Out big band dancing over the weekend, and was reminded of the strangeness of a musical form that is terrific, but (except for a few daring practitioners) essentially frozen in time. At one point, the band tried to play something from the 1970's, and everything ground to a halt. Everyone went to the bar, started talking to each other, and so on. As soon as they went on to "Satin Doll", everyone headed onto the dance floor again. I talked to the singer, and she said to me, Oh, yes, if I try and sing something out of the period, it dies: the bubble bursts. And this was in a hall full of teenagers as well as somewhat older people, none of whom were alive for this music the first time around. Something similar infects concert halls (still churning out Beethoven 200 years later), people with hit records (Don McLean and the umpteenth "American Pie"), and most musical forms that somehow captured a moment and are forever tied to that moment by the style, the nostalgia, the audience demand. It is a strange fate, reminiscent of characters like Paolo and Francesca in Dante's Inferno, locked together in their moment of ecstasy forever, the moment endlessly replaying horribly for them as the most terrible punishment. Still, one marvels for the 1,000 time over the intricate beauty of that most white bread of all big band songs -- "In The Mood" -- and heads out onto the dance floor, swing steps at the ready. (p.t.)