When it comes to plain terror, it's hard to beat the silence after the conclusion of the fourth of Anton Webern's 1909 Six Pieces for Orchestra. It's labeled as a funeral march—in this case, a funeral not of this earth but in some nightmare cortege of the mind. Webern mostly wrote miniatures in which the sounds seem laid with utmost tact over an encroaching void. In the Six Pieces, written after his mother's death, Webern shaped one of the most viscerally wrenching works in the musical literature. The "Marcia funebre" features a percussion roll that mounts to a consuming roar punctuated by screaming brass until it falls suddenly into an abyss of nothingness.
Two American composers, each in his way, were fascinated with effects of chance in music, echoing the way sound happens in unplanned ways in concrete reality. In his youth, Charles Ives had listened to church congregations singing gloriously out of tune, drunk bandsmen playing in the wrong key in holiday parades, and the superimposed sounds of multiple bands on the march. He was the first composer to consider those phenomena not just as accident or incompetence but a vital part of the music. Whatever is authentic and real in life, Ives believed, is material for art. One of the signs of his reach for authenticity is the characteristic Ivesian ending, which seems to evanesce into silence, as if the music were continuing somewhere out of hearing. An example is the ecstatic end of his tone poem The Housatonic at Stockbridge, which builds up into a visionary whirlwind that cuts off to reveal an ambiguous fading harmony that suggests some other music heard by chance behind the foreground music.
It's similar to the Webern ending, but to opposite effect: Webern is existentially bleak where Ives is ethereal and transcendent.
John Cage pursued a career of making anything at all into music, and, naturally, he was drawn to silence—it's the title of his first book of essays. Silence was the overriding symbol for Cage's agenda. Artists from time immemorial had wanted their work to do something, mean something. Cage was having none of that. "How To Improve the World (You Will Only Make Matters Worse)" goes the title of several of his essays. He aspired to meaninglessness, not in a German existential way but in a Zen way: All his music, whether for 12 radios (playing whatever happens to be on) or water gurgling in a seashell, aspired to the pure emptiness of silence. In his "Lecture on Nothing," he declared, "I have nothing to say and I am saying it and that is poetry as I need it." The epitome of that aesthetic, of course, was his most celebrated piece, the piano solo 4'33", in which the pianist sits there for the stated time playing nothing.
So there you have the power of nothing as it can be mysterious, funny, angry, tragic, sexy, terrifying, exalting, or an avatar of the spotless mind.