It's a reminder that the temple at Jerusalem was destroyed; even in the midst of the joy of a wedding, there is sorrow at the destruction of that prior glory. Traditionally, I think it's often a glass, not a bottle. My mother tells the story that she was worried someone would get hurt stomping on the glass at my parents' wedding, so she sewed a lightbulb instead of a glass inside the little ceremonial bag, which shattered more easily.

Chocolate Pi