explain xkcd - User contributions [en]

2785: Marble Run

2023-06-07T12:52:45Z

Swansilhouettes:

{{comic
| number = 2785
| date = June 5, 2023
| title = Marble Run
| image = marble_run_2x.png
| imagesize = 438x512px
| noexpand = true
| titletext = I have so many plans. It would incorporate a Galton board, a Ranque-Hilsch marble vortex tube, and a compartment lined with pinball bouncers with a camera-and-servo Maxwell's Demon that separated the balls into fast and slow sides.
}}

==Explanation==
{{incomplete|Created by MAXWELL'S DEMON - Please change this comment when editing this page. Do NOT roll away this tag too soon.}}
A {{w|Rube Goldberg machine}} is a fancifully complex system (either real or imagined), which makes use of an overly elaborate chain of actions. The name comes from an American cartoonist who was one of those who became famous for depicting convoluted and outlandish processes for accomplishing simple tasks.

There's a long history of people building actual contraptions along these lines. Such devices are almost never intended for practical purposes, but exist entirely for entertainment, and as an exercise in building complex and carefully planned systems. This has become particularly common in the internet age, as videos of particularly interesting examples can gain popularity online. The most common category of these devices is probably the marble run (also known as a {{w|rolling ball sculpture}}), in which the goal of the system is to move one or more balls or marbles from the beginning of the device to the end in interesting ways. This contrasts to the {{w|Domino toppling|domino run}} where motions are transferred by many intermediate pieces painstakingly arranged, although both aspects are commonly combined in such contrivances.

When [[Megan]] tries to show [[Cueball]] an example of such a video, he refuses, not because he lacks interest, but because of how he predicts it will impact him. Cueball (likely as a stand-in for [[Randall]]), has sufficiently strong interest in things like designing, building and engineering complexity that he's certain he will eventually adopt building such devices as a hobby, and that it will dominate his time and attention. Accordingly, he appears to be deliberately delaying his exposure to such devices so that he can continue to pursue other hobbies, with the assumption that he will eventually succumb to this one.

Megan responds that he knows where he's going, but is taking "a really interesting and circuitous path" to get there. This points out the irony that the very avoidance of building Rube Goldberg machines follows the same principle on which such machines work.

The title text mentions specific ideas Cueball plans to incorporate into such a device.

A {{w|Galton board}} is a device that distributes falling balls into a {{w|normal distribution}}. Its design is similar to those used in {{w|pachinko}}-style games.

A Ranque-Hilsch {{w|Vortex tube}} is a device for separating compressed gas into hot and cold streams. While such a device isn't directly applicable to marbles, one can imagine using the principle to separate a stream of marbles based on speed.

Pinball bouncers are properly supposed to be the {{w|Pinball#Bumpers|Bumpers}} in {{w|Pinball}} machines. In Randall's marble run there will be a compartment where the walls are lined with these bumpers. Supposedly there will be many marbles on the floor of this segment of the run, which will hit these bumpers and get a kick so they will move fast and randomly around the compartment, which is where the Demon comes in.

{{w|Maxwell's Demon}} is a thought experiment by James Clerk Maxwell which would violate the Second Law of Thermodynamics. Maxwell proposed that, if a container of air was separated by a divider, with a door that allowed only one molecule through at a time, and a theoretical "demon" were to control the door to sort high-energy atoms into one side and low energy atoms into the other, the two sides would develop a temperature difference with no energy input. The problems are many, first of all, how would the door open and close without using energy. And how would the demon gain knowledge of the speed and position of all the molecules (and at the same time, that is even impossible due to Heisenberg's {{w|uncertainty principle}}. So it is just a though experiment on the molecular scale.

However, Randall's version of this apparently involves a large number of marbles bouncing around inside the bouncer lined compartment, with an automated system to divert the fastest moving marbles into one side, and the slowest moving into the other. As these are macroscopic scales this would not be impossible, just really difficult. Would be interesting to see the result, but soon one segment would have slow moving balls and the other lots of fast moving balls if it was possible to construct the device. Randall foresees the amount of time he might use if he first began trying to construct his ideas into a marble run.

Knowing Randall and his fans, some might design something using his ideas from this comic.

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

:[Megan is walking towards Cueball and showing her phone. Cueball holds a hand to his face and looks away.]
:Megan: Check out this cool video of a Rube Goldberg marble run.
:Cueball: No! Not yet.

:[Megan has lowered her phone. Cueball has his hand in a fist.]
:Cueball: I've always known I'm doomed to eventually become one of those people who builds elaborate marble runs in their garage.
:Cueball: I can feel the pull.
:Cueball: So satisfying.

:[Close-up on Cueball.]
:Cueball: I just want to do as many other things as I can before I give in and disappear into that world.

:[Megan and Cueball are walking.]
:Megan: So you know where you're going to end up, but you're trying to take a really interesting and circuitous path to get there.
:Cueball: Exactly. Bounce around, maybe go off a few jumps.

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Physics]]
[[Category:Statistics]]

353: Python

2021-07-27T12:40:14Z

Swansilhouettes: fix typo

{{comic
| number = 353
| date = December 5, 2007
| title = Python
| image = python.png
| titletext = I wrote 20 short programs in Python yesterday. It was wonderful. Perl, I'm leaving you.
}}

==Explanation==
{{w|Python (programming language)|Python}} is a programming language designed specifically to make it easy to write clear, readable programs. Flying is often used as a metaphor for freedom and ease, and here Randall shows Cueball literally flying in response to using Python.

A {{w|"Hello, World!" program}} is a very simple program that prints the phrase "Hello, World!", used in textbooks to illustrate a given programming language. While this sounds simple, it can be nontrivial in some programming languages where you need to explicitly import a library that contains the <code>print</code> function (for instance, in C you need to begin with <code>#include <{{w|stdio.h}}></code>) or do complicated things with classes and variables (see [https://en.wikibooks.org/wiki/Computer_Programming/Hello_world#Java the Java "Hello, World!"] for one example). Python doesn't need any of that: <code>print("Hello, world!")</code> (or in Python 2, <code>print "Hello, world!"</code>) really is all you need to do.

{{w|Dynamic typing}} and {{w|significant whitespace}} are two controversial features of Python, which make some people—like Cueball's friend—hesitant to use the language.

Dynamic typing means that variables do not have types (like "list of short integers" or "a bunch of letters"); any value of any type can be placed in any variable. Dynamic typing allows for more flexible languages, but it means that certain kinds of errors (like trying to subtract a letter from a number) can't be caught until a program is run, and some people think this is too dangerous for the tradeoff to be acceptable.

Whitespace is a string of invisible text characters, like spaces or tabs. In programming, blocks of code controlled by a statement are usually indented under that statement. Most languages require you to use braces (<code>{…}</code>) or special keywords (<code>BEGIN…END</code>) to delimit these blocks; in Python, the indentation itself is the delimiter. Many Python programmers find that this makes code more readable, but many other programmers find it too "magical" and don't trust it.

Classes, functions, and constants in Python are packed into modules. To use a module, you write "<code>import ''module''</code>" at the top of your source file (you can do this anywhere in the file, but it's usually at the top so you can use the module throughout the code). Python comes with a very powerful standard library of modules to do everything from parsing XML to comparing two sets of files for differences, and new modules can be easily installed from the PyPI repository, which has more than 79,000 more to choose from (as of April 2016). [[Cueball]] can fly because he imported the <code>antigravity</code> module. Python still works for Cueball in [[482: Height]].

In the final panel, Cueball admits that his ability to fly may actually be because he has "sampled everything in the medicine cabinet," though he's sure it is the Python anyway. An implication of this is that ingesting everything in the medicine cabinet has given him the feeling of freedom and ease that "flying" represents - or that he is hallucinating himself flying and having a conversation with the other character about it. Here, the metaphor of "feeling like you're flying" while using Python is transformed back from being literal (Cueball is actually flying) to being metaphorical (Randall feels like he is flying because Python is so easy to use... or because he had too many strange drugs).

{{w|Perl}}, mentioned in the title text, is another programming language with the same target audience as Python, as both are {{w|High-level programming language|high-level}}, {{w|General-purpose programming language|general-purpose}}, {{w|Interpreter (computing)|interpreted}}, {{w|dynamic programming language}}s.
However they strongly oppose each other in their language design:
* Perl’s philosophy for its syntax is "{{w|There's more than one way to do it}}," so each coder can choose their own coding style to do exactly the same thing.
* Python’s {{w|Zen of Python|philosophy}} for its syntax is "There should be one — and preferably only one — obvious way to do it," so the written code is more consistent.
Since he has discovered Python, [[Randall]] doesn't like Perl anymore, probably because its syntax is less consistent or perhaps due to his problems with [[1171|Regular expressions]]. What [[224|God]] has to say about Randall's renunciation of Perl has not yet been documented.

==Transcript==
:[A Cueball-like friend is talking to Cueball, who is floating in the sky.]
:Friend: You're flying! How?
:Cueball: Python!
:Cueball: I learned it last night! Everything is so simple!
:Cueball: Hello world is just print "Hello, World!"
:Friend: I dunno... Dynamic typing? ''Whitespace?''
:Cueball: Come join us! Programming is fun again! It's a whole new world up here!
:Friend: But how are you flying?
:Cueball: I just typed 'import antigravity'
:Friend: That's it?
:Cueball: ...I also sampled everything in the medicine cabinet for comparison.
:Cueball: But I think this is the python.

==Trivia==
*In response to this comic, the Python developers implemented the module <code>antigravity</code> in version 2.7+. When you <code>import</code> it, the default web browser will open this comic. Also, in version 3+, the module contains a [[426: Geohashing|geohashing]] function.
{{comic discussion}}
[[Category:Comics featuring Cueball]]
[[Category:Programming]]

2454: Fully Vaccinated

2021-04-24T00:55:50Z

Swansilhouettes: Remove "citation needed" on a statment that was not blatantly obvious

{{comic
| number = 2454
| date = April 23, 2021
| title = Fully Vaccinated
| image = fully_vaccinated.png
| titletext = "You still can't walk into someone's house without being invited!" "What? Oh, I see your confusion. No, this vaccine is for a bat VIRUS. I'm fine with doorways and garlic and stuff."
}}

==Explanation==
{{incomplete|Created by a FULLY VACCINATED VAMPIRE, which wants to know more about the vampire lore invoked in the title text, and who and how it is misunderstood and who says what...}}
This comic is another in a [[:Category:COVID-19|series of comics]] related to the {{w|2019–20 coronavirus outbreak|2020 pandemic}} of the {{w|coronavirus}} {{w|SARS-CoV-2}}, which causes {{w|COVID-19}}, specifically regarding the [[:Category:COVID-19 vaccine|COVID-19 vaccine]].

The {{w|Centers for Disease Control and Prevention}} (CDC) has stated that once people are fully vaccinated, they are able to visit other people's houses (and not risk spreading/catching coronavirus). The implication, of course, is that you can visit people that you would also have visited before the outbreak. The humor in this comic comes from [[Megan]] who is just going to visit a random stranger's house. She explains this is okay because she is fully vaccinated, telling the person in the house that she is two weeks past her second dose. This was part of the topic of the last vaccine comic [[2450: Post Vaccine Social Scheduling]].

Restrictions to socializing, brought in as various governments reacted to the emergent COVID-19 pandemic, often disallowed or discouraged visiting family, friends, etc, beyond a mutually isolating 'support bubble', which meant that many house visits that might have occurred beforehand were no longer advisable. With the development and distribution of vaccines, and the eventual receiving of a second dose as applicable, the rules have been modified to allow those vaccinated to once again resume some degree of their prior outgoing behavior where the risks have been mitigated.

In this instance, though, Megan has taken the advice even further. Rather than opening back up to a situation closer to the 'old normal', she has taken it as an official sanction to ''exceed'' the old social limits and pester complete strangers. Alternately, this ''is'' what she always used to do, and only stopped 'for the duration', this unlucky householder being (one of) the first to be subjected to this 'guerilla visiting' now that there seems to be no reason not to continue.

In the title text, the owner of the house explains to Megan that just because she has been vaccinated she just can't enter into someone's house without being invited - a commonly understood form of property law.

But due to the vaccine type Megan thinks the owner has mixed this up with a commonly understood element of vampire lore, that vampires must be {{tvtropes|MustBeInvited|invited into a home}} before they can pass through the doorway.
In vampire lore, vampires are often able to transform into bats, and these two are thematically associated with each other. Since the coronavirus is likely a {{w|bat virome}} that has entered into humans, Megan misunderstands the owner's objection to her entry, believing that the homeowner thinks that the vaccine has made her a vampire. (The virus may have either gone directly to a human from a bat, or it could have come to humans through another animal, see {{w|Bat virome#Coronaviruses|this section}} on the bat virome page).

Megan thus begins to explain that the vaccine works on a bat virus and has nothing to do with bats. And since she is thus not a vampire she has no problems entering a doorway uninvited, and further explains she also tells that she is also not repelled by garlic or other classic weakness of vampires. Vampire lore states that they are [https://blog.nationalgeographic.org/2010/02/22/six-ways-to-stop-a-vampire/ repelled by garlic], crosses, holy water, sunlight and wooden stakes through the heart (the last is a problem for humans in general, vampiric or otherwise).

The owner is attempting to explain that Megan does not have the legal or moral right to enter simply because she is vaccinated, but this seems to not register with Megan.

Doing ridiculous things that were never allowed, even normally, after being vaccinated of low-risk, was also the theme of [[2434: Vaccine Guidance]].

==Transcript==
:[Megan is standing in front of a three-step stair leading up to an open door. She has one hand in the air while talking to someone inside the house, who replies. The ground outside has small tufts of grass.]
:Megan: Hi, I'm here to visit!
:Voice, from inside the house: Do I know you?
:Megan: No, it's cool, I'm two weeks past my second dose.

:[Caption below the panel:]
:Remember, once you're fully vaccinated, the CDC says you're free to visit other people's houses.

{{comic discussion}}

[[Category:COVID-19]]
[[Category:COVID-19 vaccine]]
[[Category:Comics featuring Megan]]
[[Category:Social interactions]]

2433: Mars Rovers

2021-03-06T04:58:08Z

Swansilhouettes: Make link clickable

{{comic
| number = 2433
| date = March 5, 2021
| title = Mars Rovers
| image = mars_rovers.png
| titletext = I just Googled 'roomba sojourner mod' and was sorely disappointed. Be the change, I guess!
}}

==Explanation==
{{incomplete|Created by a CUTE ROBOT. Please mention here why this explanation isn't complete. Do NOT delete this tag too soon.}}
This article is [[Randall]]'s placement of the various Mars rovers on a cuteness v capabilities chart.

He finds the ''{{w|Curiosity (rover)|Curiosity}}'' and ''{{w|Perseverance (rover)|Perseverance}}'' rovers to be very capable / useful, but not very cute. ''{{w|Spirit (rover)|Spirit}}'' and ''{{w|Opportunity (rover)|Opportunity}}'' are cuter than the first two, but less capable. The recently launched ''Perseverance'' rover contains a drone helicopter, ''{{w|Ingenuity (helicopter)|Ingenuity}}'', which Randall finds very cute, but he is unsure how capable / useful it is. The way the error-range is indicated 'coincidentally' gives the Ingenuity image-plot a sense of movement in mid-air, especially the up and down motion which is the helicopter's (hopefully) most obvious dynamic once it is deployed and being tested.

Finally, on the very right of the chart is the ''{{w|Sojourner (rover)|Sojourner}}'' rover, launched in 1997. He considers this rover extremely cute, but ultimately not that capable in terms of space exploration.

In the title text, Randall is disappointed that there aren't many people who have modified their {{w|Roomba}} vacuums to look like (or act like?) the ''Soujourner'' rover. Results at the time of posting are mainly reports mentioning the {{w|iRobot}} company, since one of its founders worked on the Soujourner rover.

[[:Category:Roomba|Roomba]] has been mentioned in many xkcd comics.

The cuteness of Sojourner has been mentioned before in [[1585: Similarities]].

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

{{comic discussion}}
[[Category:Mars rovers]]
[[Category:Scatter plots]]
[[Category:Roomba]]

2412: 1/100,000th Scale World

2021-01-15T23:27:55Z

Swansilhouettes: Remove unrelated sentence.

{{comic
| number = 2412
| date = January 15, 2021
| title = 1/100,000th Scale World
| image = 1_100000th_scale_world.png
| titletext = The floor should be slightly curved, but we haven't figured out artificial gravity yet, so for now we just added a trace intoxicating gas to the air that messes with your inner ear and gives you a sense that the ground is tilting away from you.
}}

==Explanation==
{{incomplete|Created by a TOXIC AURORA. Missing an explanation entirely. Do NOT delete this tag too soon.}}

This comic is a sequel to the [[2411: 1/10,000th Scale World|previous one]]. There is a 1/100,000th scale world in this comic.

{| class="wikitable"
!Rule
!Reason
!Notes
|-
|Our aurora are probably non-toxic but please stop trying to taste them
| The aurora in the image is now temptingly at head height
| The plural of "{{w|aurora}}" should actually be "auroras" or "aurorae"
|-
|No breaking off pieces of the ice caps to put in your drink
|
|
|-
|Warning: Limited cell network coverage above the ionosphere, crouch down to get more bars
| The ionosphere reflects radio signals, in this case keeping terrestrial cellular phone signals from reaching phones higher up
|
|-
|Do not step on Mt. Everest
| Mt. Everest, the highest peak on Earth, is several inches tall at 1:100,000 scale
|
|-
|Caution! Ocean floor slippery when wet
| Due to the smaller scale, the ocean depths would only be a few inches deep at most; this amount of liquid would cause more of a 'slippery surface' than a 'water region'.
|
|-
|Wear sunscreen; the ozone layer only protects you below the knees.
|
|
|-
|Beware of chest-level meteors
|
|
|-
| -100° mesopause vest recommended
|
|
|-
|If Lake Tahoe or the Dead Sea dries up, refill them with this 5oz wine glass
|
|
|-
|Safety glasses required for protection from reentering spacecraft
|
|
|-
|Do not anger the sprites
| {{w|Sprite (lightning)|Sprites}} are poorly understood electrical phenomena in the upper atmosphere. They are enormous but very short-lived.
| Sprites are also a name given to a form of forest spirit known for mischievous and sometimes harmful behaviour. In some fairy tales a warning would be given to not anger the spirits in case of grave repercussions.
|-
|Please stop digging through the Moho. Staff are tired of cleaning up large igneous provinces.
|Short for the {{w|Mohorovičić discontinuity}}, the Moho is the boundary surface separating the Earth's crust from the mantle. It can be found at a depth of 6-7 miles under the ocean bed, and about 24-30 miles under the continents.
|Using Randall's 1/100,000th scale world, 6-7 miles would be approximately 4 inches, while 24-30 miles would be about 16 inches, making the Moho easily accessible via digging. It would indeed create large igneous provinces, and make a big mess of lava that the staff would have to clean up, which would not be fun. The lava has a decent chance to burn through a mop or something, so it would be pretty tricky to clean up as well, since your cleaning stuff would light on fire unless soaked in water or something.
|-
|ISS (14 feet up) Returns every 90 minutes - Hit it with a nerf dart, win a prize!
| The {{w|International Space Station}} is the largest human-made object in space, and orbits the Earth once every 90 minutes.
| This idea of treating modern research as a toy is in the same general panel area as the weather balloon smacking from the previous comic.
|}

The title text states that the floor should be slightly curved. In fact, given that the model in the comic is about 10 meters long, it represents about 1000 km of Earth, that spans about 9 degrees of a great circle. Therefore, if the model wasn't larger than the part shown in the panel, its edges would have a very noticeable slope of 4.5 degrees.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
RULES:
Text: For visitors to my 1/100,000th scale world
1 meter = 100 km, 1 ft=100,000ft≈20 miles

Text: ISS (14 feet up)
Returns every 90 minutes
Hit it with a Nerf dart to win a prize!

Text: Our Aurora are probably non-toxic, but please stop trying to taste them

Text: [one cell bar] Warning: Limited cell network coverage above the ionosphere. Crouch down to get more bars

Text: Safety glasses required for protection from reentering spacecraft
Cueball: OW!
(off-screen): What?
Cueball: I got a Soyuz in my eye

Text: Beware of chest level meteors

Text: -100°C Mesopause vest recommended
{{comic discussion}}
[[Category:Illustrations of scale]]