Hyperspace is a plot device sometimes used in science fiction. It is typically described as an alternate region of space co-existing with our own universe which may be entered using an energy field or other device. Travel in hyperspace is frequently depicted as faster-than-light travel in normal space.
Hyperspace is sometimes used to enable and explain faster than light (FTL) travel in science fiction stories where FTL is necessary for interstellar travel or intergalactic travel.Spacecraft able to use hyperspace for FTL travel are sometimes said to have a hyperdrive.
Detailed descriptions of the mechanisms of hyperspace travel are often provided in stories using the plot device, sometimes incorporating some actual physics such as relativity orstring theory in order to create the illusion of a seemingly plausible explanation. Hyperspace travel is nevertheless a fictional technology.
Authors may develop alternative names for hyperspace in their works, such as theImmaterium (used in Warhammer 40,000), slip space in the Halo universe, Z space in Animorphs, or "Underspace" (U-space), commonly referred to in the works of Neal Asher.
Normal Space
In normal 3-D space, the "shortest path" between two events A and B is found in the following way. First, look at all paths in 4-D space-time between A and B, and find the space-time path that takes the shortest time to traverse. Because of relativity, there is no such thing as universal time: so let the time be measured with respect to a clock whose motion matches the space-time path. Call this space-time path "P". Then the shortest path in space is simply the path in space traced by the space-time path P.
In strict mathematical terms, it may be impossible to define such a path, along which matter can travel. However, it usually is possible to find an infinite sequence of paths that converge uniformly to some limit, that is, some "limiting" path. Of course, under relativity, matter may not be able to travel along this limiting path, but light can travel along this path. In fact, the path of the light beam from A to B is the theoretical limit. No ship in normal space could follow the path of light in 4-D space time, but it can get arbitrarily close (until the energy required to go any faster exceeds the energy available).
This path (or limiting path) may not be unique: there may be many "shortest paths." Also, no path may exist; for example, suppose A lies in a black hole and B lies outside the black hole—since nothing can exit a black hole, such a path would not exist. (Although black holes do emit Hawking radiation) Finally, because of the general relativity, this path is not a "straight line" in the strict Euclidean sense, but is "curved." For example, if we aimed a rocket at the Moon traveling near the speed of light, the shortest path to the Moon is still a curved path. In fact, even if we aimed a photon of light at the Moon, it will follow a curved path, since gravity bends all things, even light. It is still possible to travel in a straight line to the Moon, yet since the curved light beam is the best, the curved path close to this beam is better than the straight path. Of course, if we take energy expenditures into account, then the minimum energy paths are just transfer orbits and gravity boosts that Earth space agencies predominantly use although these are not 'fast'.
Travel
Generally speaking, the idea of hyperspace relies on the existence of a separate and adjacent dimension. When activated, the hyper drive shunts the starship into this other dimension, where it can cover vast distances in an amount of time greatly reduced from the time it would take in "normal" space. Once it reaches the point in hyperspace that corresponds to its destination in real space, it re-emerges.
In other words, some (or all) paths in hyperspace may have a travel-time less than the time it takes to traverse the "shortest-path" in normal space, defined above. The time it takes to travel in hyperspace is measured in the same way time is measured in normal space, unless the hyperspace is discontinuous. For example, the path in hyperspace may not be smooth but a sequence of points, and the time change from jumping from one point to another may be abrupt. In this case, add the time jumps. Some may be positive (jumps to the future), and some negative (jumps to the past), depending on how the hyperspace is defined.
Explanations of why ships can travel faster than light in hyperspace vary; hyperspace may be smaller than real space and therefore a star ship's propulsion seems to be greatly multiplied, or else the speed of light in hyperspace is not a barrier as it is in real space. Whatever the reasoning, the general effect is that ships traveling in hyperspace seem to have broken the speed of light, appearing at their destinations much more quickly and without the shift in time that the Theory of Relativity would suggest.
In much science fiction, hyper drive jumps require a considerable amount of planning and calculation, with any error carrying a threat of dire consequences. Therefore, jumps may cover a much shorter distance than would actually be possible so that the navigator can stop to "look around" -- take their bearings, plot their position, and plan the next jump. The time it takes to travel in hyperspace also varies. Travel may be instantaneous or may take hours, days, weeks or more. Some theories state that a route traveled for a long time may continuously stay open.
A different concept, sometimes also referred to as "hyperspace" and similarly used to explain FTL travel in fiction, is that the manifold of ordinary three-dimensional space is curved in four or more "higher" spacial dimensions (a "hyperspace" in the geometric sense; see hyper surface, tesseract, Flatland). This curvature causes certain widely separated points in three-dimensional space to nonetheless be "adjacent" to each other four-dimensionally. Creating an aperture in 4D space (a wormhole) between these locations can allow instantaneous transit between the two locations; a common comparison is that of a folded piece of paper, where a hole punched through two folded sections is more direct than a line drawn between them on the sheet. This idea probably arose out of certain popular descriptions of General Relativity and/or Riemannian manifolds, and may be the original form from which later concepts of hyperspace arose. This form often restricts FTL travel to specific "jump points".
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