explain xkcd - User contributions [en]

2719: Hydrogen Isotopes

2023-01-03T13:24:58Z

Char1983: Made the explanation for instant hydrogen a bit more clear

{{comic
| number = 2719
| date = January 2, 2023
| title = Hydrogen Isotopes
| image = hydrogen_isotopes_2x.png
| imagesize = 442x250px
| noexpand = true
| titletext = Oops, All Neutrons is also known as Neutral Quadrium, Nydnonen, and Goth Tritium.
}}

==Explanation==
{{incomplete|Created by a BREAK ROOM DE BROGLIE MICROWAVE USER. Do NOT delete this tag too soon.}}

{{W|Hydrogen}} is the simplest of the chemical atoms, usually consisting of an electron orbiting an proton. This comic imagines other humorous fictional forms of hydrogen as follows:

{| class="wikitable"
! "Isotope"
! Real?
! Description
|-
|Hydrogen
|Yes
|Hydrogen is the most common {{w|isotope}} of hydrogen, with one proton and one electron, shown with the electron orbiting the proton. It is also known as protium.
|-
|Deuterium
|Yes
|Deuterium is the second most common isotope of hydrogen, with one electron and both a neutron and proton in its nucleus. About one of every 6,760 hydrogen atoms in seawater is deuterium.
|-
|Tritium
|Yes
|Tritium is the third most common isotope of hydrogen, with one electron and a nucleus of one proton and two neutrons, for an atomic mass of about three {{w|Dalton (unit)|daltons}}. It is radioactive with a half-life of about twelve years, and is very rare (but not as rare as unbound "instant hydrogen" neutrons.)
|-
|Ium
|Not as such
|This imaginary isotope consists of one electron orbiting around nothing. The name relates to the fact that the two heavier isotopes are named from a prefix designating the number of {{w|nucleons}} followed by the suffix "-ium", which is sometimes used satirically, e.g., in "unobtainium." Free electrons are always in motion, {{w|Fermi energy|even at absolute zero temperature}}, but not in stationary orbits.
|-o
|Wheelium
|No
|This fictional form consists of a proton, electron, and neutron orbiting around nothing, shaped similarly to a wheel. The neutron would either bind to the proton, or more likely simply drift away.
|-
|Instant hydrogen (ready in 15 minutes)
|Yes, but rare
|This is just a single neutron. Unbound neutrons will take about fifteen minutes to decay into a proton, an electron, and a neutrino. The neutrino will carry away momentum, while the proton and electron ''can'' form into a hydrogen atom. However, this [https://van.physics.illinois.edu/ask/listing/1207 only happens about four times in a million.] (the proton could also capture another electron, though). The name is likely a reference to "instant" meals that require less preparation time than traditional varieties (e.g. instant noodles.)
|-
|Hydrogen (maximum strength)
|No
|This fictional isotope consists of a proton, an electron, and what appear to be at least 14 neutrons. This isotope's proton would not be bound to all the neutrons. It would immediately decay by {{w|Nuclear drip line|dripping}} most all of them away.
|-
|Oops, All Neutrons
|Maybe
|This fictional form consists of four neutrons, a {{w|tetraneutron}}, with one orbiting around a group of three. The name is likely a reference to an American breakfast cereal called {{w|Cap'n Crunch#Variations|Oops! All Berries}}.

The title text provides three other names of this form: 1. "Neutral Quadrium": The proton and electron in tritium have both been replaced with neutrons, making this fictional atom neutral, and it's named with the "quad-" prefix designating four nucleons. 2. "Nydnonen" is likely a derivation of "hydrogen" with three of its consonants replaced with the letter 'n' so it has four of them representing the four neutrons. 3. "Goth Tritium": All the particles in the depiction are black, resembling stereotypical {{w|gothic fashion}}, and in the same configuration as the particles of tritium.
|}

{{notice2|The Mountain View, California Public Library is hosting an online chat with [[Randall Munroe]] Tuesday, January 31 at 11am Pacific.<br/>[https://libraryc.org/mountainviewlibrary/22032 Register here to send your question(s) to the moderators.]|image=Crystal Project Agt announcements.png}} 

==Transcript==
:[Eight drawings of different versions of hydrogen atoms are shown. They are arranged in two rows of four. The depictions use the planetary model version with for instance a negative electron (with a "-" written inside a small circle) orbiting a positive proton (with a "+" written inside a larger circle) and a black neutron depicted as a circle of the same size as the neutron, as in the second atom - Deuterium. Each has a label underneath. Here, they are listed ion reading order:]
:[An electron orbiting a proton:]
:Hydrogen

:[An electron orbiting a proton connected with a neutron:]
:Deuterium

:[An electron orbiting a proton connected with two neutrons, so they form a triangle:]
:Tritium

:[An electron orbiting nothing:]
:Ium

:[An electron a proton and a neutron all orbiting on the same circle around nothing. They are placed equidistant from each other forming a large triangle:]
:Wheelium

:[A single proton:]
:Instant Hydrogen (ready in 15 minutes)

:[An electron orbiting a proton connected with many neutrons, 13 visible with six touching the proton which are in front. Four more are close to those six and mostly shown and then three are only just visible behind the others. Looking closely there are also two smaller dots near the edge indicating at least two more, for 15 that can be seen. And several more would be behind the visible neutrons if this forms a spherical shape. The electrons orbit just barely goes around the outer neutrons:]
:Hydrogen (maximum strength)

:[Four neutrons arranged like the particles in Tritium with a neutron orbiting a triangle of neutrons.]
:Oops, all neutrons

{{comic discussion}}

[[Category:Charts]]
[[Category:Physics]]
[[Category:Chemistry]]

2712: Gravity

2022-12-18T23:15:14Z

Char1983: Added description about the fact that the integration method does not conserve angular momentum.

{{comic
| number = 2712
| date = December 16, 2022
| title = Gravity
| image = gravity_2x.png
| imagesize = 740x700px
| noexpand = true
| 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 several 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. 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)
|
|
|
|
|The starting planet. The player begins on the launch pad in a landed position. Collecting the orbiting cannonball will transform you into a more advanced rocket.
|-
|<code>earth</code>
|'''Earth'''
|
|(27867,-35648)
|Y
|
|
|Y
|A planet with among other things:
* A 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 volcano
* 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]
|-
|
|Earth's core
|
|
|
|
|
|
|[[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)
|
|
|
|
|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! 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
|
|
|A reference to [[618: Asteroid|Asteroid]]. The little prince is having his asteroid blown up as it was heading towards Earth, apparently.
|-
|<code>dogplanet</code>
|'''Dog park planet'''
|
|(1240, 11230)
|
|
|
|
|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
| 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 may 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)
|
|
|
|
|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.
|-
|
|'''What If? 1 scenario planet'''
|
|
|
|
|
|
|
|-
|<code>roads</code>
|'''Cat blocking traffic flowing through portals'''
|
|
|
|
|
|
|
|-
|<code>outside</code>
|'''Edge of the 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. 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><br>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'''
|
|
|
|Y
|
|
|Beret Guy stands on the surface of a large ball labeled "The Great Attractor". Gravity is so strong that escaping is impossible. 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><br>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)
|
|
|
|
|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)
|
|
|
|
|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 Dump==

View the data on [[2712: Gravity/Data|this page]].

==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.<br>
'''Click to expand:'''<br>

<div class="mw-collapsible mw-collapsed leftAlign" style="width:100%">
<br>
*'''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.
*'''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>
<br>

===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]]