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Database Nation by Simson Garfinkel

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What Was That?

Sound is very different from light. On a physical level, light is made up of particles called photons that move through space. Sound, in contrast, is made up of compression waves that move through air, solids, or liquids. Light exists without a medium; sound cannot. This key difference has a variety of practical implications. It is much easier to record sound than video, but it is much harder to record sound at a distance. That's because while light waves travel in a straight line, sound waves spread out and bounce.

To experience the difference for yourself, just go to a park on a warm summer day. With a small telescope, you can easily spy on a small family picnic a quarter mile away. You can see what the family is eating and whether or not the children are well-behaved. But if you actually want to listen in on the conversation, you'll probably need to sneak over and plant a hidden microphone. Background noise, combined with the fact that sound waves quickly disperse, gives us some measure of acoustical privacy, even in public.

It's not surprising, then, that most acoustical surveillance involves some kind of physical invasion as well. Sometimes the invasion can be hard to detect. In 1946, Soviet schoolchildren presented U.S. Ambassador Averell Harriman with a large carved wooden seal of the United States. The Ambassador was so impressed with the seal that he hung it in his office at the U.S. Embassy in Moscow. What the Ambassador didn't know was that the seal was booby-trapped. ...

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