff|talk]]) 12:52, 3 August 2012 (UTC)
:I agree with Rikthoff, I don't think this is Cueball. Being bald is one of his main features and this guy definately has hair.--[[User:Popuppete|Popuppete]] ([[User talk:Popuppete|talk]]) 13:42, 12 September 2012 (UTC)

The issue date might be off. All files since #101 have been created on April 11th, 2006. Anyone with an actual issue date? [[User:Rikthoff|Rikthoff]] ([[User talk:Rikthoff|talk]]) 12:53, 3 August 2012 (UTC)

Could it be possible that Megan's dad died because of something the other character (let's not call him Cueball until we know for sure) did in the future to "make sure his parents got together and helped his dad to be less of a loser"? {{unsigned|Tesshavon|14:38, 24 July 2013‎ (UTC)}}

:It's more likely to have been the result of a airliner full of jet fuel crashing into the tower, causing it to burn and collapse. Megan is probably thinking that Cueball (I'm still going to call him Cueball, sorry) could maybe have alerted somebody that this was going to happen. In the past. Him having access to a time machine and all. [[Special:Contributions/108.162.219.58|108.162.219.58]] 20:31, 24 January 2014 (UTC)

Why do we take for granted alt text refers to the Cueball/Hairy and not the father? [[Special:Contributions/141.101.89.210|141.101.89.210]] 21:55, 29 March 2014 (UTC)

What if the alt text refers to Marty McFly and not Cueball/Hairy? You don't have to think about the comic very hard to know C/H was an asshole, but I think the implication is that Marty could have taken the DeLorean and done less petty, personal things with it. --[[Special:Contributions/173.245.54.47|173.245.54.47]] 21:51, 12 May 2014 (UTC)

:If it did refer to MM, Randall's interpretation of the movie is skewed. MM only did what he needed to do to repair the damage he unintentionally did. There was no personal benefit intended other than saving his own life, and that of his siblings. Randall has taken some creative license with the way C/H explains the plot.[[Special:Contributions/172.69.70.251|172.69.70.251]] 07:52, 25 January 2018 (UTC)

::Exactly — Marty McFly ''could'' have (for example) saved many people's lives, but instead he only saved "his own life, and that of his siblings," so Marty McFly ''is'' "kind of an asshole, when you think about it." [[User:Yfmcpxpj|Yfmcpxpj]] ([[User talk:Yfmcpxpj|talk]]) 11:18, 1 December 2019 (UTC)

Have people forgotten? The DeLorean time machine was destroyed at the end of the third film - it spent less than a day in total in 1985 (first used 1.20 am, destroyed by a train c. midafternoon). Cueball even references this in the comic. {{unsigned ip|108.162.250.223|14:07, 5 September 2014 (UTC)}}

:Megan can still contact the friend and get her own time machine... maybe. [[User:Greyson|Greyson]] ([[User talk:Greyson|talk]]) 05:11, 22 October 2015 (UTC)

:The DeLorean that Marty used to travel from 1885 to 1985 was, indeed, destroyed (somewhat ironically by a fast-moving, modern train). But what of the DeLorean Doc stashed in the cave in 1885? That's what he used to create the flying train. [[User:PoconoChuck|PoconoChuck]] ([[User talk:PoconoChuck|talk]]) 20:19, 9 May 2016 (UTC)

::Actually, that cave DeLorean had to stay there after Doc buried it in 1885, or else 1955 Doc and Marty couldn't dig it out to go back to 1885 to get Doc. It is surmised that parts from the hoverboard (that remained in 1885 with Doc and Clara) were used in the making of the Time Train. [[Special:Contributions/172.69.70.251|172.69.70.251]] 07:52, 25 January 2018 (UTC)

:The conversation in the comic occurs some time after September 11, 2001, and Hairy/Cueball says "''this weekend'', my professor friend built a time machine," so the DeLorean in this comic could be a completely different DeLorean than the one in the movies. But either way, it can travel through time, so it could be present at any point in time, regardless of if/when it was destroyed, yes? [[User:Yfmcpxpj|Yfmcpxpj]] ([[User talk:Yfmcpxpj|talk]]) 11:42, 1 December 2019 (UTC)

'He' could also be her father, thus explaining why he wasn't saved. --[[Special:Contributions/172.68.47.132|172.68.47.132]] 06:14, 27 August 2018 (UTC)

I think that the title text can't possibly be referring to Megan's father. First of all, Cueball/Hairy and Megan seem to be close friends, since Megan saying "you remember" implies that she brought it up previously. Most people don't call their friend's father an asshole to justify letting them die. Also, Hairy/Cueball seems to genuinely not get what Megan said. And the title text is in present tense, while we tend to talk about deceased people in past tense. [[Special:Contributions/162.158.62.63|162.158.62.63]] 00:38, 21 February 2021 (UTC)

I believe that this is the same person because otherwise it seems that Megan didn't tell the character on the right with hair (presumably Marty McFly) about her father therefore diminishing the humor. {{unsigned ip|141.101.99.19|10:08, 6 June 2021 (UTC)}}

I don't know which part of saying he could have prevented the 2011 Japanese earthquake/tsunami is more bizarre, that you can't prevent earthquakes, or that it didn't occur until 5 years after the comic was made. I hope this was intentional, but given the minimal intellect of most human beings I can't be certain. — [[User:Kazvorpal|Kazvorpal]] ([[User talk:Kazvorpal|talk]]) 17:33, 29 January 2024 (UTC)
: Well, you can't prevent an earthquake{{Actual citation needed}}, but perhaps you can prevent the ''disaster'' of the earthquake. Somehow. Without setting up your knowledge by pre-predicting something else (to get the authorities/public to listen to you), it might be harder. Though nudging any 'national earthquake drill'/surrogate activity to have more people prepared to not be in danger at the actual moment might work (or be counter-productive... the actual common earthquake fore-warnings at the speed of SMS, ahead of the speed of mere seismic waves, might be mistaken for 'drill warnings' and not obeyed).
: Though the best part of having a time-machine (given certain conditions of time-travel, and enough capabalities to take advantange of that for a given time-travelling-device) is that you can actually fine-tune your intervention to discover the most optimal 'best way of avoiding disaster' you can imagine. Find ''the'' person who is most pursuadable ''and'' influential to get either your direct or indirect assistance used to the fullest extent. Even if that's just getting <insert social media boss> to promote a "Get Outside And Take A Photo Of The Nearest Hill Day" promotion, which might get a significant number of the most influencable people to get out of the way of urban damage (and at least ''ready'' to escape to higher ground). But there'll be many other approaches. For example developing a fake 'detector' that is shown to be utterly accurate in predicting minor seismic events (pre-programmed from your time-travelling 'cheat sheet') and then (again, pre-programmed) gives the warning for the "big one"... though what you do then (keep on feeding it with future data, indefinitely? ...or have it 'accidentally' destroyed and unreconstructable in the process, leaving it a mystery how it worked (and perhaps a nasty red-herring solution!) and leaving the 'more future bits of your native past, present and future' just as vulnable in every other respect) is a bit of a moral question, as well as practical).
: And, with access to (the right kind of) time-machine, you could have gone ''forward'' five+ years and checked out what info you might want to have ready to help the present ''and future'' of 2009. (Alongside that sports almanac...)
: Imagination. Once you're over the bizareness of temporal engineering/etc, I don't see anything too mich more bizarre with what you ''do'' with it... [[Special:Contributions/162.158.74.48|162.158.74.48]] 18:32, 29 January 2024 (UTC)