2775: Siphon

Explain xkcd: It's 'cause you're dumb.
Jump to: navigation, search
ADDITIONAL NOTES: Fixed a bug that caused some rocks to generate virtually infinite heat while just sitting there.
Title text: ADDITIONAL NOTES: Fixed a bug that caused some rocks to generate virtually infinite heat while just sitting there.


Cueball and Megan have set up a simple experiment to test how a siphon works, using the gravitational force on a lower portion of liquid-filled tube, atmospheric pressure on the upper reservoir, and molecular cohesion within the liquid, to move a liquid upwards through a bit of tube at a higher gravitational potential. In short, the liquid passes over a higher peak to reach a lower exit. Randall has also mentioned siphons in whatif 143 and in his book, "How To," section "How to Throw a Pool Party".

Siphons are commonly used in modern society (e.g., most American residential toilets are flushed by siphon action). Siphons should not be confused with capillary action.

Apparently, even though Cueball and Megan have set up the experiment correctly, the water no longer demonstrates a siphon by flowing from the upper bucket to the lower. Cueball observes in surprise that "it's true," that siphoning doesn't work anymore. Thus indicating that this is a very recent development, and Megan remarks that it was honestly weird that it ever worked, and muses over why we ever thought that was a normal thing.

The punchline of the comic comes in the caption, which delivers a piece of Physics News: "The 2023 update to the universe finally fixed the "siphon" bug." The joke here is that the entire complex and multifaceted system of physics in and of itself is treated as though it is simply the coded logic running the universe (or perhaps the sometimes unintentional result of various default configuration options like in a video game - see 1620: Christmas Settings), and that siphoning (rather than being an interesting physical phenomenon worth studying) was nothing more than a bug in the Universe. It has now been fixed, somehow and for some reason, being considered a glitch and not the intended behavior.

In reality, siphons still very much exist in our universe. Siphons require filling beforehand to function, either by initially actively sucking liquid through or by first immersing the siphon tube in any compatible liquid then ensuring it retains its contents as it draped over the obstacle and each end positioned properly into the respective receptacle, so it is plausible to imagine skeptical people “proving” they do not function by refraining from providing the initial priming. However, the small amount of water in the bottom of the bucket near Megan indicates that there was at least some water in the tube, and that this just ran down on either side, leaving the tube empty and a bit of water in Megan's bucket and a bit more in Cueball's bucket. So they did set up the experiment correctly, but since the latest update siphons do not work anymore. Or as they state it, the universe now works correctly and the siphon bug has been corrected.

A siphon requires that the weight of the liquid column on the "higher" side of the channel peak not exceed atmospheric pressure, or else the liquid will split, leaving a partial vacuum. The observed failure could be caused by several kinds of changes to the universe. If there was a significant decrease in the ratio between the pressure of Earth's atmosphere and the force of gravity, the siphon would stop working. Eventually, the water in the "lower" side of the tube would dribble out, letting air in, and the water in the "higher" side would also drain back into the reservoir. If the density of water increased enormously, the increased weight of the liquid column would lead to a similar failure. If the molecular cohesion of water decreased drastically and the flow rate of the siphon was slow, air could bubble into the "lower" end more quickly than the water was flowing through, and eventually the tube would empty. The siphon could also fail more mundanely if the water had a lot of gas dissolved in it under pressure (as with soda water), because the gas would come out of solution and collect at the highest point of the tube.

The idea that we live in a computer simulation is also prevalent in our modern pop culture, most famously shown in The Matrix (See 566: Matrix Revisited).

The title text is an additional note to the 2023 physics update stating that the update has: "Fixed a bug that caused some rocks to generate virtually infinite heat while just sitting there."

This is a reference to radioactive materials that keep emitting energy (heat) almost indefinitely (on a human timescale). This is mainly a reference to uranium and thorium and their decay chain.

This is similar to the comic 2115: Plutonium, because plutonium (though man-'made', during nucleosynthesis) is used to power spacecraft. In that comic the title text has the same idea that someone controls the universe: It's like someone briefly joined the team running the universe, introduced their idea for a cool mechanic, then left, and now everyone is stuck pretending that this wildly unbalanced dynamic makes sense.

The entire comic is one of many where Randall muses over strange aspects of our universe, and wonders why we (people) ever think that it seems normal, the way the Universe works (or how humans work - see for instance 1268: Alternate Universe).


[Cueball is standing next to two buckets while Megan is looking on from the other side of the buckets. The left bucket is on a stool and is almost filled with water while the other is on the ground and has a very small amount of water in it. Cueball is holding an empty tube between the two buckets. The end to the left is deep into the water in the left bucket while the other end hangs into the empty bucket to the right.]
Cueball: Wow, it's true—the water doesn't flow up the tube anymore.
Megan: Honestly, it's weird that it ever did.
Megan: Why did we think that was normal?
[Caption below the panel:]
Physics news: The 2023 update to the universe finally fixed the "Siphon" bug.


Siphons are separate from a similarly counter-intuitive phenomenon of capillary action, where a liquid flows through narrow spaces (even upwards, entirely against gravity) in that a siphon need not be of such small diameter. Capillary action will also move liquid into an initially empty channel, whilst a siphon must be 'primed', by filling the tube, in order to draw liquid over a high point to ultimately always drop down into a lower container. Capillary action is caused by surface tension and attractive forces between the liquid and the walls of the channel; the liquid level will rise until the weight of the column of liquid matches the attractive forces. Capillary action can lift liquid higher than the maximum height of the "higher" side of a siphon with the same liquid, if the attractive forces are strong enough.

comment.png add a comment! ⋅ comment.png add a topic (use sparingly)! ⋅ Icons-mini-action refresh blue.gif refresh comments!


My understanding was that siphoning can essentially be explained by the Bernoulli equation? There is a difference in potential energy between the upper and lower container so it flows. The weight of water in the downhill part of the tube pulls water up the uphill section of the tube (think like a vacuum), and so on until there's either no difference in head or no more water. Siphoning will work with any diameter tube. 15:43, 12 May 2023 (UTC)

That's right. The only mention of capillary action in the siphon wikipedia article is when talking about phenomenon that *isn't* a siphon. Barmar (talk) 16:15, 12 May 2023 (UTC)

Agree, capillary action does not seem to be referenced or implied in the comic, presenting only the (not "functioning") siphon phenomenon. 16:23, 12 May 2023 (UTC)

Seconded/thirded. Capillary action isn't even what they were expecting. The small amount of water in the lower recepticle indicates they correctly filled the tube, but then as the longer length drained it did not then induce further flow up and over through the shorter length. e.g. nature no longer abhored the resulting vacuum (or there was increased negative-pressure vapourisation, beyond that previously expected, or other method of seepage 'airlock'-breaking) and thus the short-end also drained straight back out again instead of becoming a potentially self-sustaining inflow to the whole siphoning setup.
If the upper end got restricted (say by touching the side of the bucket) the loss of flow would allow air to enter the bottom end and drain out the tube. I've done this. :-( RIIW - Ponder it (talk) 19:07, 12 May 2023 (UTC)
Indeed, even having an especially large diameter "tube" (/pipe etc) can allow air from the bottom to flow up to the peak & break the siphon effect. For reliable results, the lower end needs to be kept immersed or the hose needs to be relatively small in diameter. ProphetZarquon (talk) 14:11, 13 May 2023 (UTC)
While the capilliary action element could induce the start of a rather limited 'empty' siphon setup to start (maybe, I'd have doubts about the 'fluid friction' actually acting against the gravity-feed part, once the surface-tension bit has "climbed the mountain" and started to merely seep out of the other end, almost incidentally, for a sufficiently thin tubing where CA is a significant factor), this suddenly failing for whatever reason (surface-tension effects being nullified) wouldn't then send a token amount of water into the low bucket, nor particularly stop unrelated siphon-flow from continuing properly (in fact, suddenly 'interaction-free' liquid and tubing might siphon faster, with effectively zero fluid boundary effects dragging on the induced flow).
But perhaps someone with more QFD experience could explain where my assessment is wrong. So not going to personally rewrite the current Explanation intro just now. 16:21, 12 May 2023 (UTC)
I'd like to contribute as one more data point. I also don't see capillary action as being relevant. In particular, as another commenter said, the water in the lower bucket quite clearly supports the idea that the siphon effect was the subject of the characters' confusion. How else is Randall supposed to depict the siphon effect anyway? I agree that the drawing alone could also suggest capillary action is what's being investigated, but I don't think it suggests that the caption has incorrectly referred to it as the siphon effect. 18:44, 12 May 2023 (UTC)

Of course, if some physical law would actually stop working, people wouldn't be confused. They would drop dead. Due to physical laws working on level of elementary particles, every change would have lot of different effects ... and living organism live only thanks to being very carefully balanced in lot of regards. -- Hkmaly (talk) 20:49, 12 May 2023 (UTC)

Bug report 6EQUJ5: Odd signal emitted from Sagittarius constellation. Status: Closed - could not reproduce. 03:20, 13 May 2023 (UTC)

(I get that reference... :) However, launching off that to say: ) There's an old (short?) story... H.G. Wells era, possibly, but not him I think... where someone (who happened to be the first decent but amateur astronomer to get a cloudless patch of sky, one night) realises the Moon is in the wrong place, and the news then reaches (and troubles) the professional community who get a chance to observe/notice the change for the first fime and confirm it.. A 'glitch' seems to have passed through space and moved/retimed it, for a limited time, before it later snaps back to where (in the orbit) it now should be.
The trace of the glitch are seen further afield (implying a 'beam' of 'wrongness'), and ultimately it spawns something like Experimental Theology whereby observations of such clear "hand of the Creator" changes (implying we're essentially in a simulated universe being operated by a 'universal programmer', but in pre-computer terms) merge or muddy the boundaries between scientific rationalism (which clearly falls short) and religious philosophy (where undeniable 'proof' of something godlike is now suddenly an ironically confounding factor).
Cannot remember much about where I read it, I may be presuming some details about it that aren't actually there (even removing obvious mix-ups with similar brands of tale) and my Google-Fu fails to establish any obvious online reference to it (even just title+synoposis), so instead I'm setting down the 'spoilers' without reservation. 13:04, 15 May 2023 (UTC)

Siphoning is NOT because of capillary action! That should be changed!! 15:35, 13 May 2023 (UTC)

I guess I was wrong that siphons work because of capillary action. TianHanFei (talk) 1:57, 15 May 2023 (UTC)

As someone who's been publicly wrong here before, it can be stressful, but if it's any consolation, you're one of today's (probably much fewer than) 10,000: https://xkcd.com/1053/ -- thanks for having a sense of humor about it Dextrous Fred (talk) 17:18, 15 May 2023 (UTC)

Potential inspiration

One potential source of inspiration for this comic is the Twitter account @Earth_Updates, which produces a lot of similar content. PotatoGod (talk) 19:54, 12 May 2023 (UTC)

I think if I added it to the article body it would get reverted, but the content seems very similar to how AI media produced delusional worlds for so many factions of people. It is not at all a big stretch to imagine people stepping into a metaverse or matrix where they aren’t sure what is real and physical laws match their intuition more than is actually correct. 08:23, 13 May 2023 (UTC)

Title text

Isn't the title text about stars like our sun rather than about plutonium? 00:55, 13 May 2023 (UTC)h

Seems to me unlikely that anyone would refer to stars as 'rocks'.Catherine (talk) 02:54, 13 May 2023 (UTC)
There is Slate that turn into lava spontaneously after lying around for thousands of years. I think the area they are in is called "Smoking Hills". There was recent research why that slate does this while in much the rest of the world slate is just flat, black rocks. I still believe this title text is about plutonium, though, as that slate produces so much heat, that one still hasn't managed to measure how hot it gets - but it produces that heat not for an near-infinite duration.--Gunterkoenigsmann (talk) 01:48, 14 May 2023 (UTC)
The only Smoking Hills that came to mind was natural shale-fires (chemical burning, and not hot enough for remelting to magma/lava.
Possibly there is a situation where it has done as you say (in some natural mass of rock, spotted somewhere in this planet's lithosphere, or elsewhere out there), but given the fine line between nicely sustaining and runaway chain-reactions, I'm not sure how easy it is for nature to 'engineer' a way to land on the middle ground and not go supercritical.
In order for accumulating ores to not just start a low-level fizzle (as above), over millenia, you might need separate ore-patches either side of a fault to come together in a suddenish techtonic slip, rather than a slow buckling of layers to increase effective ore-densities. And then you've got earthquakes, already, so not sure if the very low-grade nuclear explosion that is awfully close to being possible in this chance contrived example (at one end of the probability curve, unless U238 content is somehow preferentially leached out?) is going to be noticable.
But just hot enough for lava? If not already close to melting, anyway, under local temperatures and pressures? Not sure we've seen anything like it, even if it is technically feasible given enough happenstance setups by geology(/exo-geology), since planets formed. 09:16, 14 May 2023 (UTC)
Any sufficiently large rock containing sufficiently high concentrations of radioactive materials (such as the Earth) will partially melt. The energy is released slowly by decay not through fission. The large size ensures that the center is well enough insulate that slow heating accumulates until it reaches lava temperatures. The finite size ensures that enough heat leaks out that the magma does not become gas. 18:29, 16 May 2023 (UTC)

Title Text-Radiation

The title text is referring to the heat created by natural radioactive decay, not humans harnessing it in reactors.

The literal rocks of particularly radioactive elements still in the ground are constantly producing small amounts of heat without our assistance 06:27, 14 May 2023 (UTC)

Relevant xkcd: https://www.explainxkcd.com/wiki/index.php/1172:_Workflow

Re:Actor: Siphon heat rocks water is the basis for my workflow. Randall please add a option, so siphon heat rocking can be re-enabled on demand. 19:23, 16 May 2023 (UTC) PicassoCT

siphon't 15:22, 13 May 2024 (UTC)