for many people something is real if it can be touched, a tangible reality....
most people's definitions are a bit broader than that as they believe, in addition to the physical, that all emotive things are also real.
for me the world is nothing but a symbiotic mush of occurances. and to speak in physical or at least more scientific terms, everything is frequencies of waves and thereby from our subjective viewpoint everything appears to be existing, but nothing is necessarily. If we were to perhaps shift our perspective a minute to the future or a minute to the past then nothing would be existing as far as our observations are concerned.. space would be empty.
so in a sense if objects are comprised of only waves then could music become physical?
