What is it with Folkies and John Cage? To give piece it's proper title, 4'33" has precious little to do with silence, on the contrary.

4'33", pronounced "four minutes, thirty-three seconds", (Cage himself referred to it as "four, thirty-three") is often mistakenly referred to as Cage's "silent piece". He made it clear that he believed there is no such thing as silence, defined as a total absence of sound. In 1951, he visited an anechoic chamber at Harvard University in order to hear silence. "I literally expected to hear nothing," he said. Instead, he heard two sounds, one high and one low. He was told that the first was his nervous system and the other his blood circulating. This was a major revelation that was to affect his compositional philosophy from that time on. It was from this experience that he decided that silence defined as a total absence of sound did not exist. "Try as we may to make a silence, we cannot," he wrote. "One need not fear for the future of music."

For more, please read: http://solomonsmusic.net/4min33se.htm.