Turtles All The Way Down

A well-known scientist
once gave a public lecture
on astronomy. He described
how the earth orbits around the sun and how the sun,
in turn, orbits around the center of a vast collection
of stars called our galaxy.
At the end of the lecture,
a little old lady at the back of the room got up and said: "What you have told us is rubbish. The world is really a flat plate supported on
the back of a giant tortoise."
The scientist gave a superior smile before replying,
"What is the tortoise standing on?"
"You're very clever,
young man, very clever,"
said the old lady.
"But it's turtles all the way down!"
--Stephen Hawking