Lorenz

Explanation:
This was the fifth April fools' comic released by Randall . The previous April fools' comic was 1193: Externalities from Monday April 1st 2013. The next was 1506: xkcloud released on Wednesday April 1st 2015. This comic was posted a day earlier than normal (on Tuesday instead of Wednesday) to honor April Fools' Day of 2014.
This is an interactive and dynamic comic similar to the Choose Your Own Adventure series , where players flip to different pages based on the option they chose. The first picture shown on top of this page is the start of this comic, with a possible combination of text options to choose from (see above). The picture is always the same but the order of the four sentences (and the sentences themselves) is chosen randomly (and there can be more than four). The result of all the interactions by the readers led to the generation of crowd-sourced content .
The title 'Lorenz' is referring to Edward Norton Lorenz who, among other subjects, was famous for Chaos theory and the Butterfly effect (mentioned later in the title text of 1519: Venus ). This comic is an example of a Choose Your Own Adventure story, as mentioned in the title text.
The title text is also a reference to how the storyline of this comic will be chaotic by nature, since it includes all of the user submitted dialogue and updates over time based on statistics of user clicks. In this manner, it is a reference to the butterfly effect: a phrase coined by Edward Lorenz to describe how a small initial change can lead to wide variations in outcome in a chaotic system.
Every time a story comes to a point where the user can either choose something or contribute when asked to Suggest a line , a link will appear by hovering the mouse over the bottom right corner of the last image. This is named a permalink , as it is a link that will recreate this particular story up to the point, making it permanent. It will not save the options listed below that image (i.e. the order of these will change, new options may appear, either because more than four are already present or new options will be added and some options may even disappear). An option is thus only saved by choosing it and then saving the next permalink — see more below .
The best way to enjoy this comic is to try it yourself! If you didn't do that already, reading any below will spoil you from truly enjoying the comic, and maybe make some interesting discoveries yourself! So here is a spoiler alert if you read on. If you do, then see also the section below about Functionality and bugs .
Any particular storyline will typically only have one or two of the many themes possible in the comic, but some very long stories may have several: see the Record section below. Several of the themes refer to previous comics or generally recurring themes in xkcd. (Most obviously is the blowtorch theme which is a reference to the previous comic 1349: Shouldn't Be Hard , where the last comment is I'll find a blowtorch as a response to Cueball's frustration over his problems.)
Because it is not always ending as "well" as with a burnt PC, they might instead end up in a shark infested ocean — see the Ocean theme , which is a reference to 349: Success : a comic that came exactly 1000 comics before the other one referenced in the same computer problem theme. In that comic, the sharks had not appeared yet; but here there may be several (and sharks are also a recurring topic in xkcd).
These issues with computers is generally a reference to the computer problem themes that precedes both the burning of the laptop and the ocean storylines, as Knit Cap tries to install BSD ; and when it fails, she takes her friend Hairy with her in the fall, the water, space or into a Pokémon fight (as they are the two main character of this comic). Also Cueball (as a politician vs. another politician with hair) and White Hat have small appearances, but only in a small sections of particular storyline. Only few others interact directly with the main characters in the rest of the possible stories.
Other themes that are recurring in xkcd are Politics , Pokémon , Boomerangs and Dinosaurs . Dinosaurs enter the comic in the form of the green talking T-rex from Dinosaur Comics : a clip-art-based webcomic that uses the same artwork with different captions for every strip. This particular Dinosaur Comics has a title text that actually refer to Randall and xkcd, and the comic has previously appeared on xkcd in 145: Parody Week: Dinosaur Comics .
A way to combine more than one storyline is to let characters wake up from a dream or a nightmare, as can be see in the Dreams theme (and dreams are also a recurring topic ). Here, it can even get recursive, so there can be dreams within dreams. One of the way to wake from a dream is, of course, by encountering a dinosaur that tries to step on your house (with you inside). Another is in reference to the possible rocket trip that may take the characters into space: see the Space theme (another recurring topic ).
There are a few other topics that are covered by Randall himself, but many others will be referenced in the text in the comic. However, since most of the options the users have is in itself created by user input (including naming the characters different names), any reference made by the text is not considered part of Randall's work and thus only sporadically be mentioned below under the themes section and not be included as a category. Here is an example with a permalink where the last comment, in the ocean with a shark, references Malaysia Airlines Flight 370 that disappeared less than a month before this comic was released [and has yet to be found years later]. But this is a user input, not Randall's.
Some of the idea of this comic was used again in the next year's April Fools' comic 1506: xkcloud , where user input also generated a very complex comic and the concept of permalink was used again.
This comic was the first time that Knit Cap has a main part to play. Since this comic, she has been given a category as a supporting character in xkcd, but in most other comics knit cap is seen as a man. The name knit cap for his hat has also been debated .
[This transcript only transcribes what can be seen in the picture shown at the top of the explanation here.]
[The comic starts with two panels. In the top panel we see Knit Cap sitting at a desk in front of her laptop typing. There is a speech line up to a gray but empty speech bubble.] [The second panel below has the same gray background as the empty speech bubble above. Here is presented four options to what Knit Cap could be saying. They are marked a, b, c and d written in small white rectangles next to the text. There is a small arrow at the top pointing to the first panel:]
a Hurry! We're in talks with Facebook. b These stupid tiles... I'll just play one more game. c Refresh... No new email... Refresh... No new tweets... Refresh... d Oh. Hey. There's some kind of political thing going on.
[Once the reader chooses one of the options, the text will appear in the speech bubble where the gray area is replaced with the usual white background. The lower gray panel disappears. Now the comic really begins.] [A new panel is shown after the selection, again with one to four options to choose from in the new gray panel below. This will continue until it comes to an end where the reader finally only has the choice to suggest the next line.]
[The order of the up to four options are random, and changes every time you begin again (or even go back to a previous frame). This means that the a–d in the transcript is not the same next time. In some few panels there are even more than four options. To see the fifth you have to reload, then you may find this fifth option next time. The first panel is one of those with five options.] [The fifth not shown above is: Let's see if BSD is any easier to install nowadays. (see image with this option in the trivia section ).]
[In the first days of the comic, when it developed quickly, new options appeared only to later disappear. Gravity. Lots of it. is one of those lost options from the first panel. At one time there was also, by mistake, two versions of one of the other five mentioned above. This was later deleted. Below in the trivia section there are permalinks to all the different starting options, including the now lost gravity story.]
[Although it may be impossible to finish (?), there has been an attempt to make a complete interactive transcript .]
The reader is initially presented with only one panel, where Knit Cap is sitting in front of her computer. The reader is given multiple choices concerning what exactly Knit Cap is thinking. Upon choosing any option, the chosen text will appear where his gray speech bubble was (which will disappear), and then a second panel appears to the right to give continuity to the story. Each new panel may have a new set of options, or just the button "Continue", to see the next panel without making any choice in particular. Eventually, one reaches a dead end in which the story is interrupted, and the reader is presented with a text box to suggest how it should continue. Some of the suggestions given should eventually become available as new options.
Normally, there are a total of 4 options to make: a/b/c/d. Their order changes constantly. Sometimes, there are 3 or fewer options, with the text box to suggest an alternative option. Sometimes, a given panel actually has 5 or more available options, although even in this case only 4 options appear at a time. Refreshing the comic changes randomly which of the available options are visible and which are hidden. As of late April 2014, the existence of 5 options seems to occur only in a few rare cases, including the first panel itself. There seem to be no longer any panels that have six options.
Instead of clicking with the mouse, you can move more quickly through the panels using the keyboard:
It appeared that new panels were generated by Randall in near real time, as user suggestions to dialog were submitted around the release of the comic.
This text can (now) be found under the official transcript at xkcd:
The dialog options could be based on click-through rates, and hence will change over time based on which choices are clicked most using A/B measurement techniques . This will mean that the most popular choices for dialog lines will prevail as the statistics build up. In some cases, dialog line options do not depend on the continuity of the storyline followed, suggesting that some parts of the story are planned. For example, several of the story lines involve one of the two main characters waking up and, for instance, telling the other character, "I had the strangest dream..." or even reliving the dream. This may be due to common submissions across story lines. Of course, there is the other option that Randall has used the first week of April to look though some input and choose himself. These possibilities are not mutually exclusive. Some of the options that were there very early were in quite poor English. Later, the same idea was still there, but in a more refined sentence. However, after the first week or two, no new panels seemed to appear, which suggests that some were drawn to match the story's progression.
A " permalink " is a portmanteau of "permanent-link". Each panel has a "permalink" button which generates a unique URL for all the choices made by the reader — so a reader can save the chosen choices to compare them to other ways going through the selections. The permalinks do only save the chosen options, not the order or the visible options in the image where the permalink is recorded, so it is not possible to save a copy where the options are only in the same order as they are in the 1/120 version shown at the top. Also, if you go back in the story from a permalink, you can risk that when passing back through a panel with five options, the option you just got back from is no longer available; as it is the option randomly not shown this time.
Sometimes it is possible to add your own suggestions in a panel where there are still other choices, but, if not before, the story will always reach a "final" panel (dead-end) where the reader only has the option left to "suggest a line..." By doing so, and pressing enter, this text is then shown in the speech bubble — but these suggestions can't be saved, as there are no permalink buttons after this. The reader has to do a screenshot in order to save their own remark. After a few weeks had progressed, there were probably so few new suggestions that Randall stopped changing the comic. A few images have been found months (or even more than a year) after the release, but there has been little to no reason to believe that Randall continued to make new panels after the first few weeks of April. Maybe he returned occasionally to do one once in a while; but, for certain, the options and text continue to evolve.
Since this interactive comic relies on many servers in the background to provide the response to the reader's actions, there are some problems reported here:
As a consequence of these bugs, many readers had trouble understanding how this interactive comic worked.
There used to be a sixth option: "Gravity. Lots of it." However, it no longer appears.


Metamaterials

Explanation:
Metamaterials , artificially-created structures typically made from several materials in a microscopic checkerboard pattern, are famous for allowing bizarre optical properties, such as invisibility cloaks . This comic imagines that metamaterials can change the color of light passing through them.
In the real world a metamaterial can alter the spatial distribution of light and also its frequency, like done in fluorescent lamps — but this would not resemble the entire picture in a different color. In photography many filters are used to enhance the quality and appearance of the image. These filters do not alter colors but block some of them, so the result is shown in a different color than the original. Nevertheless, no application like this is able to switch a single color to another as it can be done by most modern computer photo programs.
Megan uses a box made of her metamaterial to switch the colors of the cliché Valentine's Day poem, " Roses are red, violets are blue, sugar is sweet and so are you. "
The title text references this with Randall pondering making a metamaterial that reverses the effect of instagram filters, likely by placing the material between the camera and the subject just before the picture is taken without the photographer noticing - a so-called photobombing . Instagram is a photo application that applies one of a variety of filters like hue-shift or contrast adjustments meant to simulate the look of old photographs. These filters may be able to interchange blue and red - as they are not real material filters.
[An image of a violet that is colored red.] Megan (off-screen): Violets are red [An image of a rose that is colored blue.] Megan (off-screen): And roses are blue [Megan and Cueball are standing around a table, on which a screen is in front of the rose and violet. Megan is in front of a lectern with a mic. All of this is on a stage.] Megan: When metamaterials [Same scene, but Megan moves the screen away from in front of the rose and violet. It is revealed that the flowers' actual colors are those from the original poem, i.e. the violet is blue and the rose is red.] Megan: Alter their hue.


Cosmologist on a Tire Swing

Explanation:
Cueball and the curious Science Girl walk through a landscape with trees in the background and with many small pools of water. The setting of trees interspersed with these many small pools resembles the Wood between the Worlds , a meta-verse described in C.S. Lewis's The Magician's Nephew ; each pool leads into a different universe — one of these is ours, another is Narnia , and Charn (the world of Jadis the White Witch ) is also visited through these pools.
Science Girl asks about the time before the Big Bang . Cueball says he thinks there was no time before — which is implied by most forms of the Big Bang theory. But then they happen upon a cosmologist , Megan , on a swing who has several other theories about the universe.
Simply put, the tire swing is a symbolic representation of our universe. Scientific observations tell us that both space and time began with the Big Bang ~13.8 billion years ago. We don't know if there was such a thing as "before" the universe, or what that might be.
The first 6 panels reference ongoing speculation about where the universe came from and why it even exists in the first place. The last two panels relate to recent observations of the accelerating universe in which galaxies are now receding from each other at higher and higher speeds, due to dark energy .
The swing itself is likely a reference to the Cyclic Model , where the universe expands from a Big Bang, then contracts back in on itself under its own gravity for a Big Crunch , before bouncing outward again in another Big Bang, and repeating the whole process. On the other hand, the swing is accelerating as the universe — so it may also be a reference to the entire universe. We are all "trapped" on this swing — and it's accelerating! For the layman (and most scientists as well) cosmology is pretty confusing as Science Girl states at the end, to which the cosmologist just replies Wheeeee! and enjoys her ride with this accelerating swing/universe.
Another interpretation of the acceleration may referring to the physics of orbital motion in which a centrifugal force is always causing constant acceleration toward the center of the motion.
The title text references questions about the shape of the universe and what could lie "outside" of it. By the current understanding on physics laws, we can't see outside of the observable universe , but it's likely that the universe is bigger than this observable universe and uniform on large scale. Even though nobody can leave our own universe, Megan bets that such unknown worlds do exist - because this universe is here, and it must have come from somewhere — like her tire.
The shape of our universe was visited soon after in 1365: Inflation where we can see what the outer boundaries of our universe looks like.
Science Girl is seen later in conjunction with a tire swing in 1659: Tire Swing ; maybe she is preparing to become a cosmologist herself. Also this may explain from where the tire came from...
[A tall panel with Cueball and Science Girl walking together through a landscape with three trees in the background and with many small pools of water. Their reflection is showing in the pool nearest to them.] Science Girl: What was before the big bang? Cueball: I think time began with the big bang. Cueball: So it doesn't make sense to ask what came before it. Cosmologist (off panel): Look out
[The next six panels are between the first tall panel and a similar panel at the end. They should be read from above and down in two columns of three images. The bottom of the first panel at the top is partly hidden by the second panel which is likewise partly hidden by the lower panel, and this repeats in the second column.] [A cosmologist looking like Megan comes swinging left past Science Girl and Cueball, who turns to look after her. She sit on an upstanding tire swing and the movement is indicated by two lines going from right to left.} Cosmologist: Wheeee Hi I'm a cosmologist on a tire swing!
[The cosmologist swings back right, hanging in her arms with her body almost vertical. The other two also turns right.] Cosmologist: We don't know whether time
[Going left, similar to the first of the small panels.] Cosmologist: started at the big bang.
[Going right, similar to the second of the small panels, but with the cosmologist sitting more upright.] Cosmologist: It might have!
[Going left, similar to the first of the small panels.] Cosmologist: Or maybe not! We don't know! Cueball: Oh. OK!
[Going right, similar to previous going right panels.] Science Girl: ...Your tire swing looks fun! Cosmologist: I can't stop!
[The last panel is again a full panel, with Cueball and Science Girl looking towards the right after the cosmologist who continued the last swing to the right from the last small panel, having just reach the upper part of the curve and has thus turned left to face them, before the swing will go down left again. The background is completely white with no indications of the trees and pools from the first panel.] Science Girl: Won't the swing stop on its own? Cosmologist: I thought it would, but it seems to be accelerating. Science Girl: Cosmology sounds pretty confusing. Cosmologist: Wheeeee!


Heartbleed

Explanation:
The Heartbleed bug refers to a critical bug in the OpenSSL cryptographic library. This bug was publicly revealed on Monday, 7 April 2014. Due to a programming error in OpenSSL versions 1.0.1 through 1.0.1f — meaning the bug had existed for two years — attackers could read random server memory by sending specially prepared HeartbeatRequest messages to an affected server.
OpenSSL is a very commonly used library to implement SSL/TLS , a cryptographic protocol not only used to secure web traffic but also for mail clients and much more. Only the user and the server can read the communication. On the web the protocol is https:// (HTTP Secure), instead of the open http:// standard. SSL is often used to protect sensitive web traffic, such as login requests, which contains the user names and passwords in the requests. The server sends a certificate to the browser before the secure connection is established. If the certificate is registered the browser accepts it automatically, otherwise the user gets a popup to accept or reject this insecure certificate.
A vulnerability that lets an attacker read random clumps of memory on the server would possibly let an attacker find recent username/password requests, allowing them to gain unauthorized access to user accounts. Even worse, this vulnerability could read the server's private key, enabling anyone to impersonate the server and/or decrypt any future traffic that relies on that key, and any previously-obtained prior traffic also, unless a "perfect forward secrecy" cipher is used. Furthermore, the Heartbleed exploit occurs during the handshake phase of setting up a connection, so no traces of it are logged, i.e. you can be attacked and never be the wiser.
More information is available at heartbleed.com or under the reference CVE-2014-0160 at nvd.nist.gov .
In the last panel, Megan interprets Cueball's question ("is everything compromised?") expansively. She responds that, being a computer bug, Heartbleed can only affect information which is stored on computers. Cueball concludes that information recorded in analog media, such as that written on paper or etched in clay tablets, is safe. Megan adds that imaginations are also unaffected by Heartbleed, and Cueball is reassured. The reader may wonder how our society would fare in the face of the leakage of all electronically stored private information, but having our imaginations intact is certainly reassuring.
The title text cites the Tears in rain soliloquy , the dying words of the replicant and main antagonist Roy Batty (played by Rutger Hauer ) in the 1982 film Blade Runner , implying that the 64KiB HeartBleed buffer is so complete it includes memories from replicant brains. This is ironic as in the soliloquy, Roy Batty stated "All those moments will be lost in time".
The title text also suggests to patch OpenSSL oneself, which might refer to the patched version of OpenSSL by Debian, which turned out to be vulnerable in 2008, and was the topic of 424: Security Holes .
In addition to the below, see xkcd's explanation in the next comic.
Transport Layer Security (TLS), the successor to SSL , is a protocol that provides end-to-end encryption for data transmitted over the internet, and is described in RFC 5246 . The Heartbeat extension to TLS introduced in 2012 (described in RFC 6520 ) provides a protocol for keeping an encrypted TLS session alive (preventing inactivity timeouts), so you do not have to do a costly TLS handshake with the server for subsequent transfer of information.
The Heartbeat protocol involves the client sending a packet with an arbitrary payload (often a random 16 to 32 byte number) that the server periodically sends back to the client to tell the client that the TLS session is still alive. When the client sends the packet to a vulnerable version of OpenSSL, the OpenSSL server reads a payload_size from the header sent by the client. This is a 2-byte number (0 to 0xffff=65535) that is supposed to describe the size of the payload. The OpenSSL library writes the payload to memory, but it does not check that the size of the payload written to memory matches the payload_size taken from the client's header. When the vulnerable server sends back the Heartbeat KeepAlive response to the client, it will readout payload_size number of bytes and send them back to the client. If you send a payload that is actually 16 bytes, but claims it is 0xffff bytes you will read the next 64KiB of memory of the vulnerable process starting from wherever the payload was written. An attacker can repeat this attack many times and can do this attack early in the TLS handshake, so the attack will not in any way be logged unless they are logging every incoming packet which is not typical and would result in many passwords being logged. As private keys often have an identifiable format, it is often possible for an attacker to find the private TLS key, so if they eavesdrop on network traffic they can decrypt and/or alter it.  For more detailed information see: 1 , 2 , 3 .
It is worth noting that modern operating systems use a virtual memory abstraction above physical memory. This means every process can only access memory assigned to it, so it would be impossible for a vulnerable web server to read memory assigned to another process (like a text editor that has erotic fan fiction stored to memory) on the same computer. For more info, see: 4 .
It also should be noted that this heartbleed bug only affects certain versions of OpenSSL, and does not affect other TLS/SSL implementations, or OpenSSH which does not even use the TLS protocol, but uses the SSH-2 protocol (described in RFC 4251 ). SSH is typically used for remote logins on unix and linux computers.
Vulnerable sysadmins need to update to a patched version of OpenSSL or one with the Heartbeats disabled. Unless their TLS keys were protected by hardware, they probably also need to revoke their old TLS keys, and generate new TLS keys. To learn how to do this visit Leo Green . There you will find all the information you need.
Users of vulnerable systems should change their passwords after the sysadmins have revoked their old key and issued new ones (as their passwords may have been compromised). Users can check whether a given website is vulnerable via a Heartbleed test also available as open source . The Lastpass heartbleed diagnostic also indicates whether the signature on the TLS key predates the publication of the heartbleed vulnerability.
The vulnerable commit was introduced Dec 31st, 2011 by Robin Seggelmann, the first co-author of the heartbeats RFC, and went live when OpenSSL version 1.0.1 was released on 2012-03-14 and the vulnerability was widely announced 2014-04-07.
Megan: Heartbleed must be the worst web security lapse ever. Cueball: Worst so far. Give us time.
Megan: I mean, this bug isn't just broken encryption. Megan: It lets website visitors make a server dispense random memory contents.
Megan: It's not just keys. It's traffic data. Emails. Passwords. Erotic fanfiction. Cueball: Is everything compromised?
Megan: Well, the attack is limited to data stored in computer memory. Cueball: So paper is safe. And clay tablets. Megan: Our imaginations, too. Cueball: See, we'll be fine.


Heartbleed Explanation

Explanation:
The Heartbleed bug has received a lot of news coverage recently and was also the topic of the previous comic 1353: Heartbleed . This comic explains how the bug may have been discovered and can be exploited to reveal a server's memory contents.
A Megan -like character named Margaret (or "Meg") sends heartbeat requests to the server, the server responds to the heartbeat request by returning the contents of the body of the request up to the number of letters requested. The first two requests are well formed, requesting exactly the number of characters in the request body. The server's memory is showing Meg's request with many other requests going on at the same time.
Meg then ponders this and tries to another request asking for "HAT" but requests that it be 500 letters long instead of only 3; the server —not checking it or simply unaware that 500 letters is larger than the request body— returns "HAT" plus 497 letters that happened to be next to the word "HAT" in its memory (more will follow than are shown in the server's speak bubble as there are only 251 letters/symbols in the shown reply). Included are many sensitive bits of information, including a master key and user passwords. One of the passwords shown is "CoHoBaSt", a reference to 936: Password Strength , which suggests using " co rrect ho rse ba ttery st aple" as a password.
Often popular explanations of security bugs require the issue to be simplified a lot and to leave out a lot of details. In this case Randall didn't have to do much simplifying; the bug is actually that simple. Also, it should be noted that any client which can connect to the server typically can exploit this bug in the underlying OpenSSL software — the use of the term "User Meg" does not imply that Meg had to authenticate first.
Although Randall shows Meg recording the data by hand, on paper, it is more likely that a person exploiting the bug would have a computer record the data, perhaps on its hard drive or on a flash drive.
The title text is a reference to Are You There God? It's Me, Margaret. , a novel by Judy Blume , and plays off of the "server, are you still there?" line in every panel where she did start a request. The novel is the theme of another comic 1544: Margaret too. Meg can be a nickname for Margaret as well as Megan who Margaret resembles.
[Caption above the panels:] How the Heartbleed Bug works:
[Meg, a girl with more curly hair than Megan, stands to the left in a panel. At the center of the panel is a black and gray server with red and green diode lights showing. During all six panels the server stays the same. Meg is standing with her arms down in four panels. It will be noted when she does not. Meg talks to the server. The server "thinks" all the time, i.e. we see its memory in all panels. The top and bottom line is breaking the edge of the thought bubble making it difficult to discern. In every second panel it replies to Meg. In these panels the number of letters requested by Meg is highlighted with yellow color.]
[Meg speaks, server thinks:] Meg: Server, are you still there? If so, reply "POTATO" (6 letters). Server thinking: wants pages about "boats". User Erica requests secure connection using key "4538538374224" User Meg wants these 6 letters: POTATO. User Ada wants pages about "irl games". Unlocking secure records with master key 5130985733435. Maggie (chrome user) sends this message: "Hi
[Server thinks, the same as above, although cut a little different at the edges, with POTATO highlighted in yellow and it replies the highlighted part in a rectangular speak bubble.] Server thinking: wants pages about "boats". User Erica requests secure connection using key "4538538374224" User Meg wants these 6 letters: POTATO. User Ada wants pages about "irl games". Unlocking secure records with master key 5130985733435. Maggie (chrome user) sends this message: "Hi Server: POTATO
[Meg speaks, server thinks:] Meg: Server, are you still there? If so, reply "BIRD" (4 letters). Server thinking: User Olivia from London wants pages about "man bees in car why". Note: Files for IP 375.381.283.17 are in /tmp/files-3843. User Meg wants these 4 letters: BIRD. There are currently 348 connections open. User Brendan uploaded the file selfie.jpg (contents: 834ba962e2ceb9ff89bd3bff8c ...
[Server thinks, the same as above, although cut a little different at the edges, with BIRD highlighted in yellow and it replies the highlighted part in a rectangular speak bubble. Meg has taken her hand to her chin thinking:]
Server thinking: User Olivia from London wants pages about "man bees in car why". Note: Files for IP 375.381.283.17 are in /tmp/files-3843. User Meg wants these 4 letters: BIRD. There are currently 348 connections open. User Brendan uploaded the file selfie.jpg (contents: 834ba962e2ceb9ff89bd3bff8c ... Server: BIRD Meg: Hmm...
[Meg has taken her hand down again and speaks, server thinks, now with her line at the top:]
Meg: Server, are you still there? If so, reply "HAT" (500 letters). Server memory: a connection. Jake requested pictures of deer. User Meg wants these 500 letters: HAT. Lucas requests the "missed connections" page. Eve (administrator) wants to set server's master key to "14835038534". Isabel wants pages about "snakes but not too long". User Karen wants to change account password to "CoHoBaSt". User
[Server thinks, the same as above, although cut a little different at the edges, with everything from (and including) "HAT" highlighted in yellow and it replies the highlighted part and even more in a rectangular speak bubble. Meg has taken a note book and a pen and it writing something.:]
Server memory: a connection. Jake requested pictures of deer. User Meg wants these 500 letters: HAT. Lucas requests the "missed connections" page. Eve (administrator) wants to set server's master key to "14835038534". Isabel wants pages about "snakes but not too long". User Karen wants to change account password to "CoHoBaSt". User Server: HAT. Lucas requests the "missed connections" page. Eve (administrator) wants to set server's key to "14835038534". Isabel wants pages about "snakes but not too long". User Karen wants to change account password to "CoHoBaSt". User Amber requests pages


Airplane Message

Explanation:
Large banners are sometimes flown behind airplanes to advertise a product or event to a large number of people. Here, Randall suggests replacing the ad with some interesting facts. This would tell people who see the banner something new and interesting about the world, rather than try to sell them something. He presents two possible facts: Adriamycin , a cancer therapy, and Iry-Hor , the earliest human we know by name.
The chemotherapy drug doxorubicin , trade name Adriamycin, is based on a strain of the bacterium Streptomyces peucetius , first isolated from a soil sample taken at Castel del Monte in Andria , Italy.
As mentioned at the title text Iry-Hor was an ancient, predynastic pharaoh of ancient Egypt — no earlier documents exist today.
This fact is also placed at exactly 3100 BC (or BCE ) in 1732: Earth Temperature Timeline . The week after that comic came out improving cancer research was the subject of 1736: Manhattan Project . That became the first cancer related comic since this one, even though more than two years had passed and with cancer being a recurring subject on xkcd... It could be a coincidence, but seems strange that both facts were directly/indirectly referenced within two weeks more than two years later, and there is even a banner in the cancer comic...
[There is a plane with a banner behind.] Banner: Adriamycin, one of our most potent chemotherapy drugs, comes from the dirt from an Italian castle.
My hobby: Breaking into airplane hangars and replacing the ads on their giant banners with cool facts.


Orbital Mechanics

Explanation:
Randall roughly plots how high school physics, undergraduate-level physics and a job at NASA somewhat increased his knowledge of orbital mechanics . But this learning was apparently nothing compared to the "direct" experience of playing Kerbal Space Program , a rocket building and piloting sandbox game .
Orbital mechanics can be somewhat counterintuitive. The art of changing orbits involves relative velocities, positions, and times in complex interactions. As soon as you try deviating from a perfectly regular orbit, or start having to deal with N-body problems and orbital resonances , you have to coordinate your movements in possibly counterintuitive ways. One example is that if you want to reach an object ahead of you, on the same orbit, you actually have to 'brake' to reach a lower orbit. Once at that lower orbit, your angular velocity is faster, and you can start to overtake your target. After that manoeuver, you then have to accelerate to increase your orbital altitude again, which will end up reducing your angular speed so that you intercept your target.
At the title text Randall admits that at the time when he did work at NASA he was not involved in orbital mechanics—which is also true for most other NASA employees—but everybody was talking about this which in the end did increase his knowledge a little, as can be seen in the curve after the Job at NASA arrow.
How Well I Understand Orbital Mechanics: [There is a graph with the x-axis labeled as 'time' increasing to the right. The y-axis is unlabeled but it can be assumed that it could be labeled 'understanding'.] The line stays flat until the first bump, which is annotated "Took High School Physics". The line decreases, then grows to a higher maximum with the annotation "Got Physics Degree". There is a small amount of decrease until a gradual bump in the graph labeled "Actual Job At NASA". It gradually decreases to pre-NASA levels, but then begins to increase exponentially. The annotation reads "Started Playing Kerbal Space Program".


Free Speech

Explanation:
Both on the Internet and in the physical world, people with unpopular or poorly thought out opinions may complain that their freedom of speech is being restricted because others express their distaste for those opinions. As a defense, these individuals may invoke the First Amendment to the United States Constitution , which provides, among other things, freedom of speech for any entity or person under legal jurisdiction of the U.S. More specifically, it states that "Congress shall make no law [...] abridging the freedom of speech, or of the press". Originally intended as a restriction on the powers of U.S. federal government, which the Constitution defines, structures, and delimits, over time the First Amendment, as well as several others, were "incorporated" via the Fourteenth Amendment to apply to state and local governments as well. This protection of free speech, however, does not extend to illegal activities (for example, the concept of a "clear and present danger"), and it does not compel others to listen to or acknowledge the speech. The intended targets of the speech may simply choose to stop listening, or to speak louder in protest.
An example of this is the incident involving the TV program Duck Dynasty in December 2013, in which television network A+E Networks suspended the host after he made homophobic remarks , causing some to comment that his rights had been infringed upon. Similarly in April 2014 controversy erupted when Brendan Eich was forced to resign as CEO of Mozilla because it was revealed he had donated money to anti-gay marriage efforts in California. In actuality, the First Amendment was never meant to provide immunity from any and all consequences.
Cueball , representing Randall , is addressing those who use the freedom of speech argument as a defense against societal censorship. He states that one’s legal right to take a stance on an issue does not require others to listen to said stance. In addition, he also states that this right does not require a commercial or social entity—such as a TV network, a website, or its community—to support a person in spreading their message, even if it had supported you in the past. If someone says something which others find unjustified or offensive, they should be ready to accept the consequences of others' responses.
The title text points out that regardless of how free speech works, anyone appealing to it as a defense for their argument or opinion is not being persuasive in any case. If the only thing that someone can say in support of an argument is effectively that it is not illegal , then they are severely undermining it by essentially admitting that they don't have any better defense for it.
It should be noted that the first panel of this comic conflates, under certain schools of thought about justice and rights, a right such as free speech and the legal protections of such. Many viewpoints consider rights to be granted by the government; others consider rights to be innate regardless of what the government does. The former is frequently reflected throughout governments in Europe while the latter is more common throughout the Americas. According to the former, the first panel is technically correct by definition, because the right of free speech is granted by the government's laws and, as such, can only affect the government's influence: thus, the 1st Amendment grants the right to free speech, which by definition cannot be restricted by congress. According to the latter, the first panel is strictly nonfactual because the 1st Amendment only recognizes that the right of free speech exists and, rather than delimiting the right, it instead proscribes the government's actions. However, between these two school of thought, the remaining panels aren't affected by whether or not the first panel is factual by definition.
Cueball: Public Service Announcement: The Right to Free Speech means the government can't arrest you for what you say.
Cueball: It doesn't mean that anyone else has to listen to your bullshit, or host you while you share it.
Cueball: The 1st Amendment doesn't shield you from criticism or consequences.
Cueball: If you're yelled at, boycotted, have your show canceled, or get banned from an Internet community, your free speech rights aren't being violated.
Cueball: It's just that the people listening think you're an asshole,
[A picture of a partially open door is displayed.] Cueball: And they're showing you the door.


NRO

Explanation:
Where's Waldo? (the North American renaming of the British Where's Wally? ) is a children's puzzle book in which you have to locate 'Waldo', a character with a distinctive striped shirt and hat, in a picture crowded with hundreds of characters. This is harder than it sounds, since the characters are both very small and quite densely packed on the page, and the pages (especially in later books) are often littered with "decoy" characters wearing similar articles of clothing to Waldo's. In some cases, almost all characters as well as several objects have the red-and-white stripes.
Cueball and his friend are using satellite imaging to find Waldo, by holding the book up to the sky and viewing it on the computer, presumably using some advanced image processing software to identify Waldo among the crowd. This would require a very advanced camera, as resolutions are usually much lower than would be necessary to resolve the characters in a Where's Waldo book. But since Cueball works at the National Reconnaissance Office (NRO), the US government agency responsible for operating spy satellites, he probably has access to some powerful satellite-mounted cameras.
The humor in this being, while he could be using that power for much more important things, he's instead trying to solve a simple game. Further, the Cueballs could probably hook up the image parsing software to a smaller camera on the ground, rather than a satellite-mounted camera. They would get even better results without using a camera by scanning the image and running it through the same image processing software.
The title text is implying that the Cueball operating the computer has accidentally launched a drone at the co-ordinates, which would be where he and his friend are standing. The drone is presumably a military drone armed with explosive weaponry — not a good thing for those on the receiving end.
Cueball and a friend are in a remote area. The friend is holding a Where's Waldo? book towards the sky. Laptop: [ Target located ] Cueball: Got him. Left edge, two inches down. The National Reconnaissance Office has an unusual approach to Where's Waldo .


Phone Alarm

Explanation:
The flowchart shows a problem Randall has with using alarms built into phones. Notably, that the sound is similar to a normal ring tone (probably related to 479: Tones ), making it sound like someone is calling him, and not waking him up. This results in him having a false awakening , where he dreams about answering the phone, talking, and eventually hanging up. Of course this doesn't stop the actual phone from ringing, and he ends up answering the phone again. The looping arrow around the "beep beep" box implies that the phone keeps ringing only until he attempts to answer it, which would be quite a coincidence. This is an example of an endless loop , where there is no given way for the flowchart to end, just as in 1195: Flowchart . Now, smartphones typically support customization of tones for different apps so that your alarm doesn't have to sound like your ringtone and many apps load their own distinctive tone now by default.
The title text, consisting of Randall shouting at the phone in his dream, enforces the fact that he can't tell between his ringtone and his alarm. In doing so he believes that a prank caller is harassing him which infuriates him. Alternatively, "the worst person in the world" could just refer to the confused logic in dreams, where a caller could, inexplicably yet unquestionably, be the worst person in the world.
A list of all the flowchart comics can be found here .
[A flowchart:]
[Alarm goes off] → [Beep beep beep beep!] ↺ One line with an arrow goes back to: [Beep beep beep beep!] → Another line goes to: ["???"] → Then: [Answer phone in dream] → [Talk] → [Hang up] → Finally a line goes back to: [Beep beep beep beep!]
My problem with phone alarms


Old Files

Explanation:
This comic came out the day after Sky News published the story of original Andy Warhol artwork, created in 1985 on an Amiga 1000 , which was recovered from recently found floppy disks.
Cueball is shown literally digging through a pile of old files; which is a metaphor for looking through old files on his computer. The layers of the pile are arranged much like geological rock formations where older strata are deeper down than younger layers. The files are in concentric layers because each directory is embedded in the previous directory. Therefore, the "Documents" folder contains an "Old Desktop" folder, which contains a folder with files recovered from an older system, which itself contains a "My Documents" folder, which contains a folder with files copied from a Zip Disk from high school. The result is that files from high school have survived in his present-day machine. These older folders serve as a time capsule of sorts, storing old files from AOL , NYET, and Kazaa . These files are meant to be analogous to the fossils and artifacts found in lower, older rock layers.
The sizes of the files decrease as Cueball goes deeper, since data storage has gotten cheaper over time. When the Zip Drive first came out, it cost $200 USD (plus $20 per 100 MB floppy). As of 2019, $200 could buy you at least an 8 TB portable external hard drive. In the 1990s, during AOL's heyday, 10+ GB hard drives were prohibitively expensive and a terabyte of data was unimaginable to most users.
Deep down, Cueball discovers several files he is surprised about, including a poetry file which embarrasses him as he does not remember writing poetry.
In the title text, he mentions also finding an " Animorphs Novel", which may be a text copy of one of the original books or a fan fiction of the Animorphs series (his reaction of quickly eradicating it may either be to prevent him being caught with a presumably-illegal copy of an Animorphs book or as a result of embarrassment at his fan fiction - the former is less likely than the latter considering some of the other files mentioned, so it is most likely a fan fiction). The series was released between 1996 and 2001, consistent with the fact that these files were created during Cueball/ Randall's high school years. The series was extremely popular at the time. Animorphs has already been mentioned in the title text of 1187: Aspect Ratio , and later it was the main joke in 1380: Manual for Civilization and 1817: Incognito Mode .
The folders and files in detail:
Documents (47 GB): A large folder containing many of Cueball 's personal files.
Old desktop (12 GB): A backup from a former computer.
Recovered from drive crash (4 GB): When a hard drive crashes, some or all data may be recovered.
My Documents (570 MB): Windows XP user accounts came with a "My Documents" folder that was widely used for storing personal files. The items in this archive came from the era when Windows XP was popular.
High school Zip disk (94 MB): The most popular form of superfloppy , introduced in 1994 with a capacity of 100 MB.
AAAFILES (9.4 MB): Some of Cueball 's oldest documents, likely prefixed with "AAA" to put the folder at the top of an alphabetically-sorted list.
TXT (850 K): Old text files, which include poetry he didn't remember writing.
[Cross-sectional view of what look vaguely like stratigraphic layers underground. A crevice leads down through these concentric layers to a cave-like cavity in the middle, where Cueball is going through the deepest, most central, and incidentally smallest of the files. Above, Megan stands at "ground level", looking down into the crevice.]
Megan: You OK down there?
Documents (47 GB) misc.txt Video projects Old desktop (12 GB) Facebook pics Pics from other camera Temp Misc PDFs MP3 Recovered from drive crash (4 GB) Temp Work misc Audio books My Documents (570 MB) Downloads Kazaa shared AYB EV Override Angband GIFs FIGHT CLUB.wmv Elasto Mania AIM Direct Connect files 4chan ICQ logs High school Zip disk (94 MB) Korn MIDI Photos3 (Prom) lovenote.txt Gorilla.bas Dream.txt James.txt AOL (Citadel) QBasic NYET Jokes.txt AAAFILES (9.4 MB) TXT (850 K) Cueball (deep inside the AAAFILES section looking at his txt files): Oh my god. I wrote poetry .


Google Announcement

Explanation:
At the time of this comic's release, Vic Gundotra had recently left Google . Because he was the head of Google+ , this had caused many people, including TechCrunch , to theorize that Google+ was going to be shut down, despite the continuing comments from Google that it would remain active and updated. It lasted five more years, finally being closed on April 2nd, 2019.
Google has a history of closing popular services .
The comic extrapolates this to an announcement that Google would be closing all its popular services, up to and including its e-mail service, Gmail, and even the core business of the company, its Internet search engine, to wholly concentrate on a relatively obscure part of its product lineup. According to Google, its Public DNS servers (Domain Name System servers), better known by their IPv4 addresses 8.8.8.8 and 8.8.4.4 , are supposed to be a faster alternative to using one's ISP's DNS servers (because of caching effects due to a large user base), as well as less susceptible to censorship. When Turkey started blocking access to Twitter and YouTube in March 2014, Turkish ISPs first did this on the DNS level by manipulating the results from their own name servers. The most popular workaround was using Google's DNS server instead, so much so that its address was written as graffiti on the side of a building .
The joke may also be related to the fact that 8.8.8.8 is an IP address heavily used by network administrators to perform connectivity tests ( ping ) because it is easy to remember and fast to type. Google would want to concentrate on this feature to build a business model using that fact.
The reason behind this decision may be that Google considers a DNS server, a fairly low-level component of the Internet's service stack, to be the optimal place to collect information on its users, an accusation leveled at Google ever since it introduced the service.
The title text refers to the impression held by some that Google will shut down services that prove less popular than desired at short notice, even though they may in fact have a significant user base. A recent example of that is the closure of the RSS aggregation service, Google Reader, in July 2013. While the same DNS service is provided under both addresses, the more memorable 8.8.8.8 is likely to receive far more requests than 8.8.4.4.
[Cueball is standing at a lectern marked Google.] Cueball: The rumors are true. Google will be shutting down Plus— Cueball: Along with Hangouts, Photos, Voice, Docs, Drive, Maps, Gmail, Chrome, Android, and Search— Cueball: To focus on our core project: Cueball: The 8.8.8.8 DNS Server.


Morse Code

Explanation:
Cueball recounts the last message sent in morse code by the French maritime radio station Le Conquet radio upon retiring its 500 kHz channel.
The poetic, and potentially angsty-sounding nature of the message reminds him of the on-line journal website LiveJournal , which was popular until the late 2000s (it was launched in 1999), and stereotypically used by angst-ridden teenagers to post song lyrics, poems, or cryptic messages to express their emotions and possibly fish for attention. Since Cueball never uses his LiveJournal account any more, he wonders if he can find the password again. He might be considering posting the final Morse Code message as his own last and final message on his LiveJournal.
The popularity of the site died down considerably with the arrival of social networking sites like MySpace , Facebook , Google Plus and the advent of microblogging platforms like Twitter and Tumblr . LiveJournal has also lost a lot of users since a Russian company bought them out; Russian dissidents used LiveJournal to present their opinions, and the Russian government used to retaliate by creating "denial of service" attacks which make LiveJournal unusable for all its users, sometimes for days. Nowadays (May 2014) LiveJournal is still quite popular among Russian-speaking people, including dissenters, but its administration was forced to show HTTP 451 error in some cases (e. g., when a user with a Russian IP is trying to read Alexei Navalny blog) with new laws. Thus when Megan is upset with his desire to let LiveJournal die out like the Morse Code, Cueball describes it as "a nice place to go for some peace and quiet".
The title text is Megan's (or Randall's ) sarcastic remark indicating that Facebook is no less filled with angst-ridden thoughts than LiveJournal was, nor is it free from problems or controversies around other issues such as security or privacy.
[Cueball and Megan are lying in a grassy, lonely plain.]
Cueball: When the French navy retired morse code in 1997, they broadcast a final message: "Calling all. This is our last cry before our eternal silence."
Cueball: I wonder if I can find my Livejournal login. Megan: Hey, I like Livejournal. Cueball: It's a nice place to go for some peace and quiet, I suppose.
Randall is no stranger to LiveJournal. xkcd started on LiveJournal [1] before xkcd.com was created and is no longer live today. The blog was updated parallel to the website up to 2006 whereupon the introduction of a new RSS feed and automated update tools for the website allowed Randall to shut it down.
The Morse code for the final message "this is our final cry on 500 khz before eternal silence" is:
A period is a very short tone while the hyphen represents a slightly longer one. Between each character there is a small pause. This message was typically sent within less than half a minute.


xkcd Phone

Explanation:
This comic is a parody of a multitude of mobile-technology related issues that, when brought together, create a general satire of smartphone advertising. It was the first entry in the ongoing xkcd Phone series with the next 1465: xkcd Phone 2 released about nine months later.
The advertised features here either make previously useful capabilities useless or add features nobody wants. Except for "your mobile world (going) digital", which is old news.
The first generation of cell phones (introduced in the early 1980s) used analog radio signals to send voice traffic - and this was the standard used by the first ever smartphone, the IBM Simon. But the second generation (2G) standards, introduced from 1991 onwards, were digital, and analog services had been phased out by 2010 in most countries, long before this comic was published in 2014.
To market something as "going digital" implies that the corporation has found a way to integrate computers and/or the internet into a market that previously existed without them; the market for mobile phones has always involved computers, [ citation needed ] making the xkcd phone's marketing feel dated and clueless.
From the top, going clockwise:
The ominous warnings and disclaimers in the title text are probably a reference to the Saturday Night Live parody ad for Happy Fun Ball ( watch on YouTube ).
[An image of a smartphone standing up with a small dot on the side and a single button at the bottom. Many labels are pointing to different parts of it. Clockwise from the top left they read:] Runs custom blend of Android and iOS Simulates alternative speed of light (default: 100 miles per hour) and adjusts clock as phone accelerates Wireless Accelerometer detects when phone is in free fall and makes it scream When exposed to light, phone says "Hi!" FlightAware partnership: Makes airplane noise when flights pass overhead Realistic case Clear screen Side-facing camera
Introducing The xkcd Phone Your mobile world just went digital®


Like I'm Five

Explanation:
Megan tells Cueball that she is working on her math thesis . A thesis consists of original research and generally deals with material that is difficult for the uninitiated to understand. Cueball anticipates that it will be difficult to understand, and asks her to "explain it like I'm five". "Explain it like I'm five" is a way of asking for a simpler explanation of some difficult topic, in a way that a five-year-old child would be able to understand. Megan sarcastically (or perhaps not) treats Cueball as if he is an actual 5-year-old without his parents, expressing her concern that a 5-year-old is without any supervision. This is an example of idiomatic language being taken literally, something that Randall has explored in other comics as well, such as 1454: Done .
In the title text, Megan feigns concern that she will have to abandon her work to take care of this supposed lost child and takes this role-playing further by refusing to respond to Cueball until he phrases his comments as a 5-year-old would.
The common expression "Explain it like I'm five" is inspired by a line by Groucho Marx in his movie Duck Soup . " Why a four-year-old child could understand this report! Run out and find me a four-year-old child, I can't make head or tail of it. " [1]
Cueball: What've you been up to? Megan: Doing tons of math for my thesis. Cueball: Can you explain it like I'm five? Megan: "Oh my god, where are your parents?"


Inflation

Explanation:
The comic is inspired by the now disproven BICEP2 discovery of gravitational waves from the early universe, hence providing evidence for the cosmic inflation hypothesis. Megan is excited about this and tells Ponytail all about it. She is impressed by the fact that these waves were created when the universe was extremely small and the expanding universe has "imprinted" the gravity waves. (See also 1642: Gravitational Waves ).
She compares this to the nature of a microscope - which optically expands a small image, just like the universe has done to itself. Ponytail is impressed by it until Megan looks at the image captured by the Wilkinson Microwave Anisotropy Probe (WMAP) .
The concept of an expanding universe is sometimes explained by the "balloon model", where the two-dimensional skin represents our three-dimensional universe and the inflation of the balloon represents expansion over time. But instead of showing a balloon, Randall uses a basketball, which cannot inflate as easily as a balloon.
The elliptical Mollweide projection of this cosmic microwave background (CMB) image of the sky makes the map look a bit like a basketball. Randall further exaggerates this by superimposing the traditional curves that are visible on a basketball and the Spalding company logo over the original image available at the bottom here. The mentions of scale and basketballs in this comic might be a reference to the "If the Earth were the size of a basketball" comparison, similarly to 1074: Moon Landing and 1515: Basketball Earth .
Megan and Ponytail are both disconcerted by this, and the title text references the 1996 basketball movie Space Jam by promising images of main characters Michael Jordan and Bugs Bunny if the polarization of the view is changed to E-mode , a type of polarization of the cosmic background radiation arising from the radiation scattering off non-uniform plasma.
The image was updated between 7 AM and 8:30 AM EST on May 7. Originally the Spalding logo was shown from left-to-right; however, in the updated image, the Spalding logo is shown in reverse. The WMAP image has the correct orientation in both versions. This was likely due to a mistake on Randall's part, as the comic suggests the universe is contained inside a Spalding basketball. Seen from the inside, the Spalding logo would be shown in reverse, as seen in the updated image. The first image can be found here . Both the original and updated version don't exactly match the pattern on a typical basketball. Most basketballs are divided into eight identical (ignoring reflection) pieces in a pattern that allowed traditional leather basketballs to be made from a single template, while the image shows a pattern that would split a basketball into two types of pieces.
[Megan sits at a computer, conversing with Ponytail.] Megan: Imprinted on the sky are the gravity waves that were sloshing across the universe when it was this big.
Megan: So really, we're using the entire universe as a giant microscope pointed at itself when it was small.
[Megan turns to face the computer.] Ponytail: That's neat. Megan: Yeah. But... Ponytail: But what? Megan: Well, look.
Ponytail: Oh. Hmm. Megan: Yeah. Ponytail: What... Megan: I don't know.
[Below is an image of the universe showing the cosmic microwave background, featuring a series of circles and the Spalding basketball logo, as though the universe had been imprinted with the image of a basketball.]


Train

Explanation:
This comic, which appeared the day before National Train Day , plays on the fact that a choice of a reference frame is arbitrary, leading to the "Principle of relativity" in Albert Einstein 's theories of special relativity and general relativity . But at speeds much lower than the speed of light it also applies to the newtonian mechanics .
Rather than viewing this situation as a train causing itself to move relative to an immobile Earth, Randall provides the unconventional perspective of a train remaining fixed in space while causing the Earth itself and all the stars in the sky to rotate instead. In principle either perspective is equally valid — though in practice different trains often move in mutually-exclusive directions, thus each train would have to define its own frame of reference. It is said that Einstein once asked a ticket collector, "What time does Oxford stop at this train?"
Changing the reference frame into the inside of the train only means that you see the outside world in a different reference, since the train doesn't really move the Earth (the train's engine and the friction of the wheels aren't even remotely powerful enough) it simply appears that way from the inside.
From the Newtonian perspective this choice of frame is valid, but results in unnecessarily complicated math; the equation of motion would include terms for centrifugal, Coriolis and other so-called "fictional forces" (see 123: Centrifugal Force ). Newton supposes the existence of "inertial frames", in which these forces are zero, and the surface of the Earth approximates an inertial frame well. In General Relativity, the presence of mass in a system curves the spacetime around of it. The train-earth system could be modelled in general relativity, taking the train as fixed. However the resulting equations would be complex, and not amenable to an exact solution.
The title text expands on this to include elevators, which change a person's position relative to the center of the Earth. From a passenger's perspective, it would appear as though the Earth's position was instead being changed in space.
These examples use the train and the elevator as fixed points to define relative travel. The more common method to define movement is to use the Earth's surface as fixed point, but other reference points could be the Earth's center , the Sun , predefined "fixed" stars or the center of our galaxy . Each of these would result in a completely different movement speed:
The train, as seen from an inertial frame, doesn't seem to rotate the earth, but it does in fact have a minute, immeasurable effect on the Earth's rotation (see what-if? 41: Go West and 162: Angular Momentum ).
Train: [On the upper edge of a circle representing the Earth, Cueball is in a train car looking to his left.] Cueball:...almost... [The train tracks run between another person standing at the 2:00 position, and Hairy standing at the 9:30 position. There's yet another person standing at the 6:00 position, between some snow-capped mountains and some low hills.] [There's a counterclockwise arrow in the middle of the circle, and motion lines indicate that everyone and everything on the planet is moving counterclockwise, except for the train, which is motionless.]
A machine that grabs the Earth by metal rails and rotates it until the part you want is near you


Installing

Explanation:
This comic refers to the kind of "inventions" which seem new from the point of view of a smartphone (handheld computer ) user, but have already been around for a long time on desktop or laptop /notebook computers.
Cueball has a clever idea to skip the installing of applications on mobile phones: he would host the applications online instead, and provide links to the servers. The apps wouldn't stay on the phone all the time; instead the phone would download each app again every time the user wanted to run it.
However, web pages and web applications already work like this. Clicking a link will make the browser download a web page and render HTML code and JavaScript that it links to.
The page usually isn't saved long-term on the user's computer; instead the browser downloads it again when needed. HTML5 does however offer the option of caching web application files locally so it can remain operational when there is no network connection.
In the title text, Cueball's idea for local application storage already exists in the HTTP protocol as cookies . The more flexible web storage was originally part of the HTML5 specification, but it's now in a separate specification.
Native phone applications and web applications are not completely interchangeable. Web applications may not allow access to more advanced or platform-specific resources. Projects like Apache Cordova make these resources available to web applications by creating a native application wrapper for the web application.
[Cueball and Megan are standing next to each other.] Cueball: Installing things has gotten so fast and painless. Cueball: Why not skip it entirely, and make a phone that has every app "installed" already and just downloads and runs them on the fly?
[Caption below the panel:] I felt pretty clever until I realized I'd invented webpages.


One Of The

Explanation:
Another of Randall's many Pet Peeves , this times on reporters.
Cueball is a news anchor describing the Gateway Arch as one of the most recognizable arches in St. Louis . In this case the designer the reporter is likely referring to is Eero Saarinen .
When describing things, reporters try to make only factual statements. If reporters use absolutes (that something is the largest or the smallest thing of its class, or that it is unprecedented, to give several examples) they risk making errors: it is possible that some other example of the thing exists that is even larger or even smaller or that there was some similar incident in the past, and they were not aware of it. If a reader or viewer points out the existence of that thing, even if obscure or trivial, the reporter must issue a correction. As a result, reporters learn to hedge by using formulations such as "one of the biggest" or "a rare example of."
Randall states that it is his pet peeve when reporters avoid absolutes unnecessarily — that is, in cases where there's vanishingly little risk of error. As an absurd example, Randall depicts one such reporter using this language about the Gateway Arch. As the most well-known monument in Missouri and the largest free-standing arch in the world, it's indisputable that this would be the most recognizable arch in St. Louis.
In the title text, Randall jokes about what could happen if you misunderstand the practice of avoiding absolutes; he thus appears to think it is an ostentatious display of faux objectivity, as opposed to a correction-avoiding strategy. The title text refers to novelty mugs (and T-shirts, and other printed items) that use superlative descriptions such as "World's Greatest Mom" or "World's Greatest Dad." Obviously, such a statement is an expression of personal affection on the part of the family member who gave such a gift and is not meant to be understood as a literally true fact about the world. Using a parody of reporter-speak (like giving a mug to your mother that says "one of the world's greatest moms") would ruin the compliment by suggesting to her that you thought some other people's moms were as good or better.
The title text also refers to Mother's Day , which in the US was three days before this comic was published.
[Cueball is a news anchor sitting in front of a screen showing the Gateway Arch with some landscape features around it.] Cueball: ...And he went on to design the Gateway Arch, one of the most recognizable arches in St. Louis.
[Caption below the panel:] Pet peeve: Reporters unnecessarily hedging with "one of the"


TMI

Explanation:
"TMI" is an acronym that means "too much information". It is typically used as a response to someone "oversharing" — telling personal details ("Sorry I just missed your call - I was urinating when the phone rang") that the listener would rather not have heard. Here, however, Cueball may be using it in a more literal and absolute sense: he feels overwhelmed by the colossal amount of information that is now generally available to anyone with an Internet connection.
The title text amplifies this interpretation by evoking the image of an individual person who is overcome as he stands at the edge of the ocean, contemplating its vastness.
[Cueball is sitting at a desk, looking at a laptop.] Cueball: Ugh, TMI.
Offscreen: Oh? What?
Cueball: Just... Everything. Offscreen: True.


President

Explanation:
This strip shows a discussion between an adult and a teenager about an aspect of the future. Randall likes this setup, allowing to put in perspective the various "decay" predictions and shows his optimism.
Here, the subject is scandal. How will a generation that is documenting and leaving behind a permanent public record of its juvenile misadventures - immature and impolitic writings, photographs of inebriation at parties posted on Facebook, Twitter posts about breakups, etc. - produce successful future politicians? Won't future opposition researchers and reporters have enough embarrassing material to destroy any Millennial's public reputation? In previous generations, juveniles were freer to go through this phase of development without leaving behind a digital record, making it easier to sidestep or paper over rumors of youthful misbehavior. See, e.g., George W. Bush, who dismissed questions about his rumored use of drugs in his youth by saying only, "When I was young and irresponsible, I was young and irresponsible."
The child's answer, in addition to teasing the adult about her generation's coming obsolescence, is that the next generation will be fine because in the future no one will care. The title text amplifies this optimistic message, suggesting that old blog posts by former teenagers will just seem boring, not salacious. Randall offers no explanation for this upbeat spin, but it is a recurring topic and some have argued elsewhere that the potential power of Internet-chronicled youthful indiscretions will be defused because everyone will be in the same boat, making future voters (and, in another context, employers) more tolerant of such things.
The strip also contains an existential twist, as shown in the child's answer. It alludes to every generation's dismissal of the next, as actually being due to psychological insecurities. We may disguise our dismissals by attacking their faults & different lifestyles. But in truth, these dismissals are actually rooted in our innate fear of becoming obsolete, useless, surpassed, and lost in a bewildering world that has passed us by.
[Ponytail and Science Girl are walking together.] Ponytail: I can't imagine anyone who grew up on the Internet being able to run for President.
[Closeup of Science Girl.] Science Girl: Why? Because it'd mark the handover of a world that no longer needs you to a generation you don't understand?
[Ponytail and Science Girl have stopped walking and are facing each other.] Science Girl: ...Or because there would be embarrassing pictures of us as teenagers?
[Closeup of Ponytail.] Ponytail: Um. The pictures one? Science Girl (off-screen): Pictures of teens! How will we even survive??


Brightness

Explanation:
Exoplanets are planets outside of our solar system, and exoplanet astronomers are astronomers who attempt to discover and study such planets.
Megan is using a common exoplanet discovery technique to discover a planet around a nearby star. When a planet passes between an observing astronomer and a star, the planet will block some tiny part of the light coming from that star, causing it to appear dimmer for some amount of time. The Kepler telescope used this technique to find evidence for exoplanets.
But here Megan is standing on the surface of the Earth at night, looking at the ground, and therefore presumably looking in the direction of the sun. By observing that it is completely occluded at night, she correctly concludes that the Sun is orbited by at least one planet: the Earth. This is obviously an absurd usage of that method. Reasons include the fact that exoplanets are not big enough to block out all of their stars' light when seen from Earth [ citation needed ] , making what Megan says a massive understatement, and that the period of the brightness oscillations would correspond to the length of a day, not a year as it would for exoplanets.
The title text alludes to using more complicated techniques to observe light reflected by small planets like the Earth, for example by detecting polarized light reflected from the planet's atmosphere. In some sense, observing the light that reflects off of the Earth during the day is in fact how we see everything around us. It also implies that astronomers, who because of their career choice are more likely to work at night, might be completely unaware of Earth's existence in the daytime and thus surprised to "discover" it from their nighttime work.
[A black panel with white text and a white Megan who is standing staring at the ground.] Megan: Based on this decrease in the star's brightness, I believe it is orbited by at least one planet.
[Caption below the panel:] Exoplanet astronomers at night


Smartwatches

Explanation:
Smartwatches are fairly recent innovations which function something like smartphones which are attached to one's wrist, although the screens are often shorter than those of typical smartphones, and they typically need to be attached via bluetooth to a smartphone. This comic shows someone " Case modding " some smartwatches and a broken smartphone; that is, taking the electronic innards of two smartwatches and putting them into the sawn-in-half case of a smartphone before attaching the two halves with a hinge, allowing it to open and close like flip phones, a type that was popular before the rise of smartphones.
The Western Electric Model 2500 is the last standard desk-style domestic telephone set issued by the Bell System in North America. It contains the # key and the * key, so it can be said it has same application features as the first cellphones, but it's obviously much bigger, and of course not wireless. Smartphones usually have much more functionality. Case modding is the art of building machines (usually computers) into nicely shaped non-standard cases. The opinion about "niceness" of the result vary, as usual in art. The point is that changing the case doesn't change the functionality, so the niceness (or, usually, "coolness") is generally the only relevant feature (although, badly done modding can affect cooling).
It appears that Randall has a rather low opinion of smartwatches, as he suggests that it would be better to take out their screens and mount them onto a dead iPhone than to use them the way smartwatches are normally used.
However, Randall's suggestion to cut open the dead phone with a hacksaw is unsound for several reasons:
1. Any attempt to saw through glass will cause it to shatter. To cut glass, one needs to grind it, not saw it.
2. Even if the phone is dead, the battery may be charged (if dead means that the battery is dead, not that the phone does not work, in which case the procedure destroys a perfectly functional iPhone). Saw blades conduct electricity, so the person might get electrocuted.
3. Some batteries contain chemicals that are toxic or explosive.  Even if the battery is discharged, sawing through it is very dangerous.
To add which, the hinge depicted in the cartoon is an ordinary household hinge. It is overly large for using in electronics compared to hinges on old clamshell-style cell phones, and drilling holes in the watch cases to attach one would potentially damage the internal electronic circuits. It could also puncture the battery, causing it to catch fire. Either render the watch useless.
4. Also, it's possible the watches wouldn't fit that nicely into the iPhone.
While no phones such as the one depicted existed at the time of the comic (2014), in November 2019, Motorola officially announced a new Android phone, to be released under the Razr name, which is extremely similar in form-factor to the fictitious phone shown in this comic, albeit with a single flexible OLED screen, rather than two separate screens.
A USE FOR SMARTWATCHES: [Depicted are two smartwatches, both labelled as "Working" and showing generic colour displays, and one smartphone labelled as "Dead" with a blank screen.]
[A hacksaw cutting through the smartphone, throughout the middle of the long edge of the case.]
[The two smartwatches are shown with the wristband and case broken around the edge of the display because the displays with the associated electronics are removed. Arrows are shown coming from the smartwatch cases to the smartwatch displays, then from the displays to the smartphone case halves.]
[The smartphone halves are installed with the smartwatch components and a hinge with screws beside is shown. Another view shows the hinge screwed into the back of the smartphone case.]
[The smartphone with the working smartwatch components installed is shown, with the hinge three-quarters open and fully closed - resembling an early flip-phone.] World's first flip iPhone


Screenshot

Explanation:
Randall is viewing a screenshot of a text-message exchange via his own phone's web browser. Such screenshots are frequently posted online, to show content ranging from humorous typos to creepy behavior . In this screenshot, in addition to the text messages' content, we see a battery bar reflecting a charge of 6%; this effectively " photobombs " (or distracts Randall from) the actual content of the original screenshot. On the other hand, the phone on which the shot is viewed is charged at a healthy 85%.
The phone the screenshot is taken from is an iPhone, while the phone being viewed is an Android. Another iPhone screenshot was the joke in 1815: Flag .
The title text suggests that Randall has plugged in his phone to quell the anxiety induced by the 6% charge in the screenshot, mistaking it for the actual battery indicator of his own phone. This measure is obviously unsuccessful, as charging his own phone does nothing to change the charge of the phone in the picture. A similar phenomenon is when a screenshot is viewed and the viewer attempts to use the controls (e.g. buttons) in the image.
Randall's fear of losing power to his phone was later explored in 1802: Phone and 1872: Backup Batteries , where he brings extra batteries and it is also part of the joke in comic 1965: Background Apps .
An alternative interpretation for the title text is that the screenshot was posted as part of a thread asking why their phone isn't charging. This would be ironic, as Randall's focusing on the battery level means his eyes are being drawn to the very problem being spoken about, yet he is too distracted by it to read that this is the problem!
This may also be a reference to mirror neurons . Mirror neurons are according to many neurobiologists a biological basis of empathy. If you see someone stick a needle in their hand, it feels as if you hurt yourself and some people experience a tightness of the chest when hearing a wheezing asthma patient on the radio. Here, Randall's mirror neurons start to fire as he feels the anxiety associated with a phone losing battery power.
Screenshot quality was discussed later in 1863: Screenshots . This comic is one of a small set of comics with the same or almost the same title as another comic (only plural form of word screenshot being difference).
[Caption above the panel:] When someone posts a screenshot of their phone,
[The panel shows the screen of an Android phone. At the top there is a black Android status bar with icons like WiFi, battery charge and the time, all in white:] 85% 10:02 PM
[Below the status bar is the open program, which is an internet browser, which shows the address field with an unreadable address and the tap icon to the right and the three dots for options. Below that is the page viewed in the browser. It seems to be a post from a person. Below the address bar is a picture of a user with dark hair in a square frame. To the right are two lines of unreadable user information. The post contains a picture posted by the user, and it is a screenshot of a chat/SMS conversation from another phone. The screen is light blue and the conversations has three blue speech bubbles to the left and two replies in between those in green to the right. All posts are unreadable, as are all other words in the picture. At the bottom of the picture the top of another users post, i.e. half the users image, can be seen. At the top of the picture, the status bar from this iPhone screen shot can be seen with icons both left, center and right. To the right the charge icon battery shows a very low charge, indicated with a small red line at the bottom of the battery. Around this low charged battery icon there is drawn a large red circle like spiral, circling the battery symbol two or three times, and four exclamation marks are written above this. The only thing that can be read in the picture is the charge percentage:] !!!! 6%
[Caption below the panel:] I can't pay attention to the content if their battery is low.


Urn

Explanation:
A common tool for explaining concepts in elementary probability theory are games involving the drawing of coloured balls from a container, such as a bag, or hat. In older statistics related texts, a convention developed of describing the container as an urn. This is so common that such problems are often called urn problems .
While an urn can have many uses, in modern times the most common context in which it is used is to contain the burned remains of deceased individuals after a cremation . This is likely because as interior decor has grown more minimalist, other types of urn became less common and the association of the word urn with cremation has become ubiquitous in the vernacular.
Megan , when asked to imagine drawing balls from an urn, imagines a cremation urn containing not only balls, but also human remains. She may be referring to a real grandfather who has been cremated, or is simply improvising a joke at Cueball's expense.
The title text refers to two distinct scenarios in the coloured ball experiment: The balls may be replaced between each drawing, or not. In the former case, each draw is independent of the previous, in the latter the chances of picking a particular (remaining) ball the next time have increased. Megan (or rather Randall if it is he who speaks in the title text) would prefer to put the ashes back into the urn. She might also want to have her grandfather back, and be playing with the word "replacement".
The distinction between repeated drawing with and without replacement is used in most presentations of elementary probability because it illustrates a subtle but important theoretical distinction: if the balls are replaced, one at a time, before drawing the next, the number of balls of a certain colour has the binomial distribution , but if the balls are not replaced, so that the same ball cannot be drawn twice, you instead get the hypergeometric distribution .
There are myriad reasons why Megan would want to draw with replacement, the most simple of which being that she has nowhere to put ashes other than in their designated urn. Ashes by their nature need a container, or they will make a mess; cremated remains in particular come with the additional requirement that the container be respectful to the deceased.
[Cueball is standing in a classroom with Megan at a desk.] Cueball: Imagine that you're drawing at random from an urn containing fifteen balls - six red and nine black. Megan: OK. I reach in and... ...My grandfather's ashes?!? Oh God! Cueball: I... what? Megan: Why would you do this to me?!?


Astronaut Vandalism

Explanation:
Signs like this normally show the distance to places on earth's surface. This sign also has an arrow pointing away from earth and towards "space", with a distance of 62 miles (100 km), due to "astronaut vandalism". The 62 mile distance is the Kármán line , one of the conventional demarcations of the beginning of " outer space ".
We think of space as being very far away. This comic puts into perspective that it's really a lot closer to space than to many destinations we're used to getting to by car or airplane. We think of 62 miles as being an easy trip on the ground, but that same 62 miles is incredibly hard when going vertically, against the force of gravity.
The title text references the fact that while the Fédération Aéronautique Internationale (FAI) defines the Kármán line , the boundary between Earth's atmosphere and outer space (i.e., the start of space), to be 100 kilometers (62 miles) above mean sea level, the U.S. Air Force and other military branches will award astronaut wings to rated astronauts who fly higher than 50 miles (80 km).  In 2005 NASA changed from using the FAI definition to using the USAF definition for consistency across organizations, and thus some NASA test pilots who had flown the X-15 retroactively received astronaut wings for their greater-than-50 mi (80.5 kilometers) flights. (Air Force pilots of the X-15 in the 1960s had long since received astronaut wings for such flights.)  Thus in the title text, Air Force pilots surreptitiously change the sign to conform to their definition of "space".
Although most authorities use the FAI definition of space - the Kármán line - since the FAI is the international organization of record for aeronautics, there are good scientific reasons for the U.S. Air Force definition.  The line is named for Theodore von Kármán , who originally calculated the height at which an vehicle would have to travel faster than orbital velocity to generate lift from wings, therefore making the vehicle an object in orbit rather one using air to generate lift.  Von Kármán originally calculated this height as 51.9 miles (83.6 km) - closer to the USAF definition than to what is now called the Kármán line.  Additionally, the boundary between the mesosphere and the thermosphere is traditionally taken to be 53 miles (85 km), also close to the Air Force definition.  On the other hand, some newer research suggests the mesopause (the line between the mesosphere and thermosphere) may have peaks between 53 and 62 miles (85-100 km).  Also the turbopause - the line where gas molecules cease mixing atmospherically and begin stratifying by molecular weight as if they are in orbit - is generally taken to be about 100 kilometers (62 miles).
All of the atmospheric boundaries are variable, however, changing from day to day and season to season with no clear boundary.  Additionally, objects cannot reliably orbit below 130-150 km (80-93 miles) due to drag from even the sparse atmosphere in the lower thermosphere.  Despite this comic associating "space" with having a definite start the way you might definitely know when you cross the city limits of a town, the reality is that the transition from atmosphere to space takes place gradually over tens of kilometers.  Interestingly, since it is too high for aircraft and high altitude balloons, but too low for spacecraft in orbit, this "near space" transition region is one of the least-visited and least-used regions of the larger atmosphere. This comic thus both points out that the limit where space starts is arbitrarily chosen and also that space is often much closer than, for instance, two nearby cities in some randomly chosen location in the US.
The two distances shown on the signpost can occur only at certain points on Earth. One possible location is Grenada, MS, which is about 100 miles from Memphis, TN and about 114 miles from Jackson, MS. Alternatively "Jackson" could mean Jackson, TN, in which case Tupelo, MS or Kenneth, MO are both viable options for the location of the signpost. However, in Tupelo the roads to Jackson and Memphis meet at a right angle, instead of pointing in opposite directions as in the comic.
[A signpost with three arrows.] [Arrow pointing up:] Space 62 [Arrow pointing right:] Jackson 115 [Arrow pointing left:] Memphis 98


Jump

Explanation:
Cueball is presumably experiencing a common dream subject, flying or floating. As in many varieties of such a dream , the ability to fly, float or glide only gradually manifests, going from longer and longer jumps to a sort of flight or hovering. In Cueball's case, his jumps become longer and 'lighter' until at last he is gliding just above the surface of the Earth. He has apparently had such a dream before, with just such a flight mechanic manifesting itself, as he indicates that he 'loves' these dreams.
In his presumed dream, Cueball finally achieves his gliding flight just as he reaches the shoreline, and his gliding carries him over the water's edge and out to sea. After a moment's reflection, he realizes that if he were really gliding out to sea without any real apparent means of control, his situation would presumably be rather perilous — death by starvation or thirst, gradually slowing down and becoming 'stuck' over the water with no way to land, the loss of his gliding ability as suddenly as it came, etc., all suggest themselves as possible perils he would now be subject to if, in fact, his 'dream' were actual reality. Thus he eventually indicates that he hopes it is a dream, in contrast to his feeling at the comic's opening.
The title text adds a further worry not immediately apparent unless one considers the possibility that Cueball's 'gliding' will continue in a straight line in relation to the Earth's surface. In that case he would continue moving straight while the Earth's surface would curve away beneath him, sending him out into space instead of the relatively preferable scenario of merely floating across the ocean to the opposite shore. After all, if the laws of physics had changed to permit hovering/flying, consequences would be unpredictable — i.e. there'd be no assurance one would maintain a constant hovering height rather than take leave of the planet as one flies forth. One thing about miracles is that all bets are off!
Also note that this situation is similar to the case of Newton's cannonball . However, that is actually in very-low-earth-orbit — and you would need to be going 7,300 m/s, or about 16,000 mph (26,000 km/h) to stay in orbit. At that speed, of course, air friction would quickly destroy the cannonball or person. This is clearly not the case in the dream.
Getting weightless and drifting around was a fantasy in 226: Swingset . The comic 417: The Man Who Fell Sideways has some resemblance to this one.  In 942: Juggling , Cueball throws some balls and later a book.  They miss the ground .
In the book Thing Explainer Cueball jumps to score with a basketball in the explanation for Playing Fields only to find that he keeps rising steadily along a straight curve up above the hoop. Very similar to this jump that just lets Cueball float straight afterwards.
[In the first panel Cueball is seen as a stop motion cartoon (12 drawings of the same Cueball) as he is jumping down a small hill — jumping longer and longer between sentences. Jump is written over the head of Cueball that perform the jump until he floats.] Cueball: I love these dreams Jump Cueball: Each jump is a little longer Jump Cueball: Each push off the ground a little softer Jump Cueball: Until I G l i d e
[In the second panel Cueball (five drawings) glides over a fence and the dunes before the beach — then he glides out over the sea. The fourth Cueball just passing over the sea looks back towards the shore. Four birds are flying behind him around the coast line.]
[In the third panel Cueball (four drawings) glides across the open sea — three birds circling around the first Cueball, a fish is jumping out of the water splashing down again beneath the second Cueball.] sploosh Cueball: ...I hope this is a dream.
...I hope this is a dream. Or that I'm at least following the curve of the Earth around to land...


Fish

Explanation:
The Fermi paradox is the contradiction that arises between high estimates of the likelihood of extraterrestial life and the fact that no evidence for it has thus far been found.
Cueball and Megan are having a conversation regarding this — since new planets are found all the time around distant stars, Cueball comments that this makes it an even greater paradox. Megan suggests that perhaps our search for extraterrestrial life is like looking at a patch of ocean floor looking for a fish. The diver knows that there must be a fish somewhere, but is unable to actually find it. She then goes on to ask why the fish would be hidden — i.e. camouflaged, and what it means about the remaining fish. The suggestion is that the fish would be hidden to avoid being eaten by predators, and perhaps the reason no extraterrestrial life is sending any sign of existence back is that they fear they might be destroyed soon after they revealed their location. Maybe they have even actively tried to hide the presence of their entire planet if they obtain the technological means. This potentially refers to the Deadly Probes scenario where a space faring species has developed deadly probes that self replicate and spread through the void between the stars - homing in on radio signals and destroying young civilizations in the cradle...
The camouflaged fish could be identified by using more sophisticated technologies like infrared cameras. Looking at the Earth from space beyond Low Earth orbit only with the naked eye wouldn't show any hint to our ecosystem . This is like the actual possibility in astronomy when observing exoplanets — the nature of those more than 1,500 known planets is unknown due to the lack of better technologies to the scientists. And there are a couple of hundred billion planets at our galaxy still camouflaged to human scientists.
The final panels take the metaphor further, suggesting that there is literally a planet sized shark swimming through space eating planets, and since the view is panning away from earth and over to the shark, the shark seems to be heading our way. It looks like Earth is the next fish, presumably because we did not reach a high enough technology level in time to recognize the danger and hide.
This also explains the title text that has the theme from the movie Jaws playing while astronomers look into their telescopes. This may also be a reference to the film Alien , which was pitched with the three word proposal " Jaws in Space."
Stephen Hawking famously warns, "If aliens visit us, the outcome would be much as when Columbus landed in America, which didn't turn out well for the Native Americans." Chinese sci-fi author Liu Cixin wrote an award-winning sci-fi trilogy called the Remembrance of Earth’s Past trilogy, which draws on a similar idea; the title of the second book, The Dark Forest , is a reference to the same Fermi paradox solution described in the comic. Even Carl Sagan called the practice of Broadcasting and Signaling presence of Life on Earth "deeply unwise and immature," and recommended that "the newest children in a strange and uncertain cosmos should listen quietly for a long time, patiently learning about the universe and comparing notes, before shouting into an unknown jungle that we do not understand."
[Cueball and Megan are walking down a hill.] Cueball: The Fermi paradox keeps getting worse. If planets are common, where is everybody?
Megan: Imagine you're a scuba diver looking at the ocean floor. You know there's a fish there, but you can't see it. Why?
Cueball: Maybe the fish looks like sand. Megan: Yeah...
[Zoom out to the Earth from space.] Megan: ...and what would that tell you about the ecosystem?
[Earth moves slightly out of the panel.]
[Earth moves halfway out of the panel.]
[Blank panel.]
[A shark swims through space.]