No, silence is not sound.Okay, so this is an old thread by now, but how about this?…
Music is art related to sound…
• This could be sound heard through the air
• sound heard internally within one's consciousness
• the absence of sound
It's like with money (should be easier to understand my point) - let's say you have a bank account with 0$. Then you have just an account, no money.
You can even record the silence. Then you have a recording, but no sound and no music.
Music is sound.
Sound that have been composed and performed. But not every sound is music. We learn from others to differentiate between them (there is an important social/cultural aspect involved here - this allows for evolution of what we perceive as music). There are many aspects of sound that help us identify music - rhythm, melody and harmony, and less obvious like duration or timbre. Our brain performs an abstraction of these aspects. The abstraction is not very strict but rather fuzzy. This means we can easily disregard thunderclap or dog barking as music (both used as effects on a few recordings!), but if you look at phone ringing tones it's getting really complicated the more you go away from "traditional" telephone sounds.
Now we slightly touch the subject - music with strong repetitive patterns (pop/rock) can be easier remembered, recognised and recalled, it is simply easier for our brain. Is is not an incidence that Ravel's Bolero is one of the most recognisable pieces of music. Conversely, avant-garde music requires much more effort from us and is considered as noise by many. This will never change, as avant-garde is always at the boundary or beyond of what is considered as music at the moment.
This definition leaves out the internal sounds and for a good reason, as the performance aspect is really important. The internal sounds can be part of compositional process or listening experience, but do not constitute music as a whole. Now it's worth looking at the Bach's Kunst der Fuge, which had not been performed before composer's death. (Therefore so many different interpretations of this superb piece.) So what was it before its first performance? - "only" the composition.
Just my few cents,