Quotation

One to Nine

the Inner Life of Numbers
Tie a pair of shoes to each other with (suitably long) shoe-laces. Now rotate one shoe completely round, so that the laces get twisted too. Rotate again, in the same direction, so the laces are doubly twisted. You will find that you can untwist the laces by passing the shoe between them, without rotating it at all. Only a double rotation can be undone like this. === Explain why a mirror exchanges right and left, but not up and down. === It is a weak but also a profoundly weird force, with an extraordinary property: it is asymmetric. The weak force knows left from right just as definitely as does a helix of DNA. This was only shown unequivocally by Chien-Shiung Wu in 1956. Her experiment, though it has never become a popular icon of science, marks a major step in the understanding of space and its Two-ness.