explain xkcd - User contributions [en]

1611: Baking Soda and Vinegar

2015-12-18T22:58:35Z

JT74: Fixed misspelling.

{{comic
| number = 1611
| date = December 2, 2015
| title = Baking Soda and Vinegar
| image = baking_soda_and_vinegar.png
| titletext = Sure, it may not meet science fair standards, but I want credit for getting my baking soda and vinegar mountain added to the Decade Volcanoes list.
}}

==Explanation==
{{incomplete|Does it miss something about the reaction although that may not count as "real" science?}}
In popular fiction (and maybe in part in fact) the "{{w|Sodium bicarbonate|Baking Soda}} and {{w|Vinegar}}" {{w|volcano}} is often a staple image of the science nerd at the science fair (see [https://sciencebob.com/the-erupting-volcano/ example here]), unless all the science nerds are doing ''real'' imaginative science and the student(s) with the volcano exhibit are dragging out the old hackneyed stereotype. It may also be age-dependent, this being something that is relatively advanced science for the lower grades but rather a childish experiment in the hands of older students.

As [[Ponytail]] is probably about to point out, the 'volcano' exhibit doesn't (usually) actually demonstrate anything about volcanic activity, it is just simple chemistry - involving the reaction of acetic acid in vinegar and sodium hydrogencarbonate in baking soda to give sodium acetate and bubbles of carbon dioxide - dressed up to look more impressive, often with dye or other additives to make the 'eruption' look more realistic, but it often fails to replicate important features of every volcanic eruption such as the flow of lava, associated seismic events or the collapse of part of the volcanic crater. In most soda volcano projects people don't even explain what's happening.

The girl with hair bun (possibly [[Danish]]) has made a little more of her volcano, however, as it seems to go beyond simple chemistry. The model replicates many of the dangers (aside from the pure lava) of a volcano, and appears to have been given scaled-down vehicles (not visible in the comic) trying (and failing) to escape the dangers of the resultant mud-flows (a.k.a. {{w|lahar|lahars}} in professional terminology) being modelled. Ponytail contradicts her early reaction by also not liking the more realistic model.

Even more, this is not an isolated 'model volcano' but a vinegar-powered representation of a geological 'hot spot', such as with the islands of Hawaii, in which the spot moves with respect to the Earth's crust (or vice-versa) and generates a new volcano some way off. Despite this model being supported on a table, it appears that the 'project' extends some way beyond that and has somehow contrived further eruptions away from the table, the room and probably even the building.

The 'project' seems to be turning into a very thorough model of a much larger geological process (a {{w|Supervolcano}} like {{w|Yellowstone Caldera|the one}} under {{w|Yellowstone National Park|Yellowstone}}) and destined to produce a ''very real'' {{w|volcanic winter}}. Where a magma-powered volcano could produce vast clouds of dust, preventing the sun's energy from warming the Earth, in this case it's the airborne salt (probably sodium acetate) from the chemical reaction that appears to be in danger of causing crop failure. There's no mention of the corresponding environmental effects of the vast amounts of carbon dioxide (and/or aqueous carbonic acid) necessarily released in proportion to the ejected salt (presumably itself not left in solution).

It is especially troubling that the child even mentions that her model volcano is an offshoot of a baking soda ''super''volcano. Supervolcanoes are massive volcanoes, far larger than even those on the list of {{w|Decade Volcanoes}} (mentioned in the title text), whose eruption would likely trigger species-level extinction events comparable to the dinosaur extinction. Humanity can only hope the child is exaggerating in her description, but the symptoms witnessed by the adult looking out the window suggest otherwise. {{w|Campi Flegrei}} is actually a real life example of her project.

When someone (presumably the dark haired woman) says she wants to stop learning, the girl with the bun grimly states that "Soon, we all will", alluding to their impending doom.

[[Randall]] has mentioned supervolcanoes before in [[1053: Ten Thousand]] (title text) and [[1159: Countdown]], making it a recurring interest of his. The volcano Mount Doom was depicted to the far left in the game [[1608: Hoverboard]] released a week before this comic. It may not be a supervolcano, but quite potent anyway...

In the title text the student expects extra credit for getting her model volcano added to the Decade Volcanoes list, a list maintained by {{w|International Association of Volcanology and Chemistry of the Earth's Interior}} of the world's most dangerous volcanoes (currently 16). It is either an absurd notion or a very troubling achievement that a science fair project could achieve the threat level posed by the likes of {{w|Mount Vesuvius}} (which destroyed ancient Pompeii in Italy, and threatens modern-day Naples in the same manner), {{w|Mount Rainier}} (whose lahars could potentially destroy parts of Seattle) or {{w|Mauna Loa}} (which could create a massive landslide, triggering a major tsunami that would threaten all of Hawaii). But if the volcano erupting outside is scaled down to match the scale of her original model volcano, at least that means that it was only a "local" volcano event and not a supervolcano event that she created, so it would only doom the local area.

==Transcript==
:[Ponytail is standing behind a small girl with a hair bun who has one hand up. They are looking at a table with a model volcano.]
:Girl: My science project is a baking soda and vinegar volcano!

:[A larger frame that includes Megan who stands to the right. Ponytail is a little further back and the girl has taken her hand down. The baking soda volcano erupts in a small upwards explosion.]
:Ponytail: Why do people make these? It isn't really even a science project. It doesn't teach anything about-
:Volcano: '''''FOOM!'''''

:[Smaller frame again. Ponytail has moved closer to the table, the girl moves around the table to the right, pointing at the volcano while Megan walks closer. The "lava" flows down the volcano on both sides.]
:Girl: See how the baking soda and vinegar mix with mud and ice to form deadly flowing lahars?

:[Zoom in on the girls head close to the stream of lava going down the lower part of the volcano's right slope.]
:Girl: You can see the tiny cars trying to flee.
:Girl: Whoops! Too slow.

:[Zoom in on Ponytail.]
:Ponytail: Um. This is a bit grim.
:Girl (off panel): Learning!

:[The girls stand to the right of the table looking at the now still volcano. Shaky lines surround a sound effect written over the top of this slim frame:]
:Sound effect: ''RUMBLE''

:[Back to showing all three as before. The girl looks at something in her hand (a stopwatch maybe?)]
:Girl: And now we're learning that this volcano is an offshoot of a vinegar hotspot rising from deep within the earth.
:Girl: ''Annnd...''

:[The girls turns away from the table looking right as a loud noise can be heard off-panel, depicted in white text on a wavy black bubble:]
:''BOOOOM''

:[Megan has walked over to a window to the right. It has the blinds drawn down. She opens a hole in the blinds by pulling down in the middle. It is dark outside. The other two are outside the frame to the left.]
:Girl (off panel): The baking soda supervolcano erupts, injecting clouds of salt into the stratosphere.
:Megan: Why is it getting dark outside?
:Girl (off panel): Learning is fun!

:[We see the girl standing close to the table, of which only the right leg can be seen. She holds up a tablet with a graph showing a rising trend. The other two are both out of the frame.]
:Girl: Sunlight dims. The earth cools. Summer frosts form. Crops die. We check the markets. Grain prices are rising.
:Megan (off panel): I want to stop learning now.
:Girl: Soon, we all will.

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

1597: Git

2015-10-30T15:04:46Z

JT74: Minor grammar fix

{{comic
| number = 1597
| date = October 30, 2015
| title = Git
| image = git.png
| titletext = If that doesn't fix it, git.txt contains the phone number of a friend of mine who understands git. Just wait through a few minutes of 'It's really pretty simple, just think of branches as...' and eventually you'll learn the commands that will fix everything.
}}

==Explanation==
{{incomplete|Title text - with he name of the friend not explained yet.}}

{{w|Git (software)|Git}} is a {{w|Version control|version control}} system often used to track changes to (usually) plain text files, such as computer code. Within a folder and its subfolders, the user can tell Git which files to keep track of changes for. All the files that are being tracked in this manner make up a repository. Internally, Git works by saving the differences between various versions of the files, rather than creating a new copy each time the user "commits" the current version of the code. This approach allows the user to switch between various versions of the code fairly quickly. However, this can be confusing for new users because when changing between versions, Git effectively rewrites the files under its control to match that version - one file may have several different versions depending on which state Git has set it to, but only one of these versions is visible at any given moment. The others are not hidden or moved, they do not exist until Git modifies the file to match that version.

In addition to allowing the user to track changes to the files over time using "commits" (versions of the files stored by the user), Git also allows the user to develop several versions of the files in parallel using "branches" (mentioned in the title text). This allows a programmer to, for example, keep a stable, functioning version of their code in one branch, while developing a new feature in a separate branch. When the new feature is ready, Git provides tools to efficiently "merge" the changes from the development branch back into the main branch. While powerful, there are also several pitfalls which can confuse users. For example, a file may have only been committed in one branch (so it is only visible in that branch), causing a user who has switched to a different branch to think that file was lost somehow.

Sharing a Git repository with other users is done through a remote repository, such as [https://github.com/ GitHub], [https://about.gitlab.com/ GitLab], or one set up by the user themselves. This remote repository acts as a central location through which collaborates share their work. Changes do not automatically propagate between users; instead, once someone has changes they are ready to share, they must upload ("push" in Git terminology) their changes to the remote repository. Other users can then download ("pull") those changes. This allows each user complete control over when changes are applied to their version of the files. Once one user has pushed his or her changes, all other users will need to merge those changes into their code before they can push. Depending on how much the changes conflict, Git may be able to automatically combine both users' versions, or the user may need to do so manually.

In programming, Git is a very popular way to share source code of programs between computers and users and thus work on projects collaboratively.

However, problems often arise when, for example, one attempts to upload code to a file someone else has already edited.
Git has quite a few tricks to handle "merging" itself.

One way of simplifying collaboration is to work in a "branch", the same files that everyone has, but your changes do not become visible to other users yet. Only when you merge (there we go again) your branch with the master branch, other users will see your "commits".

But, due to the complex nature of Git (and its notoriously counter-intuitively named commands), a large portion of users are unable to use it beyond basic commands. They consider it usually much more efficient just to save the code to a different file, download a newer copy, and then re-apply their original changes to the new copy than to try and understand and use Git's own convoluted built-in commands to attempt to fix it properly.

Git was originally created by {{w|Linus Torvalds}}, the same person who originally created {{w|Linux}}.

==Transcript==
:[Cueball points to a computer on a desk while Ponytail and Hairy are standing further away behind an office chair.]
:Cueball: This is Git. It tracks collaborative work on projects through a beautiful distributed graph theory tree model.
:Ponytail: Cool. How do we use it?
:Cueball: No idea. Just memorize these shell commands and type them to sync up. If you get errors, save your work elsewhere, delete the project, and download a fresh copy.

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring Hairy]]
[[Category:Programming]]
[[Category:Computers]]
[[Category:Internet]]

1559: Driving

2015-08-03T14:45:44Z

JT74: Grammar fix

{{comic
| number = 1559
| date = August 3, 2015
| title = Driving
| image = driving.png
| titletext = Sadly, it probably won't even have enough gas to make it to the first border crossing.}}

== Explanation ==
A {{w|self-driving car}} is a car that requires no human interaction to navigate streets to a destination. Thus, when [[Black Hat]] places the rock that weighs "as much as a small adult" into the car's seat, he begins the process of fooling the car into thinking it has an occupant when it does not. His purpose in doing so appears to be to send the car to {{w|Anchorage}}, {{w|Alaska}}, which is presumably far from where Black Hat and [[Cueball]] are standing, thus taking the car far away from its owner with relatively little effort on the part of Black Hat. This is the kind of evil prank Black Hat is infamous for.

The title text references the fact that driving to Alaska from the continental or continuous 48 states requires two border crossings, once into Canada from the mainland, and once from Canada into Alaska. The car apparently begins some distance from the Canadian border, since it will likely run out of gas before reaching Canada. Black Hat expresses regret about this probable failure; presumably he was looking forward to the encounter between the border guards and the vehicle's "occupant". However even if the car does not go to Anchorage he will have created a serious problem for its owner. A typical car can travel 300 to 800 miles (500 to 1300 kilometers) on a tank of gas, and with no way to know the car was going to Alaska, the owner will have to search an area with that radius, and will probably fail to find the car before it is towed.

Nevada was the first state to allow the testing of self-driving cars on public roads. But there are now several states in the US (as well as several countries in Europe) that allow this type of test. It is thus not possible to place Black Hat and Cueball based on this, except that they are in mainland USA, Mexico, or Central America (the regions connected by overland routes to Alaska, but at least two border crossings away). At the time of the release of this comic there were no places where these cars could be used privately. So unless a tester left his car running (unlikely), then this comic must be set in the (near?) future.

==Transcript==
:[Black Hat, carrying a large rock, is walking toward Cueball. Small fragments (earth?) falls of the rock leaving a trail after Black Hat.]
:Black Hat: Would you guess this weighs as much as a small adult?
:Cueball: What?
:Cueball: Uh, probably.

:[Black Hat walks past Cueball who turns to look after him.]
:Black Hat: Great!

:[Black Hat has walked out of the frame. Cueball is looking in the direction he left. Several noises and voices are coming from off-panel.]
:Off-panel: <nowiki>*</nowiki>Thump*
:Car voice (off-panel): ''Please fasten your seatbelt.''
:Off-panel: <nowiki>*</nowiki>click*
:Black Hat (off-panel): Take me to Anchorage, Alaska.
:Car voice (off-panel): ''Navigating''
:Off-panel: <nowiki>*</nowiki>slam*

:[Black Hat walks back in the panel towards Cueball.]
:Car driving off:''Vrrrrrrrrrrrrrrrrrrrrrrr''
:Black Hat: I love self-driving cars.
:Cueball: ...Whose car was that?
:Black Hat: Dunno, but they shouldn't have left it running.

{{comic discussion}}

[[Category:Comics featuring Black Hat]]
[[Category:Comics featuring Cueball]]

1551: Pluto

2015-07-15T13:36:34Z

JT74: Removed redundant "and"

{{comic
| number = 1551
| date = July 14, 2015
| title = Pluto
| image = pluto.png
| titletext = After decades of increasingly confused arguing, Pluto is reclassified as a "dwarf Pluto."
}}

When the image is clicked the latest [http://www.nasa.gov/feature/new-horizons-spacecraft-displays-pluto-s-big-heart-0 NASA post] opens up.
==Explanation==
{{incomplete|New Page.}}

This comic was posted on Tuesday, July 14th 2015, in honor of the {{w|New Horizons}} deep space probe making its flyby at {{w|Pluto}}. It thus breaks the regular Monday/Wednesday/Friday cycle for the [[xkcd]] comics. [[Randall]] has taken the largest released image by this day and drawn humorous {{w|Pareidolia|pareidolia}} on top of it.

It can be compared to preliminary descriptions by geologists, e.g. [http://www.planetary.org/blogs/emily-lakdawalla/2015/07140911-new-horizons-best-look-at.html?referrer=http://t.co/ExQJ6cKS1Q New Horizons' best look at Pluto before close approach | The Planetary Society].

The comic probably winks at {{w|Percival_Lowell|Percival Lowell}} whose observatory photographed Pluto (then "known" as Planet X) in 1915. Unfortunately the things Percival Lowell is most famous for are his drawings of the {{w|Martian_canal|Canals on Mars}}.

The title text refers to the debate as to whether Pluto should be classified as a full or dwarf planet. This debate was particularly brought into the public eye, and came to be seen as a matter of controversy, following the 2006 {{w||IAU_definition_of_planet||}. The text images that this debate winds on, with definitions being created and revised until a ridiculous state is reached whereby Pluto has a special class of celestial body named after it (called a 'Pluto'), but fails to fulfil the (arbitrary) criteria set up for it, and hence is called a 'dwarf Pluto'.

===Table of objects===
{| class="wikitable"
|-
! Description
! Explanation
|-
| Candy shell
| Suggests Pluto is a confection.
|-
| JPEG plumes
| The {{w|JPEG}} image format has the common issue of slightly distorting an image with {{w|Compression artifact}}s. The artifacts shown here do not appear in the official version of this image, and may have been added by [[Randall]] (or edited out by NASA). But there have been tweets about people seeing plumes associated with active volcanoes and the like, which were explained as being artifacts.
|-
| Frontal bone
| Interpreting Pluto as a head, the {{w|frontal bone}} could be the light-colored region next to the darker top (the north pole).
|-
| Grease stains
| The darkened area of Pluto's north pole is attributed to grease.
|-
| Bugs
| Could refer to possible extraterrestrial life on Pluto in to form of {{w|insects}}, or "bugs". (In the animated TV series ''Roughnecks: Starship Troopers Chronicles'', an adaptation of Robert Heinlein's novel ''Starship Troopers'', the first battles with the alien "Bugs" took place on Pluto.)
|-
| Bullet holes
| A string of small round features which Randall suggests were the result of Pluto getting shot repeatedly.
|-
| New Netherlands
| Reference to [[1519: Venus]] and also a [[what if?]] about draining the Earth's oceans onto Mars. In that What If?, the Netherlands issued forth from the portal that drained the oceans to claim Mars as New Netherlands. Presumably something similar happened on Pluto.
|-
| Disputed territory
| Since the base photograph is identified as "today's ''New Horizons'' image," this indicates that a section of Pluto has immediately become the subject of some controversy, possibly a territorial claim or one of several references to the fact that Pluto was demoted from full planet status in 2006.
|-
| Snake pit
| A generic map hazard.
|-
| Full text of the Wikipedia article on pareidolia
| {{w|Pareidolia}} is the human brain's tendency to see patterns where they don't exist. While probably a reference to the famed {{w|Face on Mars}}, the joke is also recursive: You'd be seeing the text of a Wikipedia article explaining to you that you couldn't actually be seeing the text of a Wikipedia article.
|-
| Tadpole
| One of a number of pareidolic features Randall has outlined.
|-
| Kuiper Belt loops
| The {{w|Kuiper belt}} is a region in our solar system that contains a large concentration of icy bodies, including Pluto. Randall jokingly refers to Kuiper Belt as the same kind of belt that's used to fasten clothing, and identifies features on Pluto's surface as loops for the belt.
|-
| Serenity
| An outline of the ''Firefly''-class spaceship ''Serenity'', which was the titular vessel from the 2002 TV series ''{{w|Firefly}}''. One of a number of pareidolic features Randall has outlined.
|-
| Dinosaur
| One of a number of pareidolic features Randall has outlined.
|-
| The good part
| A random, arbitrary selection of Pluto that is somehow better than the rest of Pluto.
|-
| Moon bud
| This could be interpreted as a moon growing/emerging out of pluto, as a bud is "a compact knob-like growth". A round growth is seen at the location marked, resembling a small, emerging moon.
|-
| Ghost
| A reference to the classic video game ''{{w|Pacman}}'', wherein the primary antagonists are one of four Ghosts. The Ghost on Pluto appears to have a mouth, however, unlike most depictions of the ''Pacman'' Ghosts. One of a number of pareidolic features Randall has outlined.
|-
| Pluto dinosaur extinction crater
| Suggests Pluto had dinosaurs and lost them the same way Earth did.
|-
| Heart
| One of a number of pareidolic features Randall has outlined, and the only one (currently) also informally named as such by NASA.
|-
| Coronary artery disease
| Also known as {{w|ischemic heart disease}}, which causes degradation of heart tissue. The region identified in the comic looks less 'healthy' (is darker and more ragged) compared to the rest of the 'Heart', which Randall suggests is caused by the disease.
|-
| Mount Mons
| Referring to the general practice of naming extraterrestrial mountains {{w|Mons (planetary nomenclature)|"X Mons"}} (e.g. {{w|Olympus Mons}}, a mountain on Mars and the largest mountain in the Solar System), as well as naming terrestrial mountains "Mount X". Since "mons" is Latin for "mountain", the feature's suggested name translates as "Mount Mountain".
|-
| Charging socket
| A terrain feature suitable for connecting an outside source of electricity for the benefit of implied internal batteries. Compare "dock connector," below.
|-
| Cracks (beginning to hatch)
| Implying that Pluto is some manner of giant egg. Possibly a reference to the ''Doctor Who'' episode ''Kill the Moon'', in which the Moon is revealed to be an egg from which a monster is hatching. An 2014 article from ''The Onion'', [http://www.theonion.com/article/moon-finally-hatches-36414 "Moon Finally Hatches,"] makes the same joke. Also possibly a reference to ''The Light Fantastic'', a ''Discworld'' novel in which similar objects are revealed to be the eggs of the world turtle.
|-
| Scars from predator attacks
| Since it's all-caps, we can't tell if "PREDATOR" is a proper noun, but this is possibly a reference to the movie series ''{{w|Predator (franchise)|Predator}}'', about a race of aliens who hunt other beings for sport. Alternatively, a planetary predator may have previously scarred Pluto.
|-
| Reset button
| The structure indicated is a small black dot (at least at this distance this picture was taken). Reset buttons on home electronics are often small buttons or holes used to reset the software of the electronic device.
|-
| Megaman
| One of a number of pareidolic features Randall has outlined, this one in the shape of a {{w|Mega_Man_(character)|popular video game protagonist.}}

|-
| Debate Hole

Where we're putting all the people still arguing about Pluto's planet status
| Pluto was reclassified as a {{w|dwarf planet}} rather than a {{w|planet}} following the latter term's controversial {{w|redefinition in 2006}} by the {{w|International Astronomical Union}}. Arguments about the classification continue to pop up. The same argument is referenced in the title text.
|-
| Area missed during ironing
| The area indicated is near the {{w|Terminator (solar)|terminator}} and shows some intriguing topographic relief.
|-
| Probably Benign
| A {{w|neoplasm}} or tumor is an abnormal growth of tissue. Randall is suggesting that the abnormal region near the heart has been evaluated by a doctor and determined to be {{w|Benign tumor|benign}}.
|-
| Chocolate frosting
| Suggests the discrepancy in color over Pluto's surface may be a function of what cake frosting was used where.
|-
| Vanilla frosting
| As above, suggests the discrepancy in color over Pluto's surface may be a function of what cake frosting was used where.
|-
| Border of pride lands
| A reference to the Disney animated feature ''The Lion King.'' In the movie, the Pridelands is the bright and prosperous region ruled by the Lion King while a dark territory beyond its border is controlled by hyenas. The border identified in the comic corresponds with a feature NASA calls the "whale's tale," with the rest of the whale being the large dark splotch.
|-
| Hyena country
| A continuation of the ''Lion King'' reference above.
|-
| Dock connector
| From the point of view of the photograph, this feature of Pluto is at the planet's "bottom," where iPod dock connectors are. Compare "charging socket," above.
|}

==Transcript==
:'''PLUTO'''
:Some of the features already identified in today's ''New Horizons'' image

:[Many marks on the image of Pluto follow:]

:Candy shell
:Frontal bone
:Grease stains
:Bugs
:JPEG plumes
:Full text of the wikipedia article on pareidolia
:Bullet holes
:New Netherlands
:Disputed territory
:Snake pit
:Tadpole
:Pluto dinosaur extinction crater
:Kuiper beltloops
:Serenity
:Ghost
:Dinosaur
:The good part
:Moon bud
:Scars from predator attacks
:Reset button
:Megaman
:Charging socket
:Cracks (beginning to hatch)
:Plug (inflating/deflating)
:HEART
::Mount Mons
::Coronary artery disease
:Debate hole
::Where we're putting all the people still arguing about Pluto's planet status
:Chocolate frosting
:Probably benign
:Vanilla frosting
:Dock connector
:Border of pride lands
:Hyena country
:Area missed during ironing

:Image credit: NASA/JHUAPL/SWRI - click for original

{{comic discussion}}
[[Category:Space]]
[[Category:Astronomy]]