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Dear Dr. Staff: Why is glass transparent? I mean, I can't see through most things, but I can see through glass. Why is that? And if you can see through it, why can't you hear through it?

--a Physics-inquiring Adolescent Naive Electrician

Dear Naive: You must not have any children. The word "transparent" comes from the Latin words "trans," meaning "through," and "parent," meaning "parent." As you may surmise from this entomology, only people who aren't parents can see through glass. A special genetic change takes place in both participants during the conception process that affects their eyes and makes it so they can't see through transparent things anymore. The explanation for this peculiar phenomenon lies with birds, who are further back on the evolutionary scale. Young birds need to be able to see through the windows of a birdfeeder, to see what kind of food is inside. But, by the time they are mommy and daddy birds, they already know what kinds of food are in different feeders. When they're older, it's more useful to a bird to see glass as opaque, so they don't try to fly through windows and hurt themselves. This feature was built into the avian visual system, and has passed down through the generations to humans, who evolved from birds.

--a Source of Happiness And a Real Physics dude

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