In ordinary quantum mechanics, the observables of a system are a bit odd in one sense --- they are no longer variables, but operators. In a broader sense, however, they are not so odd. If you can measure the position of a particle in classical mechanics, you can measure its position in quantum me... (more)
A Cosmic Parable Once upon a time, there was a long string with evenly spaced beads on it.
In honor of Valentine's Day, I submit to you this classic video, and its lyrics, which I have linked to Wiki (and a Wolfram) articles: