Tuesday, July 26, 2011

Color My Mother Chartreuse

When I was a graduate student in physics, a friend of mine (who was more into art and poetry) invited me over to dinner at his place. While his wife was busy in the kitchen, we were chatting near a window in the late afternoon sunlight. Suddenly, he pointed at a bowl of fruit on a table near the window and asked me why the shadow it cast was colored purple and not black. Looking back on it, I think it was a test—that art vs. science thing. Nonetheless, I was in a profoundly philosophical mood and immediately rejoined: "It's an optical illusion. What's for dinner?" It would be another decade before I would even begin to realize how much I did not understand about color. I had no inkling then that vision and color perception are computational processes, that the brain is a differential analyzer and computed differences carry relative errors (perceptual illusions).

More recently, in a faint reprise of that illuminating but ancient episode, I was amazed to learn from Nathan and Giordano that the naming of colors is a similarly profound process, and since they are both experts, I could not be as dismissive with them as I was with my arty friend. On the contrary, I was forced to reflect on how I personally came to learn certain color names. In that landscape, my mother cuts a dominant figure.

Thursday, July 21, 2011

The Pauli Effect

Spin down

My favorite Pauli-effect story has to do with Walter Heitler defending his thesis topic or giving some kind of lecture. After the lecture, Wolfgang Pauli (in typical form) got up on the rostrum and launched into an expansive critique whilst pacing up and down. At some point he was headed towards Heitler, who was by now sitting in a chair at the end of the podium. As Pauli came closer and closer, Heitler leaned further and further back in the chair until he suddenly fell off the end of the stage: at which point some bright spark (possibly George Gamow) called out "Pauli effect!"