“In this world, everything has a pulse or a vibration. This sound is unique to each living or non-living thing and in itself creates a music that no-one can hear. I believe that this has a very powerful resonance with, and a deep effect on, our lives. What would happen if we took this further and applied it to bigger things, more powerful things; like an entire solar system or galaxy say, what would that sound like?
Musica Universalis is the ancient theory that every celestial body, the sun, the moon and the stars, has an inner music. This is a harmonic and mathematical concept derived from the movements of the planets in the solar system. The music created is inaudible to the human ear.
Music of the Spheres is my interpretation of this theory. Every planet and every star; the whole universe has music within it that no-one can hear. This is what it would sound like if it was set free. This is Music of the Spheres.”

Vol. II, p. 30
1980s, Letters to the Schools (1981, 1985)
Context: Attention involves seeing and hearing. We hear not only with our ears but also we are sensitive to the tones, the voice, to the implication of words, to hear without interference, to capture instantly the depth of a sound. Sound plays an extraordinary part in our lives: the sound of thunder, a flute playing in the distance, the unheard sound of the universe; the sound of silence, the sound of one’s own heart beating; the sound of a bird and the noise of a man walking on the pavement; the waterfall. The universe is filled with sound. This sound has its own silence; all living things are involved in this sound of silence. To be attentive is to hear this silence and move with it.

Se não formos capazes de viver inteiramente como pessoas, ao menos façamos tudo para não viver inteiramente como animais.
Source: Blindness (1995), p. 116

"Lecture on Nothing" (1949)
1940s

On the conditions of the "Schrödinger's cat" thought-experiment, as presented in The Present Situation in Quantum Mechanics (1935), translated by John D. Trimmer http://www.tu-harburg.de/rzt/rzt/it/QM/cat.html

Song for St. Cecilia's Day (1692).
Context: When time itself shall be no more,
And all things in confusion hurl'd,
Music shall then exert it's power,
And sound survive the ruins of the world:
Then saints and angels shall agree
In one eternal jubilee:
All Heaven shall echo with their hymns divine,
And God himself with pleasure see
The whole creation in a chorus join.

Winter § I, p. 213
The Private Papers of Henry Ryecroft (1903)

physis
Source: Religion and Nothingness (1983), p. 149

Source: The Morning Gift

My Heart Will Always Be The B-Side To My Tongue (2004), Ultimate Guitar Interview (2008)