In modern science-fiction stories, it is frequently necessary to move quickly across large stretches of the galaxy. Ordinary speeds attained in ordinary ways are insufficient for the purpose. Something special is needed so the spaceship is made to pass through something called "hyperspace" and in the twinkling of an eye—or sometimes in several twinklings—we move away from the sun and are in the neighborhood of some star that is dozens of light-years away.
But what is hyperspace? Is it a term that science-fiction writers have invented out of nothing?
Well, suppose that you were in a vehicle that could move along a single line and could never leave that line. You could imagine a train, for instance, moving along a railroad line with no turn-offs. It could move forward or backward along the line, but in no other way. Another example is an elevator, which can move up or down but no other way.
If the vehicle is at a standstill and you wish to locate it, you need give only one number. If you say that the elevator is 27 meters above ground‐ level, you know exactly where it is. If you say the train is 175.4 kilometers from the eastern terminus, you know exactly where it is.
Because movement that is restricted to a line makes it possible to locate an object by giving only one number, a line is said to be one-dimensional.
But suppose you were wandering over a large, flat field. You could walk in a straight north-south line, or in a straight east-west line, or anything in between. You can change direction freely, turning right or left to whatever degree you wish. The same is true for a ship traveling over the trackless ocean.