Glass viscosity calculations debunk the myth of flow in medieval windows (2017)

https://ceramics.org/ceramic-tech-today/glass-viscosity-calculations-definitively-debunk-the-myth-of-observable-flow-in-medieval-windows

by aoki • 6 years ago

123 149 6 years ago

ceramics.org

nikisweeting5• 6 years ago

Finally! I always knew my 7th grade science teacher was full of shit on that one, she was so adamant about some things that turned out to be wrong.

This one was maybe more excusable because it was common to teach at the time. Maybe it ended up making us better students in the end because we learned to fact-check our teachers, and not to be adamant about things we only think are true (though I'm still guilty of that myself sometimes)...

torben-friis• 6 years ago

What other unsubstantiated claims did she make?

zamfi• 6 years ago

I'm not the original poster, but I was shocked by how many of the otherwise super smart friends I had in college were taught common falsehoods in high school. For example: the idea that your veins look blue through your skin because the deoxygenated blood in them is blue, and that it only turns red outside your body because it's exposed to oxygen.

nikisweeting5• 6 years ago

To be fair it was usually small, inconsequential things, not major parts of the curriculum.

The only major one I remember is that water is conductive by itself. And that "C++ is the best programming language" (hah).

K2h• 6 years ago

Only 1 set of ‘primary’ colors

jeffbee2• 6 years ago

That traits of human physiology are heritable binaries.

https://udel.edu/~mcdonald/mythintro.html

pjmorris2• 6 years ago

Not the OP, but a fourth grade substitute teacher made the claim that we always saw the same side of the moon because it didn't rotate. I don't know what got to me the most: that she didn't understand, that my attempt to explain it didn't go over, or that the other kids in the class didn't get it either. In any case, I've been working on improving my explanations ever since.

nemo44x10• 6 years ago

Almost everything we think (including me) is probably trash. We just need to accept we are mostly idiotic. Unless we put the time in to understand something that _maybe_ is somewhat understood by people that have put their lives into it.

Truth is (heh) we are all mainly full of shit. We think we know more than we do. We confuse truth for BS constantly. We spend countless breaths debating unfalsifiable opinions as if they’re true - like we really know something. We are all mainly dumb at most things.

elliekelly• 6 years ago

"You won't always have a calculator in your pocket." - Every math teacher before 2005

askvictor• 6 years ago

Centrifugal force is a common one: https://xkcd.com/123/

causality0• 6 years ago

I had an electronics professor who in 2012 was adamant that in five years smartphones would be using x-ray transceivers to communicate with cell towers.

deelowe• 6 years ago

I think your professor read about millimeter wave and misunderstood. I've had others confuse the two in conversation as well.

dheera• 6 years ago

Lots of grade school teachers are full of shit.

I had one that claimed that a pentagon had 1 line of symmetry because "the top is bigger than the bottom".

elmomle• 6 years ago

Allow me to be dumb for a second--isn't that the case? I mean, if you label the vertices/edges then yes a regular pentagon has five distinct lines of symmetry, but typically people talk about lines of symmetry in a context where vertices are unlabeled, no?

nemo44x10• 6 years ago

Most school teachers are full of it, but they don’t mean to. They are simply low level clerics in the church of truth. They recite a very lossy account of what they were ordained with at a likely low level institution. It’s not really their fault - people need jobs, the ministry needs repeaters, and the pay is bad.

Your teachers weren’t the disease - they were just a symptom.

bosswipe• 6 years ago

This idea of a shadowy unified people that control everything is a poor way to try to make sense of the world.

flatline• 6 years ago

I mean, the HS teacher that told me this had a masters in Mech E. Or so he claimed, hmm...

_fi0w2• 6 years ago

If only teachers were as intelligent and wise as HN’s anonymous commenters.

lordnacho4• 6 years ago

This is a great analogy. The teachers in school are not there to teach you the most detailed model of the world, they are mostly there to make you exercise your model critiquing ability on some toy models that are simple to deal with. Your math teacher might draw a blank when you tell him he taught you an inconsistent notion of limits in calculus, and your physics teacher will certainly admit that there are holes in the high school version of gravity.

But the point wasn't to tell you the exact version of what we know, it was to make you think about how models work.

ars• 6 years ago

The article says the glass does actually have a viscosity, so maybe she was not quite that wrong - just about the magnitude.

I think glass has a viscosity, but other solids do not, but will creep.

I hope my understanding is correct - if not, can anyone help explain?

aoki2• 6 years ago

I believe you are correct. I had to shorten the title, and removed “observable” because the word “medieval” already refers to the science class meme that the viscous flow is at human history timescale (as opposed to ~1 nm/10^7 years).

GuB-422• 6 years ago

That's the reason why I love the internet. Things are so easy to fact check now, at least compared to the way it was before.

Many people talk about the problem of "fake news". What they may not realize is that falsehood have always existed, but we now have unprecedented tools to debunk them.

When I was a kid, I learned loads and loads of bullshit, the glass thing was one of it. The problem was, how could I know it was wrong? Obviously, I didn't know enough about material science to figure it out by myself, and I didn't know any material scientist. Books were mostly useless for that purpose, searching for the answers would have taken days at best, and I didn't have that much time to debunk something that insignificant. Now just searching "glass thicker at the bottom" on the web yields exactly what I need.

In fact, I am quite sure, there is much less bullshit going on today, but it looks like there is more because that these are so much easier to figure out.

abeppu• 6 years ago

In fact, I am quite sure, there is much less bullshit going on today, but it looks like there is more because that these are so much easier to figure out.

You're "quite sure" but how would one fact check this?

Other possibilities:

- There are more new claims being made and circulated, even if the same proportion of them initially are false, the fraction that any given person can follow up on to validate or debunk decreases, and then the share of propagated claims which is false is higher.

- The share false "facts" is higher because the ability to disseminate information has been democratized, but us amateurs have a lesser commitment to fact-checking than press professionals a generation ago.

- The share of bullshit is greater today than when you were a kid because the internet makes it financially rewarding to churn out content regardless of accuracy.

Kye• 6 years ago

See also: the myth of taste buds with specific functions neatly layered on the tongue.

onion2k2• 6 years ago

The problem is that it's obviously wrong with a simple experiment - just look at a few really old windows. I live about 1/4 mile from a church that was built 1300 years ago (https://en.wikipedia.org/wiki/St_Peter%27s_Church,_Monkwearm...). There's not much of the original glass left but where there is the thicker part is occasionally at the top of the pane because that's how it was originally mounted.

Teachers (and everyone else) will be wrong about things. That's OK. The problems happen when people don't bother to do any simple checks themselves, and just accept things as fact without doing any critical thinking or experimentation of their own.

lookalike1974• 6 years ago

I would not disagree that your teachers failed you or vice-versa. But making grand pronouncements about people ("everyone else") and their problems as you see them ("without doing any critical thinking or experimentation of their own") and teachers too - and apparently based solely upon your personal experience in school and your thoughts on one church that just happens to be physically nearby you - isn't gonna convince anyone. Your comment is ignorant and offensive to teachers.

inetknght• 6 years ago

Teachers (and everyone else) will be wrong about things. That's OK. The problems happen when people don't bother to do any simple checks themselves, and just accept things as fact without doing any critical thinking or experimentation of their own.

While not doing checks against teachers is a problem... there is a bigger problem of teachers who don't accept being wrong.

tinus_hn• 6 years ago

I seem to remember research has found some windows were placed upside down so these would now support the story that glass flows up.

JoeAltmaier• 6 years ago

I was taught in physical sciences that friction was proportional to weight and surface area. We were given blocks and a 'force meter' that was a bendy springy length of metal in a wooden calibrated frame. So pull blocks on a surface with the meter to measure friction. Try different surface area, stack them for multiples of weight, plot on a graph. Mine weren't coming out on a straight line. Other people noticed theres' weren't either, so they fudged their data points. I put down the honest ones. I got it 'wrong', they got it 'right'.

Of course that old myth was nonsense, my experimental method was correct, and I've felt the injustice for decades now!

eitland• 6 years ago

Our physics teacher were clearly happy when we got weird results and actually wrote down what we saw and wrote a comment on the difference between expect and observed results.

Jakobeha• 6 years ago

but tarmac does flow at an observable rate, although only observable over the course of years

nikisweeting5• 6 years ago

Especially if you live somewhere where the sun heats it over 50ºC! Then you get huge ruts from the trucks and potholes...

aoki2• 6 years ago

The related example that I always remember is: https://en.m.wikipedia.org/wiki/Pitch_drop_experiment

Cactus2018• 6 years ago

Wikipedia - List of Common Misconceptions

https://en.wikipedia.org/wiki/List_of_common_misconceptions

ternaryoperator• 6 years ago

Their measurements reveal that medieval glass has a much lower viscosity than expected at room temperature—16 orders of magnitude less than previous estimates

It's pretty rare to read an article in which the degree of previous error is sixteen orders of magnitude.

4ad• 6 years ago

The way viscosity is measured doesn't follow naive expectation though.

Water at 0C has over six times the viscosity of water at 100C, yet to the untrained human they seen to flow about the same. Olive oil is 100 times more viscous that water. Yoghurt about 10000 times more viscous than water.

chabad360• 6 years ago

Fair, but keep in mind that it's orders of magnitude we're taking about.

supernova87a• 6 years ago

While this was specifically about glass from the middle ages, is there certain window glass more recently that does flow measurably? The soda lime glass referenced?

Or when you see waves in window glass in 1930s buildings, is that too from the original imperfections in the glass fabrication itself?

JimTheMan• 6 years ago

I wonder if the craftsmen also knew that the windows were a little wedge shaped from manufacture and put the thick bit at the bottom. That's what I'd do at least, makes sense structurally.

Then later, random people made guesses as to the 'flow' of glass because all the windows are thick on the bottom...

If anyone can confirm this theory, you and I will feel eternally smug. Best of luck!

mensetmanusman• 6 years ago

How does this viscosity compare to gold or silver? Those also have brownian motion under the force of gravity.

I bet it’s higher than 1 nm / billion years.

heikkilevanto• 6 years ago

Yeah, I learned this "fact" in school as well. Later I found a simple refutation: If a church window pane would deform by a measurable amount in 1000 years (say 0.5mm), then a 100-year old telescope or camera lens would be totally useless, and yet they seem to function all right.

gattr2• 6 years ago

To add some detail: a common minimum quality criterion for optical surfaces is λ/4 (divergence from an ideal surface), where λ is the wavelength used. For visible light this gives about 100 nm (though large professional telescopes are "figured" to more like λ/20). Any alleged glass creep visible in window panes over a few hundred years would quickly ruin any astronomical mirror (which definitely does not happen).

Traster• 6 years ago

I mean... the obvious answer to that is that we don't use the same techniques to manufacture a telescope or camera lens that we used to manufacture church windows. In fact we don't use glass for large telescopes specifically because they'll deform under their own weight.

I'm not saying that original fact is correct, I'm just saying I don't think what you're saying disproves the idea that that glass could deform over time.

gattr2• 6 years ago

That's incorrect. We do use glass for large mirrors and it works just fine ([1], [2.1], [2.2]). Do not confuse these two effects:

1. Viscous liquid-like creep (does not occur).

2. Elastic deformation (sagging) under gravity - this of course takes place, and is compensated for by multipoint support and, in larger professional telescopes, "active optics" (actuactors that counter the deformation depending on mirror's orientation; not to be confused with "adaptive optics", which deform a mirror with high frequency to counteract atmospheric image distortion).

[1] https://en.wikipedia.org/wiki/Hale_Telescope

[2.1] https://en.wikipedia.org/wiki/Large_Binocular_Telescope

[2.2] https://www.newswise.com/articles/steward-observatory-mirror...

yters• 6 years ago

Well, glass is still a liquid, which was the most counter intuitive claim to me, whether or not the flow is humanly perceptible. In fact it is even more counter intuitive now, since glass is an even more solid liquid.

Pulcinella• 6 years ago

It makes more sense (to me at least) to think of glass as an amorphous solid and expand the concept of “states of matter.” It doesn’t have a repeating crystalline structure.

I think expand the concept of states of matter is key. It really helps make sense of a lot more things when you move beyond just solid, liquid, and gas (and plasma). A good example are liquid crystals, in LCDs yes but also cell membranes. What state of matter is the cell membrane? It makes more sense to create a new phase to categorize it. The lipid molecules are arranged in a certain orientation to each other (crystalline) but are also free to shuffle past each other (liquid). This is not just academic. Your body uses cholesterol to modify the fluidity vs. crystalinity of your cell membranes so they don’t “freeze) (stiffen too much) in the winter or melt in the summer.

Glass viscosity calculations debunk the myth of flow in medieval windows (2017)

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