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| Time Machine Conversation |
 Title text: It's possible to do sea navigation without a compass, but you'll have to get some spoilers from the Polynesians. |
Explanation
This comic plays on the problem of the potential for the creation of temporal paradoxes in scenarios where time travel is possible. Cueball has used a time machine to travel to the Iron Age and has a conversation with an ancient-times version of Hairbun (who seems to be a farmer, since she's holding a pretty modern-looking hoe). In his surprise at compasses not having been invented yet, he inadvertently starts explaining them to her. Rather than being worried about the potential radical impact he might have on history by introducing this concept earlier than should have happened, he is more concerned that he may have given her a spoiler for upcoming history. Presumably he feels he has deprived her (or humankind more generally) of the joy that would have come with its eventual discovery. The magnetic compass was first invented in China around 200 BCE, well after the end of the Iron Age, and it wasn't used for navigation until the 11th century AD. For an Iron Age farmer the concept of a - as Cueball puts it - 'weird rock that always points north' would seem quite ridiculous.
He is then also concerned that he has managed to 'spoilerise' the concept of 'the spoiler'. The modern meaning of "spoiler" didn't arise until the 1970s, which post-date the Iron Age. Spoiler warnings became common on Usenet newsgroups in the late 1980s. Cueball may have created a temporal paradox by introducing the concept thousands of years earlier, although any such 'change' made to that time might easily have been forgotten again in the two or three thousand years since this encounter. In any event, while telling people thousands of years ago that there was a way to make a compass might have changed history significantly, telling them that there are stories that they would enjoy less if they knew the ending before hearing the story seems less likely to have made a significant impact. It's also likely that, even if the term 'spoiler' was adopted by these Iron Age people, it would long have fallen out of use by the time it came to be invented in the late twentieth century. However, according to chaos theory, this interaction might cause a chain of events that will lead to Cueball not existing, creating a paradox, if it isn't already already a different kind of paradox through being a pre-existing component of Cueball's original timeline.
The title text has Cueball about to unleash another spoiler on how to navigate without a compass, but he stops himself before saying it. However, he does still end up accidentally revealing that Polynesians know about it, though whether this was another unintentional slip or a deliberate clue left for Hairbun is unclear. It is thought that so-called 'Polynesian navigation' used other methods of marine navigation (celestial navigation, observation of birds, ocean swells, and wind patterns). However, as the Polynesians lived in the Pacific, which would be difficult to reach from Hairbun's location, and probably unknown to her, the clue is useless. It is unclear where Hairbun is, but it is likely that she is in Europe, which is quite far from the Pacific.
The comic is based on shaky ground, as it's not clear how they're able to communicate so easily, unless it's part of the function of the time-travel technology. While humans did have language for thousands of years by this time, it would be very far removed from modern English, yet somehow they understand each other's speech. It also appears that the very existence of time travel is not being considered as a spoiler for an Iron Age person, or seems in any way remarkable โ this might imply that the farmer is already very well aware of such phenomena (or even that Cueball will later have already visited the same society/farmer at an earlier date), which perhaps is one way to explain apparently fluent conversational American English being spoken.
Time travel is a recurring theme on xkcd.
Transcript
- [1st Panel. Cueball is on the left with a ghostly halo around him. Hairbun is on the right, holding a hoe vertically.]
- Cueball: Oh hi! Guess my time machine works. How's life in the Iron Age?
- Hairbun: Not bad. Developing new kinds of plows.
- Cueball: Cool.
- Hairbun: And my brother was just lost at sea.
- [2nd Panel. Only Cueball is shown, with Hairbun out of the panel.]
- Cueball: I'm sorry.
- Hairbun [from outside the right side]: It's OK. I think sea navigation is probably impossible.
- [3rd Panel. Cueball and Hairbun are both shown again.]
- Cueball: Oh yeah, you don't have the compass, right?
- Hairbun: The what?
- Cueball: The weird rock that always points north?
- Hairbun: What are you talking about?
- [4th Panel. Cueball and Hairbun are both shown. Cueball holds his hand to his chin.]
- Cueball: It does sound ridiculous when I say it out loud. Anyway, spoilers for the magnetic compass. Sorry.
- Hairbun: What's a spoiler?
- Cueball: ...Spoilers for the concept of a spoiler, too.
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