explain xkcd - User contributions [en]

3039: Human Altitude

2025-01-18T21:56:16Z

162.158.42.221:

{{comic
| number = 3039
| date = January 17, 2025
| title = Human Altitude
| image = human_altitude_2x.png
| imagesize = 508x495px
| noexpand = true
| titletext = I wonder what surviving human held the record before balloons (excluding edge cases like jumping gaps on a mountain bridge). Probably it was someone falling from a cliff into snow or water, but maybe it involved something weird like a gunpowder explosion or volcano.
}}

==Explanation==
{{incomplete|Created by a BOT currently in free fall off a hot air balloon- Please change this comment when editing this page. Do NOT delete this tag too soon.}}
The comic purports to show the altitudes of humans over time, starting from a little after 1700. The conceit is that it indicates the ''single'' most altitudinous individual at any given time, so does not follow any particular person but would switch focus to whichever representative of humanity becomes "the highest up" (whether by rising above the previous leader, or by remaining high as the other loses their own elevation). There will necessarily be a degree of artistic interpretation and presumed trajectory of this particular marker, although the general trend of the line appears to be inspired by (some) actual factual realities. It uses a logarithmic vertical scale in order to indicate the finer details of 'low level' altitudes, yet fit the highest achievements onto the page. The measurements do not count altitude ''due'' to the ground beneath them, so a resident of {{w|Tibet}} or the {{w|Andes|high Peruvian Andes}} (for example) does not normally gain any particular advantage.

Prior to 1783, the {{w|Montgolfier brothers#Piloted flight, autumn_1783|first confirmed ascent}} of a human in a balloon, the line's high-points are indicated to be due to "various falls", i.e. a person who ''was'' on the top of a particularly high building/cliff/tree suddenly finding themselves (for an instant or two, at least) the person 'lucky' enough to be considered the furthest above the ground (it is at times like this that living at a higher absolute altitude ''might'' grant an 'advantage' to the individual who suddenly discovers their previously high standing-spot to no longer be as reliable as they thought). It also suggests that "catapult accidents", such as accidentally, or maybe [https://www.theguardian.com/uk/2005/nov/01/highereducation.students not so accidentally] being caught in a sling on a {{w|trebuchet}} when it is fired (indicated as "hilarious") may also contribute to the (momentary) gain in altitude. The limit to this period's ability to exist at altitude appears to be around 100 metres, which is perhaps mostly what a particular precipitous (and precarious) cliff-top might contribute to the situation.

Once {{w|balloon}} flights start, heights of up to 10km are attained. And though there were some {{w|List of ballooning accidents|dangers}} from this, as early aeronauts discovered, it might at least now be presumed that some of these peaks were attained by individuals who had previously marked a prior instantaneous altitude on the graph.

Shortly after the 1900s, {{w|airplanes}} dominate the graph. And the rise in utility of passenger aircraft (before World War 2; but especially afterwards, following a period where regular and extended high-altitude flight has been experienced by bomber pilots of various nations) ensures not only that there are people attaining greater and greater altitudes, but also that there are also always ''other'' people in the air, ensuring that the lesser 'maximum altitude' periods still have people a significant number of kilometres in the air.

Interestingly, the lower-limit, all the way up to the invention of the airplane, seems to stay at about two metres (around 1881, the lowest marked position seems to be only slightly above 1 metre), which might represent the possibility of there always being at least ''someone'' climbing up a ladder and/or jumping off of a hay-cart.

Once {{w|spaceflight}} becomes a thing (interestingly, marked around the late 1960s, though it actually started in April 1961), that greatly increases the upper spikes for the (implied) duration of the {{w|Orbital spaceflight|orbital flights}}.

The {{w|Apollo Program}} is then indicated by both label and a notable spike as (between {{w|Apollo 8}} in December 1968 and {{w|Apollo 17}} in December 1972), men from Earth were sent around the Moon and attained altitudes 'above the Earth' of approximately 400,000km in the process. Note that the disclaimer "(very approximate)" in the chart's title also applies here, as the graph shows less spikes than actual Moon orbitings or landings performed.

Since the end of the original Moon landings, the upper spikes settled down quite significantly back to 'only' generally low orbital distances, but the very latest era, marked "Space Station", seems to coincide with the current continuous inhabitation of space, which officially started in November 2000. Since that date, there has ''always'' been someone at approximately 400km altitude (give or take changes in the orbit, and of the terrain below), with occasionally some yet higher person(s) on certain missions (e.g. servicing the {{w|Hubble Space Telescope}}, May 2009 at 515km). The graph does not ''seem'' to show the blip created by {{w|Polaris Dawn}}'s 1,400 km 'new record' of September 2024, but this may be ''just'' off the right-hand edge of the graph.

Though the historical validity is sometimes argued, it is interesting to note that (as early as the 6th century CE), experiments with man-flying kites may have produced (semi-)brief spikes in the altitude record for the time. Gliders of the later era (starting roughly at the start of the 1800s) were probably eclipsed by the indicated balloons, but may have produced ''some'' of the spikes seen (above 10 metres but well below the multi-kilometre peaks), as occasional departures off the tops of hills were accomplished without quite so much ill-fortune, or at least without being ''entirely'' unintentional.

Also, workers and bell-ringers in medieval cathedrals, or attendants at the Lighthouse of Alexandria, would have been substantially above the "tens of meters" level. Moreover, the Eiffel tower has been open to visitors since its opening in 1899, which would have ensured some people to be at at least 276m, during the opening hours. This indicates that people standing on buildings and tall structures do not count for the purpose of the graph.

Tornadoes are another possible cause of high-altitude humans. There are multiple credible stories, [https://www.youtube.com/watch?v=pEPf6K-Y7GA| like this one], of people being lifted off the ground and surviving. In theory, they could have been lifted well over 100 meters and still survived.

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

:Height above Earth's surface of the highest-altitude human over time
:(very approximate)

:[A line graph is shown, with frequent spikes on the line. The y-axis is a logarithmic scale from 1 meter to 1,000,000 km. The x-axis shows years from about 1710 to 2025.]

:[Label between 1720s and 1780s, maximum height is roughly 100 meters:]
:Various falls and hilarious catapult accidents

:[Label with multiple arrows, from 1780s to 1910s, maximum height is roughly 10 km:]
:Balloon flights

:[Label with multiple arrows, from 1910s to 1960s, maximum height increases to roughly 100 km:]
:Airplane flights

:[Label with arrow, in the late 1960s, maximum height is roughly 500 km:]
:Spaceflight

:[Label with arrow, in the 1970s, maximum height is roughly 500,000 km:]
:Apollo Program

:[Label between 1990s and 2025, the average height after 2000 is roughly 500 km:]
:Space station

{{comic discussion}}

[[Category:Line graphs]]
[[Category:Timelines]]
[[Category:Space]]
[[Category:Aviation]]

3038: Uncanceled Units

2025-01-15T16:30:06Z

162.158.42.221:

{{comic
| number = 3038
| date = January 15, 2025
| title = Uncanceled Units
| image = uncanceled_units_2x.png
| imagesize = 323x355px
| noexpand = true
| titletext = Speed limit c arcminutes^2 per steradian
}}

==Explanation==
{{incomplete|Created by THE PLANCK CONSTANT, WHICH IS TECHNICALLY A FREQUENCY AND CAN THUS BE EXPRESSED IN HERTZ - Please continue to explain the joke and possible interpretations. Do NOT delete this tag too soon.}}
Another of [[Randall]]'s [[:Category:Pet Peeves|pet peeves]], this comic expresses disapproval of units that could be mathematically simplified.

[[White Hat]] is presenting a refrigerator to [[Cueball]], claiming it only uses 3 kWh per day. Kilowatt-hours is a commonly used unit of electrical energy in the United States, being the amount of energy consumed by one kilowatt of power usage for one hour. As the unit in which power rates are typically reported and bills calculated, it's the most useful piece of information to the average consumer. This measure, however, could be simplified, since a kilowatt is equivalent to a kilojoule per second. Rather than adding a second unit, energy could simply be reported in megajoules (1 kilowatt-hour is 3.6 megajoules)

Appliances, however, frequently report their typical power use in terms of kilowatt-hours per day (or per month or year). Once again, this is useful to consumers, because it makes it easier for them to understand how much money it will cost them to run. However, it's an inelegant way to use units, because it uses power, which is already a measure of energy per time, multiplies it by one time unit, and then divides it by another. This clunky method apparently chafe's at [[Randall]]'s mind, possibly due to his scientific background (which encourages simplifications of units). The "hour" and "day" terms, both being units of time, can simply cancel out by dividing the whole number by 24, meaning that the refrigerator averages 0.125 KW, or 125 watts, to run. It should be noted that this doesn't mean the refrigerator constantly draws this amount of power, since the compressor in the refrigerator only runs intermittently, but running it over the course of a day (with typical use) is expected to give that average power use.

Cueball (possibly representing Randall) sardonically wonders whether the refrigerator would fit in his kitchen, since the ceiling is only 50 gallons per square foot high. This is clearly an abnormal and unhelpful way of reporting height. This unit turns a normal measurement of height (feet and inches, in the US, meters and centimeters, most other places) into weird collection of uncancelled units. Gallons can be transformed to cubic feet (1 US gal ≈ 0.1337 ft3), which can be divided by the square feet, yielding a ceiling height of around 203.7 cm, or around 6 feet 8 inches. (Using imperial gallons [1 UK gal ≈ 0.1605 ft3], the height is approximately 244.7 cm, roughly 8 feet.) This is intended to lampoon the use of uncancelled units by showing how odd things become if they're generally used.

''[[what if? (blog)|what if?]]'': [https://what-if.xkcd.com/11/ Droppings] also covers strange instances of unit cancellation, including a measure of volume per distance converted to area; similar to Cueball's measure of volume per area representing a distance (the height of his ceiling).

A common source of unit drama occurs between lay people who are looking for every day practicality and science/engineering types who are inclined towards formalized mathematical operations. For example customary units which support even divisibility versus metric units which prioritize base 10 scales. In this case telling the average customer the energy use in joules per day or average consumption in watts would require them to perform more complicated conversions to get to the figure they actually care about, the actual cost per day. White Hat could just give this cost figure directly, but does not know what every customer pays for electricity (an explicit yearly cost estimate would be included on the government required energy efficiency label).

In the title text, a speed limit is given as c arcminutes2 per steradian, where c is presumably the speed of light in vacuum, 2.998×108 m/s (meters per second) or 186282 mi/s (miles per second). A steradian (sr) is the SI unit for solid angle, subtended by a section of a sphere, like a radian is a unit of angle subtended by a section of a circle. A square arcminute is also a unit of solid angle, equivalent to a section of a sphere of 1/60 of a degree by 1/60 of a degree. There are ((1/60)*(π/180))2 = 8.462×10-8 sr in a square arcminute. Then multiplying by c gives a speed of 56.75 mph (probably 55 mph, based upon the {{w|National Maximum Speed Law|'traditional' US speed limit}}, before rounding errors in the reverse direction), or 91.33 km/h, showing that you can combine an outrageously high speed with two unnecessary units that cancel each other to form a normal road speed.

It is worth noting that although some of these examples are ridiculous, uncancelled units can be helpful to better understand the concept, the {{w|Hubble's law|Hubble Parameter}} can be expressed as 2.17132212×10-18 hertz, 67 km/s/Mpc is directly related to how it is measured and gives a better understanding of what it means. Another example would be fuel efficiency in cars, as mi/gal and km/l technically simplify to area, but by expressing it in volume and distance it allows easy estimations of range and travel cost, while mm2 or in2 would require significant unit conversions.{{cn}}

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

:[White Hat and Cueball are standing to either side of a refrigerator. The fridge has two top compartments and one bottom compartment. The top left compartment has a tall handle on its right, the top right compartment has a tall handle on its left, and the bottom compartment has a long handle on its top. The top left compartment has a paper attached to it with unreadable text, possibly an advertisement.]
:White Hat: This fridge uses only 3 kWh per day!
:Cueball: But will it fit in my kitchen? The ceiling there is only 50 gallons per square foot.

:[Caption below the panel:]
:Pet peeve: Uncanceled units

{{comic discussion}}

[[Category:Comics featuring White Hat]]
[[Category:Comics featuring Cueball]]
[[Category:Math]]
[[Category:Pet Peeves]]

Talk:3011: Europa Clipper

2024-11-14T00:09:42Z

162.158.42.221:

I'm not brave enough to actually add an explanation myself, quite yet, but ... I guess this is a reference to the fact(?) that Europa looks a bit like a creme brulee', when viewed from space? https://science.nasa.gov/jupiter/moons/europa/ It does look tasty ... :) [[User:ModelD|ModelD]] ([[User talk:ModelD|talk]]) 12:53, 13 November 2024 (UTC)
:I suspect it's more due to the need to drill through a couple miles of ice to get to the ocean; much like breaking through the sugar crust on a creme broule! [[User:Seebert|Seebert]] ([[User talk:Seebert|talk]]) 13:16, 13 November 2024 (UTC)

Thank you to the people at 9AM Post things on another website to try and explain XKCD Comics. -Forgotten_Mail {{unsigned ip|172.69.33.177|13:30, 13 November 2024}}

The comically large spoon!!!!!!!!!! I love those. -[[User:Psychoticpotato|P?sych??otic?pot??at???o ]] ([[User talk:Psychoticpotato|talk]]) 16:38, 13 November 2024 (UTC)

I think the "Crème brûlée is from France, France is in Europe, the moon is called Europa" connection is a bit of a stretch...?
[[User:Yorkshire Pudding|Yorkshire Pudding]] ([[User talk:Yorkshire Pudding|talk]]) 18:36, 13 November 2024 (UTC)

"only a spoonful" moment 💔 [[User:CalibansCreations|'''Caliban''']] ([[User talk:CalibansCreations|talk]]) 19:20, 13 November 2024 (UTC)

Someone should add a reference to XKCD's previous mention of a Planetary Protection Officer: https://what-if.xkcd.com/117/ [[Special:Contributions/162.158.42.221|162.158.42.221]] 00:09, 14 November 2024 (UTC)

3010: Geometriphylogenetics

2024-11-12T04:03:40Z

162.158.42.221:

{{comic
| number = 3010
| date = November 11, 2024
| title = Geometriphylogenetics
| image = geometriphylogenetics_2x.png
| imagesize = 316x391px
| noexpand = true
| titletext = There's a maximum likelihood that I'm doing phylogenetics wrong.
}}

==Explanation==
{{incomplete|Created by an UNUSUALLY POINTY CIRCLE - Please change this comment when editing this page. Do NOT delete this tag too soon.}}

{{w|Phylogenetics}} refers to the practice of examining relationships among things that follow the principle of "descent with modification". In the course of descent with modification, one thing may give rise to two if different modifications happen to progeny of the original thing, and those modifications become established. Iterated "splits" over time yield a tree of objects; it is the purpose of phylogenetics to recover these trees, and use the information gained to inform study of the things contained. Phylogenetics has been most commonly applied to the classification/taxonomy of biological species and investigations of their evolutionary history, but it has also been used to examine the evolution of genes and biosynthetic pathways, and also in the study of human languages and their evolution. Data for phylogenetic analyses may come from any attributes ("characters") of the things being examined; rigorous techniques for these analysis became available starting in the {{w|Willi_Hennig|1950s}}. In phylogenetic studies of organisms, their DNA is far and away the most data-dense source of information, and consequently, most present-day investigations are based on analyses of selected genes and, increasingly, whole genomes. It is commonplace for such studies, especially on relatively understudied creatures, to reconstruct an evolutionary history that is radically different from what had previously been assumed.

Such modifications may result in relationships between different species evolutionarily.

Through evolution, affected by the environment or social factors, one species may over a great length of time diverge into two new, different species. These two new species still share a common ancestor, the original species, and therefore are more closely related than a species not sharing this common ancestor. For instance, although humans and dogs share a common ancestor, we share a much more recent common ancestor with apes: on a phylogenetics chart, this would be shown by the human and ape branch connecting quickly, and then further down the line this joint branch would connect to the common ancestor of dogs.

Geometriphylogenetics is a play on words, combining "{{w|geometry}}" with "phylogenetics" and insinuating it is the phylogenetics of shapes. The chart Randall made shows the relationships between shapes as they evolved from "common ancestors". Shapes such as triangles and squares didn't actually evolve from older, now-extinct shapes (citation needed?), which is what the title text might be saying. The caption states that triangles are actually more closely related to circles than squares, proven by genetic analysis. This is shown on the chart by triangles having a closer common ancestor than squares.

Portmanteau discipline was previously seen in comic [[Geohydrotypography|here]].

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

:[A tree diagram, or a cladogram is shown, consisting of lines that branch off from left to right, starting with one horizontal line on the left. Eight results are shown on the right: ellipse on Path 1, circle on Path 2, triangle on Path 3, parallelogram on Path 4, trapezoid on Path 5, square on Path 6, rectangle on Path 7, and a pentagon on Path 8. The paths are listed in order top to bottom.]
:[Path 3 and the triangle are bold black, while the other branches are dimmer. The paths are connected as follows: Path 2 and 3 are connected, then both connect together to Path 1; Path 4 and 5 are connected, as are Path 6 and 7, and these two paths are connected altogether; Path 8 is then connected to the branch containing Paths 4 to 7. All of Paths 1 to 3 are then connected to Paths 4 to 8, the branches all culminating in a single line on the left.]

:[Caption below the panel:]
:The phylogenetic revolution continues:
:Triangles were long believed to be related to squares, but genetic analysis proves that they are actually very pointy circles.

{{comic discussion}}

[[Category:Geometry]]
[[Category:Biology]]