if we keep trying to get deeper into philosophy and physics... there is no silence and no sound without each other, because soundwaves (as other forms of energy/matter) vibrate by alternating between crests and troughs.... i.e., it could be said the whole universe is constantly alternating between silence and sound... only our sensory organs don't usually register most things that way...
see the monster you've created, cage?!?!?
Boy, this discussion has gotten into some pretty deep areas, hasn't it?
If I remember correctly, John Cage hasn't been the only "classical" musician to cause us to re-examine the musical/aesthetic experience via his enigmatic works. There are many others, too -- for example, Beethoven, Wagner, Ravel, Debussy, Scriabin, Bartok, Stravinsky, Schoenberg, Gershwin, etc.).
When they were composing, many of these composer's ideas were considered revolutionary, even objectionable -- but, as listeners became acclimated to each of their styles, most of their works (I still don't know about Schoenberg's and Webern's 12-tone works) became accepted, and even admired for their creativity. The Rite of Spring
by Stravinsky comes to mind as just one example: when he was rehearsing the orchestra in 1913, some of the players called the work "unplayable"; and apparently the audience of the time considered the work "unlistenable." But, several decades later -- and continuing into the 21st century -- The Rite of Spring has become accepted as being part of an orchestra's "standard" repertoire -- and just about every orchestral performer can play it without complaint (I think!).