Henry Ernest Dudeney/Puzzles and Curious Problems/327 - Two Paradoxes/Solution
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Puzzles and Curious Problems by Henry Ernest Dudeney: $327$
- Two Paradoxes
- $(1): \quad$ Imagine a man going to the North Pole.
- The points of the compass are, as everyone knows:
$\qquad \qquad \qquad \begin{array} {ccc} & \text N & \\ \text W & & \text E \\ & \text S & \\ \end{array}$
- He reaches the pole and, having passed over it, must turn about to look North.
- East is now on his left-hand side, West on his right-hand side, and the points of the compass therefore:
$\qquad \qquad \qquad \begin{array} {ccc} & \text N & \\ \text E & & \text W \\ & \text S & \\ \end{array}$
- which is absurd.
- What is the explanation?
- $(2): \quad$ When you look in the mirror, you are turned right round, so that right is left and left is right,
- and yet top is not bottom and bottom is not top.
- If it reverses sideways, why does it not reverse lengthways?
- Why are you not shown standing on your head?
Solution
- $(1): \quad$ As you go over the pole, and are facing South, so also are West and East changed over.
- So, without turning round to face North, West is already on your right and East on your left.
- So when you turn round to face North, West is on your left and East on your right, and all is well with the world.
- $(2): \quad$ When you look in a mirror, it is not left and right which are exchanged, but front and back.
Historical Note
The paradox concerning the mirror is discussed by Martin Gardner in his $1964$ work The Ambidextrous Universe: Mirror Asymmetry and Time-Reversed Worlds.
Sources
- 1932: Henry Ernest Dudeney: Puzzles and Curious Problems ... (previous) ... (next): Solutions: $327$. -- Two Paradoxes
- 1968: Henry Ernest Dudeney: 536 Puzzles & Curious Problems ... (previous) ... (next): Answers: $526$. Two Paradoxes