Faster-than-light travel

Faster-than-light travel (often abbreviated to FTL) refers to the purported ability or potential to break the universal speed limit of light.

How fast is it, Doc?
The maximum speed of light is exactly 299,792,458 meters per second (this is possible because the meter is actually defined by the speed of light), but is usually known as 3×108 meters per second. Although this is the speed of unstructured light in a vacuum and the speed of light is affected by the material through which it passes, the speed of light under any given circumstance is the maximum possible speed at that circumstance.

Some claim that this fundamental constant of the universe can be broken. But the amount of energy it takes to accelerate an object with rest mass rises sharply as c is approached until a discontinuity is reached. It would require infinite energy to cross the final gap.

Possibility of travel faster than the speed of light
Einstein's theory of general relativity does not rule out the existence of shortcuts in spacetime called  which could permit the travel of a ship from one part of the galaxy to the other, bypassing the intervening interstellar space. An extraordinarily advanced civilization could conceivably construct artificial wormholes connecting a group of stars like a subway system. Carl Sagan described such a network in his novel Contact. However, even using wormholes to bypass the speed of light limit opens up possibilities of making "go back in time machines" (unless the science fiction author is very careful in restricting how wormholes can be made).

The is another hypothetical possibility. It requires the existence of negative mass. Even if negative masses exist, it would take as much energy as the sun produces over its entire lifetime just to create an Alcubierre warp field, let alone to make such a field move. However, a means of reducing the mass-energy requirements tremendously was theorized by physicist Harold White in 2012.