Pixels
[Cueball is stacking turtles, and is about to put the fourth turtle on his pile. At the bottom right there is a small panel. Inside this is written:] Scroll to zoom
[When zooming in there will be several panels with text. The transcript of these may not be possible to complete - but add the transcript of these panels here: interactive transcript ]
The following code can be found by inspecting the comic's source code: [[A large picture of a person kneeling on the ground, stacking turtles.]] ((In this strip, when you zoom into the panel, each pixel becomes its own panel. Each of those panels can be scrolled into, for the same effect. The story progresses as you scroll deeper.)) [[The Earth as seen from space with the words BOOK LAUNCH.]] [[A stick-Randall holding a copy of 'What If?' saying, "So excited about my book launch!"]] [[A copy of the cover of 'What If?' labeled "book."]] [[Stick-Randall is assembling parts from a box labeled 'rocket parts' and preparing to 'launch' his book.]] [[Various stages of assembly.]] [[A second person comes in, looks at SR's rocket set-up and says, "Needs more struts."]] [[SR adds more struts.]] [[The rocket launches.]] [[A big cloud of smoke, which then dissipates.]] [[SR and the other person look skywards at the launched book.]] [[The book is shown leaving Earth's orbit.]] [[The other person turns to SR and says, "I think that was the only one."]] [[The two walk away.]] ((The panels after this are a random assortment of these mostly stand-alone panels.)) [[A momma duck with several ducklings in a row behind her, labeled 'Evolution.']] [[The other person floating around in the sky.]] [[A stick figure with a sploshing bucket of water saying, "I'm gonna shut down the server!"]] [[Two people walking along, one saying, "But if the Time-Turners worked after Book 3, Rowling would have used one to go back and remove the Time Turner from Book 3."]] [[The code: ~$ du -s video
4170882256 ~$ du -hs video
A lot. ~$]] [[A cloud.]] [[A flock of birds.]] [[MU]] [[A pixel.]] [[A person using a computer on the floor.]] [[HOLISM]] [[Saturn]] [[An atom.]] [[Two people star-gazing on a hill.]] [[Person one says, "Someone once told me the great kings of the past look down on us..." Person two says, "From the stars?" The first person replies, "Just in general."]] [[The start of Mario World 1-1.]]

{{Title text: It's turtles all the way down.}}
This gallery contains the 79 images used in this comic . The images are related in a directed graph .
This google sheet describes all possible images, their associated codes, and what possible images can be used as sub-images for each zoom level: https://docs.google.com/spreadsheets/d/1nldKAkeVcK606CY12KI9bah9rDmK9E7CZOyinsEj2Lo/edit?usp=sharing
This gist recursively downloads all possible images: https://gist.github.com/Aaron1011/d3b56325881cd639506a

This interactive comic begins with a panel where Cueball is stacking turtles. This is a reference to the idiom " turtles all the way down ", which refers to the problem of infinite recursion: if everything in the universe is "on top of" something else, so to speak, there must be a "bottom." A joking solution to the paradoxical nature of such a bottom is the proposition that the world rests on a semi-infinite stack of turtles.
The origins of the turtle story are uncertain. It has been recorded since the mid 19th century, and may possibly date to the 18th. One recent version appears in Stephen Hawking 's 1988 book A Brief History of Time , which starts:
A well-known scientist (some say it was Bertrand Russell ) once gave a public lecture on astronomy. He described how the earth orbits around the sun and how the sun, in turn, orbits around the center of a vast collection of stars called our galaxy. At the end of the lecture, a little old lady at the back of the room got up and said: "What you have told us is rubbish. The world is really a flat plate supported on the back of a giant tortoise." The scientist gave a superior smile before replying, "What is the tortoise standing on?" "You're very clever, young man, very clever," said the old lady. "But it's turtles all the way down!"
—Hawking, 1988
Several ancient myths , dating back thousands of years, involve a turtle which supports the whole world, or a part of it, although it is usually just one turtle, not an infinite regression.  This is also repeated in Terry Pratchett 's Discworld novels, in which the world is supported by four elephants standing on the back of a single turtle called Great A'Tuin .
As can be read you should "scroll to zoom" . This can be done by placing the cursor inside the panel of the comic. When scrolling up (using the mouse wheel) the picture zooms in on the pixel beneath the cursor. Moving the cursor will also move the point to which the picture zooms. You can then zoom in until the pixels are visible. When you continue to zoom in on a pixel it then resolves into another comic picture, with black-on-white comic panels making up the white pixels and white-on-black panels making up the black pixels. Scrolling on until you can see the pixels of the comic picture you are now zooming into the process is repeated again and will be so for all subsequent sets of comic panels. Not all white and all black panels are the same; some sets involve more than two different panels, but all involve repetitive tiling.
Once you have zoomed in, you are able to click and drag the picture, thus enabling you to move from black to white picture pixel. This is reminiscent of the earlier interactive comic 1110: Click and Drag .

Apart from the first image there are two more with a single turtle in them. In one of these the turtle thinks "I am a turtle". This is a reference to 889: Turtles . It may say so to the Cueball that is seen standing all alone in another picture.

There is a panel featuring just Cueball, followed by is a picture of the What If? book, large enough that all of the text is visible on the front cover. But there is also another version where the author's name is crossed out and replaced with Stephen King , the word "Spooky" has been added above the title, and the word "xkcd" below has been struck and replaced with "being afraid" to form the phrase "creator of being afraid".  Stephen King is one of the most prolific and well-known horror authors of all time.

This comic was released on September 3, 2014, the day after Randall's book What If was launched. The book is shown and referred to in a number of frames; for example, it is literally launched as a part of an rocket up goer built by Cueball. There is also a picture with Cueball holding his book, while being excited about the launch.
The model up goer is made of Rocket Parts from KSP . KSP is the Kerbal Space Program , a spaceflight simulator which was also part of the latest interactive comic 1350: Lorenz . Perhaps xkcd's "parts" refers to KSP's large community of mod developers who contribute 'parts' to the game, although it was likely intended as nothing more than the humorous supposition that one could purchase physical rocket parts from a simulator. The frames showing the book launch use URLs that include the text "upgoer" in reference to the Up Goer Five comic.
In the end the up goer leaves the Earth after one orbit and then flies through space.

Struts are structural members in engineering, and are one of the components used in Kerbal Space Program to construct rockets. "Needs More Struts" is a meme amongst players of Kerbal Space Program along the lines of "when in doubt, overengineer"; it stems from a time when the ragdoll physics in the Unity engine underlying KSP was unstable enough to necessitate their overuse. Megan deems Cueball's rocket to be insufficiently structurally sound, and declares that it " Needs More Struts ".
The first three images depict Cueball building a Kerbal Space Program rocket out of parts from a box, labelled "KSP Rocket Parts". The top part of the rocket, usually where the crew module would be located, is made from the What If..? book. In the fourth panel Megan declares that it needs more struts, and in the next three panels, Cueball takes her advice and adds more struts.
Panel 8 shows the Earth from a distance, with somebody (presumably Megan) saying again "More Struts". Panel 9 shows the Earth alone, and panel 10 shows the Earth with the rocket nearby, having just launched.

This series of panels parallels the "Needs More Struts" series. The first four panels shows the rocket lifting off, and the subsequent gasses dissipating.
Cueball and Megan look up at the ascending rocket, and then turn to each other having just launched the What-If book rocket into space (construction and launch are seen in other panels). Perhaps Megan realizes they may have misunderstood the term "book launch", and that they may have just lost the only copy of the book.
Panel 7 shows the Earth from space; panel 8 also shows the Earth, with the words "Book Launch".  The next three panels show the rocket circling around the Earth once before heading into deep space, and the last shows the rocket by itself on its journey.

Here are five objects in space.  It is possible that the What-If book rocket passes them by, or that these images are seen from the point of view of the rocket.
First is the Sun, shown with visible solar prominences . Next is the Moon, shown in a crescent view with stars behind it. This is followed by Saturn, also in a crescent view with stars behind it.
There follow two images with just stars.
This is a reference to 428: Starwatching :
In four pictures Cueball and Megan are sitting below the stars. In the second the following conversation takes place:
Cueball: Someone once told me the great kings of the past look down on us... Megan: From the stars? Cueball: Just in general.
The second panel is a reference to Disney's The Lion King . Early in the film, Mufasa tells Simba that the great kings of the past look down on them from the stars. Later on, Simba recalls this to his companions, Timon and Pumba (who don't take him seriously). In the film, the kings of the past literally look down on — and watch over — the characters, which is how Megan interprets Cueball's initial statement. Cueball's reply that they just look down on us in general shows that he means the kings of the past figuratively look down on us (they view us as inferior or beneath them).
In the next image a shooting star is seen above them. The final picture is almost identical to the first (only four stars and a few pixels of ground are different).

A series of 8 images are called Mario . The first is called entry , and has a picture of a TV on a low stand. The next four has Megan in front of said TV, holding a video game controller. The cable is connected to something inside the stand. She first kneels, then sits. In the third picture she is lying down. What follows is a picture which is an inverse of the sitting picture.
The last three images seem to depict a level from one of the Super Mario Bros. games. In the upper right one can see the iconic bricks which Mario can smash, two clouds appear stationary in the background, and a crude depiction of Mario is standing in the lower left. Over the course of the three images, a galaxy rises into the sky. It does not look like the Milky Way would from anywhere on Earth.
The view is reminiscent of a quote from Carl Sagan: "...from a planet orbiting a star in a distant globular cluster, a still more glorious dawn awaits. Not a sunrise, but a galaxy rise. A morning filled with 400 billion suns. The rising of the milky way." The quote was also referenced in 681: Gravity Wells
Randall often allows images of transcendent awe to take over mundane scenes. In this case, the galaxy-rise is a surprising twist revealing the true setting of the Super Mario Brothers games. At the same time it conveys how long Megan has been playing the game - day has turned into night in her room, and also within the game itself. Instead of playing it, she is simply watching the galaxy-rise, as the character on the screen has not moved. The view may contain a hidden pun, by calling to mind Super Mario Galaxy .

Cueball tells an offscreen character that he is going to shut down the server , while carrying a bucket of water.
Usually shutting down a server is done via the operating system or software. Directly turning it off or pulling the power plug also would technically work though not recommended for obvious reasons. But in this case it appears that Cueball is going to attempt to shut off the server by dousing it with water. This will likely result in serious water damage to the hardware, thus forcing it off as it no longer is able to function.

In five pictures Megan is floating in the clouds. The first shows Megan flying to the right, the second and third show just clouds, the fourth shows Megan flying to the left, and the fifth shows birds flying.

In two images Cueball and Megan are seen walking. The first is a normal black-on-white close up, and the second an inverted image seen from afar. They are talking while walking; after the first walking image they discuss Stockholm syndrome and then Time Turners , and after the second walking image Black Hat discusses a fire hydrant with a firefighter.
Stockholm syndrome is the name for a psychological phenomenon, in which hostages develop sympathy, empathy and/or positive feelings towards their captors. These feelings are usually seen as irrational, seeing as the hostage is held against their wishes, usually with the threat of physical harm or death.
This panel asks "How do we know anyone really wants to live in Stockholm?", questioning whether everyone who lives in the city of Stockholm is in fact held hostage there and only stays because they have developed to like life there (due to Stockholm Syndrome).
The time turner is a device from the Harry Potter series of novels by JK Rowling . It allows the user to re-live a period of time over again. In the third novel Hermione is given the time-turner to allow her to take extra classes, however it is eventually used to spare Buckbeak the hippogriff from execution. This prompted many questions regarding why time-turners weren't used on other occasions to save people's lives (among other things).
While J.K Rowling has " solved the problem to her own satisfaction " she admits that she entered into the subject of time-travel too lightly.
This panel jokes that if the real life JK Rowling had a fictional time-turner which worked, she would have gone back and removed the time-turner plotline from the book, saving her all the hassle of dealing with the resulting time-travel questions. This act would result in a time-travel paradox.
Black Hat is talking to a fireman, with a fire engine on fire in the background, he asks "To be fair, what else would you expect to come out of a " fire hydrant "?"
Black Hat appears to have managed to replace the usual water supply to the fire hydrant with actual fire. Thus when the hydrant is used, the result is, quite literally, fire (or oil with possibly flint and steel contraptions to cause fire). In Black Hat's logic, a hydrant which delivers water should be called a water hydrant.
This completely ignores the meaning of the word "hydrant", a pipe which supplies water (derived from the English root hydro- meaning relating to water , which is in turn from the Greek hudōr meaning water ).
An alternative explanation is that Black Hat has replaced the water that would normally come out of the fire hydrant with a strong alcoholic beverage, colloquially called firewater ,  with a high enough ethanol content to burn. If this were the case, the ability to douse a fire would be severely decreased, both due to the flammable component and because ethanol can absorb less heat per volume than water.

Megan hears a very long stretched EEEEEEEEEEEEE sound which goes over 6 images. It turns out it is a large letter E that shouts EEEEEEE!!! . In total there are 64 small E emanating from the big one. There is also a picture with two big white E on black background. Those E are larger than the E that shouts.

The March of Progress image is a famous and instantly recognisable image showing the stages of human evolution by way of a series of primate figures as if marching in a line. The panel parodies the March of Progress image, with 5 ducklings following an adult duck . In this case, rather than portraying selected individuals millions of years apart, the March shows evolution in action on a human timescale, the mother taking care of her ducklings. The comic has some resemblance to 537: Ducklings .

Four ropes cross diagonally across this black picture. They might be strings.

There are two chess boards on black and white background with smaller chessboards drawn upon them in a Fractal pattern.
One panel contains a number of lines and dots, which are in fact a depiction of the first 5 steps of a Cantor Ternary Set , mirrored about the horizontal centreline (see reference image ). The Cantor ternary set is constructed by repeatedly deleting the open middle thirds of a set of line segments.  In the comic, the two upper-left most segments and the two lower-right most segments are misaligned slightly.
The Cantor Set is one of the canonical examples of a fractal, a shape whose individual parts resemble the whole. The use of the Cantor Set in this comic is self-referential, in that the comic, itself, is composed of parts of the same shape as the whole.

There is a picture of tiny particles, quite spaced out. These probably represent atoms, and given how distant they are, they may well be a gas.
There follows a picture of a Bohr Model atom with point electrons surrounding a nucleus of protons and neutrons. The atom is a Carbon atom which is essential for all living matter and therefore for evolution. There is also a picture of what is probably a vibrating cosmic string fragment (a concept in string theory ). Despite Heisenberg's Uncertainty Principle , zooming down to the string does not mean that the cartoon viewer has reached the "bottom" of the comic - zooming in on the loop will show a picture of string.

These three words refer to "A MU offering", an essay by Douglas Hofstatder in his book Godel, Escher, Bach (which was referenced by Randall in 24: Godel, Escher, Kurt Halsey ). It includes a similar multiple level drawing: the word MU is composed of copies of the words HOLISM and REDUCTIONISM , each of which are in turn made of smaller copies of the other, which are in turn made of tiny copies of the word MU .
Mu is an important word in Buddhism . Literally, it means "no" or "not", but in Buddhism it also refers to a state of being or thinking - or rather, of not being and not thinking. It could be said that the pairs of panels in this series are each other's Mu, being negative (white-on-black and black-on-white).
Holism is a philosophical principle that systems should be considered as a complete whole, not as a set of individual parts. For example, a human viewed holistically is a whole interconnected being which can only be fully understood in its own context.
Reductionism is essentially Holism's opposite, a philosophical principle that any complex object can be reduced to a collection of simpler objects. A human can be considered as a set of organs (e.g. the heart), which in turn is composed of tissue (in this case muscle), composed of many cells.  Cells can then be reduced to organelles, such as the nucleus; this contains chromosomes, made of DNA, a molecule made of atoms; atoms are made of components including protons; and protons are composed of quarks (which may be considered as one-dimensional strings). Reductionism holds that a full understanding of the simplest components of a system, and how they interact, can lead to a full understanding of the system as a whole. The word was later reduced in 1734: Reductionism .
Holism and reductionism are complementary, rather than competing, philosophies, as both have their strengths and weaknesses. Holism can be very effective in understanding the larger-scale effects of a system by observing macroscopic events and how they are linked, but it ignores the more in-depth understanding gained by considering the smaller-scale components.  Reductionism can in theory give us a complete understanding of the entire system by building it up from the smallest and simplest parts, but for a complex system, this is effectively impossible (a typical human contains roughly 10 29 quarks, whose interactions cannot possibly be computed and understood in human terms or timescales).
"Pixels" is an example of a system best understood with a combination of holism and reductionism.  Each panel can be fully explained in its own terms, but is more completely understood as part of a small series of panels. The interconnectedness of all the panels shows a more holistic understanding, yet even this cannot explain comic fully, which must be experienced, with its interactivity and sense of exploration.
These panels can be found inside panels with Megan.

" du " is a POSIX (think Linux / Mac OS X ) command to indicate the "disk usage" of a file or directory.
This is a command that shows how large all the files are in this user's "video" directory - presumably where they store their personal videos. The units of the result is probably kilobytes (depending on settings, could also be the number of 512-byte blocks).
This number is clearly large and difficult to parse, and the units are not clear (to a bystander). More appropriate units would be gigabytes rather than bytes. The du command offers an option to display units in "human readable format", which will adapt to use kilobytes, megabytes, gigabytes, terabytes, etc. as appropriate. The next command purports to request the same result in more human-readable form.
It seems that the computer, rather than giving a specific answer, simply says that the size of the video directory is "A lot."
The final line indicates the computer is now ready to accept a new command.
[Cueball is stacking turtles, and is about to put the fourth turtle on his pile. At the bottom right there is a small panel. Inside this is written:] Scroll to zoom
[When zooming in there will be several panels with text. The transcript of these may not be possible to complete - but add the transcript of these panels here: interactive transcript ]
The following code can be found by inspecting the comic's source code: [[A large picture of a person kneeling on the ground, stacking turtles.]] ((In this strip, when you zoom into the panel, each pixel becomes its own panel. Each of those panels can be scrolled into, for the same effect. The story progresses as you scroll deeper.)) [[The Earth as seen from space with the words BOOK LAUNCH.]] [[A stick-Randall holding a copy of 'What If?' saying, "So excited about my book launch!"]] [[A copy of the cover of 'What If?' labeled "book."]] [[Stick-Randall is assembling parts from a box labeled 'rocket parts' and preparing to 'launch' his book.]] [[Various stages of assembly.]] [[A second person comes in, looks at SR's rocket set-up and says, "Needs more struts."]] [[SR adds more struts.]] [[The rocket launches.]] [[A big cloud of smoke, which then dissipates.]] [[SR and the other person look skywards at the launched book.]] [[The book is shown leaving Earth's orbit.]] [[The other person turns to SR and says, "I think that was the only one."]] [[The two walk away.]] ((The panels after this are a random assortment of these mostly stand-alone panels.)) [[A momma duck with several ducklings in a row behind her, labeled 'Evolution.']] [[The other person floating around in the sky.]] [[A stick figure with a sploshing bucket of water saying, "I'm gonna shut down the server!"]] [[Two people walking along, one saying, "But if the Time-Turners worked after Book 3, Rowling would have used one to go back and remove the Time Turner from Book 3."]] [[The code: ~$ du -s video
4170882256 ~$ du -hs video
A lot. ~$]] [[A cloud.]] [[A flock of birds.]] [[MU]] [[A pixel.]] [[A person using a computer on the floor.]] [[HOLISM]] [[Saturn]] [[An atom.]] [[Two people star-gazing on a hill.]] [[Person one says, "Someone once told me the great kings of the past look down on us..." Person two says, "From the stars?" The first person replies, "Just in general."]] [[The start of Mario World 1-1.]]

{{Title text: It's turtles all the way down.}}
This gallery contains the 79 images used in this comic . The images are related in a directed graph .
This google sheet describes all possible images, their associated codes, and what possible images can be used as sub-images for each zoom level: https://docs.google.com/spreadsheets/d/1nldKAkeVcK606CY12KI9bah9rDmK9E7CZOyinsEj2Lo/edit?usp=sharing
This gist recursively downloads all possible images: https://gist.github.com/Aaron1011/d3b56325881cd639506a
