Sean wrote:
evileeyore wrote:
FreeFlier wrote:
Is the TAD field FTL?
I believe TAD propagates at the speed of gravity.
Yup, work that one out.
Well...according to Honor Harrington, gravity is a handy way to communicate FTL, but I think real gravity propagates at the speed of light.
The postulates of special relativity are:
(0) Mathematical physics works (aka our math is valid and can describe the universe, this isn't usually listed but it is needed)
(1) There is a preferred speed (aka there is a measurable speed that is a physical constant of the universe)
(2) There is not a preferred inertial frame (aka there is no such thing as speed except as measured relative to some other object).
If you accept these postulates, then the same math that gives you the Lorentz-Fitzgerald contraction equations as a consequence gives you that the preferred speed is unique. (Because the size of the effects are directly dependent on the preferred speed, if gravity goes at some speed other than "c", call it "d" then the observed contraction has to be consistent with both "c" and "d" being used in the same spot in the same equations, which means they are the same.)
Thus, if gravity has a consistent speed, it must be "c". Note that "instantaneous" is also a measurable speed, so that's not it.
SF that allows FTL typically exists in a universe where one of (0), (1), or (2) is incorrect. Since (0) is kind of fundamental, and (1) is observably true, I tend to go with (2) being wrong in those universes. In which case, gravity CAN have a different speed.
I strongly suspect the fact that gravity waves have been observed and match prediction, makes it very hard to justify instantaneous gravitational effects in the real universe.