explain xkcd - User contributions [en]

2924: Pendulum Types

2024-04-29T06:00:59Z

Olaf: interactive simulation of the inverted pendulum

{{comic
| number = 2924
| date = April 24, 2024
| title = Pendulum Types
| image = pendulum_types_2x.png
| imagesize = 589x302px
| noexpand = true
| titletext = The creepy fingers that grow from a vibrating cornstarch-water mix can be modeled as a chain of inverted vertical pendulums (DOI:10.1039/c4sm00265b) and are believed to be the fingers of Maxwell's Demon trying to push through into our universe.
}}

==Explanation==
{{incomplete|Embed animation of double pendulum crom wikipedia page. Created by CREEPING TENDRILS OF STARCH - Please change this comment when editing this page. Do NOT delete this tag too soon.}}
This comic shows and describes several {{w|pendulums}}. The first three are actual physics models, while the last one is made up for absurdity. This is a recurring format of xkcd comics, as shown in [[2289: Scenario 4]].

[[File:Oscillating pendulum.gif|200px|right|thumb|The motion and dynamics of simple pendulum]] The simple pendulum consists of a joint, rod, and weight, and when released (inside a gravity field or other accelerating force), it swings in a regular fashion. The "period" of a pendulum is the amount of time it takes to complete one cycle, swinging back and forth. In a simple pendulum, the period is consistent, predictable, and depends primarily on the length of the pendulum (being largely independent of both mass and length of arc). This predictability makes pendulums useful in applications such as timekeeping, where the earliest accurate clocks (such as a {{w|grandfather clock}}) made use of pendulums as regulators.
 
[[File:Double-compound-pendulum.gif|200px|left|thumb|The typical motion of a double compound pendulum]] The {{w|double pendulum}} consists of 2 joints, 2 rods, and a weight, and when released, it swings in a {{w|chaos theory|chaotic fashion}}. Interestingly, this follows by the mathematical definition of chaotic, being that small changes in initial conditions result in vast differences in end results. This pendulum is thus nearly unpredictable, and due to this chaotic nature, real life applications are very limited.
 
The {{w|inverted pendulum}} consists of a simple pendulum that is placed upside down, with some powered apparatus underneath vibrating it vertically to keep it upwards. If left unpowered it will fall, hence the "unstable" part. The comic appears to depict {{w|Kapitza's pendulum}}. See a [https://www.youtube.com/watch?v=5oGYCxkgnHQ video demonstration by Harvard Natural Sciences] or an interactive simulation [https://www.myphysicslab.com/pendulum/inverted-pendulum-en.html here].

The nightmare pendulum appears to be an inverted double pendulum, with an additional uninverted pendulum swinging within its much more substantial weight (which is also adorned with archaic/mystical symbols). The comic claims that this pendulum summons {{w|Maxwell's demon}}, jokingly implying that Maxwell’s demon is an actual entity. In fact, Maxwell's demon is a thought experiment in which a being - the demon - is posted at a tiny door between two gas vessels. It lets only slow-moving (cold) gas molecules move through the door in one direction, and only fast-moving (hot) ones in the other direction. One vessel gradually becomes hot and the other cold, appearing to violate the {{w|second law of thermodynamics}}. It doesn't, but the thought experiment has stimulated much discussion since it was first proposed by {{w|James Clerk Maxwell}} in 1867.

The title text continues this joke explicitly, by referencing a real paper titled [https://pubs.rsc.org/en/content/articlelanding/2014/sm/c4sm00265b Vibro-levitation and inverted pendulum: parametric resonance in vibrating droplets and soft materials] and implying that the paper ties the [https://www.youtube.com/watch?v=3zoTKXXNQIU "creepy fingers"] produced in this way to Maxwell's demon. The paper only actually suggests that the phenomenon is related to inverted pendulum dynamics. This gives a humorous example for the abuse of citations. Technically, the cited reference only supports the claim immediately before it, that the behavior of a cornstarch-water mix (also known as {{w|Non-Newtonian fluid#Oobleck|oobleck}}) can be modeled as inverted pendulums. But by proximity the reference also seems to support the part about Maxwell's demon. The illusion is helped by the description of the cornstarch as creepy, which is added in the beginning without any visible separation from the actual content of the citation.

==Transcript==
:[Four types of pendulums are shown in a single panel. Each has a bullet list below the depiction.]

:[Label:]
:Simple pendulum
:[A basic pendulum consisting of a joint, rod, and weight swinging in a regular arc]
:* Periodic
:* Stable
:* Useful for timekeeping

:[Label:]
:Double pendulum
:[A pendulum consisting of 2 joints, 2 rods, and a weight swinging in a more loopy arc]
:* Aperiodic
:* Chaotic
:* Moderately cursed

:[Label:]
:Inverted pendulum
:[An upside-down basic pendulum with some apparatus underneath vibrating up and down]
:* Finely balanced
:* Unstable
:* Becomes stable when vibrated

:[Label:]
:Nightmare pendulum
:[An inverted double pendulum, with an additional uninverted pendulum swinging within a large weight adorned with archaic/mystical symbols]
:* Forbidden
:* Unphysical
:* Summons Maxwell's Demon

{{comic discussion}}

[[Category:Comics with cursed items]] 
[[Category:Physics]]

2925: Earth Formation Site

2024-04-29T05:46:51Z

Olaf: historical markers in other countries are usually just a table, without the upper part

{{comic
| number = 2925
| date = April 26, 2024
| title = Earth Formation Site
| image = earth_formation_site_2x.png
| imagesize = 478x521px
| noexpand = true
| titletext = It's not far from the sign marking the exact latitude and longitude of the Earth's core.
}}

==Explanation==
{{incomplete|Created by TWO 4,450,002,024-YEAR-OLD PRESIDENTIAL CANDIDATES - Please this edit this comment when editing this page. Do NOT delete this historical tag too soon.}}

In this comic, [[Cueball]] stands in front of a sign that declares itself to be an historical location, the formation of the {{w|Earth}}. The humor of the comic is twofold:
# the amusing illogic of the assertion
# the impossibly precise date

'''#1: The amusing illogic of the assertion'''

First, the Earth formed at its center, not its surface, so an “Earth formed here” sign on its surface is factually incorrect.

One may argue that technically the sign is above the right spot, just as every location on Earth is above the right spot. However, the sign refers to “this location,” not to a spot underground.

If an omniscient observer wanted to mark the spot in space where the Earth started forming, an historical marker on the surface of the Earth could not be accurate for longer than one split second in time. That’s due to {{w|Sun#Motion|Sun's 225-million year long orbit around the center of the}} {{w|Milky Way galaxy}} and the movement of the galaxy itself through space relative to other objects. From this perspective, the Earth’s formation did not occur anywhere ''on'' Earth.

'''#2: The impossibly precise date'''

Secondly, specifying a single year of formation is an amusingly precise choice, absurd in the context of the [https://science.nasa.gov/exoplanets/how-do-planets-form/ tens or hundreds of millions of years] thought to be required for planet formation. It would require some specific definition of when the gradually-coalescing mass could be considered a planet, as well as the ability to determine when that mass met the definition.

Note: The date shown for the formation of the Earth, 4.45 billion years, also differs from the commonly accepted date, [https://pubs.usgs.gov/gip/geotime/age.html 4.54 (±0.05) billion years]. The difference lies in the transposition of two digits, potentially a mistake.

This comic satirizes US historical markers by using their standard tone and structure. Typically, these signs are placed at precise locations where historical, religious, and even mythological events happened —- such as where battles have been fought, or where famous people resided or accomplished something, or where something ''supposedly'' happened.

The ''title text'' refers to the 'exact latitude and longitude of the Earth's core,’ Of course, since the lat-long geographic coordinate system is used for locating places on the ''surface'' on the Earth, the center of the Earth does not have latitude and longitude.

The comic and its title text are actually inverse jokes of each other: The historical marker in the comic assigns attributes of the Earth’s '''center''' (the site of formation) to a spot on its '''surface''', while the title text assigns attributes of '''surface''' locations (latitude and longitude) to the Earth’s '''center'''.

This title text language is similar to signs marking {{w|File:Equator sign kenya.jpg|specific}} {{w|File:Arctic Circle sign.jpg|latitudes}}, {{w|File:Prime meridian.jpg|longitudes}} or other {{w|File:2022-06-06 18 39 21 Sign reading "Highest Point on Interstate 80 East of the Mississippi River" along eastbound Interstate 80 (Keystone Shortway) just east of Exit 111 in Pine Township, Clearfield County, Pennsylvania.jpg|notable}} {{w|File:World's lowest point (1971).jpg|locations}}.

==Transcript==
{{incomplete transcript|Generated by EARTH — Do NOT delete this tag too soon.}}

:[Cueball is standing in front of a sign in a field of grass. Rocks and plants are scattered across the ground. The sign reads:]
:HISTORICAL MARKER
:<big>EARTH</big>
:FORMATION SITE
:--- 4,450,000,000 BCE ---
:At this location in the year 4,450,000,000 BCE, a cloud of dust and gas gravitationally collapsed to form the Earth.

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Geology]]

2734: Electron Color

2023-02-08T09:47:43Z

Olaf: +amber

{{comic
| number = 2734
| date = February 6, 2023
| title = Electron Color
| image = electron_color_2x.png
| imagesize = 568x256px
| noexpand = true
| titletext = There's quark color, but that's not really color--it's just an admission by 20th century physicists that numbers are boring.
}}

==Explanation==
{{incomplete|Created by A SUPER-INTELLIGENT SHADE OF THE COLOUR BLUE - Do NOT delete this tag too soon.}}
In this comic [[Miss Lenhart]] is teaching a school physics class. One of her students asks what the color of electrons is.

This is a relevant question for a kid to ask since on many scientific diagrams of atoms, the subatomic particles have been assigned colors to identify them for the reader. Neutrons are generally red, green, or gray; protons red or green and electrons might be blue or yellow. But there is no accepted rule for coloring such diagrams, so the kid may be confused. Additionally, some scientific diagrams use color coding rather than actually representative colors, and the kid may be wondering what color particles actually are.

In completely off character style, Miss Lenhart actually gives a correct explanation and states that, unlike the diagrams, which are colored for convenience, the particles are not colored. She even gives the correct explanation for this fact: ''They're too small to interact with visible light, so "color" isn't even defined for them.'' For a more typical Miss Lenhart see for instance [[1519: Venus]].

Of course she then continues by saying that electrons are definitely yellow. It isn't clear if she means they should be yellow on diagrams, because she feels this is the correct way to depict them in drawings of atoms, or she is referring to the Greek etymology of the word electron ({{w|elektron (resin)|elektron}} is an old name for amber, a yellow gem), or if she is just teasing her young pupils. But her off-panel pupils take her word for it. One of the kids says "I knew it", to the "fact" that electrons are yellow, and likewise the other pupils completely ignore what Miss Lenhart just told them. The debate then starts as one pupil claims ''and protons are red?'', and another chimes in, with a ''No, they're gray!'' This only makes sense in a debate of how to draw atoms, not regarding their actual color, as Miss Lenhart just explained.

The opinions over the colors are probably based on what kind of diagrams people were initially exposed to, leading to a predisposition to think that those colors are 'correct'.

Although individual electrons do not have a color, it's possible to produce a solution of {{w|Solvated_electron|so-called 'solvated' electrons}}. In ammonia and amines, in certain concentrations, the solution color is blue, and in higher concentrations metallic gold to bronze.

The title text refers to the {{w|color charge}} property of quarks, a property which is part of {{w|quantum chromodynamics}}. In quantum chromodynamics, a quark's color can take one of three values or charges: red, green, and blue. An antiquark can take one of three anticolors: called antired, antigreen, and antiblue. As mentioned by [[Randall]], these have nothing to do with color as we know it, but is just a way to represent interactions between quarks in a sufficiently analogous fashion that avoids inventing entirely new words to describe a particular threefold quality of the necessary {{w|color confinement|inter-quark groupings}}. And he jokingly says that the 20th century physicists that came up with the three color system did this as as admission that numbers are boring. They could just have called the color charges "1", "2" and "3", though this may imply an unwarranted hierarchy, progression or other standard mathematical relationship that does not actually apply.

==Transcript==
:[Miss Lenhart is teaching a class. A boy with spiky hair sits at his desks with his hand raised asking a question. Science Girl sits in front of him looking back at him while leaning an arm on the back of her chair.]
:Miss Lenhart: You have a question?
:Boy: Yeah-What color are electrons and protons? Are they yellow? Red? Blue?

:[Zoom in on Miss Lenhart's head.]
:Miss Lenhart: Subatomic particles don't have a color.
:Miss Lenhart: They're too small to interact with visible light, so "color" isn't even defined for them.

:[Zoom back out but only showing Miss Lenhart. Three pupils reply from off-panel with speech lines coming from starburst at the right edge of the panel.]
:Miss Lenhart: That said, electrons are '''''definitely''''' yellow.
:Off-panel voice 1: I knew it!
:Off-panel voice 2: And protons are red, right?
:Off-panel voice 3: ''What?'' No! They're gray!

{{comic discussion}}

[[Category:Comics featuring Miss Lenhart]]
[[Category:Comics featuring Science Girl]]
[[Category:Kids]] 
[[Category:Physics]]

2712: Gravity

2022-12-20T02:57:39Z

Olaf: this feature doesn't work on Firefox

{{comic
| number = 2712
| date = December 16, 2022
| title = Gravity
| image = gravity_2x.png
| titletext = It's a long way down.
}}

*To experience the interactivity, visit the [http://xkcd.com/2712/ original comic].
==Explanation==
{{incomplete|Created by THE UNIVERSE FROM A PIECE OF FAIRY CAKE- Please continue expanding and describing the various bodies. Do NOT delete this tag too soon.}}
In this interactive comic, the viewer pilots a small spaceship throughout a vast area in space. The viewer is capable of exploring various bodies and planets within the play area, many containing easter eggs alluding to the book What If? 2 and previous xkcd comics. The flight mechanics are largely, if not entirely, Newtonian, so the vessel is capable of using the gravity of planets to alter its trajectory or even enter orbit. The spaceship has indicator circles around it which appear when a gravitational body comes into range, showing the direction towards their center of gravity and the size of the body (this feature doesn't work on Firefox). A circle also appears around the spaceship whenever it collides with a gravitational body, acting as a shield. The shield remains until the player orients the spaceship upright so its landing gear can deploy.

'''Playing with a keyboard:''' The arrow keys rotate the spaceship and accelerate it forward and backward. You can also use the 'w', 'a', 's' and 'd' keys to control the spaceship. On mobile the comic will full screen, pressing either side of the center rotates the spaceship, and pressing in the center accelerates it forward. It is fairly easy to fly between planets as long as you pay attention to orbital mechanics; don't just floor the accelerator. The background stars show your velocity and orientation relative to the nearest gravity well. If you are having difficulties navigating space, point towards a gravity orb and accelerate for only a few seconds. Wait until the background stars spin wildly, and then reduce your velocity to 0 before gently accelerating towards to object.

'''Playing on mobile:''' Various additional glitches may occur. Having a starting position slightly below the take-off pad means you're already 'glitched' inside the planet from the off. Escaping the planet may need inverted 'accelerating' (turning perpendicular to the local vertical, and thrusting ''backwards'' until you can glitch back out into more open space. You may also be trapped within the cannonball 'orbit', with seemingly inconsistent collision-detection, such that you can be sat ''with landing gear extended'' upon features (projectile tracks, etc) that seem not to count as solid for most other purposes.

There is no "universal" point of view — the bottom of the window, "down", is oriented towards the object exerting the most gravity upon the player. Multiple things found in this comic draw attention to this, such as how on Earth Ponytail says to White Hat, "I checked downforeveryoneorjustme.com and it says just me", and he replies "Yeah, I guess down isn't down for everyone."

Throughout the play area are coins that change the spaceship into different rockets and non-space based vehicles, including humans.

The comic promotes Randall's new book [https://xkcd.com/what-if-2/ What If? 2], which was released in September and is available for purchase. Many of the planets contain references to various What If? articles.

The comic is similar to [[1608: Hoverboard]], which celebrated Thing Explainer instead.

===Celestial Bodies===

The following is an incomplete table of features:

{|class="wikitable sortable"
!
!
!
!
! colspan="4"|References
!
|-
! ID
! Description
! Transcript
! Tiles (X, Y)
! What If
! XKCD
! Movies
! Other
! Explanation
|-
|<code>origin</code>
|'''Starting planet'''
|
Cueball: "To celebrate the world of ''What If? 2'', here is your very own tiny planet to explore!

Megan: "Welcome!"

Ground caption: "Give someone the science question-and-answer book ''What If? 2'' for the Holidays: xkcd.com/whatif2"

Cueball feeding T-Rex: "Burger?"

Isaac Newton: "Robert Hooke must be down there ''somewhere!''"

Megan to Cueball: "If you ever get lost in space, just fly down. That's where the ground is."

Beret Guy to squirrel: "Hi!"
|(0, 0)
|Y
|
|
|Y
|The starting planet. The player begins on the launch pad in a landed position. Collecting the orbiting cannonball will transform you into a different rocket, although it does not improve your abilities.

Cueball feeding the T-Rex is possibly a reference to What If #78: {{what if|78|T-rex Calories}}.

{{w|Isaac Newton}} is referencing the {{w|Newton's cannonball}} thought experiment, where a cannon is fired at greater and greater speeds until the cannonball goes into orbit. Newton's comment suggests that instead of demonstrating orbits, he is firing repeatedly to hit his rival, {{w|Robert Hooke}}.
|-
|<code>earth</code>
|'''Earth'''
|
|(27867,-35648)
|Y
|Y
|
|Y
|A planet with among other things:
* A [https://what-if.xkcd.com/162/ crane dropping a comet] onto a dinosaur,
* Unusually high speed squirrels (creating a sonic boom)
* Megan inviting Cueball into a pool
* A region where the frame rate is intentionally limited
* A flagpole
* A literal {{w|burrow|rabbithole}} referencing the figuratively speaking [[wikt:rabbit hole|rabbit hole]]
* Someone aiming at a satellite with an arrow
* A lake with an eel
* The [https://what-if.xkcd.com/157/ earth-moon firepole]
* A "doot cone," a reference to [[Volcano Types]]
* Two figures being attacked by a third with a sword
* Two kids playing soccer (Catching the ball will turn the ship into a soccer ball)
* A farmer on a tractor being stuck in gooey candy
* A banana pile being consumed by "Bananas Georg" to make the per capita annual banana count round, referencing the "[https://reallyreallyreallytrying.tumblr.com/post/40033025233/average-person-eats-3-spiders-a-year-factoid Spiders Georg]" meme.
* Megan and Cueball digging a hole (in the center of this planet is the "earth's core", referenced below)
* The [https://what-if.xkcd.com/147/ Niagara Falls water being redirected into the LHC] (Large Hadron Collider)
* Japan(?) leaving earth
* A tube to the bottom of the ocean
* Ponytail and White Hat making a reference to [downforeveryoneorjustme.com]
* Two mini asteroid moons: A tiny version of B612 with Little Prince and the rose, plus one with just Cueball standing on it. They can be found by flying straight up from the Super Mario flagpole.
|-
|
|Earth's core
|
| (28850, -28570)
|
|
|
|
|[[Cueball]] and [[Megan]] floating in a small space in the center of the planet in inverted rotations. Can be legally accessed using a high velocity collision onto the surface of the planet, although requires tapping the up arrow afterwards many, many times.
|-
|<code>europa</code>
|'''Europa'''
|
|(13180, -2540)
|Y
|
|
|Y
|Europa, one of Jupiter's many moons (in real life). A broken, icy crust has a single path into its core.
|-
|
|Europa's crust
|
"It's so unfair we don't get to compete in EuroVision."

"The region of the solar system where liquid water can exist on the surface is the habitable zone, and the region where it can exist beneath the surface of moons is the Eurozone."

"WHIRRRR"
|
|Y
|
|
|
|Europa's crust, with a single entrance into the core demarcated by an octopus leaving a hole.
Cueball states that Europa is in the Eurozone, a pun on the ''other'' Eurozone, with liquid underneath its surface.

A roomba whirs across the icy crust.

Cueball has a hairdryer and is melting the surface of the crust. A direct reference to [https://what-if.xkcd.com/35/ What If's Hairdryer].
|-
|
|Europa's core
|"We've always used neutrinos for astronomy, but if we place my 'optical telescope' in orbit above the kryosphere, we could potentially observe the universe using electromagnetic waves. Who knows what else there is out there besides stars! There could be other worlds!"

"Hi, I'm Annie. Welcome to the depths of Europa. There's some weird stuff down here."

"We were caught in a powerful November gale on the Great Lakes outside Whitefish Bay. Our ship foundered and sank here." "This is Jupiter's moon Europa." "It was a REALLY powerful gale."

"Does our book club really need this much secrecy?" "That sounds like a question a SPY would ask."
|
|
|
|
|
|A watery ocean with octopi looking out into the great unknown using telescopes. This is a reference to octopus's intelligence here on earth! It may also be a reference to (Spoilers!) a certain 2013 science-fiction film featuring Europa, if not a 1987 book. There's also a secret path leading to a book club, through the wreck of the Edmund Fitzgerald.
|-
|<code>b612</code>
|'''B-612'''
|
Probe: "Asteroid deflection mission to earth. The package is delivered. Commencing planetary threat neutralization."

Sign: "Welcome to B-612"
|(2610,3700)
|y
|Y
|
|Y
|A reference to [[618: Asteroid|Asteroid]]. In a tragic turn of events, the Earth-bound asteroid being blown up is the home of [https://en.wikipedia.org/wiki/The_Little_Prince the little prince].
|-
|<code>dogplanet</code>
|'''Dog park planet'''
|
|(1240, 11230)
|y
|
|
|
|A planet with a dog park. Covered in dogs, along with dog walkers and some fences. There's a hole being dug by two dogs and a dog bone empty space in the center.
|-
| <code>goodhart</code>
|'''What If? 2 scenario planet'''
|
Cueball to White Hat: "The tower over there is the Vehicle Assembly Building, and then behind it is the Vehicle Disassembly Building."

Ponytail to Cueball: "You know how tires pollute the environment with rubber particles? Well, I've developed a solution."

"MMM SPIDERS HOMF HOMF"

Shooting star caption: "THE MORE YOU KNOW"
Sauropod: "Oh no!"

Person on uncontrolled helicopter: "AAAAAA"

Geyser: "Fwoosh!"
Cueball and Megan: "Oooh!"

Giant phone crushing city: "ALERT" "Giant phone crushing city" "Dismiss" "More"

Cueball with jetpack: "Wheeeee!"

Cueball to Megan: "Do you ever look up at the night sky and think, "Wow, I bet those little white dots taste ''delicious!''"

Neighbor: "Why is my house on fire ''again?!''
Cueball: "Dunno"
Laser captioned: "Laser"

Person with Washington Monument: "Okay, let it drop!"
|(-13300,-3260)
|y
|y
|
| Y
| Contains a reference to Kerbal Space Program, whimsically referring to the launchpad as the Vehicle Disassembly Building.

Contains a figure in a cave saying "MMM SPIDERS HOMF NOMF", which refers to [[1268: Alternate Universe|Alternate Universe]] and may also be a reference to the [https://reallyreallyreallytrying.tumblr.com/post/40033025233/average-person-eats-3-spiders-a-year-factoid Spiders Georg] meme.
|-
|<code>sun</code>
|'''The Sun'''
| "The sun is governed by magnetohydrodynamics, or 'Magic' for short"

"My countertop!"

"This will make a good soup base"

"Can I touch it yet?" "No, be patient. It's still too hot. Give it another 20 or 30 billion years."

"It's okay. I'm wearing five layers of sunscreen."

TV Anchor: "The forecast for today is lots of sun"

"This should be enough sunscreen"
|(-14950, 12080)
|y
|
|
|
|Difficult to escape from if you hit the core.
|-
|
|Sun's core
| Cueball: "The core of the sun may seem hot, but it only produces about as much energy per volume as a lizard" Megan: "Wow. So how many lizards are there?" Cueball: "No-one knows."
|
|Y
|
|
|
|Difficult to escape from. Can be escaped by rotating around the sun until an escape-like velocity could be reached.
|-
|<code>soupiter</code>
|'''Soupiter'''
|"I think it's chicken noodle? Hard to tell."
|(-800, -9040)
|Y
|
|
|
|A planet made of soup, with a core. As commented by Cueball, noodle soup. Has several small versions of other planets floating around it.
|-
|<code>nojapan</code>
|'''Earth without Japan'''
|"Something is missing."
|(-7680, -5850)
|Y
|
|
|
|Earth, except it's missing japan.
|-
|<code>japanmoon</code>
|'''Just Japan'''
|
|(-5930, -5800)
|Y
|
|
|
|A moon with water surrounding... just Japan.
|-
|<code>pigeons</code>
|'''A blob labeled "Pigeons"'''
|
|(-9020, -2490)
|Y
|
|
|
|A reference to Chapter 6 of What If? 2, where it would take 1.6 x 10^25 pigeons to lift you and a chair up to the halfway point of Australia's Q1 skyscraper.
|-
|<code>enterprise</code>
|'''Starship Enterprise'''
|
|(2389, -60879)
|Y
|
|
|
|Star Trek reference: The Enterprise-C, yes 2344,commanded by Captain Garrett's. While defending a Klingon outpost, the weapons discharges resulted in the creation of a temporal rift, through which the badly damaged Enterprise drifted. In the comic, there is a large, invisible gravity distortion near the Enterprise-C
|-
|<code>qwantz</code>
|'''Dinosaur planet'''
|"Welcome... to Jurassic Park."
| (20403,-49559)
|
|
|Y
|
|An homage to [https://www.qwantz.com/ Dinosaur Comics], a webcomic Randall has mentioned several times before. All the dinosaurs on the planet are black-and-white versions of the clip art dinosaurs in that comic. Also references the Jurassic Park movies, with CEO John Hammond welcoming paleontologists Dr. Sattler and Dr. Grant to the planet. The long grass depicted is a plot point in later films. It seems like crashing into this planet hard enough will let you dive into the core, but that only lets you out on the other side. Then the system seems to glitch and have the ship phase into and out of the planet.
|-
|
|'''What If? 1 scenario planet'''
|
|
|
|
|
|
|
|-
|<code>roads</code>
|'''Cat blocking traffic flowing through portals'''
|
|
|
|
|
|
|
|-
|<code>outside</code>
|'''Edge of the Universe'''
|"Welcome, traveler!" (found inside the edge of the bubble universe)
| ( 6081, 26138 )
|
|
|
|
|It looks like a planet labeled "edge of the universe". Outside the universe, so inside the "edge of the universe" planet, is another universe, the bubble universe, whose outside is labeled "edge of the bubble universe". Hidden entrance is between 10 and 11 'o clock.
|-
|<code>roads</code>
|'''A tree larger than the planet it's growing on'''
|
|
|
|Y
|
|
|May be a reference to [[2: Petit Trees (sketch)|Petit Trees]]. More probably, a reference to ''The Little Prince'', a French children's novel about a traveler from a distant asteroid. In the novel, baobab trees are a serious threat to the Prince's home asteroid, as they are so large that their roots would engulf the asteroid entirely. Randall has alluded to The Little Prince numerous times before, especially in what-if articles.
|-
|<code>outside</code>
|'''Milliways'''
|
| in code: <code>[0,-14500]</code> in game: <code>[0,29000]</code>
|
|
|Y
|Y
|A reference to Milliways, the Restaurant at the End of the Universe from ''The Hitchhiker's Guide to the Galaxy''. On one side of the planet, Ponytail, Cueball, Megan, and other characters gather on the patio of the Milliways restaurant; on the other side, the Sojourner rover examines a rock.
|-
|<code>greatattractor</code>
|'''The Great Attractor'''
|
|(-596048, 247952)
|
|Y
|
|
|Beret Guy stands on the surface of a large ball labeled "The Great Attractor". The gravity is extremely strong (over 200 times that of the black holes), leading to various bugs and collision issues. It's a reference to [[Great Attractor]], in which Beret Guy is gravitationally attracted to the Great Attractor more strongly than usual.
|-
|<code>present</code>
|'''Present'''
|
"I didn't do any of my Christmas shopping yet because I was too busy drawing tiny planets."

"I'm done with my shopping! I got everyone What if? 2"

"...You got me my own book?"

"Yeah! I figured that since you wrote it, it must be right up your alley."

"It does make a good gift, though. You can get it at xkcd.com/whatif2"

"I got you this present!"

"Is it an angry bobcat?"

"It might not be."
|in code: <code>[22820,-18920]</code> in game: <code>[45640,37840]</code>
|
|Y
|
|
|The XKCD cast react to giving each other What if 2? as a present. Gravity at the bottom of the missing quarter of the planet is inescapable. Black Hat gives Cueball a "gift" which he claims "might not be a bobcat", a reference to [[A-Minus-Minus]]
|-
|<code>maw1</code>, <code>maw2</code>, ... <code>maw14</code>
|'''Black hole cluster'''
|
|
|
|
|
|
|A cluster of black holes with extremely high gravitational strength, set to the maximum of 2048. Not particularly easy to land on with multiple conflicting gravitational fields, but once landed on, rather difficult to escape.
|-
|<code>remnant</code>
|'''Remnant'''
|"All right, that's close enough"
"Oh no"

{{w|Walkin' on the Sun|"So don't delay, act now, supplies are running out"}}

"In 5 billion years, the Sun will run out of fuel and suffer gigennial burnout."

"The immense gravity of the sun's remnant means that this is the tallest possible skyscraper."
|(19620, 3800)
|
|
|
|
|A stellar remnant, with high gravity (making it difficult to escape, although it's possible to achieve escape velocity by flying sideways). Has various small landmarks, including a "skyscraper" and suspension bridge. There are bombs being dropped from above the planet, with one that seems to be sledding on the planet.
|-
|<code>steerswoman</code>
|'''Steerswoman Planet'''
|"As a Steerswoman, I have to answer any question anyone asks me, or I'm expelled from the order."
"What's one question that you would be unwilling to answer?"
"Oh no."

"Handle this artifact with great care. It contains a magical wizard's potion which the ancients called 'trinitrotoluene'"
|(-35070,-2500)
|
|
|
|Y
|A reference to the Steerswoman series of books by Rosemary Kirstein. Includes a number of references to the series, including a group of people observing a small object orbiting the planet.

Trinitrotoluene is better known as {{w|TNT}}, a powerful explosive.
|-
|<code>peeler</code>
|'''Peeler'''
|
|(-9270, 620)
|Y
|
|
|
|A reference to the question posed by "What If 2: Lose Weight the Slow and Incredibly Difficult Way". A large potato peeler is seen removing the earth's crust.
|}

===Ships===
{|class="wikitable sortable"
|-
! Name
! Description
! Location
! Filename
! Image
|-
|Default
|The starting ship.
|It is possible to change back to this ship by collecting a dot located within the Black Hole cluster
|ship2
|
|-
| Tintin
|
| On the starting planet; can be obtained by collecting the cannonball in orbit
| ship-tintin
|
|-
| Figure
|Stick figure
|On Goodhart, atop the mountain up which Sisyphus is pushing his boulder.
|ship-figure
|
|-
| Soccer ball
| Soccer ball shaped ship
| On Earth, between two figures playing ball
|ship-soccer
|
|-
|Alternative Ship
|Slightly thicker version of default ship
|Only available by using console to change Comic.ship
|ship1
|}

==Data and Maps==

View the data that is embedded in the comic on [[2712: Gravity/Data|this page]].

Maps created by the Community:
*https://bacontime.github.io/xkcd2712 | A zoomable map of the universe with markers for all planets, coins and with the option to highlight secret passages
*https://www.reddit.com/r/xkcd/comments/zpe7bz/i_rendered_the_entire_what_if_2_universe_as_a/ | The whole universe rendered as one big image

==Hacks==
Various modes and hacks have been found or developed by the community, and can be activated by opening the Javascript Console (F12 [Or Command-Alt-I in most browsers under Mac OS X] to open Developer Tools, then Console tab) and writing corresponding commands. 
'''Click to expand:''' 

<div class="mw-collapsible mw-collapsed leftAlign" style="width:100%">
 
*'''Speedhack:''' <code>ship.engines = "warp"</code> - Speed hacking, sets speed to 1.4x. set to "standard" to reset to normal speed
*'''Teleport to planet:''' <code>[Comic.voyager.pos.x, Comic.voyager.pos.y] = Comic.planetRects.'''''origin'''''.slice(0,2)</code> - teleport near a planet, in this example near earth. You'll still have to fly a bit towards the nearest planet to reach it. Replace '''''origin''''' with the ID of the planet you want to go to, from the table above.
*'''Teleport to coordinate:''' <code>[Comic.voyager.pos.x, Comic.voyager.pos.y] = '''''[0, -2000]'''''</code> - teleport to an exact coordinate. <code>[0, -2000]</code> happens to take you to the starting area.
*'''Improved radar:''' <code>Comic.wayfinderFarDistance = Infinity</code> - make the direction of all objects visible. This can be hard to understand though.
*'''Chaos Mode:''' <code>ship.engines="infinite improbability drive"</code> - Seems to randomly teleports the ship. A reference to its namesake in Hitchhiker's Guide to the Galaxy.
*'''Insta Death:''' <code>ship.shields = false</code> - Kill the player if they land on a planet, the code never sets it to false, so it seems to be always true.
*'''No Clip:''' <code>noclip = true</code> - Enables noclip. Also disables gravity.
*'''Select ship:''' <code>Comic.ship = "ship-tintin"</code> - Select ship (use filename from list of ships)
*'''Autorotate:''' <code>Comic.cameraRotation = false</code> - View does not rotate with ship
*'''Goggles:''' <code>ze.goggles()</code> - returns a warning: "they do nothing!". This is a reference to Hoverboard, where ''ze.goggles()'' would give you the ability to see false walls. Which itself is most likely a reference to the Simpsons where Radioactive man complains that his safety goggles do nothing against a deluge of acid.
*'''Python:''' <code>python("import antigravity")</code> - reverses gravity, so the ship falls away from planets. A reference to [[353: Python|Python]].
</div>
 

==Trivia==
The objects in the mini-universe of this browser game are all at fixed positions and do not interact through gravity, however, the ship controlled by the player is affected by gravity. While this makes it technically a relatively easy integration problem (of the position of the player ship forward in time), the integrator used seems to be a relatively simple one - and certainly not a symplectic one, because it does not conserve angular momentum. This can be seen when one manages to get into orbit around some object, e.g. the core of the sun. The orbit slowly decays over time.

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

Welcome!

To celebrate the world of what if? 2, here is your very own planet to explore!

Give someone the science question-and-answer book what if? 2 for Christmas:
xkcd.com/whatif2

{{comic discussion}}
[[Category:Space]]
[[Category:Book promotion]]
[[Category:Interactive comics]]
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Black Hat]]
[[Category:Bobcats]]