P1 A well-known scientist (some say it was Bertrand Russell)

A well-known scientist (some say it was Bertrand Russell) 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 gian tortoise.”
The scientist gave a superior smile before replying,
    “What is the tortoise standing on”
    “You’re ver clever, young man, very clever,”
said the old lady.
     “But it’s turtles all the way down!”