Why does 'breaking' not occur in liquids and gases?

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Prannu
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I'm not exactly sure whether this qualifies as quantum mechanics, but it has to do with how atoms work: suppose a glass plate falls and breaks (into two pieces, let's say, to keep things simple) on the floor. Is it possible to put it back together so that there is no longer a crack between the two pieces?
Rule: you cannot melt the glass to remake the plate.

I think it is not possible, but I am not sure why. Is it because the atoms at the edge of one piece of the glass no longer have the proper electron configurations to bond with the other piece? Basically, what does it mean to 'break', and why does 'breaking' not occur in liquids and gases?
 

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Several reasons.
- In practice, it will not break into two pieces. Tiny shards will bust off, leaving the two edges incompatible.
- If the glass contains any impurities, the fresh edges will start to oxidize.
- Also, there will be air molecules trapped between the two halves as you try to put them back together. Might not seem like a lot, but it only had to prevent the atoms of silicon from joining back together within a molecule's distance.
 
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Google for "cold welding vacuum" for an example of the conditions under which solids can be persuaded to fuse together - removal fo contaminants from the surfaces and vacuum to keep air molecules from getting in the way.
 
Also try a google search for "Optical contacting". This is about as close to what you describe as it is possible to get. Two very flat, very clean glass surfaces are brought into contact and effectively fuse together. It's used in the manufacture of certain optical components.
 
Daz said:
Also try a google search for "Optical contacting". This is about as close to what you describe as it is possible to get. Two very flat, very clean glass surfaces are brought into contact and effectively fuse together. It's used in the manufacture of certain optical components.
I seem to remember that, when bent by a small amount, a glass sheet may open up tiny cracks in the outside surface of the curve and that these will rejoin when the sheet is straightened again. When the bending is repeated, different cracks appear. So the surface has 'healed' after the initial distortion. I guess that foreign atoms getting into a crack could prevent it healing up so the experiment may have to be done in a vacuum.