
Why Is Glass Rigid? Signs of Its Secret Structure Emerge - rbanffy
https://www.quantamagazine.org/why-is-glass-rigid-signs-of-its-secret-structure-emerge-20200707/
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itcmcgrath
The most important part is at the end:

According to Agnieszka Grabska-Barwinska, a member of the team, the graph
neural network learned to encode a pattern that physicists call correlation
length. That is, as DeepMind’s graph neural network restructured itself to
reflect the training data, it came to exhibit the following tendency: When
predicting propensities at higher temperatures (where molecular movement looks
more liquid-like than solid), for each node’s prediction the network depended
on information from neighboring nodes two or three connections away in the
graph. But at lower temperatures closer to the glass transition, that number —
the correlation length — increased to five.

“We see that the network extracts, as we lower the temperature, information
from larger and larger neighborhoods” of particles, said Thomas Keck, a
physicist on the DeepMind team. “At these different temperatures, the glass
looks, to the naked eye, just identical. But the network sees something
different as we go down.”

Increased correlation length is a hallmark of phase transitions, in which
particles transition from a disordered to an ordered arrangement or vice
versa. It happens, for instance, when atoms in a block of iron collectively
align so that the block becomes magnetized. As the block approaches this
transition, each atom influences atoms farther and farther away in the block.

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hatmatrix
They used molecular dynamics (MD) simulation to train the model - couldn't the
correlation length be calculated from the MD simulations directly without the
graph network to gain the same insight?

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etaioinshrdlu
The article seems to promote the myth that glass flows slowly over time ...
[https://io9.gizmodo.com/the-glass-is-a-liquid-myth-has-
final...](https://io9.gizmodo.com/the-glass-is-a-liquid-myth-has-finally-been-
destroyed-496190894#:~:text=By%20studying%20a%20glob%20of,flows%20slowly%20like%20a%20liquid.&text=But%20the%20myth%20that%20glass%20flows%20has%20persisted%20over%20time).

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dia80
I was in a cellar once with some really old wine and the necks of the bottles
were drooping down the way. Any idea why that might be?

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throwaway_pdp09
I have seen that. I suspect it's from production. If so, why do people orient
the droops downwards, becomes the question.

~~~
adw
The other orientation is much less stable; it’s a stationary point but if
nudged will rotate _away_ from droop-up.

Similar reason old pre-float-glass windows are mostly found thick side down;
easier to fit that way because they’re more stable. The myth that they flowed
over time is just that. :-)

~~~
NinjaViking
And they're less likely to leak in rain when installed that way.

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centimeter
I often wonder if research into neural networks is taking air away from other
kinds of research that would yield similar results, but also yield a
comprehensible takeaway in the form of principles or equations, rather than
vague hints that we can (if we’re lucky) reverse engineer from the structure
of an NN.

~~~
082349872349872
Although I completely agree with you on the general observation, here's a rare
but significant exception:

In 1951, Kleene wrote _Representation of Events in Nerve Nets and Finite
Automata_ which was motivated by reverse engineering biological NNs, but
turned out to have been a discovery in CS instead.

[https://www.rand.org/pubs/research_memoranda/RM704.html](https://www.rand.org/pubs/research_memoranda/RM704.html)

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adw
If you’re interested in the theory of phase transitions, Landau theory
([https://en.m.wikipedia.org/wiki/Landau_theory](https://en.m.wikipedia.org/wiki/Landau_theory))
is a good on-ramp.

We know the glass transition isn’t a true phase transition because we do not
observe a discontinuity in (derivatives of) the free energy at Tg, the glass
transition temperature. What results like this suggest is that in some sense
the glass transition asymptotically approaches a true phase transition, which
is fascinating.

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peter_d_sherman
>"At the molecular level, glass looks like a liquid."

[...]

>"Glass is formed by cooling certain liquids. But why the molecules in the
liquid slow down so dramatically at a certain temperature, with no obvious
corresponding change in their structural arrangement — a phenomenon known as
the glass transition — is a major open question."

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hoseja
This could be useful if applied on vitrification of water, a critical step for
cryo-electron microscopy and one that is not nearly as simple as it appears
since some stable, buffered protein solutions resist proper vitrification.

