Once a Physicist was giving a talk to a community group.

An older woman listened patiently, then politely informed him that his model of the Universe simply was not right.  A wise man had taught her that the world rested on the back of a giant tortoise.

The physicist gently pointed out that this left the problem of what the tortoise was standing on.

She replied:  "You're very clever, young man, very clever.  But it turtles, all the way down!"