Understanding Glass: Is it a Solid or Liquid?

[zoobyshoe]

Yeah - glass is a glass. We also discussed it a little HERE .

That whole thread is interesting, not just the glass part.

 

[Gokul43201]

Yeah - glass is a glass. We also discussed it a little HERE .

Glasses get a bad deal there. The representation of a glass as merely an amorphous solid is incorrect. Glasses are unlike normal amorphous solids, which can be described by equilibrium statistical mechanics. In such solids, fluctuations in thermodynamic and transport properties are on timescales that are small compared to typical measurement times. This is not true of glasses.

And in addition to "glass" glasses you have spin glasses, Fermi glasses, Bose glasses and metallic glasses (to name a few others).

 

[zoobyshoe]

And in addition to "glass" glasses you have spin glasses, Fermi glasses, Bose glasses and metallic glasses (to name a few others).

Do these share "glass" glass' transparency to light?

 

[Gokul43201]

Do these share "glass" glass' transparency to light?

Not at all. That works only for the "glass"glass.

 

[Nereid]

Mk, your definitions of a liquid lack any mention of time scales. A piece of glass, given sufficient time, will flow to fill a container and exert pressure on the side walls. But while some will call glass a liquid, most still like to think of it as a solid.

In pondering this, and definitions in general, perhaps we could add something about physical scale? To a bacterium, an aerogel may look something like a cave system (or a multistorey building) does to us; 'microscopic structure' is a purely human convention; 'atomic' or 'molecular' scale would be less arbitrary ... but then, how would you define the solid/liquid distinction at that level? In terms of 'microscopic solid/liquid/gas constituents', what is a tree, or a cell comprised of?

Going 'big', or involving gravity at a different scale, materials exhibit different behaviours - high tensile steel, or perhaps spider silk, would retain its 'shape' to much greater physical scale (against self gravity, which would tend to make it spherical) than, say, pure gold. If we go even stronger (gravity), to the surface of a cold white dwarf or neutron star, in what sense are our earthly, classical definitions applicable?

 

[Gokul43201]

How often do you find terms like liquid or solid quoted in scientific literature ?

The words are very useful for communicating the nature of common things around us, but not so good for scientific communication. "Solidity" is not a physical property, as far as I'm aware.

 

[Nereid]

Sorry readers, there's a context to my remarks. I'm engaged (elsewhere) in a discussion on the underpinnings of the concepts we use so blithely, and how this can lead to unrealised inconsistencies. The particular examples I was working with were 'space' and 'time', and the limits to which anything sensible could be said about 'before the Big Bang', especially without reference to a theory.

I'm beginning to realize that one doesn't need to enter the Planck regime (where GR and QFT are wildly incompatible) to show that intuitive notions can be seriously misleading ... and that there's nothing, a priori, that can guide you to how (i.e. in what way) your intuitions mislead you.

 

[Ruslan_Sharipov]

Glass is definitely a solid material

Here's a good article on the subject of glass.

Yes, it is a good article. However, in the conclusion part, Philip Gibbs, the author of this article, does not give a definite answer to the main question. He says: "There is no clear answer to the question "Is glass solid or liquid?".

The matter is that the plastic flow of solids and the flow of liquids (even very viscous ones) are two different phenomena. Viscous liquids resist to shear deformation because of the velocity gradients produced when applying such a deformation. Solids, to the contrary, resist to shear deformation even when all velocity gradients relaxed and no motion is present at all. In the case of plastic solids (both amorphous and crystalline), the force of resistance will subside in time. So, the definite answer is that "glass is solid".

I would like to suggest the following papers, where the exact mathematical description for plastic deformations of solids is being developed. There are two unproved corollary there. You are welcome to discuss and prove them in your own papers.

http://arxiv.org/abs/cond-mat/0304190
http://arxiv.org/abs/cond-mat/0408433
http://arxiv.org/abs/math-ph/0410006
http://arxiv.org/abs/cond-mat/0410552
http://arxiv.org/abs/cond-mat/0411148
http://arxiv.org/abs/math-ph/0502007
http://arxiv.org/abs/cond-mat/0504180

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