Interesting Wikipedia reading:
4′33″ … is a three-movement composition by American avant-garde composer John Cage (1912–1992). It was composed in 1952 for any instrument (or combination of instruments), and the score instructs the performer not to play the instrument during the entire duration of the piece throughout the 3 movements (The first 30 seconds, the second 2 minutes and 23 seconds and the third 1 minute and 40 seconds). Although commonly perceived as “four minutes thirty-three seconds of silence”, the piece actually consists of the sounds of the environment that the listeners hear while it is performed. Over the years, 4′33″ became Cage’s most famous and most controversial composition.
Here it is being performed: