Geophysicists use sound waves to build a picture of the magma and rock beneath this active volcano, most of which is underwater. It’s like CT scanning the Earth.
When a sound is made, it spreads. And when it hits a hard surface that is far away, it bounces back and comes back to where the sound was made. That’s what we call an echo.
From Long Range Acoustic Devices used to disperse protesters to ear-splitting military drones to songs blasted on rotation to prisoners, ours is an age in which sound has been repositioned as a tool of terror.
Shortly after Glen MacPherson started hearing strange humming noises, he created the World Hum and Database Project so people around the world could document their own experiences with the Hum.