Wednesday, 30 July 2008

Glass in the New York Times

When people think of physics they tend to think of particle accelerators, string theory, E=mc² and so on, so when I tell them I'm studying glass they always look a little disappointed. Anyway, a couple of weeks ago we got a New York Times article from a guy called Kenneth Chang so we're all quite pleased about it. I had written a long post about it but I ended up just repeating what's in the article, so I've decided to list some main points and provide a few extra links.

He managed to give a good sense as to how much debate there is in the field. One thing everyone agrees on however, and where the article begins, is that cathedral windows do not sag because the glass has flowed.
"Medieval stained glass makers were simply unable to make perfectly flat panes, and the windows were just as unevenly thick when new."
If you want something that does do that then let me point you in the direction of pitch, which drips about once a decade but shatters when hit with a hammer. So what is glass then? Is it a liquid or what?

Glass has the same structure as a liquid. If you take a photo you couldn't really tell the difference. A liquid that's on its way to being a glass, a supercool liquid, is the same as well. If instead of a photo you look at a video you'll see that it's actually really different. Weeks and company have actually done this and you can see regions really close to one another, some with lots of motion, some hardly moving at all. This is the dynamic heterogeneity, mentioned in the article, that goes along with the hugely increasing viscosity. Their website has loads of great stuff, including movies and a link to a freely available version of the Science paper, I recommend taking a look.

The region that I'm roughly poking about in at the moment is to do with vibrations and rigidity. This is touched on in the article a couple of times. Matthieu Wyart and others have spent a lot of time developing the idea of a glass as a marginally rigid solid (the introduction to Wyart's thesis is actually quite readable and freely accessible). It's looking at how the random liquid structure affects things at low temperatures.

Anyway, I'll leave it there. If I've missed any important links just stick them in a comment. Been a bit too busy writing my thesis to do this properly. Dear God let it end soon!

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