By Peter Anderson
Imagine this beginning: a molecule rides in your own exhale, water in the form of vapor, rising in a warmer stream of air to meet the cooler floor of a cloud, a cloud that the prevailing wind has nudged up against the western slope of a nearby mountain. Inside of the cloud, let’s say this molecule, once a part of your own being, bumps into a grain of a grain of a grain of sand. And let’s say some other water molecules mingling nearby drift into that same particle. Pretty soon, all those molecules, including your own, are linking up like star-to-the-right square dancers on a Saturday night.