Think of how busy the air is.
Think of how much information, in the form of radio energy, there is flying through the air, all around us, all over the world, right now and all the time. AM, FM, UHF, WHF, shortwave radio, television, CB radio, walkie-talkies, cell phones, cordless phones, telephone satellites, microwave relays, faxes, pagers, taxi calls, police, sheriff, hospitals, fire departments, telemetry, navigation, radar, the military, government, financial, legal, medical, the media, etc., etc., etc. Trillions and trillions and trillions and trillions of separate little bits of electronic information flying all around the world through the air at all times. Think of that. Now realize this: A hundred years ago there was none. None. Silence.
—George Carlin, Brain Droppings