OK, it's not my purpose to start a bleeding discussion here. I'm just asking this question to people involved in music theory in order to get a proper definition of music.
You and me both. Keep in mind that even music in the baroque/classical periods had different aesthetics/reasons behind it than it did in the Romantic or modern eras. Music isn't even always thought of as an art form. Or a way of conveying emotion. People have been wrestling with the definition of music for ages, and you are (I truly regret to tell you, it bugs me too) unlikely to find the answer in a Music Q+A site.
"one of the foundations of art is the ability to create different
emotions to different people with the same work"
Um... Is it really? I think good art should cause most, if not everyone, who sees it to experience the same emotions that the artist did when he conceived of it.
Otherwise, what's the point? A feisty discussion about politics could achieve the goal of causing different reactions. Truly worth pursuing is the ability to convey the thoughts and emotions that you're experiencing to others.
Additionally, there is some discrepancy between music and visual art. Because visual art tends to be more specific to the ideas it may be related to than instrumental music (i.e. a sculpture/painting of a dog), there is more room for differing opinions to find their way into discussions about visual art than there is with the almost purely emotional content of straight up music.
Obviously, some people will have different reactions to music than others, but most often, given the proper cultural context, people will be able to experience the same thing when faced with music, even if they describe it with slightly different words.
And if there are differing reactions, these are not necessarily the intention of the artist. When an artist sets out to make something -- a painting, a piece, whatever -- they generally do it with a particular emotion or feeling that they want to convey. Their art form then takes on the function of a language to express this. Usually, the more skilled the artist with his medium, the more likely an audience is to understand what the artist was feeling when they see/hear the work.
By your friend's definition, a performance of Brahms's 1st Symphony wherein everyone gets goosebumps at the blaring trumpet soli at the end wouldn't be music.
Likewise at that EDM concert, if instead of head banging (or whatever you do at an EDM concert), some people suddenly stood up and started heckling the performers, maybe yelling "This isn't music!", all of the sudden the EDM would be music -- some dudes had a different emotional response.
Tell your friend that his definition is bogus.
some people bored, some other relaxed, or smiling, others gently following the melody with their heads...
And these are supposed to be indicative of the emotional responses induced by the performance? I think that's a poor metric.
Bored people probably aren't paying attention. Relaxed/smiling/gently nodding are not necessarily tied to separate emotions. You can be relaxed and smiling and nodding at the same time. As far as we know, they're all experiencing the same thing. Or maybe none of them are paying attention and they're all faking it.
A better way to measure emotions would be to show many people a performance of a piece of music, and then have them take a multiple choice answer survey to describe how it made them feel.
That was long and kind of a collated stream of thought. Hopefully this will give you some ammunition against the wack.