Time is generally measured as how long it takes something with constant velocity to travel a constant distance. Unfortunately, since velocity is also
relative to time, it is kind of hard to determine one independently of the other. For example, if I'm traveling at 60 mph, then in one hour I travel
60 miles. You could say that one hour is then the time it takes me to travel 60 miles. But if I somehow travel that distance in less (or greater)
time, then was it because I started accellerating/decellerating or because the time measured wasn't constant?
Generally speaking, light is used for this measure, and a second is the length of time it takes light to travel 186,000 miles in a vacuum. Of course,
this is still an interdependant calculation, because we can also look at it as 186,000 miles is the distance that light travels in one second (in a
vacuum.) In fact, if I remember correctly, that's how the figure for the speed of light came to be; it was measured against time, instead of time
being measured against it.
Another measure for time, mainly used by atomic clocks, is determining how long it takes an atom to vibrate a given number of times. That is more
appropriate in my opinion, but it's still somewhat interdependant. In order to determine the proper number of vibrations in a second, you have to
have your stopwatch there and count the number of vibrations that happen in one second.
While T_Jesus is right, mathematically speaking the speed of light is the physical limit on velocity, one thing I always found interesting with
relativity is you can use it to disprove that part of the theory. A bit of an explanation of the theory is in order here though.
Relative velocity is measured as one object moves in relation to another. An example Einstein himself used was this: you have two trains moving next
to each other on a platform, train A at 15 mph and train B at 20 mph. They're both moving in the same direction. From train A's perspective, train
B is pulling ahead at 5 mph. From train B's perspective, train A is moving backwards at 5 mph.
If they're moving in opposite directions at the same speeds (15 and 20), then if you look at one as being stationary, the other is moving away at 35
mph. This is using each train individually as a frame of reference. If you're standing on the platform and using the platform as your reference
frame, then each train is moving in it's direction at the speed stated.
The disproving of the speed limitation follows a similar pattern. If I'm on an extremely fast train moving at 60% the speed of light, and there's
another one moving away at 60% the speed of light, then in relation to each other we're traveling at 120% the speed of light, obviously faster than
the physical limitation.
(I can't remember if that has been disproven or is considered in the theory; if it has, then please forgive me.)
Warping space, in essence, is not FTL travel, because even though you are travelling a technically greater distance from point A to point B, you
aren't travelling the space in between. That said, you technically aren't travelling the "time" in between either. (I'm going off of
speculation here; no studying or research at all, just my own reasoning as flawed as it may be.) You could argue that it is time travel, because you
end up at one location the moment you left the other location.
For example, if you maintain a velocity of 60 mph, and you are planning on travelling a distance of 120 miles, it should take you 2 hours to get
there. You start at noon, you arrive at 2 pm. If you manage to bend space enough to elminate a 90 mile stretch in between, you only have a half hour
drive. You arrive 90 minutes sooner than you should have. You could reason that you travelled back in time 90 minutes from your original
destination. However, it isn't time travel in the sense that you would go back to a point in time before you left per se; don't get any ideas about
stopping Oswald (or the CIA, or Mafia, or whomever) by creating a Star Trek-esque warp drive.
Ok, now my head hurts too...I hope this made some kind of sense to someone