A CATALOG OF SOUNDS
The most reposed sounds are those which are least energetic. These may include slight ripples on a pond produced by a gentle breeze, the infinitesimal movement of molecules on a still day, or the slightest interaction of particles in a magnetic field.
The simplest sound is a pure tone, or so-called sine wave. Most sounds consist of many sound waves containing different vibrations, while a pure tone contains only a single vibration.
The greatest density of sound on Earth may occur in the tropical rain forest, where millions of sound-producing creatures are packed into a single listening environment. Although, rush-hour in any major city of the world will produce an impenetrable cacophony of sound.
Microacoustic waves are the smallest known sound waves. The smallest sounds on Earth are generated spontaneously by heat fluctuations of the trapped particles within a normal sound wave. In addition, microacoustic waves are generated by spontaneous vibrations within the bone structure of the middle ear, and in plasmas and superconductors.
The largest sounds are macroacoustic waves which are large-scale oscillations that are generated within, on, or near planetary bodies, stars, and galaxies, including large-scale disturbances of a planetary atmosphere, hydrosphere, or lithosphere. These oscillations include global weather patterns, ocean waves, and seismic waves, as well as solar waves, large-scale fluctuations of the solar wind and interstellar dust clouds, and galactic waves.
Imagine the very first sound on Earth. The first sounds used for the purpose of communication on Earth were probably made by insects.
Imagine the last sounds on Earth. Imagine the sounds of a collapsing solar system. Imagine the final sounds of an exploding or imploding universe.