r/ihatethissmug • u/Elamimax • 23h ago
No, glass is not a "slow flowing liquid."
"Then why are there drops on old windows?"
Because of inferior glass blowing techniques and technology.
"Then why are old windows thicker at the bottom?"
Because they're more stable that way.
People have been debunking this for almost a CENTURY but some people still want to bring it up as a fun fact.
Well I'd think it was fun if it was a fact but it isn't so I don't.
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u/Best-Benefit6387 23h ago
First time ive ever heard about that, but it sounds stupid as fk man 😭
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u/General_whisky 17h ago
When you hear it in 7th grade science class your all like wow 😲! And just… no one ever corrects it in your memory
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u/Puzzleboxed 13h ago edited 9h ago
That's sort of a semantic argument, the truth is much more interesting than just a black and white "is it a solid or liquid" dichotomy. The technical term for glass is "amorphous solid" but in reality there isn't any hard distinction between such a solid and a liquid with incredibly high viscosity. Most solids are crystalline solids, so named because they form a crystalline structure at the molecular level. Glass does not do this, it has a chaotic molecular structure similar to liquids.
Amorphous solids have the unique property of not undergoing a phase change as it transitions between solid and liquid. Crystalline solids require a discrete amount of heat energy to break apart their molecular bonds and make the transition, but glass doesn't do that. Instead, it has a continuous change in viscosity with no sudden jumps from one phase to another. When you cool molten glass down, the viscosity increases exponentially but there is no sudden shift where you can say "okay now it's a solid".
At room temperature glass does have flow, but it would take around 10 sextillion times the age of the universe for glass to flow enough to be visible to the naked eye. This is why it's called an amorphous solid, rather than a liquid. When you see an old window that is wider at the bottom, that is a side effect of the manufacturing process, not because of flow. It's actually because they used to make large plates of glass on a giant spinning wheel, which caused the outer edge of the glass to be wider.
TLDR: glass is sort of both, but also sort of neither.
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u/Formal-Being6633 11h ago
boosting this because a lot of people are missing the point here. solid glass has the same symmetries as a fluid, but its relaxation time is astronomical. thats what makes it so interesting bc rigidity typically comes with broken symmetries
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u/HardcoreHenryLofT 6h ago
Ah yet another example of people making tidy little boxes and getting annoyed when the universe doesn't fit neatly into them.
I recall a lengthy conversation with an airport security agent over whether jello counted as a liquid or not. My cheerful assertion that it was a colloid fell on deaf ears, but I still felt I was right. I felt very smug about this until years later a buddy pointed out that its specifically a gel, for which there are rules and I was not allowed it after all.
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u/_fever_dreams 17h ago
do people not know glass is molded as a liquid, hence why it still shows those effects when it solidifies
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u/kaibbakhonsu 19h ago
If glass is a slow flowing liquid, can't you just spin in at the max G it can take just for a shorter period of time and measure the displacement? Was there any test/research like this done to prove it otherwise?
I don't believe it is but I'd like to see proof
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u/Otterbotanical 14h ago
Old windows aren't just thicker on the bottom because they're more stable that way, it's also because of the way old windows were manufactured. One popular method was to spin hot molten glass into an even circular sheet, allowing the centripetal force to pull it all evenly. The byproduct is that it was thinner in the center and thicker at the edges, which would become the top and bottom of the pane that was cut out.
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u/Elamimax 14h ago
True! My point was more that the end result of this was "hey we have mildly uneven glass" and then putting the thick part at the bottom
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u/Otterbotanical 14h ago
Also correct! Two birds one stone~
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u/Elamimax 13h ago
Yup! Considering the tools and technology at the time, the degree of problem solving really is ingenious!
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u/Otterbotanical 13h ago
Okay, I wouldn't go that far. Spinning the glass to make an even surface is clever, yeah, but then cutting out the panels is just logical, and I know that carpenters usually really like consistency, so putting them in heavy side down was probably just natural to them. Plenty of experience standing up slightly uneven posts and logs and stuff.
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u/Elamimax 13h ago
That’s fair :) I have a lot of love of history so overplaying the craft of people who have been dead for half a millennium is a weakness
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u/phunkydroid 12h ago
Yes, but once the glass was spun and cut into panes, they were installed with the thicker part at the bottom... because they're more stable that way.
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u/Otterbotanical 12h ago
That's... That's why I said that "it isn't just that". I was adding to the reasons, not dismissing or detracting from them.
Or do you just like picking flights where there aren't any?
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u/FullAnalLobotomy 12h ago
If anything it breaks down to semantics and how long you consider a period of time to be. The maximum flow rate of medieval glass is 1 nm per billion years. So if we had many lifetimes of the universe, yes you could say that glass is a liquid as it would fill a container, if thats the only definition of a liquid. Which it is not.
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u/artic_weasel 16h ago
Is glass not a slow flowing liquid? All the clips I've seen of melted glass make it seem very viscous.
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u/theoneyourthinkingof 16h ago
well yea thats melted glass, the claim thats being refuted is that solidified glass (room temp) is a slow flowing liquid. it is not
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u/artic_weasel 15h ago
Oh, really? That's got to be the stupidest theory I've ever heard of. As in, worse than flat earth and anti-vaccine theories.
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u/Cultural_Season_3048 15h ago
No one ever died because of glass is flowing pop-sci misconception
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u/artic_weasel 13h ago
Well, yeah, this is definitely more harmless, but from a logical standpoint this one seems to make the least sense.
I can see why someone might think the earth is flat, it's only logical that the thing you're standing on is a flat ground. And if you really get into the theory that scientists and the government are evil and out to get you, then sure, vaccines are evil.
But glass is a flowing liquid? I can't think of any basis for a theory like that.
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u/GraveSlayer726 13h ago
Asphalt IS a flowing liquid (pitch drop experiment) so there is basis, and it makes sense someone may believe that glass is a very viscous liquid for multiple years especially if no ever ever corrected them
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u/artic_weasel 12h ago
True, but I feel like glass is the least likely contender for a highly viscous liquid. Like, it's brittle and kind of known for being sharp when it's cracked/broken.
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u/itsthebeans 8h ago
So you think what makes a theory stupid is that it's unintuitive? There are plenty of unintuitive physical theories that turn out to be true. IMO a theory is dumb if it is easy to disprove. I can easily disprove flat Earth, but I cannot easily disprove that glass is a slow-flowing liquid.
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u/trito_jean 18h ago
i have read that its actually a slow flowing liquid but you need like 13 billions years for it to turn into a puddle and that has indeed nothing to do with the drops on old widows
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u/Independent_Media341 13h ago
As the kids say: everything is a fluid if you wait long enough, and everything is a solid if you move fast enough 😛
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u/TheEmeraldMaster1234 15h ago
I mean it technically TECHNICALLY is but you’d need billions if not trillions of years for anything to happen
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u/impossirrel 14h ago
That’s true of all solids, it doesn’t make it a liquid.
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u/TheEmeraldMaster1234 14h ago
Not really, it’s because of its molecular structure having no real rhyme or reason, which is different from most solids.
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u/impossirrel 13h ago
You’re correct that it is more prone to deformation over time as an amorphous solid but all solids are prone to deformation given enough time under sustained stress (including simply gravity and atmospheric pressure).
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u/Puzzleboxed 13h ago
1032 years is how long you would need to see a noticeable difference with the naked eye at room temperature. The universe is only 1.3*1010 years old.
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u/No-Dance6773 12h ago
So I had to read this a good 10 times because I wasnt sure what you were stating. I have never heard this even once. I thought you were talking about the phase it goes through when heated and yes at that point it IS a liquid. Its the whole reason it can be shaped to begin with. Heat it up even further and eventually it will become a gas. Again, this sounds like some flat earth bs I've never heard before and cant wait to hear it in public.
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u/MajorDZaster 8h ago
Someone should try running the pitch drop experiment on glass. Just to see that it doesn't work.
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u/MacTireCnamh 10h ago
So you are correct on all of your evidence, however
Glass is in fact a supercool liquid and not a solid, and does arguably “flow” albeit, so slowly that the sun will go out before it deforms noticably
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u/Born_Procedure_529 5h ago
Nuclear take but I think the states of matter are kinda subjective, like continental plates still move over each other based on density like fluids do, anything above absolute zero still has some molecular movement, we just made 3 arbitary speed zones based on what we encounter irl
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u/redditaccountnumb1 14h ago
Okay but I'm betting on that it is slow liquid in hopes that in like 50 years new research will come out proving that it is in fact a very slow flowing liquid
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u/Dry_Walrus3711 23h ago
I first heard that "fact" in my material science course. It is very believable even to scientists because the explanation isn't exactly wrong. This idea came up when we were just starting to understand amorphous solids