Fantastic timing as I'm working on a book about the implications of living in a plenum on the mechanics of how we affect and are affected. I believe space is indeed filled, absolutely, with all the stuff you succinctly lay out. But I want to say that space is dense with other materials, as well — materials that are conspicuously neglected by most scientists today: affect, mood, notions, images, ideas. That is, not just invisible material — sound, smell, radiation are invisible — but material that can't be quantified per se (although we do in fact measure our moods all the time — we're affected more or less by different events, people, art, etc). Anyway, excuse the aside: I was just writing to say thanks.