explain xkcd - User contributions [en]

2035: Dark Matter Candidates

2018-10-23T22:07:16Z

141.101.105.72: /* Explanation */

{{comic
| number = 2035
| date = August 20, 2018
| title = Dark Matter Candidates
| image = dark_matter_candidates.png
| 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.
}}

==Explanation==
{{w|Dark matter}} is a hypothetical, invisible 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. The most plausible explanation for all of these phenomena is that there is some "dark matter" that has gravity, but is otherwise undetectable. In cosmology, dark matter is estimated to account for 85% of the total matter in the universe.

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 10−15 to 10 3 kg are given in grams together with appropriate prefixes, while the ton takes the place of 103 kg.

Only massive objects ranging from subatomic particles up to super massive ones are covered in this comic. There are also {{w|Dark matter#Alternative hypotheses|alternative hypotheses}} trying to modify general relativity with no need of additional matter. The problem is that these theories can't explain all different observations at once. Nonetheless dark matter is a mystery because no serious candidate has been found yet.

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.

==== Axion ====
An {{w|Axion|axion}} is a hypothetical elementary particle postulated in 1977 to resolve the strong CP problem in {{w|Quantum chromodynamics|quantum chromodynamics}}, a theory of the strong force between {{w|Quark|quarks}} and {{w|Gluon|gluons}} which form {{w|Hadron|hadrons}} like {{w|Proton|protons}} or {{w|Neutron|neutrons}}. If axions exist within a specific range of mass they might be a component of dark matter. The advantage of this particle is that it's based on a theory which could be proved or also disproved by measurements in the future. Other theories, not mentioned in this comic, like the {{w|Weakly interacting massive particles|weakly interacting massive particles (WIMPs)}} are much more vague.

==== Sterile neutrino ====
{{w|Sterile neutrino|Sterile neutrinos}} are hypothetical particles interacting only via gravity. It's an actual candidate for dark matter. The well known {{w|Neutrino|neutrinos}} are also charged under the {{w|Weak interaction|weak interaction}} and can be detected by experiments.

==== Electrons painted with space camouflage ====
{{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.

==== Neutralino ====
A {{w|Neutralino|neutralino}} is a hypothetical particle from {{w|Supersymmetry|supersymmetry}} and is also a current candidate for dark matter. But there is not evidence whether or not supersymmetry is correct and none of the predicted particles have been found yet.

==== Q-ball ====
In theoretical physics, a {{w|Q-ball}} is a stable group of particles. It's an actual candidate for dark matter.

(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.)

==== Pollen ====
{{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.

==== No-See-Ums ====
{{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, because dark matter is invisible and the name "no-see-ums" implies that the flies are invisible.

==== Bees ====
Insects of the clade {{w|Bee|Anthophila}} 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.

==== 8-balls ====
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. The 8-ball is also a popular unit of sale for black market pharmaceuticals like cocaine, where it stands for ⅛ ounce (3.5 g). This doesn't make sense as a dark matter candidate either – unless dark matter is hard to detect because it's illegal & trying to avoid the cops.

==== Space cows ====
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)|beloved space western TV show}}, as Muppet cow [http://muppet.wikia.com/wiki/Natalie Natalie] in the Sesame Street News Flash (and [https://tvtropes.org/pmwiki/pmwiki.php/Main/SpaceWestern others less-remembered]), 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". {{w|Spherical cow|Spherical cows}} have also been used (humorously) by physicists needing to simplify some source of mass in a given problem.

==== Obelisks, monoliths, pyramids ====
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.
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).

==== Black holes ruled out by: ====
{{w|Black hole|Black holes}} are known to occur in sizes of a few solar masses (about 1030-1031 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 solar masses). But recent gravitational wave detections indicate that black holes at 50 or 100 solar 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. While black holes are widely reported to be ruled out as a candidate for dark matter for various reasons Randall has listed, such constraints are based on "monochromatic" mass distributions -- meaning that all such black holes are assumed to have the same mass -- which is considered physically implausible for populations of merging bodies which are known to have vastly different masses. See: [https://arxiv.org/pdf/1709.07467.pdf Primordial Black Holes as Dark Matter (2017)] and [https://arxiv.org/pdf/1705.05567.pdf Primordial black hole constraints for extended mass functions (2017)] (That this is a common practice in cosmology may be part of the reference to "buzzkill" astronomers.) He rules out all black holes in the range of approximately 1010 kg to 1033 kg even when below some gaps at the bars appear.

Except the last item, all range below the mass of the sun (2x1030 kg) while the smallest known black hole is about four solar masses.
* Gamma rays: If dark matter were black holes of this size, the black holes could be evaporating by the predicted {{w|Hawking radiation}}, and we'd see a buzz of gamma rays from every direction if many of those objects would exist. Nonetheless this radiation is still hypothetical and not been observed on any known black holes. Furthermore those objects would be very small because the Schwarzschild radius of a 1012 kg black hole is approximately 148 fm (1.48×10−13 m), which is between the size of an atom and an atomic nucleus.
* 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.
* 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.
* 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 more distant 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.
* 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 1024 to 1030 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.
* Buzzkill Astronomers: Black holes above a certain size are thought by some astronomers to be impossible to miss, due to the effects they have on nearby matter. At the mass of some 1030 kg there must be many supernova remnants we still haven't found. Black holes of about 1035 kg have long been considered dark matter candidates by a minority group of cosmologists, as could be seen here [https://arxiv.org/pdf/1001.2308.pdf Primordial Black Holes as All Dark Matter (2010)] and the Milky Way's first discovered intermediate mass black hole falling in this range shown here [https://www.nao.ac.jp/en/news/science/2016/20160115-nro.html Signs of Second Largest Black Hole in the Milky Way].
Not covered by this comic are {{w|Massive compact halo object|massive astrophysical compact halo objects (MACHOs)}} composed of hard to detect dim objects like black holes, neutron stars, brown dwarfs, and other objects composed of normal {{w|Baryon|baryonic}} matter. Nevertheless observations have shown that the total amount of baryonic matter in our universe on large scales is much smaller than it would be needed to explain all the measured gravitational effects.

==== Maybe those orbit lines on space diagrams are real and very heavy ====
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 probably 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.

==== Title text ====
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 of hydrogen consists of {{w|Avogadro constant|6.022 × 1023 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.

==Transcript==
:Dark matter candidates:
:[A line graph is shown and labeled at left quarter in eV and further to the right in g together with some prefixes.]
:[The labels read:]
:µeV, meV, eV, keV, MeV, GeV, TeV, 10-18kg, ng, µg, mg, g, kg, TON, 106kg, 1012kg, 1018kg, 1024kg, 1030kg

:[All items are shown in bars ranging between two approximately values:]
:< 1 µeV - 10 meV: Axion

:1 eV - 10 keV: Sterile neutrino

:0.5 MeV (exactly): Electrons painted with space camouflage

:10 GeV - 10 TeV: Neutralino

:100 TeV - 10-17 kg: Q-ball

:1 ng - 100 ng: Pollen

:0.1 mg - 1 mg: No-See-Ums

:10-1 g (exactly): Bees

:10 g - 100 g: 8-balls

:100 kg - TON: Space cows

:TON - 109 kg: Obelisks, monoliths, pyramids

:109 kg - 1033 kg: Black holes ruled out by:
::109 kg - 1013 kg: Gamma rays
::1013 kg - 1017 kg: GRB lensing
::1015 kg - 1022 kg: Neutron star data
::1021 kg - 1030 kg: Micro lensing
::1024 kg - 1030 kg: Solar system stability
::1030 kg - 1033 kg: Buzzkill astronomers

:1033 kg - >1036 kg: Maybe those orbit lines on space diagrams are real and very heavy

{{comic discussion}}

[[Category:Science]]
[[Category:Physics]]
[[Category:Astronomy]]
[[Category:Line graphs]]

2009: Hertzsprung-Russell Diagram

2018-10-23T22:02:31Z

141.101.105.72: /* Table */

{{comic
| number = 2009
| date = June 20, 2018
| title = Hertzsprung-Russell Diagram
| image = hertzsprung_russell_diagram.png
| titletext = The Hertzsprung-Russell diagram is located in its own lower right corner, unless you're viewing it on an unusually big screen.
}}

==Explanation==
{{incomplete|Fill out the table. Do NOT delete this tag too soon.}}

The {{w|Hertzsprung–Russell diagram}} is a scatterplot showing absolute luminosities of stars against its effective temperature or color. It's generally used to understand a star's age.

The axes are labeled in {{w|Kelvin}} (degrees {{w|Celsius}} above {{w|absolute zero}}) for {{w|effective temperature}} and, unlike many Hertzsprung–Russell diagrams, {{w|Watts}} for {{w|luminosity}}. While most Hertzsprung–Russell diagrams are labelled in units of {{w|solar luminosity}} or {{w|absolute magnitude}}, all three are perfectly valid measures of {{w|luminosity}}, which refers to the total power emitted by the star (or other body). {{w|Effective temperature}} refers to temperature of a blackbody with the same surface area and luminosity. This is meant to provide an estimate of the surface temperature of the object.

Roughly speaking, the luminosity (i.e. total power radiated) by an object is proportional to (1) the total surface area of the object, multiplied by (2) the (absolute) temperature raised to the fourth power. So a high luminosity generally results from either a very hot or a very large object, or a combination of the two. The surface-area dependence explains why the whale and the cruise ship are more luminous than the hotter campfire.

Regular Hertzsprung–Russell diagrams cover ranges of about 1,000K to 30,000K, and what is labeled on this diagram as 1021 to 1033 watts—i.e. the upper-left corner. Extended diagrams increase the luminosity range only to include the "Brown Dwarfs". This diagram has been extended to much lower magnitudes on both axes. The joke comes from the absurdity of a diagram meant for stars including much smaller objects, such as planets ... and astronomers.

Though not included in the diagram, the title text notes that the diagram itself would probably be plotted somewhere in the lower right corner due to its (relatively) low power output and temperature. On its face this is nonsensical - the diagram itself, being mere information, possesses neither power output nor temperature - but one can read this as the power output and temperature of a typical screen displaying the diagram. Bigger screens have a higher total output (in terms of luminosity) and are thus positioned further towards the diagram's top. An "unusually big screen" would have to be something like a JumboTron or a projector for its luminosity or temperature to put it outside of the lower right corner.

==Table==

{| class="wikitable sortable"
!style="width:10%"|Item
!style="width:10%"|Effective Temperature
!style="width:10%"|Luminosity
!style="width:70%"|Explanation
|-
|{{w|Main sequence}}
|
|
|Most stars lie along the main sequence, one of several labelled regions in a typical {{w|Hertzsprung–Russell diagram|Hertzsprung-Russell (HR) diagram}}, and are thus classified as main sequence stars. Progressing from the lower-right toward the upper-left end of the main sequence, stars become more massive, hotter, and more luminous. The HR diagram in this comic includes three main sequence stars.
|-
|{{w|Giant star|Giants}}
|
|
|A giant star is larger and more luminous than a main sequence star of the same temperature. The HR diagram in this comic does not specifically include any giant stars.
|-
|{{w|Supergiant star|Supergiants}}
|
|
|Supergiant stars are among the largest and most luminous stars that exist. The HR diagram in this comic includes the supergiant star Betelgeuse.
|-
|{{w|White dwarf|White dwarfs}}
|
|
|In a white dwarf star, nuclear fusion has ceased. A white dwarf still radiates energy due to stored heat that was generated from fusion earlier in the star's life, but white dwarfs are much less luminous than stars that are still undergoing fusion. The HR diagram in this comic does not specifically include any white dwarf stars.
|-
|{{w|Brown dwarf|Brown dwarfs}}
|
|
|Brown dwarfs are too small to be classified as stars, but are larger than planets. The HR diagram in this comic does not specifically include any brown dwarfs.
|-
|{{w|Betelgeuse}}
|3200 K
|1.6 × 1031 W
|Betelgeuse is a red supergiant star. At 3200 K, it is cooler than the sun but has a higher luminosity owing to its larger size.
|-
|{{w|Vega}}
|10,000 K
|1.8 × 1028 W
|Vega is a main sequence star that is both hotter and more luminous than the sun.
|-
|{{w|Sun}}
|5800 K
|3.6 × 1026 W
|The sun is a main sequence star. On a typical {{w|Hertzsprung–Russell diagram|HR diagram}}, the luminosity of the sun is usually the basis of the luminosity scale, i.e. the sun is at "1" or 100 on the diagram's vertical scale.
|-
|{{w|Proxima Centauri}}
|2700 K
|2.0 × 1023 W
|Proxima Centauri, the closest star to the sun, is a main sequence star that is both cooler and less luminous than the sun.
|-
|{{w|HD 189733 b}}
|2100 K
|4.8 × 1021 W
|This is an exoplanet discovered in 2005. It is comparable in size to Jupiter, but hotter and more luminous owing to its close proximity to its own sun.
|-
|Interior of a {{w|Thermonuclear weapon|hydrogen bomb}} during detonation
|~108 K
|~1020 W
|
|-
|{{w|Jupiter}}
|285 K
|1.2 × 1018 W
|
|-
|{{w|Venus}}
|330 K
|5.0 × 1017 W
|
|-
|{{w|Earth}}
|300 K
|3.0 × 1017 W
|Non-luminous objects on Earth are typically the same temperature as Earth, around 300 K. As shown in the diagram, Earth-based objects like France, the cruise ship, the blue whale, and the astronomer all have temperatures in the vicinity of 300 K.
|-
|{{w|Mars}}
|255 K
|2.0 × 1016 W
|
|-
|{{w|Moon}}
|300 K
|1.2 × 1016 W
|
|-
|Nuclear Fireball
|8000 K
|2.0 × 1014 W
|The glowing, rising mass of air that appears just after a nuclear bomb is detonated.
|-
|{{w|France}}
|300 K
|2.0 × 1014 W
|This is part of Earth (and more precisely a part of Europe), the same temperature as Earth, but less luminous in proportion to its surface area. Including this may be a joke referencing the two possible meanings of ‘Europa’ (see the next entry). [https://goo.gl/images/H8Dmu3 France emits less light at night than neighbouring countries], perhaps due to lower population density.
|-
|{{w|Europa (moon)|Europa}}
|90 K
|3.5 × 1014 W
|While this term could refer to Europe (a part of Earth, of which France (the previous entry) is a further part), the temperature and luminosity are both too small for that, so it must refer to the moon of Jupiter instead.
|-
|Lightning Bolt
|30,000 K
|30 GW
|
|-
|{{w|Ivanpah Solar Power Facility|Ivanpah Solar Plant}} Salt Tank
|1200 K
|1.2 GW
|The {{w|Ivanpah Solar Power Facility}} is a large solar power generator in the Californian Mojave desert. It concentrates sunlight from 173,500 reflectors onto three water-boiler towers. Randall appears to have mistakenly confused this power plant with the nearby Crescent Dunes, which uses tanks of molten salt to store energy. https://insideclimatenews.org/news/16012018/csp-concentrated-solar-molten-salt-storage-24-hour-renewable-energy-crescent-dunes-nevada
|-
|Medium-sized Lava Lake
|800 K
|32 MW
|
|-
|Cruise Ship
|325 K
|30 MW
|
|-
|Campfire
|870 K
|7.0 kW
|
|-
|{{w|Blue whale}}
|280 K
|78 kW
|Must be average surface temperature as whales are warm-blooded at 37 °C internally, interestingly this and the cruise ship may be the only entries where a significant amount of power produced is conducted away rather than radiated. Also the power seems high compared to what I can find. [https://www.researchgate.net/publication/321972840/figure/fig1/AS:574004013604864@1513864629274/Visible-and-infrared-spectrum-images-of-various-humpback-whale-surfacing-features.png These images] suggest a surface temperature around 295K - 300K for a Humpback whale when surfacing
|-
|{{w|Arc lamp}}
|6500 K
|150 W
|A light source that passes an electrical current through a gas (as in a mercury or sodium vapor lamp) rather than a solid filament (as in a standard incandescent lightbulb) or a semiconductor (as in an LED).
|-
|Lightbulb
|4800 K
|75 W
|The temperature value here refers to colour temperature, which for an incandescent bulb is the same as the filament temperature. However tungsten filament lights, commonly referred to as "bulbs", have a colour temperature of between 2400 and 3600 K, and tungsten melts at 3695 K.
|-
|LED Bulb
|5800 K
|8 W
|The temperature value here refers to colour temperature, not physical temperature. Color temperature is a better match to effective temperature than physical temperature. As typical semiconductors might be rated for a maximum of 150 °C or about 420 K, the physical temperature of an LED Bulb is considerably lower than its colour temperature.
|-
|Astronomer
|310 K
|100 W
| The body temperature of a human (astronomer or otherwise) is about 310 K (37 °C). Skin surface temperature (which would fit the meaning of effective temperature better) is typically 31–35 °C. An astronomer standing outside in a thick coat on a cold night would have a much lower surface temperature.

A human being generating 100 W for 24 hours needs 2065 kcal or 8.64 MJ. According to the UN FAO this is e.g. the typical daily energy output of women with weight 55 kg between 18 and 59 years having a light activity lifestyle of 1.55 times the BMR (basic metabolic rate).

|}

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:Expanded Hertzsprung-Russell Diagram
:[A scatter plot is shown, with the x-axis labeled Effective Temperature (in kelvins), and the y-axis Luminosity (watts).]
:[Circled items in the top left (high temperature and high luminosity):]
:Supergiants
:Giants
:Main sequence
:White dwarfs
:Brown dwarfs
:[Items shown as points and their values:]
:Betelgeuse: 3200 K, 1.6 * 1031 W
:Vega: 10,000 K, 1.8 * 1028 W
:Sun: 5800 K, 3.6 * 1026 W
:Proxima Centauri: 2700 K, 2.0 * 1023 W
:HD 189733 b: 2100 K, 4.8 * 1021 W
:Interior of a hydrogen bomb during detonation: ~108 K, ~1020 W
:Jupiter: 285 K, 1.2 * 1018 W
:Venus: 330 K, 5.0 * 1017 W
:Earth: 300 K, 3.0 * 1017 W
:Mars: 255 K, 2.0 * 1016 W
:Moon: 300 K, 1.2 * 1016 W
:Nuclear Fireball: 8000 K, 2.0 * 1014 W
:France: 300 K, 2.0 * 1014 W
:Europa: 90 K, 3.5 * 1014 W
:Lightning Bolt: 30,000 K, 30 GW
:Ivanpah Solar Plant Salt Tank: 1200 K, 1.2 GW
:Medium-sized Lava Lake: 800 K, 32 MW
:Cruise Ship: 325 K, 30 MW
:Campfire: 870 K, 7.0 kW
:Blue whale: 280 K, 78 kW
:Arc lamp: 6500 K, 150 W
:Lightbulb: 4800 K, 75 W
:LED Bulb: 5800 K, 8 W
:Astronomer: 310 K, 100 W

{{comic discussion}}

[[Category:Scatter plots]]
[[Category:Astronomy]]

1043: Ablogalypse

2018-10-13T09:34:02Z

141.101.105.72: Fixed the link

{{comic
| number = 1043
| date = April 16, 2012
| title = Ablogalypse
| image = ablogalypse.png
| titletext = Plus the reaction in the Tumblverse is always 'repeatedly get hit by a dog and fall down the stairs'.
}}

==Explanation==
This comic plays with the [https://trends.google.com/trends/explore?date=all&geo=US&q=tumblr,blog,wordpress,livejournal Google trends for the terms "blog", "tumblr", "wordpress", and "livejournal"].

*{{w|Blog}}: a website with opinions and comments
*{{w|Tumblr}}: a "micro-blogging" site, which has taken off due to the prevalence of animated gifs and funny photos.
*{{w|WordPress}}: a type of blog software.
*{{w|LiveJournal}}: a sort of personal blog site that hasn't been very popular since 2004-2005. [[Randall]] published [[:Category:Comics posted on livejournal|his first comics]] there.

As you can see in the caption and then the title text, there is no way that newscasters will reference the "Tumblverse" because all the reactions will be filled with animated gifs of a person in [http://www.youtube.com/watch?v=v-Zph323Dos a raptor suit falling over] or [http://knowyourmeme.com/memes/yes-this-is-dog a dog answering a phone].

This actually came to pass, with the change over occurring between October and November 2012, as can be seen using the link above.

==Transcript==
:[A line graph with four lines, each representing 'Google Trends Search Volume' of different search terms over time from prior to 2005 to just after 2012. A blue line represents "blog," which trends gradually but significantly upwards from well before 2005 until it reaches a peak between 2008-2009, and starts to very slowly descend to today. A red line represents "Tumblr", which is at zero until it slowly starts to trend upward in early 2010, and then sharply increases in late 2010 and through 2011 and 2012. As of the date of this comic, 'blog' still beats 'Tumblr' in terms of search volume, but a dotted line projection of the trend shows that on October 12, 2012, the two lines will cross. A yellow line represents 'Wordpress,' which has very low volume until a very small and gradual increase in 2007, which gradually increases to this day but doesn't come close to meeting the volume of either 'blog' or 'Tumblr'. A green line represents 'LiveJournal,' which started out prior to 2005 at around the level 'Wordpress' is at now, but declined through 2005 and 2006 until it has plateaued until virtually nothing.]
:In about six months, the word "Tumblr" will eclipse "blog" in Google popularity.
:I doubt TV anchors will start talking about "reactions in the Tumblverse," but then again, I still can't believe we got them to say "blogosphere."

==Trivia==
*Randall's forecast wasn't far off: [http://www.google.com/trends/explore#q=blog%2C%20tumblr&date=1%2F2011%2037m&cmpt=q "tumblr" surpassed "blog"] in November 2012.

{{comic discussion}}
[[Category:Line graphs]]
[[Category:Comics with color]]

128: dPain over dt

2018-10-13T02:39:23Z

141.101.105.72: /* Transcript */

{{comic
| number = 128
| date = July 14, 2006
| title = dPain over dt
| image = dPain_over_dt.png‎
| titletext = You laugh to keep from crying, you do math to keep from crying...
}}

==Explanation==

Another one of the math-love relationship comics, a mathematical depiction of pain as a {{w|differential equation}} is shown. It is hoped that ''dPain/dt'', or the rate of pain (in this case, shrinking), decreases quickly so that the pain will vanish quickly. He's hoping the value for ''d'' will not be larger than a few days or some weeks. Assuming that ''How much she's still in my life'' is a constant ''G'' then [http://www.wolframalpha.com/input/?i=dP%2Fdt+%3D+%28-k1*P%2BG%29*%281%2F%281%2Bexp%28-%28t-k2%29%2Fd%29%29%29 solving the differential equation] leads to the following solution (with unknown ''c1''):
P(t) = c1*(ek2/d+et/d)-d*k1+G/k1

If ''k1'' was positive or if ''k2'' was a large value, the value of ''dPain/dt'' would approach zero. Ideally, ''k1'' would be "How much she's in my life"/''Pain'' (we assume both these values are positive), while ''k2'' would ideally be extremely large. Either of these scenarios approach what would be a situation where the value of ''dPain/dt'' is close to zero. But we don't know the meaning of ''k1'' or ''k2'', these variables are just unpredictable.

In the title text, [[Randall]] changes the famous "laugh to keep from crying" statement to Math.

==Transcript==
:<math>\frac{dPain}{dt} = \left(-k_1\, Pain + [\text{image of Megan}]\right) \left(\frac{1}{1 + e^{-\left(t-k_2\right)/d}}\right)</math>
:''k''1=?
:''k''2=?
:[Image of Megan]=How much she's still in my life
:Please let ''d'' only be a few days... or weeks
:I guess there's some kind of a cutoff after years, where it stops mattering and we can be friends. Do I want that?
:Is ''k''1 positive? Is ''k''2 large?
:Will I ever stop feeling like this?

{{comic discussion}}
[[Category:Analysis]]
[[Category:Romance]]
[[Category:Comics featuring Megan]]

128: dPain over dt

2018-10-13T02:38:06Z

141.101.105.72: /* Transcript */

{{comic
| number = 128
| date = July 14, 2006
| title = dPain over dt
| image = dPain_over_dt.png‎
| titletext = You laugh to keep from crying, you do math to keep from crying...
}}

==Explanation==

Another one of the math-love relationship comics, a mathematical depiction of pain as a {{w|differential equation}} is shown. It is hoped that ''dPain/dt'', or the rate of pain (in this case, shrinking), decreases quickly so that the pain will vanish quickly. He's hoping the value for ''d'' will not be larger than a few days or some weeks. Assuming that ''How much she's still in my life'' is a constant ''G'' then [http://www.wolframalpha.com/input/?i=dP%2Fdt+%3D+%28-k1*P%2BG%29*%281%2F%281%2Bexp%28-%28t-k2%29%2Fd%29%29%29 solving the differential equation] leads to the following solution (with unknown ''c1''):
P(t) = c1*(ek2/d+et/d)-d*k1+G/k1

If ''k1'' was positive or if ''k2'' was a large value, the value of ''dPain/dt'' would approach zero. Ideally, ''k1'' would be "How much she's in my life"/''Pain'' (we assume both these values are positive), while ''k2'' would ideally be extremely large. Either of these scenarios approach what would be a situation where the value of ''dPain/dt'' is close to zero. But we don't know the meaning of ''k1'' or ''k2'', these variables are just unpredictable.

In the title text, [[Randall]] changes the famous "laugh to keep from crying" statement to Math.

==Transcript==
:<math>\frac{dPain}{dt} = \left(-k_1\, Pain + \text{[image of Megan]}\right) \left(\frac{1}{1 + e^{-\left(t-k_2\right)/d}}\right)
:''k''1=?
:''k''2=?
:[Image of Megan]=How much she's still in my life
:Please let ''d'' only be a few days... or weeks
:I guess there's some kind of a cutoff after years, where it stops mattering and we can be friends. Do I want that?
:Is ''k''1 positive? Is ''k''2 large?
:Will I ever stop feeling like this?

{{comic discussion}}
[[Category:Analysis]]
[[Category:Romance]]
[[Category:Comics featuring Megan]]

563: Fermirotica

2018-10-13T02:34:19Z

141.101.105.72: /* Transcript */

{{comic
| number = 563
| date = April 1, 2009
| title = Fermirotica
| image = fermirotica.png
| titletext = I love how Google handles dimensional analysis. Stats are ballpark and vary wildly based on time of day and whether your mom is in town.
}}

==Explanation==
The {{w|Fermi paradox}} describes the contradiction between the high probability of {{w|extraterrestrial life}} and the lack of empirical evidence thereof. Age and size of the universe suggest that intelligent life should have occurred somewhere, and that some alien civilizations should have developed technology for {{w|interstellar travel}}. Therefore, one might expect the universe full of life. However, no evidence for any lifeforms on other planets has yet been found by humans. This inconsistency was first noted by {{w|Enrico Fermi}} in 1950 when he posed the question "Where is everybody?". The phenomenon, often called ''The Great Silence'', was later examined more thoroughly in a paper by {{w|Michael H. Hart}}.

A decade after Fermi's observation, {{w|Frank Drake}} formulated the {{w|Drake equation}}, which aims at estimating the number of active, communicative extraterrestrial civilizations in the {{w|Milky Way}} galaxy. The formula presents itself as the product of several probabilistic factors which would be required for such a civilization to exist. Several parameters are unknown and the equation assumes that all factors are weighed equally, therefore the equation is not useful for computing any actual result.

The comic presents a somewhat related equation which computes the average distance from the observer wherein a couple can be found copulating. (The example parameters given in the comic yield 139 metres.) The implication of the equation is that we are surrounded by sex in our everyday lives. Nevertheless, we rarely encounter couples during the act itself. Borrowing from the Fermi paradox, the ''Fermirotica'' paradox poses the question: "Where is everybody having sex?". Of course, the lack of empirical evidence of couples having sex can easily be explained by the fact that most couples only have intercourse in privacy. A similar approach might also offer an explanation to the original problem: Alien species might conceal themselves from our observations, e.g. in order to {{w|Prime directive|avoid interfering in the development of civilizations}}. This answer to the Fermi Paradox is commonly called {{w|zoo hypothesis}}.

The second panel has [[Cueball]] sexually aroused by the statistical probability of a couple practising intercourse. This fantasy of his is termed ''statistical {{w|voyeurism}}'' by an off-frame speaker, and is evidently upset by it. Possible reasons for being upset are that he considers it an inappropriate use of statistics, or because it accurately predicts an ''actual'' copulation he is aware of and would rather keep private (e.g. the off-frame speaker is actually about to have sex).

The title text refers to the {{w|Goggle search#calculator|Google calculator}} and praises its capabilities of {{w|dimensional analysis}}, and more specifically {{w|unit conversion}}. [[Randall]] assumes that most readers will enter the equation with the example parameters into the {{w|Google}} search engine. The built-in calculator will output the result in the correct {{w| SI unit}} ''metre'', although the population density was given as ''people per square mile''. The second part of the title text states that the examples are nothing more than an educated guess, and that the equation is simplified. In reality, more parameters must be taken into account, e.g. the time of day, since most people will have sex in the evening or night. The insulting suggestion that the probability of sex rises when the reader's (supposedly promiscuous) mother is in town represents a ''{{w|Yo Mama joke}}''.

Note that this comic was released on April 1st without being an April Fools' Day comic. But Randall made another April Fool on his reader, see the [[#Trivia|trivia section]].

==Transcript==
:Pd Regional population density (e.g. 18,600/mi²)
:Xf Average person's frequency of sex (e.g. 80/year)
:Xd Average duration of sex (e.g. 30 minutes)
:<math>r=\sqrt\frac{2}{\pi P_d X_f X_d}</math>
:On average, someone within distance r of you is having sex.
:[Cueball standing at easel.]
:Cueball: Mmm, That probable couple 150 meters away is so hot. Oh yeah, theoretically work it, baby.
:From out of frame: Hey! No statistical voyeurism!

==Trivia==
*This comic was released on April 1 2009.
**The comic itself has no obvious ties to {{w|April Fools' Day}} and is thus not one of [[Randall|Randall's]], [[:Category:April fools' comics|April fools' comics]]!
**But on that day Randall, Jeph Jacques and Ryan North altered their {{w|Domain_Name_System|DNS}} records to point to each others websites. So xkcd.com would show the [http://questionablecontent.net/ Questionable content] website, questionablecontent.net would show the [http://www.qwantz.com/ Dinosaur comics] website and www.qwantz.com would show the [http://www.xkcd.com xkcd] website.

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Sex]]
[[Category:Math]]
[[Category:Your Mom]]

977: Map Projections

2018-10-09T03:13:36Z

141.101.105.72: /* A Globe! */

{{comic
| number = 977
| date = November 14, 2011
| title = Map Projections
| before = [[#Explanation|↓ Skip to explanation ↓]]
| image = map_projections.png
| titletext = What's that? You think I don't like the Peters map because I'm uncomfortable with having my cultural assumptions challenged? Are you sure you're not... ::puts on sunglasses:: ...projecting?
}}
__TOC__
==Explanation==
{{w|Map projection}}, or how to represent the spherical Earth surface onto a flat support (paper, screen...) to have a usable map, is a long-time issue with very practical aspects (navigation, geographical shapes and masses visualization, etc.) as well as very scientific/mathematical ones, involving geometry or even abstract algebra among other things. There is no universal solution to this problem: Any 2D map projection will always distort in a way the spherical reality. Many projections have been proposed in various contexts, each intending to minimize distortions for specific uses (for nautical navigation, for aerial navigation, for landmass size comparisons, etc.) but having drawbacks from other points of view. Some of them are more frequently used than others in mass media and therefore more well-known than others, some are purely historical and now deprecated, some are very obscure, etc.

[[Randall]] suggests here the idea that someone's "favorite" map projection can reveal aspects of their personality, then goes through a series of them to show what they can mean.

He may actually believe that all map projections are in a way bad. This could be inferred from the fact that he much later began publishing a series of [[:Category:Bad Map Projections|Bad Map Projections]], starting with [[1784: Bad Map Projection: Liquid Resize]], which was Bad Map Projection #107 on his list, and was followed up by #79: [[1799: Bad Map Projection: Time Zones]]. The projections below could be #1-#12 on that list, although the last one, where Randall hates those that love it, might be somewhat further down the list.

===Mercator===
[[File:MercatorProjection.jpg|frame|The Mercator projection]]
The {{w|Mercator projection}} was introduced by Flemish cartographer Gerardus Mercator in 1569. The main purpose of this map is to preserve compass bearings; for example 13 degrees east of north will be 13 degrees clockwise from the ray pointing toward the top of the map, at every point. A mathematical consequence is the mapping is conformal, i.e. if two roads meet at a certain angle on the surface of the Earth, they will meet at that same angle on the map. It also follows that at every point the vertical and horizontal scales are the same, so locally i.e. considering only a small part of the map, geographical features (shapes, angles) are well represented, which helps a lot in recognizing them on-the-field, or for local navigation in that small part only. For this reason, that projection (or a close variant) is used in several online mapping services, such as Google Maps, which means that it is frequently encountered by the general public. A straight line on the map corresponds to a course of constant bearing (direction), which was very useful for nautical navigation in the past (and thus made that projection very well-known).

However, from a global point of view, this projection is radically incorrect in how it shows the size of landmasses (for instance, Antarctica and Greenland seem gigantic), and furthermore, it always excludes a small region around each pole (otherwise the map would be of infinite height), so it doesn't provide a complete solution for the problem of map projection. The comic implies that people who like that projection aren't very interested with map issues, and typically use what they are offered without thinking much about it.

{{clear}}

===Van der Grinten===
[[File:VanDerGrintenProjection.jpg|frame|The Van der Grinten projection]]
The {{w|Van der Grinten projection}} is not much better than the Mercator. It was adopted by {{w|National Geographic}} in 1922 and was used until they updated to the Robinson projection in 1988.

The Van der Grinten projection is circular as opposed to the Mercator projection. The fictional person believes a circular map is more fitting to the real Earth's three-dimensional spherical nature because both are round. This belief fails to recognize that a two-dimensional circle has very little in common with the surface of a sphere, and thus this projection still causes a vast distortion of space and area. Because of this, Randall implies the Van der Grinten enthusiast to be optimistic and childishly simple-minded (e.g. "you like circles").

{{clear}}

===Robinson===
[[File:RobinsonProjection.jpg|frame|The Robinson projection]]
The {{w|Robinson projection}} was developed by {{w|Arthur H. Robinson}} as a map that was supposed to look nice and is often used for classroom maps. National Geographic switched to this projection in 1988, and used it for ten years, switching to the {{w|Winkel tripel projection|Winkel-Tripel}} in 1998.

{{w|The Beatles}} was a rock band that enjoyed great commercial success in the 1960s, and are widely considered the best act ever in the genre of popular music. The Beatles, coffee, and running shoes are all things that are very commonly enjoyed and largely uncontroversial, as well as being comforting. Liking these specific things suggests an ordinary, easygoing lifestyle paralleled by the projection.

{{clear}}

===Dymaxion===
[[File:DymaxionProjection.jpg|frame|The Dymaxion projection]]
Also called the Fuller Map, the {{w|Dymaxion map}} takes a sphere and projects it onto an icosahedron, that is a polyhedron with 20 triangular faces. It is far easier to unwrap an icosahedron than it is to unwrap a sphere into a 2D object and has very little skewing of the poles. {{w|Buckminster Fuller}} was an eccentric futurist who believed, for example, that world maps should allow no conception of "up" or "down". He was therefore more than happy to defy people's expectations about maps in the pursuit of mathematical accuracy.

Randall associates the projection to geek subculture and niche markets:
*{{w|Isaac Asimov}} was an American science-fiction writer, who (as well as publishing many textbooks) is considered the father of the modern concept of robots. He invented the {{w|Three Laws of Robotics}}. He also worked on more than 500 books throughout his career.
*{{w|XML}} is the eXtensible Markup Language. It is used to represent data in a format that machines can read and understand, as well as being human-readable. In practice, XML is cumbersome to read.
*{{w|Vibram FiveFingers|Toed shoes}} are a [[1065: Shoes|favorite]] of Randall's to pick on. In society they are seen as a {{w|geek}} clothing item.
*Brought to the world by {{w|Dean Kamen}}, the {{w|Segway PT}} was supposed to be a device that changed the way cities were built. In reality, most principalities have put in place rules specifically against Segways, making them a frustration to own and use within the law (in some states in Australia, it is illegal to use them on public footpaths or roads). Also, the former owner of {{w|Segway Inc.}}, the late {{w|Jimi Heselden}}, accidentally rode his Segway off a cliff in 2010.
*At the time of comic release, 3D goggles, nowadays widely known as {{w|Virtual reality headset|VR headsets}}, were considered a gimmick at best. The original idea is as old as 3D graphics, but it never really took off until mid-2010s. Earlier products were very unwieldy and offered poor graphics quality, so no one took this technology seriously.
*{{w|Dvorak Simplified Keyboard|Dvorak}} is an alternate keyboard layout to {{w|QWERTY}}. According to legend, QWERTY was invented to help keep manual typewriters from jamming (by placing the most used keys far from each other) but Dr. {{w|August Dvorak}} performed many studies and found the mathematically optimal keyboard layout to reduce finger travel for right handed typists. While some claim Dvorak is technically better than QWERTY, QWERTY had become the standard. All the keyboards were laid out in QWERTY format, and retraining the brain after becoming a touch typist is extremely difficult (although some software exists to make this learning process much easier). It has become a [[:Category:Dvorak|recurrent theme]] on xkcd.
**It seems likely that Randall looked at this comic when he made the [[1784: Bad Map Projection: Liquid Resize]], and given that he then released a comic about Dvorak, [[1787: Voice Commands]], the week after that, it seem like this old comic may also have inspired that Dvorak reference, see this [[1787: Voice Commands#Trivia|trivia item]].

{{clear}}

===Winkel-Tripel===
[[File:Winkel-TripelProjection.jpg|frame|The Winkel Tripel projection]]
Proposed by Oswald Winkel in 1921, the {{w|Winkel tripel projection}} tried to reduce a set of three (German: Tripel) main problems with map projections: area, direction, and distance. The {{w|Kavrayskiy VII projection|Kavrayskiy projection}} is very similar to the Winkel Tripel and was used by the USSR, but very few in the Western world know of it.

The comic links this projection to {{w|hipster}} subculture. The hipster stereotype is to avoid conforming to mainstream fashions. "Post-" refers to a variety of musical genres such as {{w|post-punk}}, {{w|post-grunge}}, {{w|post-minimalism}}, etc. that branch off of other genres.

;Trivia
In German "Winkel-Tripel-Projektion" means Winkel's triple projection, and therefore the hyphen shouldn't be there: "Winkel Tripel" or "Winkel tripel".

{{clear}}

===Goode Homolosine===
[[File:GoodeHomolosineProjection.jpg|frame|The Goode Homolosine projection]]
The {{w|Goode homolosine projection}} takes a different approach to skewing a sphere into a roughly circular surface. An orange peel can be taken from an orange and flattened with fair success; this is roughly the procedure that {{w|John Paule Goode}} followed in creating this projection. Randall is suggesting that people who like this map also prefer relatively easy solutions to other things in life, despite those solutions having nuanced problems that are more difficult to address.

Common people make arguments that if normal people would run the United States, then the US wouldn't be in the trouble it is. This is from the belief that career politicians are simply out to make money and will only act in the interest of their constituency when their continued easy life is threatened (usually around election time).

Airline food is another, much maligned, problem. How do you store enough food to feed people on long airplane trips? What kind of food can be served in an enclosed, low-air-pressure environment? The common solution is to use some kind of prepackaged, reheated meal. Randall is saying that the people in favor of the Goode Homolosine wonder why the airlines don't simply order meals from the restaurants in the airport, store that food, and serve it, rather than using bland reheated food.

Older cars burned oil like mad fiends, and oil back then would become corrosive to the innards of an engine, so oil had to be changed often. But, with the introduction of synthetic motor oil and better designed engines, new cars only need their oil changed about every 10,000 to 15,000 miles. A common conspiracy theory is that modern automobile oil manufacturers still recommend that car owners change their oil every 3,000-5,000 miles to "drum" up more business, even though that frequency is unnecessary.

All of these references suggest that people who like the Goode Homolosine projection are fans of easy solutions to problems. However, the solutions would not necessarily work in practice. For instance: the restaurants might have trouble making enough food for the whole plane, and it could get cold before being served; the air conditions [http://www.nbcnews.com/health/one-reason-airline-food-so-bad-your-own-tastebuds-6C10823522 aboard planes] can affect taste, so airlines say they optimize for this; there is no such thing as a "normal" person, and if there were, he/she would have virtually no chance at actually getting into government office; and the Goode Homolosine projection, while mostly resembling a flattened orange peel as suggested by the earlier analogy, does indeed cut down on distortion, but also has serious problems of its own, such as leaving huge gaps of nothingness between the continents, making distances across the oceans difficult to visualize.

{{clear}}

===Hobo–Dyer===
[[File:Hobo-DyerProjection.jpg|frame|The Hobo–Dyer projection]]
The {{w|Hobo–Dyer projection}} was commissioned by Bob Abramms and Howard Bronstein and was drafted by Mick Dyer in 2002. It is a modified {{w|Behrmann projection}}. The goal was to be a more visually pleasing version of the Gall–Peters.

As is discussed in the Gall–Peters explanation, the Gall–Peters was developed to be equal area, so that economically disadvantaged areas can at least take comfort in the fact that their country is represented correctly by area on maps.

Randall associates the Hobo–Dyer projection to "crunchy granola" — a stereotype associated with vegetarianism, environmental activism, anti-war activism, liberal political leanings, and some traces of {{w|hippie}} culture.

With feminism becoming mainstream and alternative genders being more widely accepted, some have begun to invent gender-neutral pronouns so that when referring to a person whose gender is not known they cannot be offended by being referred to by the wrong pronouns. In {{w|Middle English}} 'they' and 'their' were accepted gender-less pronouns that could replace 'he', 'she' as well as be used to represent a crowd, but this usage is considered by some to be grammatically incorrect because of the plural/singular debate ([http://www.merriam-webster.com/video/0033-hisher.htm stupid Victorian Grammarians!]). None of the {{w|gender-neutral pronoun#Invented pronouns|many attempts at popularizing invented gender-neutral pronouns}} have achieved any degree of success in the mainstream.

{{clear}}

===Plate Carrée===
[[File:PlateCarreeProjection.jpg|frame|The Plate Carrée projection]]
Also known as the {{w|Equirectangular projection}}, it has been in use since, apparently, 100 AD. The benefit of this projection is that latitude and longitude can be used as x,y coordinates. This makes it especially easy for computers to graph data on top of it.

According to the comic, the projection appeals to people who find much beauty in simplicity.

{{clear}}

===A Globe!===
[[File:GlobeProjection.jpg|frame|The Globe "projection"]]
In any good discussion there has to be at least one smart-ass. This is a comic about map projections, that is, the science of taking a sphere and flattening it into 2 dimensions. The smart-ass believes that we shouldn't even try: a sphere is, tautologically, the perfect representation of a sphere.

To quote ''{{w|The Princess Bride}}'': "Yes, you're very smart. Shut up."

A globe is, of course, the map projection used by {{w|Google Earth}}, and recently by other mapping software as computers and phones get increasingly powerful 3D graphics.

{{clear}}

===Waterman butterfly===
[[File:WatermanButterflyProjection.jpg|frame|The Waterman Butterfly projection]]
Similar to the Dymaxion, the {{w|Waterman butterfly projection}} turns a sphere into an octahedron, and then unfolds the net of the octahedron, which was devised by mathematician {{w|Waterman polyhedron|Steve Waterman}} based upon the work of {{w|Bernard J.S. Cahill}}.

Bernard Cahill published a [http://www.genekeyes.com/B.J.S._CAHILL_RESOURCE.html butterfly map] in 1909. Steve Waterman probably has the only extant "ready to go" map following the same general principles, though Gene Keys may not be far behind. Waterman has a poem with graphics in a similar vein to this xkcd comic that is worth reading.[http://web.archive.org/web/20120118095915/http://watermanpolyhedron.com/worldmap.html]

[http://www.progonos.com/furuti/MapProj/Normal/ProjPoly/projPoly2.html Polyhedral projections] like Cahill, Dymaxion or Waterman typically offer better accuracy of size, shape and area than flat projections, at the expense of compass directionality, connectedness, and other complications.

The joke is that the person responding deeply understands map projections; anyone who knows of this projection is a person that Randall would like to get to know.

{{clear}}

===Peirce quincuncial===
[[File:PeirceQuincuncialProjection.jpg|frame|The Peirce Quincuncial projection]]
The {{w|Peirce quincuncial projection}} was devised by {{w|Charles Sanders Peirce}} in 1879 and uses {{w|complex analysis}} to make a {{w|conformal mapping}} of the Earth, that conforms except for four points which would make up the midpoints of sides and lie on equator (the equator is represented by a square and the corners connect the sides in the middle.)

{{w|Inception}} was a 2010 movie about {{w|meta}} {{w|lucid dream}}ing. It has a complex story that is difficult to follow and leaves the viewer with many questions at the end, and almost needs to be watched multiple times to be understood.

The human brain is not well developed to deal with oddly obvious things. One example is that everyone has a skeleton, but everyone is surprised to see a part of their body represented by an X-ray. Another is the fascinating complexity of the human hand, a machine which is amazingly complex, driven by a complex interplay of electrical and chemical signals; yet is the size of the hand and so useful. A fascination with or fixation on [http://tvtropes.org/pmwiki/pmwiki.php/Main/ContemplatingYourHands such thoughts] is often associated with an altered state of mind brought on by marijuana consumption. Therefore, Randall may be implying that this map would appeal to stoners.

{{clear}}

===Gall–Peters===
[[File:Gall-PetersProjection.jpg|frame|The Gall–Peters projection]]
The {{w|Gall–Peters projection}} is mired in controversy, surprising for a map. {{w|James Gall}}, a 19th-century clergyman, presented this projection in 1855 before the {{w|British Association for the Advancement of Science}}. In 1967, the filmmaker {{w|Arno Peters}} created the same projection and presented it to the world as a "new invention" that put poorer, less powerful countries into their rightful proportions (as opposed to the Mercator). Peters played the marketing game and got quite a few followers of his map by saying it had "absolute angle conformality," "no extreme distortions of form," and was "totally distance-factual" in an age when society was very concerned about social justice. All of these claims were in fact false. The Mercator projection distorts size in favor of shape, and Gall-Peters distorts shape in favor of size, being especially inaccurate at the equator and the poles.

Anyone who loves such a politically charged map that has become popular by way of marketing stunts, Randall would rather not have anything to do with.

{{clear}}

===Title text===
The title text makes a joke that goes to the familiar meme from ''{{w|CSI: Miami}}'', in which the star, David Caruso starts a sentence, then puts on his sunglasses and ends the sentence with a corny pun. In this case, the pun is on {{w|map projection}} and {{w|projection (psychology)|projection}} in psychology. Psychological projection is an unconscious defense mechanism wherein a person who is uncomfortable with their own impulses denies having them and attributes them to other people, and blames these people for these impulses. The Sunglasses internet meme has been used [[:Category:Puts on sunglasses|in other comics]] as well.

==Transcript==
:What your favorite
:'''Map Projection'''
:says about you
:[All of these are organized as Title, a copy of the particular projection underneath, and what it says about you under that.]

:*Mercator
:**You're not really into maps.
:*Van der Grinten
:**You're not a complicated person. You love the Mercator projection; you just wish it weren't square. The Earth's not a square, it's a circle. You like circles. Today is gonna be a good day!
:*Robinson
:**You have a comfortable pair of running shoes that you wear everywhere. You like coffee and enjoy The Beatles. You think the Robinson is the best-looking projection, hands down.
:*Dymaxion
:**You like Isaac Asimov, XML, and shoes with toes. You think the Segway got a bad rap. You own 3D goggles, which you use to view rotating models of better 3D goggles. You type in Dvorak.
:*Winkel-Tripel
:**National Geographic adopted the Winkel-Tripel in 1998, but you've been a W-T fan since ''long'' before "Nat Geo" showed up. You're worried it's getting played out, and are thinking of switching to the Kavrayskiy. You once left a party in disgust when a guest showed up wearing shoes with toes. Your favorite musical genre is "Post–".
:*Goode Homolosine
:**They say mapping the Earth on a 2D surface is like flattening an orange peel, which seems enough to you. You like easy solutions.You think we wouldn't have so many problems if we'd just elect ''normal'' people to Congress instead of Politicians. You think airlines should just buy food from the restaurants near the gates and serve ''that'' on board. You change your car's oil, but secretly wonder if you really ''need'' to.
:*Hobo-Dyer
:**You want to avoid cultural imperialism, but you've heard bad things about Gall-Peters. You're conflict-averse and buy organic. You use a recently-invented set of gender-neutral pronouns and think that what the world needs is a revolution in consciousness.
:*Plate Carrée (Equirectangular)
:**You think this one is fine. You like how X and Y map to latitude and longitude. The other projections overcomplicate things. You want me to stop asking about maps so you can enjoy dinner.
:*A Globe!
:**Yes, you're very clever.
:*Waterman Butterfly
:**Really? You know the Waterman? Have you seen the 1909 Cahill Map it's based— ...You have a framed reproduction at home?! Whoa. ...Listen, forget these questions. Are you doing anything tonight?
:*Peirce Quincuncial
:**You think that when we look at a map, what we really see is ourselves. After you first saw ''Inception'', you sat silent in the theater for six hours. It freaks you out to realize that everyone around you has a skeleton inside them. You ''have'' really looked at your hands.
:*Gall-Peters
:**I ''hate'' you.

{{comic discussion}}

[[Category:Maps‏‎]]
[[Category:Dvorak]]
[[Category:Puts on sunglasses]]

1935: 2018

2017-12-29T17:24:08Z

141.101.105.72: Added explanation

{{comic
| number = 1935
| date = December 29, 2017
| title = 2018
| image = 2018.png
| titletext = We should really start calculating it earlier, but until the end of December we're always too busy trying to figure out which day Christmas will fall on.
}}

==Explanation==
{{incomplete|Created by a BOT - Please change this comment when editing this page. Do NOT delete this tag too soon.}}

Modern cryptography relies on the fact that it is difficult to factorise large numbers. Megan is applying this concept to the year, claiming that it is hard to determine whether or not 2018 is a multiple of four and hence is a leap year. In reality integer division, which is needed here, is fairly easy and even if it weren't 2018 is a sufficiently small number that it can be factorised quickly

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

{{comic discussion}}

Talk:1834: Lunch Order

2017-05-15T06:08:15Z

141.101.105.72:

First! Hee Hee... Anyways... I've been waiting for the site to come back up to find out about "the time autocorrect stopped a nuclear war"... I was sure any such potential war would have been years ago (which this description confirmed), so any such saving would technically be a typo or a mere misspelling and not autocorrect, but I figured that's what this meant. Seeing the explanation now, is this situation just a hypothetical from Randall? The comic is just portraying that? (I didn't make the launch/lunch connection until now, I can only see the title text on this site, which was down) :) - NiceGuy1 [[Special:Contributions/108.162.219.16|108.162.219.16]] 21:31, 12 May 2017 (UTC)

It might be a long shot, according to wikipedia WarGames the movie released on May 7th 1983. 34 years and a day before this comic was posted (IMDB state May 19th 1983 as the release date). [[Special:Contributions/141.101.105.72|141.101.105.72]]

1784: Bad Map Projection: Liquid Resize

2017-01-11T10:28:01Z

141.101.105.72: Typo fix - 'such' in wrong position in paragraph.

{{comic
| number = 1784
| date = January 11, 2017
| title = Bad Map Projection: Liquid Resize
| image = bad_map_projection_liquid_resize.png
| titletext = This map preserves the shapes of Tissot's indicatrices pretty well, as long as you draw them in before running the resize.
}}

==Explanation==
{{incomplete|Partial -- explains a few underlying concepts but needs a lead section}}

South America fits into Africa almost as it did in the era of the super-continent [[wikipedia:Pangaea|Pangaea]].

[[wikipedia:Tissot's indicatrix|Tissot's indicatrices]] are equally sized small circles overlaid on a globe to show the distortion of a particular map projection.

The title text suggests that the shapes of Tissot's indicatrices would be pretty well preserved by the Liquid Resize transformation, 'as long as you draw them in before running the resize'. Since drawing in the indicatrices first would fill all the blank areas between the continents with little circles, the Photoshop filter (which tries to fill blank space) would then no longer be able to find much contiguous blank space anywhere anymore, and in effect leave the input image almost unchanged.. which indeed would cause the shapes of the indicatrices, along with everything else, to be pretty well preserved.

==Transcript==
{{incomplete transcript}}
[Caption at the top of the panel:]

Bad Map Projection #107:

The LIQUID RESIZE

A political map compressed using Photoshop's content-aware resizing algorithm to cut down on unused blank space

[A map of the world divided and colored by political boundaries, with outlines around each continent in black and around each country in dark gray. Antarctica is colored in light gray, bodies of water in white, and countries in pale shades of red, orange, yellow, green, blue, and purple. The map is heavily distorted, with Africa in the center and the other continents curving around it, approximating the bounds of a square with rounded corners.]

{{comic discussion}}

[[Category:Maps]]

1784: Bad Map Projection: Liquid Resize

2017-01-11T10:26:08Z

141.101.105.72:

{{comic
| number = 1784
| date = January 11, 2017
| title = Bad Map Projection: Liquid Resize
| image = bad_map_projection_liquid_resize.png
| titletext = This map preserves the shapes of Tissot's indicatrices pretty well, as long as you draw them in before running the resize.
}}

==Explanation==
{{incomplete|Partial -- explains a few underlying concepts but needs a lead section}}

South America fits into Africa almost as it did in the era of the super-continent [[wikipedia:Pangaea|Pangaea]].

[[wikipedia:Tissot's indicatrix|Tissot's indicatrices]] are equally sized small circles overlaid on a globe to show the distortion of a particular map projection.

The title text suggests that the shapes of Tissot's indicatrices would be pretty well preserved by the Liquid Resize transformation, 'as long as you draw them in before running the resize'. Since drawing in the indicatrices first would fill all the blank areas between the continents with little circles, the Photoshop filter (which tries to fill blank space) would then no longer be able to find much contiguous blank space anywhere anymore, and in effect leave such the input image almost unchanged.. which indeed would cause the shapes of the indicatrices, along with everything else, to be pretty well preserved.

==Transcript==
{{incomplete transcript}}
[Caption at the top of the panel:]

Bad Map Projection #107:

The LIQUID RESIZE

A political map compressed using Photoshop's content-aware resizing algorithm to cut down on unused blank space

[A map of the world divided and colored by political boundaries, with outlines around each continent in black and around each country in dark gray. Antarctica is colored in light gray, bodies of water in white, and countries in pale shades of red, orange, yellow, green, blue, and purple. The map is heavily distorted, with Africa in the center and the other continents curving around it, approximating the bounds of a square with rounded corners.]

{{comic discussion}}

[[Category:Maps]]