late post to this, someone wrote:
"art must be physically represented to be called art."
actually not so. the ideas of duchamp in the 19-teens was that he wanted to return the ideas of art to the realm of the mind and away from the realm of visual sensation (he was responding to the ideas of modern art at that time: impressionism, post-impressionism, expressionism, early cubism,etc). i believe that he quit painting altogether in the late teens (maybe 1919, can't remember exactly) and focused on his ideas of the ready-made.
and his ideas were of course adapted/used for the 60's movement of conceptualism, which had the intent of moving away entirely from the idea of the "art object" and the idea of putting things in museums/galleries, but again the idea was to focus entirely on the idea of "idea", or "information". a lot of conceptualism focused on the process of "process itself" or on documenting process, etc., 2 movements that also developed concurrently w/ this was the fluxus movement, which was also a strain of anti-art, similar to the dada movment after WWI, and the other was "earth art", the idea of again removing art from the confines of gallery/museum and out in the world. it should be pointed out that both dada & fluxus used sound, performance, theatre aspects that were not "object oriented".
i also remember frank zappa talking about his solos as "sound sculptures".
and in the realm of music, sure there is physical objectness of cd/tape/record, printed music, but music itself has no physical-ness to it, it is sound waves/sensation that we hear...i remember reading an article that most music from the 20th century is "electronic music" , being that we experience it from listening to recorded source, and not live....
end of my 2 cents.....