“Some things are hurrying into existence, and others are hurrying out of it; and of that which is coming into existence part is already extinguished . . . In this flowing stream then, on which there is no abiding, what is there of the things which hurry by on which a man would set a high price?”
—The Meditations, by Marcus Aurelius1
1. Thomas Bushnell, “The Meditations,” 1994, http://classics.mit.edu/Antoninus/meditations.mb.txt.
Ideally, we would like to obtain perfect-fidelity evidence, with zero impact on the environment. For copper wires, this would mean only observing changes in voltages without ever modifying them. For fiber cables, this would mean observing the quanta without ever injecting any. For radio ...