Your dad probably told you this one during a visit to some old house; that the wibbly wobbly glass is caused by it slowly, imperceptibly flowing over time. Although experts are still squabbling over exactly what is up with glass, it is generally agreed that it isn't slowing melting out of its window frames. The uneven texture of old glass is generally due to the manufacturing process at the time, which was less that perfect. Additionally, the thicker end of the glass was usually placed at the bottom of the frame for structural reasons which makes it look for all the world as though it's all slipped to the bottom over time. The general lack of this "flowing" in other glass objects such as sculptures and lenses would also seem to point to this being a myth. Glass is currently classed as an "amorphous solid" which can "flow" in a manner of speaking, but it has been estimated that your average widow at room temperature would take many times the age of the Earth to flow at all.
