explain xkcd - User contributions [en]

Talk:2748: Radians Are Cursed

2023-04-14T15:43:15Z

1844161:

how do transcript [[Special:Contributions/172.70.127.37|172.70.127.37]] 19:23, 10 March 2023 (UTC)

https://en.wikipedia.org/wiki/Square_degree may be of some help with this one. [[Special:Contributions/162.158.166.124|162.158.166.124]] 19:44, 10 March 2023 (UTC)

The comic isn't actually correct. A radian is not equal to the length of a circle's radius; it is equal to the length of the radius, multiplied by 2π, divided by the perimeter, which is why it has no units, while the length does. In other words, radian/2pi=length of radius/length of perimeter. [[Special:Contributions/172.70.46.84|172.70.46.84]] 19:51, 10 March 2023 (UTC)

As suggested by the above Wikipedia link, square degrees are in fact often used in astronomical contexts. Also, it's quite standard to say that radian=1; see for example [https://en.wikipedia.org/wiki/SI_derived_unit SI derived unit]. An angle is the ratio between the arc length and the radius, and we just optionally append "radian" for clarity. So 1 = 57.3 degrees is correct; Randall simply used the wrong argument to obtain it. [[User:Aseyhe|Aseyhe]] ([[User talk:Aseyhe|talk]]) 20:57, 10 March 2023 (UTC)
:I always understood radian to be the name of the unit, so by definition 1 radian=1. [[User:Barmar|Barmar]] ([[User talk:Barmar|talk]]) 21:17, 10 March 2023 (UTC)
:It is a shame that astronomers don't use the proper unit for such things: the steradian. It is literally there for describing the 3D equivalent of angle. Oh well... --[[Special:Contributions/172.69.79.137|172.69.79.137]] 04:16, 11 March 2023 (UTC)
::It is a shame that astronomers don't use the proper for length, preferring ad-hoc units based on the solar system. But if you use a different ad-hoc unit based on the properties of the solar system they throw a hissy fit.[[Special:Contributions/172.70.38.150|172.70.38.150]] 06:51, 12 March 2023 (UTC)
:::Indeed, what ''is'' the "proper [distance unit?] for length"? Light-year, based on Earth's orbital period. AU, based upon Earth's orbital radius. (Kilo)metre, based (approximately, and quartered) upon Earth's circumpolar circumference. Parsec, based upon Earth's orbital radius and a notionally arbitrary subdivision of angle. (Which can be avoided by mathematically more pure "paradians"???) Planck-lengths, might be not solar-/geo-centric but creates horribly huge numbers even at the human scale. ;) [[Special:Contributions/172.70.86.128|172.70.86.128]] 16:07, 12 March 2023 (UTC)
::::Planck length could work. Large Number problem can be resolved by 10insert number here Planck Lengths, since astronomers already do it, and round _insert number here_!! [[User:1844161|1844161]] ([[User talk:1844161|talk]]) 15:43, 14 April 2023 (UTC)

Someone fix the vandalism, how do you upload images? --[[User:Purah126|Purah126]] ([[User talk:Purah126|talk]]) 03:06, 11 March 2023 (UTC)
:I'm doing it but that user needs to be blocked.
:To revert images, scroll down and click the revert link next to the last good version.
:And do not feed the trolls. ~ [[user:megan|Megan]] she/her [[user talk:megan|talk]]/[[special:contribs/megan|contribs]] 03:10, 11 March 2023 (UTC)

On reading this I vividly remembered a maths teacher once asking our class "What's 10% of a straight line?", and the looks of disgust and bewilderment when he said the answer was 18 degrees. [[Special:Contributions/172.70.86.147|172.70.86.147]] 08:31, 11 March 2023 (UTC)
:I just hope that was Celsius degrees (or Kelvin), rather than Fahrenheit(/Rankine). ;) [[Special:Contributions/172.71.242.190|172.71.242.190]] 10:51, 11 March 2023 (UTC)
::If you use Kelvin with degrees you have already lost...[[Special:Contributions/172.68.51.178|172.68.51.178]] 13:29, 11 March 2023 (UTC)

So the volume of the sky is 4/3 π r³ = 7,092,429 cubic degrees

I remember in the quantum mechanics class we figured that if \hbar is defined to be h/2π, then we might as well introduce the notation \pibar as an alternative for 1/2. [[User:Captain Nemo|Captain Nemo]] ([[User talk:Captain Nemo|talk]]) 11:08, 12 March 2023 (UTC)

The logic is fine once you recall the formula s = r x theta. The arc length subtended by an angle is equal to the radius times the angle. On the unit circle, the radius is 1 (no unit). Therefore, the subtended arc length of 1 radian is s = 1 x 1 radian = 1 radian. [[Special:Contributions/172.71.22.117|172.71.22.117]] 21:45, 12 March 2023 (UTC)
:"...the radius is 1 (no unit)." There's definitely a unit. It's whatever the unit the unit circle is reflecting (even if that's mathematical Unity). And in the case of dimensional analysis, it's a particular dimension that you'd need to account for, and the difference between this radians thing and the degrees thing is only the inclusion of dimensionless pi-based constant of conversion. Doesn't change the understanding of the issue, but I believe that some explanations/comments aren't then conveying it onwards accurately. [[Special:Contributions/172.69.79.184|172.69.79.184]] 22:15, 12 March 2023 (UTC)
::I mean, I'm sorry, but respectfully, you are wrong. The unit circle is *by definition* a circle of radius 1. There is no unit attached to that. [[Special:Contributions/172.71.82.41|172.71.82.41]] 01:55, 13 March 2023 (UTC)
:::Correction: The unit is that of the radius, ''by definition''. It is one of that unit, whatever that unit may be. You attach whatever unit you want to it, when you want to, but it isn't actually a unitless value when you start comparing it with othe values whose relationship and own unit are known. [[Special:Contributions/172.71.178.207|172.71.178.207]] 03:59, 13 March 2023 (UTC)

There is actually some dispute about whether angles should be measured using units. I can't find it now, but there was an article by someone arguing that the current SI definition of the radian as 1 rad = 1 m / 1 m was flawed. He felt that units of angle should have a dimension, A, and rewrote several formulae slightly to accommodate this. But more often today, the radian is considered dimensionless with a value of exactly 1, making it not actually a "unit" so much as a hint telling how the angle was measured. In this definition, an angle has a measure of x (radians) iff the circular arc it intercepts as a central angle has an arclength of x times the circle's radius. Under this definition, the following become mathematically correct:
:rad = 1
:° = π/180
:Radius of unit circle = 1 = (180/π)(π/180) = (180/π)° = 57.29577...°
:(1°)² = π²/32400
There is really nothing mysterious about it. Here, we are just defining the radian and degree as real numbers. This is how we treat them in Calculus. For instance, d/dx sin(2x rad) = 2 cos(2x rad), not (2 rad) cos(2x rad) as the chain rule implies. This is because 2 rad = 2. This also helps explain why Phil Plait's bizarre dimensional analysis actually does work. In particular, the last equation above would normally be written with "rad" on the right-hand side, giving a conversion between square degrees and square radians. Using the fact that the area of a sphere is 4πr², we see that the area of the unit sphere must be 4π square radians, and thus 4π * (32400/π²) * (1°)² = (129600/π)°² = 41252.961...°². Note that a "square radian" is also equal to a "steradian" by definition, which is the solid angle that subtends 1/(4π) of the surface of the sphere. [[Special:Contributions/172.70.127.38|172.70.127.38]] 02:56, 13 March 2023 (UTC)
: In complex analysis we defined the exponential function as a power series. Pure complex numbers, no units or even a hint that there is such a thing as an angle in the definition. Many theorems and lemmas about the properties of exp(z) follow, including derivatives, integrals, Eulers formula, Eulers identity. Sin() and cos() are defined as the real and imaginary parts of exp(); pi is defined as a number via Eulers identity. No circles or angles involved. In the last lecture the properties of the exponential combine in a few lemmas to show that it can trivially solve a bunch of problems such as the simple harmonic oscillator and trigonometry.
: The point is we can define exp(), hence sin() and cos(), without using angles. There is no need for a unit for angles until you start working with angles, just as there is no need for a unit for elephants until you start counting elephants. You could reorder the textbook, put the trigonometry chapter before complex analysis and define angles first, but you'd have to be a masochist or a high school teacher to do it that way.[[Special:Contributions/172.70.174.160|172.70.174.160]] 05:24, 13 March 2023 (UTC)

:: Sure, but in the same way "number of elephants" is dimensionless, "measure of angle" is also dimensionless. That's not true of physical quantities like distance or area. And in this convention, we do have radian = 1. (The SI even defines the radian as 1 m / 1 m, so clearly it has to equal 1.) [[Special:Contributions/172.71.254.135|172.71.254.135]] 19:18, 13 March 2023 (UTC)

:::2 pi is a full circle, also in another galaxy, or in another universe. All real units contain (are, in fact) some arbitrarily chosen factor. --[[Special:Contributions/172.71.246.11|172.71.246.11]] 08:07, 14 March 2023 (UTC)
::::They {{w|Natural units|needn't be}}... [[Special:Contributions/172.70.162.135|172.70.162.135]] 13:16, 14 March 2023 (UTC)

Anyone else surprised Randall didn't save this comic for Pi Day? It would've been a perfect fit, and just 4 days later! [[User:PotatoGod|PotatoGod]] ([[User talk:PotatoGod|talk]]) 06:30, 15 March 2023 (UTC)

Talk:2753: Air Handler

2023-04-14T15:36:49Z

1844161:

I called the device an Air Handler in the transcript, but should we change that? [[User:E'); DROP TABLE users;--|E'); DROP TABLE users;--]] ([[User talk:E'); DROP TABLE users;--|talk]]) 5:11, 23 March 2023 (UTC)

"It is not particularly usual to directly monitor the number of bees in an air-stream" - understatement of the week :o) [[Special:Contributions/172.68.210.41|172.68.210.41]] 05:46, 23 March 2023 (UTC)
:And statements like these are the reason why explainxkcd is so great :D [[User:Elektrizikekswerk|Elektrizikekswerk]] ([[User talk:Elektrizikekswerk|talk]]) 11:06, 23 March 2023 (UTC)

I think the transcript is complete, will be deleting unless someone proves otherwise in four hours. [[User:E'); DROP TABLE users;--|E'); DROP TABLE users;--]] ([[User talk:E'); DROP TABLE users;--|talk]]) 11:50, 23 March 2023 (UTC)

Some of these parameters have an ideal range (temperature, humidity, pressure), but others should be minimized (dust, smoke, odors, number of bees). Well, not into the negative range, but I think you'll understand me! ~ [[user:megan|Megan]] she/her [[user talk:megan|talk]]/[[special:contribs/megan|contribs]] 23:44, 23 March 2023 (UTC)

:Well, if there are config files, you can just set the range to be from 0 to 0. Then again, this is Black Hat... [[Special:Contributions/198.41.238.10|198.41.238.10]] 03:15, 24 March 2023 (UTC)
::connect it to a computer with a (maybe USB-C or some other) cable and go and add "minBees = 0;
maxBees = 0;" to /scripts/ControlAir/config.conf [[Special:Contributions/172.68.183.13|172.68.183.13]] 13:27, 28 March 2023 (UTC)
:::I think it'll need a USB-EE connector, actually... [[Special:Contributions/172.70.162.158|172.70.162.158]] 02:07, 29 March 2023 (UTC)
::I think that he made it so that "number of bees" had to be nonzero. Also, I think that the negative range could be available, and would be... weird. --[[User:Purah126|Purah126]] ([[User talk:Purah126|talk]]) 12:38, 24 March 2023 (UTC)
:::I personally would like to see a device that generates negative bees... I'm deathly phobic. [[User:RandalSchwartz|RandalSchwartz]] ([[User talk:RandalSchwartz|talk]]) 18:24, 26 March 2023 (UTC)
::::I hope doesn't generate anti-bees. That would be slightly problematic since anti-bees react exothermically with most common materials, including air, water, and (to scare off some chemists) glass. ~ [[user:megan|Megan]] she/her [[user talk:megan|talk]]/[[special:contribs/megan|contribs]] 18:47, 26 March 2023 (UTC)
:::MinBees = 0.5;
:::MaxBees = 1.5;[[Special:Contributions/172.71.242.191|172.71.242.191]] 08:03, 27 March 2023 (UTC)

This immediately got me wondering how it would deal with excess bees. It's not like you can filter them out as they pass through the device. It'd have to launch some kind of tiny flying robot to attack them or something. And then if there's too few bees, well… Let's just say I was pretty confident that the title text would use the word "drones" at least twice. -- [[User:Angel|Angel]] ([[User talk:Angel|talk]]) 09:15, 24 March 2023 (UTC)
:1) Filtration through mosquito-net would be possible, and since these nets are frequently metallic, durability is a moot point.
2) Bee storage unit (perhaps those captured excess bees could be stored themselves to reduce bee wastage) could be a component. [[User:1844161|1844161]] ([[User talk:1844161|talk]]) 15:36, 14 April 2023 (UTC)

I could see a VR rig adding a (controlled) pulse of H2S when you enter a sewer. With hardware limits to prevent any dangerous concentrations of course. {{unsigned ip|172.71.158.7}}

"Amount of bees" doesn't seem to make sense unless the air handler can view the contents of the entire room. "Concentation of bees" makes more sense. ~ Megan she/her [[user talk:megan|talk]]/[[special:contribs/megan|contribs]] 18:52, 26 March 2023 (UTC)
:A standard air-conditioner can only work with the air in its own air-channel (and maybe detect the state of the air that touches it, if it has external sensors) so I'd say that it's perfectly valid to do a count of bees that [[571: Can't Sleep|get spotted moving through/by it]].
:But then this is a Black Hat, doing this. Who knows quite what he's implmented... ;) [[Special:Contributions/141.101.99.113|141.101.99.113]] 19:22, 26 March 2023 (UTC)
:Is a "normal amount of bees" a floating point? imagine – darkness bright 07:35, 1 April 2023 (UTC)

My first thought on reading the panel is that the device might not actually do anything. For example if the lower limit for temperature is set to absolute zero and the upper limit as the temperature of the universe at the time of the big bang.[[Special:Contributions/172.71.254.135|172.71.254.135]] 04:39, 12 April 2023 (UTC)

Talk:2762: Diffraction Spikes

2023-04-14T15:24:21Z

1844161:

I tried to make an initial explanation, but then someone beat me to it and I made a fool of myself on the page trying to add a comment where it didn't go. I fixed it, but I am ashamed ;~; [[Special:Contributions/172.69.34.15|172.69.34.15]] 23:31, 12 April 2023 (UTC)
:It's all good. As long as you learn from it, and we learn what useful things you want to say, nothing at all to worry about... All power to your typing fingers! [[Special:Contributions/172.70.85.66|172.70.85.66]] 00:15, 13 April 2023 (UTC)
Exoplanets nevertheless exist because, alongside the visible diffraction spikes that chop them up, there are invisible defraction [sic] spikes that reassemble them. [[Special:Contributions/162.158.158.136|162.158.158.136]] 00:32, 13 April 2023 (UTC)
:Pretty sure gravity causes the pieces to drift back together. [[Special:Contributions/172.69.58.86|172.69.58.86]] 20:33, 13 April 2023 (UTC)

Why does the spike slice the planet instead of the planet breaking the tip off the spike? Are the spikes like enormous light sabers? [[User:Barmar|Barmar]] ([[User talk:Barmar|talk]]) 00:43, 13 April 2023 (UTC)
:The spikes are stellar artifacts of distant observers, with all the mass of the star behind them. The Sun hardly moves much if you dunk the Earth into it, why should the exoplanet move the spike? At best you'd get a similar effect to karate chopping a stream of water from a hose. [[Special:Contributions/172.71.150.175|172.71.150.175]] 04:49, 13 April 2023 (UTC)
::Please stop dunking the Earth into the Sun.[[Special:Contributions/172.71.242.172|172.71.242.172]] 08:11, 14 April 2023 (UTC)
:Adding to 172.71...'s point, the spikes are made of star, so it will be incandescent gas with plasma corona. How do you "break" a gas?

Is it inspired by some movie that features this "spike pointing on some person" effect? I remember seeing one, but I don't seem to remember its name. [[User:Unreliable Connection|2659: Unreliable Connection]] ([[User talk:Unreliable Connection|talk]]) 02:07, 13 April 2023 (UTC)

:This comic also reminded me of fractal images. [[User:Memo Spike Connector|2503: Memo Spike Connector]] ([[User talk:Memo Spike Connector|talk]]) 09:06, 13 April 2023 (UTC)

:Is there also some joke here about double vision (if you cross your eyes you will see two planets), you use lens occlusion to see expolanets? ([[garbled]])) 10:55, 14 April 2023 (UTC+1)

From an edit comment "(Refractor telescopes (using only lenses) don't give refraction spikes, reflector telescopes (using mirrors) do.)". Yeahbut, nobuf... It's just the struts, also mentioned, that are the key. You can build pure-refractor telescopes that still have struts (probably not optimal, but a design option) and therefore spikes. And you can make one with mirrors and ''no'' struts (more complicated and less of a practical shape for most mounting/launching purposes) which would therefore be spikeless. [[Special:Contributions/172.70.162.160|172.70.162.160]] 12:00, 13 April 2023 (UTC)

:Some telescopes get diffraction spikes from the shape of the mirror. The JWST is a notable example of this. --[[Special:Contributions/172.71.178.186|172.71.178.186]] 14:13, 13 April 2023 (UTC)
::It's the sharp, angled edges that provide interference patterns (a set of "one-sided diffractions", rather than two-sided ones around an obstruction). A full round mirror on its own would not produce any spikes. Nor if the light from the edge areas cannot possibly reach the sensors, but that would mean less use of the mirror(s) they took great pains to send up there. And the secondary mirror ''has'' struts (in a Y-shape, I think, for technical reasons), thus why there's two minor spikes (actually six, but four are aligned to be hidden within the major spikes) as well as the hexagon-edge-induced set of six. Which also helps you understand in which orientation (or which two possibilities) the JWST was, in order to make any images you see from it.
::But this is already over-explained, really. You ''can'' design a mirror set to a avoid spikes, but with other technical compromises/etc. And above is correct, in that refractive telescopes can find themselves showing spikes (struts, if so designed, and other internal angles that may intrude into the light-path's edge). [[Special:Contributions/172.71.242.86|172.71.242.86]] 17:27, 13 April 2023 (UTC)

The transcript is very long... Too long : as of now, 2055 characters. That "transcript" section is intended for people who can't see the image (blind people for example), so it should be almost as fast to read as it is for you to look at the comic. There is really no need the exact angles of the diffraction spikes or anything, just a description of what's happening so that we can get the joke. You should not try to write a vectorization of the image, there are automated tools for that. [[Special:Contributions/172.71.122.208|172.71.122.208]] 18:04, 13 April 2023 (UTC)
:The comment speaks to the difficulty of creating a transcription of an image that is meaningful to a person who cannot access the image. It would be good to hear from such folk about this.[[Special:Contributions/172.70.110.215|172.70.110.215]] 22:15, 13 April 2023 (UTC)

Why is the asteroid belt mentioned in the explanation? [[Special:Contributions/172.71.222.129|172.71.222.129]] 19:13, 13 April 2023 (UTC)k
:If "all stars" have diffraction spikes, then there should be no planets around Sol. We exist, so Sol must be an exception to "all stars". But the asteroid belt (chopped-up planet(s)) also exists, so perhaps Sol had diffraction spikes sometime in its history. Yes, there's a real, and satisfactory, explanation for the Solar System's Jovian asteroid belt. But, context.[[Special:Contributions/162.158.154.150|162.158.154.150]] 21:58, 13 April 2023 (UTC)

I guess this refers to a solar storm predicted to go on in 2023, which does great damage to the earth's atmosphere like a spike. [[User:ClassicalGames|ClassicalGames]] ([[User talk:ClassicalGames|talk]]) 06:07, 14 April 2023 (UTC)

Talk:2763: Linguistics Gossip

2023-04-14T15:21:07Z

1844161:

Added initial explanation [[User:Bamboo|Bamboo]] ([[User talk:Bamboo|talk]]) 14:08, 14 April 2023 (UTC)Bamboo

Added possible explanation of title text [[User:Bamboo|Bamboo]] ([[User talk:Bamboo|talk]]) 14:14, 14 April 2023 (UTC)Bamboo

Has anyone asked O what they think of all this?[[Special:Contributions/172.70.91.152|172.70.91.152]] 14:32, 14 April 2023 (UTC)

NOTE: I'm assuming the IE/VE ligature is IE, where the I is tilted
Could this also be a reference to the historical Latin pronunciation of Æ, and its separation into "AA" (which could be represented by "ar" in English ("r" is silent), hence the ligature "AR") and "IE" (which would be pronounced "ee" as in "relieve") [[User:1844161|1844161]] ([[User talk:1844161|talk]]) 15:21, 14 April 2023 (UTC)