explain xkcd - User contributions [en]

2760: Paleontology Museum

2023-04-10T01:08:31Z

172.69.134.99:

{{comic
| number = 2760
| date = April 7, 2023
| title = Paleontology Museum
| image = paleontology_museum_2x.png
| imagesize = 485x155px
| noexpand = true
| titletext = Nowadays the only ones left that do anything are turtles.
}}

==Explanation==
{{incomplete|Created by a ROCK - Please change this comment when editing this page. Do NOT delete this tag too soon.}}
In this comic, Cueball and Megan went to a {{w|paleontology}} museum and are looking at the {{w|Fossil#Permineralization|fossilized}} skeleton of a ''{{w|Stegosaurus}}''.
Dinosaurs encompassed a wide variety of species that would be amazing to see alive today, including T. rexes, Stegosaurus, Velociraptor, etc.{{fact}} Cueball is remarking that the "bones" they are looking at [https://www.amnh.org/dinosaurs/dinosaur-bones are now actually rock], and that 'rocks' then were way cooler (e.g. inside a dinosaur) than modern rocks. He may be under the impression that dinosaurs looked like their skeletons and therefore, were "rocks" that could walk, making them more cool than our modern inanimate rocks (except for turtles).

The title text refers to {{w|turtles}}. This could be interpreted in two ways. In the first interpretation, you could say that their hard shells make them seem like rocks that are able to move on their own. This gives the latest approximation to modern "rocks" that do more or look cooler than just plain old rocks. In the second interpretation, the text could be generalizing the idea of bone-based armor as "rocks" to other animals. This would include other armored animals like armadillos and pangolins.

==Transcript==
:[Cueball, who is standing to the right of Megan, are in what is presumably a museum, and are viewing a stegosaurus skeleton. The skeleton, which has everything starting from the pelvis cut off by the edge of the panal, is on a pedestal and there is a placard on a stand in front of it.]

:[Panel of just Cueball and Megan.]
:Cueball: Wow.

:[Cueball and Megan standing.]
:Cueball: Rocks used to be '''''so cool'''''.

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Dinosaurs]]
[[Category:Geology]]

Talk:2623: Goofs

2023-04-10T00:53:46Z

172.69.134.99: Sorry, I'm in a hurry

I'm getting a 404 error when I try to go to the comic by number. But it shows up on the main xkcd.com home page. [[User:Barmar|Barmar]] ([[User talk:Barmar|talk]]) 16:39, 23 May 2022 (UTC)
: https://xkcd.com/2623/ works for me. [[User:Sollyucko|Sollyucko]] ([[User talk:Sollyucko|talk]]) 16:52, 23 May 2022 (UTC)

Any New Yorkers here to confirm if there's a harpoon store a few blocks from Union Square? If not, that needs to be listed here as a "goof"... I really do love that line suggesting "harpoon stores" are common enough but the nearest one doesn't have an outdoor display. [[User:Ids1024|Ids1024]] ([[User talk:Ids1024|talk]]) 17:18, 23 May 2022 (UTC)
: Remember that it needs to be a harpoon store that was operating in 2018. I think there was a Whalers Я Us near Union Square before it permanently closed during Covid. [[Special:Contributions/172.71.30.33|172.71.30.33]] 20:27, 23 May 2022 (UTC)
:: This comment is facetious, right? [[Special:Contributions/108.162.221.81|108.162.221.81]] 04:38, 24 May 2022 (UTC)

There may not be a store explicitly called a "harpoon store", but there is at least one diving equipment store that has harpoons. [[Special:Contributions/162.158.78.65|162.158.78.65]] 17:27, 23 May 2022 (UTC)
: Yeah, harpoons might be sold at a store that doesn't exclusively or even primarily only sell harpoons, though that wouldn't necessarily change there not being a source for them at the location of the movie scene, let alone the fact that a store that carried them probably wouldn't have them on an outdoor display rack.--[[Special:Contributions/172.69.70.39|172.69.70.39]] 23:36, 24 May 2022 (UTC)

I'm glad Randall Munroe also hates CinemaSins. [[User:Lordpipe|Lordpipe]] ([[User talk:Lordpipe|talk]]) 17:32, 23 May 2022 (UTC)
:WHERE does he reference CinemaSins? As a fan of both I'd LOVE to see some indication Randall is even aware of CinemaSins, :) [[User:NiceGuy1|NiceGuy1]] ([[User talk:NiceGuy1|talk]]) 04:11, 28 May 2022 (UTC)

Nobody tell Randall about [[https://www.moviemistakes.com/]] [[User:Kev|Kev]] ([[User talk:Kev|talk]]) 17:41, 23 May 2022 (UTC)

IMDB is also referenced in: [[2441]], [[155]] (ish), and [[1460]] (in the title text) [[Special:Contributions/172.70.174.91|172.70.174.91]] 20:34, 23 May 2022 (UTC)Bumpf

Do any Muppets movies contain billboards for themselves? That feels like something a Muppets movie would do. [[User:GreatWyrmGold|GreatWyrmGold]] ([[User talk:GreatWyrmGold|talk]]) 20:48, 23 May 2022 (UTC)
:I don't remember any in A Muppets Christmas Carol. But it's been a while since I saw it, so... [[Special:Contributions/172.70.90.145|172.70.90.145]] 22:13, 23 May 2022 (UTC)

as soon as i saw the "goofs" section of the explanation itself i started wheezing harder than i had at any other explainxkcd page ever. whosoever idea that was, you are a genius --[[Special:Contributions/172.70.34.171|172.70.34.171]] 02:09, 24 May 2022 (UTC)
:I just dropped by to say "Bravo!" to whoever worked on the GOOFS section. (I didn't check the page history.) [[User:Nitpicking|Nitpicking]] ([[User talk:Nitpicking|talk]]) 02:39, 24 May 2022 (UTC)
:: I did check the page history but couldn't figure out who started and added to "Goofs." I agree that the section is genius. [[Special:Contributions/108.162.221.81|108.162.221.81]] 04:38, 24 May 2022 (UTC)
::: It looks like it was [[User:Kev|Kev]] how added the "goofs" section [[User:Kvarts314|Kvarts314]] ([[User talk:Kvarts314|talk]]) 10:19, 24 May 2022 (UTC)
::::Yes he added the first entry, but others have added the rest. I'm uncertain I think it belongs here, but it is funny. Maybe move it down under the transcript?--[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 11:50, 24 May 2022 (UTC)
:::::IMO, it has the same 'status' as a Trivia section (it is one of those in almost every regard, after all), which is traditionally placed post-Teanscript. But I'm not a prescriptionist, at least not in this case, just saying I think it'd be consistent. If you even need my anonymous support for such a trivial within-page move. [[Special:Contributions/141.101.98.11|141.101.98.11]] 11:57, 24 May 2022 (UTC)
:::::In my opinion it does not "nothing to explain the comic" - quite the contrary: It's the best way to explain what the comic is about. See https://tvtropes.org/pmwiki/pmwiki.php/Main/SelfDemonstratingArticle and https://tvtropes.org/pmwiki/pmwiki.php/Main/ComicallyMissingThePoint [[User:Elektrizikekswerk|Elektrizikekswerk]] ([[User talk:Elektrizikekswerk|talk]]) 13:17, 24 May 2022 (UTC)
:::::You people are the reason I always press "Go to this comic explanation" first thing I visit. Love you all![[Special:Contributions/172.68.50.91|172.68.50.91]] 18:04, 24 May 2022 (UTC)

Random movie goof validates Randall, as expected: 
I picked "The Game", one of my favourites, but also because it's set in SF and has many outdoor scenes. 
Sure enough, there were several trivial goofs, but not location-wise. 
Check this one out: 'In the end credits, rigging grip Michael Santoro's name is spelled "Micheal".' 
Followed by this: 'In the end credits, there's an extra space between actor André Brazeau's first and last names.' [[User:Beechmere|Beechmere]] ([[User talk:Beechmere|talk]]) 04:22, 24 May 2022 (UTC)Beechmere
:This is why there are now different types, so you can jump over the borring to those with plot points, or errors by characthers... --[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 11:52, 24 May 2022 (UTC)

"Spaceballs" is a notable exception to "Most movies do not exist within the fictional world they portray." When will then be now? Soon! [[Special:Contributions/172.70.175.146|172.70.175.146]] 14:27, 25 May 2022 (UTC)

:As is the Muppet Movie - Dr. Teeth and the Electric Mayhem are able to find and rescue our stranded heroes by reading the screenplay [[Special:Contributions/172.70.126.49|172.70.126.49]] 15:43, 14 July 2022 (UTC)

As an IMDb contributor - mainly Trivia and Goofs - I feel targeted here, LOL! Thankfully I don't submit such nitpicky things, and obviously future and alternate versions of real life places are allowed these (maybe the street was renamed and another harpoon store opened up in the meantime). [[User:NiceGuy1|NiceGuy1]] ([[User talk:NiceGuy1|talk]]) 03:59, 28 May 2022 (UTC)

Recently, a lot of spam posts were found in the [[Template:sandbox]] page, including some "goofs". [[Special:Contributions/172.69.134.99|172.69.134.99]] 00:53, 10 April 2023 (UTC)

2753: Air Handler

2023-04-04T04:01:33Z

172.69.134.99: Elaborated a bit

{{comic
| number = 2753
| date = March 22, 2023
| title = Air Handler
| image = air_handler_2x.png
| imagesize = 591x228px
| noexpand = true
| titletext = It maintains odor levels in a normal familiar range, so if you open the windows and the air gets too fresh, it filters it through some dirty laundry samples to compensate.
}}

==Explanation==
{{incomplete|Created by an UNUSUAL AMOUNT OF BEES - Please change this comment when editing this page. Do NOT delete this tag too soon.}}

[[Black Hat]] is demonstrating an air-conditioning unit that covers a wide-variety of air qualities, as opposed to a heater that just warms air, a filter that just removes dust or a dehumidifier with the main purpose of removing moisture from the air.

In many devices that manage certain atmospheric conditions in a building using one device, an operational range is usually defined, and not one number. For example, when using a {{w|heat pump}}, if the interior temperature drops below a preset lower limit, then the heating function would be activated. If the interior temperature rises above another preset upper limit, the cooling function would be activated. This kind of ranged function is common with humidifier/dehumidifier units as well, to create a comfortable condition not too dry nor damp for comfort. By specifying upper and lower limits for the operation of the device in question, minor variations of the controlled value will not cause the device to be rapidly turning on and off, even working against itself, improving efficiency and reducing unnecessary wear and tear on the device and the building contents.

Devices that manage temperature and humidity are often installed in buildings to improve occupant comfort. Beyond that, the listed qualities become increasingly problematic and even dangerous.

Changing the pressure of the air could lead to <s>unintended</s> effects like large winds blowing through any cracks in the building.

The air handler also attempts to force the parameters of dust, smoke, odors, and number of bees into an "ideal" range. However, as opposed to being in a certain range, most people who live indoors prefer that these be minimized.{{fact}} It's also worth noting that "a normal amount" of bees varies widely depending on the situation. A typical honeybee colony contains [https://www.science.org.au/curious/earth-environment/honeybee-hive 60,000 to 80,000 bees], and a typical {{w|Swarming_(honey_bee)|swarm}} (bees looking to establish a new hive) is anywhere from [https://www.bee-commerce.com/content/freedownloads/FactsAboutSwarms.pdf 1,500 to 30,000]. To pollinate an acre of fruiting trees typically requires a minimum of [https://treefruit.wsu.edu/orchard-management/pollination/honey-bees/ 20,000 bees], or approximately five bees per square meter.

It is not particularly usual to directly monitor the number of bees in an air-stream (usually, insect-screens are the main way to filter out any pesky creatures that might find themselves likely to be caught up in that way), and one might imagine that the upper limit ''should'' be zero, for use indoors in standard living/working spaces, but it might be technically feasible to accurately count bees (with or without distinguishing from wasps and other flying insects) and be able to allow ''some''. But, unlike temperature or humidity, it would be rare (outside of a location used for agriculture) to have a non-zero ''minimum'' desirable quantity of bees. Even more so to then be directly equipped to upwardly correct the current value. For any minimum value that is not zero, this machine would be equipped to deal with it by, presumably, releasing bees (it seems to have at least one trapped inside it ready to be released, judging by the buzzing sound), or by generating smoke, dust and odors – something one would typically not miss if lacking.

As the title text elaborates, the machine analyses and adjusts the 'freshness' of the air. A smart system in charge of odor-control (by spraying smell-suppressing chemicals and/or more desirable and dominant scents) could be made less wasteful by only trying to 'freshen' the air when it detects enough necessity. But, of course, this machine also has an opposing limit. And, when the air is considered ''too'' fresh, it has a way of ''adding'' staleness/stinkiness to meet expectations with dirty laundry.

==Transcript==
:[Black Hat is standing to the right of an "air handler", talking to Cueball and Megan on the left side, probably presenting the sales pitch for the air handler in between them.]
:Black Hat: Our device monitors your home's air and keeps every variable between a lower and upper limit.

:[Zoom in on Black Hat]
:Black Hat: Temperature, humidity, pressure, dust, smoke, odors, number of bees...

:[Zoom out similar to Frame #1]
:Megan: Wait.
:Megan: What's the '''''lower''''' limit for "number of bees"?
:Black Hat: A normal amount.
:Air Handler: ''Bzzzzzz''

{{comic discussion}}

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

2520: Symbols

2023-03-20T07:13:30Z

172.69.134.99:

{{comic
| number = 2520
| date = September 24, 2021
| title = Symbols
| image = symbols.png
| titletext = "röntgen" and "rem" are 20th-century physics terms that mean "no trespassing."
}}

==Explanation==
This comic refers to elements of (mostly mathematical or engineering) notation commonly used in various fields of math and science. Each piece of notation is presented as "symbolizing" not what it specifically means, but a typical ''context'' in which it might be encountered, see [[#Symbols|below]].

Many of the individual descriptions look like verbiage that might be found on informational or warnings signs or placards, although typically with a silly edge.

The title text refers to two non-SI units of radiation measurement, {{w|Roentgen (unit)|röntgen}} and {{w|Roentgen equivalent man|rem}}. In the mid-20th century when they were in use, the dangers of radiation weren't as well understood as today, so an area with radiation that was noteworthy back then is [https://archive.md/v3dME probably dangerous], hence the no trespassing part.

Later [[Randall]] made a similar comic, [[2586: Greek Letters]], regarding the use of Greek letters in math.

===Symbols===
'''d⁄dx: An undergrad is working very hard''' d/dx is the symbol for a single-variable {{w|Derivative|derivative}}. This is one of the basic operations in {{w|calculus}} and consequently is ubiquitous in the work of undergraduates in the sciences. A hard-working undergraduate in the relevant fields would churn through exercises using this symbol.

'''∂⁄∂x: A grad student is working very hard''' The replacement of the standard "d" letters with the curly letters "∂" denotes the partial derivative, which generalizes the ordinary derivative to multi-variable calculus. Problems with partial derivatives, especially partial differential equations, can be extremely challenging. Although PDEs would typically be first taught at an undergraduate level, difficult partial derivatives would be encountered in graduate-level work.

'''ħ: Oh wow, this is apparently a quantum thing''' ħ (pronounced "h-bar") is a symbol used for (the reduced) {{w|Planck's constant}}, a universal, fundamental constant in quantum physics. ħ is equal to the energy of a photon divided by its frequency, and angular momentum in quantum mechanical systems is measured in quantized integer or half-integer units of ħ.
Classical physics appears as a limit of quantum physics if all "actions" (quantities of dimension energy * time, momentum * length, or angular momentum) are much larger than ħ. Conversely, you can also formally set ħ=0 to get classical results from quantum formulae. This means that effects that are proportional to some power of ħ cannot be explained classically, and instead are "a quantum thing".

'''Rₑ: Someone needs to do a lot of tedious numerical work; hopefully it's not you''' The {{w|Reynolds number}} (which is usually denoted by "Re," not "Re" as it appears in the comic) is the most important dimensionless group in fluid mechanics. Named for Osborne Reynolds, Re characterizes the relative sizes of inertial and viscous effects in a moving fluid. Large values of Re are indicative of turbulent flow, which cannot usually be retrieved analytically, and so numerical modeling is necessary. Accurate numerical studies of high-Reynolds-number flows are notoriously difficult to create and program.

Alternatively, Rₑ could stand for electronic {{w|transition dipole moment}} in a molecule. This appears in quantum-mechanical calculations of transition probabilities and also includes a lot of unpleasant numerical work. Rₑ is also a term used for the radius of the Earth at mean sea level, though this is not necessarily a complex term in and of itself.

Another alternative is that Rₑ could refer to Relative Error, a measurement of precision or accuracy. Used often in the analysis of scientific data and numerical analysis.

'''(Ta⁴ - Tb⁴): You are at risk of skin burns''' The {{w|Stefan-Boltzmann law}} says that a perfectly absorbing ("black body") source emits electromagnetic radiation with a power per unit area of σT4, where σ is a known constant and T is the absolute temperature. The quantity (Ta4 – Tb4) thus appears in any calculation of purely radiative energy transfer between two bodies, one at temperature Ta and the other at Tb. When the radiative transfer is large enough to be the most important form of heat interchange, it is normally also large enough to sear the skin with thermal or ultraviolet burns.

'''NA: You are probably about to make an incredibly dangerous arithmetic error''' NA, or {{w|Avogadro's number}}, is the number of molecules in a mole of a substance, approximately the number of carbon atoms in exactly 12 grams of carbon-12. This is an enormous number, exactly 6.022 140 76 × 10²³, or 602 214 076 000 000 000 000 000. Working with NA, it is easy to accidentally divide by it instead of multiplying or vice versa, leading to erroneous and nonsensical answers such as ~10-23 molecules (even though you can't have less than 1 whole molecule) or ~1046 moles (>1043 to 1045 kilograms, depending on the chemical) of a substance.

'''µm: Careful, that equipment is expensive''' {{w|Micrometre|Micrometer}}s are a very small unit of distance. Micrometers are commonly used to measure wavelengths in the infrared, and infrared detectors are very expensive, compared with visible wavelength counterparts. Of course, micrometers are used as a measurement of distance in other contexts, but any distance-measuring device capable of accurately measuring micrometer distances would also be expensive. Similarly, tools used to create or calibrate items within micrometer tolerances can also be expensive.

'''mK: Careful, that equipment is very expensive''' {{w|Kelvin}} is a temperature scale roughly speaking similar to Celsius, but taking absolute zero as its zero point instead of the freezing point of water (rigorously speaking, its definition is now {{w|2019_redefinition_of_the_SI_base_units#Kelvin|based on the Boltzmann constant}}). {{w|Millikelvin}}s (1/1000 of a Kelvin) are used for high precision temperature work. Frequently this is used in processes of cooling temperatures to nearly absolute zero - such as superconductors or other quantum effects that occur when atoms are almost still. This is suggesting that the symbol appears on a sensitive experimental system probing quantum mechanical behavior that would likely only exist in an advanced laboratory. Any equipment that works down at mK temperatures, or at least to mK precision and accuracy, is likely to be very expensive.

'''nm: Don't shine that in your eye''' {{w|Nanometer}}s are frequently seen in the listed wavelengths for lasers. Pointing a visible or infrared laser at someone's eye is notoriously dangerous; the tightly-focused coherent light can cause permanent damage very quickly.

'''eV: Definitely don't shine that in your eye''' {{w|Electron volt}} energies are typical of moderate-energy particle beams, produced by accelerating electrons (or protons) over macroscopic voltages. These particle beams can be {{w|Anatoli Bugorski|even more damaging (and are probably a direct reference to Anatoli Bugorski)}} to soft tissues than optical-wavelength lasers.

'''mSv: You're about to get into an Internet argument''' The {{w|millisievert}} is a unit of radiation dose absorbed. It is a very small dosage, but the joke refers to Internet trolls debating the effects of low-dose radiation sources, such as 5G wireless networks. [[Randall|Randall's]] comment may also be referring to [https://xkcd.com/radiation/ this chart].

'''mg/kg: Go wash your hands''' This unit measures the dose of a drug or other chemical in milligrams per kilogram of body mass. If the appropriate dose - or worse, the lethal dose - is measured in mg/kg (parts per million), then the substance may be quite toxic.

'''µg/kg: Go get in the chemical shower''' A unit 1/1000 times the size of mg/kg. If a dosage is measured in micrograms per kilogram (parts per billion), any accident probably requires whole-body decontamination procedures.

'''π or τ: Whatever answer you get will be wrong by a factor of exactly two''' π is defined as the ratio of a circle's circumference to its diameter, while τ is defined as the ratio of a circle's circumference to its radius (and is therefore equal to 2π). {{w|pi|π}} has been used as the primary constant for describing the circumference and area of circles millennia ago, but proponents of {{w|Turn (angle)|τ}} claim that τ is more natural in most contexts since it makes working in radians more straightforward. Actually, "Pi" symbol used to be occasionally used for the constant now called Tau. The joke here is that whichever constant you use, it will probably be the wrong one (off by a factor of two, one way or the other) for the formula you are trying to use. The debate over Tau vs Pi was solved by Randall in this compromise: [[1292: Pi vs. Tau]].

==Transcript==
:[A list with 14 different scientific constants/symbols are shown. Next to each symbol is a description. Above the list is a heading and beneath that a subheading.]
:::::<big>Symbols</big>
::::And what they mean

:::d⁄dx    An undergrad is working very hard
:::∂⁄∂x    A grad student is working very hard
:::ħ       Oh wow, this is apparently a quantum thing
:::Rₑ     Someone needs to do a lot of tedious numerical work; hopefully it's not you
:(Ta⁴ - Tb⁴)    You are at risk of skin burns
:::NA    You are probably about to make an incredibly dangerous arithmetic error
:::µm    Careful, that equipment is expensive
:::mK    Careful, that equipment is very expensive
:::nm    Don't shine that in your eye
:::eV     '''''Definitely''''' don't shine that in your eye
:::mSv  You're about to get into an internet argument
::mg/kg      Go wash your hands
::µg/kg      Go get in the chemical shower
::π or τ      Whatever answer you get will be wrong by a factor of exactly two

{{comic discussion}}

[[Category:Math]]
[[Category:Physics]]
[[Category:Chemistry]]
[[Category:Biology]]
[[Category:5G]]