explain xkcd - User contributions [en]

1154: Resolution

2013-03-23T14:04:12Z

72.92.8.14: /* Explanation */

{{comic
| number = 1154
| date = December 31, 2012
| title = Resolution
| image = resolution.png
| titletext = If at first you don't succeed, that's one data point.
}}

==Explanation==
This comic is a little reminder that it's the last day of 2012, and it's time to make your resolutions!

[[Cueball]] wants to break a very common habit of resolving to do something (go on a diet, for example), not doing it, and then trying the same, dysfunctional plan again, thinking it will work "this year." This is another way of stating a common folk definition of insanity: to keep doing what you always do yet expecting different results.

The irony is that Cueball resolved the same thing last year, and it is implied it didn't work, but he says it'll be different "this year."

The title text is a parody of the saying "if at first you don't succeed: try, try, try again."

{{comic discussion}}

[[Category:Comics featuring Cueball]]

849: Complex Conjugate

2013-03-23T13:43:26Z

72.92.8.14: /* Explanation */

{{comic
| number = 849
| date = January 19th, 2011
| title = Complex Conjugate
| image = complex_conjugate.png
| titletext = Fun fact: if you say this every time a professor does something to a complex-number equation that drops the imaginary part, they'll eventually move the class to another room and tell everyone else except you.
}}

==Explanation==
This comic is a joke on the common phrase "Shit just got ''real''", meaning that something has suddenly increased in difficulty so it is now a real challenge. [[Cueball]] is standing in front of a board delivering a lesson, and is about to multiply a wavefunction by its complex conjugate. In mathematics, the product of a complex number and its conjugate removes the imaginary part, effectively making it "real". Accordingly, Cueball dictates that the people who are not skilled enough should leave.

The title text states that if you joke about this every time it's applicable, that will be annoying enough that the class will ditch you and attempt to take place in another room.

==Transcript==
:[Cueball is standing at a whiteboard covered in equations, one of which is the time dependent Schrodinger equation.]
:Cueball: Okay, anyone who's feeling like they can't handle the physics here should probably just leave now.

:Cueball: Because I'm multiplying the wavefunction by its complex conjugate.
:Cueball: That's right.

:[Dramatic zoom. It appears the teacher is writing on the side of the panel.]
:Cueball: Shit just got ''real''.
{{comic discussion}}
[[Category:Comics featuring Cueball]]
[[Category:Math]]
[[Category:Physics]]

861: Wisdom Teeth

2013-03-23T13:30:37Z

72.92.8.14: /* Explanation */

{{comic
| number = 861
| date = February 16, 2011
| title = Wisdom Teeth
| image = wisdom_teeth.png
| imagesize =
| titletext = I heard the general anesthesia drugs can cause amnesia, so when I woke up mid-extraction I started taking notes on my hand so I'd remember things later. I managed 'AWAKE BUT EVERYTHING OK' before the dental assistant managed to find and confiscate all my pens.
}}

==Explanation==
{{w|Wisdom teeth}}, as many of you are no doubt {{w|Wisdom teeth#Post-extraction problems|painfully aware}}, are the third set of molars found in humans. Because human jaws are smaller than our ape ancestors, most of us don't have room for a third set of molars, and the teeth become impacted (i.e. they grow straight into the other teeth), requiring a painful, debilitating procedure to remove them.

Because recovering from dental surgery often entails a period of rest following the operation and the use of prescription painkillers, [[Cueball]] prepares to play Minecraft for the entire time. {{w|Minecraft}} is a PC game known for its addictive qualities; the game itself primarily revolves around a three-dimensional world in which the goal of the player is centered on the aspects of structural creation using blocks found in the environment and the creation of different materials for use in building these structures. Despite its addictive nature, the game doesn't provide the player with a goal, so most people take to building lots of nifty stuff, such as large cities, computers made out of redstone logic gates, massive scale replicas of Earth, etc.

Due to the inhibitory effects of the painkillers, Cueball has instead opted to flatten the entire continent and sort it into layers (by type of block, presumably). While there's no real indication of how big the continent is as Minecraft worlds are randomly generated, sea level in Minecraft is at Zlevel 62, which means he sorted at least 63 layers of a continent large enough to be sufficiently developed, so it is clear that this task would take a lot of time. (Collecting a block in Minecraft takes a certain minimum amount of time, depending on the block type, so even if he did everything as fast as he possibly could there's a substantial lower bound.)

Ironically, in the second panel [[Megan]] says she'll set Cueball up on her server, which indicates she probably uses a whitelist to secure the server from griefers who might destroy structures created by others, not expecting that Cueball would do exactly that. The last panel simply illustrates that painkillers tend to make one loopy.

The title-text refers to people waking up during surgery. Because anesthesia requires a lot of careful calibration and dosage (there's a reason anesthesiologists are paid hundreds of dollars an hour to be there, after all), it's possible to sometimes get it wrong, resulting in the patient waking up in the middle of the surgery. The three most important parts of anesthetics used for surgery are an analgesic (blocks pain), a sedative (puts you to sleep), and a paralytic (keeps you from moving). The worst-case scenario that most people hear about is when the analgesic and sedative are under-dosed, but the paralytic is correct, leaving the person awake, able to feel pain, but unable to alert the surgeons that anything is wrong. As a result, some countries and medical institutions have passed laws requiring surgeons to monitor brain activity so that these problems can be quickly remedied. The situation the title text is describing, with all three parts of the anesthetic wearing out (leaving the person able to write notes), would be quite unlikely.

==Transcript==
:Cueball, on phone: Hey! Know how you've been bugging me to play Minecraft for the past year? I'm game.
:Megan, on phone: But you said you didn't want to "get hooked and spend days on end moving virtual cubes around while sitting motionless." What changed?

:Cueball, on phone: I'm having my wisdom teeth out, and I'll be useless and doped up on painkillers for the next few days, so that actually sounds like the perfect distraction.
:Megan, on phone: Oh. I'll set you up on our server!

:72 hours later...
:[Megan sitting at computer.]
:Megan, on phone: Hey — starting to feel better? Enjoying the game? Let's see what you've... What the hell? Where ''IS'' everything?

:[View of a Minecraft screen showing a vast empty expanse of land.]
:Megan, offscreen: ... You made the entire continent perfectly flat?
:Cueball, offscreen: And sorted it into layers.
:Megan, offscreen: ...
:Cueball, offscreen: I feel good about things. This is a good game.

:[Cueball sitting on the floor at his laptop, bleeding from the mouth, surrounded by bloody wadded-up tissues and holding a bottle of medication.]
:Megan, on phone: ... What exactly is in the painkillers they gave you?
:Cueball, woozy: I can't read the label because I'm a hologram.

{{comic discussion}}


[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Comics with color]]

861: Wisdom Teeth

2013-03-23T13:29:41Z

72.92.8.14: /* Explanation */

{{comic
| number = 861
| date = February 16, 2011
| title = Wisdom Teeth
| image = wisdom_teeth.png
| imagesize =
| titletext = I heard the general anesthesia drugs can cause amnesia, so when I woke up mid-extraction I started taking notes on my hand so I'd remember things later. I managed 'AWAKE BUT EVERYTHING OK' before the dental assistant managed to find and confiscate all my pens.
}}

==Explanation==
{{w|Wisdom teeth}}, as many of you are no doubt {{w|Wisdom teeth#Post-extraction problems|painfully aware}}, are the third set of molars found in humans. Because human jaws are smaller than our ape ancestors, most of us don't have room for a third set of molars, and the teeth become impacted (i.e. they grow straight into the other teeth), requiring a painful, debilitating procedure to remove them.

Because recovering from dental surgery often entails a period of rest following the operation and the use of prescription painkillers, [[Cueball]] prepares to play Minecraft for the entire time. {{w|Minecraft}} is a PC game known for its addictive qualities; the game itself primarily revolves around a three-dimensional world in which the goal of the player is centered on the aspects of structural creation using blocks found in the environment and the creation of different materials for use in building these structures. Despite its addictive nature, the game doesn't have an intrinsic goal, so most people take to building lots of nifty stuff, such as large cities, computers made out of redstone logic gates, massive scale replicas of Earth, etc.

Due to the inhibitory effects of the painkillers, Cueball has instead opted to flatten the entire continent and sort it into layers (by type of block, presumably). While there's no real indication of how big the continent is as Minecraft worlds are randomly generated, sea level in Minecraft is at Zlevel 62, which means he sorted at least 63 layers of a continent large enough to be sufficiently developed, so it is clear that this task would take a lot of time. (Collecting a block in Minecraft takes a certain minimum amount of time, depending on the block type, so even if he did everything as fast as he possibly could there's a substantial lower bound.)

Ironically, in the second panel [[Megan]] says she'll set Cueball up on her server, which indicates she probably uses a whitelist to secure the server from griefers who might destroy structures created by others, not expecting that Cueball would do exactly that. The last panel simply illustrates that painkillers tend to make one loopy.

The title-text refers to people waking up during surgery. Because anesthesia requires a lot of careful calibration and dosage (there's a reason anesthesiologists are paid hundreds of dollars an hour to be there, after all), it's possible to sometimes get it wrong, resulting in the patient waking up in the middle of the surgery. The three most important parts of anesthetics used for surgery are an analgesic (blocks pain), a sedative (puts you to sleep), and a paralytic (keeps you from moving). The worst-case scenario that most people hear about is when the analgesic and sedative are under-dosed, but the paralytic is correct, leaving the person awake, able to feel pain, but unable to alert the surgeons that anything is wrong. As a result, some countries and medical institutions have passed laws requiring surgeons to monitor brain activity so that these problems can be quickly remedied. The situation the title text is describing, with all three parts of the anesthetic wearing out (leaving the person able to write notes), would be quite unlikely.

==Transcript==
:Cueball, on phone: Hey! Know how you've been bugging me to play Minecraft for the past year? I'm game.
:Megan, on phone: But you said you didn't want to "get hooked and spend days on end moving virtual cubes around while sitting motionless." What changed?

:Cueball, on phone: I'm having my wisdom teeth out, and I'll be useless and doped up on painkillers for the next few days, so that actually sounds like the perfect distraction.
:Megan, on phone: Oh. I'll set you up on our server!

:72 hours later...
:[Megan sitting at computer.]
:Megan, on phone: Hey — starting to feel better? Enjoying the game? Let's see what you've... What the hell? Where ''IS'' everything?

:[View of a Minecraft screen showing a vast empty expanse of land.]
:Megan, offscreen: ... You made the entire continent perfectly flat?
:Cueball, offscreen: And sorted it into layers.
:Megan, offscreen: ...
:Cueball, offscreen: I feel good about things. This is a good game.

:[Cueball sitting on the floor at his laptop, bleeding from the mouth, surrounded by bloody wadded-up tissues and holding a bottle of medication.]
:Megan, on phone: ... What exactly is in the painkillers they gave you?
:Cueball, woozy: I can't read the label because I'm a hologram.

{{comic discussion}}


[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Comics with color]]

865: Nanobots

2013-03-23T13:24:55Z

72.92.8.14: /* Explanation */

{{comic
| number = 865
| date = February 25, 2011
| title = Nanobots
| image = nanobots.png
| imagesize =
| titletext = I think the IETF hit the right balance with the 128 bits thing. We can fit MAC addresses in a /64 subnet, and the nanobots will only be able to devour half the planet.
}}

==Explanation==
In this comic, the two characters are in orbit in space while evil nanobots are devouring the earth in a swarm. The nanobots stop after devouring 40% of the planet. This is a take on the "gray goo" scenario in which self-replicating nanobots destroy the earth while creating more and more of themselves non-stop.

However, the nanobots are only able to destroy 40% of the planet because 40% of the earth mass = (# of IPv6 addresses) x (A few cubic microns). Without more IP addresses, the nanobots cannot continue to replicate (assuming that each nanobot must be individually addressable).

This is a joke on the shortage of IPv4 addresses. The only difference is that we are on {{w|IPv4}} and the nanobots are on {{w|IPv6}}.

1998 is when the [http://tools.ietf.org/html/rfc2460 IPv6 Specification (RFC 2460)] was published and IETF is the Internet Engineering Task Force.

==Transcript==
:[Megan and commander are on a space station.]
:Megan: Commander! Come quick!
:Megan: It's the nanobots—
:Megan: They've STOPPED!

:Megan: They devoured 40% of the Earth, and then just ... quit! They're just sitting there!
:Megan: Why?!

:Ponytail: It's a mystery. ... unless ... What's the volume of each nanobot?
:Megan: A few cubic microns. Why?
:Ponytail: I think the year 1998 just bought us some time.

:[Earth's surface, covered in mountains of nanobots.]
:In the swarm:
:Nanobot: What do you mean, "Run out of addresses?"
:Other Nanobot: Look, we should've migrated away from IPv6 AGES ago ...

{{comic discussion}}
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Ponytail]]

866: Compass and Straightedge

2013-03-23T13:22:27Z

72.92.8.14: /* Explanation */

{{comic
| number = 866
| date = February 28, 2011
| title = Compass and Straightedge
| image = compass and straightedge.png
| titletext = The Greeks long suspected this, but it wasn't until April 12th of 1882 that Ferdinand von Lindemann conclusively proved it when he constructed himself the most awesome birthday party possible and nobody showed up.
}}

==Explanation==
{{w|Compass and straightedge constructions}} are a class of problems in classical geometry. They take the form "Using only a compass and a straightedge, construct X", where X is a geometric figure such as a regular pentagon. The subject is typically covered in high school mathematics. Three such constructions remained unsolved for thousands of years before being shown impossible with the use of modern algebraic techniques.

The comic begins as if it were stating a problem in classical geometry but veers into an observation that no amount of technical knowledge can substitute for human companionship. An additional layer of humor is that [[Cueball]] is a stick figure so technically it is possible to create friends with a straightedge and a compass.

{{w|Ferdinand von Lindemann}} was a German mathematician who showed in 1882 that pi is not a zero of any polynomial with rational coefficients, i.e. it is a transcendental number. Transcendental numbers cannot be constructed with straightedge and compass.

==Transcript==
:I learned in high school what geometers discovered long ago:
:[Cueball, holding a compass and straightedge, looks sad.]
:Using only a compass and straightedge, its impossible to construct friends.

{{comic discussion}}
[[Category:Comics featuring Cueball]]
[[Category:Math]]

888: Heaven

2013-03-23T12:57:02Z

72.92.8.14: /* Explanation */ fix misspelling; make Tetris a link

{{comic
| number = 888
| date = April 20, 2011
| title = Heaven
| image = heaven.png
| imagesize =
| titletext = If you've never had sex, this is what it feels like. Complete with the brief feeling of satisfaction, followed by ennui, followed by getting bored and trying to make it happen again.
}}

==Explanation==
This comic is a reference to the video game {{w|Tetris}}, in which you use different shaped pieces to fill in lines to score points. The more lines you fill at a time results in more points.

In this comic, Heaven is when you get the perfect piece in Tetris that fills out all the empty space you have on the board.

In the title text, ennui means a feeling of utter weariness and discontent resulting from satiety or lack of interest.

A fan even made a modified version of the classic Tetris game, where at a certain frequency, a 'heaven' perfectly fitting block comes along. The game can be found on. http://www.gudmagazine.com/games/heaven/.

Also see comic [[724: Hell]], which presents an opposing situation in which the game is impossible to play.

==Transcript==
:[The display is a tetris game. A large oddly shaped piece is falling towards the board. The piece fits into the gaps exactly to complete multiple rows at once. The next piece is simply a very long brick.]
:Top 0002187
:Score 0002186
:Level 5
:(The above are within the game; the next line is outside the game.)
:Heaven

{{comic discussion}}
[[Category:Comics with color]]

1184: Circumference Formula

2013-03-23T04:57:31Z

72.92.8.14: /* Explanation */ make “footnote” a link to Wikipedia

{{comic
| number = 1184
| date = March 11, 2013
| title = Circumference Formula
| image = circumference_formula.png
| titletext = Assume r' refers to the radius of Earth Prime, and r'<nowiki/>' means radius in inches.
}}

==Explanation==
The {{w|circumference}} C of a {{w|circle}} is 2{{w|pi|π}}''r'', where ''r'' is the {{w|radius}} of the circle. Randall then makes a {{w|Note (typography)|footnote}} about ''r'', using 2. This creates a typographical ambiguity, since a superscript 2 can also be an exponent (as in ''x''2). Randall's formula now looks like a strange hybrid of the correct formula and the formula for the ''{{w|area}}'' of the circle: A = π''r'' 2.

The ′ and ″ that follows the r's in the title text are the {{w|prime symbol|prime}} and double prime symbols. {{w|Prime (symbol)#Designation of units|Among other things}}, these are often used in mathematics to tell apart corresponding properties of different objects.

In this case, ''r'' is already used to notate the radius of any circle. ''r'' ′ ("r-prime") could then be used to notate radii of things that are not circles (like the [http://www.mathsisfun.com/definitions/radius-polygon-.html radius of any regular polygon], or the radius of any {{w|sphere}}). [[Randall]] chooses the radius of {{w|Earth Prime}}.

"Prime" can mean first or original, and "Earth Prime" is a term sometimes used in works of fiction involving parallel universes to refer to ''our'' Earth (e.g. in {{w|The Long Earth}}), or to a world with a minimum of divergence points from Earth as we know it. (The radius of Earth Prime would thus not differ much from the {{w|radius of the Earth}}; 6 371 km.)

As the title text also plays on, another of the uses of the double prime symbol (″) is to designate {{w|inches}}.

2 These are not intended to indicate the presence of a footn... oh, nevermind.

==Transcript==
:Circumference of a circle:
:2πr2
:2The circle's radius

{{comic discussion}}
[[Category:Math]]