Maturity entails a readiness, painful and wrenching though it may be, to look squarely into the long dark places, into the fearsome shadows. In this … - Carl Sagan

Maturity entails a readiness, painful and wrenching though it may be, to look squarely into the long dark places, into the fearsome shadows.

The problems of simultaneity do not apply to sound as they do to light because sound is propagated through some material medium, usually air. The sound wave that reaches you when a friend is talking is the motion of molecules in the air. Light, however, travels in a vacuum. There are restrictions on how molecules of air can move which do not apply to a vacuum. Light from the Sun reaches us across the intervening empty space, but no matter how carefully we listen, we do not hear the crackle of sunspots or the thunder of the solar flares. It was once thought, in the days before relativity, that light did propagate through a special medium that permeated all of space, called “the luminiferous aether.” But the famous Michelson-Morley experiment demonstrated that such an aether does not exist.

El siglo XX será recordado por tres grandes innovaciones: medios sin precedentes para salvar, prolongar y mejorar la vida, medios sin precedentes para destruirla (hasta el punto de poner por vez primera en peligro nuestra civilización global) y conocimientos sin precedentes sobre nuestra propia naturaleza y la del universo. Las tres evoluciones han sido fruto de la ciencia y la tecnología, una espada de dos filos bien cortantes. Las tres tienen raíces en el pasado remoto.

Our loyalties are to the species and the planet. We speak for Earth. Our obligation to survive and flourish is owed not just to ourselves, but also to that Cosmos, ancient and vast, from which we spring.