Phunky Physics VIII: I Can See Clearly Now
Glass is a solid; right? You can’t bend it unless you get it real hot, and it takes some effort and a sharp drill to poke a hole through it. In some cases it’s even bulletproof. Glass can be made in great thickness, yet still remains optically clear. This brings up a good question: If glass is so solid, then how can we see through it?
We’re all familiar with the three basic states of normal matter; solid, liquid and gas. Most solids are not transparent, at least to visible light, yet glass is “clearly” different. To understand this a little better, let’s see how glass is made.
Basically, man-made glass is melted sand that has been poured out on a flat surface and allowed to cool. Natural glasses, such as volcanic quartz and obsidian, are also the products of melting and re-solidification. By definition, any glass must necessarily have been a liquid at one time.
The atoms in most solids are methodically aligned with each other, usually in some orderly fashion overlapping each other in a tight grouping that’s much too dense for visible light to penetrate. That’s why solids are strong, rigid, and usually opaque unless sliced very thin. Even though most atoms are practically all empty space, when you align enough of them into a solid they tend to form a permanent pattern that easily absorbs light.
Most liquids, however, consist of atoms that associate with each other on a highly random basis, thus allowing plenty of room between them for light to pass while still maintaining the characteristics of the molecules themselves. That’s why most pure liquids and practically all gases are transparent. So what does this have to do with glass?
Remember, glass is simply molten sand that has solidified. Silica is one of those lighter materials whose atoms don’t interfere with visible light, and its random molecular alignment remains after the glass is no longer molten. Still random, but now frozen in place.
So why can’t we see through molten iron? Well, there are two reasons. For one, iron atoms are much more complex than silicon, with more chance to overlap each other in any state. Secondly, molten iron glows with its own light, which would effectively scramble any other light that tried to penetrate it. Molten glass isn’t transparent either, at least until the molten glow goes away.
Views From Benny Hill is a series by Jerry Smith
Thanks Jerry. I’m still trying to figure out why I understand all of this. Maybe my brain atoms are separating and letting in some smarts.
Random arrangement of thoughts will allow that, Mark.