so is it possible, in existence, for a tree to fall without making a sound?

yes it is. For a deaf person the tree won't make a sound, still, the existence is being proofed by his other senses. He can see it, he can smell it, he can feel the tree falling down. For this person the tree exists, even though he can not hear the wisper of air, nor the fall.

Same with the unicorn, or god question. Both exist, because I take it as a fact. Both may be just a thought of mine, but what exactly is the meaning of the word Existence. Are there really other galaxies? I never saw them myself, never felt, nor touched them, but they are there. But would they exist if I could not in this moment be able to Think?

What is the universe for a tree? Watter, air, Sun. Tree realizes his surrounding in a completely diferrent way, but still there is a universe for him. If there would not be the sun, no gravitation .. and so on.

Well ... I need a drink, I tired myself by these thoughts. Fuck .. does the drink exist?