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　　Marian and Michael are traveling in Thailand and decide to take a glass-bottomed boat tour.

　　Michael:So, once we get on board, do we have to wear slippers so we don't step through the bottom of the boat?

　　Marian:That's right. And jumping up and down is also strictly forbidden.

　　Michael:You know, I've never understood why glass, or any material for that matter, is transparent.

　　Marian:Well, you know that light acts like a wave of electromagnetic energy, right? Any material that can conduct

　　the wave is transparent.

　　Michael:I see. It's got something to do with the structure of a material.

　　Marian:Right. It's kind of complicated. If the electrons in a material cannot absorb any energy, then the wave will

　　pass through undisturbed.

　　Michael:So the material will be transparent.

　　Marian:And if the electrons can absorb energy, then the material isn't transparent.

　　Michael:But what about coal and diamonds? One is black and the other is transparent, yet they're both made up of

　　the same carbon atoms with the same electrons.

　　Marian:The electrons in coal aren't tied up as tightly as they are in diamonds. So they're free to grab the light and

　　prevent it from passing through.

　　Michael:Now it all makes sense. Ready to board, Ms. Einstein?

　　Marian:Let's go. My lab coat doubles as a life jacket.

　　---by Brian Greene/Sonya Roy