Title text: 'Why did you get into fluid dynamics?' 'Well, SOME planet has to have the coolest clouds, odds are it's not ours, and rockets are slow.'
There are planets. A lot of them, even. Like our planet, for instance. In 3D software, depictions are often rendered at a lower quality when the viewer's perspective is far away from them, to save on computational work for aspects the user can't clearly discern. This idea is built upon here, conceivably to suggest how simulations of universes might seem different than base reality to observers within them.
In this comic, Cueball and Megan theorize that complicated cloud formations occur naturally on other planets in other solar systems. On planets with no observers to look at the clouds closely, our universe, or the simulation thereof, might not afford to render a visual depiction of the atmosphere in higher quality. Meteorologists and physicists on Earth might notice that such exoplanet atmospheres do not obey formal Navier-Stokes fluid dynamics, but instead reflect low-quality corner-cutting of such calculations, such as exhibiting only smooth laminar flow instead of turbulence, its alternative. The foregoing would make sense if the Universe were actually simulated by a computer (a 43% probability) and the being(s) who are running the physics simulator, or have coded our universe, wanted to speed things up.
| Further considerations
- Much more computing power could be saved by skimping on the chemistry of the quattuordecillions of atoms in the oceans than the clouds in the sky (especially considering that it would not be necessary to simulate every individual atom and molecule in the sky (for the purpose of making realistic clouds with fluid dynamics); the computer program could instead divide all of the gas particles (e.g., dinitrogen, dioxygen, water vapor, argon, and carbon dioxide) into small chunks, simulate how each chunk would move, and update the chunk boundaries every so often), but skimping on oceanic chemistry would make biogenesis much less feasible. However, Earth has life.
- It would be difficult to judge when "no one is looking closely". There are many organisms that have some degree of at least rudimentary sight but would have no idea (and in fact no way to conceptualize) whether the computer simulating the Universe is skimping on the cloud-rendering calculations or not. It would be difficult to make some foolproof intelligent-sight-detecting code that would render the clouds with much greater precision once a planet had life that would notice if the clouds were following lazy fluid dynamics.
- For one thing, this would not only depend on the intelligence of a species but also on its knowledge of physics, e.g., humans did not develop the Navier-Stokes equations right after evolving large enough brains to conceive and understand them. Even coding a computer program to detect sight-having life would be difficult, at least for a computer program only looking at the positions and velocities of atoms, electrons, and photons; for example, a blue photon hitting a retinal molecule in a cone cell, causing it to change shape, which triggers a signal transduction cascade that sends a nervous signal to the optical cortex somewhat resembles an ultraviolet photon hitting a DNA strand, leading to the creation of a thymine dimer whose detection by DNA-repairing enzymes triggers a signal transduction cascade that increases the production of melanin, but only one counts as sight.
- Furthermore, assuming that the computer simulates each part of the Universe in a manner that is is about synchronized according to most celestial bodies, when the computer simulating the Universe simulates a planet, it does not know whether a civilization on a planet a dozen or two light-years away that has advanced enough to have telescopes capable of detailed views of the clouds of planets light-years away will point any telescopes at that planet dozens of light-years later.
- Even if the advanced civilization on another planet does not have such powerful telescopes yet, even a low-resolution (in terms of that planet's entire solar system being one pixel) spectrometer would be enough to reveal that something is up with the fluid dynamics simulations on that planet. Observers light-years away could deduce how much condensed water vapor there is in the atmosphere by calculating the atmosphere's absorbance in a wavelength where condensed water has a low but detectable absorptivity and everything else in that planet's atmosphere either has a negligible absorptivity or can be compensated for, and then one can deduce how compact the clouds are from that and the absorbance of a wavelength where condensed water has a high absorptivity and everything else in that planet's atmosphere either has a negligible absorptivity or can be compensated for. (Actually, in order to calculate the amount and compactlygroupedness of condensed water in the atmosphere from the raw numbers/direct measurements, the scientists would have to know not only the absorptivity of condensed water suspended in air as clouds but also characteristics of the planet such as its radius and the thickness of its atmosphere. There are also other complicated factors, such as that some of the aerosolized water in clouds is in the form of solid ice, not liquid water. However, the scientists would still notice if the raw numbers from the more rudimentary observational equipment suddenly changed the second, they switched on a more powerful telescope, so the following point still stands.) If the computer simulating the Universe did not switch to the more precise simulation of the planet's atmosphere in time for the scientists to only see spectrographs of the planet's atmosphere rendered with precise calculations, then if the scientists later developed a more powerful telescope, like the one described earlier, and then pointed it at the planet, either they would see poorly-rendered clouds and know that the Universe is simulated by a computer that skimps on the fluid dynamics calculations for the atmospheres of certain planets, or the measurements from transit spectrographs would suddenly change, so the scientists would know that something weird was going on—although probably not exactly what. This is important because it is more feasible for a society to develop low-resolution transit spectrographs quickly enough to catch the computer simulating the Universe off-guard than it would be for a society to develop the technology required for a telescope advanced enough to look at the clouds of a planet in another solar system with high enough resolution to determine whether the atmosphere is simulated by a computer that is skimping on the fluid dynamics calculations quickly enough to catch the computer simulating the Universe off-guard. However, either could conceivably catch the computer simulating the Universe off-guard because it would be difficult for a computer to deduce whether a planet has life and how technologically advanced the life of any planet that has life is when the only raw data for the computer to work with are the positions and velocities of atoms, electrons, and photons.
- If atmospheric physics suddenly changed upon the evolution of a species capable of distinguishing whether the atmosphere is simulated by a computer program that is skimping on the fluid dynamics calculations, that would likely cause sudden changes in the climate, and the resulting heat waves, droughts, freezes, famines, floods, storms, and/or other (formerly) extreme weather would likely drive that species extinct (considering that it had just evolved, so it would have a small population and therefore be especially susceptible to natural disasters) because it would not have evolved to survive in such conditions. Such disasters and climate changes) would not have to directly kill all members of the species in order to drive it extinct; they could instead diminish the size of the gene pool by killing most of the members or divide the once-larger population into smaller, genetically isolated populations (e.g., by causing the creation of uncrossably swollen rivers dividing what used to be a single genetically-interconnected range into several smaller populations), either of which would cause an unsustainable level of inbreeding that would eventually lead to extinction. However, our species was not driven extinct shortly after it first developed.
Of course, most people do not think that the Universe is a simulation, but society does not know that it isn't a simulation with absolute certainty. There is a direct relationship between the question of the simulation hypothesis in metaphysics and Pascal's wager in theism, i.e., whether God(s) exist(s), with weighty implications regarding free will and determinism, such as which raise the question of non-naturalist compatibilism.
Megan proposes an additional theory that the universe is intended to make cool swirly clouds, and that the presence of life to observe these clouds is a bothersome coincidence. This goes against the theory that the Universe must not care about making cool swirly clouds since it wants to skimp on their fluid dynamics calculations. Even among followers of the simulation hypothesis, ascribing sentiment, emotion, or motivations to the entire universe is usually considered to be in jest, because of the dissimilarities between sentient beings and cosmologically distant sets of galaxies. This jest forms the basis of the comic's humor. Neither ascribing motivations to the Universe nor positing the purpose of a constructed simulation of our reality are falsifiable hypotheses subject to scientific inquiry, although they may imply logical and mathematical inferences.
The title text includes a dialogue with one person asking another why they got into fluid dynamics. The answer implies that the motivation was to simulate the clouds of planetary atmospheres unreachable by today's rocket technology.
- [Cueball and Megan standing on a field, looking out at a landscape of clouds]
- Cueball: It's weird to think there are countless planets with air and stuff but no life.
- Cueball: Billions of years of clouds making cool shapes with no one to look at them.
- [Just Cueball and Megan standing next to each other]
- Megan: Yeah, it seems like a waste. The universe getting the complex fluid dynamics right for every momentary swirl of cloud.
- Megan: Just a huge amount of work.
- [Cueball and Megan walk away to the right]
- Cueball: Maybe atmospheres have smooth laminar flow until someone looks closely.
- Megan: Or maybe the universe just likes making swirly clouds, and is annoyed that we're watching.
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3-D video games? HUH??184.108.40.206 09:33, 27 August 2022 (UTC)
- It's not how I would have started the Explanation, but I think it'll quickly be rewritten enough that this element is downplayed/subsumed in some more generalised attempt to explain everything from QFD to the CBR. As I'm only just reading this now, just before I have to wander off to do something else, I shall have to defer my own dabbling edits until later, by which time it will have been matured (or at least remixed) into a more thorough text, so no point me worrying upon how to improve the necessary but rarely inviolable initial attempt to Explain. 220.127.116.11 11:51, 27 August 2022 (UTC)
- Maybe in some combination with the Observer effect (physics), it's an attempt to get at the simulation hypothesis maybe?
- I absolutely do not get whatever it is that the title text is saying, so I'm sitting this one out. 18.104.22.168 14:56, 27 August 2022 (UTC)
- I'd interpret it as them studying fluid dynamics in hope of discovering a way to create the coolest possible cloud. --22.214.171.124 15:07, 27 August 2022 (UTC)
- Aye. Given we can't see the 'best clouds' here (because the chances are low that we can) and we can't go and see the absolute best clouds (due to limitations on visiting every likely place out there), by intensely studying the phenomenon that in part dictates how all clouds look one might create (or visually predict the look of) the superior type through rigorous simulation/emulation/etc. 126.96.36.199 15:53, 27 August 2022 (UTC)
Much more computing power could be saved by skimping on the chemistry of the quattuordecillions of atoms in the oceans than the clouds in the sky ... but skimping on oceanic chemistry would make biogenesis much less feasible. However, Earth has life.
Wait, what if this is the solution to the Fermi paradox? /jk Xkcdjerry (talk) 02:49, 28 August 2022 (UTC)
"Of course, most people do not think that the Universe is a simulation..." feels like a genuine  to me. I can't say with confidence that it's the prevailing theory, but it's been gaining so much traction in this day and age that it feels weird to claim with confidence that the majority of people don't think it.
- Agree. On the other hand, I don't think the Universe simulation cheats to save computing resources. With the scale it works in, it must be massively parallel system which isn't able to reallocate resources from one area to other. Also, if whoever programmed the simulation would be willing to cheat, they would start with not designing the physical laws so complicated. Or alternatively, they would cheat big, changing our memories to make everything seem to work correctly. -- Hkmaly (talk) 23:44, 28 August 2022 (UTC)
- Yes. If the universe were like The Matrix—i.e., its main goal were to house beings possessing minds—then simulating only the input to each being’s senses would be the most economical.
- However, the amount of computation to identify beings and what information constitutes their input might be so hard as to be analogous to the halting problem, or technically undecidable (but subject to likely useful heuristics, depending on the purpose of any such simulation.) This gets into non-naturalist compatibilism on the free will question, but it's not clear whether such a discussion would add anything directly to an explanation of the comic, but is worth considering. Maybe in the "Further considerations" block. 188.8.131.52 20:29, 29 August 2022 (UTC)
Am I the only one who feels like the Explanation is lacking its customary explanatoriousness? I propose a table in the form of Pascal's wager, which when projected on the Mandelbrot set, looks like clouds. 184.108.40.206 03:12, 29 August 2022 (UTC)
I don't think this is an accurate description or explanation of the title text, so I am moving it here:
- "The response is, more or less, that the second person wants to see “the coolest clouds”. If one devised a system to determine what would qualify as the coolest clouds (an entirely subjective thing), then one could rank planets on how cool their clouds were. Since only one planet would have the best clouds and there is a great number of planets, it is statistically unlikely that Earth - or any of the other planets in our system - will be the winner. Thus, in order to see the coolest clouds, one must either travel to another system or learn fluid dynamics to simulate them. Compared to the vast distances a ship must travel to reach even the nearest star, even rockets seem slow, and it would take a long time to get even a fraction of the way there. Because of this, the latter is chosen."
220.127.116.11 03:59, 29 August 2022 (UTC)
- I was surprised to see that removed. It looked exactly like the explanation for the TT, to me. The alternative seems to lack so much of the implied rationale. But maybe the simulation of this site provided to my brain is different from the simulation of this site provided to yours (assuming you exist, and you aren't a confounding factor included 8n my whole simulation of what I might or might not be experiencing).... 18.104.22.168
- It assumes that different atmospheric compositions could produce cooler clouds, which is tautological given the subjectivity of the criterion, but questionable from the perspective of mean opinions over a wide population such as the readership. The current two sentence explanation of the title text sidesteps that issue, and is much easier and faster to read. 22.214.171.124 20:54, 29 August 2022 (UTC)
I was reminded by this strip of the fact that THIS planet, the only planet in our solar system where the natural satellite has the correct relationship with the sun to occasionally block it out in an extremely cool way (with the 'diamond ring' corona effect), is also the only planet (so far as we know) where such , solar eclipses can be APPRECIATED...
MarquisOfCarrabass (talk) 06:23, 29 August 2022 (UTC)
This is the WORST explainxkcd "Explanation" I have ever seen. There is absolutely NOTHING in the comic that has ANYTHING to do with 3D videogames and any such ideas come COMPLETELY from out of the blue. SHEESH! 126.96.36.199 10:40, 29 August 2022 (UTC)
- Agreed. The comic is about planets and clouds, there is nothing about simulations or rendering at all. The last panel is a hint at anthropomorphizing (if that's a word) the universe for humour, as if it just creates neat clouds for fun. 188.8.131.52 07:18, 30 August 2022 (UTC)
- Getting fluid dynamics right being a lot of work is absolutely a reference to simulation, and I don't see how such in the context of observations of our reality can escape entailing the simulation hypothesis. 184.108.40.206 00:43, 31 August 2022 (UTC)
As for the "Further consideration" section, it's a whole big pile of . . . something . . . that belongs somewhere else but not here. 220.127.116.11 10:46, 29 August 2022 (UTC)
- Click the Expand link, pay the consequences :D 18.104.22.168 23:48, 29 August 2022 (UTC)
Is there a difference between ascribing motivations to the Universe and positing the purpose of a constructed simulation of our reality? 22.214.171.124 23:37, 29 August 2022 (UTC)
- Neither are falsifiable hypotheses, to begin with. 126.96.36.199 23:45, 29 August 2022 (UTC)
- Yes; there is a difference. The first says nothing about where the motivations come from and the second is specific about it. If the Universe has motivations they could come from any number of unknown sources . . . . 188.8.131.52 10:43, 30 August 2022 (UTC)
Feels like this deserves a link to the Cloud Appreciation Society Miamiclay (talk) 07:07, 31 August 2022 (UTC)
- Feels like you could replace the whole explanation with that link and it would be more explanatory. I understood the comic more before I tried to read the explanation than I do afterwards. 184.108.40.206 11:36, 2 September 2022 (UTC)