Instead of shunting the ship into a higher-dimensional continuum like hyperdrives, warp drives instead bend the space-time of our own universe around the ship. This creates a region of subjective space-time that is out of synch with the rest of the universe. Einstein's Theory of Relativity clearly demonstrates that no physical object can travel faster than light. However, how fast spacetime itself can move in relation to itself is unknown, and can theoretically be moved at any speed. Because it is "detached" from normal space, a region of warped spacetime--including any ship within it--can be moved faster than light.
Like with most other FTL schemes, how exactly to achieve this extreme warping of the fabric of space remains conveniently obscure in most science fiction sources. Engineering powerful artificial gravity sources as well as expert manipulation of quantum effects seems to be implied in Star Trek. In Alcubierre's scheme, the ability to harness and manipulate large amounts of negative energy--still a very theoretical notion--would be necessary.
ALCUBIERRE WARP DRIVE
Tech Level: 19
In 1994, Miguel Alcubierre, a physicist at the University of Wales, described a means of space travel that bore an remarkable resemblance to the warp drive of science fiction.
In his paper published in the May 1994 issue of Classical and Quantum Gravity, Alcubierre described using large amounts of negative energy to create distortions of space/time around a spaceship. In front of the ship, the fabric of space is compressed, contracting the distance between the ship and its destination. In back of the ship, the fabric of space is expanded, increasing the distance between the ship and its point of departure. These distortions move along with the ship, creating a "wave", as some have described it, of distorted spacetime that the ship rides to its target. Because it is space/time itself which is moving and not any physical object within the "wave", this motion does not violate Relativity, even though to an observer outside it would very much appear that the ship was moving at FTL speeds.
Another way to think of Warp Drive movement is to visualize space as a stretched sheet of rubber, and the section of "normal" spacetime between the two extreme distortions created by the Alcubierre drive (referred to sometimes as a warp "bubble") as a marble resting on its surface. Instead of moving the marble directly, you push into the rubber sheet with your finger directly in front of the marble, while someone your finger on your other hand pushes up on the rubber directly behind the marble. By moving your fingers at a fast enough rate, you can move the marble all the way across the sheet, by creating a constantly-moving "warp" in the rubber the marble is continually trying to fall into. Extend this analogy into four-dimensional space and you have the basis for the Alcubierre warp drive.
STAR TREK WARP DRIVE
|The starship Enterprise activates its warp engines. Image (c) Paramount|
No discussion of warp drives can be complete without an examination of Star Trek's famous fictional engines. Though the "official" explanation for just how the Federation's ships zoom around space has changed over the course of the franchise (and with over 700 hours of on-screen stories spread across 40 years to keep track of, consistency can be understandably dicey), we will explore the most likely explanation for it.
When Star Trek was originally conceived, the warp drives were simply explained as being able to warp space/time in some mysterious way as to allow faster than light travel. Like with Star Wars' Hyperdrive, they mostly travelled at the speed of exposition--they always took as much or as little time to reach their destination as the script demanded.
However, during Star Trek: The Next Generation and throughout most of Star Trek: Deep Space Nine, the series creators seemed to get much more serious about warp theory, introducing the idea of warping subspace.
Subspace can be a difficult concept to understand. It is NOT a different dimension or a different universe or even a different "level" of our own universe--not exactly. From what I was given to understand watching the series and from various online sources, subspace is instead the strata of our own space/time, intricately interwoven to form the structure of our reality.
One way to conceptualize subspace is to think of our universe as the number 3. Let's pretend 3 is the very critical number that defines existence, because if the universe added up to even a tiny smidgen less than 3, the whole thing would fall apart and the universe would blink into nothingness. If everything didn't add up to 3, nothing would exist at all.
Subspace would therefore be like all the tiny decimals that exist between zero and three. A layer of subspace would be at 0.5, another would be at 1.4, and still another at 2.9998, etc. All of these numbers must exist for 3 to exist, and if you take away even the smallest of them the whole thing collapses. So think of all these small, fractal, semi-dimensions of subspace being layered and woven together intricately to form our universe. Some of these subspace fractal dimensions are intricately woven into our everyday existence (such as the ones that determine known physical laws), other may exist only tangentially to our common experience of reality (such as the subspace layers used in Star Trek to allow FTL travel), still others may have collapsed into the planck-scale level of the universe and may manifest themselves only in certain circumstances (such as some of the "spatial anamolies" found in the various Star Trek series.)
The Star Trek warp drive does not brutally manhandle the whole fabric of space/time like the Alcubierre drive, it subtly manipulates select layers of subspace--substrata of our own universe--like a musician deftly plucking the strings of a violin. Like the Alcubierre version, the Star Trek warp drive stretches and compresses the fabric of space/time, but does it only to those layers that most relate to its rate of travel. Using the stretched sheet of rubber analogy above, it would be like only stretching the topmost layers of rubber to move the marble (the warp bubble) rather than distorting the entire thickness of the sheet.
Different subspace layers would affect and/or make up the physical constants of our universe, so by warping these layers the engines could theoretically alter the local limit of lightspeed or the relative inertia of the ship. Finding these layers and learning to manipulate them subtly enough to allow superluminal speeds but not to screw up the physical laws that keep our bodies and technology functioning would require a great deal of technical sophistication, hence the Star Trek Warp Drive’s very high Tech Level compared to most other ship-dependent FTL schemes.
The area of warped space/time around the Federations’ ships are two-lobed, explained in the official material that the differing "subspace pressures" between the front and back lobes drive the ship forward. In practice, these would probably just be subspace versions of the contracted/expanded spacetime that drive Alcubierre’s version of the concept.
WARPED SPACE CORRIDORS
Tech Level: 24
An idea that occassionally manifests itself along with discussions of Alcubierre’s warp drive. Instead of just temporarily warping spacetime around a moving ship, a highly advanced civilization will permanently alter the space in between two points to allow faster travel. These warp "highways" would resemble broad corridors between star systems, wherein the spacetime would be altered in such a way as to allow FTL travel, at least relative to the universe outside the corridor.
However, within the corridor, spacetime is either compressed so as to shorten the distance between the two points, or the speed of light is greatly elevated to allow much greater velocities to be achieved. No special engine is needed to utilize the corridors--any sublight engine would suffice, as the FTL properties would be contained in the corridor itself, independent of the ship.
Warp corridors would be very much unlike wormholes, in that the ship can enter and exit the corridor at anytime with no harm, whereas a wormhole must be entered and exited only at its mouths.
Undertaking such an immense and exotic engineering project would require a near mind-boggling level of technical sophistication, as it would require an insane amount of negative energy to create interstellar conduits of warped space light years long. And of course advanced civilizations would more than likely build huge webs of such corridors throughout their region of space.
How stable such corridors would be is unknown. They would likely degrade over time and need constant upkeep similar to normal highways.