Once there was an astronomer speaking on the subject of earth. He described the ways of gravity and centripetal force and how they keep the planet in position in space. Afterwards a little old lady walked up to him.

“You’ve got it all wrong,” she declared. “The earth does not hang in mid-air. It rests on the back of a turtle.”

The astronomer, learned man that he was, calmly pointed out the problem that then there would be nothing for the turtle to rest on.

“Oh, you just don’t understand,” she replied. “It’s turtles all the way down!”