explain xkcd - User contributions [en]

2976: Time Traveler Causes of Death

2025-08-04T22:51:50Z

82.132.244.251: Undo revision 383236 by Jkshapiro (talk) The title text talks about having "Googled" (definitive hyponym, not "googled" as a hypernym). Anyway Lycos/AskJeeves/etc preceded only by a year or five.

{{comic
| number = 2976
| date = August 23, 2024
| title = Time Traveler Causes of Death
| image = time_traveler_causes_of_death_2x.png
| imagesize = 332x677px
| noexpand = true
| titletext = Many a hungry time traveler has Googled 'trilobites shellfish allergy' only to find their carrier had no coverage in the Ordovician.
}}

==Explanation==
Time travel is a common sci-fi/fantasy plot, in which someone from one era is sent forward or backward in time to another era. Normally, the travel itself goes off without a hitch, with the usual threats to the time traveler being what happens at some point ''after'' they arrive at their destination. More rarely, a time traveler might immediately encounter some hazard because of where their time travel method has deposited them.

This comic takes the latter situation to the extreme, observing different causes of death for potential time travelers through the ages based on the geologic evolution of Earth from its formation over 4 billion years ago to the present; see detailed explanation in the [[#Table of death causes|table]]. The chart shows only the most likely cause for a given period of time, although the title text reveals that there may always be others possible.

The title text suggests that an alternative fate within the "eaten by fish" era is the exact opposite - eating something hazardous. A time traveler, having fortuitously avoided the primary "Starving" fate of the prior era, may try eating a {{w|trilobite}}, a kind of shellfish. They may find that either some existing allergy is triggered by this prehistoric shellfish, or that the creatures of that age spark a new allergic condition that (as a modern human) they were not previously aware they could develop a reaction against. A person with a known allergy might check for the possible presence of a problematic ingredient in a potential snack by referencing online resources - a facility that is not available here, with the smartphone stuck in the past, long before any network is available to connect to (notwithstanding that Google Search has not existed historically for more than three decades). Alternatively, suspecting the food they've eaten has not agreed with them, they could find they are denied easy access to the best online information on how to properly treat their symptoms.

===Table of death causes===
{| class=wikitable
! scope="col" | Cause of death
! Scope=“col” | Time frame
! scope="col" | Explanation
|-
| Lava || Earth Forms || During the formation of the Earth, the surface was a hellish landscape of lava.
|-
| Asphyxiation || 4 billion years ago || Before {{w|cyanobacteria}} started photosynthesizing and producing oxygen, the atmosphere of the Earth was mainly composed of hydrogen sulfide, methane and carbon dioxide, without the significant amount of oxygen that humans need to breathe.
|-
| Meteors || 3.9 billion years ago || During the hypothesized {{w|Late Heavy Bombardment}}, the Earth's surface was subjected to a large number of asteroid and comet impacts, destroying much of Earth's early crust. According to the table, the heavy bombardment was so severe that this was the most likely cause of death during a period when there was still no oxygen. Even when these meteors came at an alarming rate, however, the chance of being hit by one of these before asphyxiation due to an atmosphere without any oxygen seems remote. Of course, if the time machine had some oxygen along with it and the reason people died from lack of oxygen was that they stayed there for a long time, the chance of death-by-meteor would increase.
|-
| Asphyxiation || 3 billion years ago || See above.
|-
| Slightly slower asphyxiation || 2 billion years ago|| Cyanobacteria had started photosynthesizing, leading to the {{w|Great Oxygenation Event|Oxygen Catastrophe}}, but oxygen levels still weren’t high enough to support human life.
|-
| Freezing || Less than 1 billion years ago || During the {{w|Cryogenian|Cryogenian Ice Age}}, the Earth’s temperature fell to -12°C, much too cold to support human life if not properly prepared.
|-
| Starving || 600 to 485 million years ago || During this time, the temperature was mild and comfortable; however, the only life during this time was single-cell organisms and – especially later – tiny multicellular organisms, which are very difficult to gather and may not be sufficiently healthy and nutritious. (Imagine surviving only on bacteria today.)
|-
| Eaten by fish || 485 to 250 million years ago || During the {{w|Great Ordovician Biodiversification Event}} and subsequent times, fish {{w|Evolution of fish|evolved jaws}} and some species grew quite large.
|-
| Trampled || 252 to 66 million years ago || The {{w|Mesozoic Era}} is often called the “Age of Dinosaurs." The majority of these dinosaurs were herbivorous and many were quite large, so being eaten would be less likely than being trampled on.
Note that this is an almost exact inversion of what happens in the classic story ''{{w|A Sound of Thunder}}'', in which the traveler survives personally unscathed but tramples an 'age of dinosaur' creature (to unfortunate effect).
|-
| Eaten by mammals || 66 million years ago to sometime before now || The {{w|Cenozoic Era}}, which began 66 million years ago, is often referred to as the "Age of Mammals". Though some eras have more likely causes of death (such as wars, but that would basically be during the "Now" period in the table), overall being eaten by large mammals is probably the biggest risk.
|-
| Time machine door gets stuck || Roughly present day || As the timeline approaches the present day, the conditions on Earth become more than suitable enough for a human time traveler to survive extended periods of time — as evidenced by the fact hominids and early humans begin to emerge. As such, when it comes to hazards that can kill the time traveler before they can do anything at their destination, there's nothing else more likely to kill them than a problem with the time machine itself; the example given is being unable to open the door of the time machine (whether because the door is broken or the time machine is parked right up against an obstacle) and dying of thirst or starvation (or, if the time machine is air-tight, asphyxiating). This assumes the time machine is also a {{w|Faraday Cage}} (that can block the signal of an emergency call) or the traveler doesn't take their phone with them, although the title text indicates they will. Or that the "Now" period extends back before cell phones and compatible cellular networks, maybe covering the entire period of human civilization. But mostly it is a punchline comparing severely dangerous situations to severely harmless ones.
|-
|}

==Transcript==
:[A chart with a time line going from top to bottom is shown. Starting when the Earth forms and ending at present day. The chart is a rectangle divided into 11 segments. Each segment has a label written inside it, except the bottom which is too thin, thus the label is to the right of the chart with an arrow pointing to the segment. The left side of the chart is a timeline with ticks and labels for the time period. At the top an arrow points to the top left corner of the chart with a label indicating the starting time. And then there are 5 ticks, the first four equidistant and then only half the distance for the last tick. A final label is at the bottom of the chart. Above the chart there is a heading:]
:Top causes of death for time travelers by geologic era:

:[Text in the table from the top, with the time to the left differentiated from the labels which are indented:]
:Earth forms
::Lava
::Asphyxiation
:4 billion years ago
::Meteors
::Asphyxiation
:3 billion years ago
:2 billion years ago
::Slightly slower asphyxiation
:1 billion years ago
::Freezing
::Starving
:500 million years ago
::Eaten by fish
::Trampled
::Eaten by mammals
:Now
::Time machine door gets stuck

== Trivia ==

Modern adults can actually have great difficulty surviving without modern conveniences, and may die of freezing if released into an earlier era than they are familiar with. Children of certain ages may thrive well, neither freezing or being eaten by mammals, after a period of adaptation.

{{comic discussion}}

[[Category:Timelines]]
[[Category:Time travel]]
[[Category:Geology]]
[[Category:Animals]]

3124: Grounded

2025-08-04T22:38:00Z

82.132.244.251: /* Explanation */ Had difficulty finding a reference to the jet backwash, best option found, amongst various mutually linking pages...

{{comic
| number = 3124
| date = August 4, 2025
| title = Grounded
| image = grounded_2x.png
| imagesize = 294x335px
| noexpand = true
| titletext = We should have you at the gate in just under two hours--two and a half if we get pulled over.
}}

==Explanation==
{{incomplete|This page was created recently by a COP ASKING IF THE PILOT KNOWS WHY THEY WERE PULLED OVER. Don't remove this notice too soon.}}

This comic depicts a plane that has been delayed due to unfavorable weather. The pilot and first officer have considered simply driving the plane to the destination instead of waiting for favorable weather to fly, noting that they have considered their maximum taxiing speed and bridge clearance heights. Driving a plane on the public highway is probably illegal, under transportation and vehicle registration laws, plus impractical due to the excessive width and height (and maybe length) of the vehicle and the {{w|Jet (fluid)|backwash from the engines}}, and because jetliners taxi at only 25-35 mph — far slower than simply taking a car or bus — and rolling at nearer to {{w|Rotation (aeronautics)|rotation}} speed for prolonged periods would be mechanically problematic, especially on non-straight roads.

The title text further extends the joke, saying that driving might get them pulled over by police and further extend the drive time. However, the drive would probably be extended by more than 30 minutes, and the plane would most likely be stopped, resulting in the drive/flight being curtailed.

==Transcript==
{{incomplete transcript|Don't remove this notice too soon.}}
[Plane connected to airport in picture]
This is your captain speaking. As you've probably noticed, we're still grounded due to weather
but the first officer and I have been looking at bridge clearance maps and our top taxiing speed, And we have an idea.
[Voice is coming from the plane]

[Title text]
We should have you at the gate in just under two hours--two and a half if we get pulled over.
{{comic discussion}}<noinclude>

3124: Grounded

2025-08-04T22:31:56Z

82.132.244.251: Tyop

{{comic
| number = 3124
| date = August 4, 2025
| title = Grounded
| image = grounded_2x.png
| imagesize = 294x335px
| noexpand = true
| titletext = We should have you at the gate in just under two hours--two and a half if we get pulled over.
}}

==Explanation==
{{incomplete|This page was created recently by a COP ASKING IF THE PILOT KNOWS WHY THEY WERE PULLED OVER. Don't remove this notice too soon.}}

This comic depicts a plane that has been delayed due to unfavorable weather. The pilot and first officer have considered simply driving the plane to the destination instead of waiting for favorable weather to fly, noting that they have considered their maximum taxiing speed and bridge clearance heights. Driving a plane on the public highway is probably illegal, under transportation and vehicle registration laws, plus impractical due to the excessive width and height (and maybe length) of the vehicle and the backwash from the engines, and because jetliners taxi at only 25-35 mph — far slower than simply taking a car or bus — and rolling at nearer to {{w|Rotation (aeronautics)|rotation}} speed for prolonged periods would be mechanically problematic, especially on non-straight roads.

The title text further extends the joke, saying that driving might get them pulled over by police and further extend the drive time. However, the drive would probably be extended by more than 30 minutes, and the plane would most likely be stopped, resulting in the drive/flight being curtailed.

==Transcript==
{{incomplete transcript|Don't remove this notice too soon.}}
[Plane connected to airport in picture]
This is your captain speaking. As you've probably noticed, we're still grounded due to weather
but the first officer and I have been looking at bridge clearance maps and our top taxiing speed, And we have an idea.
[Voice is coming from the plane]

[Title text]
We should have you at the gate in just under two hours--two and a half if we get pulled over.
{{comic discussion}}<noinclude>

3124: Grounded

2025-08-04T22:30:45Z

82.132.244.251: /* Explanation */

{{comic
| number = 3124
| date = August 4, 2025
| title = Grounded
| image = grounded_2x.png
| imagesize = 294x335px
| noexpand = true
| titletext = We should have you at the gate in just under two hours--two and a half if we get pulled over.
}}

==Explanation==
{{incomplete|This page was created recently by a COP ASKING IF THE PILOT KNOWS WHY THEY WERE PULLED OVER. Don't remove this notice too soon.}}

This comic depicts a plane that has been delayed due to unfavorable weather. The pilot and first officer have considered simply driving the plane to the destination instead of waiting for favorable weather to fly, noting that they have considered their maximum taxiing speed and bridge clearance heights. Driving a plane on the public highway is probably illegal, under transportation and vehicle registration laws, plus impractical due to the excessive width and height (and maybe length) of the vehicle and the backwash from the engines, and because jetliners taxi at only 25-35 mph — far slower than simply taking a car or bus — and rolling at nearer to {{w|Rotation (aeronautics)|rotation}} speed for prolonged periods would be mechanically problematic, especially on non-straight roads.

The title text further extends the joke, saying that driving might get them pulled over by police and further extend the drive time. However, the drive would probably be extended by more than 30 minutes, and the plane would most likely be stopped, resulting in the drive/flight being curtailled.

==Transcript==
{{incomplete transcript|Don't remove this notice too soon.}}
[Plane connected to airport in picture]
This is your captain speaking. As you've probably noticed, we're still grounded due to weather
but the first officer and I have been looking at bridge clearance maps and our top taxiing speed, And we have an idea.
[Voice is coming from the plane]

[Title text]
We should have you at the gate in just under two hours--two and a half if we get pulled over.
{{comic discussion}}<noinclude>

Talk:3124: Grounded

2025-08-04T22:22:29Z

82.132.244.251:

I don't get the joke at all
The idea is to simply drive the plane on the ground to the destination.
Ok, should we mention this is because they mention the taxing speed

Even if a plane could taxi at around 60 MPH (car highway speed), 2 hours is only 120 miles. Not many flights on commercial jets are so short. [[User:Barmar|Barmar]] ([[User talk:Barmar|talk]]) 21:37, 4 August 2025 (UTC)

:Taxiing speed, not taxing speed. The pilots are not mulling how quickly they can file their 1040s. [[Special:Contributions/136.226.19.75|136.226.19.75]] 21:23, 4 August 2025 (UTC)

I would hope that Randall was aware of John Finnemore's radio sitcom "Cabin Pressure", as a very compatible sense of intelligent humour (with the 'u', 'cos British!). Though maybe not ('cos British radio, might be too fringe a taste), and so the fact that one of the episodes has a somewhat similar plotpoint to it (not saying which, and how, as anyone who'd like to start listening might just appreciate not knowing "this is the one where..." before it happens) probably isn't worth fully analysing (with an 's', 'cos British! :p ) in the explanation. But just mentioning it here, in passing, given that it reminds me of it.
<br/>...also, as well as bridge heights, I hope they have a good idea about carriageway widths, for the undercarriage, and road furniture (like lampposts/roadsigns, and telegraph/powerline poles) ''plus'' structures (buildings, and bridge-spans, and even groundworks like cuttings through an overlying grade) , for the wings. Though maybe a flight(/taxi) between two places in a relatively undeveloped landscape, having just wide surfaced roads and nothing more immediately prominent than relatively sliceable giant saguaro cactii. Which I can imagine (for the sake of the joke) in the US, but would probably rule out absolutely every possible road route here in the Uk, for any aircraft bigger than a microlight. (Or an autogyro, with the rotors tied front/back, or doing a Mad Max 2 because of prior damage, but that was also in feature-sparse desert...) [[Special:Contributions/82.132.244.251|82.132.244.251]] 22:22, 4 August 2025 (UTC)

classhole

2025-08-04T20:45:09Z

82.132.244.251: Undo revision 383207 by FaviFake (talk) There's already https://www.explainxkcd.com/wiki/index.php?title=Classhole&redirect=no and maybe this should even be made a Page To Delete. And then deleted!

#REDIRECT [[72: Classhole]]
'''''Why?'''''

3122: Bad Map Projection: Interrupted Spheres

2025-08-04T20:35:14Z

82.132.244.251: Only one person thinks there's a 'time limit' to the TRADITIONAL BOT JOKE, at least before actual incompleteness is removed. No need for bullets, using actual long-standing style in the reconstruction. Or just 'formalise' page, to taste, then remove all.

{{comic
| number = 3122
| date = July 30, 2025
| title = Bad Map Projection: Interrupted Spheres
| image = bad_map_projection_interrupted_spheres_2x.png
| imagesize = 740x573px
| noexpand = true
| titletext = During the most recent glacial maximum, it's believed that land bridges extended from the surfaces and connected several of the spheres together.
}}

==Explanation==
{{incomplete|This page was recently created by AN INTERRUPTED EDITOR. Could use a slightly more, ahem, ''formal'' vocabulary... Don't remove this notice too soon.}}

This is the ninth comic in the [[:Category:Bad Map Projections|Bad Map Projections series]] displaying Bad Map Projection #194: Interrupted Spheres. It follows [[2999: Bad Map Projection: The United Stralia]], released nine and a half months prior.

There is no perfect way to draw a map of the world on a flat piece of paper. Each one will introduce a different type of distortion, and the best projection for a given situation is sometimes disputed. As was mentioned in [[977: Map Projections]], the smartass response to this dilemma is to use a globe - which maps the world onto a ''sphere'', thus minimizing distortion by using roughly the same shape as the world itself. This "map projection" goes a step past the smartass and proceeds straight into absurdity, by projecting ''each continent'' onto a sphere. This bends entirely too far in the other direction to the dilemma; whereas a typical map projection adds distortion by trying to show the (curved) planet on a flat surface, this "map projection" adds distortion by showing the (relatively flat) continents on a much more sharply-curved sphere than the planet they are actually part of.

The title text refers to {{w|land bridges}}, narrow bits of land between larger landmasses. When glaciers covered much of the Earth, the water locked up in the glaciers meant that sea levels were lower, as well as the overlying icepacks being higher, and things like the {{w|Bering land bridge}} spanned areas between continents that are currently ocean. [[Randall]] suggests that these formed connections in the gaps between the spheres. This implies the absurd idea that the projection reflects an underlying reality where the continents ''actually'' exist on separate spheres, rather than this simply being an attempt at a "better" way to display Earth's landmasses. In this situation the land of the 'bridges' would reach like spires, vertically upwards from the surface of each sphere, until they descend down onto their counterpart neighbouring sphere.

==Transcript==
:[This comic depicts seven circles each representing globes. Above these circles there is the following text:]
:Bad map projection #194:
:'''<big>Interrupted spheres</big>'''
:To avoid the distortion inherent to a single flat world map, each continent is projected onto its own globe.

:[Each of the seven globes has some part of the landmasses of Earth projected on to it, with a label of said areas name. The globes are arranged in position so their landmasses lies roughly where they would be on a standard map with North America in the upper left and Australia in the lower right part of the picture. That is except Antarctica which is placed beneath Asia close to but left of Australia. The labels on the seven spheres in the three columns they form from left to right are:]
:North America
:South America
:Europe
:Africa
:Asia
:Antarctica
:Australia

==Trivia==

In this comic [[Randall]] indicates that he believes there are seven continents. This is {{w|Continent#Number|up for debate}}, especially with Europe being considered part of the larger Eurasian continent, rather than distinct from Asia, and whether the Americas are two continents or one, temporarily joined via the Caribbean oceanic plate. See for instance {{w|CGP Grey}}'s [https://www.youtube.com/watch?v=3uBcq1x7P34 What are Continents?] video for a discussion. (Grey concludes that there are five, in his opinion.)

{{comic discussion}}<noinclude>

[[Category:Bad Map Projections]]