If you've ever played a game of racquetball, you know that a hollow rubber ball can be deadly in the wrong hands. As the ball bounces from your racquet, to the ground, the wall, the other wall, the ceiling, and the other wall before smacking you in the eye, you've got a lot of time to think about your life choices.

Just like racquetballs—except maybe a tad less deadly—sound waves reflect off of walls, racquets, and even eyes. We tend to call that reflection an echo. If you know

• the speed of sound,
• how much of the wave a surface is going to absorb,
• what the background noise of the area is,

you can pull a Sherlock Holmes and mathematically deduce unknown information about the physical environment. All you need is a way to send out some sound waves and time the difference between when it was sent and when it echoed back.

That's the definition of echolocation, by the way.

Society tends to favor sight over other senses because human brains are pretty good at processing visual signals from light waves. Once the light waves are gone, we're in the dark compared to dolphins and bats. Instead of relying on light, those guys use sounds and their echoes to find, locate, and identify objects.

Maybe someday human brains will catch up. Till then, there's always sonar.