https://www.explainxkcd.com/wiki/api.php?action=feedcontributions&user=172.68.189.91&feedformat=atomexplain xkcd - User contributions [en]2020-01-24T16:45:41ZUser contributionsMediaWiki 1.30.0https://www.explainxkcd.com/wiki/index.php?title=538:_Security&diff=176760538: Security2019-07-16T15:50:26Z<p>172.68.189.91: /* Explanation */</p>
<hr />
<div>{{comic<br />
| number = 538<br />
| date = February 2, 2009<br />
| title = Security<br />
| image = security.png<br />
| titletext = Actual actual reality: nobody cares about his secrets. (Also, I would be hard-pressed to find that wrench for $5.)<br />
}}<br />
<br />
==Explanation==<br />
The "crypto nerd" would be concerned with strongly encrypting data on their personal machine. This would conceivably come in handy when "villains" attempt to steal information on his computer. The crypto nerd imagines that due to his advanced encryption, the crackers will be ultimately defeated. [[Randall]] suggests that in the real world, people with the desire to access this information would simply {{w|Rubber-hose cryptanalysis|use torture}} to coerce the nerd to give them the password. Both panels also reference the amount of money used to access the data. In the first the villain is willing to use millions of dollars to construct a {{w|TWIRL|super computer}}, while in the second, he simply uses a $5 wench. The comic effectively states, completely accurately, that the weakest part of computer security is usually not the computer, but the user.<br />
<br />
{{w|RSA (algorithm)|RSA}} is a commonly used public key encryption method. Current standards typically use 1024, 2048, and (more recently) 4096 {{w|Key size|bit keys}}. These encryption methods are not yet (feasibly) breakable. A 4096-bit key will remain unbreakable for the foreseeable future.<br />
<br />
The title text pokes fun at typical users, who do not have data that would be worth anything to anyone but themselves. Therefore, it is unlikely that the above situation would ever occur. Additionally, the wench used in the second panel is large, and presumably more than the $5 referenced by the thug.<br />
<br />
==Transcript==<br />
:A Crypto nerd's imagination:<br />
:[Cueball is holding a laptop, and his friend is examining it.]<br />
:Cueball: His laptop's encrypted. Let's build a million-dollar cluster to crack it.<br />
:Friend: No good! It's 4096-bit RSA!<br />
:Cueball: Blast! Our evil plan is foiled!<br />
<br />
:What would actually happen:<br />
:[Cueball is holding a piece of paper and giving his friend a wrench.]<br />
:Cueball: His laptop's encrypted. Drug him and hit him with this $5 wrench until he tells us the password.<br />
:Friend : Got it.<br />
<br />
{{comic discussion}}<br />
[[Category:Comics featuring Cueball]]<br />
[[Category:Cryptography]]</div>172.68.189.91https://www.explainxkcd.com/wiki/index.php?title=2174:_First_News_Memory&diff=1764252174: First News Memory2019-07-10T19:21:40Z<p>172.68.189.91: Challenger explanation.</p>
<hr />
<div>{{comic<br />
| number = 2174<br />
| date = July 10, 2019<br />
| title = First News Memory<br />
| image = first_news_memory.png<br />
| titletext = Psychology researchers say our 'flashbulb' memories of big events can be unreliable, but I clearly remember watching live on CNN as Challenger crashed into and destroyed the Berlin Wall.<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by a FAULTY FIRST NEWS MEMORY. Please mention here why this explanation isn't complete. Do NOT delete this tag too soon.}}<br />
The Challenger exploded in 1986, so Harry's teacher was not showing them the launch live.<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
<br />
{{comic discussion}}</div>172.68.189.91https://www.explainxkcd.com/wiki/index.php?title=Talk:2173:_Trained_a_Neural_Net&diff=176386Talk:2173: Trained a Neural Net2019-07-09T23:40:14Z<p>172.68.189.91: reply</p>
<hr />
<div><!--Please sign your posts with ~~~~ and don't delete this text. New comments should be added at the bottom.--><br />
<br />
Of course it's cheating as human's neural nets came pre-trained. I mean, unless you trained infant to do it, and even then, some things in image recognition are hardwired. In any contest between modern software and infant in face recognition or "is that face happy" recognition, I'm betting on infant. -- [[User:Hkmaly|Hkmaly]] ([[User talk:Hkmaly|talk]]) 21:03, 8 July 2019 (UTC)<br />
:Face recognition might be innate, but higher level tasks are not. You're not born knowing how to ride a bicycle or do algebra (there may be some simple counting circuits in the brain), your neural network has to be trained so you can do these.[[User:Barmar|Barmar]] ([[User talk:Barmar|talk]]) 22:04, 8 July 2019 (UTC)<br />
<br />
Ahh -- a short and sweet comic and explanation! I'd propose not bloating the explanation too much; the joke has been explained perfectly fine already. [[Special:Contributions/172.68.51.16|172.68.51.16]] 22:16, 8 July 2019 (UTC)<br />
<br />
Perhaps we should just all adhere to Randall's own advice in [[1475|1475:Technically]]:<br />
<br />
:'My life improved when I realized I could just ignore any sentence that started with "technically."'<br />
<br />
<br />
[[Special:Contributions/162.158.154.115|162.158.154.115]] 11:36, 9 July 2019 (UTC)<br />
:But this one doesn't start that way. [[Special:Contributions/141.101.99.77|141.101.99.77]] 14:41, 9 July 2019 (UTC)<br />
:Technically correct is only technically the best kind of correct during the all-but two week window when astrology doesn't work. [[Special:Contributions/172.68.141.82|172.68.141.82]] 18:13, 9 July 2019 (UTC)<br />
<br />
Yay! We trained a neural net to explain XKCD [[User:Elektrizikekswerk|Elektrizikekswerk]] ([[User talk:Elektrizikekswerk|talk]]) 13:23, 9 July 2019 (UTC)<br />
<br />
I'm not convinced that the paragraph on the neural net for answering questions about Wikipedia content is helpful at explaining the comic, but I am convinced that including 6 separate links within that short paragraph is entirely disruptive to that goal. Either the quantity of links should be severely curtailed or the paragraph needs to be removed from the explanation! [[User:Ianrbibtitlht|Ianrbibtitlht]] ([[User talk:Ianrbibtitlht|talk]]) 19:38, 9 July 2019 (UTC)<br />
:I'm a little concerned that you called it spam, given Randall's affinity for Wikipedia, and it being the best example. Can we workshop [https://www.explainxkcd.com/wiki/index.php?title=2173%3A_Trained_a_Neural_Net&type=revision&diff=176369&oldid=176354 it here?] I am happy to replace the many links to one at an intermediate page, e.g.[https://phabricator.wikimedia.org/T166929#5319562] [[Special:Contributions/172.68.189.91|172.68.189.91]] 23:40, 9 July 2019 (UTC)</div>172.68.189.91https://www.explainxkcd.com/wiki/index.php?title=2035:_Dark_Matter_Candidates&diff=1616292035: Dark Matter Candidates2018-08-21T04:56:34Z<p>172.68.189.91: /* Explanation */</p>
<hr />
<div>{{comic<br />
| number = 2035<br />
| date = August 20, 2018<br />
| title = Dark Matter Candidates<br />
| image = dark_matter_candidates.png<br />
| titletext = My theory is that dark matter is actually just a thin patina of grime covering the whole universe, and we don't notice it because we haven't thoroughly cleaned the place in eons.<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Every section needs to be filled and explained. Do NOT delete this tag too soon.}}<br />
{{w|Dark matter}} is a hypothetical form of matter used by the vast majority of astronomers to explain the far too high apparent mass of objects at large scales in our universe. In galaxies, stars are orbiting faster than the gravitational force of the sum of the masses of visible matter in the galaxy could cause, and entire galaxies are observed moving much faster around each other than their visible masses could explain. In galactic collisions, the mass can appear to separate from the visible matter, as if the mass doesn't collide but the visible matter does. A small handful of galaxies have been observed to not have this property, suggesting that it is a *thing* that a galaxy can have more or less of and is separable from. At scales of our solar system, those effects are too small and can't be measured. In cosmology, dark matter is estimated to account for 85% of the total matter in the universe.<br />
<br />
This comic gives a set of possibilities for what dark matter could possibly be, charted by mass from smallest (given in {{w|Electronvolt#Mass|electronvolts}}) to largest (given in kilograms). Masses in the range 10<sup>-15</sup> kg to 10<sup>-3</sup> kg are given in grams together with appropriate prefixes, while the ton takes the place of 10<sup>3</sup> kg.<br />
<br />
The joke in this comic is that the range of the mass of the possible particles and objects stretch over 81 powers of ten, with explanations suggested by astronomers covering only some portions of that range. [[Randall]] fills the gaps with highly absurd suggestions.<br />
<br />
;Axion<br />
An {{w|axion}} is a hypothetical elementary particle that might be a component of dark matter.<br />
<br />
;Sterile neutrino<br />
{{w|Sterile neutrino|Sterile neutrinos}} are hypothetical particles interacting only via gravity. It's an actual candidate for dark matter.<br />
<br />
;Electrons painted with space camouflage<br />
{{w|Electron|Electrons}} are fundamental particles which compose the outer layers of atoms. A large number of electrons in the galaxy would be relatively easy to detect, as they not only interact with light (which dark matter does not appear to), but also have a strong electric charge. Presumably, space camouflage is a positively-charged coating which prevents electrons from interacting with light. (Needless to say, this is not an actual candidate for dark matter.) The mass of an electron is about 0.5 MeV which fits well into the graph.<br />
<br />
;Neutralino<br />
A {{w|neutralino}} is a hypothetical particle from {{w|Supersymmetry|supersymmetry}}, it is an actual candidate for dark matter.<br />
<br />
;Q-ball<br />
In theoretical physics, a {{w|Q-ball}} is a stable group of particles. It's an actual candidate for dark matter.<br />
<br />
(In billiards, a cue ball is the white (or yellow) ball hit with the cue in normal play. In addition, [[Cueball]] is the name explainxkcd uses for the most common xkcd character.)<br />
<br />
;Pollen<br />
{{w|Pollen}} is a joke candidate, though people with seasonal allergies may suspect that the universe is genuinely made up entirely of pollen in the springtime. <br />
<br />
;No-See-Ums<br />
{{w|Ceratopogonidae|No-See-Ums}} are a family (Ceratopogonidae) of small flies, 1–4 mm long, that can pass through most window screens. Another joke candidate.<br />
<br />
;Bees<br />
Insects of the clade {{w|bee|Antophila}} are major pollinators of flowering plants. In recent years {{w|Colony collapse disorder|bees have been disappearing}} at an alarming rate; {{w|The Stolen Earth|Doctor Who explained}} that they are in fact aliens leaving Earth prior to a Dalek invasion.<br />
<br />
;8-balls<br />
In pool, the {{w|Pool (cue sports)|8-ball}} is a black ball numbered 8. It's a pun with Q-ball/cue ball. Unless undetected aliens have discovered billiards and become addicted to it, 8-balls are found only on Earth and are, hence, unlikely dark matter candidates.<br />
<br />
;Space Cows<br />
Cows are {{w|Bovinae|bovines}} extensively farmed on Earth for milk and meat. Although there is folklore concerning cows {{w|Hey diddle diddle|achieving circum-lunar orbits}}, not to mention their appearance on a {{w|Shindig (Firefly)|space western TV show}}, they have yet to be found elsewhere in the Universe. In the television show "Too Close for Comfort", one of the characters is the cartoonist of a comic strip called "Cosmic Cow".<br />
<br />
;Obelisks, Monoliths, Pyramids<br />
While those human constructions are huge on a human scale, they're negligible at universe-scale. It would take a large number of such constructions, distributed through space, to replicate the effects of dark matter; while a scenario could be envisioned where enough such constructs existed, with properties and distribution allowing them to match observations, this is obviously not a likely explanation.<br />
They often show up in fiction and pseudo-scientific literature as alien artifacts generating immense unknown power out of nowhere, with the most famous and influential example being the three monoliths from {{w|2001: A Space Odyssey (film)|2001: A Space Odyssey}} (with the largest having a mass of about 500,000 tonnes).<br />
<br />
;Black Holes ruled out by:<br />
{{w|Black hole|Black holes}} are known to occur in sizes of a few sun masses (about 10<sup>30</sup>-10<sup>31</sup> kg) as remnants of the core of former big stars, as well as in quite large sizes at the centers of galaxies (millions or even billions of sun masses). But recent gravitational wave detections indicate that black holes at 50 or 100 sun masses also exist, though their origin is still not understood. Randall doesn't mention this but some astronomers hope that these could fill at least a part of the gap. Regardless, they have been ruled out as a candidate for dark matter for various reasons Randall has listed.<br />
<br />
Except the last item, all range below the mass of the sun (2x10<sup>30</sup> kg) while the smallest known black hole is about four sun masses.<br />
* Gamma rays: If dark matter were black holes of this size, the black holes would be evaporating in bursts of {{w|Hawking radiation}}, and we'd see a buzz of gamma rays from every direction.<br />
* GRB lensing: {{w|Gamma-ray burst|Gamma-ray bursts}} (GRBs) are the brightest events in the universe and have been observed only in distant galaxies. While gravitational microlensing (see below) is an astronomical phenomenon, it doesn't make much sense here. GRBs are short (milliseconds to several hours) and are often detected only by space-borne sensors for gamma-rays -- rarely at any other wavelengths. Measuring lensing effects would be very difficult. This [https://arxiv.org/abs/1406.3102 paper] discusses the probability of detecting lensing effects caused by {{w|Dark matter halo|galactic halo objects}} among the known GRBs given sufficient objects to represent the missing mass. <br />
* Neutron star data: {{w|Neutron star|Neutron stars}} aren't black holes, but they're also very small highly compact objects at about 1.4-2.16 solar masses. While black holes can't be observed directly, neutron stars are detectable in many wavelengths. The number of them gives a clue about the number of black holes close to the mass of the sun, a number which is far too low to make up dark matter.<br />
* Micro lensing: {{w|Gravitational microlensing}} is a gravitational lens effect, (the path of radiation is changed by passing through space bent by nearby mass). This was predicted by Einstein's {{w|General Relativity|Theory of General Relativity}} and was first confirmed in 1919 during a solar eclipse, when a star which was nearly in line with the sun appeared closer to the sun than usual. Astronomers have found many so called {{w|Einstein ring|Einstein rings}} or Einstein crosses where a massive object in front of other galaxies bends the light toward us. Those massive objects may be black holes, but the number is far too low to explain dark matter.<br />
* Solar system stability: Our {{w|Solar system|solar system}} is 4.5 billion years old and has been very stable since shortly after its formation. If not, we wouldn't exist. If dark objects at 10<sup>24</sup> kg - 10<sup>30</sup> kg (mass of Earth up to mass of Sun) accounted for dark matter and were distributed throughout galaxies, there should be many of them in the vicinity of our solar system and the system wouldn't be stable at all.<br />
* Buzzkill Astronomers: Black holes above a certain size would be impossible to miss, due to the effects they have on nearby matter. But at the mass of some 10<sup>30</sup> kg there must be many supernova remnants we still haven't found.<br />
<br />
;Maybe those orbit lines on space diagrams are real and very heavy<br />
Diagrams of our solar system (or any planetary system) often show lines representing the elliptical paths the planet takes around its sun. These lines don't show real objects, though. Astronomers just draw them on pictures of the solar system to show where the planets move. If you draw a line on a map to give someone directions, that line isn't an object in real life; it's just on the map. If these lines were real, they would be ''huge'' (Earth's would be 940 million km long (2π AU) and Neptune's would be 28 ''billion'' kilometers long). [https://www.youtube.com/watch?v=0fKBhvDjuy0 Powers of Ten (1977)] gives a good sense of just how large these orbit lines need to be in order to be visible in space diagrams. If these orbit lines were also very dense, they would have a huge mass and could possibly account for the missing 85% of the mass in the universe. But they would also constantly be impaling the planets, including the Earth, which would be a problem. Their mass would also affect planetary motions in ways which we would detect. A related worry about space travel was expressed in previous centuries; it was thought that the planets were embedded within {{w|Celestial spheres|crystal shells}} (spheres or Platonic solids), and a rocket into space could smash the shells and send planets plummeting to Earth. Another joke candidate.<br />
<br />
;Title text<br />
The title text refers to the fact that space is just vast emptiness where a little bit of dirt could be overlooked. Actually the mean density of detectable matter in the universe, according to NASA, is equivalent to roughly [https://map.gsfc.nasa.gov/universe/uni_matter.html 1 proton per 4 cubic meters]. And because this matter is mostly located in galaxies -- and inside there in stars and clouds -- the space between is even more empty. For comparison, one gram hydrogen consists of {{w|Avogadro constant|6.022 x 10<sup>23</sup> atoms}}. Like at home wiping with a cleaning cloth in which we can see the dirt that wasn't clearly visible on the surface we have wiped, Randall believes that some few atoms more per cubic meter could stay undetected in the same way. This isn't true because in the space between galaxies astronomers can detect matter as it spreads over thousands or millions cubic light years. Atoms can't hide; there is always radiation.<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
<br />
:Dark matter candidates:<br />
:[A line graph is shown and labeled at left quarter in eV and further to the right in g together with some prefixes.]<br />
:[The labels read:]<br />
:µeV, meV, eV, keV, MeV, GeV, TeV, 10<sup>-18</sup>kg, ng, µg, mg, g, kg, TON, 10<sup>6</sup>kg, 10<sup>12</sup>kg, 10<sup>18</sup>kg, 10<sup>24</sup>kg, 10<sup>30</sup>kg<br />
<br />
:[All items are shown in bars ranging between two approximately values:]<br />
:< 1 µeV - 10 meV: Axion<br />
<br />
:1 eV - 10 keV: Sterile neutrino<br />
<br />
:0.5 MeV (exactly): Electrons painted with space camouflage<br />
<br />
:10 GeV - 10 TeV: Neutralino<br />
<br />
:100 TeV - 10<sup>-17</sup> kg: Q-ball<br />
<br />
:1 ng - 100 ng: Pollen<br />
<br />
:0.1 mg - 1 mg: No-See-Ums<br />
<br />
:10<sup>-1</sup> g (exactly): Bees<br />
<br />
:10 g - 100 g: 8-balls<br />
<br />
:100 kg - TON: Space cows<br />
<br />
:TON - 10<sup>9</sup> kg: Obelisks, monoliths, pyramids<br />
<br />
:10<sup>9</sup> kg - 10<sup>33</sup> kg: Black holes ruled out by:<br />
::10<sup>9</sup> kg - 10<sup>13</sup> kg: Gamma rays<br />
::10<sup>13</sup> kg - 10<sup>17</sup> kg: GRB lensing<br />
::10<sup>15</sup> kg - 10<sup>22</sup> kg: Neutron star data<br />
::10<sup>21</sup> kg - 10<sup>30</sup> kg: Micro lensing<br />
::10<sup>24</sup> kg - 10<sup>30</sup> kg: Solar system stability<br />
::10<sup>30</sup> kg - 10<sup>33</sup> kg: Buzzkill astronomers<br />
<br />
:10<sup>33</sup> kg - >10<sup>36</sup> kg: Maybe those orbit lines on space diagrams are real and very heavy<br />
<br />
{{comic discussion}}<br />
<br />
[[Category:Science]]<br />
[[Category:Physics]]<br />
[[Category:Astronomy]]<br />
[[Category:Line graphs]]</div>172.68.189.91https://www.explainxkcd.com/wiki/index.php?title=2034:_Equations&diff=1614602034: Equations2018-08-19T01:46:00Z<p>172.68.189.91: /* Simplified Explanations */ Added another observation about pi in the number theory equation.</p>
<hr />
<div>{{comic<br />
| number = 2034<br />
| date = August 17, 2018<br />
| title = Equations<br />
| image = equations.png<br />
| titletext = All electromagnetic equations: The same as all fluid dynamics equations, but with the 8 and 23 replaced with the permittivity and permeability of free space, respectively.<br />
}}<br />
<br />
This comic gives a set of equations supposedly from different areas of science in mathematics, physics, and chemistry. To anyone not familiar with the field in question they look pretty similar to what you might find in research papers or on the relevant Wikipedia pages. To someone who knows even a little about the topic, they are clearly very wrong and only seem even worse the more you look at them. In many disciplines, the mathematical description of a large area is summed up in a small number of equations, such as Maxwell's equations for electromagnetism. In similar fashion, the equations here purport to encompass the whole of their given field.<br />
<br />
==Simplified Explanations==<br />
{{incomplete|Created by a mere human. Do NOT delete this tag too soon.}}<br />
<br />
;All kinematics equations<br />
Kinematics is the study of the motion of objects. More specifically, it describes how the location, velocity, and acceleration of an object vary over time. The equation shown contains two of these standard kinematic variables, velocity ''v'' and time ''t'', in addition to several quantities (''E'', ''K<sub>0</sub>'', and ''&rho;'') that are completely unrelated to kinematics.<br />
<br />
;All number theory equations<br />
Number theory is a branch of mathematics concerned primarily with the study of integers. However, the equation shown contains the non-integer number ''e'' (approximately equal to 2.718...), and uses the Greek letter ''&pi;'' as an integer, even though ''&pi;'' is almost exclusively used in mathematics to denote the well-known, ''non''-integer number 3.14159.... It also treats ''&pi;'' as a variable component in a summation, rather than as a constant.<br />
<br />
;All chemistry equations<br />
This shows a parody of the common example chemistry equation of burning Methane and Oxygen (with added heat), to form water and carbon dioxide. However in this form "HEAT" is an actual molecule, rather than simply indicating the presence of heat to start the reaction. Thus the equation is modified to incorporate the fictional "HEAT" into the reaction. While the H in "HEAT" is the chemical symbol of the element hydrogen, none of the letters E, A, or T are symbols of any actual elements.<br />
<br />
TODO: other simplified explanations.<br />
<br />
==Technical Explanations==<br />
{{incomplete|Created by an EQUATION. Do NOT delete this tag too soon.}}<br />
<br />
<br />
<br />
;All kinematics equations<br />
:<math>E = K_0t + \frac{1}{2}\rho vt^2</math><br />
{{w|Kinematics}} describes the motion of objects without considering mass or forces.<br />
<br />
This equation here literally states: "Energy equals a constant <math>K_0</math> multiplied by time, plus half of density multiplied by speed multiplied by time squared". <br />
<br />
The first term here is hard to interpret: it could be correct if <math>K_0</math> is a constant power applied to the system, but this symbol would more normally be used to denote an initial energy, in which case multiplying by <math>t</math> would be wrong. Alternatively, the term is similar to <math>k_B T</math> (sometimes written as ''kT''), a term that often appears in {{w|Statistical_mechanics|statistical mechanics}} equations, where ''k<sub>B</sub>'' (or ''k'') is {{w|Boltzmann_constant|the Boltzmann constant}}, and ''T'' is the {{w|Thermodynamic_temperature|absolute temperature}}. In this latter case, the term would have units of energy, consistent with the left side of the equation.<br />
<br />
The second term looks similar to the kinetic energy term <math> \frac{1}{2}\rho v^2 </math> in [http://hyperphysics.phy-astr.gsu.edu/hbase/pber.html the Bernoulli equation] for fluids (or, more properly, the kinetic energy ''density'' in the fluid). <br />
<br />
The whole equation appears to be a play on the kinematics formula: <math>s = ut + \frac{1}{2}\ at^2</math>, where distance travelled (''s'') by a constantly accelerating object is determined by initial velocity (''u''), time (''t''), and acceleration (''a'')<br />
<br />
Kinematics is often one of the first topics covered in an introductory physics course, both at the high school and freshman college levels. As such, mixing in material from more advanced topics like statistical mechanics and the Bernoulli equation, even if done correctly, would be very confusing for a typical student learning kinematics.<br />
<br />
;All number theory equations<br />
:<math>K_n = \sum_{i=0}^{\infty}\sum_{\pi=0}^{\infty}(n-\pi)(i-e^{\pi-\infty})</math><br />
{{w|Number theory}} is a branch of mathematics primarily studying the properties of integers.<br />
<br />
Taken literally the equation says: "The nth K-number is equal to: the sum for all i from 0 to infinity, the sum for all pi from 0 to infinity; subtract pi from n, and multiply it with i minus e to the power of pi minus infinity". A twofold misconception can be seen here. The first is the reassignment of pi as a variable instead of the constant (3.14...). This might be a jab at how in number theory letters and numbers are used interchangeably, but where some letters are all of a sudden fixed constants. The second misconception is the use of infinity in the latter part of the formula. Naively this would signify that (with the reassigned pi values) the part in the power would range from minus infinity to zero. However, infinity is not a number and cannot be used as one without using a limit construct.<br />
<br />
;All fluid dynamic equations<br />
:<math>\frac{\partial}{\partial t}\nabla\cdot \rho = \frac{8}{23}<br />
\int\!\!\!\!\!\!\!\!\!\;\;\bigcirc\!\!\!\!\!\!\!\!\!\;\;\int<br />
\rho\,ds\,dt\cdot \rho\frac{\partial}{\partial\nabla}<br />
</math><br />
{{w|Fluid dynamics}} describes the movement of non-solid material. In particular for gases, the density <math>\rho</math> is often the most interesting quantity (for liquids, this is often just constant). A unique feature of fluid-dynamic equations is the presence of {{w|Advection|advection terms}}, which take the form of often strange-looking spatial derivatives. This equation turns this up to a new level by differentiating with respect to a differential operator <math>\nabla</math>, which does not make any sense at all. Also it has a contour integral which seems reminiscent to a closed-circle process like in a piston engine, but this does not really fit in the context (differential description of a gas), and it has a pair of {{w|Magic number (programming)|unexplained numbers}} <math>8</math> and <math>23</math>, probably alluding to the {{w|Heat capacity ratio|specific heat ratio}} which is often written out as the fraction <math>\tfrac{7}{5}</math>, whereas most other physics equations [[899: Number Line|avoid including any plain numbers higher than 4]].<br />
<br />
The title text stating that the electromagnetism equation is the same as the fluid dynamics equation, but with the arbitrary 8 and 23 replaced with the permittivity and permeability of free space is likely because electromagnetism equations often have relations to fluid dynamics, and because those two constants appear in the vast majority of electromagnetism equations.<br />
<br />
;All quantum mechanic equations<br />
:<math>|\psi_{x,y}\rangle = A(\psi) A(|x\rangle \otimes |y\rangle)</math><br />
{{w|Quantum mechanics}} is a fundamental theory in physics which describes nature at scales of atoms and below. It typically uses the {{w|Bra–ket notation|bra–ket notation}} in its formulae.<br />
<br />
This equation takes a state psi in the dimensions of x and y and equates it to an operator A performed on psi multiplied by the same operator performed on the tensor product of x and y. Since the state psi is already the tensor product of the states x and y, this is equivalent to performing the same unknown operator twice on psi, and unless this operator is its own inverse such as a bit-flip or Hermitian operator, this equation is therefore incorrect.<br />
<br />
;All chemistry equations<br />
:<math>\mathrm{CH}_4 + \mathrm{OH} + \mathrm{HEAT} \rightarrow \mathrm{H}_2\mathrm{O} + \mathrm{CH}_2 + \mathrm{H}_2 \mathrm{EAT}</math><br />
A {{w|Chemical equation|chemical equation}} represents a chemical reaction as a formula, with the reactant entities on the left-hand side, and the product entities on the right-hand side. The number of each element on the left side must match those on the right side. The energy produced or absorbed in this process is not included in that formula.<br />
<br />
This is a modification of the combustion of methane. The correct form is often taught and a good example problem but obviously there are more chemistry problems.<math>\mathrm{HEAT}</math> is normally shorthand for {{w|activation energy}}, but in Randall's version it's jokingly used as a chemical ingredient and becomes <math>\mathrm{H}_2\mathrm{EAT}</math>, taking the hydrogen atom freed by the combustion equation shown. The proper methane combustion equation would be: <math>\mathrm{CH}_4 + 2 \mathrm{O}_2 \rightarrow 2 \mathrm{H}_2\mathrm{O} + \mathrm{CO}_2</math><br />
<br />
;All quantum gravity equations<br />
:<math>\mathrm{SU}(2)\mathrm{U}(1) \times \mathrm{SU}(\mathrm{U}(2))</math><br />
This is more similar to expressions which appear in {{w|Grand_Unified_Theory|Grand Unified Theory}} (GUT) than general quantum gravity. Unlike some of the other equations, this one has no interpretation which could make it mathematically correct. This is similar to the notations used to describe the symmetry group of a particular phenomena in terms of mathematical {{w|Lie_Group|Lie Groups}}. A real example would be the Standard Model of particle physics which has symmetry according to <math>\rm{SU(3)\times SU(2) \times U(1)}</math>. Here, <math>\rm{SU}</math> and <math>\rm{U}</math> denote the special unitary and unitary groups respectively with the numbers indicating the dimension of the group. Loosely, the three terms correspond to the symmetries of the strong force, weak force and electromagnetism although the exact correspondence is muddied by symmetry breaking and the Higgs mechanism.<br />
<br />
Of course, an expression missing an "=" sign, is difficult to interpret as an "equation", because equations normally express an "equality" of some kind. Nobody knows whether Randal refers to a horse, zebra, donkey or other equine here. <br />
<br />
Randall's version clearly involves some similar groups although without the <math>\times</math> symbol it is hard to work out what might be happening. A term like <math>\rm{SU(U(2))}</math> has no current interpretation in mathematics, if anyone thinks otherwise and possibly has a solution to the quantum gravity problem they should probably get in touch with someone about that.<br />
<br />
;All gauge theory equations<br />
:[[File:All gauge theory equations.png]]<br />
In physics, a {{w|Gauge theory|gauge theory}} is a type of field theory which is invariant to local transformations. The term gauge refers to any specific mathematical formalism to regulate redundant degrees of freedom.<br />
<br />
This equation looks broadly similar to the sorts of things which appear in gauge theory such as the equations which define {{w|Yang–Mills_theory#Quantization|Yang-Mills Theory}}. By the time physics has got this far in, people have normally run out of regular symbols making a lot of the equations look very daunting. The actual equations in this field rarely go far beyond the Greek alphabet though and no-one has yet to try putting hats on brackets. The appearance of many sub- and superscripts is normal (this links to the group theory origins of these equations) and for the layperson it can be impossible to determine which additions are labels on the symbols and which are indices for an {{w|Einstein_notation|Einstein Sum}}.<br />
<br />
The left-hand side <math>S_g</math> is the symbol for some {{w|Action_(physics)|action}}, in Yang-Mills theory this is actually used for a so-called "ghost action". On the right-hand side we have a large number of terms, most of which are hard to interpret without knowing Randall's thought processes (this is why real research papers should all label their equations thoroughly). The <math>\frac{1}{2\bar{\varepsilon}}</math> looks like a constant of proportionality which often appears in gauge theories. The factor of <math>i = \sqrt{-1}</math> is not unusual as many of these equations use complex numbers. The <math>\eth</math> symbol looks similar to a <math>\partial</math> partial derivative symbol especially as the {{w|Dirac_equation#Covariant_form_and_relativistic_invariance|Dirac Equation}} uses a slashed version as a convenient shorthand. <br />
<br />
The rest of the equation cannot be mathematically correct as the choice of indices used does not match that on the left-hand side (which has none). In particle physics subscripts (or superscripts) of greek letters (usually <math>\mu</math> or <math>\nu</math>) indicate terms which transform nicely under Lorentz transformations (special relativity). Roman indices from the beginning of the alphabet relate to various gauge transformation propetries, the triple index seen on <math>p^{abc}_v</math> would likely come from some <math>\rm{SU(3)}</math> transformation (related to the strong nuclear force). Since <math>S_g</math> has none of these (and is thus a scalar which remains constant under these operations), we would need the right-hand side to behave in the same way. Most of the indices which appear are unpaired and so will not result in a scalar making the equation very wrong. For those not familiar with this type of equation, this is similar to the mistake of messing up units, for instance setting a distance equal to a mass.<br />
<br />
;All cosmology equations<br />
:<math>H(t) + \Omega + G \cdot \Lambda \, \dots \begin{cases} \dots > 0 & \text{(Hubble model)} \\ \dots = 0 & \text{(Flat sphere model)} \\ \dots < 0 & \text{(Bright dark matter model)} \end{cases}<br />
</math><br />
This is a parody of equations defining the {{w|Hubble's_law#Derivation_of_the_Hubble_parameter|Hubble Parameter}} <math>H(t)</math> although it looks like Randall has become bored and not bothered to finish his equation. Such equations usually have several <math>\Omega</math> terms representing the contributions of different substances to the energy-density of the Universe (matter, radiation, dark energy etc.). In this context <math>G</math> could be Newton's constant and <math>\Lambda</math> is the cosmological constant (energy density of empty space) although seeing them appear multiplied and on the same footing as <math>H</math> is unusual (the dot is entirely unnecessary). Choosing to make <math>H</math> a function of time <math>t</math> and not of redshift <math>z</math> is also unusual.<br />
<br />
The second section looks like the inequalities used to show how the equation varies with the shape of the Universe, based on the value of the curvature parameter <math>\Omega_k</math>. A value of 0 indicates a flat Universe (this is more or less what we observe) while a positive /negative value indicates an open /closed curved Universe. Randall's choice of labels further makes fun of the field as both a flat sphere and bright dark matter are oxymoronic terms which would involve some rather strange model universes.<br />
<br />
;All truly deep physics equations<br />
:[[File:All truly deep physics equations.png]]<br />
<math>\hat H</math> is the Hamiltonian operator, which when applied to a system returns the total energy. In this context, U would usually be the potential energy. However, there is also a subscript 0 and a diacritic marking indicating some other variable. Much of physics is based on Lagrangian and Hamiltonian mechanics. The Lagrangian is defined as <math>\hat L = \hat K - \hat U </math> with K being the kinetic energy and U the potential. Hamiltonian mechanics uses the equation <math>\hat H = \hat K + \hat U </math>. The Hamiltonian must be conserved so taking the time derivative and setting it equal to zero is a powerful tool. The "principle of least action" allows most modern physics to be derived by setting the time derivative of the Lagrangian to zero.<br />
<br />
==Transcript==<br />
:[Nine equations are listed, three in the top row and two in each of the next three rows. Below each equation there are labels:]<br />
<br />
:E = K<sub>0</sub>t + 1/2 &rho;vt<sup>2</sup><br />
:All kinematics equations<br />
<br />
:K<sub>n</sub> = &sum;<sub>i=0</sub><sup>&infin;</sup>&sum;<sub>&pi;=0</sub><sup>&infin;</sup>(n-&pi;)(i-e<sup>&pi;-&infin;</sup>)<br />
:All number theory equations<br />
<br />
:&#x2202;/&#x2202;t &nabla; &sdot; &rho; = 8/23 (&#x222F; &rho; ds dt &sdot; &rho; &#x2202;/&#x2202;&nabla;)<br />
:All fluid dynamics equations<br />
<br />
:|&psi;<sub>x,y</sub>&#x232a; = A(&psi;) A(|x&#x232a;&#x2297; |y&#x232a;)<br />
:All quantum mechanics equations<br />
<br />
:CH<sub>4</sub> + OH + HEAT &rarr; H<sub>2</sub>O + CH<sub>2</sub> + H<sub>2</sub>EAT<br />
:All chemistry equations<br />
<br />
:SU(2)U(1) &times; SU(U(2))<br />
:All quantum gravity equations<br />
<br />
:S<sub>g</sub> = (-1)/(2&epsilon;&#x0304;) i &eth; (&#x302; &xi;<sub>0</sub> +&#x030a; p<sub>&epsilon;</sub> &rho;<sub>v</sub><sup>abc</sup> &eta;<sub>0</sub> )&#x302; f&#x0335;<sub>a</sub><sup>0</sup> &lambda;(&#x0292;&#x0306;) &psi;(0<sub>a</sub>)<br />
:All gauge theory equations<br />
<br />
:[There is a brace linking the three cases together.]<br />
:H(t) + &Omega; + G&sdot;&Lambda; ... <br />
:... > 0 (Hubble model)<br />
:... = 0 (Flat sphere model)<br />
:... < 0 (Bright dark matter model)<br />
:All cosmology equations<br />
<br />
:&#x0124; - u&#x0327;<sub>0</sub> = 0<br />
:All truly deep physics equations<br />
<br />
{{comic discussion}}<br />
<br />
[[Category:Science]]<br />
[[Category:Physics]]<br />
[[Category:Math]]<br />
[[Category:Chemistry]]<br />
[[Category:Astronomy]]</div>172.68.189.91https://www.explainxkcd.com/wiki/index.php?title=2033:_Repair_or_Replace&diff=1612572033: Repair or Replace2018-08-15T20:35:44Z<p>172.68.189.91: /* Explanation */</p>
<hr />
<div>{{comic<br />
| number = 2033<br />
| date = August 15, 2018<br />
| title = Repair or Replace<br />
| image = repair_or_replace.png<br />
| titletext = Just make sure all your friends and family are out of the car, or that you've made backup friends and family at home.<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by a BOY - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
<br />
This comic compares the repair of cars with that of computers or other similar electronic devices. <br />
<br />
Cueball, likely representing Randall, is in his car. He says that there is a weird sound, so Hairy, representing a car mechanic, asks him to lift his {{w|Hood (car)|hood}}, exposing the engine, to further identify the cause of the problem. Cueball then says that his hood latch, the lever used to open the hood, is also broken. The solution, according to Hairy, is to "replace" the car with a new car. In reality, fixing the catch on the hood is a simple task for a skilled mechanic and would not justify writing-off the car.<br />
<br />
When a car is malfunctioning, the usual response is to attempt to repair it. A car is designed so that many of the parts can be replaced or adjusted.<br />
<br />
By contrast, when a computer or electronic device is malfunctioning, it is often judged to be difficult to repair, and the usual action is to purchase a new device. Most parts are not designed to be replaceable, and if they fail it is normally cheaper to replace than repair. <br />
<br />
It would be extremely inefficient for a car dealership or mechanic to simply "replace" a car when there is a problem with it. Likewise, Randall asserts that it is also inefficient for electronic devices to be thrown away at the first sign of a problem, and not repaired.<br />
<br />
The title text refers to data stored on a computer or electronic device. Before replacing the device, it is recommended to remove and/or {{w|backup}} all your personal files, so that you have future access to them. Randall likens this to having your friends and family exit the vehicle, or making backup friends and family.<br />
<br />
;The economics<br />
Cars are much more expensive than computers or other electronic devices, and become obsolete less quickly. The point at which it becomes cheaper to purchase a new computer or phone rather than repair an old one comes much more quickly.<br />
<br />
Also, although the comic implies that replaced electronics are destroyed (like a car pushed into a pit), in fact they are often sent off to be repaired or refurbished elsewhere. This provides a better experience for the customer (they get a working device right away instead of waiting for repair) and is more efficient for the company (a consolidated repair facility can have the experience and equipment to repair a device much more quickly than at a retail location).<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
:[Cueball sits in a car arriving from the left while Hairy stands in front of it and points to a big black hole on the right behind him.]<br />
:Cueball: My engine's making a weird noise. Can you take a look?<br />
:Hairy: Sure, just pop the hood.<br />
:Cueball: Oh, the hood latch is also broken.<br />
:Hairy: Ok, just pull up to that big pit and push the car in. We'll go get a new one.<br />
<br />
:[Caption below the frame:]<br />
:I'm sure the economics make sense, but it still freaks me out how quick companies are to replace computing devices instead of trying to fix them.<br />
<br />
{{comic discussion}}<br />
<br />
[[Category:Comics featuring Cueball]]<br />
[[Category:Comics featuring Hairy]]<br />
[[Category:Computers]]</div>172.68.189.91https://www.explainxkcd.com/wiki/index.php?title=Talk:2029:_Disaster_Movie&diff=160962Talk:2029: Disaster Movie2018-08-08T18:50:10Z<p>172.68.189.91: </p>
<hr />
<div><!--Please sign your posts with ~~~~ and don't delete this text. New comments should be added at the bottom.--> <br />
DATASETS is one word. {{unsigned ip| 172.68.59.24}}<br />
:And ''data sets'' are two ;) (BTW: Please sign your posts) --[[User:Dgbrt|Dgbrt]] ([[User talk:Dgbrt|talk]]) 20:52, 6 August 2018 (UTC)<br />
:[https://en.oxforddictionaries.com/definition/data_set oxford] says it's data set(s) --[[User:Gusser93|Gusser93]] ([[User talk:Gusser93|talk]]) 21:36, 6 August 2018 (UTC)<br />
::Sorry for my sarcasm, both is possible as can be seen here at Wikipedia: {{w|Data set|A data set (or dataset) is a collection of data...}}. Oxford doesn't cover the US. And on the other hand {{w|Shapefile|shapefile}} is really a single valid term belonging to the geographical information system (GIS). --[[User:Dgbrt|Dgbrt]] ([[User talk:Dgbrt|talk]]) 22:08, 6 August 2018 (UTC)<br />
::On a modem, there is a pin signal called "DSR" for "Data Set Ready," which would suggest that IBM (I think the terminology started with them) thought it should be two words (sometime back in the 1960's). (Side note: The "data set" in this case was the modem itself; "set" being used in the context of "a bunch of components in a box", as in "TV set") (side note, part II: Grammerly is marking all the "data set"s here and suggesting they be written as "dataset") [[User:JamesCurran|JamesCurran]] ([[User talk:JamesCurran|talk]]) 18:30, 7 August 2018 (UTC)<br />
<br />
Not by any means an expert, so I don't want to remove it without commenting, but I don't think the section on why "GIS survey team" is unrealistic holds up - I know the ShoreZone project (http://www.shorezone.org/) on the US and Canadian west coast uses almost exactly that kind of scientists-in-helicopters methodology. [[Special:Contributions/172.68.174.100|172.68.174.100]] 01:54, 7 August 2018 (UTC)<br />
:That project sounds like it's collecting much more fine-grained data than simply coastal geometry - especially high resolution imagery, which does need to be taken from an aircraft. [[User:Stevage|Stevage]] ([[User talk:Stevage|talk]]) 02:54, 7 August 2018 (UTC)<br />
<br />
Cowboy Bebop, episode 24: "Hard Luck Woman." This is exactly what Radical Edward's father did. [[Special:Contributions/162.158.63.100|162.158.63.100]] 02:27, 7 August 2018 (UTC)<br />
<br />
Shapefiles are an actual format: .shp It is defined, released to the public and is the format that is used to share vector files in GIS [[Special:Contributions/172.68.189.49|172.68.189.49]] 21:42, 7 August 2018 (UTC)<br />
:Yes, hence this sentence: "A Shapefile is a proprietary data format for spatial data which remains in widespread use, despite being created in the early 90s, and based on an even older database format." Is there something you feel is missing from that? [[User:Stevage|Stevage]] ([[User talk:Stevage|talk]]) 23:27, 7 August 2018 (UTC)<br />
:: We usually share data with teh public, inlcuding coastlines, in shapefile format, rather than geospatial database. To share in geospatial database is to make a database public, and that is generally not safe.<br />
<br />
Similar take on Hollywood tropes can be found in [[734: Outbreak]] (medical / zombie thrillers), and [[633: Blockbuster Mining]] (adapting stories, action movies). --[[User:JakubNarebski|JakubNarebski]] ([[User talk:JakubNarebski|talk]]) 08:28, 8 August 2018 (UTC)<br />
<br />
The Title Text notes that this would not be as urgent as the proposed movie would portray, since updates are made quarterly. I think the embellishment is similar to many Hollywood procedural shows, where test results (e.g., DNA matching) that take quite a bit of time in reality are available practically on demand. [[Special:Contributions/108.162.241.160|108.162.241.160]] 15:37, 8 August 2018 (UTC)<br />
<br />
Just for the record (from a HI volcanalogist (?) I know), they do actually publish new maps several times a week during events like this, with updated coastlines. [[User:Afbach|Afbach]] ([[User talk:Afbach|talk]])</div>172.68.189.91https://www.explainxkcd.com/wiki/index.php?title=2022:_Sports_Champions&diff=1604522022: Sports Champions2018-07-25T04:29:12Z<p>172.68.189.91: Make a note of the progression of increasing implausibility</p>
<hr />
<div>{{comic<br />
| number = 2022<br />
| date = July 20, 2018<br />
| title = Sports Champions<br />
| image = sports_champions.png<br />
| titletext = For a long time, people thought maybe Usain Bolt was the one for running, until the 2090s and the incredible dominance of Derek Legs.<br />
}}<br />
<br />
==Explanation==<br />
In an example of {{w|nominative determinism}}, the comic lists people whose surname relates to their participation in various sports. It is presented as though it was created in the far future, reflecting on champions over the decades through to the 2080s. The first three are real sportspeople, the remainder are imaginary players of the future. The names progress from real, to fictional-but-plausible, to rare or highly unusual, to utterly implausible and impractical names.<br />
<br />
The caricatures are participating in their sport, except for Jebediah who is standing at a {{w|lectern}}.<br />
<br />
{| class="wikitable"<br />
!style="width:20%"|Name<br />
!style="width:10%"|Years<br />
!style="width:15%"|Sport<br />
!style="width:55%"|Explanation<br />
|-<br />
|Margaret Court<br />
|1960s<br />
|Tennis<br />
|{{w|Margaret Court}} is an Australian tennis player, former world number 1, who won many competitions in the 1960s and 70s. A {{w|tennis court|tennis '''court'''}} is the playing arena used in that sport.<br />
|-<br />
|Gary Player<br />
|1970s<br />
|Golf<br />
|{{w|Gary Player}} is a South African golfer who won nine major championships in the 1960s and 70s. Competitors are often known as '''player'''s, such as, in {{w|The Players Championship}}.<br />
|-<br />
|Lonzo Ball<br />
|2020s<br />
|Basketball<br />
|{{w|Lonzo Ball}} is an American professional basketball player, currently with the Los Angeles Lakers. The 2020s decade predicts future success, as he began playing professionally in 2017. Basketball is, of course, a {{w|ball game|'''ball''' game}}.<br />
|-<br />
|Jake Halfpipe<br />
|2030s<br />
|Skateboarding<br />
|A '''{{w|half-pipe|halfpipe}}''' is a structure used in extreme sports such as skateboarding and snowboarding.<br />
|-<br />
|Sarah Goggles<br />
|2030s<br />
|Swimming<br />
|'''{{w|Goggles}}''' are protective eyewear used in many sports, such as swimming or skiing.<br />
|-<br />
|Kevin Slurve<br />
|2050s<br />
|Baseball<br />
|A '''{{w|slurve}}''' is a baseball throwing technique, a portmanteau of '''sl'''ider and c'''urve'''.<br />
|-<br />
|Julia Chairlift<br />
|2050s<br />
|Skiing<br />
|A '''{{w|chairlift}}''' is an aerial machine often used to transport winter sports participants up mountains.<br />
|-<br />
|Dwight Shuttlecock<br />
|2060s<br />
|Badminton<br />
|A '''{{w|shuttlecock}}''' is a projectile used in the sport of badminton.<br />
|-<br />
|Brandon Sponsorship<br />
|2060s<br />
|Unclear<br />
|Sporting professionals are often {{w|Sponsor (commercial)|sponsored}} by corporations. Brandon is holding a pair of shoes, which are probably a branded '''sponsorship''' item.<br />
|-<br />
|Kate Dopingscandal<br />
|2070s<br />
|Cycling<br />
|There have been many '''{{w|List of doping cases in cycling|doping scandal}}s''' in the world of cycling. Doping refers to the "use of physiological substances or abnormal methods to obtain an artificial increase in performance." <br />
|-<br />
|Jebediah Disasterous Postgame-PressConference<br />
|2080s<br />
|Unspecified<br />
|At the end of sporting events - <i>i.e.</i> post-game - there is often a {{w|News conference|press conference}} where the competitors discuss the result. Sometimes, these live interviews are a disaster. Randall has chosen to spell his name as "Disasterous", rather than the more conventional "Disastrous". <br />
|-<br />
|(in title text, not depicted)<br />
Usain Bolt and Derek Legs<br />
|2090s<br />
|Sprinting<br />
|From the title text, {{w|Usain Bolt}} is the retired world record holder for the {{w|100 metres|100 meter sprint}} Randall considers him a solid contender for this list since he can '''bolt''' down the track. However the fictional Derek '''Legs''' ends up replacing Bolt on the list, either as an even faster sprinter, or because “legs” more clearly and unambiguously relates to running than “bolt” does.<br />
|}<br />
<br />
==Transcript==<br />
:[Two rows of people wielding sports equipment are shown, six in the upper row, five in the lower, only the last has no equipment but is standing behind a lectern with a microphone attached to it. Below each person, their name is given and the decade in which they were champions of their sport is given below their name, in brackets. Here is a list of the 11 people:]<br />
<br />
:[Woman with dark hair holding a tennis racket]<br />
:Margaret Court<br />
:(1960s)<br />
<br />
:[Cueball with a golf club]<br />
:Gary Player<br />
:(1970s)<br />
<br />
:[Cueball with a basketball]<br />
:Lonzo Ball<br />
:(2020s)<br />
<br />
:[Hairy on a skateboard]<br />
:Jake Halfpipe<br />
:(2030s)<br />
<br />
:[Woman with dark hair wearing a swim cap and goggles]<br />
:Sarah Goggles<br />
:(2030s)<br />
<br />
:[A man with a baseball cap throwing a baseball to the right]<br />
:Kevin Slurve<br />
:(2050s)<br />
<br />
:[A woman with long black hair in a knit cap and wearing ski googles is standing on skis holding ski poles]<br />
:Julia Chairlift<br />
:(2050s)<br />
<br />
:[Hairy holding a badminton racket bouncing a shuttlecock on it]<br />
:Dwight Shuttlecock<br />
:(2060s)<br />
<br />
:[Hairy holding a pair of shoes in his hand]<br />
:Brandon Sponsorship<br />
:(2060s)<br />
<br />
:[Hairbun standing next to a bicycle.]<br />
:Kate Dopingscandal<br />
:(2070s)<br />
<br />
:[Hairy standing behind a lectern with a microphone on it.]<br />
:Jebediah Disasterous Postgame PressConference<br />
:(2080s)<br />
<br />
:[Caption below the panel:]<br />
:Fun fact: Every sport eventually produces a champion competitor named after a common element of the game.<br />
<br />
<br />
{{comic discussion}}<br />
<br />
[[Category:Comics featuring Cueball]]<br />
[[Category:Comics featuring Hairy]]<br />
[[Category:Comics featuring Hairbun]]<br />
[[Category:Comics featuring real people]]<br />
[[Category:Sport]]<br />
[[Category:Baseball]]<br />
[[Category:Basketball]]</div>172.68.189.91https://www.explainxkcd.com/wiki/index.php?title=Talk:1973:_Star_Lore&diff=154999Talk:1973: Star Lore2018-03-29T02:55:21Z<p>172.68.189.91: Reminds me of the Doonesbury cartoon from 2007</p>
<hr />
<div><!--Please sign your posts with ~~~~ and don't delete this text. New comments should be added at the bottom.--><br />
Doesn't appear that "Five Sisters" is a reference to anything, according to my Google searches. Does anyone have anything on that? [[Special:Contributions/108.162.221.53|108.162.221.53]] 15:13, 28 March 2018 (UTC)Martin<br />
If I had to guess, it's most likely a reference to the Pleiades (Seven Sisters), which is a constellation.[[Special:Contributions/172.68.34.94|172.68.34.94]] 15:18, 28 March 2018 (UTC)<br />
<br />
I can't be certain, but I believe this is a direct quote from a Star Wars comic I read a few days ago. I will try to dig it up. [[Special:Contributions/172.69.142.46|172.69.142.46]] 23:44, 28 March 2018 (UTC)Dave<br />
<br />
I keep 'cellulose' tape over my LEDs, darkened with permanent marker, to dim their harsh glare when the rooms are unlit. On important ones, I keep a small sliver uncovered, so that from the right angle (like from the doorway) they can be seen even with the lights on. I do wish more devices had a "dim" setting on a timer, so the LEDs could be bright during the day & barely lit at night. In particular, my backup power battery has a large, obnoxious blue screen that lights up the whole room unless I keep it facing the wall. [[User:ProphetZarquon|ProphetZarquon]] ([[User talk:ProphetZarquon|talk]]) 15:48, 28 March 2018 (UTC)<br />
<br />
The red LED probably is a super bright LED :-) Sebastian --[[Special:Contributions/162.158.111.37|162.158.111.37]] 16:00, 28 March 2018 (UTC)<br />
:(Also responding to ProphetZarquon) I agree that super bright LEDs are annoying, especially the one on my monitor! But I don’t think that status LEDs can appear impressive, like in the comic. The superbright ones, which are standard today, illuminate the room too much. [[Special:Contributions/141.101.104.203|141.101.104.203]] 19:32, 28 March 2018 (UTC)<br />
<br />
"Five Sisters" is a reference a pentagon-shaped constellation from Isaac Asimov's ''Foundations Edge'' ~~Tyler<br />
<br />
The second part of the title text could be a reference to the word "planet" which comes from a Greek word meaning "wanderer". [[Special:Contributions/162.158.155.38|162.158.155.38]] 17:17, 28 March 2018 (UTC)<br />
<br />
It seems plausible that the title is partially a veiled reference to the Marvel Comics character {{w|Star Lord}}, which sounds almost the same as "Star Lore." [[User:JohnHawkinson|JohnHawkinson]] ([[User talk:JohnHawkinson|talk]]) 23:53, 28 March 2018 (UTC)<br />
<br />
The cluster of 5 lights is likely either a modem or router. Modems usually have a row of lights to indicate power, uplink, downlink, sync, and traffic at a minimum, whereas a router might have multiple lights indicating connections to a number of network ports. I can really relate to this comic, especially during the peak period of active gear in my home office at one time (It's not so eerie these days)! [[User:Ianrbibtitlht|Ianrbibtitlht]] ([[User talk:Ianrbibtitlht|talk]]) 01:42, 29 March 2018 (UTC)<br />
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This reminds me of a Doonesbury cartoon [http://images.ucomics.com/comics/db/2007/db070506.gif Mardi Gras] [[Special:Contributions/172.68.189.91|172.68.189.91]] 02:55, 29 March 2018 (UTC)</div>172.68.189.91https://www.explainxkcd.com/wiki/index.php?title=1973:_Star_Lore&diff=1549981973: Star Lore2018-03-29T02:47:15Z<p>172.68.189.91: /* Explanation */ ensure - make it show, assure - tell me it is so</p>
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<div>{{comic<br />
| number = 1973<br />
| date = March 28, 2018<br />
| title = Star Lore<br />
| image = star_lore.png<br />
| titletext = That one is a variable star which pulses every 30 seconds. Its name comes from a Greek word meaning "smoke alarm."<br />
}}<br />
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==Explanation==<br />
{{incomplete|Created by a BOT running on a COMPUTER with TOO MANY STATUS LEDs - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
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Computers, chargers, and other electronic items often have status lights in various colors. In a dark room, these lights appear as pinpricks of light, similar to constellations. Presumably Randall's room has many such items, though this may be like [[My Hobby]] in the sense that his room doesn't really look like that but he claims it does for humor value. It's also not clear whether this refers to Randall's bedroom (typical US usage of "my room" refers to one's bedroom) or some other room Randall spends a good deal of time in.<br />
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The comic's narrator is explaining how some of his lights remind him of stars, which gives him an opportunity to show off his knowledge of astronomic trivia. "The Five Sisters" is a reference to a pentagon-shaped constellation from Isaac Asimov's book ''Foundation's Edge'', though it could not have been 'known to the ancients' since it was less than 100 years old. It could also be in reference to the cluster of 5 lights next to the speech bubble, which is reinforced by the next bubble talking specifically about the red light in the cluster.<br />
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Interestingly, there are some green stars. Stars might look green due to a neighbouring star, but {{w|Green star (astronomy)|green stars are actually impossible}} due to the principle of black body radiation.<br />
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In the title text, the narrator describes his {{w|smoke alarm}} status light as a pulsing variable star. A smoke alarm is a device that detects smoke, which would indicate a fire. These are commonly placed in houses as a safety precaution. Typically, many smoke alarms have a status light that blinks to assure that they are still functioning.<br />
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==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
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:[Assorted dots of various colors scattered around the panel, with two speech bubbles placed in the panel.]<br />
:Speech bubble 1: That cluster was known to the ancients as the Five Sisters.<br />
:The red one was a supergiant and will probably explode within the next million years.<br />
:Speech bubble 2: Wow!<br />
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:[Caption below the panel:] <br />
:There are too many status LEDs in my room.<br />
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{{comic discussion}}<br />
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[[Category:Comics with color]]</div>172.68.189.91https://www.explainxkcd.com/wiki/index.php?title=1908:_Credit_Card_Rewards&diff=1474071908: Credit Card Rewards2017-11-05T06:02:29Z<p>172.68.189.91: /* Explanation */</p>
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<div>{{comic<br />
| number = 1908<br />
| date = October 27, 2017<br />
| title = Credit Card Rewards<br />
| image = credit_card_rewards.png<br />
| titletext = I should make a list of all the things I could be trying to optimize, prioritized by ... well, I guess there are a few different variables I could use. I'll create a spreadsheet ...<br />
}}<br />
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==Explanation==<br />
{{incomplete|VERY basic explanation.}}<br />
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A credit card, at its most basic form, is a loan contract to an individual from a bank. Like all contracts, the bank will offer several different types in an attempt to appeal to a large number of individuals. Unlike traditional loans which focus on a single item (car, house, boat, etc), a credit card is an unsecured loan geared towards daily and weekly transactions. Because these transactions cover a wide variety of items, credit cards can be further tweaked towards offering benefits in certain areas. For example, gas purchases, or even gas purchases through a single retail chain, can offer higher rewards on one type of plan vs. other plans.<br />
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These benefits, typically called rewards, have several different options. "Cash back" is a reward where the individual is given money back when they make a purchase that follows certain rules spelled out in the contract. "No interest" is a reward where the individual is not charged interest on their purchases if they pay the loaned money back within a specified amount of time. "Points" are similar to the cash back program, but are typically reserved towards purchasing a single large item or plan. Points towards a vacation is a popular option. Besides these three types of rewards, the number of actual rewards to pick from are limited only by the creativity and fiscal limitations of the issuing bank's CEO.<br />
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Cueball is trying to choose the optimal credit card program (the one that will result in biggest savings with the yearly fiscal median (YFM) he has). He realizes that he has to subtract the cost of him spending time on optimizing, so he wants to optimize the time needed to do the optimizing. But in order to to that efficiently, he first has to optimize the time spent on optimizing the time.<br />
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Hairy notices a hidden assumption that Cueball will spend his time on something more productive than this (i.e. that his time has value); Cueball's obsession with optimization is lame enough to suggest that he does not actually have more worthwhile interests to pursue. Cueball responds that he can "fail to optimize so many better things!" This means that Cueball is aware both of the big flaw in his reasoning and the fact that, when he attempts to optimize things, the attempt seldom really helps his situation.<br />
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The title text further expands the idea. Cueball wants to present a list of things to optimize to Hairy. However, he still needs to optimize the priorities of that list, before optimizing the list itself. Making and working with lists like this often involves a spreadsheet, which may also be a reference to [[1906: Making Progress]].<br />
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==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
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:[Cueball sits at a desk and is on his laptop. Hairy stands behind him.]<br />
:Cueball: I'm trying to figure out which of these credit card rewards programs is best given my spending.<br />
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:[Cueball leans backwards in a frameless panel.]<br />
:Cueball: But at some point, the cost of the time it takes me to understand the options outweighs their difference in value.<br />
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:[Close-up of Cueball's head and torso.]<br />
:Cueball: So I need to figure out where that point is, and stop before I reach it.<br />
:Cueball: But... when I factor in the time to calculate <i>THAT</i>, it changes the overall answer.<br />
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:[Cueball has his arms outstretched.]<br />
:Hairy: I question the assumption that you'd otherwise be spending your time on something more valuable.<br />
:Cueball: Come on, I could be failing to optimize so many better things!<br />
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{{comic discussion}}<br />
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[[Category:Comics featuring Hairy]]<br />
[[Category:Comics featuring Cueball]]<br />
[[Category:Time management]]</div>172.68.189.91