Higher Dimensions
A knot in three dimensions can be untied when placed in four dimensional space. This is done by changing crossings. Suppose one strand is behind another as seen from a chosen point. Lift it into the fourth dimension, so there is no obstacle (the front strand having no component there); then slide it forward, and drop it back, now in front. Analogies for the plane would be lifting a string up off the surface, or removing a dot from inside a circle.
In fact, in four dimensions, any non-intersecting closed loop of one-dimensional string is equivalent to an unknot. First "push" the loop into a three-dimensional subspace, which is always possible, though technical to explain.
Read more about this topic: Knot Theory
Famous quotes containing the words higher and/or dimensions:
“The foot of the heavenly ladder, which we have got to mount in order to reach the higher regions, has to be fixed firmly in every-day life, so that everybody may be able to climb up it along with us. When people then find that they have got climbed up higher and higher into a marvelous, magical world, they will feel that that realm, too, belongs to their ordinary, every-day life, and is, merely, the wonderful and most glorious part thereof.”
—E.T.A.W. (Ernst Theodor Amadeus Wilhelm)
“The truth is that a Pigmy and a Patagonian, a Mouse and a Mammoth, derive their dimensions from the same nutritive juices.... [A]ll the manna of heaven would never raise the Mouse to the bulk of the Mammoth.”
—Thomas Jefferson (1743–1826)