Since we're pretty sure FTL is pure fiction and not possible in reality, that likely won't be an issue. Just because we don't know everything, doesn't mean we don't know anything.
We are, by no means, sure of that. There are numerous theoretical possibilities that fit current theory. Not least of which is the Alcubierre Drive: https://en.wikipedia.org/wiki/Alcubierre_drive
Mathmatically compatible with GR (which is known to be incomplete) doesn't mean possible in reality, in fact, read your own source, it makes that clear..
> Although the metric proposed by Alcubierre is mathematically valid (in that the proposal is consistent with the Einstein field equations), it may not be physically meaningful, in which case a drive will not be possible.
That drive is nothing more than speculative science fiction.
Alcubierre's drive is a solution to Einstein's field equations which simply means the math checks out in theory for warp drive.
The resulting practical problem is that the energy requirements necessary for the solution are far greater than what we can feasibly achieve now or in the future (exotic matter's existence notwithstanding).
But the fact that a physicist was able to derive this metric (energy requirements aside) is significant. Given the history of science, I would not discount the possibility that someone else will come along in the future with another solution which lowers the energy requirements to something feasible. But we can't predict this.
But isn't it amazing that the math checks out at all? I find it inspiring...
I'm not so sure the energy requirements are all that high. Alcubierre suggested that the sort of exotic matter needed would actually be fairly easy to create. NASA's been running experiments hoping to measure it with inconclusive results:
> In 2012, a NASA laboratory announced that they had constructed an interferometer that they claim will detect the spatial distortions produced by the expanding and contracting spacetime of the Alcubierre metric. The work has been described in Warp Field Mechanics 101, a NASA paper by Harold Sonny White.[5][6] Alcubierre has expressed skepticism about the experiment, saying "from my understanding there is no way it can be done, probably not for centuries if at all".
> In 2013, the Jet Propulsion Laboratory published results of a 19.6-second warp field from early Alcubierre-drive tests under vacuum conditions.[33] Results have been reported as "inconclusive".[34]
Wormholes are another. There's some debate whether or not the idea of creatable wormholes really exists in our physical models. But the idea of existing shortcuts through space time certainly does.
No, but if we leave today with a trip time of 1000 years and in 100 years we invent a way to travel .2c, then the people on the ship with the new tech will arrive in 120 years instead of 1000. Don't need FTL tech to make generation ships a silly prospect.
The other thing you guys are missing is relativistic time dilation: get the ship moving fast enough and time will pass more slowly inside the ship than outside. The ship may take a century or two to get to the destination, but only a few years will have passed for the travelers.
You have to go really, really fast to get 100:1 time dilation (like, 99.99% c) -- probably fast enough to make interstellar travel hazardous in a "collide with a hydrogen atom, it hurts" kind of way.
Your mistaken, and this opinion is what the second sentence was for; just because we don't know everything doesn't mean we don't know anything. FTL is likely not physically possible. That's not to say it's impossible, just that it's not likely given the vast number of things we do know about physics.