explain xkcd - User contributions [en]

2609: Entwives

2022-04-21T22:18:44Z

Mmchch: /* Explanation */ Minor additional commentary on the "accuracy" of the comic.

{{comic
| number = 2609
| date = April 20, 2022
| title = Entwives
| image = entwives.png
| titletext = No, we actually do have a woman who's basically part of our fellowship. She lives in Rivendell, you wouldn't know her.
}}

==Explanation==
In {{w|The Lord of the Rings}}, the {{w|Ent|Ents}} are a species of tree-like humanoids, such as the one depicted in this comic. Part of the backstory of the Ents is that all of the women of their species (the Entwives that this comic is named for) had disappeared thousands of years before. Their sexes had lived in separate locations, and eventually, when the male Ents went to visit the Entwives, the latter were seemingly nowhere to be found. The Ents have been searching for their lost mates ever since. The loneliness of the Ents' all-male society is considered a great tragedy in their culture.

This comic uses that plot point to satirically comment on the extreme gender imbalance of the cast of Lord of the Rings; when presented with the all-male Fellowship of the Ring, the Ent assumes that they must come from a culture afflicted by a similar tragedy. In reality, of course, the dwarves (to an extent), elves, hobbits, and men all have a roughly even gender ratio. The total absence of women from the fellowship is presumably due to strict gender roles in their society which excludes women from an adventuring party. In a broader sense, this is likely a commentary on how few female characters there are the trilogy overall. This is likely due to the cultural biases of the era in which the novels were written, where female characters (if included at all) were often relegated to supporting roles.

The clickable link on the image leads to a [https://www.youtube.com/watch?v=mt2qCjL6-n4 video claiming to show the singular scene where two women interact], which is there to emphasize how few women there are in the franchise. The inclusion of this clip may be a reference to the {{w|Bechdel test}}, a metric for judging the representation of women in a piece of media that requires two women to have a conversation about something other than a man. Whether this three-and-a-half-word exchange is sufficient to pass the test is debatable.

The title-text most likely refers to the character of Arwen; while somewhat important to the story, she is nowhere near on the level of the Fellowship, and even if she were, a single important woman wouldn't counterbalance the heavily male-centric storytelling. The way that the title text is phrased is a reference to the proverbial (and implicitly imaginary) "{{tvtropes|GirlfriendInCanada|Girlfriend in Canada}}," a trope in which a single character claims to have a girlfriend that their friends wouldn't know "because she lives in Canada" (or some other sufficient separation such as "goes to another school"), when in reality the reason that nobody else has met her is because she doesn't exist. {{w|Canada}} is one of the United States' two neighboring countries, making it a potentially plausible place for some American's long-distance girlfriend to live, and presumably the Fellowship consider the Elf kingdom to be sufficiently distant to allow the Ent to accept the plausibility of the statement without any further delving into potentially awkward details.

The image is inaccurate inasmuch as it shows three hobbits: during the Ents' interactions with the Fellowship, two of the four hobbits (Frodo and Sam) were elsewhere in Middle Earth.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}

:[Ent Man stands to the left, facing right. Aragorn, Gimli, Legolas (holding a bow), and three hobbits stand to the right of Ent Man, facing him.]
:Ent Man: Alas, there are no Ent women. The Entwives all vanished in the second age, during Sauron's war.
:Aragorn: I'm so sorry.
:Ent Man: And what about you all? Same story, I assume?
:Aragorn: Huh? No, what do you mean?

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

2079: Alpha Centauri

2018-12-03T04:04:56Z

Mmchch: Typos

{{comic
| number = 2079
| date = November 30, 2018
| title = Alpha Centauri
| image = alpha_centauri.png
| titletext = And let's be honest, it's more like two and a half stars. Proxima is barely a star and barely bound to the system.
}}

==Explanation==
{{incomplete|Created by a SOLAR SAIL. It would be good to enumerate similar projects. Do NOT delete this tag too soon.}}
{{w|Alpha Centauri}} is the closest star system to our solar system, being 4.37 {{w|light-year}}s away. As such, there are numerous ongoing plans and projects to journey to, and explore the star system, especially since {{w|Proxima Centauri b}} was found in 2016 to possibly have liquid water oceans and a very thin atmosphere. Ponytail announces such a project using a {{w|Voyager program|Voyager}}-like probe.

However, the offscreen person is against her idea, for the strange logic that "Alpha Centauri sucks". He says that he looked "online" and that the system "only has three stars". This is a pun regarding online reviews. Online rating systems, such as {{w|Yelp}}, often use {{w|Star (classification)|star rating system}}s, with more stars indicating higher quality, up to an arbitrary maximum, such as five stars to indicate the best rating. Thus 3 stars out of 5 stars in a 5-star rating system would theoretically be a "middling" rating, equating to a C grade, whereas in a 10-star rating system 3 stars out of 10 stars would be below mediocre quality. The Alpha Centauri star system has 3 ''physical'' {{w|star}}s: Alpha Centauri A, Alpha Centauri B, and Proxima Centauri. The offscreen person has misconstrued this fact of the system as some kind of review.

A previous comic, [[1098: Star Ratings]], points out that star ratings below 4 out of 5 tend to be seen as "crap".

The title text furthers the pun. Some online star rating systems also allow partial stars, such as a half-star, to allow more precision in rating (e.g. rating 2.5 stars instead of being forced to chose 3 stars or 2 stars), or display an average collective rating as partial stars (e.g. showing 2.5 stars when five people have rated 3 stars and five people have rated 2 stars). Alpha Centauri's "half star" refers to Proxima Centauri, a {{w|red dwarf}}, which is a type of low-mass star. According to the offscreen person, this barely qualifies it to be a star. Furthermore, Proxima Centauri is nearly 13,000 AU (0.21 light years) away from the other 2 stars in the system, so it was long unknown whether Proxima Centauri was gravitationally bound to the Alpha Centauri star system.

===Calculations===
All numbers are rounded after subsequent calculations.

4.367 light years / 35 years = 0.12477 light years/year

0.12477 light years/year * 5.879e+12 miles/light year = 733,484,000,000 miles/year

733,484,000,000 miles/year / 365 days/year / 24 hours/day = 83,000,000 Miles/hour / 1.60934 miles/kilometer = 134,000,000 Kilometers/hour

According to [https://www.space.com/41447-parker-solar-probe-fastest-spacecraft-ever.html space.com] the fastest spacecraft ever will be the Parker Solar Probe which will reach 430,000 mph (692,000 km/h) as it reaches its closest point orbiting the sun. This is just over half of 1% of the needed speed of the Alpha Centauri vehicle proposed in the comic. The Voyager 1 spacecraft, launched in 1977, is currently traveling at about 38,000 mph (61,000 km/h).

The above math assumes a constant speed, and requires a speed of ~0.0001c. Assuming a constant acceleration from rest (non-relativistic math follows):

35*365.25*24*60*60 = 1.10e+9 seconds in 35 years

4.367 * 5.879e+12 = 2.57e+13miles, 4.13e+13 km, 4.13e+16 m.

x = 1/2*a*t2

a = 2*x*t -2

Assuming constant acceleration to the halfway point and constant deceleration to the destination, (otherwise you streak through the system, barely observing anything):

ttrip = 2*thalfway

a = 2*2.06e+16*(5.50e+8) -2 = 0.136 m/s2, roughly 1/80 gravity.

vhalfway = a*thalfway.

Top Speed: 75,000,000 m/s ~ 1/4*c.

Assuming E = F*d, 0.136*1*4.13e+16 = 5.37e15 Joules will be required for each kilogram carried to Alpha Centauri in 35 years.

This would require an unimaginable amount of mass for a conventional chemical rocket, and is a completely impractical power requirement for any sort of passive solar sail concept.

Further, the top speed is fast enough to require a recalculation using relativistic physics to model the problem. This means that the energy budget will need to increase, as the relativistic mass of the probe will increase, requiring more force (and thus more energy) to accelerate and decelerate near its top speed than this calculation returns.

[https://en.wikipedia.org/wiki/Breakthrough_Starshot Active], laser based propulsion methods require currently non-existent and purely specualtive laser and materials technologies, as well as a powerplant equivalent to 12,500 of the [https://www.power-technology.com/features/feature-largest-nuclear-power-plants-world/ World's Largest Nuclear Plant] to transport sub-gram masses on this timescale. This also assumes that any probes can be steered accurately enough across interstellar distances to come close enough to image with any resolution the bodies they will be passing at a non-trivial fraction of c.

Short of FTL travel or near-perfect mass-energy conversion technology, transporting more than a fraction of a gram of material to Alpha Centauri in a human lifetime will be unachievable. Short of an enormous breakthrough in power generation, transporting even a fraction of a gram is impossible.

Nonetheless, [http://breakthroughinitiatives.org/challenges/3 Breakthrough Starshot] is attempting to send many gram-sized probes to Alpha Centauri within the century. Following current technological trends, they expect the efficiency of laser-based propulsion to increase by launch time, allowing launches driven by an unreasonably-large-but-achievable amount of power. The top speed needed is halved by refraining from slowing at all at the destination: the probes will aim a distance away from the target, so that it traverses by slowly enough for a camera to rotate and track it, even at near-light speeds. To account for error and space dust, the plan is to launch many tiny probes simultaneously. They may only be able to accomplish their goal if they can get enough funding to actually affect the global economy enough to make the technologies they require more efficient to produce. Launches would additionally burn incredible quantities of natural gas.

==Transcript==
:[Ponytail stands on a podium giving a presentation in front of a slide with an image of a [https://wikipedia.org/wiki/Voyager_1 Voyager-like] spacecraft.]
:Ponytail: Our probe can reach Alpha Centauri in under 35 years.
:Offscreen voice: We should go somewhere else. Alpha Centauri sucks.
:Ponytail: Huh? It's the closest, most convenient system!
:Offscreen: Yeah, but I checked online and it only has three stars.

{{comic discussion}}

[[Category:Comics featuring Ponytail]]
[[Category:Space probes]]
[[Category:Online reviews]]

2010: Update Notes

2018-06-25T05:37:51Z

Mmchch: Typo

{{comic
| number = 2010
| date = June 22, 2018
| title = Update Notes
| image = update_notes.png
| titletext = v3.0.2: Hey, if anyone still using this app is headed to the beach, can you stop at 4th and River St and grab the sunscreen from my car? Trunk should be unlocked. Thanks!
}}

==Explanation==
{{incomplete|Created by an APP - Please change the changelog when editing this page. Do NOT delete this tag too soon.}}
Update notes or {{w|release notes}} are notes (or documents) released when software has been updated, to inform the user of any important changes to the software.

In this comic, Randall and his friend are using release notes of their {{w|Mobile application|app}}s as a form of chat service, instead of actual software change information. He says this is possible because the two apps are no longer being maintained, so theoretically, there are not many people using the app who would read the update / change notes. Incidentally, one can still argue that the chat is still technically update notes, only instead of updating users on what has changed about an app, it is now giving Randall and his friend status "updates".

This comic has a similar theme as https://xkcd.com/1305/ (Undocumented Feature) both use old software forums as a chat application.

This "chat service" would not be in real time, so presumably, Randall and his friend would have to be constantly checking each other's apps to see if there are updates.

On the "stars" app, the last "actual" notes says "Introduced bugs and degraded performance". This is a typical change, but not a change that a software developer would want to inform a user.

The comic also refers to a meteor shower occurring in August, most likely the {{w|Perseids|Perseid meteor shower}}.

The title text says that Randall, who is at the beach, has left his {{w|sunscreen}} in his car, but that the {{w|Trunk (car)|trunk}} is unlocked, for whoever is still reading the updates for this app. This may invite the attention of thieves, who are now informed that Randall's trunk is unlocked. However they may not know what city Randall lives in, and conversely readers of the release notes could be anywhere in the world so most are probably not in a position to physically make contact with Randall's car.

This comic could be seen as a subtle reference to how plain sight communication such as gang codes and steganography are used by people, possibly out of coerced necessity, to communicate information both deniably and publicly. It is likely that this often happens in real app update messages in real life. This kind of communication would more realistically allow a criminal worker to communicate with a contact point without endangering their anonymity by associating with them directly.

This comic could also be poking fun at the non-descriptive updates many popular apps post in the "What's new" or change log. One example of this would be the Uber app stating "We update the app as often as possible" as a "new" feature every update. Apple recently changed AppStore guidelines[https://developer.apple.com/app-store/review/guidelines/#accurate-metadata] to require clear descriptions of new features and product changes, effectively putting an end to the problem Randall is highlighting.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:[There are two panels that show smartphone-esque screens with two different apps with different update notes, showing a conversation between two people. New updates are added to the top, so to follow the conversation flow one would start from the bottom and alternate between the second app and the first one.]

:[The first app's icon is an "A" symbol.]
:Updates

:Version 3.0.1
:June 22, 2018

:Update Notes:

:v3.0.1
:I'm actually off work Monday so that's perfect.

:v3.0
:Oh, that sounds fun! What night?

:v2.8.31
:Are you around this weekend? We're heading to the beach.

:v2.8.3
:Hey Mike, you there?

:[The second app's icon consists of three stars.]
:Updates

:Version 7.0
:June 22, 2018

:Update Notes:

:v7.0
:It peaks August 12-13th.

:v6.8.16
:Sorry, no, going to a wedding. But do you want to camp out for the meteor shower in August?

:v6.8.15
:Yeah, what's up?

:v6.8.14
:Introduced bugs and degraded performance[.]

:[Caption below the panels:]
:My friend and I both have apps we've stopped maintaining, so we just use the updates to chat.

For convenience, here are the update notes in order of release [note that the first comment is not part of the conversation]:

"A" app (v6.8.14): Introduced bugs and degraded performance[.]

3-star app (v2.8.3): Hey Mike, you there?

A (v6.8.15): Yeah, what's up?

3-star (v.2.8.31): Are you around this weekend? We're heading to the beach.

A (v6.8.16): Sorry, no, going to a wedding. But do you want to camp out for the meteor shower in August?

3-star (v3.0): Oh, that sounds fun! What night?

A (v7.0): It peaks August 12-13th.

3-star (v3.0.1) I'm actually off work Monday so that's perfect.

{{comic discussion}}

2011: Newton's Trajectories

2018-06-25T05:29:13Z

Mmchch: Velocity is the relevant parameter here rather than force.

{{comic
| number = 2011
| date = June 25, 2018
| title = Newton's Trajectories
| image = newtons_trajectories.png
| titletext = With just one extra line, he could have anticipated the 2003 film The Core, but some things are too audacious for even the greatest visionaries.
}}

==Explanation==
{{incomplete|Created by a cannonball - Please change this comment when editing this page. Do NOT delete this tag too soon.}}
The comic shows a sphere, representing the Earth, with three sets of what appear to be spaceships on three trajectories. One set is released with sufficient velocity to remain in a stable (elliptical and not circular in theory as they are not shot horizontally) orbit, while the other two fall towards the Earth. This is a replica of Newton's famous thought experiment involving a cannon on a high mountain, which demonstrates the effects of gravity on objects orbiting the Earth.

Here, Newton's thought experiment is used to make the figurative and at the same time literal observation that a slight variation in parameter (impetus of the push) leads to totally different results. Society can choose the way of peaceful colonization of space and be able to explore the stars. Or it can choose to wage war and send intercontinental ballistic missiles (ICBMs) on a crash course and end the human civilisation in fire.

Some - e.g. Elon Musk or Stephen Hawking and probably Arthur C. Clarke prominently - think or thought, respectively, the only chance of the human species to survive on long-term is to go to other planets.

The title text alludes to the film The Core in which the trajectory would go straight to the center of the earth. This would be only possible, if you also change the angle (to straight upwards or straight downwards) and not only the force or by steering during the flight/the drill.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}

{{comic discussion}}