To make an experiment is to pose a question to the Nature. 
But Nature is very discreet and doesn't use to respond.
Only when she does, she provides us with a new tool to know her better.

But that's what I was thinking last week.

I think I'll be able to respond to the compromise aquired by suscribing the Declaration of the Symposium of Barcelona with a reproduction of the first paragraphs of a work I published in the book "Alter Músiques Natives" (other native music) which are already in english (thank you Alain for your help translating the rest).

As the text is quite long, it doesn't make sense to include it here, so I just add a citation of Llorenç Barber that appears later:

"To me, experimental music is quite simply music that offers, both for the musican and for the listener, a turning–point or black hole. Something that isn't explicit in the previous offer. There is, or can be in this music, a crack; one can lose oneself in a way that is presumably enriching and, by analogy, similar to the way mystics dexcribe the ascent to Mount Carmel: 'to reach what you don't know, you have to go the way you don't know' (...) this music puts all the emphasis on accident, gesture, atmosphere, ceremonial elements, etc. as well as on the catastrophic use of the most neutral technologies..."

(Llorenç Barber, Zehar, butlletin of Arteleku, 1993)

Universe A: There is no such thing as experimental music.
Universe B: There is such a thing as experimental music.

Universe B: Report.

"Man, represented by a primitive humanoid, is consumed by the environment he himself has created, eventually to be replaced by a new creature, even more primitive, imperfect, but vaguely capable of ruling the world." (The Residents)

The genre music circles tend to reject everything that doesn't pay inmediate homage to stylistic orthodxy. They often fall back on media language to express their rejection: "not commercial", "too noisy", "weird", "minority", "mad", etc.
New and different music, pioneer music, experimental music, avant–garde music, progressive music, stylistic short cuts, imaginary folklore... These are some ways of defining what is undefinable. Some of them are very inaccurate and others are imaginative enough to instill more mystery into it. Some of them are the industry's reply: for which a possible market is falsely weird (snobbery?). Some are poetic approximations to the unknown: this is non–genre music, other invented or imagined

soundtracks of the present future. Sensitive models which men and women generate for their own use and which the media macro–society incorporates with greater or lesser fortune.
We are therefore discussing sound ideas that share what lies outside the borders of today's music, whether jazz, contemporary music, pop, rock, flamenco, folk or new age, that have a place of their own characterized by innovation and stylistic risk, off the leisure/industrial circuits we call genre circuits. Music that makes some kind of conscious stylistic transgression and proposes a personal world, one radicalized as regards the pigeon–hole worlds of the stylistic map of the music of the last five decades.
Obviously what is produced isn't the future, it's the present. So it's wrong to speak of "new" music in relation to other music, perhaps we should peak of "traditional" music in relation to the music we're dealing with.
Very often this music starts from a genre or an instrument and tries to develop the expresive language; but very often an expression of sound is reached through personal, extramusical, literary, artistic or other experiences.
As soon as we speak of "personality", everything gets far more complicated than when we speak of "genres", "schools" or "trends".

"Who can find a word strange when hardly anyone knows the names of the flowers that can be found in an ordinary garden?" (Boris Vian)

That's why labels in this case are generally vague, ambiguous and narrow and only add to the tendency for mediatros to warn exaggeratedly about the supposed "difficulty" of certain musical expressions.
In quantum mechanics, the experiment with Schroedinger's cat places us before an uncertainty: inside the box, the cat may be alive or may be dead. There is a 50% chance of either opinion. But the cat can't be 50% alive or 50% dead. If we don't open the box, the cat is as much alive as it is dead. There are two parallel universes, in each of which the cat is in a different situation. We have chosen the option in which it is alive, and that's why there is such a thing as experimental music. Perhaps in other universes it doesn't exist, but that no longer concern us, although by taking this decision we submit to Heisenberg's uncertainly principle: it's imposible to know both the position and the movements of this phenomenon. Either we see where it is or we find out where it's going. We're not futurists, so here we'll just look at the other music that has existed healthily for the last half century, at what it is, what it does or what it isn't and what it doesn't do.
And yet another citation:

"...such music questions formal certainties, gives rise to new aesthetic situations, and foreshadows more human worlds. "
(Declaration of the first Symposium of European Experimental Composers, Copenhagen 3–14 October 1996)