Superluminal travel, or faster-than-light (FTL) travel, is a method of travel for getting across a galaxy. It is one of the solutions to the problem of galaxies being extremely huge, the problem being that going to another habitable planet with the space between two planetary systems would take too much time in a human's lifetime to transverse at slower-than-light speeds.
Traveling faster than light is a particularly interesting problem that only quite-technologically advanced civilizations can solve. It was originally thought to be impossible in conventional physics, but as the sound barrier was broken, the light barrier was broken as well. In fact, there are multiple known ways to go faster than light.
A popular, and a quite effective way of traveling faster than light. It is often used in more advanced forms to go even faster.
The primary problem with traveling faster than light is that infinite energy would be needed to go any faster than the speed of light. Because the mass of an object increases the higher its velocity is, it increasingly requires more and more force to go faster.
However, it is resolved with mass negation, involving a mass-less, invisible bubble that engulfs the spaceship and makes its mass invisible to the physics of the universe, although mass still works inside the bubble, so the occupants of the ship still feel mass. And because zero times n equals zero, the mass doesn't increase the faster the ship goes. Additionally, it is very easy to accelerate the ship.
Self-acceleration is used to propel the ship forward, and depending at the constant rate of acceleration, the very best ship can very quickly go around 7,800,000 times the speed of light, requiring only about 5 standard days to get from one side of the Milky Way Galaxy to the other. Stopping is also done by self-acceleration.
However, for unknown reasons, the bubble will break down at extremely high velocities, limiting the speed at which a ship can travel. It varies, breaking easily in cheaper FTL engines, although generally being stronger the better the mass negation drive is. The strongest engine developed so far will have its bubble only break at faster than 7,800,000 times the speed of light. If the bubble breaks when the ship is traveling at an extremely fast speed, the ship will collapse into a tiny black hole due to its extreme mass, and the black hole will decay from Hawking radiation. This is why mass negation drives will refuse to go any faster than a set limit as a safety feature, although some people have been known to disable or raise this restriction.
A fortunate side-effect of mass-negation is that the ship goes through other objects. As the ship is massless, it does not interact with matter that does have mass. The bubble and ship also looks invisible to others outside the bubble because of this. Finally, space ships using mass negation are unaffected by gravity.
However, it is possible to make the ship not look invisible, by shining light onto the ship itself inside the bubble. As light from inside the bubble escapes from the bubble, it becomes apparent to vision. Light that goes through the bubble from outside will not interact with the ship, however, and completely goes through the bubble.
The effects of extremely high velocities that break the bubble have been observed, and are now used in weapons to break and disable the bubble on another ship, to allow the attacking ship to hit it with conventional weaponry in space wars. The same technology causes the attacking ship to be unable to activate mass negation as well, however. It is often that when two or more ships are involved in fighting, neither sides can escape until the conflict is over or resolved. Bubble-destruction techniques do not work when the ship is going at more than several hundred times the speed of light.
Mass negation is most often used for locally traveling in a planetary system.
Another, popular way of going faster than light involves traveling through hyperspace. Hyperspace is an empty, alternative dimension where the laws of special relativity do not apply, and only the Newtonian laws apply. Therefore, this means a spaceship is able to enter, travel through it faster than light, and come out of hyperspace at the destination.
A hyperdrive engine built inside the ship is used to jump into hyperspace, and to self-accelerate through the dimension. Due to the slightly different properties of the dimension, a mass negation bubble will fail to work, although modified versions of a mass negation engine will decrease the mass of the ship, allowing the ship to go faster.
Hyperdrive engines are often modified to allow for jumping into dimensions other than hyperspace. It has been proven that similar technology can allow for time travel as well.
Another way to achieve FTL travel is to actually fold space itself, allowing the destination point to move to the spaceship's location without the spaceship actually moving. Space folding is among the most efficient ways of space travel, yet also one of the most advanced. Because the folding of space usually requires advanced powers, it is not used very often. Magic can be used to fold space, as can very advanced technology.
Alchemy cannot fold space, since alchemy deals in matter.