Feature Math

Knot Possible

Better ways to tell a tangled circle from a knotted loop

By Ivars Peterson

- More than 2 years ago

Magicians are experts at tying knots that look intractable yet unravel on command. Befuddled spectators find it difficult to distinguish between such phony tangles and truly knotted ropes.

Robert Sharein

Different views of the figure eight knot. Robert Sharein

Robert Sharein

With these three Reidemeister moves, mathematicians can untangle a messy loop that has no true knot.