Faster-than-light

Faster-than-light (also superluminal or FTL) communications and travel are staples of the science fiction genre. However, according to currently understood physics, these concepts require exotic conditions that current technology can't establish, and that may be directly forbidden by more complete models of the universe's physical laws. Current theories of physics suggest that FTL travel or communication would necessarily involve time travel and thus would almost certainly cause problems with causality.

Terminology

In the context of this article, FTL actually refers to the transmission of information or matter faster than c, a constant equal to the speed of light in a vacuum, roughly 300 million metres per second. This is not quite the same as travelling faster than light, since:

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

• there are some processes which do propagate faster than c, but which can't actually carry information (See the Apparent FTL section in this article).
• light itself will travel slower than c when not in a vacuum (causing refraction), and in certain materials other particles can travel faster than it (but still slower than c), leading to Cherenkov radiation.

Neither of these phenomena violate special relativity or create problems with causality, and thus do not qualify as FTL as described here.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~